阅读说明：本技术 Dc/dc转换器及其控制 (DC/DC converter and control thereof ) 是由 A.索马尼 X.夏 A.撒帕 G.卡斯特里诺 于 2018-02-13 设计创作，主要内容包括：本公开提供了一种DC/DC转换器系统,其包括用于在第一端口和第二端口的电压水平之间进行转换的双向DC/DC转换器,以及用于控制DC/DC转换器的控制系统。双向DC/DC转换器包括连接到第一端口的第一转换级和连接到第二端口的第二转换级,第二转换级与第一转换级接口连接。该控制系统包括外部控制回路单元和内部控制回路单元。该外部控制回路单元将用于第一端口和第二端口之一处的电压水平、电流水平或功率中的任何一个的命令与第一端口和第二端口之一处的电压水平、电流水平或功率水平的实际值进行比较,并基于比较结果输出接口电流命令。内部控制回路单元将接口电流命令与第一转换级和第二转换级的接口处的接口电流的实际值进行比较,并基于该比较结果来控制开关信号占空比值。(The present disclosure provides a DC/DC converter system comprising a bidirectional DC/DC converter for converting between voltage levels of a first port and a second port, and a control system for controlling the DC/DC converter. The bidirectional DC/DC converter comprises a first conversion stage connected to the first port and a second conversion stage connected to the second port, the second conversion stage interfacing with the first conversion stage. The control system includes an outer control loop unit and an inner control loop unit. The outer control loop unit compares a command for any one of a voltage level, a current level, or a power at one of the first and second ports with an actual value of the voltage level, the current level, or the power level at the one of the first and second ports, and outputs an interface current command based on the comparison result. The inner control loop unit compares the interface current command with an actual value of the interface current at the interface of the first conversion stage and the second conversion stage and controls the switching signal duty cycle value based on the comparison result.)

1. A DC/DC converter system comprising:

a bidirectional DC/DC converter for converting between voltage levels at a first port and a second port, the bidirectional DC/DC converter comprising:

a first switching stage connected to the first port and comprising a plurality of switches; and

a second switching stage interfaced with the first switching stage, the second switching stage connected to the second port and comprising a plurality of switches;

a control system for controlling the DC/DC converter, the control system comprising:

an outer control loop unit configured to compare a command for any one of a voltage level, a current level, or a power at one of the first port and the second port with an actual value of the voltage level, the current level, or the power level at the one of the first port and the second port, and to output an interface current command based on a result of the comparison;

an inner control loop unit configured to compare the interface current command with an actual value of the interface current at the interface of the first and second conversion stages and to control a switching signal duty cycle value based on the comparison result.

2. The DC/DC converter system of claim 1, wherein the inner control loop unit comprises a first conversion stage controller and a second conversion stage controller, and the inner control loop unit is further configured to:

comparing the interface current command to an interface current comparison value to generate a first interface current command and a second interface current command;

comparing the first interface current command and the second interface current command to an actual value of interface current, wherein:

the first conversion stage controller controls the duty cycle value of the switching signal of the first conversion stage according to the comparison result of the first interface current command and the actual value of the interface current; and

the second switching stage controller controls a duty cycle value of a switching signal of the second switching stage in accordance with a comparison of the second interface current command with an actual value of the interface current.

3. The DC/DC converter system of claim 2, wherein, in comparing the interface current command to an interface current comparison value, the inner control loop unit is configured to:

subtracting the interface current comparison value from the interface current command to generate the first interface current command;

adding the interface current comparison value to the interface current command to generate the second interface current command;

comparing the first interface current command with an actual value of an interface current and controlling, by the first conversion stage controller, a duty cycle value of a switching signal of the first conversion stage based on a result of the comparison; and

comparing the second interface current command with an actual value of the interface current and controlling, by the second switching stage controller, a duty cycle value of a switching signal of the second switching stage based on the comparison result.

4. The DC/DC converter system of any of claims 2-3, wherein the first and second conversion stage controllers comprise one of a Proportional Integral Derivative (PID) controller, a Proportional Integral (PI) controller, a proportional (P) controller, and a hysteresis controller.

5. The DC/DC converter system of any of claims 1-4, wherein the outer control loop comprises one of a Proportional Integral Derivative (PID) controller, a Proportional Integral (PI) controller, a proportional (P) controller, and a hysteresis controller for receiving a comparison of a voltage or current command to an actual voltage or current to control the interface current.

6. The DC/DC converter system of any of claims 1-6, wherein the first conversion stage converts the voltage at the first port to an output voltage output at the second port when the voltage at the first port is higher than the voltage at the second port,

the second conversion stage converts the voltage at the second port to an output voltage output at the second port when the voltage at the second port is higher than the voltage at the first port, and

each of the first and second conversion stages is operative to control the voltage at the first port and the voltage at the second port when the voltage at the first port and the voltage at the second port are substantially equal.

7. The DC/DC converter system of any of claims 1-6, wherein:

the first switching stage comprises a first half-bridge and a second half-bridge connected in series between a first terminal and a second terminal of a first port; and

the second switching stage comprises a third half-bridge and a fourth half-bridge connected in series between a third terminal and a fourth terminal of the second port.

8. The DC/DC converter system of claim 7, wherein:

the first half-bridge comprises a pair of first switches connected in series between a first terminal of the input port and a junction of the first half-bridge, and the second half-bridge comprises a pair of second switches connected in series between the junction of the first half-bridge and the second half-bridge;

the third half-bridge includes a pair of switches connected in series between a junction of the third half-bridge and the fourth half-bridge, and the fourth half-bridge includes a pair of fourth switches connected in series between a junction of the third half-bridge and the fourth half-bridge.

9. The DC/DC converter system of any of claims 1 to 8, wherein the first and second conversion stages are interfaced through first and second inductors or through an isolation transformer.

10. The DC/DC converter system of claim 8, wherein the first conversion stage and the second conversion stage are interfaced by a first inductor and a second inductor,

a first terminal of the first inductor is connected to a junction of the pair of first switches, and a second terminal of the first inductor is connected to a junction of the pair of third switches; and

a first terminal of the second inductor is connected to a junction of the pair of second switches, and a second terminal of the second inductor is connected to the pair of fourth switches.

11. The DC/DC converter system of claim 8, wherein the first conversion stage and the second conversion stage are connected by an isolation transformer interface, and

one side of a first winding of the isolation transformer is connected to a junction of a pair of switches of the first half-bridge and the other side of the first winding is connected to a junction of the pair of switches of the second half-bridge, an

One side of a second winding of the isolation transformer is connected to a junction of a pair of switches of the third half-bridge and the other side of the second winding is connected to a junction of the pair of switches of the fourth half-bridge.

12. The DC/DC converter system of any of claims 1-11, wherein the first conversion stage is connected to an energy storage unit at the first port and the second conversion stage is connected to a PV array at the second port.

13. The DC/DC converter system of any of claims 7 to 12, further comprising:

a first capacitor coupled to the first half bridge;

a second capacitor coupled to the second half-bridge; and

the control system further comprises a capacitance control system for controlling a voltage difference between a voltage across the first capacitor and a voltage across the second capacitor, the capacitance control system being configured to:

calculating a difference between a voltage across the first capacitor and a voltage across the second capacitor;

calculating a duty cycle offset from a difference between a voltage across the first capacitor and a voltage across the second capacitor;

applying the duty cycle offset to the duty cycle value output by the first conversion stage controller.

14. The DC/DC converter system of any of claims 7-13, further comprising:

a third capacitor coupled to the third half-bridge;

a fourth capacitor coupled to the fourth half-bridge; and

the control system further comprises a capacitance control system for controlling a voltage difference between a voltage across the third capacitor and a voltage across the fourth capacitor, the capacitance control system being configured to:

calculating a difference between a voltage across the third capacitor and a voltage across the fourth capacitor;

calculating a duty cycle offset from a difference between a voltage across the third capacitor and a voltage across the fourth capacitor;

the duty cycle offset is applied to the duty cycle value output by the second conversion stage controller.

15. A method for controlling a bidirectional DC/DC converter comprising a first conversion stage connected to a first port and a second conversion stage connected to a second port, the first conversion stage interfacing with the second conversion stage, wherein each of the first conversion stage and the second conversion stage comprises a plurality of switches, the method comprising:

comparing a command for one of a current level, a voltage level or power at one of the first port and the second port with an actual value of the current level, the voltage level or power at one of the first port and the second port and controlling an interface current command based on the comparison; and

comparing the interface current command with an actual value of the interface current at the interface of the first and second conversion stages and controlling the switching signal based on the comparison result.

16. A method for controlling a bi-directional DC/DC converter as claimed in claim 15, wherein comparing the interface current command with an actual value of the interface current at the interface of the first and second conversion stages and controlling the switching signal based on the comparison result comprises:

comparing the interface current command to an interface current comparison value to generate a first interface current command and a second interface current command;

comparing the first interface current command and the second interface current command to an actual value of interface current;

controlling a duty cycle value of a switching signal of the first switching stage according to a comparison of the first interface current command with an actual value of an interface current;

and controlling the duty ratio value of the switching signal of the second conversion stage according to the comparison result of the second interface current command and the actual value of the interface current.

17. The method for controlling a bi-directional DC/DC converter of claim 16, wherein comparing the interface current command to an interface current comparison value to generate first and second interface current commands and control duty cycle values of switching signals of the first and second conversion stages comprises:

subtracting the interface current comparison value from the interface current command to generate the first interface current command;

adding the interface current comparison value to the interface current command to generate the second interface current command;

comparing the first interface current command with an actual value of the interface current and controlling a duty cycle value of a switching signal of the first switching stage based on the comparison result;

the second interface current command is compared with an actual value of the interface current and the duty cycle value of the switching signal of the second switching stage is controlled based on the comparison result.

18. A method for controlling a bi-directional DC/DC converter as claimed in any one of claims 15 to 17, wherein the first conversion stage is connected to an energy storage unit at the first port and the second conversion stage is connected to a PV array at the second port.

19. A DC/DC converter comprising:

a first switching stage comprising a first half-bridge and a second half-bridge connected in series between a first terminal and a second terminal of a first port; and

a second switching stage coupled to the first switching stage, the second switching stage comprising a third half-bridge and a fourth half-bridge connected in series between a third terminal and a fourth terminal of a second port; wherein

A first conversion stage for converting a first voltage at the first port to a desired output voltage for output at the second port when a magnitude of the first voltage at the first port is greater than a magnitude of a second voltage at the second port, an

A second conversion stage is to convert a second voltage at the second port to a desired output voltage for output at the first port when a magnitude of the second voltage at the second port is greater than a magnitude of a first voltage at the first port.

20. The DC/DC converter of claim 19, wherein the first switching stage is connected to the second switching stage such that the first, second, third and fourth half-bridges form a cascade connection of series half-bridges.

21. The DC/DC converter of claim 19 or 20, wherein the first half-bridge comprises a pair of first switches connected in series between the first terminal of the first port and a junction of the first half-bridge and the second half-bridge.

22. The DC/DC converter of any of claims 19 to 21, wherein the second half bridge comprises a pair of second switches connected in series between the second terminal of the first port and a junction of the first half bridge and the second half bridge.

23. The DC/DC converter of any of claims 19 to 22, wherein the third half-bridge comprises a pair of switches connected in series between the first terminal of the second port and a junction of the third half-bridge and the fourth half-bridge.

24. The DC/DC converter of any of claims 19 to 23, wherein the fourth half-bridge comprises a pair of switches connected in series between the second terminal of the second port and a junction of the third and fourth half-bridges.

25. The DC/DC converter of any of claims 19 to 24, further comprising:

a first inductor having a first terminal connected to a junction of the pair of first switches and a second terminal connected to a junction of the pair of third switches; and

a second inductor having a first terminal connected to a junction of the pair of second switches and a second terminal connected to the pair of fourth switches.

26. The DC/DC converter of any of claims 19-25, further comprising a center point connection connecting a junction of the first and second half bridges to a junction of the third and fourth half bridges.

27. The DC/DC converter of any of claims 19-26, further comprising:

first and second capacitors closely coupled to the first and second half bridges; and

third and fourth capacitors closely coupled to the third and fourth half bridges.

28. The DC/DC converter of any of claims 19-27, wherein the first conversion stage and the second conversion stage are connected by an isolation transformer interface, and

one side of a first winding of the isolation transformer is connected to a junction of a pair of switches of the first half-bridge and the other side of the first winding is connected to a junction of the pair of switches of the second half-bridge, an

One side of a second winding of the isolation transformer is connected to a junction of a pair of switches of the third half-bridge and the other side of the second winding is connected to a junction of the pair of switches of the fourth half-bridge.

29. The DC/DC converter of any of claims 19 to 28, wherein the first port is configured to be coupled to an energy storage unit and the second port is configured to be coupled to a photovoltaic array.

Background

Electrical power conversion devices and associated control systems are used to connect various energy sources. For example, an electrical power system may include various interconnected distributed energy sources (e.g., generators and energy storage units) and loads. The power system may also be connected to a utility grid or microgrid system. Power systems employ electrical power conversion to convert power (e.g., AC/DC, DC/DC, AC/AC, and DC/AC) between these energy sources.

In power electronics, a DC/DC converter converts a source from one voltage level to another. The DC/DC converter includes a buck converter in which an output voltage is lower than an input voltage and a boost converter in which an output voltage is higher than an input voltage. DC/DC converters employ various topologies to step up or step down an input voltage to a desired output voltage. For example, a DC/DC converter may employ a switching topology in which switches, such as IGBTs, receive gate signals to convert an input voltage to a desired output voltage. DC/DC converters can be used in a variety of applications, including microgrid applications, where a DC/DC converter converts a voltage output from an energy source into a voltage suitable for a microgrid.

Disclosure of Invention

Embodiments of the present invention include a DC/DC converter in which the magnitude of the voltage at one port can be controlled to be higher, equal to, and lower than the voltage at the opposite port.

In one aspect, a DC/DC converter system includes: a bidirectional DC/DC converter for converting between voltage levels at the first port and the second port, and a control system for controlling the DC/DC converter. The bidirectional DC/DC converter comprises a first conversion stage connected to the first port and comprising a plurality of switches; and a second switching stage interfaced with the first switching stage, the second switching stage connected to the second port and including a plurality of switches. The control system comprises an outer control loop unit configured to compare a command for any one of a voltage level, a current level or a power at one of the first and second ports with an actual value of the voltage level, the current level or the power level at the one of the first and second ports and to output an interface current command based on the comparison result; an inner control loop unit configured to compare the interface current command with an actual value of the interface current at the interface of the first conversion stage and the second conversion stage and to control the switching signal duty cycle value based on the comparison result.

The inner control loop of the DC/DC converter system may comprise a first conversion stage controller and a second conversion stage controller, and the inner control loop unit may be configured to:

comparing the interface current command to an interface current comparison value to generate a first interface current command and a second interface current command; comparing the first interface current command and the second interface current command with an actual value of the interface current, wherein: the first conversion stage controller controls the duty ratio value of the switching signal of the first conversion stage according to the comparison result of the first interface current command and the actual value of the interface current; and the second switching stage controller controls the duty cycle value of the switching signal of the second switching stage in dependence on the comparison of the second interface current command with the actual value of the interface current.

In comparing the interface current command to the interface current comparison value, the inner control loop unit may be configured to: subtracting the interface current comparison value from the interface current command to generate a first interface current command; adding the interface current comparison value to the interface current command to generate a second interface current command; comparing the first interface current command with an actual value of the interface current and controlling, by the first switching stage controller, a duty cycle value of a switching signal of the first switching stage based on the comparison result; and comparing the second interface current command with the actual value of the interface current and controlling, by the second switching stage controller, the duty cycle value of the switching signal of the second switching stage based on the comparison result.

The first and second conversion stage controllers may comprise one of a Proportional Integral Derivative (PID) controller, a Proportional Integral (PI) controller, a proportional (P) controller and a hysteresis controller.

The outer control loop may include one of a Proportional Integral Derivative (PID) controller, a Proportional Integral (PI) controller, a proportional (P) controller, and a hysteresis controller for receiving a comparison of the voltage or current command and the actual voltage or current to control the interface current.

The first conversion stage may convert the voltage at the first port to an output voltage output at the second port when the voltage at the first port is higher than the voltage at the second port.

The second conversion stage may convert the voltage at the second port to an output voltage output at the second port when the voltage at the second port is higher than the voltage at the first port. Each of the first conversion stage and the second conversion stage operates to control the voltage at the first port and the voltage at the second port when the voltage at the first port and the voltage at the second port are substantially equal.

The first switching stage may comprise a first half-bridge and a second half-bridge connected in series between a first terminal and a second terminal of the first port. The second switching stage may comprise a third half-bridge and a fourth half-bridge connected in series between a third terminal and a fourth terminal of the second port.

The first half-bridge may include a pair of first switches connected in series between the first terminal of the input port and a junction of the first half-bridge, and the second half-bridge includes a pair of second switches connected in series between the junction of the first half-bridge and the second half-bridge. The third half-bridge may include a pair of switches connected in series between a node of the third half-bridge and the fourth half-bridge, and the fourth half-bridge may include a pair of fourth switches connected in series between the node of the third half-bridge and the fourth half-bridge.

The first and second conversion stages may be interfaced through the first and second inductors or an isolation transformer.

When the first and second conversion stages are interfaced through the first and second inductors, a first terminal of the first inductor may be connected to a junction of the pair of first switches and a second terminal of the first inductor may be connected to a junction of the pair of third switches; and a first terminal of the second inductor may be connected to a junction of the pair of second switches, and a second terminal of the second inductor is connected to the pair of fourth switches.

When the first switching stage and the second switching stage are connected by the isolation transformer interface, one side of the first winding of the isolation transformer may be connected to a junction of a pair of switches of the first half-bridge and the other side of the first winding is connected to a junction of a pair of switches of the second half-bridge, and one side of the second winding of the isolation transformer is connected to a junction of a pair of switches of the third half-bridge and the other side of the second winding is connected to a junction of a pair of switches of the fourth half-bridge.

The first conversion stage may be connected to an energy storage unit at a first port and the second conversion stage may be connected to a PV array at a second port.

The DC/DC converter system may further include: a first capacitor coupled to the first half bridge; a second capacitor coupled to the second half-bridge; and the control system may further comprise a capacitance control system for controlling a voltage difference between a voltage across the first capacitor and a voltage across the second capacitor, the capacitance control system being configured to: calculating the difference between the voltage across the first capacitor and the voltage across the second capacitor; calculating a duty cycle offset according to a difference between a voltage across the first capacitor and a voltage across the second capacitor; the duty cycle offset is applied to the duty cycle value output by the first conversion stage controller.

The DC/DC converter system may further include: a third capacitor coupled to the third half-bridge; a fourth capacitor coupled to the fourth half-bridge; and the control system may further comprise a capacitance control system for controlling a voltage difference between a voltage across the third capacitor and a voltage across the fourth capacitor, the capacitance control system being configured to: calculating the difference between the voltage across the first capacitor and the voltage across the second capacitor; calculating a duty cycle offset according to a difference between a voltage across the first capacitor and a voltage across the second capacitor; the duty cycle offset is applied to the duty cycle value output by the first conversion stage controller.

In another aspect, a method for controlling a bidirectional DC/DC converter comprising a first conversion stage connected to a first port and a second conversion stage connected to a second port, the first conversion stage interfacing with the second conversion stage, wherein each of the first conversion stage and the second conversion stage comprises a plurality of switches, the method comprising: comparing a command for one of a current level, a voltage level or power at one of the first port and the second port with an actual value of the current level, the voltage level or the power at the one of the first port and the second port and controlling the interface current command based on the comparison result; and comparing the interface current command with an actual value of the interface current at the interface of the first conversion stage and the second conversion stage and controlling the switching signal based on the comparison result.

Comparing the interface current command with an actual value of the interface current at the interface of the first conversion stage and the second conversion stage and controlling the switching signal based on the comparison result may comprise: comparing the interface current command to an interface current comparison value to generate a first interface current command and a second interface current command; comparing the first interface current command and the second interface current command to an actual value of the interface current; controlling a duty cycle value of a switching signal of the first switching stage according to a comparison of the first interface current command with an actual value of the interface current; the duty cycle value of the switching signal of the second switching stage is controlled in dependence on the result of the comparison of the second interface current command with the actual value of the interface current.

Comparing the interface current command with the interface current comparison value to generate a first interface current command and a second interface current command and control duty cycle values of switching signals of the first conversion stage and the second conversion stage may include: subtracting the interface current comparison value from the interface current command to generate a first interface current command; adding the interface current comparison value to the interface current command to generate a second interface current command; comparing the first interface current command with an actual value of the interface current and controlling a duty cycle value of a switching signal of the first switching stage based on the comparison result; the second interface current command is compared with the actual value of the interface current and the duty cycle value of the switching signal of the second switching stage is controlled on the basis of the comparison result.

The first conversion stage may be connected to an energy storage unit at a first port and the second conversion stage may be connected to a PV array at a second port.

In another aspect, a DC/DC converter may include a first conversion stage and a second conversion stage. The first switching stage comprises a first half-bridge and a second half-bridge connected in series between a first terminal and a second terminal of the first port. The second switching stage is coupled to the first switching stage, the second switching stage comprising a third half-bridge and a fourth half-bridge connected in series between a third terminal and a fourth terminal of the second port. The first conversion stage is for converting the first voltage at the first port to a desired output voltage for output at the second port when the magnitude of the first voltage at the first port is higher than the magnitude of the second voltage at the second port. The second conversion stage is for converting the second voltage at the second port to a desired output voltage for output at the first port when the magnitude of the second voltage at the second port is greater than the magnitude of the first voltage at the first port.

The first switching stage may be connected to the second switching stage such that the first half-bridge, the second half-bridge, the third half-bridge and the fourth half-bridge form a cascade connection of series half-bridges.

The first half-bridge may comprise a pair of first switches connected in series between the first terminal of the first port and a junction of the first half-bridge and the second half-bridge.

The second half-bridge may comprise a pair of second switches connected in series between the second terminal of the first port and a junction of the first half-bridge and the second half-bridge.

The third half-bridge may comprise a pair of switches connected in series between the first terminal of the second port and a junction of the third half-bridge and the fourth half-bridge.

The fourth half-bridge may comprise a pair of switches connected in series between the second terminal of the second port and a junction of the third half-bridge and the fourth half-bridge.

The DC/DC converter may further include: a first inductor having a first terminal connected to a node of the pair of first switches and a second terminal connected to a node of the pair of third switches; and a second inductor having a first terminal connected to a junction of the pair of second switches and a second terminal connected to the pair of fourth switches.

The DC/DC converter may further include: first and second capacitors closely coupled to the first and second half bridges; and third and fourth capacitors closely coupled to the third and fourth half bridges.

The first switching stage and said second switching stage may be connected by an isolation transformer interface, and one side of a first winding of the isolation transformer is connected to a junction of a pair of switches of the first half-bridge and the other side of the first winding is connected to a junction of a pair of switches of the second half-bridge, and one side of a second winding of the isolation transformer is connected to a junction of a pair of switches of the third half-bridge and the other side of the second winding is connected to a junction of said pair of switches of the fourth half-bridge.

The first port may be configured to be coupled to an energy storage unit and the second port may be configured to be coupled to a photovoltaic array.

Brief description of the drawingsthe accompanying drawings (non-limiting examples disclosed)

Advantages of the present invention will be readily appreciated, as the same becomes better understood, when the following detailed description is considered in conjunction with the accompanying drawings, wherein:

fig. 1 is a schematic diagram of a DC/DC converter according to an embodiment of the invention.

Fig. 2 is a schematic diagram of a DC/DC converter according to another embodiment of the present invention.

Fig. 3 is a control structure of a DC/DC converter according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of a DC/DC converter controlled by the control structure shown in fig. 2 according to an embodiment of the present invention.

Fig. 5 is a control structure of a DC/DC converter according to an embodiment of the present invention.

Fig. 6 is an exemplary power system employing a DC/DC converter in accordance with an embodiment of the present invention.

Fig. 7 is a control structure for controlling a voltage difference between voltages across capacitors of a first port and a second port according to an embodiment of the present invention.

Detailed Description

Reference is now made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments. The principles described herein, however, may be embodied in many different forms. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals may be placed throughout the different views to designate corresponding parts.

In the following description of the present invention, certain terminology is used for the purpose of reference only and is not intended to be limiting. For example, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is also to be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed terms. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, step operations, elements, components, and/or groups thereof.

A typical DC/DC converter may be connected to a source, such as a battery, so that the source voltage may be increased (or decreased) to the intermediate DC bus. For example, if the battery voltage is in the range of 300-. Such designs require that the output voltage be always higher than the input voltage, while current control can be done in either direction (e.g., charging or discharging the battery). This design is limited to increasing or decreasing the source voltage.

Embodiments of the invention include DC/DC converters that are not limited to boost (i.e., step-up) or buck (i.e., step-down) operation. The DC/DC converter comprises a first port and a second port with a topology and a control system that allows flexibility in that the voltage magnitude on one port can be controlled to be higher, equal and lower than the voltage on the opposite port.

Embodiments of the invention include a DC/DC converter and a control system having a control structure for controlling the DC/DC converter to output a desired current, voltage or power reference. Embodiments of the invention include a DC/DC converter and a control system capable of ensuring interfacing of a high voltage energy storage (e.g., battery) and a Photovoltaic (PV) array while utilizing lower voltage rated switches (e.g., semiconductor transistors such as Insulated Gate Bipolar (IGBTs), Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), etc.). Embodiments of the invention also include a DC/DC converter and a control system that enables an energy storage device (e.g., a battery) to interface with a PV array, where an output/input voltage of the energy storage device and an output voltage of the PV array have overlapping voltage magnitudes.

Referring to fig. 1, a DC/DC converter 100 according to an embodiment of the present invention may include a first conversion stage 110 and a second conversion stage 120 connected to each other. The first conversion stage is connected to a first port 130, which first port 130 may in turn be connected to a power source, such as an energy storage unit (e.g., a battery). The second conversion stage is connected to a second port 140, which second port 140 may in turn be connected to a power source, such as a Photovoltaic (PV) array or another power converter (e.g., a power inverter) or a load. The first and second conversion stages 110, 120 form a bidirectional DC/DC converter (i.e. the power flow is bidirectional). In the embodiment shown in fig. 1, the magnitude of the voltage across the first conversion stage 110 at the first port 130 may be higher or lower than or substantially equal to (i.e., nearly equal to) the magnitude of the voltage across the second conversion stage 110 at the second port 140. Thus, either side of the DC/DC converter 100 may be used as a buck or boost converter. It should be noted that although fig. 1 shows the cells and PV array connected to the first port 130 and the second port 140, different sources and/or loads may alternatively be connected to the first port 130 and the second port 140, and thus the present invention is not limited thereto.

In one embodiment, the first conversion stage 110 is operable to convert the voltage at the first port 130 to a desired magnitude (i.e., output voltage) at the port 140 when the magnitude of the voltage at the port 130 is higher than the magnitude of the voltage at the port 140. The conversion may be accomplished using any of a current command, a voltage command, or a power reference to compare with the feedback signal. The second conversion stage 120 is operable to convert the voltage at the port 140 to a desired magnitude at the port 130 when the magnitude of the voltage at the port 140 is greater than the magnitude of the voltage at the port 130. The conversion may be accomplished using any of a current command, a voltage command, or a power reference to compare with the feedback signal.

Thus, the DC-DC converter may be implemented in a design in which the voltage amplitude at either port may be within a highest predetermined voltage range, for example 1500V on either side. In this example, the voltage on port 130 or 140 can be controlled to any voltage up to 1500V while also being able to control the power flow in the DC-DC converter (i.e., control the direction of the current). Thus, for example, at port 130, the voltage may be 800V, at port 140, the voltage may be 1500V, and the current may be controlled in either direction (e.g., to charge or discharge the power supply). Similarly, port 130 may be 1500V, port 140 may be 800V, and the current may be controlled in either direction. Finally, the voltage magnitude at port 130 may be substantially equal to the voltage magnitude at port 140, and the current may be controlled to either direction.

In one embodiment, the DC/DC converter 100 includes two cascaded sets of half-bridges. The first switching stage 110 comprises a first half-bridge 112 and a second half-bridge 114 connected in series. Each of the first and second half- bridges 112, 114 may include a pair of switches Q1, Q2 and Q3, Q4. The second switching stage 120 comprises a third half-bridge 122 and a fourth half-bridge 124 connected in series. Each of the third and fourth half- bridges 122, 124 may include a pair of switches Q5, Q6 and Q7, Q8.

In the embodiment shown in fig. 1, a pair of switches Q1, Q2 of the first half bridge 112 are connected in series between the first terminal of the first port 130 and the junction of the first half bridge 112 and the second half bridge 114 (i.e., the node connecting the first half bridge to the second half bridge). A pair of switches Q3, Q4 of the second half bridge 114 are connected in series between the junction of the first and second half bridges 112, 114 (i.e., the node connecting the first half bridge to the second half bridge) and the second terminal of the port 130. A pair of switches of the third half-bridge 122 is connected in series between the first terminal of the second port 140 and the junction of the third half-bridge 122 and the fourth half-bridge 124. A pair of switches of the fourth half-bridge 124 are connected between a junction of the third half-bridge 122 and the fourth half-bridge 124 and a second terminal of the second port 140.

In one embodiment, the first switching stage 110 and the second switching stage are connected using first and second inductors L1 and L2. One terminal of the first inductor L1 is connected to the junction of a pair of switches Q1, Q2 of the first half-bridge 112 (i.e., the node connecting switches Q1 and Q2). The other terminal of the first inductor L1 is connected to the junction of a pair of switches of the third half bridge 122. One terminal of the second inductor L2 is connected to the junction of the pair of switches Q3, Q4 of the second half bridge 114, and the other terminal of the second inductor is connected to the junction of the pair of switches Q7, Q8 of the fourth half bridge 124.

In another embodiment, the first inductor L1 and the second inductor L2 may be replaced by an isolation transformer T1 as shown in fig. 2. As shown in fig. 2, one side of the first winding of the isolation transformer T1 is connected to the junction of the pair of switches Q1, Q2 of the first half bridge, and the other side of the first winding is connected to the junction of the pair of switches Q3, Q4 of the second half bridge. One side of the second winding of the transformer T1 is connected to the junction of the pair of switches Q5, Q6 of the third half bridge and the other side of the second winding is connected to the junction of the pair of switches Q7, Q8 of the fourth half bridge 124.

In embodiments where the first and second conversion stages 110 and 120 are connected by inductors L1 and L2 (fig. 1), the DC/DC converter 100 may further include an optional center point connection 50. Referring to fig. 1, a center point connection 150 may connect the junction of the first and second half bridges 112, 114 to the junction of the third and fourth half bridges 122, 124. The center-point connection 150 may be advantageous, for example, where the input/output 130 is connected to an energy storage device (e.g., one or more batteries) because noise on the battery terminals is reduced by the neutral center-point connection. However, this connection requires design compromises because ripple performance (i.e., ripple current and voltage on the battery and PV ports) can be affected to some extent.

In one embodiment, each half bridge 112, 114, 122, 124 may be closely coupled to a DC bus capacitor C1-C4 to filter and reduce overshoot of the semiconductor voltage. For example, capacitor C1 is a filter capacitor for the half bridge formed by Q1 and Q2. Each of these capacitors C1-C4 may be a single capacitor or may be a series and parallel combination of several discrete capacitors to achieve an appropriate rating.

In one embodiment, the switches Q1-Q8 are semiconductor switches with back-body diodes (back-body diodes). Examples of semiconductor switches that may be used for Q1-Q8 include, but are not limited to, IGBTs, MOSFETs, and the like.

In one embodiment, an energy storage unit may be provided on the input/output side 130, and a PV array and/or a PV inverter may be connected on the input/output side 140. One such arrangement is shown in the exemplary system of fig. 6. For example, the DC/DC converter 100 may be used between the energy storage unit 510 (e.g., battery 610) and the PV array 620, and the PV array 620 may have an inverter 630 connected to a utility AC grid 650. In this particular arrangement, it is preferred that the power flow through the DC/DC converter 100 is bi-directional, so that the system has the capability to charge the battery with power from the PV array, while also being able to discharge the battery to the grid through the PV inverter. In this case, the voltage of the cell may be higher or lower than or approximately equal to the PV voltage in both directions of power flow. The battery-side converter (i.e., the first conversion stage 110) switches when the battery voltage is higher than the PV voltage. When the cell voltage is lower than the PV voltage, the PV-side converter switches (i.e., the second conversion stage 120). When the voltages are equal or substantially equal (i.e., nearly equal), the converters on both sides switch. The determination as to whether the voltages are nearly equal may be based on design considerations and programmed into the control system of the converter 100. For example, when a value obtained by subtracting the voltage amplitude of the first port 130 from the voltage amplitude of the second port 140 is less than or equal to a predetermined value, it may be determined that the voltages are substantially equal. For example, if the port voltages are within 5% or less of each other, they may be determined to be substantially the same. Thus, either side of the DC/DC converter 100 can be used as either buck or boost.

In one embodiment, the control system 660 may include one or more controllers for controlling the inverter 630 and the DC/DC converter 100. In one embodiment, the control system 660 may include a single controller for controlling each of the DC/DC converter 100 and the inverter 630. In another embodiment, the control system 660 may include separate controllers for the DC/DC converter 100 and the PV inverter, respectively. The controller of the control system 660 may be housed within the DC/DC converter 100 and/or the inverter 630, or may be housed separately from one or both. A separate master controller may also be used to send signals to and/or coordinate between the one or more controllers of the DC/DC converter and inverter 630.

Fig. 3 shows a control structure 300 of a control system for controlling a DC/DC converter according to an embodiment of the invention. Fig. 4 is a schematic diagram of a DC/DC converter controlled by the control structure 300 shown in fig. 3 according to an embodiment of the present invention. Fig. 4 is similar to fig. 1, but also includes symbols for certain measurements and gating/switching signals for the switches sent to the DC/DC converter.

Referring to fig. 3 and 4, the control architecture 300 includes an outer control loop 310 and an inner control loop 320. The external loop 310 controls the magnitude of the voltage, current, or power at the first terminal 130 or the second port 120 (in one example, this may be the magnitude of the battery/PV current or the magnitude of the battery/PV voltage). Inner loop 320 controls interface inductor current Im 1. In the exemplary embodiment shown in fig. 4, the cell current or voltage is the current or voltage at port 130 and the PV current or voltage is the voltage or current at port 140. Interface inductor current Im1 is the current at the interface of the first conversion stage and the second conversion stage. In embodiments where the first inductor L1 and the second inductor L2 are used as an interface for the first and second conversion stages 110, 120 (fig. 1 and 4), one or both of the interface inductor currents (e.g., Im1, Im2, or Im1 and Im2) are controlled. In embodiments where the first and second inductors are replaced by an isolation transformer T1 (fig. 2), inner loop 320 controls transformer current Im 1. It should be understood that although the exemplary embodiment has the battery/PV voltage or current as the source, other sources may be coupled to the ports 130 and 140, in which case the outer loop 310 will control the voltage/current/power of one of the first and second ports 130 or 140 to which the source is connected.

In the embodiment shown in fig. 3, the controller parameters (e.g., two PI parameters) may be adjusted to accommodate the hardware parameters. The adjustment may depend on a number of factors, such as: 1) required response speed-control bandwidth of the system-e.g., whether the converter is expected to reach rated current in 1ms or 100 ms; and 2) hardware parameters of the system: inductance, capacitance and switching frequency values.

The outer control loop 310 receives as one input a command regarding a certain level (i.e., magnitude) of voltage, current, or power at one of the first port 130 and the second port 140 (e.g., battery current or PV voltage), and receives as another input feedback of the actual level of voltage, current, or power (e.g., actual magnitude of battery current or PV voltage). In the case of a command for power, the power is calculated by using values obtained from voltage and current sensors at the controlled port 130 or 140. The command for a certain level (i.e., amplitude) of voltage, current, or power (e.g., battery current or PV voltage) may be a desired amplitude of voltage, current, or power (e.g., a desired amplitude of battery current or a desired amplitude of PV voltage at the first port 130 or the second port 140). These commands may be generated internally within the controller of the DC/DC converter 100 based on the desired mode of operation, or sent by the main controller. For example, a positive battery current command may be used if the battery is to be discharged, and a negative battery current command may be used if the battery is to be charged. The feedback of the cell current or PV voltage is the actual magnitude of the cell current or the actual magnitude of the PV voltage measured at the first port 130 or the second port 140. The desired amplitude is then compared with the actual amplitude, for example by taking the difference between the desired amplitude and the actual amplitude. The difference is input into the controller 312 for controlling one of the interface inductor currents (e.g., Im1) through one of the inductors (e.g., Im 1). Controller 312 then outputs a current command Im _ cmd for the interface inductor current to inner control loop 320. Here, the current command Im _ cmd may be considered a desired magnitude of the interface inductor current, which may be compared to an actual magnitude of the interface inductor current to calculate the duty cycle value D1 for one or more switching signals transmitted to the switches Q1-Q8 of the first and second conversion stages 110, 120.

In embodiments in which centerpoint connection 150 is installed, control architecture 300 may include additional outer and inner control loops for controlling Im2 in the same manner as Im1, in addition to controlling inductor current Im 1. When the centerpoint connection 150 is omitted, control of Im2 is not required since inductor current Im2 is the same as Im 1.

In the embodiment shown in fig. 3, the controllers 312 and 322 are proportional-integral (PI) controllers. However, it should be understood that these controllers are not limited to PI controllers, and in fact, the controllers may be any closed-loop controller, including, for example, proportional-integral-derivative (PID) controllers, proportional (P) controllers, hysteretic controllers, and the like

Inner control loop 320 receives as inputs inductor current command Im _ cmd and the actual magnitude of inductor current Im 1. The inductor current command Im _ cmd is then compared to the interface inductor current Im1, for example, by taking the difference between the inductor current command Im _ cmd and the inductor current Im 1. This difference is then input into the controller 322 to calculate a duty ratio value D1, which duty ratio value D1 can be used to generate the switching signals Gb1p, Gb1n, Gb2p, Gb2n, Gs1p, Gs1n, Gs2p, Gs2n (see fig. 4) input to the switches Q1-Q8. The controller 322 outputs duty ratio values or switching signals Gb1p, Gb1n, Gb2p, Gb2n, Gs1p, Gs1n, Gs2p, Gs2n to the DC/DC converter. The duty cycle value affects the duty cycle of the signal of the switch, which affects the magnitude of the step-up/step-down of the DC/DC converter 100, and the duty cycle depends on the ratio of the voltages at the first port 130 and the second port 140 of the DC/DC converter 100.

When the control structure 300 calculates the duty cycle value, the current flowing from the input/output 130 may be defined as a positive current (e.g., a battery discharge current is defined as a positive current in embodiments where the battery is located at the input/output 130), and the control structure may control the current Im1 of the upper interface inductor (it should be understood that the control structure may similarly control the current of any interface inductor). Then, the duty value (Db1) calculated from the battery-side controller is used for the gate (Gb1p) of the IGBT Tb1 p. For example, Tb1p is fully on when the duty value Db1 is 1, Tb1p is half on and half off when the duty value Db1 is 0.5, and Tb1p is fully off when the duty value Db1 is 0. With dead time, Gb1n may be the inverse of Gb1 p. Gb2p/Gb2n can be determined in various ways based on Gb1p/Gb1 n. In one embodiment, Gb2p/Gb2n (i.e., Gb2p ═ Gb1n, Gb2n ═ Gb1p) can be determined by inverting Gb1p/Gb1 n. In another embodiment, Gb2p/Gb2n can be determined by inverting Gb1p/Gb1n and shifting by half a cycle (180 degrees). Similar logic is applied to the input/output side 140 switching signals.

In some cases only the diodes of some IGBTs are needed, i.e. the IGBTs should be completely switched off. For example, when the PV side voltage is sufficiently higher than the battery side (i.e., they are not substantially equal to each other) and current flows from the battery side to the PV side, Ts1p/Ts2n should be off, only Ts1 n/Ts2p is switching. In one embodiment, it is preferable not to gate off the switches (i.e., the switches receive the gate signals even though they are not needed). However, the direction of the current is such that the switch is non-conductive. Conversely, the rear body shunt diode conducts. Even if these switches are switching, no current passes through them and therefore no losses. In converters using MOSFETs, it is desirable that the MOSFET channel conduct current instead of the back body diode-in this case, it is required not to turn off the gating.

Although the control structure of fig. 3 is capable of calculating the duty cycles of the switching signals Gb1p, Gb1n, Gb2p, Gb2n, Gs1p, Gs1n, Gs2p, Gs2n to obtain the desired output, it is difficult for the control system to avoid simultaneous switching of the first switching stage 110 and the second switching stage 120. When the voltage amplitudes at port 130 (e.g., a battery) and at port 140 (e.g., a PV array or PV inverter) are different, the switches of only one of the first conversion stage 110 and the second conversion stage 120 need to be switched. For example, only the switches of the first or second switching stage 120 at the input/ output 130 or 140 having the highest voltage need to be switched. Preferably, the switch at the other of the first and second conversion stages 110, 120 should be constantly on or off (i.e., no switching). For example, considering an embodiment where the battery is on the input/output 130 and the PV array/PV inverter is on the input/output side 140, if PV is 1000V and the battery is 500V, the battery-side conversion stage 110 should not switch and the PV-side conversion stage 120 will have a duty cycle close to 0.5.

Although the control structure shown in fig. 3 may provide control to switch the first and second conversion stages 120 to obtain the desired output, such control may result in unnecessary switching losses (in which case control may be done but switching losses may occur if all switches are switched on both sides so that the voltage across the interfaces of the first and second conversion stages is lower than the battery voltage and PV voltage on both sides).

Fig. 5 is a control architecture 500 for a DC/DC converter according to an embodiment of the invention. The control structure 500 of fig. 5 controls the DC/DC converter 100 such that only one of the first and second conversion stages 110, 120 is switching when the voltages at these conversion stages 110, 120 differ by a predetermined voltage magnitude, and both the first and second conversion stages 110, 120 are switching when the voltage magnitudes of the first and second conversion stages 110, 120 are close enough (i.e. the difference between them is within a predetermined voltage value). In addition, the control structure of FIG. 5 provides a smooth transition between the switching of one transition stage to another.

Referring to fig. 5, the control structure 500 includes an outer control loop unit 510 and an inner control loop unit 520. The outer control loop unit 510 controls one of the voltage amplitude, current amplitude or power of the port (110 or 120) and generates an interface inductor current command Im _ cmd (in embodiments where the first and second inductors are replaced by an isolation transformer T1 (see fig. 5), the inner loop 320 may control the transformer current Im 1). The inner control loop 520 receives the inductor current command Im _ cmd and generates two different inductor current commands, a first inductor current command lb _ cmd and a second inductor current command ls _ cmd, by comparing the interface current command with the interface current comparison value (or in other words, by adjusting the Im _ cmd values for the two ports using the interface current comparison value Idelta). The inner control loop 520 uses the first and second inductor current commands Ib _ cmd and Is _ cmd to generate the first and second duty cycle values Db1 and Ds 1. The first duty cycle value Db1 is used to control the switching of the switches Q1-Q4 of the first conversion stage 110, and the second duty cycle value Ds1 is used to control the switching of the switches Q5-Q8 of the second conversion stage 120.

In embodiments in which centerpoint connection 150 is installed, control architecture 500 may include additional outer and inner control loops in addition to controlling inductor current Im1 for controlling Im2 in the same manner as control Im1 when centerpoint connection 150 is omitted, since inductor current Im2 is the same as Im1, control of Im2 is not required.

In the embodiment shown in fig. 5, the controllers 512, 522, and 524 are proportional-integral (PI) controllers. However, it should be understood that these controllers are not limited to PI controllers and, in fact, the controllers may be any closed-loop controller, including, for example, proportional-integral-derivative (PID) controllers and proportional (P) controllers.

The outer control loop unit 510 receives as input a command for voltage amplitude, current amplitude, or power (e.g., battery current or PV voltage) at one of the first and second ports 130 and 140. The outer control loop unit 510 receives feedback of the voltage, current or power of the port 130 or 140 (e.g., feedback of the battery current or PV voltage) as another input. Similar to the control structure described with reference to fig. 3, it should be understood that the cell/PV voltage or current as the source is exemplary and other sources may be coupled to ports 130 and 140. The command for voltage, current, or power (e.g., battery current or PV voltage) may be a desired magnitude of voltage, current, or power (e.g., a desired magnitude of battery current or a desired magnitude of PV voltage). The feedback of the voltage, current, or power (e.g., the battery current or the PV voltage) is the actual magnitude of the voltage, current, or power (e.g., the actual magnitude of the battery current or the PV voltage) at the port 130 or 140. The desired amplitude is then compared with the actual amplitude, for example by taking the difference between the desired amplitude and the actual amplitude. The difference is input into the controller 512 to control one of the interface inductor currents (e.g., Im1) on one of the plurality of inductors (e.g., Lm 1). Controller 512 then outputs a current command Im _ cmd for the interface inductor current to inner control loop 520. Here, the current command Im _ cmd may be a desired magnitude of the interface inductor current compared to an actual magnitude of the interface inductor current.

In the inner control loop 520, the interface inductor (Lm1) current (Im1) is controlled by calculating the gate duty cycle values Db1, Ds1 for switching the signals sent to the switches Q1-Q8 so that the magnitude of the current Im1 equals the magnitude of the current command Im __ cmd received from the outer control loop. In the case where the first port 130 and the second port 140 have different voltage amplitudes, the gate duty cycle calculated by the control structure of the control system is used only for the switches on the higher voltage side (i.e., the switches of the conversion stages connected to the port 130 or 140 having the higher voltage amplitude). The gate duty cycle value for the lower voltage side switch is either a constant 1 or 0. For example, considering an embodiment where the battery is located at the input/output 130 and the PV array/PV inverter is located at the input/output side 140, if PV 1000V and battery 500V, the battery-side conversion stage 110 should be a constant 1 or 0 switch, while the PV-side conversion stage 120 will switch according to the duty cycle value Ds 1.

It should be noted that for the topology of the DC/DC converter 100, there will be a large current disturbance if the controller makes a mistake as to which side is the higher voltage (i.e. the voltage of the first conversion stage 110 or the second conversion stage 120). Considering the case where the cell is connected to the first port 130 and the PV array is connected to the second port 140, it can be appreciated that the cell voltage does not change rapidly and can be considered constant within a few seconds. However, the PV voltage can and often does vary rapidly because the PV voltage depends on the amount of sunlight incident on the PV array. If the voltage fed back to the control system is incorrect, it may be mistaken for which side voltage is higher (i.e., which of the voltage amplitudes of the first port 130 and the second port 140 is higher). Therefore, when the PV voltage rapidly exceeds the cell voltage, current disturbance easily occurs.

The control structure of the embodiment shown in fig. 5 enables a smooth transition from one transition stage to another.

In the embodiment shown in FIG. 5, the inner control loop 520 includes two controllers, a first switching stage controller 522 and a second switching stage controller 524 (e.g., two PI controllers-as described above, the controllers are not limited to PI controllers and may be any closed loop controller). The first conversion stage controller 522 controls the gate duty cycle Db1 for generating the switching signals output to the switches Q1-Q4 of the first conversion stage 110, and the second conversion stage controller 524 controls the gate duty cycle Ds1 for generating the switching signals output to the switches Q5-Q8 of the second conversion stage 120.

When implementing the control architecture in the embodiment shown in fig. 5, each of the first conversion stage 110 and the second conversion stage 120 may be considered as intended to control Im1 current. In practice, however, only one Im1 current is to be controlled. By issuing different current commands for the two PI controllers as shown in fig. 5, the result of the two controllers 522 and 524 attempting to control one current control at the same time is that the lower voltage side controller is always in saturation and cannot control the current. Therefore, the gate duty value on the lower voltage side is constant (e.g., increased to its maximum value of 1, or minimum value of 0). That is, the lower voltage side switch is fully on or off, while the higher voltage side switch is switching to control Im 1.

The current command may be calculated as follows:

Ib_cmd＝Im_cmd-Idelta；

ls_cmd＝Im_cmd+Idelta；

idelta is called the interface current comparison value. The interface current comparison value Idelta may be set to a constant positive value. However, it is preferable to change its value using Im _ cmd, as shown in the following equation.

Idelta＝Kdrp*abs(Im_cmd)

In the above formula, the interface current comparison value Idelta should be a positive value. Preferably, a minimum limit Idelta _ min is set for the interface current comparison value Idelta, so that Idelta is Idelta _ min if Kdrp _ abs (Im _ cmd) < Idelta _ min.

The reduction factor Kdrp is preferably a small proportion (e.g. 5-10%, Kdrp 0.05-0.1). Idelta _ min is preferably set to 5% of the rated current of the converter as an initial value for regulation.

The duty cycles Db1 and Ds1 are typically limited to a maximum of 1. When the voltages of the first and second ports 130 and 140 are sufficiently separated (i.e., the voltage amplitudes at the first and second ports 130, 140 are not substantially equal), one of the duty cycles (the side with the lower voltage) saturates to 1 and that side does not switch. The duty cycle on the other side is lower than 1 and the side switches. When the voltages are substantially the same (i.e., the difference between the voltage levels at the first and second ports is less than the predetermined value), the maximum duty cycle is limited to the predetermined value (e.g., to 0.95). This results in a two-sided switch. In one embodiment, there is one hysteresis band (25V in this example) to transition from one condition to another, in order to prevent rapid switching between modes when at the edge. The control system may include the following control logic for one example, in which for the case where the voltages V1 and V2 of the first port 130 and the second port 140 are considered substantially the same, the maximum duty cycle is limited to a predetermined value of 0.95, providing a hysteresis band of 25V if they are less than 50V apart:

if abs (V1-V2) <25V// when the voltage is close enough (within 25V), the maximum duty cycle is limited to 0.95

Db1_max＝0.95Ds1_max＝0.95

Otherwise, if abs (V1-V2) >50V// voltage are sufficiently separated (greater than 50V), the maximum duty cycle is released to 1

Db1_max＝1Ds1_max＝1

According to the above equation, in the inner control loop 520, the interface current command Im _ cmd controlled by the outer control loop is compared with the interface current comparison value Idelta or the interface current command Im _ cmd controlled by the outer control loop is adjusted by the interface current comparison value Idelta to output the first and second interface current commands lb _ cmd and ls _ cmd. In the embodiment of fig. 5, the comparison to the interface current comparison value Idelta includes subtracting the interface current comparison value Idelta from the interface current command Im _ cmd to produce a first interface current command lb _ cmd and adding the interface current comparison value Idelta to the interface current command Im _ cmd to produce a second interface current command. The first and second interface current commands are then compared to actual values of interface current Im1 (e.g., interface current (fig. 1) or transformer current (fig. 2) on inductor L1), e.g., by subtracting the actual values of interface current Im1 from these values, and outputting the comparison results to first and second conversion stage controllers 522 and 524. The first and second conversion stage controllers 522 then generate the gate duty cycle values Db1 and Ds1 to generate switching signals for the first and second conversion stages 110 and 120, respectively.

When performing the above control, it should be noted that the actual Lm1 current Im1 may be different from the command Im _ cmd. However, this is not problematic because the ultimate goal is the battery current or PV voltage controlled by the outer control loop 510. The current command Im _ cmd will be automatically adjusted by the outer control loop 510.

To feedback the internal control unit, the interface current Im1 is sampled. It should be noted that interface inductor current Im1 may contain high frequency ripple. The ripple rises/falls approximately linearly. The ripple frequency is equal to the switching frequency of the switches of the first and second switching stages 110 and 120 or equal to twice the switching frequency of the switches of the first and second switching stages 110 and 120. The ripple amplitude depends on the ripple frequency, the amplitude of the inductances Lm1 and Lm2, and the difference between the first port 130 (e.g., battery) and the second port 140 (e.g., PV voltage). If the sampling frequency of the Lm1 current feedback is the same as the switching frequency, there may be an error in the sampled value of the Lm1 current. Therefore, it is preferable to sample at the midpoint of the ripple, otherwise the sampled value is different from the actual average current. However, in any event, since Lm1 is not the final target, the outer control loop (which receives as input the final target value (e.g., battery current or PV voltage) and its actual value) will automatically adjust for the error in the Lm1 current.

When the DC/DC converter 100 is coupled to an energy storage device (e.g., a battery) and a PV array/inverter, the control target may be the battery current or the PV voltage for the outer control loop 310, and the control structure 500 may transition between these two targets depending on which target the user wants to control. When the target is battery current, the actual battery current is sampled for feedback in the outer loop 310; and when the target is PV voltage, the actual PV voltage is sampled for feedback in the outer loop 310. It should be noted that when the battery current is sampled, this sampling is more critical than when the interface inductor L1 current of the inner loop is sampled. Because interface inductor current Im1 is not the final target, the accuracy of Im1 current sampling is not as important because, as described above, outer control loop 510 will automatically adjust for inner control loop 520. Since the battery current is the final target, its accuracy is more important when sampling.

As described above, on the terminals of the first converter stage 110 (e.g., the battery side of the converter), there are capacitors C1 and C2. When there is current between the battery and the DC/DC converter, the (battery) current will contain some ripple or oscillation. The ripple frequency is the switching frequency (or twice). Assuming a fixed switching frequency, the battery current ripple amplitude depends mainly on the impedance between the battery and the capacitor of the converter. The battery current ripple may be out of specification if the capacitor on the battery side of the converter is not large enough or/and the switching frequency is not high enough. An additional inductor may be provided between the battery and the converter.

In addition to the higher accuracy required for battery current feedback than Lm1 current, the midpoint of the battery current also moves as the impedance between the battery and the converter changes. Therefore, it is difficult to sample the midpoint of the battery current or correct an error due to sampling at an erroneous point of the battery current. Thus, in one embodiment, the battery current for feedback is sampled at a higher frequency than the switching frequency of the switches of the first and second switching stages 110 and 120. For example, in one embodiment, 16 points of the battery current are sampled over a switching period, and then an average of the 16 points is calculated and used as feedback for battery current control. An increase in the number of sampling points increases the delay and slows down the battery current control. Thus, the number of sampling points may be determined based on the desired response time. Furthermore, if the battery current ripple is high, the number of sampling points may be increased.

Fig. 7 is a control structure/system for controlling the voltage difference between the voltages on the capacitors of the first port and the second port according to an embodiment of the present invention. It is desirable to keep the difference between the voltage on the capacitor C1 on the first port 130 and the voltage on the capacitor C2 (and similarly, the voltage on the capacitor C3 and the voltage on the capacitor C4 on the second port 140) near zero. Fig. 7 illustrates a control structure/system that may be provided with the control structure of fig. 3 or 5 to accomplish this desire. The control structure 700 may be provided in the same or a separate physical controller as the control structure of fig. 5.

Referring to fig. 7, the voltages across the capacitors C1 and C2 (fig. 1 and 2) were measured and their differences (Vc1-Vc2) were calculated. If the direction of current flow in inductor L1 is from port 130 to port 140, this value is multiplied by 1. The current in L2 or the current in transformer T1 may also be used for this purpose. If the current direction is opposite, the voltage difference is multiplied by-1. The low pass filter 710 may be used to filter the measured current and may also use the direction of the filtered current.

The value so obtained is then input into controller 702 to calculate the duty cycle offset that must be applied to the duty cycle obtained from controller 522 (in fig. 5). The output of the controller is added to the output of the controller 522 to generate the switching signals for the switches Q1 and Q2 of the first half-bridge 112 and subtracted from the output of the controller 522 to generate the switching signals for the switches Q3 and Q4 of the second half-bridge 114.

The controller 702 may be a closed-loop controller, such as a PI controller, a proportional-integral-derivative (PID) controller, a proportional (P) controller, a hysteresis controller, or the like.

A similar approach is taken to keep the voltage difference between capacitors C3 and C4 of port 140 near zero. The voltages across the capacitors C3 and C4 were measured and the difference between them was calculated (Vc3-Vc 4). If the direction of current flow in inductor L1 is from port 130 to port 140, this value is multiplied by 1. The current in L2 or the current in transformer T1 may also be used for this purpose. If the current direction is opposite, the voltage difference is multiplied by-1. The measured current may be filtered using a low-pass filter and the direction (sign) of the filtered current may also be used.

The value so obtained is then input to the controller to calculate the duty cycle offset that should be applied to the duty cycle obtained from controller 524 (fig. 5). The output of the controller 524 is subtracted from the output of the controller for generating the switching signal of the third half bridge 122 and added to the output of 524 for generating the switching signal of the fourth half bridge 124.

Although in certain exemplary embodiments discussed above, the DC/DC converter 100 is described as being coupled between an energy storage device and a PV array/inverter, it should be understood that the invention is not limited to this application. One of ordinary skill in the art will readily appreciate that embodiments of the present invention are suitable for additional applications, such as applications requiring DC/DC conversion and having superimposed voltages on the first and second 130 and 140 inputs/outputs. Other examples include backup power supplies in Variable Frequency Drive (VFD) applications. The DC/DC converter may be connected to the DC bus of the VFD. When the grid voltage is present, then the dc bus voltage is established by the grid and the VFD powers the motor. When the grid disappears (e.g., a power outage), the DC/DC converter can maintain the DC bus by discharging the battery into the VFD, thereby allowing the VFD to operate without interruption.

The control structures 300 and 500 may be embodied on a controller such as a Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA), or the like. However, it should be understood that the controller is not limited to these and may be any type of digital processor or analog or mixed signal circuit. In addition, the control structures 300 and 500 may be embodied on a single controller or multiple controllers (e.g., separate controllers for the outer and inner loops).

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed power system without departing from the scope of the disclosure. Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.