Switching strategy for improving efficiency of power converter
阅读说明:本技术 用于提高功率转换器的效率的开关策略 (Switching strategy for improving efficiency of power converter ) 是由 东栋 R.G.瓦戈纳 G.贾里雷迪 R.N.拉朱 于 2018-01-09 设计创作,主要内容包括:提供了用于操作功率转换器的系统和方法。DC-AC转换器可包括内部转换器和外部转换器。内部转换器可包括隔离变压器、第一多个开关装置。外部转换器可包括第二多个开关装置。控制方法可包括确定外部转换器的输出电压。控制方法可进一步包括至少部分地基于外部转换器的输出电压来控制内部转换器的操作。(Systems and methods for operating a power converter are provided. The DC-AC converter may include an internal converter and an external converter. The internal converter may include an isolation transformer, a first plurality of switching devices. The external converter may comprise a second plurality of switching devices. The control method may comprise determining an output voltage of the external converter. The control method may further comprise controlling operation of the internal converter based at least in part on the output voltage of the external converter.)
1. A control method for operating a DC-AC converter comprising an internal converter comprising an isolation transformer and a first plurality of switching devices and an external converter comprising a second plurality of switching devices, the method comprising:
determining an output voltage of the external converter; and
controlling the internal converter to be in an on state or an off state based at least in part on the output voltage of the external converter.
2. The control method of claim 1, wherein at least one of the first plurality of switching devices or the second plurality of switching devices comprises a silicon carbide MOSFET.
3. The control method of claim 1, wherein controlling operation of the inner converter based at least in part on the output voltage of the outer converter comprises controlling the inner converter to be in an off state when the output voltage of the outer converter is zero volts.
4. The control method of claim 1, wherein controlling operation of the internal converter based at least in part on the output voltage of the external converter comprises controlling the internal converter to be in an on state when the output voltage of the external converter is non-zero.
5. The control method of claim 1, wherein determining the output voltage of the external converter comprises identifying one or more gate commands for the external converter; and is
Wherein controlling operation of the internal converter based at least in part on the output voltage of the external converter comprises controlling the internal converter based at least in part on the one or more gate commands for the external converter.
6. The control method of claim 5, wherein controlling the internal converter based at least in part on the one or more gate commands for the external converter comprises controlling the internal converter to reach an on state when the one or more gate commands for the external converter comprise a non-zero duty cycle.
7. The control method of claim 5, wherein controlling the internal converter based at least in part on the one or more gate commands for the external converter comprises controlling the duty cycle of gate commands for the internal converter based at least in part on a duty cycle of gate commands for the external converter.
8. The control method of claim 7, wherein the duty cycle of gate commands for the internal converter is the same as the duty cycle of gate commands for the external converter.
9. The control method of claim 1, wherein the internal converter further comprises a first conversion entity and a second conversion entity;
wherein the first conversion entity is a DC-AC conversion entity;
wherein the second conversion entity is an AC-DC conversion entity; and is
Wherein the isolation transformer is coupled between the first conversion entity and the second conversion entity.
10. The control method of claim 9, wherein the external converter comprises a third conversion entity; and is
Wherein the third conversion entity is a DC-AC conversion entity.
11. The control method of claim 1, wherein the DC-AC converter comprises a plurality of DC-AC inverter blocks.
12. The control method of claim 1, wherein the DC-AC converter comprises a multi-phase DC-AC converter; and is
Wherein the control method is performed for each phase of the multiphase power converted by the multiphase DC-AC converter.
13. A power conversion system, comprising:
a DC-AC converter comprising an internal converter and an external converter, the internal converter comprising an isolation transformer and a first plurality of switching devices, the external converter comprising a second plurality of switching devices; and
a control system configured to control operation of the DC-AC converter;
wherein the control system is configured to:
determining an output voltage of the external converter; and is
Controlling the internal converter to be in an on state or an off state based at least in part on the output voltage of the external converter.
14. The power conversion system of claim 14, wherein the control system is configured to control the internal converter to reach an off state when the output voltage of the external converter is zero volts.
15. The power conversion system of claim 14, wherein when the output voltage of the external converter is non-zero, the control system is configured to control the internal converter to reach an on state.
16. The power conversion system of claim 14, wherein the control system is configured to determine the output voltage of the external converter by identifying one or more gate commands for the external converter; and is
Wherein the control system is configured to control the internal converter based at least in part on the one or more gate commands for the external converter.
17. The power converter system of claim 16, wherein when the one or more gate commands to the external converter comprise a non-zero duty cycle, the control system is configured to control the internal converter to reach an on state.
18. The power conversion system of claim 16, wherein the control system is configured to control the internal converter based at least in part on a duty cycle of a gate command for the external converter.
19. The power conversion system of claim 18, wherein the control system is configured to control the duty cycle of gate commands for the internal converter to match the duty cycle of gate commands for the external converter.
20. A wind power generation system, comprising:
a wind generator configured to generate AC power;
an AC-DC converter coupled to the wind generator, the AC-DC converter configured to convert the AC power from the wind generator to DC power;
a DC link coupled to the AC-DC converter, the DC link configured to receive DC power from the AC-DC converter;
a DC-AC converter coupled to the DC link, the DC-AC converter configured to receive DC power from the DC link; the DC-AC converter comprises an internal converter comprising an isolation transformer and a first plurality of switching devices and an external converter comprising a second plurality of switching devices, at least one of the first or second plurality of switching devices comprising a silicon carbide MOSFET; and
a control system configured to control operation of the DC-AC converter;
wherein the control system is configured to:
determining an output voltage of the external converter; and is
Controlling the internal converter to be in an on state or an off state based at least in part on the output voltage of the external converter;
wherein, when the output voltage of the external converter is zero volts, the control system is configured to control the internal converter to reach an off state; and is
Wherein, when the output voltage of the external converter is non-zero, the control system is configured to control the internal converter to reach an on state.
Technical Field
The present subject matter relates generally to power systems, and more particularly to systems and methods for improving the efficiency of power converters.
Background
Power generation systems may use power converters to convert power into a form of power suitable for a power grid. In a typical power converter, a plurality of switching devices, such as insulated gate bipolar transistors ("IGBTs") or metal oxide semiconductor field effect transistors ("MOSFETs"), may be used in an electronic circuit, such as a half-bridge or full-bridge circuit, to convert power. Recent advances in switching device technology have allowed the use of silicon carbide ("SiC") MOSFETs in power converters. The use of SiC MOSFETs allows the power converter to operate at much higher switching frequencies than conventional IGBTs.
Disclosure of Invention
Aspects and advantages of embodiments of the present disclosure will be set forth in part in the description which follows, or may be learned by practice of the embodiments.
One exemplary aspect of the present disclosure relates to a control method for operating a DC-AC converter. The DC-AC converter may include an internal converter and an external converter. The internal converter may include an isolation transformer and a first plurality of switching devices. The external converter may comprise a second plurality of switching devices. The method may include determining an output voltage of the external converter. The method may also include controlling operation of the internal converter based at least in part on an output voltage of the external converter.
Another exemplary aspect of the present disclosure relates to a power conversion system. The power conversion system may include a DC-AC converter including an internal converter and an external converter. The internal converter may include an isolation transformer and a first plurality of switching devices. The external converter may comprise a second plurality of switching devices. The power conversion system may also include a control system configured to control operation of the DC-AC converter. The control system may be configured to determine an output voltage of the external converter. The control system may be further configured to control operation of the internal converter based at least in part on the output voltage of the external converter.
Another exemplary aspect of the present disclosure relates to a wind power generation system. The wind power generation system may include a wind generator configured to generate AC power and an AC-DC converter coupled to the wind generator. The AC-DC converter may be configured to convert AC power from the wind turbine into DC power. The wind power generation system may further comprise a DC link coupled to the AC-DC converter. The DC link may be configured to receive DC power from the AC-DC converter. The wind power system may further comprise a DC-AC converter coupled to the DC link. The DC-AC converter may be configured to receive DC power from the DC link. The DC-AC converter may include an internal converter and an external converter. The internal converter may include an isolation transformer and a first plurality of switching devices. The external converter may comprise a second plurality of switching devices. At least one of the first plurality of switching devices or the second plurality of switching devices may be a silicon carbide MOSFET. The wind power generation system may further comprise a control system configured to control the operation of the DC-AC converter. The control system may be configured to determine an output voltage of the external converter. The control system may also be configured to control operation of the internal converter based at least in part on the output voltage of the external converter. When the output voltage of the external converter is zero volts, the control system may be configured to control the internal converter to reach an off state. When the output voltage of the external converter is non-zero, the control system may be configured to control the internal converter to reach an on-state.
Variations and modifications may be made to these exemplary aspects of the disclosure.
These and other features, aspects, and advantages of various embodiments will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the relevant principles.
Drawings
A detailed discussion of embodiments directed to one of ordinary skill in the art is set forth in the specification, which makes reference to the appended drawings, in which:
FIG. 1 depicts an exemplary wind power generation system;
fig. 2 depicts example elements for use in a power converter, according to an example aspect of the present disclosure;
FIG. 3 depicts a power converter according to an exemplary aspect of the present disclosure;
FIG. 4 depicts an exemplary switching strategy in accordance with an exemplary aspect of the present disclosure;
FIG. 5 depicts an exemplary switching strategy according to an exemplary aspect of the present disclosure;
FIG. 6 depicts an exemplary switching strategy according to an exemplary aspect of the present disclosure;
FIG. 7 depicts an exemplary method according to an exemplary aspect of the present disclosure; and
fig. 8 depicts elements suitable for use in a control device according to an exemplary aspect of the present disclosure.
Detailed Description
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. The examples are provided as illustrations of the invention and not as limitations of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a further embodiment. It is therefore intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.
Exemplary aspects of the present disclosure relate to systems and methods for improving the efficiency of power converters. For example, power generation systems, such as systems that use a doubly-fed induction generator ("DFIG") as a power generation unit, may use one or more power converters to convert power from low-voltage multi-phase ac power to medium-voltage multi-phase ac power. As used herein, "LV" power may be a power of less than about 1.5 kilovolts. As used herein, "MV" power may be a power greater than about 1.5 kilovolts and less than about 100 kilovolts. As used herein, the term "about" may mean within 20% of the stated value.
The power converter may include, for example, a first power converter configured to convert AC power output from a generator (such as a DFIG) to DC power and provide the DC power to a DC link. The second power converter may be configured to convert DC power from the DC link to AC power suitable for use on the grid. For example, the second power converter may be a DC-AC power converter and may utilize SiC MOSFETs as switching devices, allowing for very high switching frequencies. Other switching devices may also be used in the power converter. The DC-AC converter may include an internal converter and an external converter. The internal converter may comprise a first DC-AC conversion entity configured to convert LV DC power from the DC link into LV AC power, an isolation transformer configured to provide isolation. The second AC-DC conversion entity may be configured to convert LV AC power to LV DC power. The external converter may comprise a third DC-AC conversion entity configured to convert the LV DC power into LVAC power suitable for use on the grid. A plurality of inverter blocks (blocks) may be connected in series to build the MV AC voltage suitable for use on the MV AC power grid. Each conversion entity may comprise a plurality of bridge circuits, wherein each bridge circuit may comprise a plurality of switching devices (such as sicmosfets). The external converter may be configured to regulate the line current. Depending on the modulation strategy implemented, the output voltage of the external converter may be + Vdc, -Vdc, or zero voltage. In an embodiment, the DC-AC converter may comprise a plurality of DC-AC inverter blocks, wherein each inverter block comprises a first conversion entity, a second conversion entity, a third conversion entity and an isolation transformer as described herein. In another embodiment, the DC-AC converter may be a multi-phase DC-AC converter configured to convert multi-phase (e.g., three-phase) power output from the power generation unit.
The very high switching frequency allowed by SiC MOSFETs provides the advantage that the size and cost of the isolation transformer can be significantly reduced and the efficiency of the power converter can be improved compared to conventional IGBTs. However, in some cases, approximately 10-90% of the power loss in the DC-AC power converter may come from the isolation transformer, such as, for example, losses due to heating of the isolation transformer components. Furthermore, to meet certain power density and reliability standards, heat in the isolation transformer must be effectively removed, which can increase the cost of the cooling system required for the power converter. Additionally, the peak power rating of the power converter may be limited by thermal constraints from the isolation transformer.
In a typical configuration, the internal converter is kept running at all times to allow power flow to be available to the external converter when needed. However, during the time period when the output voltage of the external converter is zero, the power flow from the external converter to the internal converter is zero. For example, in each switching cycle of the external converter, the power flow between the internal converter and the external converter may be zero for different time periods, depending on the modulation index. Thus, during the time period when the output of the external converter is zero volts, in typical configurations, power may still flow through the isolation transformer, causing losses due to heating of the isolation transformer.
Exemplary aspects of the present disclosure relate to systems and methods of switching power converters to convert power more efficiently. For example, systems and methods according to exemplary aspects of the present disclosure may allow for turning off an internal converter during a time period when the external converter provides a zero output voltage. For example, the method may include first determining an output voltage of the external converter. The output voltage may be determined in any number of ways. For example, the output voltage may be determined by identifying one or more gate commands to the external converter. In an embodiment, the control device may be configured to identify one or more gate commands for the external converter and determine the output voltage based at least in part on the one or more gate commands. In another embodiment, the control device may be configured to determine when the output voltage is zero based on one or more measured parameters.
Further, the method may include controlling operation of the internal converter based at least in part on an output voltage of the external converter. For example, the control device may be configured to turn the internal converter into the off-state when the output voltage of the external converter is zero volts. As used herein, the term "off state" refers to an operating state in which substantially no power flows through the device. For example, the off state may be a state as follows: one or more switching devices (e.g., SiC MOSFETs) are operated in the converter such that power flow through the converter is substantially stopped. Furthermore, the control means may control the internal converter to reach the on-state when the output voltage of the external converter is non-zero (such as, for example, when the external converter provides a + Vdc or-Vdc output). As used herein, the term "on state" refers to an operating state in which power may flow through the device. For example, the on state may be the following state: one or more switching devices (e.g., SiC MOSFETs) are operated in the converter such that power flow through the converter occurs (such as through an isolation transformer).
In an embodiment, the output voltage may be determined by identifying one or more gate commands for the external converter. The operation of the internal converter may then be controlled based at least in part on one or more gate commands to the external converter. For example, the internal converter may be controlled to reach an on state when the one or more gate commands to the external converter include a non-zero duty cycle. In another embodiment, controlling the inner converter based at least in part on the one or more commands to the outer converter may include controlling a duty cycle of the gate commands to the inner converter based at least in part on a duty cycle of the gate commands to the outer converter. For example, the external converter may be operated in a pulse width modulation ("PWM") mode to regulate line current. When operating the external converter in the PWM mode, one or more gate commands may be provided to the external converter to turn on the external converter to provide pulses to generate a desired output waveform. Each pulse may include an on period and an off period. In an embodiment, the duty cycle of the gate command for the internal converter may be the same as the duty cycle of the gate command for the external converter. For example, during a time period in which the external converter is in the PWM mode and is operating in the on period of the pulse, the internal converter may be turned on. Further, the internal converter may be turned off during a time period in which the external converter is in the PWM mode and operates in the off period of the pulse.
In this manner, systems and methods according to exemplary aspects of the present disclosure may have the technical effect of allowing more efficient operation of DC-AC power converters utilizing isolation transformers by reducing core losses in the isolation transformers. For example, in some cases, core losses can be reduced by up to 50%. Furthermore, systems and methods according to exemplary aspects of the present disclosure may allow power density and reliability criteria to be more easily met by reducing the amount of heat that must be removed from the isolation transformer, thereby allowing the cost of the cooling system to be reduced. Furthermore, operating the DC-AC power converter and/or inverter block according to exemplary aspects of the present disclosure may allow for an increase in power rating while satisfying thermal constraints in cases where the peak power rating of the DC-AC power converter and/or DC-AC inverter block is limited by the thermal constraints of the isolation transformer. Thus, fewer DC-AC power converters and/or DC-AC inverter blocks in the power converter may be required to meet a particular power rating, which may improve the reliability of the power conversion system by reducing the number of components in the system.
Referring now to the drawings, exemplary aspects of the disclosure will be discussed in more detail. FIG. 1 depicts a
In exemplary wind
In an exemplary configuration, the rotor-
In some embodiments, as will be discussed in more detail with respect to fig. 2 and 3, the rotor-
The
In operation, power generated at
In wind
Various circuit breakers and switches (such as
The
Referring now to fig. 2, a topology of components in a DC-AC converter is depicted. Fig. 2 depicts an exemplary DC-
As shown, the
The
Fig. 3 depicts an exemplary line-
Each conversion module 200-204 includes a plurality of inverter blocks 206-210. For example, as shown,
In one particular exemplary embodiment, when providing power to
The
It will be appreciated that although fig. 3 depicts only the line-
Referring now to fig. 4, an example switching strategy is depicted in accordance with an example aspect of the present disclosure. Fig. 4 depicts an
Further, as depicted in fig. 4, the
Referring now to fig. 5, an example switching strategy is similarly depicted, in accordance with an example aspect of the present disclosure. Fig. 5 depicts portions of the switching strategy depicted in fig. 4, and elements that are the same as or similar to elements in fig. 4 are referred to with the same reference numerals. For example, as shown in fig. 5, during periods when the external converter
Referring now to fig. 6, an example switching strategy is depicted in accordance with an example aspect of the present disclosure. Fig. 6 depicts additional switching strategies and uses the same reference numbers to refer to elements that are the same or similar to elements in fig. 4 and 5. The external converter
Referring now generally to fig. 4-6, a switching strategy is depicted to allow the output voltage of the
Further, systems and methods according to exemplary aspects of the present disclosure may be implemented in a DC-AC converter (such as a DC-AC converter including one or more silicon carbide MOSFETs and an isolation transformer). Furthermore, systems and methods according to exemplary aspects of the present disclosure may be used in a DC-AC converter that includes a plurality of inverter blocks (such as
Referring now to fig. 7, an exemplary control method (700) for operating a DC-AC converter is depicted, according to an exemplary aspect of the present disclosure. The DC-AC converter may include an internal converter and an external converter. For example, the internal converter may be
At (702), the method (700) may include determining an output voltage of an external converter. For example, the output voltage may be determined by one or more measured parameters, such as from one or more sensors configured to measure the output voltage of the
At (704), the method (700) may include determining whether the output voltage is zero. If the output voltage of the
At (710), the method (700) may include identifying one or more gate commands for an external converter. For example, the output voltage of the external converter may be determined by identifying one or more gate commands for the external converter. Further, operation of the internal converter (such as the internal converter 240) may be controlled based at least in part on one or more gate commands to the external converter.
For example, at (712), the method (700) may include determining whether a duty cycle of the external converter is non-zero. If the duty cycle is zero, then at (714), the
In this way, controlling the
Fig. 8 depicts an
The one or
Computing device(s) 810 may also include a
The techniques discussed herein make reference to computer-based systems and the actions taken by and information sent to and from the computer-based systems. Those of ordinary skill in the art will appreciate that the inherent flexibility of a computer-based system allows for a wide variety of possible configurations, combinations, and assignments of tasks and functions between and among the components. For example, the processes discussed herein may be implemented using a single computing device or multiple computing devices operating in combination. The databases, memories, instructions, and applications may be implemented on a single system or distributed across multiple systems. The distributed components may operate sequentially or in parallel.
For purposes of illustration and discussion, the present disclosure is discussed with reference to a DFIG power generation system including a power converter utilizing silicon carbide MOSFETs. One of ordinary skill in the art, using the disclosure provided herein, will appreciate that other power generation systems and/or topologies may benefit from the exemplary aspects of the present disclosure. For example, the grounding and protection schemes disclosed herein may be used in wind power generation systems, solar power generation systems, gas turbine power generation systems, or other suitable power generation systems. Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
- 上一篇:一种医用注射器针头装配设备
- 下一篇:开关电源装置