阅读说明：本技术 用于电驱动器的降压-升压转换器 (Buck-boost converter for an electric drive ) 是由 张明远 段诚武 郝镭 姚健 于 2020-03-16 设计创作，主要内容包括：用于车辆的电驱动系统可包括承载直流(DC)母线电压的正母线轨和负母线轨、能量存储系统(ESS)、具有多个半导体开关的功率逆变器,该多个半导体开关可操作用于将DC母线电压逆变为交流(AC)母线电压,以及电机。DC-DC转换器可以连接到电容器和功率逆变器之间的母线轨,并且可以包括设置在正母线轨中的转换器半导体开关、连接到正母线轨并接收流过转换器半导体开关的电流的电感器线圈、至少一个二极管,以及连接到正母线轨并被配置为允许电流绕过转换器的旁路开关。DC-DC转换器可被配置为以与电池极性相同的极性向功率逆变器输出DC母线电压。(An electric drive system for a vehicle may include positive and negative bus rails carrying a Direct Current (DC) bus voltage, an Energy Storage System (ESS), a power inverter having a plurality of semiconductor switches operable to invert the DC bus voltage to an Alternating Current (AC) bus voltage, and an electric machine. The DC-DC converter may be connected to a bus rail between the capacitor and the power inverter, and may include a converter semiconductor switch disposed in the positive bus rail, an inductor coil connected to the positive bus rail and receiving current flowing through the converter semiconductor switch, at least one diode, and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter. The DC-DC converter may be configured to output the DC bus voltage to the power inverter with a polarity that is the same as a polarity of the battery.)

1. An electric drive system comprising:

positive and negative bus rails carrying a Direct Current (DC) bus voltage;

an Energy Storage System (ESS) connected to the positive and negative bus rails and having a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity;

a power inverter having a first plurality of semiconductor switches operable to invert the DC bus voltage to an Alternating Current (AC) bus voltage;

an electric machine having a phase winding electrically connected to the power inverter;

a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter and having: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to direct current through the power inverter and the motor via the inductor coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter and motor when the bypass switch is closed; and a second capacitor arranged across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter with a polarity that is the same as the battery polarity; and

a controller programmed to regulate operation of the DC-DC converter based on power, torque and speed values of the motor, to regulate the DC bus voltage until the DC bus voltage equals the battery output voltage, thereby selectively bypassing the DC-DC converter by closing the bypass switch under predetermined operating conditions of the motor when the DC bus voltage is equal to the battery output voltage, and selectively opening the bypass switch and thereafter regulating the DC bus voltage to a predetermined voltage, wherein the DC-DC converter outputs the DC bus voltage with a polarity identical to a polarity of the battery when the bypass switch is turned off, and wherein when the bypass switch is closed, the DC-DC converter outputs the DC bus voltage with the same polarity as the battery polarity.

2. The electric drive system of claim 1, wherein the converter semiconductor switch is a MOSFET.

3. The electric drive system of claim 1, wherein the at least one diode comprises a plurality of diodes.

4. The electric drive system of claim 1, wherein the at least one diode comprises a single diode that allows current to flow from the positive bus rail to the inverter.

5. The electric drive system of claim 4, wherein the inductor coil is connected in series between the converter semiconductor switch and the single diode.

6. The electric drive system of claim 1, wherein the at least one diode is configured to flow current from the positive bus rail into the inductor coil in a first direction.

7. The electric drive system of claim 6, wherein the inductor coil is connected to the inverter such that current flowing through the inductor coil in the first direction flows directly from the inductor coil to the positive bus rail of the inverter.

8. The electric drive system of claim 7, wherein the at least one diode comprises a second diode configured to allow current to flow in the first direction from the inductor coil to the positive bus rail of the inverter.

9. The electric drive system of claim 1, wherein the predetermined operating condition of the motor is a high power/high torque operating condition of the motor when the controller bypasses the DC-DC converter such that the DC bus voltage is equal to the battery output voltage.

10. An electric drive system for an electric machine, comprising:

positive and negative bus rails carrying a Direct Current (DC) bus voltage;

an Energy Storage System (ESS) connected to the positive and negative bus rails and having a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity;

a power inverter having a first plurality of semiconductor switches operable to invert the DC bus voltage to an Alternating Current (AC) bus voltage; and

a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter and having: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to direct current through the power inverter via the inductor coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter when the bypass switch is closed; and a second capacitor arranged across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter with a polarity that is the same as the battery polarity.

Technical Field

The present disclosure relates to buck-boost converters for electric drives.

Background

Hybrid or battery electric vehicles may employ electric machines or motor-generators to generate torque to propel the vehicle. Alternatively, the torque provided by the motor may be used to generate electricity. Electricity generated in excess of the desired amount may be stored in a battery pack for later use.

The electric machine may be implemented as a multi-phase/alternating current device, and thus the electric drive system may include a power inverter. Pulse width modulation may be used to supply power to the motor from a battery or power source, for example, where the voltage output of the power inverter is controlled via a bank of semiconductor switches that transmit electronic gate signals to the power inverter. During the generating mode, switching control of the power inverter converts the multiphase voltage from the motor to a dc voltage suitable for storage in the battery pack. Also, the switching control of the power inverter can convert the direct-current voltage into a multi-phase voltage to drive the motor during the motoring mode. Boost or buck-boost converters may also be used to selectively increase the output voltage of the battery pack and thereby meet the maximum speed requirements of the motor and connected electrical components.

Known buck-boost converter designs employ a plurality of MOSFET switches (four MOSFET switches in one known example) to selectively buck/boost the output voltage, and are therefore relatively complex and cause switching losses. In addition, known buck-boost converter designs reverse the polarity of the output voltage. Accordingly, there is a need for an improved buck-boost converter that addresses the above-mentioned shortcomings.

Disclosure of Invention

In at least some examples, an electric drive system includes positive and negative bus rails carrying a Direct Current (DC) bus voltage, and an Energy Storage System (ESS) connected to the positive and negative bus rails. The ESS may have a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity. The electric drive system may further include a power inverter having a first plurality of semiconductor switches operable to convert a DC bus voltage to an Alternating Current (AC) bus voltage, the electric machine having phase windings electrically connected to the power inverter, and a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter. The converter may include: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to conduct current flowing through the power inverter and the motor via the induction coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter and the motor when the bypass switch is closed; and a second capacitor disposed across the positive and negative bus rails. The DC-DC converter may be configured to output the DC bus voltage to the power inverter with a polarity that is the same as a polarity of the battery. The electric drive system may also include a controller programmed to adjust operation of the DC-DC converter based on the power, torque, and speed values of the electric machine to adjust the DC bus voltage until the DC bus voltage equals the battery output voltage to selectively bypass the DC-DC converter by closing the bypass switch under predetermined operating conditions of the electric machine and selectively opening the bypass switch when the DC bus voltage equals the battery output voltage, and thereafter adjust the DC bus voltage to a predetermined voltage, wherein when the bypass switch is opened, the DC-DC converter outputs the DC bus voltage with a polarity that is the same as the polarity of the battery, and wherein when the bypass switch is closed, the DC-DC converter outputs the DC bus voltage with the polarity that is the same as the polarity of the battery.

In some examples, the converter semiconductor switches are MOSFETs.

In at least some examples, the at least one diode includes a plurality of diodes.

In some example methods, the at least one diode may include a single diode that allows current to flow from the positive bus rail to the inverter. In at least some of these examples, the inductor coil may be connected in series between the converter semiconductor switch and the single diode.

In some exemplary illustrations of the electric drive system, the at least one diode is configured to cause current to flow from the positive bus rail into the inductor coil in a first direction. In these examples, the inductor coil may be connected to the inverter such that current flowing through the inductor coil in the first direction flows directly from the inductor coil to a positive bus rail of the inverter. In another subset of these examples, the at least one diode includes a second diode configured to allow current to flow from the inductor coil in the first direction to the positive bus rail of the inverter.

In some examples, the predetermined operating condition of the electric machine is a high power/high torque operating condition of the electric machine when the controller bypasses the DC-DC converter such that the DC bus voltage is equal to the battery output voltage.

Some example illustrations relate to an electric drive system for an electric machine, wherein the electric drive system includes positive and negative bus rails carrying a Direct Current (DC) bus voltage, and an Energy Storage System (ESS) connected to the positive and negative bus rails, wherein the ESS has a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity. The electric drive system may also include a power inverter having a first plurality of semiconductor switches operable to convert a DC bus voltage to an Alternating Current (AC) bus voltage, and a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter. The converter may have: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to direct current flowing through the power inverter via the inductor coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter when the bypass switch is closed; and a second capacitor disposed across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter in a polarity that is the same as a polarity of the battery.

In some of the exemplary electric drive systems, the converter semiconductor switches are MOSFETs.

In some example methods, the at least one diode comprises a plurality of diodes. In a subset of these examples, the at least one diode comprises a single diode that allows current to flow from the positive bus rail to the inverter. In some example illustrations, the inductor coil may be connected in series between the converter semiconductor switch and a single diode.

In some examples, the at least one diode is configured to cause current to flow from the positive bus rail into the inductor coil in a first direction. In some of these examples, the inductor coil is connected to the inverter such that current flowing through the inductor coil in the first direction flows directly from the inductor coil to a positive bus rail of the inverter. In some examples, the at least one diode includes a second diode configured to allow current to flow in a first direction from the inductor coil to a positive bus rail of the inverter.

In some example methods, the predetermined operating condition of the electric machine is a high power/high torque operating condition of the electric machine when the controller bypasses the DC-DC converter such that the DC bus voltage is equal to the battery output voltage.

Some example illustrations herein relate to a vehicle including an electric drive system configured to provide an output torque to at least one wheel. The electric drive system may include positive and negative bus rails carrying a Direct Current (DC) bus voltage, and an Energy Storage System (ESS) connected to the positive and negative bus rails. The ESS may have a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity. The electric drive system of the vehicle may further include: a power inverter having a first plurality of semiconductor switches operable to convert a DC bus voltage to an Alternating Current (AC) bus voltage; an electric machine having a phase winding electrically connected to the power inverter; and a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter. The converter may include: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to conduct current flowing through the power inverter and the motor via the induction coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter and the motor when the bypass switch is closed; and a second capacitor disposed across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter in a polarity that is the same as a polarity of the battery. The electric drive system of the vehicle may further include a controller programmed to adjust operation of the DC-DC converter based on the power, torque, and speed values of the electric machine to adjust the DC bus voltage until the DC bus voltage equals the battery output voltage, to selectively bypass the DC-DC converter by closing the bypass switch and selectively opening the bypass switch under predetermined operating conditions of the electric machine when the DC bus voltage equals the battery output voltage, and to thereafter adjust the DC bus voltage to the predetermined voltage, wherein when the bypass switch is opened, the DC-DC converter outputs the DC bus voltage with a polarity that is the same as a polarity of the battery, and wherein when the bypass switch is closed, the DC-DC converter outputs the DC bus voltage with the same polarity as the polarity of the battery.

In at least some exemplary illustrations of the vehicle, the vehicle is a Battery Electric Vehicle (BEV).

The invention also relates to the following technical scheme.

Technical solution 1. an electric drive system includes:

positive and negative bus rails carrying a Direct Current (DC) bus voltage;

an Energy Storage System (ESS) connected to the positive and negative bus rails and having a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity;

a power inverter having a first plurality of semiconductor switches operable to invert the DC bus voltage to an Alternating Current (AC) bus voltage;

an electric machine having a phase winding electrically connected to the power inverter;

a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter and having: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to direct current through the power inverter and the motor via the inductor coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter and motor when the bypass switch is closed; and a second capacitor arranged across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter with a polarity that is the same as the battery polarity; and

a controller programmed to regulate operation of the DC-DC converter based on power, torque and speed values of the motor, to regulate the DC bus voltage until the DC bus voltage equals the battery output voltage, thereby selectively bypassing the DC-DC converter by closing the bypass switch under predetermined operating conditions of the motor when the DC bus voltage is equal to the battery output voltage, and selectively opening the bypass switch and thereafter regulating the DC bus voltage to a predetermined voltage, wherein the DC-DC converter outputs the DC bus voltage with a polarity identical to a polarity of the battery when the bypass switch is turned off, and wherein when the bypass switch is closed, the DC-DC converter outputs the DC bus voltage with the same polarity as the battery polarity.

Technical solution 2. the electric drive system according to technical solution 1, wherein the converter semiconductor switch is a MOSFET.

Claim 3. the electric drive system of claim 1, wherein the at least one diode comprises a plurality of diodes.

Technical solution 4. the electric drive system of claim 1, wherein the at least one diode comprises a single diode that allows current to flow from the positive bus rail to the inverter.

Claim 5. the electric drive system of claim 4, wherein the inductor coil is connected in series between the converter semiconductor switch and the single diode.

Technical solution 6 the electric drive system of claim 1, wherein the at least one diode is configured to cause current to flow from the positive bus rail into the inductor coil in a first direction.

Technical solution 7 the electric drive system of claim 6, wherein the inductor coil is connected to the inverter such that current flowing through the inductor coil in the first direction flows directly from the inductor coil to the positive bus rail of the inverter.

The electrical drive system of claim 8, wherein the at least one diode includes a second diode configured to allow current to flow in the first direction from the inductor coil to the positive bus rail of the inverter.

Claim 9. the electric drive system of claim 1, wherein the predetermined operating condition of the electric machine is a high power/high torque operating condition of the electric machine when the controller bypasses the DC-DC converter such that the DC bus voltage is equal to the battery output voltage.

Technical solution 10 an electric drive system for an electric motor, comprising:

positive and negative bus rails carrying a Direct Current (DC) bus voltage;

an Energy Storage System (ESS) connected to the positive and negative bus rails and having a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity;

a power inverter having a first plurality of semiconductor switches operable to invert the DC bus voltage to an Alternating Current (AC) bus voltage; and

a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter and having: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to direct current through the power inverter via the inductor coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter when the bypass switch is closed; and a second capacitor arranged across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter with a polarity that is the same as the battery polarity.

Claim 11 the electric drive system of claim 10, wherein the converter semiconductor switches are MOSFETs.

Claim 12 the electric drive system of claim 10, wherein the at least one diode comprises a plurality of diodes.

The electric drive system of claim 10, wherein the at least one diode comprises a single diode that allows current to flow from the positive bus rail to the inverter.

Claim 14 the electric drive system of claim 13, wherein the inductor coil is connected in series between the converter semiconductor switch and the single diode.

Claim 15 the electric drive system of claim 1, wherein the at least one diode is configured to cause current to flow from the positive bus rail into the inductor coil in a first direction.

Claim 16 the electric drive system of claim 15, wherein the inductor coil is connected to the inverter such that current flowing through the inductor coil in the first direction flows directly from the inductor coil to the positive bus rail of the inverter.

The electric drive system of claim 17, wherein the at least one diode comprises a second diode configured to allow current to flow in the first direction from the inductor coil to the positive bus rail of the inverter.

The electric drive system of claim 18, wherein the predetermined operating condition of the electric machine is a high power/high torque operating condition of the electric machine when the controller bypasses the DC-DC converter such that the DC bus voltage is equal to the battery output voltage.

A vehicle according to claim 19, comprising:

an electric drive system configured to provide an output torque to at least one wheel, the electric drive system comprising:

positive and negative bus rails carrying a Direct Current (DC) bus voltage;

an Energy Storage System (ESS) connected to the positive and negative bus rails and having a battery cell and a first capacitor arranged in parallel with the battery cell to provide a battery output voltage having a battery polarity;

a power inverter having a first plurality of semiconductor switches operable to invert the DC bus voltage to an Alternating Current (AC) bus voltage;

an electric machine having a phase winding electrically connected to the power inverter;

a DC-DC converter connected to the positive and negative bus rails between the capacitor and the power inverter and having: a converter semiconductor switch disposed in the positive bus rail; an inductor coil connected to the positive bus rail and receiving current through the converter semiconductor switch; at least one diode configured to direct current through the power inverter and the motor via the inductor coil; and a bypass switch connected to the positive bus rail and configured to allow current to bypass the converter and flow through the power inverter and motor when the bypass switch is closed; and a second capacitor arranged across the positive and negative bus rails, the DC-DC converter configured to output a DC bus voltage to the power inverter with a polarity that is the same as the battery polarity; and

a controller programmed to regulate operation of the DC-DC converter based on power, torque and speed values of the motor, to regulate the DC bus voltage until the DC bus voltage equals the battery output voltage, thereby selectively bypassing the DC-DC converter by closing the bypass switch under predetermined operating conditions of the motor when the DC bus voltage is equal to the battery output voltage, and selectively opening the bypass switch and thereafter regulating the DC bus voltage to a predetermined voltage, wherein the DC-DC converter outputs the DC bus voltage with a polarity identical to a polarity of the battery when the bypass switch is turned off, and wherein when the bypass switch is closed, the DC-DC converter outputs the DC bus voltage with the same polarity as the battery polarity.

Claim 20 the vehicle of claim 19, wherein the vehicle is a Battery Electric Vehicle (BEV).

Drawings

One or more embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:

FIG. 1 is a schematic diagram depicting an example of a vehicle having an electric drive using a DC-DC converter in accordance with an exemplary illustration;

FIG. 2A is a schematic circuit diagram of the electric drive of FIG. 1 in a converter mode, wherein the switches in the converter are closed;

FIG. 2B is a schematic circuit diagram of the electric drive of FIG. 1 in a converter mode, wherein the switches in the converter are open;

FIG. 2C is a graphical representation of the voltage output of the converter of FIGS. 2A and 2B over time with the switches alternating between open and closed positions;

FIG. 3 is a schematic circuit diagram of the electric drive of FIGS. 1, 2A and 2B in a bypass mode;

FIG. 4 is a schematic circuit diagram of another converter for the electrical driver of FIG. 1, wherein the converter utilizes two diodes;

FIG. 5 is a schematic circuit diagram of a converter for the electric drive of FIG. 1, wherein the converter utilizes an interlock switch; and

FIG. 6 is an exemplary process flow diagram illustrating an exemplary method of applying an output voltage to a motor.

Detailed Description

The exemplary description herein relates generally to systems and methods for vehicles (e.g., electric or hybrid vehicles) that employ electric motor-generators for propulsion. The buck-boost converter may be used to selectively increase/decrease the output voltage to the electric motor-generator. Alternatively, in the bypass mode of the converter, the output voltage applied to the electric machine or electric motor-generator is equal to the voltage received from the vehicle energy storage system or battery.

The exemplary buck-boost converter may have a bypass design and generally improves the efficiency of the vehicle drive system and is also less complex and costly than previous approaches. When the motor is operating at relatively high power conditions (which may be typical use of bypass mode, for example), the power supply is connected directly to the DC bus. In addition, when the motor operates in a high speed condition or a low speed condition, the power supply is connected to the DC bus through the converter in a buck-boost mode, and the converter may reduce or increase the output voltage applied to the motor. The improved efficiency of the converter of the present invention results in improved energy economy, increasing the range of the vehicle under electric power. In contrast, in previous approaches, buck-boost converters were typically always operated in buck-boost mode, thereby reducing efficiency. Furthermore, in the exemplary method, the converter may employ only a single switching device in addition to the bypass switch, thereby reducing switching losses.

In the exemplary illustration herein, the DC-DC converter may be connected to the positive and negative bus rails of the electric drive of the vehicle between the capacitor and the power inverter. The converter may have a converter semiconductor switch disposed in the positive bus rail, and an inductor coil connected to the positive bus rail and receiving current flowing through the converter semiconductor switch. The converter may further include at least one diode configured to direct current flowing through the power inverter and the motor through the inductor coil and the bypass switch connected to the positive bus rail. The bypass switch may be configured to allow current to flow through the power inverter and the motor when the bypass switch is closed. A second capacitor may be disposed across the positive and negative bus rails. The DC-DC converter may be configured to output the DC bus voltage to the power inverter with a polarity that is the same as a polarity of the battery. Thus, an exemplary converter may employ a bypass switch and a single converter switch, reducing switching losses as compared to previous approaches in which there are typically multiple switches in addition to the bypass switch.

Referring now to the drawings, in which like reference numbers refer to like components throughout the several views, FIG. 1 depicts an exemplary schematic vehicle 10 having a body 11 and an electric drive system 15. The vehicle 10 may be configured as a motor vehicle as shown, and may thus be equipped with wheels 12 in rolling contact with a road surface 14. Although the vehicle 10 of fig. 1 is an example of one type of system that would benefit from the use of the present drive system 15, other applications of the drive system 15 are readily contemplated, including, but not limited to, stationary power plants, mobile platforms, and other types of land, air, or marine vehicles.

Electric drive system 15 may include a multi-phase electric motor 16 having a rotatable output shaft 18. Motor torque (arrow T) when electric machine 16 is energized via application of an Alternating Current (AC) multi-phase Voltage (VAC) to each phase winding 48 of electric machine 16_O) Generated and transferred to a coupled load, such as a wheel 12 in the motor vehicle application shown. The electric machine 16 may be embodied as a three-phase/multi-phase motor or motor/generator unit, with each of the phase windings 48 carrying a corresponding phase current. In various exemplary embodiments, the electric machine 16 may be configured as an induction machine or a synchronous machine, within the rotor thereofWith or without permanent magnets.

The electric drive system 15 of FIG. 1 may also include an Energy Storage System (ESS) 20, a direct current/direct current (DC-DC) converter 30, and a power inverter 40. The ESS 20 may include a plurality of cells 22, such as rechargeable lithium-ion cells arranged in a stacked manner, and a capacitor 24 arranged in parallel with the cells 22. The number and arrangement of the battery cells 22 may vary with the intended application. By way of example only, in an example 96 or more such cells 22 may be used in certain high voltage applications. The battery output voltages (Vbat +, Vbat-) are delivered to respective positive and negative voltage bus rails 19+ and 19-, while the DC bus voltages (Vdc + and Vdc-) appear at/on the voltage bus rails 19+, 19-downstream of/on the output side of the DC-DC converter 30 as shown.

Within electric drive system 15, power inverter 40 is electrically connected to phase windings 48 of electric machine 16 and includes a first plurality of semiconductor switches 44 and a second capacitor 41. The semiconductor switches 44 are arranged in upper and lower groups, as shown, wherein the terms "upper" and "lower" refer to the semiconductor switches 44 connected to the positive bus rail 19+ and the negative bus rail 19-, respectively. The semiconductor switches 44 may be implemented as voltage controlled bipolar switching devices in the form of Insulated Gate Bipolar Transistors (IGBTs), Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), broadband GaN devices (WBGs), or other suitable switches having corresponding gates (G) to which gate signals 51 are applied, e.g., by the controller 50, to change the on/off state of a given one of the semiconductor switches 44.

Still referring to fig. 1, in the illustrated embodiment, the DC-DC converter 30 may be configured as a buck-boost converter having a semiconductor switch 34, where the term "buck" refers to a voltage-reducing mode of operation and "boost" refers to a voltage-increasing mode of operation. As with the semiconductor switches 44 within the power inverter 40, the semiconductor switches 34 of the converter 30 may be comprised of high efficiency switches, such as wide gap gallium nitride (GaN) or silicon carbide (SiC) MOSFETs, IGBTs, or another suitable switching device. Further within the converter 30, an inductor coil 36 extends between the switch 34 and the negative bus rail 19-. In addition, a plurality of diodes 60a, 60b, 60c (collectively 60) are provided.

In some examples, for example, as shown in fig. 1 and other examples that follow, one of the diodes 60b allows current to flow from the positive bus rail 19+ to the inverter 40. In such examples, the inductor coil 36 may be connected in series between the converter semiconductor switch 34 and the diode 60 b. Thus, in the converter mode of converter 30 (i.e., when bypass switch 32 is open), diode 60b generally causes current to flow in a first direction from positive bus rail 19+ into inductor coil 36 (moving down the page in the example shown in fig. 1). The current flowing through the inductor coil 36 in this first direction then flows directly from the inductor coil 36 to the positive bus rail 19+ of the inverter 40. In some examples, and as shown in fig. 1, a second diode 60a is also provided that is positioned such that current flows through the inductor 36 in a first direction and then from the inductor 36 to the positive bus rail 19+ of the inverter 40.

The DC-DC converter 30 of fig. 1 also includes a bypass switch 32, also labeled S0. The bypass switch 32 is selectively opened or closed in response to a switch control signal 52 transmitted by the controller 50. The bypass switch 32 may comprise any convenient switching device. By way of example only, when response time is not critical, the bypass switch 32 may be comprised of an electromechanical relay, or alternatively, may be comprised of a faster acting semiconductor device, such as an effective bidirectional blocking solid state IGBT switch or a reverse blocking IGBT. As shown in fig. 1, the bypass switch 32 is disposed on the positive voltage bus 19 +. Accordingly, bypass switch 32 is closed in response to switch control signal 52 such that DC-DC converter 30 is bypassed, wherein certain conditions require closing bypass switch 32 and ultimately bypassing converter 30 as determined in real time by controller 50, as set forth below with reference to fig. 6.

The controller 50, which communicates with the electric machine 16 via a controller area network or other communication bus, such as the vehicle 10, may be configured as a single device or as a distributed control device. Although omitted from FIG. 1, the connectivity of the controller 50 to the electric drive system 15 may include transfer conductors and/or wireless control links or paths suitable for transmitting and receiving switch control signals 52. The controller 50 may include a processor and tangible non-transitory memory including read only memory in the form of optical, magnetic or flash memory. The controller 50 may also include a sufficient amount of random access memory and electrically erasable programmable read only memory, as well as high speed clock, analog to digital and digital to analog circuitry and input/output circuitry and devices, as well as appropriate signal conditioning and buffer circuitry. Computer readable instructions are recorded in a memory of controller 50 (e.g., as further described below in fig. 6) that implements method 100, wherein the processor executes such logic to cause controller 50 to manage electrical power flow within electric drive system 15.

As will be described further below, in an exemplary method, the controller 50 is programmed to receive the reported motor torque (arrow T)₁₆) E.g. approximating the motor output torque (arrow T)_O) Is estimated or calculated. It is possible to use, for example, the calculated power and the measured or reported rotational speed value (arrow N) by the electric machine 16₁₆) An indexed or referenced look-up table, which value is obtained from a motor control processor (not shown) of the electric machine 16. Controller 50 uses the reported motor torque value (arrow T)₁₆) Sum velocity value (arrow N)₁₆) To accurately determine when to open or close the bypass switch 32.

The vehicle 10 may employ a calibrated or predefined performance map (not shown) that generally describes the use of the exemplary electric machine 16 and the exemplary buck-boost converter 30/30b/30c disclosed herein based on the power and speed of the electric machine 16 at different operating points. In general, it may be desirable for the electric machine 16 to output a higher torque (depending on the power output or energy economy of the electric machine 16) for a given rotational speed of the electric machine 16 to be a greater consideration. To this end, the converter 30 may vary the output voltage sent to the motor 16, and the bypass switch 32 may be used to selectively bypass the converter 30 in the event that regulation of the battery output voltage is not desired. As just one example, the motor 16 may have a maximum rotational speed of approximately 12,000 Revolutions Per Minute (RPM) and a maximum output torque of 350 newton meters (Nm). In the event that vehicle 10 does not require 100% of the available output power of electric machine 16 at any given speed or torque of electric machine 16, converter 30 may be used to regulate the output voltage supplied to electric machine 16. In this manner, power may be conserved for the Energy Storage System (ESS) 22.

As will be explained in further detail below with reference to an exemplary method, the controller 50 of fig. 1 is configured, via programming and hardware devices, to monitor performance parameters of the electric machine 16, and to selectively operate the DC-DC converter 30 in one or more operating regions of the electric machine 16, using the DC-DC converter 30 to regulate the output voltage to the electric machine 16 as needed, in response to such monitored performance parameters. More specifically, at a given engine torque or range thereof, converter 30 may operate to "boost" the output voltage to electric machine 16 to do so in the event that it is desired to increase the output speed of electric machine 16. Alternatively, the converter 30 may reduce or "buck" the output voltage to the motor 16 where it is desired to conserve energy stored in the ESS22, for example, when the machine 16 is operating at relatively low speeds and low power conditions. Additionally, if no regulation of the output voltage is required, the converter 30 can be completely bypassed by closing the bypass switch 32. Closing bypass switch 32 may advantageously reduce switching losses due to the pulse width modulation effect of converter 30.

The exemplary method of using the converter described herein may generally be performed to ensure that the energy stored in the inductor coil 36 is effectively dissipated prior to activating the bypass switch 32, and thus to ensure effective operation of the DC-DC converter 30. For example, during buck mode or boost mode, the DC voltage at the input of power inverter 40 may be set to a fixed predetermined value to reduce cost and simplify control and obtain most of the available fuel economy benefits, or DC-DC converter 30 may be controlled to an optimal level to reduce system losses while controlling the voltage according to the speed, duty cycle, and/or power consumption of electric machine 16. Hysteresis may be added when switching from one mode of the DC-DC converter 30 to another, such as from a buck mode to a boost mode, or vice versa. When the bypass switch 32 is closed, the exemplary method may be performed such that the voltage across the bypass switch 32 remains at or near zero. This in turn may avoid undesirable voltage transients. When the bus voltage (Vdc +, Vdc-) is nearly equal to the battery output voltage (Vbat +, Vbat-) the bypass switch 32 may then be closed by operation of the controller 50.

The energy stored in the inductor winding 36 is dissipated after the DC-DC converter 30 is effectively bypassed by operation of the bypass switch 32. Energy dissipation may be achieved by controlling the open/closed state of a switch present in converter 30 (e.g., switch 34 as shown in fig. 1) in a manner that achieves short-circuiting inductor coil 36 while controlling the current flowing through bypass switch 32 to a level less than the rated current of switch 34.

Turning now to fig. 2A-2C, operation of converter 30 in the converter mode, i.e., wherein converter 30 steps down ("buck" mode) or steps up ("boost" mode) the output voltage from the input voltage received by ESS22 to motor 16 will be described in further detail. As shown in fig. 2A, with the bypass switch 32 open, the switching device 34 may allow current (shown by the arrow in the figure) to flow through the switch 34 and the inductor 36 and back to the ESS 22/capacitor 24. As just one example, the switch 34 may be a MOSFET that is controlled to allow current to flow through the switch 34. Turning to fig. 2B, when the MOSFET switch 34 is deactivated, the inductor 36 causes current to flow through the diode 60B, thereby applying voltage from the inductor 36 to the plurality of switching devices 44. By alternately activating the MOSFET switches 34, the output voltage applied to the motor 16 can be determined by the duty cycle of the switches 34, as follows:

duty ratio:

output voltage:

accordingly, converter 30 may reduce or increase the output voltage applied to motor 16 as needed to improve the energy efficiency or output speed capability of vehicle 10 as a whole, respectively. Furthermore, the polarity of the DC bus 19+ is advantageously kept the same as the supply voltage, while reducing switching losses via the use of the diode 60 and the single switch 34. In contrast, previous approaches to DC-DC converters have employed multiple switches in addition to the bypass switch, resulting in increased switching losses and increased complexity of the converter.

Turning now to fig. 3, converter 30 is shown in bypass mode with bypass switch 32 closed. Thus, the voltage of the ESS22 is applied directly to the inverter 40, bypassing the switch 34. With converter 30 in the bypass mode, the polarity of the DC bus (Vdc +) remains the same as the supply voltage (Vbat +).

Referring now to fig. 4, another exemplary converter 30b is shown. The converter 30B is identical to the converter 30 shown in fig. 2A, 2B and 3, but utilizes two diodes 60a, 60B (instead of using three diodes in the previous example). In the example converter 30B shown in fig. 4, although the direction of current flow may be different compared to the example converter 30 shown in fig. 2A, 2B, and 3, the converter 30B allows a conversion mode (i.e., buck-boost) mode and a bypass mode substantially in a manner similar to that described above for the converter 30 shown in fig. 2A, 2B, and 3. The converter 30B allows for fewer operating components and minimal complexity by using fewer diodes 60, while the additional diodes 60c in the exemplary converter 30 shown in fig. 2A, 2B, and 3 may generally simplify the change between bypass and converter modes, thereby reducing response time.

In another exemplary converter 30c shown in fig. 5, interlock switches 32, 35 are employed, although the operation of converter 30c is otherwise substantially identical to converters 30, 30 b. More specifically, interlock switches 32a, 32b may generally be used to bypass converter 30c so that the output voltage applied to the inverter is the same as the output voltage received from ESS 22. Alternatively, when the bypass switches 32a, 32b are open, the switches 35a, 35b may be closed to allow current to flow through the switch 34 and induce current in the induction coil 36.

Turning now to fig. 6, an exemplary process 100 for implementing control of the electric machine 16 in a vehicle is disclosed. At block 102, the controller 50 may determine the operating speed and torque of the motor 16. For example, in an exemplary three-phase system, voltage and current may be measured at each phase winding 48 of the electric machine 16. The torque may be measured, calculated, or estimated based on the voltage, current, and speed of the motor 16, and/or recorded in a look-up table in the memory of the controller 50. Process 100 may then proceed to block 104.

At block 104, controller 50 may determine whether it is desired to employ a buck-boost mode of converter 30, thereby allowing the output voltage applied to inverter 40 to be regulated. For example only, the output voltage may be reduced where it is desired to conserve energy stored in the ESS22, such as where the operator demand for speed is relatively low for the vehicle 10, or the vehicle operator does not demand an increase in vehicle speed. Conversely, where it is desired to increase the output voltage applied to the electric machine 16, such as where it is desired to increase the speed of the vehicle 10, the converter 30 may increase or "boost" the output voltage.

Where it is desired to use the buck-boost mode of converter 30, process 100 may proceed to block 106, where converter 30 is placed in the buck-boost mode by opening a bypass switch (e.g., bypass switch 32). For example, controller 50 may activate DC buck-boost converter 30 by opening bypass switch 32. Block 106 may include transmitting the switch signal 51 in the form of opening the bypass switch 32. Block 108 thus effectively sets the output voltage applied to inverter 40 equal to a multiple of the voltage of ESS 22. In some embodiments, the multiplier (n) may be between 2-4 times the level of the voltage of the ESS22, or greater.

Alternatively, it may be desirable to close the converter bypass switch 32 to apply the voltage of the ESS22 directly to the inverter 44. This bypass mode may be employed, for example, where the voltage of the ESS22 is within a desired range suitable for the power/energy economy requirements of the vehicle 10, or where it is desired to reduce switching losses that might otherwise occur in the buck-boost mode of the converter 30. Where it is desired to use the bypass mode of the converter, process 100 may proceed to block 108 where the bypass switch is opened. Thus, the controller 50 may disable the DC buck-boost converter 30 via control of the bypass switch 32. Closing the bypass switch 32 effectively sets the inverter input voltage equal to the voltage of the ESS22, i.e., the battery voltage.

An exemplary method such as process 100 generally allows converter 30 to be bypassed, for example, in high power operating regions of motor 26. Similarly, the converter 30 may be enabled at higher speeds and low power operating modes to improve overall drive efficiency. In boost mode, the inverter input may be set to a predetermined value suitable for capturing a desired amount of fuel economy with reduced DC buck-boost converter 30. For example, in the example of 90kW peak power for motor 26, at levels in excess of 30kW, little other improvement in the EV range is obtained. Thus, the converter 30 may be used to reduce the output voltage applied to the inverter 40, thereby reducing the power drawn from the battery 20.

It is to be understood that the foregoing is a description of one or more embodiments of the invention. The present invention is not limited to the specific embodiments disclosed herein, but is only limited by the following claims. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments as well as various changes and modifications to the disclosed embodiments will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to fall within the scope of the appended claims.

As used in this specification and claims, the terms "for example (e.g.)", "for example (foreexample)", "for example (for instance)", "such as" and "like" and the verbs "comprising", "having", "including" and their other verb forms, when used in conjunction with a list of one or more components or other items, are each to be construed as open-ended, meaning that the list is not to be considered as excluding other, additional components or items. Unless other terms are used in a context that requires a different interpretation, they should be interpreted using their broadest reasonable meaning.