Multi-bridge power converter with multiple outputs

Abstract

According to one aspect of the present disclosure, a power converter device is provided, the device comprising: at least two switch bridges connected to a direct current (DC) bus and each generating a pulse width modulation (PWM) voltage provided to a non-isolated output terminal; and an isolation transformer, the primary winding of which is connected to the output terminals of the two switch bridges and the secondary winding of which is connected to the isolated output terminal. In the non-isolated mode, the two switch bridges operate in a parallel mode to transfer power between the DC bus and the non-isolated output terminal. In the isolated mode, the two switch bridges operate in a full-bridge mode to transfer power between the DC bus and the isolated output terminal through the transformer.

Description

Technical Field

[0001] The present disclosure relates generally to the field of power electronic circuits, such as power converters used in electric vehicles. Background Art

[0002] In recent years, the renewable energy industry has experienced rapid growth, and due to this growth, there is a high demand for further improvements in power electronics technology. For example, as a large number of electric vehicles (EVs) enter the market, motor drive inverters and battery chargers have become key components of EVs. The demand for continuous improvement in cost, efficiency, size, and weight has put forward challenges for the design of EV motor drive inverters and battery chargers.

[0003] The battery packs deployed in EVs include a variety of different voltage and capacity ratings. Therefore, EVs require suitable chargers to charge under a wide range of battery voltages and current levels, which poses a challenge especially for battery charger product suppliers and commercial fast charger stations.

[0004] Battery charger power converters are potentially dangerous due to high voltage and high current. Galvanic isolation can reduce electrical safety hazards and prevent fault propagation in the event of a component failure in the power converter. Therefore, certain safety standards (such as IEC, IEEE, UL, and SAE) may require galvanic isolation, and this mandatory requirement is correct for both off-board chargers and on-board battery chargers (OBCs).

[0005] The EV battery charger includes circuitry for converting alternating current (AC) power into direct current (DC) power, and is typically designed in two stages, namely, an AC-DC stage and a DC-DC stage. The AC-DC stage converts the AC input voltage (typically from an AC ten-point power source) into a DC bus voltage, and regulates the DC bus voltage to an ideal range suitable for the DC-DC stage load. The AC-DC stage may include various electromagnetic interference (EMI) filters, and a power factor correction (PFC) converter circuit (or PFC rectifier) ​​employing multiple diodes and active switching devices.

[0006] In order to meet various EMI regulations, EMI filters are employed to reduce high frequency noise that may interfere with other devices on the EV. The PFC rectifier circuit may be implemented as a boost PFC converter that is capable of shaping the input line current into a sine wave and in phase with the sine wave input voltage of the AC power source, and thus maintaining the circuit operation at unity power factor. At the same time, the PFC rectifier circuit regulates its output to maintain the DC bus voltage within a certain target range to achieve stable power flow and safe operation.

[0007] As the segment after the AC-DC segment in the EV battery charger, the DC-DC segment is connected between the output of the DC bus and multiple batteries. The DC-DC segment may include a high-frequency switching DC-DC converter that powers an isolation transformer, which typically has a primary winding and a secondary winding. On the secondary side, another rectifier circuit is provided for regulating the output of the secondary winding of the isolation transformer to a DC voltage to charge the EV battery. The DC-DC converter is also capable of regulating the battery charging current and maintaining the battery's state of charge.

[0008] The inverter-based motor control unit (MCU) is used to drive the EV traction motor using battery power. The inverter is used to convert the battery DC voltage into a pulse width modulated (PWM) AC output voltage waveform at the motor winding terminals to regulate the motor winding current as desired. The goal is to produce high torque at the low speed region of the motor as required by the MCU and deliver high power at the high speed range of the motor, which usually causes difficult problems in the trade-offs of the motor and inverter system design.

[0009] Typically, high torque output of the motor requires more permanent magnetic material in the rotor, which reduces the maximum motor winding current and, therefore, the motor frame size. However, more permanent magnetic material of the rotor means higher induced back electromagnetic force (EMF). When the EMF reaches the DC bus voltage level, the MCU will no longer be able to push more power into the motor, or drive the motor further into the higher speed region. This design problem is usually solved by deploying field weakening control with or without a DC-DC boost converter.

[0010] A technique called field weakening control is used to offset part of the permanent magnet flux and reduce the back EMF to drop below the DC bus voltage level of the motor in the motor high speed region. The disadvantage of field weakening operation is that the motor efficiency can be greatly reduced, especially in some deep field weakening cases, the efficiency is reduced by several percentage points, which is obviously a heavy price to pay due to EV fuel economy. In addition, the inverter will have to withstand greater reactive current under field weakening operation, resulting in higher equipment ratings and costs and further lower inverter efficiency.

[0011] A DC-DC boost converter can be used to insert between the battery and the DC bus that supplies power to the inverter. When the motor is operated at high speed, the boost converter can increase the DC bus voltage. As a result, the inverter can generate a higher output voltage at the terminals of the motor windings to overcome the back EMF, and thus, continuous power delivery can be achieved at higher motor speed areas without reducing the magnetic field. This boost converter solution will incur additional costs, but the cost can be compensated to a certain extent on the inverter side due to the improvement of inverter efficiency and motor efficiency.

[0012] The powertrain components including the motor, inverter, and onboard battery charger account for a large portion of the total EV material cost. Due to the peak power requirements of the motor drive, a typical EV inverter usually has a rating of 60kW to 200kW. Due to cost and space constraints, the onboard battery charger is rated only 6kW to 22kW. The inverter does not require isolation, but the OBC power stage does require transformer isolation. Therefore, due to the necessity of isolation and the difference in power ratings, the inverter and OBC are usually embodied by separate hardware and different subsystems, respectively.

[0013] In order to further save costs and reduce size or weight, it is indeed necessary to study the possibility of integrating the inverter and OBC systems and reusing common power converter hardware between EV motor drive operation and battery charging operation. In fact, there have been many publications on inverter and OBC integration. However, there is still a lack of suitable practical solutions that provide the required isolation and compact inverter and OBC system integration in the key area of ​​power converter topology. Summary of the invention

[0014] By proposing a preferred embodiment of the present disclosure of a new concept of a multi-bridge converter (i.e., a multi-bridge converter) with multiple output terminals, those and other problems mentioned above can be basically solved or circumvented, and technical advantages are generally achieved. The multi-bridge converter generally includes two switching bridges connected to a direct current (DC) bus, each bridge generating a pulse width modulation (PWM) voltage to a non-isolated output terminal. The isolation transformer has a primary winding connected to both ends of the two bridge output terminals, and a secondary winding connected to the isolated output terminal. Using the same set of converter hardware, different gating timing controls are used to generate different PWM voltage waveforms, and the DC bus power is delivered to the non-isolated output terminal or the isolated output terminal, but not at the same time. In the non-isolated mode, the two switching bridges operate in parallel mode, and power is transmitted between the DC bus and the non-isolated output terminal. In the isolated mode, both switching bridges operate in full-bridge mode, and power is transmitted between the DC bus and the isolated output terminal through the transformer.

[0015] In non-isolated mode, the multi-bridge converter bridges are operated in parallel mode with their gate switches synchronized in phase (i.e., without phase shift) to produce the same PWM voltage waveform across the transformer. Therefore, the transformer windings are not excited by any expected effective differential voltage and no significant power is transferred across the transformer. Therefore, power is mainly transferred from the DC bus to the non-isolated output with the capability of bidirectional power flow.

[0016] In isolated mode, the multi-bridge converter bridges are controlled to operate in full-bridge mode, and their gate switching signals are phase-shifted and out of phase, so the transformer windings are excited by the expected significant differential voltage, and power is mainly transferred from the DC bus to the non-isolated output through the transformer, with the ability of bidirectional power flow. Care must be taken here to minimize or stop any power flow to the non-isolated load, which may require special arrangements for the load segment configuration. In any case, using the same hardware, the multi-bridge converter can transfer power to the non-isolated output and the isolated port output under different gate timing control.

[0017] Typically, when multiple switching bridges are operated in parallel, it is known that interleaved operation with phase shift between the bridges in the synchronized PWM gate switching signals is performed. Benefits include higher effective PWM switching frequency, lower output voltage and current switching ripple, and potentially lower EMI noise spectrum. To achieve interleaved PWM operation with the proposed multi-bridge converter, an additional disconnect switch is connected in series with the transformer winding on the primary or secondary side of the transformer. In the non-isolated operation mode, when power is transferred between the DC bus and the non-isolated output, the transformer disconnect switch is open, and the PWM switching of the bridges is synchronized and interleaved with a phase shift angle. In the isolated operation mode, the transformer disconnect switch is turned on, controlling the two bridges to operate in full-bridge mode, the PWM switching signals are phase-shifted and out of phase between the two bridges, and power is transferred between the DC bus and the isolated output through the transformer.

[0018] Under the same idea of ​​the present disclosure, the multi-bridge converter switching bridge can use a two-level, three-level, five-level or any multi-level converter topology, such as a diode neutral point clamped (NPC) multi-level converter, an active neutral point clamped (ANPC) multi-level converter, a suspended capacitor multi-level converter, or a combination of any different multi-level topologies between bridges.

[0019] Similarly, examples given in the present disclosure are that a multi-bridge converter may include three, four, or any greater number of switching bridges, either connected to multiple separate isolation transformers, or connected to the same isolation transformer having multiple windings coupled together, or a mixture of different transformer designs.

[0020] As an example circuit according to various embodiments of the present disclosure, a multi-bridge converter is configured as a three-phase PWM inverter for integrating an EV motor drive and an on-board charging system, including: a battery having a plurality of battery cells connected to a DC bus through a DC main contactor or switch; three multi-bridge converters forming a DC-AC inverter operation for driving a non-isolated output terminal of an AC motor; an isolation transformer having a primary winding connected to both ends of the converter bridge output terminal, and a secondary winding connected to any type of rectifier for outputting DC power to charge the battery pack. A power source is connected to the DC bus, which comes from an external DC power source directly connected to the DC bus or from an external AC power source indirectly connected through an AC-DC rectifier.

[0021] The controller operates the three-phase multi-bridge converter by PWM synchronization and phase shifting. During the inverter driving operation in the non-isolated mode, when the battery contactor is turned on and the external power supply is not plugged in, in each multi-bridge converter, the two switching bridges operate in parallel mode, and the power is mainly transferred between the DC bus and the non-isolated output terminal. During the battery charging operation in the isolated operation mode, when the external power supply is plugged in, the battery contactor is disconnected, and in each multi-bridge converter, the two switching bridges operate in full-bridge mode, and the power is mainly transferred between the DC bus and the isolated output terminal through the transformer.

[0022] Here, the EV motor needs to be a dual-winding motor or a dual-segment winding AC motor, where the two sets of motor windings are separated from each other. Each set of motor windings is usually connected in star connection. During the battery charging operation in the isolated operating mode, further gate switching synchronization is applied between the switching bridges connected to the same set of motor phase windings, so that each set of motor windings is excited with almost zero differential voltage at the motor terminals in order to reduce any useless motor circulating current.

[0023] As an example circuit according to various embodiments of the present disclosure, a multi-bridge converter is configured as a DC-DC boost converter for an integrated EV drive and on-board charging system. The device includes: two switching bridges formed as DC-DC boost converters, which output to a DC bus that supplies power to an EV drive inverter and an AC motor; an isolation transformer having a primary winding connected to both ends of the converter bridge output, and a secondary winding connected to a rectifier to output DC power, thereby charging a battery pack; the same battery pack is also connected to a DC contactor, then to a boost inductor, and then to a midpoint output of the converter bridge; and there is also a power supply directly connected to the DC bus or indirectly connected to the DC bus through a power converter.

[0024] The controller operates the multi-bridge converter through PWM synchronization and phase shifting. During the EV drive boost operation in the non-isolated operation mode, the battery contactor is turned on and the external power supply is not plugged in. In each multi-bridge converter, the two switching bridges operate in parallel mode, and power is transferred from the battery to the DC bus with bidirectional function. During the battery charging operation in the isolated operation mode, the battery contactor is disconnected and the external AC power supply is plugged in. In each multi-bridge converter, both switching bridges operate in full-bridge mode, and power is transferred between the DC bus and the isolated output through the transformer.

[0025] For further cost savings, the boost inductor can be partially or fully integrated into the magnetic design of the isolation transformer, and the battery input through the main contactor is connected to the midpoint of the isolation transformer primary winding, so that the transformer winding can be used as a coupled boost inductor, with or without any other separate inductor.

[0026] According to various aspects of the present disclosure, the AC-DC converter (i.e., PFC rectifier) ​​may not be another entirely additional set of hardware, but rather the rectifier hardware and power factor correction functionality may be integrated and implemented by operating part or all of the inverter bridge in the reverse power direction to draw power from the AC power source, with or without using the motor windings as the inductor required for the PFC rectifier.

[0027] Optionally, in any of the aforementioned aspects, the multiple isolation transformers at both ends of the multi-bridge converter may be separate transformers, or may be an integrated transformer having multiple primary windings coupled on the same core structure and having a common secondary winding.

[0028] Optionally, in any of the foregoing aspects, the AC motor may have multiple sets of separate armature windings, wherein each set of windings is powered by a separate inverter phase output of the multi-bridge converter. This separate winding configuration avoids any potential circulating currents in the motor windings due to common mode voltages.

[0029] Optionally, in any of the foregoing aspects, the multi-bridge converter may drive a plurality of separate AC motors, and each motor is powered by a separate inverter phase output of the multi-bridge converter.

[0030] The foregoing has summarized the features and technical advantages of the present disclosure in a simplified form quite extensively so that the following detailed description of the present disclosure can be better understood. Additional features and advantages of the present disclosure that form the subject matter of the claims of the present disclosure will be described hereinafter. It should be understood by those skilled in the art that the disclosed concepts and specific embodiments can be easily used as the basis for modifying or designing other structures or processes for achieving the same purpose of the present disclosure. It should also be recognized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present disclosure set forth in the appended claims.

[0031] For example, in the present disclosure, it is shown that the multi-bridge converter is configured as a DC-AC inverter and a DC-DC boost circuit in a non-isolated operating mode. Although not shown here, the multi-bridge converter is configured to form a DC-DC buck circuit in a non-isolated operating mode. In fact, it is much easier to draw a multi-bridge converter in a DC-DC buck circuit, and this is under the same concept and exact idea taught in the present disclosure.

[0032] As another example, a disconnect switch is connected in series with the isolation transformer winding on the primary or secondary side to achieve more functionality and better performance. Similarly, a disconnect switch can be connected in series with the non-isolated output of the multi-bridge converter, which can reduce any useless power loss or simply simplify control. However, such modifications such as adding a disconnect switch anywhere in the circuit do not depart from the spirit and scope of the present disclosure as set forth in the appended claims.

[0033] For another example, the isolated DC-DC charging circuit shown in the present disclosure is mainly a full-bridge phase-shift converter, an LLC converter, or a dual active bridge (DAB) converter. It should be understood that other isolated DC-DC topologies or combinations of different topologies are also applicable and are very suitable for the implementation of multi-bridge converter circuits. Moreover, such modifications using other different DC-DC topologies do not depart from the spirit and scope of the present disclosure as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Aspects of the present disclosure are illustrated by way of example and not limitation in the accompanying drawings.

[0035] Figures 1A to 1D Showing a circuit example of a multi-bridge converter and its operating waveform according to various embodiments of the present disclosure;

[0036] FIG. 2A to FIG. 2D Two circuit examples and operating waveforms thereof of a multi-bridge converter with an additional transformer disconnect switch according to various embodiments of the present disclosure are shown;

[0037] FIG. 3A to FIG. 3CCircuit examples showing a multi-bridge converter using a three-level bridge topology and its operating waveforms according to various embodiments of the present disclosure;

[0038] FIG. 4A to FIG. 4D Two circuit examples of multi-bridge converters using three switching bridges and their operating waveforms are shown;

[0039] Figure 5A A circuit example of a single-phase inverter based on a multi-bridge converter integrated with a battery charging system according to various embodiments of the present disclosure is shown;

[0040] Figure 5B shows a non-isolated operating mode with exemplary switching waveforms. Figure 5A Equivalent circuit of the circuit example shown in .

[0041] Figure 5C shows an isolated operating mode with exemplary switching waveforms. Figure 5A The equivalent circuit of the circuit shown in .

[0042] Fig. 6A A circuit example of a three-phase inverter based on a multi-bridge converter integrated with a battery charging system according to various embodiments of the present disclosure is shown;

[0043] Figure 6B Shows Fig. 6A Examples of switching waveforms in a non-isolated operating mode of the circuit shown in;

[0044] Figure 6C Shows Fig. 6A Examples of switching waveforms in the isolated operating mode of the circuit shown in;

[0045] Fig.6D Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0046] Fig. 6E Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0047] Fig. 7A Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0048] Figure 7B Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0049] Fig. 8AAnother circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0050] Figure 8B Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0051] Figure 8C Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0052] Fig.8D Another circuit example of a three-phase inverter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0053] Fig.9A Another circuit example of a three-phase inverter based on a multi-bridge converter and integrated with a battery charging system according to various embodiments of the present disclosure is shown, the inverter driving two motors;

[0054] Fig. 9B Another circuit example of a three-phase inverter based on a multi-bridge converter with an integrated battery charging system according to various embodiments of the present disclosure is shown, the inverter driving two motors;

[0055] Fig. 10A A circuit example of a DC-DC boost converter based on a multi-bridge converter integrated with a battery charging system according to various embodiments of the present disclosure is shown;

[0056] Fig. 10B shows the non-isolated operating mode with example switching waveforms Fig. 10A The equivalent circuit of the circuit;

[0057] Fig. 10C shows the isolated operating mode with example switching waveforms Fig. 10A The equivalent circuit of the circuit;

[0058] Fig. 10D Shows Fig. 10A An example circuit is shown with an attached transformer disconnect switch with exemplary switching waveforms in non-isolated mode;

[0059] Fig.11A Another circuit example of a DC-DC boost converter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0060] Fig. 11B shows a non-isolated operating mode with exemplary switching waveforms. Fig.11A Equivalent circuit of the circuit shown;

[0061] Fig. 11C shows an isolated operating mode with exemplary switching waveforms Fig.11A The equivalent circuit of the circuit shown in;

[0062] Fig.11D Shows Fig.11A An example circuit is shown in FIG. 1 with an additional transformer disconnect switch having exemplary switching waveforms in non-isolated mode.

[0063] Fig.12 Another circuit example of an integrated DC-DC boost converter based on a multi-bridge converter integrated with a battery charging system according to various embodiments of the present disclosure is shown;

[0064] Fig.13 Another circuit example of a DC-DC boost converter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0065] Fig.14 Another circuit example of a DC-DC boost converter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0066] Fig.15A Another circuit example of a DC-DC boost converter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0067] Fig. 15B Another circuit example of a DC-DC boost converter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown;

[0068] Fig. 15C Another circuit example of a DC-DC boost converter integrated with a battery charging system based on a multi-bridge converter according to various embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0069] The present disclosure will now be described with reference to the accompanying drawings, which generally relate to power circuits such as may be used in electric vehicles. For example, the circuits described herein may be used to charge a battery from an external source and to control power to drive a motor using the battery.

[0070] EV power systems are sensitive to component size, weight, and converter efficiency. Mainstream power converter designs using traditional metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) have reached their performance limits, and new generation power devices such as gallium nitride (GaN) and silicon carbide (SiC) MOSFET transistors can be adopted for efficiency, size, and weight benefits. In addition, using shared hardware circuits to perform different functions such as driving motors and charging batteries is effective and can save costs; and integrating motor drive and battery charging systems can further provide cost and size benefits.

[0071] Typically, an EV should be able to charge the EV's battery from at least two different power sources (e.g., DC power from a charging station and AC power from a utility AC grid). Therefore, in addition to the inverter circuit that operates the EV motor during drive mode or traction mode, the EV onboard power system may also include DC and AC charging circuits.

[0072] Charging of EV batteries can include the use of on-board charging circuits. The power from the battery can be used to power one or more motors through an inverter to propel the electric vehicle. In some cases, certain components can be shared by these circuits, which can reduce costs and improve efficiency. Integrating the on-board charging circuit and the inverter circuit using advanced high-frequency circuit topologies and using a common power converter stage (e.g., a power bridge) between the on-board charging and the inverter can reduce the overall cost, size, and weight of the EV power system. However, any integrated solution also needs to address these technical challenges brought about by different power ratings, isolation requirements, and wide voltage ranges.

[0073] It should be understood that the current embodiments of the present disclosure can be implemented in many different forms, and the scope of the claims should not be interpreted as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and the embodiments of the present invention are conceived to be fully communicated to those skilled in the art. In fact, the present disclosure is intended to cover the substitutions, modifications and equivalents of these embodiments, which are included in the scope and spirit of the present disclosure as defined by the appended claims. In addition, in the following detailed description of the embodiments of the present disclosure, many specific details are set forth to provide a thorough understanding. However, it will be clear to those of ordinary skill in the art that the embodiments of the present disclosure can be practiced without such specific details.

[0074] Figure 1AA conceptual diagram of a multi-bridge converter 100 is shown, which includes a multi-bridge 110 (which consists of two switching bridges, namely, an A-phase bridge 111 and a B-phase bridge 112, but may also consist of more than two switching bridges, as desired in various embodiments) connected to a DC bus 130 and coupled to an isolation transformer 120, the isolation transformer 120 having a primary winding connected between an output end (i.e., port A) of the A-phase bridge 111 and a B-phase output end 112 (i.e., port B). In the case where a controller 140 generates and provides different PWM gating control signals to the multi-bridge converter 100, the multi-bridge converter 100 can operate in at least two different modes, including: (i) a non-isolated operation mode, in which the two switching bridges operate in a parallel mode, and power is transferred from the DC bus 130 to the non-isolated ports A and B, and (ii) an isolated operation mode, in which the two switching bridges operate in a full-bridge mode, and power is transferred from the DC bus 130 to the isolated ports E and F through the isolation transformer 120. Generally, the multi-bridge converter 100 may be used in a DC-DC converter or a DC-AC inverter system.

[0075] Figure 1B 1 shows an example of a switching waveform for a non-isolated operating mode of the multi-bridge converter 100. For simplicity, all dead time in the PWM signal of each bridge is ignored, as is the case with all other example waveforms throughout this disclosure. The two switching bridges 111 and 112 are synchronized in the gate turn-on or turn-off signals to produce the same PWM voltage waveform across the primary winding of the transformer 120 without phase shift, so that the primary winding of the transformer 120 is not affected by any significant differential voltage (i.e., voltage V AB , representing the voltage between port A and port B) is excited, and power is mainly transferred from the DC bus to the non-isolated ports A and B, and has bidirectional power flow capability. The switching rule in the non-isolated operating mode is that the A-phase bridge 111 and the B-phase bridge 112 are completely synchronized in phase, and the switching devices S1 and S2 (such as IGBT, silicon MOSFET and silicon carbide MOSFET) in the A-phase bridge 111 are turned on and off by the same gating signal as the switching devices S3 and S4 (such as IGBT, silicon MOSFET and silicon carbide MOSFET) in the B-phase bridge 112. In other words, the A-phase bridge and the B-phase bridge 111 and 112 usually operate perfectly synchronously because they are controlled by the same gating PWM signal. And these common PWM gating signals are usually generated by multivariable input-output closed-loop regulation according to the duty cycle control or space vector modulation of the converter 100. As a result, the primary winding of the transformer 120 is controlled by the voltage V from the A-phase bridge 111. A and the voltage V from the B phase bridge 112 BThe same voltage waveform excitation, and therefore the secondary winding voltage V across the transformer 120 EF will be flat, ideally at a "0" voltage. Therefore, power is delivered from the DC bus 130 to the non-isolated Ports A and B, but not to the isolated Ports E and F. Note that in this non-isolated mode of operation, in the case of imperfect synchronization of the gating signals, the switching devices of the Phase A bridge 111 and the Phase B bridge 112 may not be turned on and off at the same timing, and short voltage pulses or glitches may be seen at the secondary Ports E and F of the transformer 120, but these short pulses can be tolerated because they do not carry any significant portion of the total power flow.

[0076] Figure 1C An example of a switching waveform for an isolated operation mode of the multi-bridge converter 100 is shown. In this mode, the two switching bridges 111 and 112 operate in full-bridge mode, the PWM switching signals are phase-shifted by 180°, and the phases between the two bridges are exactly opposite, so that the windings of the transformer 120 are excited by the expected significant differential voltage, and the power is mainly transferred from the DC bus 130 to the isolated output terminal (i.e., isolated ports E and F) through the transformer 120, and has a bidirectional power flow capability. The A-phase bridge 111 and the B-phase bridge 112 are out of phase and are not turned on and off by the same gating timing signal. In fact, the two bridges 111 and 112 can operate in opposite phases, where the switching device S1 of the A-phase bridge 111 and the switching device S4 of the B-phase bridge 112 are usually turned on at the same time without any expected phase shift, and the switching device S2 of the A-phase bridge 111 and the switching device S3 of the B-phase bridge 112 are usually turned on at the same time. As a result, a square waveform or the like is generated at the isolated port EF of the transformer 120, and thus power is mainly delivered to the isolated port EF from the DC bus 130. It is worth noting that in this isolated operating mode, the goal is to minimize the power flowing to the non-isolated ports A and B, and to achieve this goal, some careful or special arrangements of the load wiring or load configuration connected to the non-isolated ports A and B are required.

[0077] Figure 1D Another example of switching waveforms for the isolated operating mode of the multi-bridge converter 100 is shown. Here, the two switching bridges are operated in full-bridge mode, and there is an expected phase shift on the PWM switching signals between the two phase bridges (i.e., S1 / S2 and S3 / S4). For simplicity, the dead time in the PWM signal of each bridge is ignored. As a result, the transformer primary winding V AB The PWM voltage output at both ends has a bipolar waveform, that is, it has positive and negative DC bus voltages or zero voltage transitions in the middle. The same bipolar waveform will appear at the transformer secondary winding voltage VEF , ignoring all parasitic effects. In practice, the effective duty cycle or pulse width of the positive and negative voltage waveforms depends on the phase shift angle; therefore, adjusting the phase shift angle between the PWM gate signals of the two bridges will adjust the power flowing through the transformer to the isolated load. The detailed gate timing usually depends on the closed-loop regulation method of the converter 100, such as PWM, frequency modulation, phase shift control, etc. In practice, it operates in the same way as a conventional full-bridge phase-shift or LLC converter.

[0078] FIG. 2A to FIG. 2B Examples of multi-bridge converters and their operating waveforms according to various embodiments of the present disclosure are shown. Figure 2A and Figure 2B The circuit in FIG. 1 is almost the same as that in FIG. 1 , but the only difference from the circuit in FIG. 1 is that an additional disconnect switch 250, namely Kc, is connected between the output port A or B of the multi-bridge output terminal 210 and the isolation port E or F at both ends of the transformer 220, and the disconnect switch Kc can be used as shown in FIG. Figure 2A shown on the primary winding side or Figure 2B The secondary winding side of the transformer is connected in series with the transformer. With this disconnect switch Kc, the purpose is to introduce a phase shift angle in the synchronous PWM signal and achieve PWM interleaving operation between the two bridges 211 and 212 of the multi-bridge converter 200 during the non-isolated operation mode. This disconnect switch Kc can be anything such as a contactor, a relay or a semiconductor device switch. It is well known that the benefit of parallel bridge PWM interleaving is to increase the effective PWM frequency at the output terminals, thereby reducing the output voltage and current ripple, and potentially mitigating electromagnetic radiation (EMI) and audible noise.

[0079] Figure 2C 1 shows an example of PWM interleaved switching waveforms in the non-isolated operation mode of the multi-bridge converter 200. In this mode, the disconnect switch Kc remains in the open state, so the isolation transformer is not activated in the circuit function. Across the two switching bridges 211 and 212, there is a 180° phase shift angle between their synchronous PWM gating signals. Therefore, the load output voltage V AB The effective PWM switching frequency will be doubled, resulting in smaller PWM switching ripple and lower EMI noise across the load, etc.

[0080] Figure 2D FIG. 2 shows that, in the case where the disconnect switch Kc remains turned on, in the isolation mode of the multi-bridge converter 200, the circuit operation of the multi-bridge converter 200 is the same as that in the full-bridge mode, and the output waveform is the same as that in the full-bridge mode. Figures 1A to 1C The same situation as without the circuit breaker Kc. In essence, FIG. 2A to FIG. 2D In with Figures 1A to 1CExactly the same circuit principle, with the additional function of PWM phase shift interleaving and improved performance.

[0081] Figure 3A A conceptual circuit diagram of a three-level multi-bridge converter 300 is shown as an example. The multi-bridge 310 connected to the DC bus 330 consists of two switch bridges (i.e., A-phase bridge 311 and B-phase bridge 312) using a diode NPC three-level topology. Similarly, the same concept can be applied to other multi-level topologies, such as ANPC, suspended capacitors, or hybrid multi-level converters. The primary winding of the isolation transformer 320 is at both ends of the output of the A-phase bridge 311 and the output of the B-phase bridge 312 (i.e., port A and port B). The secondary winding of the transformer 320 provides an isolated output terminal at port E-port F. By generating different PWM gating signals by the controller 340, the three-level multi-bridge converter 300 can operate in at least two different modes, including: (i) a non-isolated operation mode, in which if the two switch bridges operate in parallel mode, the PWM switching signals are synchronized in phase between the two bridges, and power is transferred from the DC bus 330 to the non-isolated ports A and B; and (ii) an isolated operation mode, in which if the two switch bridges operate in full-bridge mode, the PWM switching signals are phase-shifted and out of phase between the two bridges, and thus power is transferred from the DC bus 330 to the isolated ports E and F through the isolation transformer 320. The three-level multi-bridge converter 330 can be used in a DC-DC or DC-AC inverter system.

[0082] Figure 3B An example of switching waveforms in the non-isolated operating mode of the multi-bridge converter 300 is shown. The switching rule in the non-isolated operating mode is that the A-phase bridge 311 and the B-phase bridge 312 are completely synchronized in phase and can be perfectly operated in parallel using the same PWM gating signal. As a result, the primary winding of the transformer 320 is excited by the same voltage waveform from port A and port B, and therefore the secondary winding of the transformer 320 will be maintained at a "0" voltage. Therefore, power is mainly delivered from the DC bus 330 to the non-isolated port AB, and not to the isolated port EF. Note that in this non-isolated operating mode, in the case of non-perfect gating signal synchronization, the switching devices S1 to S4 of the A-phase bridge 311 and the switching devices S5 to S8 of the B-phase bridge 312 may not be turned on and off at exactly the same timing, and short voltage pulses or glitches may be seen at the secondary ports E and F of the transformer 320. However, since they do not deliver any significant part of the total power flow, these short voltage pulses can be tolerated.

[0083] Figure 3CAn example of a switching waveform in an isolated operating mode of a multi-bridge converter 300 is shown. In this mode, the A-phase bridge 311 and the B-phase bridge 312 are phase-shifted and out of phase, and are not turned on and off by the same gating timing signal. As a result, the isolated port EF of the transformer 320 generates a multi-step square waveform or a similar waveform, and thus power is mainly delivered to the isolated port EF from the DC bus 330. In fact, the operation of the two bridges 311 and 312 is very similar to a conventional three-level full-bridge phase shift or LLC converter. The detailed gating timing generally depends on the closed-loop regulation method of the converter 300, such as PWM, frequency modulation, phase shift control, etc. It is worth noting that in this isolated operating mode, the purpose is to minimize the power flowing to the non-isolated ports A and B, and to achieve this goal, some special arrangements need to be made for the load configuration connected to the non-isolated ports A and B.

[0084] Figure 4A A conceptual circuit diagram of a three-bridge multi-bridge converter 410 connected to two separate isolation transformers 420 and 421 is shown. There are three switching bridges connected to the DC bus, namely, an A-phase bridge 411 having an output port A, a B-phase bridge 412 having an output port B, and a C-phase bridge 413 having an output port C. The primary winding of the isolation transformer 420 is connected to port A and port B. The primary winding of another isolation transformer 421 is connected to port C and port B. The secondary windings of the two transformers 420 and 421 provide isolated output terminals at ports E and F and ports G and H, respectively. Note that the polarity of the multiple transformer windings needs to be arranged in the same manner as shown to match the switching waveforms shown below.

[0085] Figure 4B A conceptual diagram of a multi-bridge converter 410 with three bridges connected to one integrated transformer 422 is shown. Figure 4A and Figure 4B The only difference between the two is the isolation transformer, but Figure 4A and 4B Both isolation transformers operate in the same manner. It is worth noting that the polarity of the multiple transformer windings needs to be arranged in the same manner as shown to match the switching waveforms shown below.

[0086] Figure 4C Show Figure 4A The switching rule in the non-isolated operation mode is that the A-phase bridge 411, the B-phase bridge 412, and the C-phase bridge 413 are completely synchronized and run in perfect parallel with the same PWM gate signal. As a result, the voltage V connected to ports A and B is A and V B and the voltage V at ports C and B C and VB The primary windings of the two transformers 420 and 421 are excited by the same voltage waveform, and therefore the output voltage V at the isolated ports E and F of the secondary winding of the transformer 420 EF and the output voltage V at the isolated ports G and H of the secondary winding of the transformer 421 GH will remain at "0" voltage. Therefore, power is mainly delivered from the DC bus to non-isolated ports A and B and non-isolated ports C and B, but not to isolated ports E and F or ports G and H. Note that in this non-isolated operating mode, with imperfect strobe signal synchronization, phases A and B and C may not be turned on or off at exactly the same timing, and short voltage pulses or glitches may be seen at ports E and F and ports G and H of transformers 420 and 421. But these short voltage pulses can be tolerated because they do not deliver any significant part of the total power flow.

[0087] Figure 4D Show Figure 4A . In this mode, the A-phase bridge 411 and the B-phase bridge 412 are out of phase and are not turned on and off by the same gating timing signal. At the same time, the C-phase bridge 413 and the B-phase bridge 412 are also out of phase. As a result, a square waveform or a similar waveform is generated at the isolated ports E and F and the isolated ports G and H of the transformers 420 and 421, and therefore power is mainly delivered from the DC bus to the isolated ports E and F and the isolated ports G and H. In fact, the operation of these three bridges 411, 412 and 413 is very similar to a conventional full-bridge phase shift or LLC converter. The detailed gating timing usually depends on the closed-loop regulation method of the converter, such as PWM, frequency modulation, phase shift control, etc. It is worth noting that in this isolated operating mode, the purpose is to minimize the power flowing to the non-isolated ports A, B and C, and to achieve this goal, some special arrangements need to be made for the load wiring or load configuration connected to the non-isolated ports A, B and C.

[0088] Figure 5AAn embodiment of a single-phase inverter based on a multi-bridge converter integrated with a battery charging system is shown. There are two multi-bridges 510 and 520 connected to the DC bus, each of which has two switching bridges. The multi-bridge 510 includes a 1A phase bridge and a 1B phase bridge, and the multi-bridge 520 includes a 2A phase bridge and a 2B phase bridge. The two multi-bridges 510 and 520 form a non-isolated single-phase output terminal with the port 1A of the 1A phase bridge and the port 2A of the 2A phase bridge, and form a parallel single-phase non-isolated output terminal with the port 1B of the 1B phase bridge and the port 2B of the 2B phase bridge. The multi-bridges 510 and 520 are connected to isolation transformers 530 and 531, respectively. Power converters 550 and 551 are connected to the secondary windings of the transformers 530 and 531, and are used as rectifiers to generate a DC voltage to charge the battery 570 through an optional contactor K2. The same battery 570 is also connected to the DC bus through the main contactor K1. Typically, the battery 570 is equipped with multiple modules of multiple batteries with a battery management system (BMS) 570 for electrical safety and thermal protection. In addition, a PFC rectifier 580 is also connected between the DC bus and the external AC power supply. The controller 590 controls the phase bridge gating timing of the multi-bridge 510 and 520 according to two different operating modes. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0089] Figure 5B Shows the non-isolated operating mode Figure 5A The equivalent active circuit portion of the circuit shown in FIG. 5 and the example switching waveforms. In this non-isolated operating mode, the battery 570 supplies power to the DC bus connected to K1, and the multi-bridges 510 and 520 provide a pair of single-phase output terminals at ports 1A and 2A and ports 1B and 2B that are connected in parallel as single-phase inverter output terminals. As shown in the example switching waveforms, the 1A phase bridge and the 1B phase bridge of the multi-bridge 510 are fully synchronized using exactly the same selection timing signal; and, the 2A phase bridge and the 2B phase bridge of the multi-bridge 520 are also fully synchronized using the same selection timing signal. Therefore, the 1A phase bridge and the 1B phase bridge generate the same PWM voltage waveform across the primary winding of the transformer 530, so under ideal conditions, when there is no power flow, the secondary winding of the transformer 530 will have a "0" voltage V at ports E and F. EF The same is true for transformer 531, whose secondary winding will produce a flat voltage V at ports G and H that remains at "0". GHNote that in this non-isolated operating mode, with imperfect strobe signal synchronization, the Phase 1A and Phase 1B bridges, as well as the Phase 2A and Phase 2B bridges, may not be turned on or off at exactly the same timing, and short voltage pulses or glitches may be seen at the secondary port EF of transformer 530 and the secondary ports G and H of transformer 531. However, these short voltage pulses can be tolerated because they do not carry any significant portion of the total power flow.

[0090] Figure 5C Shows the isolated operation mode Figure 5A The equivalent active circuit portion of the circuit shown in FIG. 5 and the example switching waveform. In this mode, the PFC rectifier 580 is in active operation to support the DC bus by drawing power from the external AC power source. The multi-bridges 510 and 520 operate out of phase, and therefore utilize a square voltage waveform to excite the isolation transformers 530 and 531, and deliver power to both ends of the isolation transformer to charge the battery 570. However, as shown in the example switching waveform, the non-isolated output ports 1A and 2A or ports 1B and 2B of the single-phase multi-bridge 510 or 520 will not have any obvious power flow. The 1A multi-bridge phase of the multi-bridge 510 and the 2A multi-bridge phase of the multi-bridge 520 are fully synchronized using the same selection timing signal; and the 1B phase bridge of the multi-bridge 510 and the 2B phase bridge of the multi-bridge 520 are also fully synchronized. Therefore, the 1A phase bridge and the 2A phase bridge generate the same PWM voltage waveform, and thus result in a "0" differential voltage across the non-isolated ports 1A and 2A. The same is true for the 1B phase bridge and the 2B phase bridge, which generate a "0" differential voltage across the non-isolated ports 1B and 2B. It is worth noting that in this isolation mode, the goal is to minimize the power flowing to the non-isolated ports 1A and 2A and ports 1B and 2B, and to achieve this goal, some special arrangements are required for the load configuration connected to the non-isolated ports 1A and 2A and ports 1B and 2B.

[0091] Fig. 6A An example circuit diagram of a three-phase inverter system based on a multi-bridge converter according to various embodiments of the present disclosure is shown. There are three multi-bridge converters 610, 611 and 612 configured to drive a dual-winding AC motor 660, and the three multi-bridge converters 610, 611 and 612 are connected to three isolation transformers 620, 621 and 622 and their rectifiers 630, 631, 632 to charge the battery 670. The PFC rectifier 640 and the EMI filter 650 are connected between the DC bus and the external AC power source. There is also a plug port for an external DC power source for charging. Using a controller 680, Fig. 6AAn example of an EV on-board integrated circuit is shown, which can perform the functions of battery charging and inverter motor drive in an efficient manner. By sharing the main power components (i.e., the same multi-bridge 610, 611, 612 hardware) between the battery charging mode and the drive mode, the component cost, the size and weight of the circuit are reduced. Both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities. In addition, the disconnect switches Kc1, Kc2, and Kc3 are connected in series with the primary windings of the transformers T1, T2, and T3, respectively. And during non-isolated operation in parallel mode, these disconnect switches will cause the multi-bridge converter to operate in a PWM phase interleaved manner to increase the effective switching frequency of the PWM voltage at the motor terminals. Benefits include reduced motor torque ripple and audible noise, etc.

[0092] Figure 6B Shown based on Fig. 6A An example of a switching waveform of a non-isolated operating mode of a three-phase inverter system of a multi-bridge converter shown in . In this non-isolated operating mode, i.e., motor drive mode, the main contactor switch K1 of the battery is turned on, and the three multi-bridge converters 610, 611, 612 operate together and act as a three-phase inverter, which is controlled in real time by PWM or space vector modulation (SVM) and torque closed-loop regulation according to the motor speed. In each multi-bridge converter, the two phase bridges in a pair (e.g., 1A and 1B, 2A and 2B, or 3A and 3B) are synchronized in phase and are always turned on and off at the same timing, so that the PWM output voltage (i.e., V 1A =V 1B , V 2A =V 2B , V 3A =V 3B ) are identical with the same waveform. Even without the disconnect switches (e.g., Kc1, Kc2, Kc3), a "0" differential voltage is actually applied between the three transformer primary windings. Therefore, as a result, the differential voltage across the secondary winding of the isolation transformer (i.e., voltage V EF 、V GH and V JK ) will also remain at "0". Therefore, the battery power is mainly delivered through its dual windings to drive the motor; and no significant power flow is delivered at the three isolation transformer terminals.

[0093] Figure 6C Shown based on Fig. 6AAn example of switching waveforms of an isolated operating mode of a three-phase inverter system of a multi-bridge converter shown in FIG. In this non-isolated operating mode, i.e., battery charging mode, the main contactor switch K1 of the battery remains disconnected, and the phase bridges of each multi-bridge 610, 611, or 612 are not turned on or off with the same timing. In fact, each multi-bridge operates like a standard LLC or phase-shifted full-bridge converter, and PWM regulation or frequency modulation is usually used to regulate the battery charging DC voltage and charging current. The battery charging power can be supplied from the AC power supply by the PFC rectifier, or by an external DC power supply.

[0094] In addition, it should be noted here Figure 6C Another important thing about the battery charging mode is that the A-phase bridges of all three multi-bridge converters 610, 611 and 612 (i.e., 1A-phase bridge, 2A-phase bridge and 3A-phase bridge) are synchronized in phase, and the output voltages of these A-phase bridges (i.e., V 1A =V 2A =V 3A ) are the same in PWM waveform. The output voltage of phase B of the three multi-bridge converters 610, 611 and 612 (i.e., V 1B =V 2B =V 3B ) also have the same waveform. As a result, the motor windings are not excited by any significant differential voltage that could cause circulating currents, especially if the two sets of motor dual windings are separated from each other.

[0095] Fig.6D Another embodiment of a three-phase multi-bridge inverter with two isolation transformers for a battery charging system is shown. An LLC converter with resonant capacitors Cr1 and Cr2 is explicitly shown in the circuit of the three-phase multi-bridge inverter. Fig. 6A The three-transformer versions operate in the same manner as the 3-transformer versions, they differ only in the reduced rating of the battery charging power capacity. Both inverter drive operation and battery charging operation have bidirectional power flow capability.

[0096] Fig. 6E Another embodiment of a three-phase multi-bridge inverter with an isolation transformer for a battery charging system is shown. An LLC converter with a resonant capacitor Cr1 is explicitly shown in the circuit of the three-phase multi-bridge inverter. Fig. 6A The three-transformer version or Fig.6D The two transformer versions operate in the same way, they differ only in that the battery charging power capacity is further derated. Both inverter drive operation and battery charging operation have bidirectional power flow capability.

[0097] As previously mentioned, although the resonant capacitor is not explicitly shown in all circuit diagrams, all example circuits shown in the present disclosure can be configured as LLC resonant converters. In fact, throughout the examples of the present disclosure, the isolated DC-DC charging circuit is shown as a full-bridge phase-shift converter, an LLC converter, or a dual active bridge (DAB) converter. It should be understood that other isolated DC-DC topologies or combinations of different topologies are also applicable and may be very suitable for the implementation of multi-bridge converter circuits. And such modifications using other different topologies do not depart from the spirit and scope of the present disclosure as set forth in the appended claims.

[0098] Fig. 7A Another embodiment of a three-phase multi-bridge inverter for a battery charging system using an isolation transformer 720 having three coupled primary windings is shown. The circuit of the three-phase multi-bridge inverter is shown with Fig. 6A The three transformer versions shown in FIG. 7 operate in the same manner, differing only in the magnetic transformer design. Alternatively, on the secondary winding of the isolation transformer 720, a passive rectifier 730 is shown that can be used for battery charging, and the main advantage will be lower cost compared to the active switching rectifier 630. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0099] Figure 7B Another embodiment of a three-phase multi-bridge inverter for a battery charging system using an isolation transformer 721 having two coupled primary windings is shown. The circuit of the three-phase multi-bridge inverter is shown with Fig.6D The two transformer versions in FIG. 7 operate in the same manner, differing only in the magnetic transformer design. Alternatively, a Vienna rectifier 741 is shown for use in a boost PFC converter to draw power from an external AC source, taking advantage of reduced cost due to reduced voltage stress and current on the active switching devices.

[0100] Fig. 8A An embodiment of a three-phase multi-bridge inverter is shown without additional PFC rectifier hardware. Instead, the phase bridge 812 is used as a boost PFC rectifier operating with reverse power flow, and the winding inductance of the motor 860 is used as a boost inductor. This will further reduce the charging hardware cost. Fig. 8A Two isolation transformers 820 and 821 and two rectifiers 830 and 831 are shown for battery charging. The single-phase AC power source is connected to the neutral point of the dual windings of the EV motor 860 through an EMI filter 850. In EV driving mode, Fig. 8AThe circuit shown operates in the same manner as previously described, and in each multi-bridge, two phase bridges operate in parallel mode. The battery charging mode is different because there is no additional PFC rectifier. During battery charging in the isolated operation mode, two phase bridges operate in full-bridge mode within each multi-bridge. In addition, the PWM duty cycle of each multi-bridge in full-bridge mode still needs to be modulated by the AC voltage reference waveform to achieve the power factor correction function. This is basically the same as the operation principle of the innate single-stage PFC enabled isolated DC-DC converter. The disadvantage is that the AC current envelope above the PWM switching ripple will make the isolation transformer core size larger. When the phase bridges 810, 811, 812 operate as PFC rectifiers to draw current through the motor windings, they need to be coordinated in terms of PWM gating timing synchronization to minimize the motor winding circulating current. Care is also required in the control design to reduce the motor pulsation torque and not allow the rotor to move during charging. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0101] Figure 8B Another embodiment of a three-phase multi-bridge inverter without additional PFC rectifier hardware is shown. Similarly, the phase bridges 810, 811, and 812 are used as boost PFC rectifiers operating in reverse power flow, and the winding inductance of the motor 860 is used as a boost inductor. The AC power supply is connected to the two neutral points of the dual windings of the motor 860 through the EMI filter 850. Figure 8B An isolation transformer 820 is shown for a battery charging system. During battery charging in isolation mode, the phase bridges 810, 811 and 812 are all operated as Fig. 8A The single-stage PFC-enabled DC-DC converter shown. In addition, the gating timing control of the same-phase synchronous multi-bridge inverters 810, 811, 812 is required to minimize the motor winding circulating current. Care is also required in the control design to reduce the pulsating torque of the motor and not allow the rotor to move during the charging process. In addition, the circuit of the three-phase multi-bridge inverter is similar to Fig. 8A Operate in essentially the same manner. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capability.

[0102] Figure 8CAn embodiment of a three-phase multi-bridge inverter with two isolation transformers 820 and 821 for charging is shown. Again, no additional PFC rectifier hardware is used here. Instead, the phase bridge 812 is used as a boost PFC rectifier operating with reverse power flow, and the two inductors La and Lb are used as boost inductors. Three multi-bridge converters formed by phase bridges 810, 811 and 812 are used to drive a dual-winding motor 860; and two isolation transformers 820 and 821 and two rectifiers 830 and 831 are used to charge a battery 870. The single-phase AC power supply is connected to the dual-winding terminals 3A and 3B of the EV motor 860 through the EMI filter 850 through the inductors La, Lb. In EV drive mode, Figure 8C The circuit shown operates in the same manner as previously described. During battery charging in the isolated operating mode, the phase bridge 812 operates as a PFC rectifier to draw current from the external AC power supply, and in order to minimize the winding circulating current of the motor 860, the other phase bridges 810 and 811 need to cooperate with the phase bridge 812 in terms of PWM gating timing. Ideally, when the gate timing is synchronized between the three multi-bridges, the PWM output voltages at ports 1A, 2A, and 3A will be the same, and the A-phase winding of the motor 860 will not have any circulating current. Similarly, the PWM output voltages at 1B, 2B, and 3B will be the same, so the B-phase winding of the motor 860 will not have any circulating current. Therefore, the rotor of the motor 860 will not move during battery charging. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0103] Fig.8D Another embodiment of a three-phase multi-bridge inverter with an isolation transformer 820 for charging is shown. Again, no additional PFC rectifier hardware is used here. Instead, the phase bridge 812 is used as a boost PFC rectifier running with reverse power flow, and the two inductors La and Lb are used as boost inductors. For the same reason, the PWM gate timing of all three multi-bridges is synchronized, and the same PWM output voltage is generated across the A-phase winding (i.e., ports 1A, 2A, 3A) and the B-phase winding (i.e., ports 1B, 2B, 3B) of the motor 860. Although an AC voltage is applied across the winding terminals 3A and 3B of the motor 860, there is no excitation of circulating current through the windings of the motor 860, so the rotor of the motor 860 will not move during battery charging. During battery charging in isolation mode, when the phase bridge 812 operates as a PFC rectifier, the PWM gate timing control for the phase bridges 810, 811 and 812 needs to be synchronized in phase to minimize the circulating current of the motor winding so that the motor will not move during charging. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0104] Fig.9A An embodiment of a three-phase multi-bridge inverter driving two AC motors 960 and 961 is shown. No additional PFC rectifier hardware is used here. Instead, the phase bridge 912 is used as a boost PFC rectifier operating with reverse power flow, and the two inductors La and Lb are used as boost inductors. There are two isolation transformers 920 and 921 and two rectifiers 930 and 931 for charging the battery 970. The single-phase AC power source is connected to the winding terminals 3A and 3B of the motors 960 and 961 through the inductors La and Lb through the EMI filter 950. Another inductor Lc is connected to the midpoint of the DC bus to form a third line at the AC input, which can be three-phase AC or split single-phase AC. In EV drive mode, Fig.9A The circuit shown operates in the same manner as previously described. During battery charging in the isolated operating mode, the phase bridge 912 is mainly operated as a PFC rectifier to draw current from the external AC power source, and in order to minimize the circulating current through the windings of the motors 960 and 961, the other phase bridges 910 and 911 need to be coordinated with the phase bridge 912 in terms of PWM switch timing synchronization. Similarly, although the AC voltage is applied to the winding terminals 3A and 3B of the motors 960 and 961, the circulating current through the windings of the motors 960 and 961 is not excited, so the rotors of the motors 960 and 961 will not move during battery charging. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0105] Fig. 9B Another embodiment of a three-phase multi-bridge inverter driving two AC motors 960 and 961 is shown, in which one isolation transformer 920 is used for battery charging. Again, no additional PFC rectifier hardware is used here. Instead, the phase bridge 912 is used as a boost PFC rectifier running with reverse power flow, and two inductors La and Lb are used as boost inductors. Another inductor Lc is connected to the midpoint of the DC bus to form a third line at the AC input terminal as a three-phase AC or a split single-phase AC. For the same reason, although an AC voltage is applied to the winding terminals 3A and 3B of the motors 960 and 961, there is no excitation of the circulating current through the windings of the motors 960 and 961, so the motors 960 and 961 will not move during battery charging. Care is needed in the design to coordinate the gating timing control of the phase bridges 910, 911, and 912 to minimize any high-frequency portion of the circulating current through the windings of the motors 960 and 961. Note that both the inverter drive operation and the battery charging operation have bidirectional power flow capabilities.

[0106] Fig. 10AAn example circuit of a DC-DC boost converter and a battery charging system based on a multi-bridge according to various embodiments of the present disclosure is shown. A multi-bridge 1010 having two phase bridges 1011 and 1012 is shown as a boost converter that converts the DC voltage of a battery 1070 into a higher voltage for a DC bus to drive an inverter 1040 to support an AC load (e.g., an AC motor load for EV traction). Two boost inductors 1060 (i.e., L1 and L2) are connected between the main contactor K1 of the battery 1070 and the non-isolated output ports A and B of the phase bridges 1011 and 1012, respectively. Inductor 1060 may also be a coupled inductor. A bidirectional PFC rectifier 1030 is provided to draw current from an external AC power source to power the DC bus when charging. The primary winding of the isolation transformer 1020 is connected across the output ports A and B of the multi-bridge 1010. At the output of ports E and F of the secondary winding of transformer 1020, bidirectional power converter 1050 is used to regulate the AC voltage of transformer 1020 to a DC voltage and charge battery 1070. Note that both the inverter mode of operation and the battery charging mode of operation have bidirectional power flow capabilities.

[0107] Fig. 10B Shows the non-isolated operating mode Fig. 10A The equivalent active switching circuit of the circuit shown in FIG. 1 and the example switching waveform. During inverter operation in non-isolated mode, the battery contactor K1 is turned on and the external power supply is not connected, and the multi-bridge 1010 is used as a DC-DC boost converter. The phase bridges 1011 and 1012 of the multi-bridge 1010 operate in parallel mode, and their PWM gate switching signals are synchronized in phase. Therefore, the same PWM voltage waveform is generated at both ends of the primary winding of the isolation transformer 1020, and the transformer winding is not subject to any significant differential voltage excitation. The power flow is mainly delivered to the inverter 1040 and further to the AC load, but, except for some transformer core losses, there is not much power flow across the isolation transformer 1020. In addition, short pulses or voltage faults may be seen at the secondary ports E and F of the transformer, but these short pulses can be tolerated because they do not transfer most of the total power.

[0108] Fig. 10C Shows the isolated operation mode Fig. 10AThe equivalent active switch circuit and example switching waveforms of FIG. 1 are shown in FIG. 1 . During the battery charging operation in isolation mode, the battery contactor k1 is disconnected and an external AC or DC power source is connected, and the phase bridges 1011 and 1012 of the two multi-bridges 1010 operate in full-bridge mode. The PWM gate switching signals are phase-shifted and out of phase between the two bridges. In fact, the two bridges 1011 and 1012 are adjusted as ordinary LLC or DAB converters with PWM regulation, frequency modulation, and phase shift control, so that the power from the AC power source is mainly delivered to the isolated output terminal (i.e., isolated ports E and F) through the transformer 1020.

[0109] Fig. 10D shows adding additional switches to Fig. 10A A modified example circuit of the circuit shown. In particular, Fig. 10D A modified equivalent active switching circuit in a non-isolated mode of operation is shown along with example switching waveforms. Fig. 10D The circuit in Fig. 10A The circuit in FIG. 1 is different only in that a transformer disconnect switch (i.e., Kc) is connected between the output of the multi-bridge 1010 and the winding terminals of the transformer 1020. With the help of the disconnect switch Kc, the purpose is to introduce a phase shift angle in the synchronous PWM signal and to achieve interleaved operation between the switch bridges 1011 and 1012 during the non-isolated operation mode. The disconnect switch Kc can be anything such as a contactor, a relay, or a semiconductor device switch. Moreover, the disconnect switch Kc can be used in a circuit such as Fig. 10D One side of the primary winding as shown or one side of the secondary winding (not shown) is connected in series with the transformer. It is well known that the benefit of interleaving the phases of the parallel bridge switches is to increase the effective PWM frequency at the load terminals, thereby reducing the load voltage and current ripple and potentially mitigating electromagnetic radiation (EMI) and audible noise.

[0110] Fig.11A Another example circuit of a multi-bridge based DC-DC boost converter and a battery charging system according to various embodiments of the present disclosure is shown. Fig. 10A Unlike the previous circuit shown, here the battery 1180, the main DC contactor K1, the inductor L1, and the midpoint of the primary winding of the isolation transformer 1120 are connected in series. During EV drive operation in the non-isolated operating mode, the primary winding of the transformer 1120 is used as a coupled boost inductor. When the inductance of the transformer 1120 is properly designed, the inductor L1 may not be required or may be represented as a parasitic inductance of wiring and cables, etc.

[0111] Fig. 11B Example switching waveforms are shown for non-isolated operation. Fig.11ADuring inverter operation in the non-isolated operating mode, contactor K1 is turned on and the external power supply is disconnected, and the multi-bridge 1110 operates as a DC-DC boost converter. Fig. 10B Similar to the situation in , the two phase bridges are operated in parallel mode and their gate switching signals are synchronized in phase. Therefore, the same PWM voltage waveform is generated across the primary winding of the transformer 1120, and the transformer windings are not subject to any significant differential voltage excitation. As a result, the power flow is mainly delivered to the inverter 1150 and then to the AC load (for example, the AC motor 1160 shown in the figure), but there is not much power loss across the isolation transformer 1120 except for the transformer core loss and other parasitic losses.

[0112] Fig. 11C shows an isolated operating mode with exemplary switching waveforms. Fig.11A During battery charging operation in isolation mode, contactor k1 is disconnected and the external AC or DC power supply is connected. Fig. 10C Similar to the situation in FIG. 1 , the two phase bridges of the multi-bridge 1110 operate in full-bridge mode, and the PWM switching signals are phase-shifted and out of phase between the two bridges. In fact, the two phase bridges can be operated as a common LLC or DAB converter with PWM regulation, frequency modulation or phase shift control, so that power is transferred between the DC bus and the isolated output terminals (i.e., isolated ports E and F) through the transformer 1120.

[0113] Fig.11D shows adding additional switches to Fig.11A A modified example circuit of the circuit shown in . In particular, Fig.11D A modified equivalent active switching circuit in a non-isolated mode of operation is shown along with example switching waveforms. Fig.11D The circuit in Fig.11A The circuit in is different only in that a transformer disconnect switch, i.e., Kc, is connected to the output of the secondary winding of transformer 1120. With the aid of this disconnect switch Kc, the purpose is to introduce a phase shift angle in the synchronous PWM signal and to achieve interleaved operation between the two phase bridges in non-isolated boost mode. The isolation switch Kc can be anything such as a contactor, a relay, or a semiconductor device switch. It is well known that the benefit of parallel bridge interleaving is to increase the effective PWM frequency at the load, thereby reducing the load current and voltage ripple, and potentially mitigating electromagnetic radiation (EMI) and audible noise.

[0114] Fig.12Another example circuit of a multi-bridge based DC-DC boost converter and battery charging system according to various embodiments of the present disclosure is shown. A PWM inverter 1230 is provided for driving an AC traction motor 1240, and the motor winding neutral point is connected to the AC power supply, with reference to the return DC bus midpoint. Connected here at both ends of the DC bus is a voltage multiplier circuit 1260, which includes two diodes D1 and D2, and separation capacitors C1 and C2 connected in series with a contactor switch Q2. The voltage multiplication function can be enabled by selectively turning on the contactor switch Q2 by the controller 1290 (i.e., when the switch Q2 is turned on, the voltage multiplication is enabled, and when the switch Q2 is turned off, the voltage multiplication is disabled). This provides additional flexibility in adapting to various AC power supply voltages. The effect of using the voltage multiplier 1260 is to provide the same stable high voltage on the DC bus in both low AC and high AC input conditions. The voltage multiplier 1260 should be disabled under inverter operation. Note that both the inverter drive mode and the battery charging mode have bidirectional power flow capabilities. Alternatively, a passive rectifier may be used at the secondary winding output of the isolation transformer 1220 instead of the active switching rectifier 1270 to save cost.

[0115] Fig.13 Another example circuit of a multi-bridge based DC-DC boost converter and battery charging system according to various embodiments of the present disclosure is shown. There are two AC traction motors 1350 and 1351 driven by two inverters 1330, 1331. A single-phase AC power source 1340 is connected across the neutral points of the windings of the two motors 1350 and 1351, and both inverters 1330 and 1331 are used for charging with bidirectional power capability. Since the charging current is balanced between the three-phase motor windings, no significant rotating magnetic force will be generated in the motors 1350 and 1351, and therefore the motor pulsating torque can be ignored. In addition to this, Fig.13 The multi-bridge circuit shown in FIG. 11 operates in substantially the same manner as FIG.

[0116] Fig.14 Another embodiment of a multi-bridge DC-DC boost converter and transformer isolated battery charging system is shown. Fig.14 The difference between the circuit shown in is that two inverters 1430 and 1431 drive an AC traction motor 1450 with dual windings in a conventional Y-type configuration. The single-phase AC power supply is connected to the two neutral points of the dual windings of the motor 1450 through an EMI filter 1460 for charging with bidirectional power capability. Since the charging current is balanced between the windings of the three-phase motor, no significant rotating magnetic force is generated in the motor 1450, and the motor pulsating torque can be ignored. The operation of this circuit is the same as the other circuits described previously.

[0117] Fig.15AAnother example circuit of a multi-bridge based DC-DC boost converter and transformer isolated battery charging system according to various embodiments of the present disclosure is shown. Fig.15A The difference between the circuit shown in is that two inverters 1530 and 1531 drive an AC traction motor 1550 with an open winding configuration. The three-phase AC power supply is connected to the three midpoints of the windings of the motor 1550 through an EMI filter 1560 and an AC contactor switch Q1 for charging with bidirectional power capability. During charging of the battery 1580, both inverters 1530 and 1531 will operate as boost PFC rectifiers and draw evenly distributed current between all three-phase windings of each motor 1550. Due to these balanced currents, the motor windings will not generate any significant rotating magnetic force, and the motor pulsating torque can be ignored. In addition to this, Fig.15A The operation of the multi-bridge circuit in FIG. 11 is the same as that in FIG. 11 .

[0118] Fig. 15B Another embodiment of a multi-bridge DC-DC boost converter is shown where a three-phase or split-phase AC input is connected to the open winding midpoints of a motor 1550 for battery charging. Fig. 15B The difference to the circuit shown in is that the AC contactor switch Q1 is configured with a common neutral point which changes the motor windings to a double wye configuration when enabled. The double wye configuration has the flexibility to run the motor in both 6-phase mode and 3-phase dual winding mode by connecting the common neutral point. The difference is in the relative current phase relationship between the motor windings with respect to space vector control. This has the benefit of reducing the back EMF voltage reflected through the DC bus at high motor speeds of the motor and increasing the motor current capability at lower motor speeds.

[0119] Fig. 15C Another embodiment of a multi-bridge DC-DC boost converter is shown, in which a single-phase AC input is connected to a three-phase motor 1550 at the midpoint of its open winding for battery charging. Note that only the midpoints of two motor windings are connected to the AC input, which is a typical single-phase AC power supply. In this case, the motor needs to have a special type of common two-section winding motor, in which each phase winding basically has two half windings, and two layers of wire overlap in the same slot with the same current direction. Since the midpoint of the coil injects equal current into the two half windings, the induced magnetic force is always balanced and offset. Therefore, the balanced motor winding current does not cause any significant ripple torque or vibration problems during PFC rectification operation.

[0120] Aspects of the present technology can be applied to various motors in various arrangements (e.g., multiple motors in an EV). Some examples are shown here, but it will be understood that these examples are not limiting and the present technology can be applied to more types of motors in more configurations.

[0121] Aspects of the present technology are not limited to any single type of motor and may be used with different motor designs including single winding motors, dual winding motors, and open winding motors, and may be used with any number of motors (same type or different types).

[0122] With respect to this document, it should be noted that the dimensions of the various features depicted in the accompanying drawings may not necessarily be drawn to scale.

[0123] For the purposes of this document, references in the specification to "an embodiment," "one embodiment," "some embodiments," or "another embodiment" may be used to describe different embodiments or the same embodiment.

[0124] For purposes of this document, a connection may be a direct connection or an indirect connection (e.g., via one or more other parts). In some cases, when an element is referred to as being connected or coupled to another element, the element may be directly connected to the other element or indirectly connected to the other element via an intermediate element. When an element is referred to as being directly connected to another element, there are no intermediate elements between the element and the other element. Two devices are "capable of communicating" if they are directly or indirectly connected such that electrical signals can be transmitted between them.

[0125] For purposes of this document, the term "based on" may be read as "based, at least in part, on."

[0126] For the purposes of this document, the use of numerical terms such as a "first" object, a "second" object, and a "third" object without additional context may not imply an order of the objects, but may instead be used for identification purposes to identify different objects.

[0127] Although the present disclosure has been described with reference to the specific features and embodiments of the present disclosure, it is apparent that various modifications and combinations thereof may be made without departing from the scope of the present disclosure. Therefore, the specification and drawings should be simply regarded as an illustration of the present disclosure as defined by the appended claims, and any and all modifications, variations, combinations or equivalents falling within the scope of the present disclosure may be contemplated.

[0128] The foregoing detailed description has been given for purposes of illustration and description. It is not intended to be exhaustive or to limit the subject matter claimed herein to the precise form(s) disclosed. Many modifications and variations are possible in light of the above teachings. The described embodiments are selected in order to best explain the principles of the disclosed technology and its practical application, thereby enabling others skilled in the art to best utilize the technology in the various embodiments, with various modifications suitable for the particular use contemplated. It is intended that the scope be limited by the appended claims.

[0129] Reference Number List

[0130] 110, 210, 310, 410, 510, 520, 610, 611, 612, 710, 711, 712, 810, 811, 812, 910, 911, 912, 1010, 1110, 1210, 1310, 1410, 1510: Multi-bridge

[0131] 111, 112, 211, 212, 311, 312, 411, 412, 413, 1011, 1012: Phase bridge

[0132] 120, 220, 320, 420, 421, 422, 530, 531, 620, 621, 622, 720, 721, 820, 821, 920, 921, 1020, 1120, 1220, 1320, 1420, 1520: Transformer

[0133] 130, 230, 330, 430, 540, 1090: DC bus

[0134] 140, 240, 340, 440, 590, 680, 780, 880, 980, 1080, 1190, 1290, 1380, 1490, 1590: Controller

[0135] 580, 640, 740, 741, 1030, 1130: PFC rectifier

[0136] 1040, 1150, 1230, 1330, 1331, 1430, 1431, 1530, 1531: Inverter

[0137] 660, 760, 860, 960, 961, 1160, 1240, 1350, 1351, 1450, 1550: Motors 550, 551, 630, 631, 730, 731, 830, 831, 930, 931, 1050, 1170, 1270, 1360, 1470, 1570: Power converter, on the secondary side of the transformer

[0138] 570, 670, 770, 870, 970, 1070, 1180, 1280, 1370, 1480, 1580: Batteries, battery management system (BMS)

[0139] 650, 750, 850, 950, 1140, 1250, 1340, 1460, 1560: EMI filters.

Claims

1. A power converter device, comprising: a multi-bridge including two switching bridges connected to a common DC bus and generating a pulse width modulated (PWM) voltage to a non-isolated output; as well as An isolation transformer having a primary winding connected to the output terminals of the two switching bridges and a secondary winding connected to the isolated output terminal, wherein: In the non-isolated mode, the two switch bridges are configured to operate in parallel mode and transfer power between the DC bus and the load at the non-isolated output, and because the two switch bridges operate in parallel, power bypasses the transformer; and In the isolated mode, the two switching bridges are configured to operate in a full-bridge mode and transfer power between the DC bus and a load at the isolated output through the transformer.

2. The power converter arrangement according to claim 1 , further comprising a controller that operates the two switching bridges according to at least two different operating modes: In the non-isolated mode, the two switch bridges are controlled by phase-synchronized PWM gate switching signals; and In the isolation mode, the two switching bridges are controlled by phase-shifted PWM gate switching signals.

3. The power converter device according to claim 1 , further comprising at least one transformer disconnect switch connected in series with the isolation transformer winding on the primary side or the secondary side and operated according to at least two different operating modes: In the non-isolated mode, the transformer disconnect switch remains open and the two switch bridges operate in an interleaved parallel mode, wherein: PWM gate switching signals are synchronized between the two bridges and staggered at a phase shift angle to increase the effective PWM switching frequency at the non-isolated output; and In the isolation mode, the transformer disconnect switch remains turned on and the two switch bridges operate in full-bridge mode.

4. A power converter device according to claim 1, wherein the two switching bridges of the converter use a two-level, three-level, five-level or any other multi-level converter topology, including a diode neutral point clamped (NPC) multi-level converter, an active NPC (ANPC) multi-level converter, a floating capacitor multi-level converter, or a combination of any different multi-level topologies used between the two switching bridges.

5. The power converter device according to claim 1, wherein: The multi-bridge includes three, four or any greater number of switching bridges connected to multiple separate isolation transformers, or to the same isolation transformer with multiple windings coupled together, or to a mix of different transformer configurations.

6. The power converter device according to claim 1, further configured as a non-isolated PWM inverter integrated with an isolated battery charging system, and comprising: having a battery connected to the DC bus via a main contactor or switch; Two or more pairs of multi-bridges, each pair of multi-bridges is connected to the common DC bus via two switching bridges to form a DC-AC inverter and generate a PWM voltage to a non-isolated output terminal; One or more isolation transformers having a primary winding connected to the non-isolated outputs of two or more pairs of multi-bridges and having a secondary winding connected to any type of power converter to charge the battery, wherein: In the non-isolated mode, the main contactor is turned on, inverter operation is performed, power is transferred from the battery to the DC bus through the main contactor, and power bypasses the isolation transformer; In the isolation mode, the main contactor is opened, a battery charging operation is performed, and power is transferred from the DC bus to the battery through the isolation transformer.

7. The power converter device according to claim 6, wherein: The non-isolated output terminals of the two or more pairs of multi-bridges provide power to drive an AC motor having two or more sets of mutually independent motor windings, and wherein, during battery charging operation in the isolated mode, further PWM gate switching synchronization is applied between the switching bridges connected to the terminals of the same set of motor windings, so that each set of motor windings is excited by an almost effectively zero differential voltage across the motor terminals to reduce any useless motor circulating current.

8. The power converter device according to claim 6, wherein: The two or more pairs of multi-bridges partially or fully function as AC-DC rectifiers during battery charging operations, wherein the switching bridges of the two or more pairs of multi-bridges operate in reverse power direction to draw power from an AC power source.

9. The power converter device according to claim 1, further configured as a non-isolated DC boost converter integrated with an isolated battery charging system, and comprising: one or more pairs of multi-bridges, each pair of multi-bridges having two switching bridges, connected to a common DC bus to form a DC-DC boost converter, the non-isolated output of which is connected to a battery via a main contactor switch and one or more inductors; as well as at least one isolation transformer having a primary winding connected to the non-isolated output terminals of one or more pairs of multi-bridges, and a secondary winding connected to the isolated output terminals, wherein the isolated output terminals are coupled to a power converter to charge the battery; wherein: In the non-isolated mode, the main contactor is turned on, a DC boost operation is performed, power is transferred from the battery to the DC bus through the main contactor, and power bypasses the isolation transformer; and In the isolation mode, the battery main contactor is opened, a battery charging operation is performed, and power is transferred from the DC bus to the battery through the isolation transformer.

10. The device according to claim 9, wherein: The apparatus also includes a PWM inverter connected to the DC bus to drive the AC motor, wherein during a battery charging operation, the PWM inverter operates in reverse power flow for the AC-DC rectifier to draw power from the AC power source.

11. A method for designing a power converter, comprising: forming a multi-bridge using two switching bridges, both of which are connected to a common DC bus and generate a pulse width modulated (PWM) voltage to a non-isolated output terminal; An isolation transformer is arranged, which has a primary winding connected to the output terminals of the two switching bridges, and has a secondary winding connected to the isolated output terminal, wherein: In a non-isolated mode, the two switching bridges operate in a parallel mode to transfer power between the DC bus and a load coupled to the non-isolated output terminal, and due to the parallel operation of the two switching bridges, power bypasses the transformer; and In isolation mode, the two switching bridges operate in full-bridge mode to transfer power between the DC bus and the load at the isolated output through the transformer.

12. The method according to claim 11, further comprising designing a controller to operate the two switch bridges according to at least two different operating modes: In the non-isolated mode, the two switch bridges are operated using phase-synchronized PWM gate switching signals; and In the isolation mode, the two switching bridges are operated using phase-shifted PWM gate switching signals.

13. The method according to claim 11, further comprising: At least one transformer disconnect switch is connected in series with the isolating transformer winding on the primary side or the secondary side, wherein: In the non-isolated mode, the transformer disconnect switch is kept open and the two switch bridges are operated in an interleaved parallel mode, wherein the PWM gate switching signals are synchronized and interleaved at a phase shift angle, thereby increasing the effective PWM switching frequency of the non-isolated output terminal; and In the isolation mode, the transformer disconnect switch is kept turned on, the two switch bridges are operated in full-bridge mode, and the PWM gate switch signals are phase-shifted between the two bridges to be out of phase.

14. An electric vehicle, comprising: A multi-bridge power converter comprising one or more multi-bridge power converter devices according to claim 1; A battery connected to the isolated output of the multi-bridge power converter, wherein the battery is connectable to the DC bus through a main contactor during the non-isolated mode.

15. The electric vehicle according to claim 14, wherein: Inverter operation is performed in the non-isolated mode, the non-isolated output terminal of the multi-bridge power converter provides power to drive an AC motor having two or more sets of independent motor windings; and, during battery charging operation in the isolated mode, further PWM gate switching synchronization is applied between the switching bridges of the multi-bridge power converter connected to the same set of motor windings, so that each set of motor windings is excited by a differential voltage of almost effectively zero across the motor terminals to reduce any useless motor circulating current.

16. An electric vehicle, comprising: a multi-bridge power converter including two switching bridges connected to a common DC bus and generating a pulse width modulated (PWM) voltage to a non-isolated output terminal to form a DC-DC boost converter, the non-isolated output terminal being connected to a battery through a main contactor and one or more inductors; as well as an isolation transformer having a primary winding connected to the non-isolated output terminals of the two switching bridges and a secondary winding connected to an isolated output terminal, wherein the isolated output terminal is coupled to a power converter to charge the battery, wherein: During DC boost operation in non-isolated mode, the main contactor is turned on and the two switch bridges are configured to operate in a parallel mode, wherein power is transferred from the battery to the DC bus through the main contactor and power bypasses the isolation transformer due to the parallel operation of the two switch bridges; and During battery charging operation in isolation mode, the main contactor is opened, configuring the two switch bridges to operate in full-bridge mode, wherein power is transferred from the DC bus through the isolation transformer to the battery.

17. The electric vehicle according to claim 16, further comprising a controller, the controller operating the two switch bridges according to at least two different operation modes: In the non-isolated mode, the two switch bridges are controlled by phase-synchronized PWM gate switch signals; In the isolation mode, the two switching bridges are controlled by phase-shifted PWM gate switching signals.

18. The electric vehicle according to claim 16, further comprising at least one disconnect switch connected in series with the isolation transformer winding on the primary side or the secondary side and operated according to at least two different operation modes: In the non-isolated mode, the transformer disconnect switch remains open and the two switch bridges are controlled in an interleaved parallel mode, wherein: PWM gate switching signals are synchronized and staggered with a phase shift angle to increase the effective PWM switching frequency at the non-isolated output; and In the isolation mode, the transformer disconnect switch remains closed and the two switch bridges are controlled in full-bridge mode.

19. The electric vehicle according to claim 16, wherein: The inductor is partially or fully integrated into the isolation transformer design, and the battery is connected to the midpoint of the primary winding of the isolation transformer through the main contactor.

20. The electric vehicle according to claim 16, wherein: The two switch bridges of the multi-bridge power converter use two-level, three-level, five-level or any other multi-level converter topology, including a diode neutral point clamped (NPC) multi-level converter, an active NPC (ANPC) multi-level converter, a floating capacitor multi-level converter, or a combination of any different multi-level topologies; Wherein, the multi-bridge power converter includes three, four or any greater number of switching bridges, which are connected to multiple separate isolation transformers, or to the same isolation transformer with multiple windings coupled together, or to a mixture of different transformer configurations.

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