Power conversion apparatus, control method therefor, and electric vehicle charging

Abstract

The embodiment of the invention provides a power conversion device, an electric vehicle charging system and a method for controlling the power conversion device. The power conversion device comprises a first power converter and a second power converter; a resonant converter coupled between the first power converter and the second power converter; and a controller configured to: control the first power converter to convert between the AC voltage or the first DC voltage and the second DC voltage based on voltage information associated with the power conversion device; controlling the resonant converter to operate at a predetermined resonant frequency to convert between a second DC voltage and a third DC voltage; and controlling the second power converter to convert between the third DC voltage and the fourth DC voltage based on the voltage information. According to the scheme, the efficiency of the power conversion device and the charging system can be improved, and the application range and scene are expanded.

Description

Technical Field

[0001] The present disclosure relates to the field of power electronics technology, and more particularly, to a power conversion device, an electric vehicle charging system, and a method for controlling the power conversion device. Background Art

[0002] In order to reduce carbon emissions and alleviate climate issues, new energy vehicles such as electric vehicles have been continuously developed and popularized. Electric vehicles are mainly driven by rechargeable energy storage devices in the vehicle without fossil energy. When the power of the rechargeable energy storage device is insufficient or exhausted, the energy storage device of the vehicle can be charged by a charger or charging system. The charger or charging system converts power from a power source such as a public power grid and provides it to electric vehicles or other types of new energy vehicles.

[0003] There are still many deficiencies in current chargers or charging systems. For example, the input voltage and output voltage range of the charger or charging system is small and the rated power level is low, or the charger or charger has very low efficiency in a large voltage range, which limits the application scope of the charger and charging system. In addition, with the development of technology, in addition to charging vehicles, chargers or charging systems are also expected to provide new functions, such as stabilizing the power grid, and assisting power generation and energy storage. However, current chargers or charging systems usually only transmit power in one direction and have limited input and output voltages, so they cannot meet these new requirements. Summary of the invention

[0004] In order to at least partially solve the above and other possible problems, embodiments of the present disclosure provide a power conversion device, an electric vehicle charging system including the power conversion device, and a method for controlling the power conversion device.

[0005] According to a first aspect of the present disclosure, a power conversion device is provided. The power conversion device includes: a first power converter and a second power converter; a resonant converter coupled between the first power converter and the second power converter, the resonant converter including an isolation transformer; and a controller coupled to the first power converter, the second power converter and the resonant converter, the controller being configured to: control the first power converter to convert between an AC voltage or a first DC voltage and a second DC voltage based on voltage information associated with the power conversion device; control the resonant converter to operate at a predetermined resonant frequency to convert between the second DC voltage and a third DC voltage; and control the second power converter to convert between the third DC voltage and a fourth DC voltage based on the voltage information.

[0006] In some embodiments of the present disclosure, a ratio between the second DC voltage and the third DC voltage is a fixed value and is associated with a transformation ratio of the isolation transformer.

[0007] In some embodiments of the present disclosure, the controller is configured to: when an AC power source is coupled to the first power converter, control the first power converter to perform AC to DC conversion and perform power factor correction for the AC to DC conversion; and when a DC power source is coupled to the first power converter, control the first power converter to perform DC to DC conversion.

[0008] In some embodiments of the present disclosure, the first power converter includes a plurality of first half-bridge branches, and wherein the controller is configured to control the plurality of first half-bridge branches to perform multi-phase interleaved DC to DC conversion when a DC power source is coupled to the first power converter.

[0009] In some embodiments of the present disclosure, the AC power source includes a three-phase AC power source or a single-phase AC power source.

[0010] In some embodiments of the present disclosure, the power conversion device further includes: a switch component coupled to the first power converter and configured to switchably couple the AC power source or the DC power source to the first power converter to provide an AC voltage or a first DC voltage, respectively.

[0011] In some embodiments of the present disclosure, the power switching device further includes: a filter coupled between the AC power source and the first power converter.

[0012] In some embodiments of the present disclosure, the resonant converter includes a first bridge circuit and a first resonant capacitor located on the primary side of an isolation transformer, and a second bridge circuit and a second resonant capacitor located on the secondary side of the isolation transformer, and wherein the controller is configured to: determine a predetermined resonant frequency based on the capacitance of the first resonant capacitor or the second resonant capacitor and the leakage inductance of the isolation transformer, and control the resonant converter to transfer power between the primary side and the secondary side of the isolation transformer at the predetermined resonant frequency.

[0013] In some embodiments of the present disclosure, the first bridge circuit and the second bridge circuit include insulated gate bipolar transistors.

[0014] In some embodiments of the present disclosure, the resonant converter includes a plurality of resonant conversion units connected in parallel with each other, and wherein the controller is configured to control the plurality of resonant conversion units to operate in a multi-phase interleaved manner.

[0015] In some embodiments of the present disclosure, the second power converter includes a plurality of second half-bridge branches, and wherein the controller is configured to control the plurality of second half-bridge branches to perform multi-phase interleaved DC to DC conversion.

[0016] In some embodiments of the present disclosure, the resonant converter includes a bypass switch coupled between the first power converter and the second power converter and configured to couple the first power converter to the second power converter when the bypass switch is turned on.

[0017] According to a second aspect of the present disclosure, an electric vehicle charging system is provided, the electric vehicle charging system comprising: a power conversion device according to the first aspect of the present disclosure; and a charging interface coupled to the power conversion device to output converted electric power.

[0018] According to a third aspect of the present disclosure, a method for controlling a power conversion device is provided, the method comprising: controlling a first power converter of the power conversion device to convert between an AC voltage or a first DC voltage and a second DC voltage based on voltage information associated with the power conversion device; controlling a resonant converter of the power conversion device to operate at a predetermined resonant frequency to convert between a second DC voltage and a third DC voltage, the resonant converter comprising an isolation transformer; and controlling a second power converter of the power conversion device to convert between a third DC voltage and a fourth DC voltage based on the voltage information, the resonant converter being coupled between the first power converter and the second power converter.

[0019] In some embodiments of the present disclosure, the ratio between the second DC voltage and the third DC voltage is a fixed value and is associated with a transformation ratio of the isolation transformer.

[0020] In some embodiments of the present disclosure, controlling a first power converter of a power conversion device to convert between an AC voltage or a first DC voltage and a second DC voltage includes: when an AC power supply is coupled to the first power converter, controlling the first power converter to perform AC-to-DC conversion and performing power factor correction for the AC-to-DC conversion; and when a DC power supply is coupled to the first power converter, controlling the first power converter to perform DC-to-DC conversion.

[0021] In some embodiments of the present disclosure, controlling the first power converter to perform DC to DC conversion includes: controlling a plurality of first half-bridge branches of the first power converter to perform multi-phase interleaved DC to DC conversion when a DC power source is coupled to the first power converter.

[0022] In some embodiments of the present disclosure, controlling a resonant converter of a power conversion device to convert between a second DC voltage and a third DC voltage includes: determining a predetermined resonant frequency based on the capacitance of a first resonant capacitor or a second resonant capacitor of the resonant converter and a leakage inductance of an isolation transformer, the first resonant capacitor being located on the primary side of the isolation transformer, and the second resonant capacitor being located on the secondary side of the isolation transformer; and controlling the resonant converter to transfer power between the primary side and the secondary side of the isolation transformer at the predetermined resonant frequency.

[0023] In some embodiments of the present disclosure, controlling the resonant converter of the power conversion device to convert between the second DC voltage and the third DC voltage also includes: controlling multiple resonant conversion units connected in parallel to operate in a multi-phase interleaved manner, and the resonant converter includes multiple resonant conversion units.

[0024] In some embodiments of the present disclosure, controlling the second power converter of the power conversion device to convert between the third DC voltage and the fourth DC voltage includes: controlling a plurality of second half-bridge branches of the second power converter to perform multi-phase interleaved DC to DC conversion.

[0025] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the disclosure, nor is it intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0027] Figure 1 A schematic diagram of a charging system, a power source, and an electric vehicle according to an embodiment of the present disclosure is shown.

[0028] Figure 2 A schematic block diagram of a power conversion device according to an embodiment of the present disclosure is shown.

[0029] Figure 3 A circuit diagram showing an exemplary implementation of a power conversion device according to an embodiment of the present disclosure is shown.

[0030] Figure 4 A schematic circuit diagram of a power conversion device in AC-DC mode according to an embodiment of the present disclosure is shown.

[0031] Figure 5 A schematic circuit diagram of a power conversion device in a DC-DC mode according to an embodiment of the present disclosure is shown.

[0032] Figure 6 A schematic circuit diagram of a power conversion device in an energy storage mode according to an embodiment of the present disclosure is shown.

[0033] Figure 7 A schematic flow chart of a method for controlling a power conversion device according to an embodiment of the present disclosure is shown.

[0034] Figure 8 A schematic flow chart showing a process of controlling a resonant converter of a power conversion device according to an embodiment of the present disclosure is shown.

[0035] Fig. 9 A schematic diagram comparing voltage and current characteristic curves of an electric vehicle charging system according to an embodiment of the present disclosure and a conventional system is shown.

[0036] Fig.10 A schematic diagram of an efficiency curve of an electric vehicle charging system according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0037] Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. Those skilled in the art can obtain alternative technical solutions from the following description without departing from the spirit and scope of protection of the present disclosure.

[0038] As used herein, the term "including" and its variations mean open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "based at least in part on". The terms "an example embodiment" and "an embodiment" mean "at least one example embodiment". Other explicit and implicit definitions may also be included below.

[0039] Figure 1 Schematic diagram of a charging system 10, a power source 20 and an electric vehicle 30 according to an embodiment of the present disclosure is shown. Figure 1As shown, the charging system 10 is coupled between a power source 20 and at least one electric vehicle 30 to convert power from the power source 20 and output the converted power to the electric vehicle 30. As an example, the power source 20 may be a utility grid, an energy storage battery, a super capacitor, a power generation device (such as a photovoltaic power generation device or a wind power generation device), a power supply device having a power converter connected to other power sources, or any other appropriate type of power source, and the electric vehicle 30 may be a pure electric vehicle, a hybrid vehicle, or any other appropriate type of vehicle having a rechargeable energy storage device.

[0040] According to an embodiment of the present disclosure, the charging system 10 may include a power conversion device 1000 and a charging interface 4000, and the charging interface 4000 is coupled to the power conversion device 1000 to output the converted power. As an example, the charging interface 4000 may be a charging pile with a charging plug, and by means of the charging plug and the charging interface 1000, the power conversion device 1000 is connected to the electric vehicle 30 to be charged. It can be understood that in addition to the charging pile, the charging interface 1000 may also be any other interface device of any appropriate type. In addition, the implementation of the charging system 10 is not limited thereto, but can be implemented in other appropriate ways. For example, the power conversion device 1000 may also be integrated in the charging pile or integrated with the charging interface 4000 in other ways.

[0041] As discussed above, the charging system usually needs to convert the power from the power source and output it to the electric vehicle to be charged. To this end, the power conversion device of the conventional charging system is provided with an LLC circuit to provide an isolation function. However, the LLC circuit can only achieve optimal efficiency in the resonant mode, which limits the voltage gain of the LLC circuit. In addition, the DC power distribution network of the charging system needs to maintain a relatively stable DC bus voltage because the bus voltage needs to be connected to the battery and other power modules, which further limits the voltage gain of the LLC stage of the power conversion device. Conventional charging systems and their power conversion devices are not suitable for large rated power outputs and have limited ranges of input voltages and output voltages.

[0042] Embodiments of the present disclosure provide an improved power conversion device and a control method thereof, and a charging system including the power conversion device. In the improved power conversion device, a three-stage converter including a first power converter, a second power converter and a resonant converter is provided. Through the control of a controller, the first power converter and the second power converter provide a voltage regulation function, and the resonant converter operates in a resonant mode to provide an isolation function. Thus, the resonant converter can operate in a state of highest efficiency at a fixed resonant frequency, and while maintaining high efficiency, the first power converter and the second power converter can greatly expand the range of input voltage and output voltage, so that the power conversion device and the charging system can be applied to more applications and scenarios.

[0043] Figure 2 FIG. 1 shows a schematic block diagram of a power conversion device 1000 according to an embodiment of the present disclosure. Figure 2 As shown, the power conversion device 1000 includes a first power converter 100, a second power converter 200, and a resonant converter 300 coupled between the first power converter 100 and the second power converter 200, and the resonant converter 300 includes an isolation transformer TX1. Just as an example, the first power converter 100 can be a power converter having at least one of rectification, DC boost and power factor correction (PFC) functions, the second power converter 200 can be a power converter having a DC buck function (to adjust the output voltage for extremely low voltage output), and the resonant converter 300 can be a CLLC circuit including an isolation transformer, which can provide an isolation function between a power source and a load and transmit power between the primary side and the secondary side of the isolation transformer at a constant resonant frequency.

[0044] According to an embodiment of the present disclosure, the power conversion device 1000 further includes a controller 400, which is coupled to the first power converter 100, the second power converter 200, and the resonant converter 300. As an example, the controller 100 may send a control signal to the first power converter 100, the second power converter 200, and the resonant converter 300. For example, the controller 100 may control the turning on and off of the power switches in the first power converter 100, the second power converter 200, and the resonant converter 300, so as to achieve the desired power conversion in the power conversion device 1000. It can be understood that the controller 400 may be implemented in a variety of ways, for example, the controller 400 may be implemented in the form of a controller with computing and processing capabilities, in the form of an analog circuit and / or a digital circuit, or in a combination of the above-mentioned multiple forms.

[0045] According to an embodiment of the present disclosure, the controller 400 is configured to control the first power converter 100 to convert between an AC voltage or a first DC voltage and a second DC voltage based on voltage information associated with the power conversion device 1000. As an example, a sensing device for measuring electrical quantities such as voltage and current may be provided in the power conversion device 1000. The controller 400 may obtain voltage information associated with the power conversion device 1000 from these sensing devices. However, the manner of obtaining voltage information associated with the power conversion device 1000 is not limited thereto, but may be other appropriate manners, such as receiving voltage information from an external device, or inputting voltage information by an operator, or a combination of multiple manners. After analyzing and processing the voltage information, the controller 400 may appropriately control the first power converter 100 to convert the AC voltage input from the AC power supply to the first power converter 100 to the second DC voltage, or to convert the first DC voltage input from the DC power supply to the first power converter 100 to the second DC voltage. Thus, the voltage on the power supply side may be regulated, so that it may be applicable to a wider range of power supply voltages or input voltages, such as 500V to 900V.

[0046] According to an embodiment of the present disclosure, the controller 400 controls the resonant converter 300 to operate at a predetermined resonant frequency to convert between the second DC voltage and the third DC voltage. Specifically, the resonant converter 300 is controlled to operate in a resonant mode. That is, the resonant converter 300 transmits power on both sides of the isolation transformer at a resonant frequency inherent to the resonant circuit, which enables the resonant converter 300 to always maintain the best working efficiency. Thus, the resonant converter 300 can maintain a high efficiency while providing an isolation function. In some embodiments of the present disclosure, the ratio between the second DC voltage and the third DC voltage is a fixed value and is associated with the transformation ratio of the isolation transformer. As an example, in the case where the resonant converter 300 includes a CLLC circuit, the overall voltage gain of the CLLC circuit depends on the transformation ratio of the isolation transformer (i.e., the turns ratio of the primary and secondary windings of the isolation transformer) and the circuit voltage gain of the CLLC circuit. The circuit voltage gain of the CLLC circuit in the resonant mode is substantially 1, so the overall voltage gain in the resonant mode is substantially equivalent to the transformation ratio of the isolation transformer and is a fixed value. However, if the CLLC circuit needs to perform voltage regulation according to the input voltage or output voltage, the CLLC circuit will be in a non-resonant mode that requires a higher circuit voltage gain, which will significantly reduce the efficiency of the CLLC circuit. Therefore, by keeping the overall voltage gain of the resonant converter 300 at a fixed value, the resonant converter 300 does not need to provide a voltage regulation function for different input voltages and / or output voltages, which helps the resonant converter 300 always operate in the resonant mode with the best efficiency.

[0047] According to an embodiment of the present disclosure, the controller 400 controls the second power converter 200 to convert between the third DC voltage and the fourth DC voltage based on the aforementioned voltage information. As an example, the second power converter 200 is used to provide a voltage regulation function on the load side to provide a desired voltage to a load such as an energy storage device of an electric vehicle. In this way, it can be applied to a wider range of load voltages or output voltages, such as 200V to 1000V.

[0048] Figure 3 A circuit diagram of an exemplary implementation of a power conversion device 1000 according to an embodiment of the present disclosure is shown. Figure 4 1 shows a schematic circuit diagram of a power conversion device 1000 in AC-DC mode, Figure 5 shows a schematic circuit diagram of a power conversion device 1000 in a DC-DC mode, and Figure 6 1 shows a schematic circuit diagram of a power conversion device 1000 in energy storage mode. As an example, the power conversion device 1000 in AC-DC mode can output power from an AC power source (e.g., a three-phase AC power grid) to a rechargeable energy storage device of an electric vehicle, the power conversion device 1000 in DC-DC mode can output power from a DC power source (e.g., a photovoltaic power generation device, a wind power generation device, or an independent energy storage device) to a rechargeable energy storage device of an electric vehicle, and the power conversion device 1000 in energy storage mode can reversely transmit (i.e., transmit from) a DC power source (e.g., an independent energy storage device, a photovoltaic power generation device, or a wind power generation device) to a rechargeable energy storage device of an electric vehicle. Figure 6 In addition, in the AC-DC mode, the power conversion device 1000 can also perform reverse transmission of electric energy, that is, the electric energy in the electric vehicle can be fed back to the AC grid, which is also called V2G (vehicle to grid) application or function, which helps to improve the stability of the public power grid by utilizing the idle electric energy in the electric vehicle.

[0049] In some embodiments of the present disclosure, the power conversion device 1000 includes a switch assembly 500, which is coupled to the first power converter 100 and is configured to switchably couple an AC power source or a DC power source to the first power converter 100 to provide an AC voltage or a first DC voltage, respectively. As an example, the switch assembly 500 can be any suitable type of switch, including but not limited to an electrical switch, a semiconductor switching device, etc. By turning on and off the switch in the switch assembly 500, different types of power sources can be coupled to the power conversion device 1000 as needed, which increases the applicable scenarios of the power conversion device 1000 and the charging system.

[0050] In some embodiments of the present disclosure, Figure 3 and Figure 4 As shown, when the AC power source is coupled to the first power converter 100, the controller 400 is configured to control the first power converter 100 to perform AC to DC conversion and perform power factor correction for the AC to DC conversion. As an example, by operating the switch component 500, the AC power source can be coupled to the first power converter 100, and the first power converter 100 can rectify and regulate the AC voltage. In addition, the first power converter 100 can perform power factor correction during the rectification and voltage regulation process. Specifically, the controller 400 can control the first power converter 100 so that the voltage at the input of the first power converter 100 can be kept in phase or substantially in phase with the current at the input. Thus, the power conversion device 1000 and the charging system can receive a wide range of AC input voltages, and avoid and alleviate the effects of harmonics and reactive power on the utility grid caused by rectification, thereby improving the power factor of the charging system. In some embodiments, the AC power source includes a three-phase AC power source or a single-phase AC power source. Specifically, by appropriately setting the switch assembly 500, the three-phase or single-phase of the AC power grid can be selectively coupled to the power conversion device 1000. Thus, a more flexible power supply mode and more application scenarios can be provided.

[0051] In some embodiments of the present disclosure, Figure 3 and Figure 5 As shown, when a DC power source is coupled to the first power converter 100, the controller 400 is configured to control the first power converter 100 to perform DC to DC conversion. For example, the first power converter 100 can perform DC to DC boost conversion. Thus, a wide range of DC input voltages can be adjusted.

[0052] In some embodiments of the present disclosure, the first power converter 100 includes a plurality of first half-bridge branches. As an example, the first power converter 100 may include a half-bridge branch consisting of power switching devices Q1 and Q2, a half-bridge branch consisting of power switching devices Q3 and Q4, and a half-bridge branch consisting of power switching devices Q5 and Q6. In addition, the first power converter 100 may also include inductors L1, L2, and L3. Thus, when a three-phase AC power source is coupled to the first power converter 100, a plurality of half-bridge branches consisting of power switching devices Q1 to Q6 may be used as a rectifier to rectify the three-phase AC power into DC power, and further, the inductors L1 to L3 may be used as PFC inductors to implement PFC operation, thereby improving the power factor of the power conversion device 1000. In some embodiments, when a DC power source is coupled to the first power converter 100, the controller 400 is configured to control the plurality of first half-bridge branches to perform multi-phase interleaved DC to DC conversion. As an example, by means of the switch assembly 500, the inductors L1, L2 and L3 respectively connected to each half-bridge branch can be connected to a DC power supply. Thus, a plurality of first half-bridge branches can form a multi-phase boost circuit, and thus the on and off of the power switch devices in each half-bridge branch can be controlled in a multi-phase staggered manner. For example, the on periods of the power switch devices Q1, Q3 and Q5 are staggered from each other. Thus, the ripple caused by the on and off of the switch in the output of the first power converter 100 can be effectively eliminated.

[0053] In some embodiments of the present disclosure, the power conversion device 1000 further includes a filter 600, which is coupled between the AC power source and the first power converter 100. For example, an additional switch may be provided for the filter 600 to couple the filter 600 between the AC power source and the first power converter 100 when the AC power source is coupled to the first power converter 100, and to decouple the filter 600 from the line between the AC power source and the first power converter 100 when the DC power source is coupled to the first power converter 100. By providing the filter 600, harmonics in the line may be effectively filtered out.

[0054] In some embodiments of the present disclosure, the resonant converter 300 includes a first bridge circuit and a first resonant capacitor C5 located on the primary side of the isolation transformer TX1, and a second bridge circuit and a second resonant capacitor C6 located on the secondary side of the isolation transformer TX1. As an example, the first bridge circuit may be composed of power switching devices Q7, Q8, Q9 and Q10, and the second bridge circuit may be composed of power switching devices Q11, Q12, Q13 and Q14. In the AC-DC mode and DC-DC mode in which the AC power supply and the DC power supply charge the load, the first bridge circuit acts as an inverter to generate an alternating current on the primary side of the isolation transformer TX1, and the second bridge circuit acts as a rectifier to rectify the alternating current on the secondary side of the isolation transformer TX1 into a DC current. In the energy storage mode in which the photovoltaic power generation device, the wind power generation device or the independent energy storage device feeds the AC power grid in reverse, or in the AC-DC mode in which the electric vehicle feeds the AC power grid in reverse, since the energy is transmitted in reverse, the first bridge circuit acts as a rectifier, and the second bridge circuit acts as an inverter.

[0055] In some embodiments of the present disclosure, the controller 400 is configured to determine a predetermined resonant frequency based on the capacitance of the first resonant capacitor C5 or the second resonant capacitor C6 and the leakage inductance of the isolation transformer TX1, and control the resonant converter 300 to transmit power between the primary side and the secondary side of the isolation transformer TX1 at a predetermined resonant frequency. Specifically, since the resonant converter 300 only provides an isolation function without a large range of voltage adjustment, the resonant converter 300 can always operate at a fixed resonant frequency. In this case, the additional resonant inductor can be removed, and the leakage inductance of the isolation transformer TX1 is used as the resonant inductor, thereby effectively reducing the number of magnetic components. For example, in AC-DC mode, when electric energy is transmitted from the AC power grid to the vehicle, the resonant frequency of the resonant circuit is determined based on the capacitance of the first resonant capacitor C5 and the leakage inductance of the isolation transformer TX1, and when electric energy is transmitted from the vehicle to the AC power grid in reverse, the resonant frequency of the resonant circuit is determined based on the capacitance of the second resonant capacitor C6 and the leakage inductance of the isolation transformer TX1. In one embodiment, the first bridge circuit and the second bridge circuit in the resonant converter 300 include insulated-gate bipolar transistors (IGBTs). For example, some or all of the power switch devices Q7 to Q14 may be IGBTs. In this way, a resonant conversion circuit such as a CLLC circuit can be simply and reliably maintained at a fixed resonant frequency, and it is easy to optimize magnetic performance and thermal management at a lower cost.

[0056] In some embodiments of the present disclosure, the resonant converter 300 includes a plurality of resonant conversion units connected in parallel with each other. As an example, each resonant unit may have a corresponding isolation transformer TX1, a first bridge circuit, a second bridge circuit, a first resonant capacitor C5, and a second resonant capacitor C6, and the plurality of resonant units are connected in parallel to the DC bus. In some embodiments, the controller 400 is configured to control the plurality of resonant conversion units to operate in a multi-phase interleaved manner. For example, the power switching devices of the plurality of resonant conversion units are turned on and off in a phase-interleaved manner (i.e., the time periods of turning on and off are staggered from each other), thereby effectively reducing the ripple generated by the switching on and off. It will be understood that the number of resonant conversion units can be set as required, and can be any appropriate number, such as 1, 2, 3 or more.

[0057] In some embodiments of the present disclosure, the second power converter 200 includes a plurality of second half-bridge branches. As an example, the second power converter 200 may include a half-bridge branch consisting of power switching devices Q15 and Q16, a half-bridge branch consisting of power switching devices Q17 and Q18, and a half-bridge branch consisting of power switching devices Q19 and Q20. In addition, the first power converter 100 may also include inductors L4, L5 and L6. In some embodiments, the controller 400 is configured to control a plurality of second half-bridge branches to perform multi-phase interleaved DC to DC conversion. As an example, a plurality of second half-bridge branches can form a multi-phase interleaved buck circuit, and therefore the power switching devices of these second half-bridge branches can be turned on and off in a phase-interleaved manner, thereby effectively reducing the ripple generated by the switch on and off.

[0058] In some embodiments of the present disclosure, the resonant converter 300 includes bypass switches K1 and K2, which are coupled between the first power converter 100 and the second power converter 200. As an example, the bypass switches K1 and K2 may be relays or other suitable types of switches. Figure 4 and Figure 5 As shown, in the AC-DC mode and the DC-DC mode, since the AC power supply or the DC power supply needs to charge the electric vehicle, the power conversion device 1000 needs to provide an isolation function. Therefore, the bypass switches K1 and K2 are turned off, and the resonant conversion unit of the resonant converter 300 is not bypassed. Figure 6As shown, in the energy storage mode, the photovoltaic power generation equipment, wind power generation equipment or independent energy storage equipment feeds back to the AC power grid through the power conversion device 1000, so the power conversion device 1000 only needs to provide power conversion function, and no longer needs to provide isolation. In this case, the bypass switches K1 and K2 are turned on, and the first power converter 100 is coupled to the second power converter 200, so that all the resonant conversion units of the resonant converter 300 are bypassed. In this way, the circuit that provides the isolation function can be bypassed in a simple way, thereby improving the overall efficiency of the system.

[0059] In an embodiment of the present disclosure, the resonant converter can operate at a constant resonant frequency with high efficiency, and since the converter always operates at high efficiency, the cooling design of the system can be simplified, thereby reducing costs. In addition, the first power converter and the second power converter in the three-stage converter can adjust the voltage on the input side and the output side, so that the range of applicable input voltage and output voltage can be greatly expanded and the rated power level can be improved. The scheme of the present disclosure can also be applied to various types of power supplies, and bidirectional power transmission can be performed, which is conducive to the realization of V2G applications and enables the power conversion device and the electric vehicle charging system to be competent for various roles, such as stabilizing the power system, and assisting power generation and energy storage. In addition, by setting a bypass switch in the resonant converter, it can be applied to application scenarios that do not require isolation, and the system efficiency can be improved by bypassing the resonant circuit. The scheme of the present disclosure can be implemented with a simple structure and control and a low cost, and the high-voltage electric vehicle charger or charging system can be upgraded with less adjustment, thereby sharing the same printed circuit board.

[0060] Combined with the above Figures 1 to 6 , describes in detail the power conversion device 1000 provided by the present application and the charging system 10 including the power conversion device 1000, and will be combined with Figures 7 and 8 , describing a method for controlling a power conversion device 1000 according to the present disclosure.

[0061] Figure 7 1 is a schematic flow chart of a method 7000 for controlling a power conversion device 1000 according to an embodiment of the present disclosure. The method 7000 may be Figure 1 The charging system 10 is implemented in the embodiment of the present invention and can be implemented by Figure 2 It can be understood that the above Figures 1 to 6 The various aspects described can be applied to method 7000. For the purpose of discussion, Figures 1 to 6 To describe method 7000.

[0062] At block 7001, the controller 400 controls the first power converter 100 of the power conversion device 1000 to convert between an AC voltage or a first DC voltage and a second DC voltage based on voltage information associated with the power conversion device 1000. In some embodiments, when an AC power source is coupled to the first power converter 100, the controller 400 controls the first power converter 100 to perform AC to DC conversion and performs power factor correction for the AC to DC conversion. In some embodiments, when a DC power source is coupled to the first power converter 100, the controller 400 controls the first power converter 100 to perform DC to DC conversion. In some embodiments, when a DC power source is coupled to the first power converter, the controller 400 controls a plurality of first half-bridge branches of the first power converter 100 to perform multi-phase interleaved DC to DC conversion.

[0063] At block 7002, the controller 400 controls the resonant converter 300 of the power conversion device 1000 to operate at a predetermined resonant frequency to convert between the second DC voltage and the third DC voltage, and the resonant converter 300 includes an isolation transformer TX1. In some embodiments, the controller 400 controls a plurality of resonant conversion units connected in parallel to operate in a multi-phase interleaved manner, and the resonant converter 300 includes a plurality of resonant conversion units.

[0064] At block 7003, the controller 400 controls the second power converter 200 of the power conversion device 1000 to convert between the third DC voltage and the fourth DC voltage based on the voltage information, and the resonant converter 300 is coupled between the first power converter 100 and the second power converter 200. In some embodiments, the controller 400 controls the plurality of second half-bridge branches of the second power converter 200 to perform multi-phase interleaved DC to DC conversion.

[0065] Figure 8 FIG. 8 is a schematic flow chart showing a process 8000 of controlling the resonant converter 300 of the power conversion device 1000 according to an embodiment of the present disclosure.

[0066] At box 8001, the controller 400 determines a predetermined resonant frequency based on the capacitance of a first resonant capacitor C5 or a second resonant capacitor C6 of the resonant converter 300 and a leakage inductance of an isolation transformer TX1, the first resonant capacitor C5 being located on the primary side of the isolation transformer TX1, and the second resonant capacitor C6 being located on the secondary side of the isolation transformer TX1.

[0067] At block 8002 , the controller 400 controls the resonant converter 300 to transfer power between the primary side and the secondary side of the isolation transformer TX1 at a predetermined resonant frequency.

[0068] Fig. 9Schematic diagram comparing the voltage-current characteristic curves of the electric vehicle charging system according to the embodiment of the present disclosure and the conventional system is shown. The voltage-current curve A corresponds to the charging system according to the embodiment of the present disclosure, which has a rated power of 45kW. The voltage-current curves B1 and B2 correspond to two conventional systems, which use LLC circuits as the DC to DC conversion stage and have a rated power of 30kW. Fig. 9 As shown, compared with the characteristic curve of a conventional system, the charging system according to the embodiment of the present disclosure can extend the output current range at a low voltage.

[0069] Fig.10 FIG. 2 shows a schematic diagram of an efficiency curve of an electric vehicle charging system according to an embodiment of the present disclosure. Fig.10 As shown in the figure, from a light load of 20% to full load, the efficiency rises to more than 97%, and can continue to increase when better switching devices (such as SiC MOSFET) are used. It can be seen that the solution disclosed in the present invention has extremely high efficiency and great flexibility in function, and can provide an efficient and flexible solution for 50kW vehicle chargers and megawatt-level power stations.

[0070] Those skilled in the art should understand that the various steps of the method disclosed above can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, optionally, they can be implemented with program codes executable by the computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present disclosure is not limited to any specific combination of hardware and software.

[0071] It should be understood that although several devices or sub-devices of the device are mentioned in the detailed description above, this division is only exemplary and not mandatory. In fact, according to an embodiment of the present disclosure, the features and functions of two or more devices described above can be embodied in one device. Conversely, the features and functions of one device described above can be further divided into multiple devices to be embodied.

[0072] The above description is only an optional embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A power conversion device (1000), comprising: A first power converter (100) and a second power converter (200); a resonant converter (300) coupled between the first power converter (100) and the second power converter (200), the resonant converter (300) comprising an isolation transformer (TX1); and A controller (400) is coupled to the first power converter (100), the second power converter (200) and the resonant converter (300), the controller (400) being configured to: Controlling the first power converter (100) to convert between an AC voltage or a first DC voltage and a second DC voltage based on voltage information associated with the power conversion device (1000); controlling the resonant converter (300) to operate at a predetermined resonant frequency to convert between the second DC voltage and the third DC voltage; as well as The second power converter (200) is controlled to convert between a third DC voltage and a fourth DC voltage based on the voltage information.

2. The power conversion device (1000) according to claim 1, wherein a ratio between the second DC voltage and the third DC voltage is a fixed value and is associated with a transformation ratio of the isolation transformer.

3. The power conversion device (1000) according to claim 1, wherein the controller (400) is configured to: When an AC power source is coupled to the first power converter (100), controlling the first power converter (100) to perform AC to DC conversion and to perform power factor correction for the AC to DC conversion; and In a case where a DC power source is coupled to the first power converter (100), the first power converter (100) is controlled to perform DC to DC conversion.

4. The power conversion device (1000) according to claim 3, wherein the first power converter (100) comprises a plurality of first half-bridge branches, and The controller (400) is configured to control the plurality of first half-bridge branches to perform multi-phase interleaved DC to DC conversion when the DC power source is coupled to the first power converter (100).

5. The power conversion device (1000) according to claim 3, wherein the AC power source comprises a three-phase AC power source or a single-phase AC power source.

6. The power conversion device (1000) according to claim 3, further comprising: A switch assembly (500) is coupled to the first power converter (100) and is configured to switchably couple the AC power source or the DC power source to the first power converter (100) to provide the AC voltage or the first DC voltage, respectively.

7. The power switch device (1000) according to claim 3, further comprising: A filter (600) is coupled between the AC power source and the first power converter (100).

8. The power conversion device (1000) according to claim 1, wherein the resonant converter (300) comprises a first bridge circuit and a first resonant capacitor (C5) located on the primary side of the isolation transformer (TX1), and a second bridge circuit and a second resonant capacitor (C6) located on the secondary side of the isolation transformer (TX1), and The controller (400) is configured to determine the predetermined resonant frequency based on the capacitance of the first resonant capacitor (C5) or the second resonant capacitor (C6) and the leakage inductance of the isolation transformer (TX1), and control the resonant converter (300) to transfer power between the primary side and the secondary side of the isolation transformer (TX1) at the predetermined resonant frequency.

9. The power conversion device (1000) according to claim 8, wherein the first bridge circuit and the second bridge circuit include insulated gate bipolar transistors.

10. The power conversion device (1000) according to claim 1, wherein the resonant converter (300) comprises a plurality of resonant conversion units connected in parallel with each other, and The controller (400) is configured to control the plurality of resonance conversion units to operate in a multi-phase interleaved manner.

11. The power conversion device (1000) according to claim 1, wherein the second power converter (200) comprises a plurality of second half-bridge branches, and The controller (400) is configured to control the plurality of second half-bridge branches to perform multi-phase interleaved DC to DC conversion.

12. The power conversion device (1000) according to claim 1, wherein the resonant converter (300) comprises a bypass switch (K1, K2), the bypass switch (K1, K2) being coupled between the first power converter (100) and the second power converter (200), and being configured to couple the first power converter (100) to the second power converter (200) when being turned on.

13. An electric vehicle charging system, comprising: The power conversion device (1000) according to any one of claims 1 to 12; as well as A charging interface (4000) is coupled to the power conversion device to output the converted electric power.

14. A method for controlling a power conversion device (1000), comprising: Controlling a first power converter (100) of the power conversion device (1000) to convert between an AC voltage or a first DC voltage and a second DC voltage based on voltage information associated with the power conversion device (1000); controlling a resonant converter (300) of the power conversion device (1000) to operate at a predetermined resonant frequency to convert between the second DC voltage and the third DC voltage, the resonant converter (300) comprising an isolation transformer (TX1); as well as The second power converter (200) of the power conversion device (1000) is controlled to convert between a third DC voltage and a fourth DC voltage based on the voltage information, and the resonant converter (300) is coupled between the first power converter (100) and the second power converter (200). 15 . The method of claim 14 , wherein a ratio between the second DC voltage and the third DC voltage is a fixed value and is associated with a transformation ratio of the isolation transformer.

16. The method according to claim 14, wherein controlling the first power converter (100) of the power conversion device (1000) to convert between an AC voltage or a first DC voltage and a second DC voltage comprises: When an AC power source is coupled to the first power converter (100), controlling the first power converter (100) to perform AC to DC conversion and to perform power factor correction for the AC to DC conversion; as well as In a case where a DC power source is coupled to the first power converter (100), the first power converter (100) is controlled to perform DC to DC conversion.

17. The method of claim 16, wherein controlling the first power converter (100) to perform DC to DC conversion comprises: When the DC power source is coupled to the first power converter (100), a plurality of first half-bridge branches of the first power converter (100) are controlled to perform multi-phase interleaved DC to DC conversion.

18. The method according to claim 14, wherein controlling the resonant converter (300) of the power conversion device (1000) to convert between the second DC voltage and the third DC voltage comprises: Determining the predetermined resonant frequency based on the capacitance of a first resonant capacitor (C5) or a second resonant capacitor (C6) of the resonant converter (300) and the leakage inductance of the isolation transformer (TX1), the first resonant capacitor (C5) being located on the primary side of the isolation transformer (TX1), and the second resonant capacitor (C6) being located on the secondary side of the isolation transformer (TX1); as well as The resonant converter (300) is controlled to transfer power between the primary side and the secondary side of the isolation transformer (TX1) at the predetermined resonant frequency.

19. The method according to claim 14, wherein controlling the resonant converter (300) of the power conversion device (1000) to convert between the second DC voltage and the third DC voltage further comprises: A plurality of resonance conversion units connected in parallel are controlled to operate in a multi-phase interleaved manner, and the resonance converter (300) comprises the plurality of resonance conversion units.

20. The method according to claim 14, wherein controlling the second power converter (200) of the power conversion device (1000) to convert between the third DC voltage and the fourth DC voltage comprises: The plurality of second half-bridge branches of the second power converter (200) are controlled to perform multi-phase interleaved DC to DC conversion.

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