Power conversion system and method of controlling the same

Abstract

The application discloses a power conversion system and a control method thereof, and relates to the technical field of power electronics. The power conversion system comprises a first DC bus, a second DC bus, a multi-stage power converter and a controller. The multi-stage power converter comprises at least a front-stage power conversion unit and a rear-stage power conversion unit. The DC end of the front-stage power conversion unit is connected with the first DC bus, and the DC end of the rear-stage power conversion unit is connected with the second DC bus. The controller determines an actual conversion ratio according to a first electric parameter of the first DC bus and a second electric parameter of the second DC bus, and performs cooperative control on the front-stage power conversion unit and the rear-stage power conversion unit according to the actual conversion ratio and a target conversion ratio, so that the actual conversion ratio follows the target conversion ratio. Therefore, when the electric parameter of any DC bus changes, the other DC bus can be adjusted correspondingly, so that the deviation between the actual conversion ratio and the target conversion ratio is reduced, and the conversion efficiency of the power conversion system is improved.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power conversion system and its control method. Background Technology

[0002] Multi-stage power converters are widely used in various energy conversion scenarios, such as energy storage systems, distributed generation, and residential power supply, due to their advantages such as electrical isolation, flexible voltage matching, and scalable power levels. Taking a two-stage architecture as an example, the front-stage power converter isolates and transforms the voltage of one DC bus before transmitting it to the other DC bus, and the rear-stage power converter completes the corresponding power conversion according to application requirements. With the continuous expansion of the DC bus voltage range requirements for applications such as photovoltaic access and grid connection, the voltage transformation ratio of the front-stage power converter is increasing (e.g., from 35~55V on the low-voltage side to 380~420V on the high-voltage side, the transformation ratio can reach 8~12 times), which places higher demands on the efficiency and reliability of the system.

[0003] Therefore, related technologies typically employ soft-switching techniques (such as LLC resonant circuits and zero-voltage switching / zero-current switching in DAB (Dual Active Bridge) systems) to reduce switching losses, enabling two-stage power converters to maintain high conversion efficiency over a wide voltage range. However, the efficiency advantage of soft-switching technology is highly dependent on the degree of matching between the actual voltage ratio and the design target ratio. If the actual ratio deviates too much from the set value, conduction and turn-off losses will increase significantly, leading to a decrease in the overall system conversion efficiency. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art. Therefore, the purpose of this application is to propose a power conversion system and its control method, which performs closed-loop control of a multi-stage power converter based on the electrical parameters of different DC buses, enabling the actual turns ratio of the multi-stage power converter to follow the target turns ratio, thereby reducing power losses caused by changes in bus electrical parameters and turns ratio deviations.

[0005] To achieve the above objectives, a first aspect of this application provides a power conversion system, comprising a first DC bus, a second DC bus, a multi-stage power converter, and a controller. The multi-stage power converter includes at least a front-stage power conversion unit and a rear-stage power conversion unit. The DC terminal of the front-stage power conversion unit is connected to the first DC bus, and the DC terminal of the rear-stage power conversion unit is connected to the second DC bus. The controller is used to determine an actual turns ratio based on a first electrical parameter of the first DC bus and a second electrical parameter of the second DC bus, and to perform coordinated control of the front-stage power conversion unit and the rear-stage power conversion unit based on the actual turns ratio and a target turns ratio, so that the actual turns ratio follows the target turns ratio.

[0006] In some embodiments, the multi-stage power converter is connected between the first DC bus and the second DC bus.

[0007] In some embodiments, the front-end power conversion unit includes a first H-bridge, and the rear-end power conversion unit includes a second H-bridge, wherein at least one of the first H-bridge and the second H-bridge is composed of switching transistors; the controller is specifically configured to: when the second H-bridge is composed of diodes and the first H-bridge is composed of switching transistors, the controller can adjust the switching frequency or phase shift angle of the switching transistors in the first H-bridge to adjust the actual turns ratio and put the second H-bridge into a rectification state or perform a protection action; when the first H-bridge is composed of diodes and the second H-bridge is composed of switching transistors, the controller can adjust the switching frequency or phase shift angle of the switching transistors in the second H-bridge to adjust the actual turns ratio and put the first H-bridge into a rectification state or perform a protection action; when both the first H-bridge and the second H-bridge are composed of switching transistors, the controller can adjust the switching frequency or phase shift angle of the switching transistors in the first H-bridge, and / or adjust the switching frequency or phase shift angle of the switching transistors in the second H-bridge to adjust the actual turns ratio.

[0008] In some embodiments, the power conversion system further includes at least one of a first bus capacitor and a second bus capacitor. The first bus capacitor is connected between the positive and negative terminals of the first DC bus, and the second bus capacitor is connected between the positive and negative terminals of the second DC bus.

[0009] In some embodiments, the multi-stage power converter is a two-stage power converter. The two-stage power converter further includes an isolation transformer connected between the AC terminal of the preceding power conversion unit and the AC terminal of the following power conversion unit.

[0010] To achieve the above objectives, a second aspect of this application provides a control method for a power conversion system, used in the power conversion system described in the first aspect of this application. The control method includes: acquiring first electrical parameters of a first DC bus and second electrical parameters of a second DC bus in the power conversion system; determining an actual turns ratio based on the first and second electrical parameters; and performing coordinated control on the front-stage power conversion unit and the rear-stage power conversion unit based on the deviation between the actual turns ratio and a target turns ratio, so that the actual turns ratio follows the target turns ratio.

[0011] In some embodiments, the first electrical parameter includes a first voltage, and the second electrical parameter includes a second voltage. Determining the actual turns ratio based on the first electrical parameter and the second electrical parameter includes: using the ratio between the first voltage and the second voltage as the actual turns ratio.

[0012] In some embodiments, the first electrical parameter includes a first current, and the second electrical parameter includes a second current. Determining the actual turns ratio based on the first electrical parameter and the second electrical parameter includes: using the ratio between the first current and the second current as the actual turns ratio.

[0013] In some embodiments, the front-end power conversion unit includes a first H-bridge, and the rear-end power conversion unit includes a second H-bridge, wherein at least one of the first H-bridge and the second H-bridge is composed of switching transistors; the coordinated control of the front-end power conversion unit and the rear-end power conversion unit according to the actual turns ratio and the target turns ratio includes: when the second H-bridge is composed of diodes and the first H-bridge is composed of switching transistors, adjusting the switching frequency or phase shift angle of the switching transistors in the first H-bridge to adjust the actual turns ratio, and controlling the second H-bridge to be in rectification mode or to perform protection action; when the first H-bridge is composed of diodes and the second H-bridge is composed of switching transistors, adjusting the switching frequency or phase shift angle of the switching transistors in the second H-bridge to adjust the actual turns ratio, and controlling the first H-bridge to be in rectification mode or to perform protection action; when both the first H-bridge and the second H-bridge are composed of switching transistors, adjusting the switching frequency or phase shift angle of the switching transistors in the first H-bridge, and / or adjusting the switching frequency or phase shift angle of the switching transistors in the second H-bridge to adjust the actual turns ratio.

[0014] In some embodiments, the control method further includes: determining the target ratio in response to a received user-defined instruction.

[0015] According to the power conversion system and control method of this application, the actual turns ratio of the multi-stage power converter is determined based on the first electrical parameters of the first DC bus and the second electrical parameters of the second DC bus. Based on the actual turns ratio and the target turns ratio, the front-stage power conversion unit and the rear-stage power conversion unit are coordinated and controlled to ensure that the actual turns ratio follows the target turns ratio. Therefore, when the first or second DC bus changes due to external disturbances or control commands, the controller can promptly adjust the operating states of the front-stage and rear-stage power conversion units, causing corresponding changes in the electrical parameters of the other DC bus, or causing coordinated changes in the electrical parameters of the two DC buses. This reduces the deviation between the actual turns ratio and the target turns ratio, maintaining the multi-stage power converter within a high-efficiency turns ratio range. Consequently, the conduction and switching losses of the power switching devices can be reduced, device heating and thermal stress can be reduced, and the probability of triggering overcurrent or overvoltage protection due to bus electrical parameter mismatch can be reduced, improving the conversion efficiency, dynamic response capability, operational stability, and reliability of the power conversion system.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] Figure 1 This is a structural block diagram of a power conversion system according to an embodiment of this application; Figure 2 This is a structural block diagram of a power conversion system according to a specific embodiment of this application; Figure 3 This is a control block diagram of the bus control process according to an embodiment of this application; Figure 4 This is a schematic diagram of the circuit structure of an LLC resonant converter according to an embodiment of this application; Figure 5 This is a schematic diagram of the circuit structure of a PSFB phase-shifted full-bridge converter according to an embodiment of this application; Figure 6 This is a schematic diagram of the circuit structure of a CLLC resonant converter according to an embodiment of this application; Figure 7 This is a schematic diagram of the circuit structure of a DAB dual active bridge converter according to an embodiment of this application. Detailed Implementation

[0018] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0019] The power conversion system and its control method according to embodiments of this application are described below with reference to the accompanying drawings.

[0020] Figure 1 This is a structural block diagram of a power conversion system according to an embodiment of this application.

[0021] In some embodiments, such as Figure 1 As shown, the power conversion system 1000 includes a first DC bus, a second DC bus, a multi-stage power converter 100, and a controller 200. The voltage of the first DC bus is denoted as Ui, and the voltage of the second DC bus is denoted as Uo. The multi-stage power converter 100 includes at least a front-stage power conversion unit 110 and a rear-stage power conversion unit 120. The DC terminal of the front-stage power conversion unit 110 is connected to the first DC bus, and the DC terminal of the rear-stage power conversion unit 120 is connected to the second DC bus.

[0022] The controller 200 is connected to the first DC bus, the second DC bus, the front-stage power conversion unit 110, and the rear-stage power conversion unit 120, respectively. The controller 200 acquires the first electrical parameters of the first DC bus and the second electrical parameters of the second DC bus, determines the actual turns ratio of the multi-stage power converter 100 based on the first and second electrical parameters, and performs coordinated control of the front-stage power conversion unit 110 and the rear-stage power conversion unit 120 based on the actual turns ratio and the target turns ratio, so that the actual turns ratio follows the target turns ratio.

[0023] Specifically, the controller 200 can coordinate the control of the front-end power conversion unit 110 and the back-end power conversion unit 120 based on the deviation between the actual ratio and the target ratio, so that the actual ratio follows the target ratio.

[0024] The deviation between the actual turns ratio and the target turns ratio can refer to the difference between the actual turns ratio and the target turns ratio, or it can refer to the proportional deviation between the actual turns ratio and the target turns ratio. For example, the deviation can also include the direction of deviation of the actual turns ratio relative to the target turns ratio, that is, whether the actual turns ratio is higher or lower than the target turns ratio, so that the controller 200 can determine the corresponding cooperative control strategy based on the direction of deviation.

[0025] The first DC bus and the second DC bus are used to transmit and distribute DC power, respectively, and they can have different rated voltages. For example, one of the first DC bus and the second DC bus can be a low-voltage DC bus, and the other can be a high-voltage DC bus.

[0026] In some embodiments, the multi-stage power converter 100 can be connected between a first DC bus and a second DC bus for voltage conversion and power transmission between the two DC buses. The terms "front stage" and "rear stage" used in this application are primarily used to distinguish power conversion units at different locations or with different functions within the multi-stage power converter 100, and do not limit the unidirectional transmission of electrical energy from the front-stage power conversion unit 110 to the rear-stage power conversion unit 120.

[0027] In other embodiments, at least one of the first DC bus and the second DC bus is an intermediate bus of the multi-stage power converter 100, that is, the multi-stage power converter 100 can be applied to a three-stage or more-stage power conversion architecture.

[0028] In this system, at least one of the front-end power conversion unit 110 and the rear-end power conversion unit 120 can be cascaded with additional power conversion units to form a multi-stage cascaded power conversion link, meeting the application requirements of higher voltage ratios or multi-port energy interaction. For example, in an energy storage system scenario, the front-end power conversion unit 110 is a DC / AC conversion unit, and the rear-end power conversion unit 120 is an AC / DC conversion unit. The multi-stage power converter 100 may also include additional DC / DC conversion units. The DC terminal of the front-end power conversion unit 110 is connected to the battery side sequentially through a first DC-DC bus and the DC / DC conversion unit, and the DC terminal of the rear-end power conversion unit 120 is connected to the load side through a second DC bus.

[0029] In some embodiments, the multi-stage power converter 100 is a two-stage power converter and further includes an isolation transformer 130. The isolation transformer 130 is connected between the AC terminal of the preceding power conversion unit 110 and the AC terminal of the following power conversion unit 120, for providing electrical isolation between the first DC bus and the second DC bus, and for achieving voltage matching through the winding turns ratio.

[0030] In some embodiments, a first bus capacitor Cin can be connected between the positive and negative terminals of the first DC bus. The first bus capacitor Cin is used to stabilize the voltage of the first DC bus and reduce voltage ripple. A second bus capacitor Co can be connected between the positive and negative terminals of the second DC bus. The second bus capacitor Co is used to stabilize the voltage of the second DC bus and reduce voltage ripple. The first bus capacitor Cin and the second bus capacitor Co can be provided simultaneously, or only one of them can be provided.

[0031] Figure 2 This is a structural block diagram of a power conversion system according to a specific embodiment of this application.

[0032] In a specific embodiment, such as Figure 2As shown, the photovoltaic panel is connected to the low-voltage DC bus via a DC-DC converter, and the battery is connected to the low-voltage DC bus via another DC-DC converter, so as to realize the collection of photovoltaic energy and battery energy at the low-voltage DC bus. Then, the power on the low-voltage DC bus is converted and transmitted to the high-voltage DC bus via a multi-stage power converter 100. Finally, the DC power on the high-voltage DC bus is converted to AC power and transmitted to the grid via an inverter connected between the high-voltage DC bus and the grid.

[0033] Figure 3 This is a control block diagram of the bus control process according to an embodiment of this application.

[0034] like Figure 3 As shown, the controller 200 can use the first electrical parameter and the second electrical parameter as inputs to the bus control controller, and determine the actual transformation ratio based on the first electrical parameter and the second electrical parameter. Specifically, the bus control controller can compare the actual transformation ratio with the target transformation ratio, and determine the desired electrical parameters corresponding to the first DC bus and the second DC bus based on the comparison result, thereby generating a first control command for controlling the front-end power conversion unit 110 and a second control command for controlling the rear-end power conversion unit 120.

[0035] The actual turns ratio is used to characterize the correspondence of electrical parameters between the first DC bus and the second DC bus. Specifically, it can be the voltage turns ratio or the current turns ratio. Taking voltage as an example, when the first electrical parameter includes the first voltage and the second electrical parameter includes the second voltage, the controller 200 can use the ratio between the first voltage and the second voltage as the actual turns ratio.

[0036] The target turns ratio can be predetermined based on the circuit parameters of the multi-stage power converter 100, the winding turns ratio of the isolation transformer 130, the soft-switching operating range, or the target efficiency range. The target turns ratio can be a fixed value or a dynamic value that changes according to power, load, or operating mode. The controller 200 can also determine the target turns ratio in response to a received user-defined instruction, which may include the allowable range or rate of change of the target turns ratio.

[0037] In some embodiments, the front-end power conversion unit 110 includes a first H-bridge, and the rear-end power conversion unit 120 includes a second H-bridge, wherein at least one of the first H-bridge and the second H-bridge is composed of switching transistors. The controller 200 can adjust the switching frequency or phase shift angle of the corresponding H-bridge according to the device configuration of the first H-bridge and the second H-bridge. Depending on the power transmission direction, soft-switching requirements, dynamic response requirements, and cost requirements, the multi-stage power converter 100 can adopt different specific topologies.

[0038] For example, such as Figure 4As shown, the multi-stage power converter 100 can adopt an LLC resonant topology. The first H-bridge consists of switching transistors S1 to S4, with its AC side connected to a resonant inductor Lr and a resonant capacitor Cr. The resonant inductor Lr, the resonant capacitor Cr, and the magnetizing inductance of the isolation transformer 130 together form an LLC resonant network. The second H-bridge consists of four diodes and is used as a full-bridge rectifier circuit. The controller 200 can adjust the voltage gain of the LLC resonant topology by adjusting the switching frequency of the switching transistors in the first H-bridge, thereby adjusting the actual turns ratio. By reasonably setting the resonant parameters and switching frequency, the switching transistors in the first H-bridge can achieve zero-voltage turn-on, and the diodes in the second H-bridge can achieve zero-current turn-off, which is beneficial to reducing switching losses and improving power conversion efficiency.

[0039] For example, such as Figure 5 As shown, the multi-stage power converter 100 can adopt a PSFB phase-shifted full-bridge topology. The first H-bridge consists of switching transistors S1 to S4, and the second H-bridge consists of four diodes. A series inductor Lr is connected between the first H-bridge and the isolation transformer 130. The DC side of the second H-bridge is connected to the output filter inductor L and the second bus capacitor Co. The controller 200 can adjust the conduction phase shift angle between the two sets of bridge arms in the first H-bridge to change the transmitted power and the actual turns ratio while keeping the switching frequency basically constant. This topology can utilize the series inductor Lr, the leakage inductance of the isolation transformer 130, and the energy stored in the output filter inductor L to enable at least some of the switching transistors to achieve zero-voltage turn-on, thereby reducing switching losses. At the same time, fixed-frequency phase-shift control also has the advantages of a relatively mature control method and relatively simple implementation.

[0040] In the aforementioned LLC resonant topology and PSFB phase-shifted full-bridge topology, the first H-bridge consists of switching transistors, and the second H-bridge consists of diodes. The controller 200 mainly adjusts the actual turns ratio by regulating the switching frequency or phase shift angle of the switching transistors in the first H-bridge, while the second H-bridge is in rectification mode or performing protection actions. This type of structure requires a relatively small number of controllable switching transistors and is suitable for applications where unidirectional power transmission is the primary function and cost is a high priority.

[0041] For example, such as Figure 6As shown, the multi-stage power converter 100 can adopt a CLLC resonant topology. The first H-bridge consists of switches S1 to S4, and the second H-bridge consists of switches S5 to S8. The primary and secondary sides of the isolation transformer 130 are respectively equipped with corresponding resonant inductors and resonant capacitors. The controller 200 can adjust the switching frequency or phase shift angle of at least one of the first and second H-bridges to adjust the actual turns ratio and control the power transmission direction. Because resonant networks are set on both sides of the isolation transformer 130, the corresponding switches can achieve zero-voltage turn-on during both forward and reverse power transmission, and the switches operating as rectifiers can achieve zero-current turn-off. This is beneficial for balancing bidirectional conversion efficiency, power density, and electrical isolation performance.

[0042] For example, such as Figure 7 As shown, the multi-stage power converter 100 can adopt a DAB dual active bridge topology. Both the first and second H-bridges are composed of switching transistors, and the two H-bridges are connected through an isolation transformer 130 and a series inductor Lr. The controller 200 can adjust the phase shift angle between the first and second H-bridges at a basically fixed switching frequency to control the power transmission direction, transmitted power, and actual turns ratio. The series inductor Lr can include an independently configured inductor, the leakage inductance of the isolation transformer 130, or a combination of both, and can utilize the energy stored within it to enable the corresponding switching transistor to achieve zero-voltage switching. This topology features relatively simple control, fast dynamic response, and flexible bidirectional power regulation, making it suitable for applications requiring bidirectional energy transmission, such as the charging and discharging switching of energy storage units.

[0043] When both the first and second H-bridges are composed of switching transistors, the controller 200 can adjust only one H-bridge or both H-bridges simultaneously. For example, in a CLLC resonant topology, adjustment can be primarily achieved through the switching frequency; in a DAB dual active bridge topology, adjustment can be primarily achieved through the phase shift angle between the two H-bridges. Therefore, the turns ratio control strategy of this application can make the actual turns ratio follow the target turns ratio based on the control parameters supported by different topologies.

[0044] When the first H-bridge is composed of diodes and the second H-bridge is composed of switching transistors, the controller 200 can adjust the switching frequency or phase shift angle of the switching transistors in the second H-bridge, and put the first H-bridge into rectification mode or perform protection actions. This structure can be used as an implementation of the aforementioned unidirectional topology in the opposite power transmission direction.

[0045] It should be noted that the above descriptions of the application of LLC resonant topology, PSFB phase-shifted full-bridge topology, CLLC resonant topology, and DAB dual active bridge topology are intended to demonstrate that the turns ratio control strategy of this application can be adapted to different multi-stage power converters, rather than exhaustively classifying multi-stage power converters into four types. The multi-stage power converter 100 can also employ other power conversion topologies that allow adjustment of the actual turns ratio through switching frequency, phase shift angle, duty cycle, or other modulation parameters.

[0046] This application also provides a control method for a power conversion system. This control method can be applied to the power conversion system in any of the above embodiments and can be executed by the controller 200.

[0047] In some embodiments, the control method includes: acquiring first electrical parameters of a first DC bus and second electrical parameters of a second DC bus in a power conversion system; determining an actual turns ratio based on the first and second electrical parameters; and performing coordinated control on a front-end power conversion unit and a back-end power conversion unit based on the actual turns ratio and a target turns ratio, so that the actual turns ratio follows the target turns ratio.

[0048] Specifically, the controller 200 can acquire the first and second electrical parameters in real time or periodically through a corresponding sampling circuit. The actual turns ratio is used to characterize the correspondence between the electrical parameters of the first DC bus and the second DC bus. Therefore, the first electrical parameter may include the first voltage or the first current of the first DC bus, and the second electrical parameter may include the second voltage or the second current of the second DC bus.

[0049] In some embodiments, the first electrical parameter includes a first voltage, and the second electrical parameter includes a second voltage. The controller 200 may use the ratio between the first voltage and the second voltage as the actual turns ratio.

[0050] In other embodiments, the first electrical parameter includes a first current, and the second electrical parameter includes a second current. The controller 200 may use the ratio between the first current and the second current as the actual turns ratio.

[0051] The controller 200 can compare the actual turns ratio with the target turns ratio and determine the turns ratio adjustment direction and adjustment amount based on the deviation between the two. Specifically, the controller 200 can generate a first control command and a second control command based on the turns ratio adjustment direction and adjustment amount, and control the front-end power conversion unit 110 according to the first control command and control the rear-end power conversion unit 120 according to the second control command.

[0052] The first and second control commands may include at least one of the following: switching frequency command, phase shift angle command, enable command, rectification status command, or protection command. The controller 200 adjusts at least one of the front-end power conversion unit 110 and the rear-end power conversion unit 120 to match the electrical parameters of the first and second DC buses, thereby gradually bringing the actual turns ratio closer to the target turns ratio.

[0053] When the front-end power conversion unit 110 includes a first H-bridge and the rear-end power conversion unit 120 includes a second H-bridge, the controller 200 can adopt a corresponding control method according to the device configuration of the first H-bridge and the second H-bridge.

[0054] When the second H-bridge is composed of diodes and the first H-bridge is composed of switching transistors, the controller 200 can adjust the switching frequency or phase shift angle of the switching transistors in the first H-bridge to adjust the actual turns ratio and put the second H-bridge into rectification mode or perform protection actions. For example, in Figure 4 In the LLC resonant topology shown, the switching frequency of the first H-bridge can be adjusted; Figure 5 In the PSFB phase-shifted full-bridge topology shown, the phase shift angle between the two arms of the first H bridge can be adjusted.

[0055] When the first H-bridge consists of diodes and the second H-bridge consists of switching transistors, the controller 200 can adjust the switching frequency or phase shift angle of the switching transistors in the second H-bridge to adjust the actual turns ratio and put the first H-bridge into rectification mode or perform protection actions. This control method is applicable to situations where power is mainly transmitted in opposite directions.

[0056] When both the first H-bridge and the second H-bridge are composed of switching transistors, the controller 200 can adjust the switching frequency or phase shift angle of the switching transistors in the first H-bridge, and / or adjust the switching frequency or phase shift angle of the switching transistors in the second H-bridge. For example, in Figure 6 In the CLLC resonant topology shown, the actual turns ratio can be controlled by adjusting the switching frequency; Figure 7 In the DAB dual active bridge topology shown, the actual transformation ratio can be controlled by adjusting the phase shift angle between the first H bridge and the second H bridge.

[0057] When a bus overvoltage, overcurrent, short circuit or other abnormal condition is detected, the controller 200 can also stop outputting drive signals to the H-bridge composed of switching transistors, or control the corresponding power conversion unit to perform protection actions.

[0058] In some embodiments, the controller 200 determines a target ratio in response to a received user-defined instruction. Specifically, the user-defined instruction may include a target value for the target ratio, an allowable range of variation, or a rate of variation. The controller 200 may adjust the target ratio from its current value to a new target value according to a set rate of variation, and during the adjustment process, make the actual ratio follow the dynamically changing target ratio.

[0059] For example, when the high-voltage DC bus is passively raised due to grid fluctuations, the controller 200 recalculates the actual transformation ratio based on the changed high-voltage DC bus voltage and adjusts the switching frequency or phase shift angle of the multi-stage power converter 100 to make the voltage of the low-voltage DC bus change in a matching manner, or adjusts the transmission power between the two DC buses so that the actual transformation ratio is close to the target transformation ratio again.

[0060] For example, when the photovoltaic panel is shaded, causing the voltage of the low-voltage DC bus to drop, the controller 200 can control the voltage of the high-voltage DC bus to make matching changes, or control the voltage of the low-voltage DC bus to recover, thereby reducing the deviation between the actual transformation ratio and the target transformation ratio.

[0061] Therefore, the controller 200 can continuously acquire the first and second electrical parameters and repeatedly execute the actual turns ratio calculation, turns ratio deviation determination, and control command update, thereby forming a turns ratio closed loop. When any DC bus changes due to external disturbances, load changes, grid fluctuations, or control commands, the other DC bus can be adjusted for matching, reducing the conduction and switching losses caused by the actual turns ratio deviating from the target turns ratio, and improving the conversion efficiency and operational stability of the power conversion system.

[0062] In summary, the power conversion system and control method according to the embodiments of this application determine the actual turns ratio of the multi-stage power converter based on the first electrical parameters of the first DC bus and the second electrical parameters of the second DC bus. Based on the deviation between the actual turns ratio and the target turns ratio, the front-stage power conversion unit and the rear-stage power conversion unit are coordinated for control, ensuring that the actual turns ratio follows the target turns ratio. Therefore, when the first or second DC bus changes due to external disturbances or control commands, the controller can promptly adjust the operating states of the front-stage and rear-stage power conversion units, causing corresponding changes in the electrical parameters of the other DC bus, or causing coordinated changes in the electrical parameters of the two DC buses. This reduces the deviation between the actual turns ratio and the target turns ratio, maintaining the multi-stage power converter within a high-efficiency turns ratio range. Consequently, the conduction and switching losses of the power switching devices can be reduced, device heating and thermal stress can be reduced, and the probability of triggering overcurrent or overvoltage protection due to bus electrical parameter mismatch can be decreased, improving the conversion efficiency, dynamic response capability, operational stability, and reliability of the power conversion system.

[0063] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0064] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0065] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A power conversion system, characterized in that, include: First DC bus and second DC bus; A multi-stage power converter includes at least a front-stage power conversion unit and a rear-stage power conversion unit, wherein the DC terminal of the front-stage power conversion unit is connected to the first DC bus, and the DC terminal of the rear-stage power conversion unit is connected to the second DC bus. The controller is configured to determine the actual turns ratio based on the first electrical parameters of the first DC bus and the second electrical parameters of the second DC bus, and to perform coordinated control of the front-end power conversion unit and the back-end power conversion unit based on the actual turns ratio and the target turns ratio, so that the actual turns ratio follows the target turns ratio.

2. The power conversion system according to claim 1, characterized in that, The multi-stage power converter is connected between the first DC bus and the second DC bus.

3. The power conversion system according to claim 1, characterized in that, The front-end power conversion unit includes a first H-bridge, and the rear-end power conversion unit includes a second H-bridge, wherein at least one of the first H-bridge and the second H-bridge is composed of switching transistors; the controller is specifically used for: When the second H-bridge is composed of diodes and the first H-bridge is composed of switching transistors, the switching frequency or phase shift angle of the switching transistors in the first H-bridge is adjusted to adjust the actual turns ratio and control the second H-bridge to be in rectification state or to perform protection action. When the first H-bridge is composed of diodes and the second H-bridge is composed of switching transistors, the switching frequency or phase shift angle of the switching transistors in the second H-bridge is adjusted to adjust the actual turns ratio and control the first H-bridge to be in rectification state or to perform protection action. When both the first H-bridge and the second H-bridge are composed of switching transistors, the actual turns ratio is adjusted by adjusting the switching frequency or phase shift angle of the switching transistors in the first H-bridge, and / or by adjusting the switching frequency or phase shift angle of the switching transistors in the second H-bridge.

4. The power conversion system according to claim 1, characterized in that, Also includes: The first bus capacitor is connected between the positive and negative terminals of the first DC bus; and / or The second bus capacitor is connected between the positive and negative terminals of the second DC bus.

5. The power conversion system according to any one of claims 1-4, characterized in that, The multi-stage power converter is a two-stage power converter. The two-stage power converter also includes an isolation transformer, which is connected between the AC terminal of the preceding power conversion unit and the AC terminal of the following power conversion unit.

6. A control method for a power conversion system, characterized in that, For a power conversion system as described in any one of claims 1-5, the control method comprises: Obtain the first electrical parameters of the first DC bus and the second electrical parameters of the second DC bus in the power conversion system; The actual turns ratio is determined based on the first electrical parameter and the second electrical parameter; Based on the actual turns ratio and the target turns ratio, the front-end power conversion unit and the back-end power conversion unit are coordinated and controlled so that the actual turns ratio follows the target turns ratio.

7. The control method for the power conversion system according to claim 6, characterized in that, The first electrical parameter includes a first voltage, and the second electrical parameter includes a second voltage; determining the actual turns ratio based on the first electrical parameter and the second electrical parameter includes: The ratio between the first voltage and the second voltage is taken as the actual transformation ratio.

8. The control method for the power conversion system according to claim 6, characterized in that, The first electrical parameter includes a first current, and the second electrical parameter includes a second current; determining the actual turns ratio based on the first electrical parameter and the second electrical parameter includes: The ratio between the first current and the second current is taken as the actual transformation ratio.

9. The control method for the power conversion system according to any one of claims 6-8, characterized in that, The front-stage power conversion unit includes a first H-bridge, and the rear-stage power conversion unit includes a second H-bridge, wherein at least one of the first H-bridge and the second H-bridge is composed of switching transistors; the coordinated control of the front-stage power conversion unit and the rear-stage power conversion unit based on the deviation between the actual turns ratio and the target turns ratio includes: When the second H-bridge is composed of diodes and the first H-bridge is composed of switching transistors, the switching frequency or phase shift angle of the switching transistors in the first H-bridge is adjusted to adjust the actual turns ratio and control the second H-bridge to be in rectification state or to perform protection action. When the first H-bridge is composed of diodes and the second H-bridge is composed of switching transistors, the switching frequency or phase shift angle of the switching transistors in the second H-bridge is adjusted to adjust the actual turns ratio and control the first H-bridge to be in rectification state or to perform protection action. When both the first H-bridge and the second H-bridge are composed of switching transistors, the actual turns ratio is adjusted by adjusting the switching frequency or phase shift angle of the switching transistors in the first H-bridge, and / or by adjusting the switching frequency or phase shift angle of the switching transistors in the second H-bridge.

10. The control method for the power conversion system according to any one of claims 6-8, characterized in that, The control method further includes: In response to a received user-defined instruction, the target ratio is determined.

Images