A power converter, control method, and related devices

Abstract

This application discloses a power converter, a control method, and related devices. The power converter includes a controller and a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. One or two phases of the three-phase power conversion circuit operate in single-phase mode. The AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid. The AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or power grid. The controller controls the power conversion circuit not operating in single-phase mode to allow the fluctuating current of the DC-side capacitor to flow into the AC-side capacitor of the power conversion circuit not operating in single-phase mode. This can avoid damage to DC-side components caused by low-frequency voltage fluctuations on the DC side and reduce the component damage rate.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power converter, control method and related device. Background Technology

[0002] Currently, during the operation of single-phase AC / DC or single-phase DC / AC circuits, low-frequency voltage fluctuations (such as second harmonic fluctuations) naturally occur on the DC side of the circuit. These low-frequency voltage fluctuations may affect components on the DC side (such as batteries, capacitors, etc.) and may even cause damage to the components on the DC side, increasing the damage rate of the components. Summary of the Invention

[0003] To address the aforementioned issues, this application provides a power converter, control method, and related apparatus, aiming to solve the problem of high component failure rates caused by low-frequency voltage fluctuations.

[0004] The embodiments of this application disclose the following technical solutions:

[0005] In a first aspect, embodiments of this application provide a power converter, including: a controller and a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. A DC-side capacitor is connected in parallel between the DC-side positive terminal and the DC-side negative terminal of the three-phase power conversion circuit. An AC-side capacitor is connected between the AC-side and the DC-side negative terminal of the power conversion circuit. One or two phases of the three-phase power conversion circuit operate in single-phase mode. The AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid. The AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or a power grid.

[0006] The controller is used to control the power conversion circuit that is not operating in single-phase mode, so that the fluctuating current of the DC side capacitor flows into the AC side capacitor of the power conversion circuit that is not operating in single-phase mode.

[0007] In conjunction with the first aspect, in some possible implementations, the four-switch Buck-Boost circuit per phase includes: a first switch, a second switch, a third switch, a fourth switch, and an inductor;

[0008] The first and second switching transistors are connected in series to form the first bridge arm. The two ends of the first bridge arm are connected to the positive and negative terminals of the DC-side capacitor, respectively. The third and fourth switching transistors are connected in series to form the second bridge arm. The first end of the inductor is connected to the midpoint of the first bridge arm, and the second end of the inductor is connected to the midpoint of the second bridge arm. The first end of the second bridge arm serves as the output terminal of the power conversion circuit, and the second end of the second bridge arm is connected to the negative terminal of the DC side. The two ends of the AC-side capacitor are connected to the first end of the second bridge arm and the negative terminal of the DC side, respectively.

[0009] In conjunction with the first aspect, in some possible implementations, when two phases of the three-phase power conversion circuit operate in single-phase mode, the controller controls the first and second switches in the power conversion circuit not operating in single-phase mode to operate complementaryly, and controls the third switch in the power conversion circuit not operating in single-phase mode to be normally on and the fourth switch to be normally off; or,

[0010] In the power conversion circuit that is not operating in single-phase mode, the first switch is normally on and the second switch is normally off. The third and fourth switches in the power conversion circuit that is not operating in single-phase mode are complementary switches.

[0011] In conjunction with the first aspect, in some possible implementations, when one phase of the three-phase power conversion circuit operates in single-phase mode, the controller controls the first and second switches in at least one phase of the power conversion circuit not operating in single-phase mode to operate complementaryly, and controls the third switch in the power conversion circuit not operating in single-phase mode to be normally on and the fourth switch to be normally off; or,

[0012] In a power conversion circuit that controls at least one phase not operating in single-phase mode, the first switch is normally on and the second switch is normally off. The third and fourth switches in the power conversion circuit that controls the at least one phase not operating in single-phase mode are complementary switches.

[0013] In conjunction with the first aspect, some possible implementations also include: an AC switching device; the first end of the AC switching device is connected to the first end of the second bridge arm, and the second end of the AC switching device serves as the output end of the power conversion circuit.

[0014] In conjunction with the first aspect, in some possible implementations, the power converter further includes: a first switching device and a second switching device; the first terminal of the first switching device is connected to the positive terminal of the DC-side capacitor, the second terminal of the first switching device is connected to the first terminal of the second switching device, and the second terminal of the second switching device is connected to the first terminal of the AC switching device of any one phase in the three-phase power conversion circuit.

[0015] In conjunction with the first aspect, in some possible implementations, the power converter also includes a third switching device; the first terminal of the third switching device is connected to the second terminal of the first switching device, and the second terminal of the third switching device is connected to the first terminal of the AC switching device of any phase in the three-phase power conversion circuit; wherein the AC switching device connected to the second switching device is different from the AC switching device connected to the third switching device.

[0016] In conjunction with the first aspect, in some possible implementations, before controlling the power conversion circuit that is not operating in single-phase mode, the controller is also used to:

[0017] Controlling the first switching device to close, controlling the second switching device to open, and controlling the AC switching device of any one phase in the three-phase power conversion circuit to close;

[0018] Alternatively, control the first switching device to close, control the second switching device to open, and control the AC switching devices of any two phases in the three-phase power conversion circuit to close.

[0019] Alternatively, the first switching device can be opened, the second switching device can be closed, and either of the two AC switching devices that are not connected to the second switching device can be closed.

[0020] In conjunction with the first aspect, in some possible implementations, before controlling the power conversion circuit that is not operating in single-phase mode, the controller is also used to:

[0021] Control the first switching device to close, control the second and third switching devices to open, and control the AC switching device of any one phase in the three-phase power conversion circuit to close.

[0022] Alternatively, control the first switching device to close, control the second and third switching devices to open, and control the AC switching devices of any two phases in the three-phase power conversion circuit to close.

[0023] Alternatively, control the first switching device to close, control the second or third switching device to close, or control an AC switching device that is not connected to the second or third switching device to close.

[0024] Secondly, embodiments of this application provide a control method for a power converter. The power converter includes a controller and a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. A DC-side capacitor is connected in parallel between the DC-side positive terminal and the DC-side negative terminal of the three-phase power conversion circuit. An AC-side capacitor is connected between the AC-side and the DC-side negative terminal of the power conversion circuit. One or two phases of the three-phase power conversion circuit operate in single-phase mode. The AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid. The AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or a power grid.

[0025] The control method includes:

[0026] Control the power conversion circuit that is not operating in single-phase mode so that the fluctuating current of the DC side capacitor flows into the AC side capacitor of the power conversion circuit that is not operating in single-phase mode.

[0027] In conjunction with the second aspect, in some possible implementations, when two phases of the three-phase power conversion circuit operate in single-phase mode, the first and second switches in the power conversion circuit not operating in single-phase mode are controlled to operate complementaryly, and the third switch in the power conversion circuit not operating in single-phase mode is controlled to be normally on and the fourth switch is controlled to be normally off; or,

[0028] In the power conversion circuit that is not operating in single-phase mode, the first switch is normally on and the second switch is normally off. The third and fourth switches in the power conversion circuit that is not operating in single-phase mode are complementary switches.

[0029] In conjunction with the second aspect, in some possible implementations, when one phase of the three-phase power conversion circuit operates in single-phase mode, the first and second switches in at least one phase of the power conversion circuit not operating in single-phase mode are controlled to operate complementaryly, and the third switch in the power conversion circuit not operating in single-phase mode is controlled to be normally on and the fourth switch is controlled to be normally off; or,

[0030] In a power conversion circuit that controls at least one phase not operating in single-phase mode, the first switch is normally on and the second switch is normally off. The third and fourth switches in the power conversion circuit that controls the at least one phase not operating in single-phase mode are complementary switches.

[0031] In conjunction with the second aspect, some possible implementations also include, before controlling the power conversion circuit that is not operating in single-phase mode:

[0032] Controlling the first switching device to close, controlling the second switching device to open, and controlling the AC switching device of any one phase in the three-phase power conversion circuit to close;

[0033] Alternatively, control the first switching device to close, control the second switching device to open, and control the AC switching devices of any two phases in the three-phase power conversion circuit to close.

[0034] Alternatively, the first switching device can be opened, the second switching device can be closed, and either of the two AC switching devices that are not connected to the second switching device can be closed.

[0035] In conjunction with the second aspect, in some possible implementations, the controller further includes, before controlling the power conversion circuit not operating in single-phase mode:

[0036] Control the first switching device to close, control the second and third switching devices to open, and control the AC switching device of any one phase in the three-phase power conversion circuit to close.

[0037] Alternatively, control the first switching device to close, control the second and third switching devices to open, and control the AC switching devices of any two phases in the three-phase power conversion circuit to close.

[0038] Alternatively, control the first switching device to close, control the second or third switching device to close, or control an AC switching device that is not connected to the second or third switching device to close.

[0039] Thirdly, embodiments of this application provide a control device, including a processor and a memory, wherein the memory is used to store programs, instructions or code, and the processor is used to execute the programs, instructions or code in the memory to perform the control method as described in the second aspect.

[0040] Fourthly, embodiments of this application provide a computer-readable storage medium storing a computer program, which is loaded by a processor to execute the control method as described in the second aspect.

[0041] The power converter provided in this application embodiment can control the power conversion circuit that is not operating in single-phase mode, so that the fluctuating current of the DC-side capacitor flows into the AC-side capacitor of the power conversion circuit that is not operating in single-phase mode. That is, by flowing the fluctuating current of the DC-side capacitor into the AC-side capacitor of the power conversion circuit that is not connected to a load or power grid, damage to DC-side components caused by low-frequency voltage fluctuations on the DC side is avoided, and the component damage rate is reduced. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A schematic diagram of a power converter provided in an embodiment of this application;

[0044] Figure 2 A schematic diagram of another power converter provided in an embodiment of this application;

[0045] Figure 3 A schematic diagram of yet another power converter provided in the embodiments of this application;

[0046] Figure 4 A schematic diagram of a three-phase three-wire system operation is provided for an embodiment of this application;

[0047] Figure 5A schematic diagram of a three-phase four-wire system provided in this application embodiment;

[0048] Figure 6 A schematic diagram illustrating operation in single-phase mode, provided for an embodiment of this application;

[0049] Figure 7a A schematic diagram illustrating another operation in single-phase mode provided for an embodiment of this application;

[0050] Figure 7b A schematic diagram illustrating operation in single-phase mode is provided for the purposes of this application embodiment;

[0051] Figure 8 A schematic diagram illustrating another operation in single-phase mode provided for an embodiment of this application;

[0052] Figure 9 A schematic diagram of another power converter provided in this application embodiment;

[0053] Figure 10 A schematic diagram of another power converter provided in the embodiments of this application;

[0054] Figure 11 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application;

[0055] Figure 12 This is a schematic diagram of another power converter provided in an embodiment of this application;

[0056] Figure 13 A schematic diagram of another power converter provided in this application embodiment;

[0057] Figure 14 A flowchart illustrating a control method for a power converter provided in an embodiment of this application;

[0058] Figure 15a A schematic diagram of current flow direction provided for an embodiment of this application;

[0059] Figure 15b A control timing diagram provided for an embodiment of this application;

[0060] Figure 15c Another control timing diagram provided for an embodiment of this application;

[0061] Figure 15d Another control timing diagram provided for embodiments of this application;

[0062] Figure 16 This is a schematic diagram of the structure of a control device provided in an embodiment of this application. Detailed Implementation

[0063] To enable those skilled in the art to understand and implement the technical solutions provided in the embodiments of this application, the architecture of a possible power converter of this application will be described below with reference to the accompanying drawings.

[0064] See Figure 1 This figure is a schematic diagram of a power converter provided in an embodiment of this application.

[0065] The power converter provided in this application includes a three-phase power conversion circuit. Each phase of the power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. The first terminals of the three-phase four-switch Buck-Boost circuits are connected in parallel to the DC-side capacitor, which is connected in parallel between the positive and negative terminals of the DC source. The second terminals of the three-phase four-switch Buck-Boost circuits are independent and connected to the three AC phases of the power converter respectively. The input voltage of the DC source is represented by Uin. The DC-side capacitor is represented by C. The AC side of the power converter can be connected to the power grid or a load through a grid-connected switch. The power grid is a three-phase grid, namely phase A, phase B, and phase C, and the three-phase voltages of the grid are ua, ub, and uc, respectively. ua, ub, and uc all represent the phase voltages of the grid. Specifically, the first terminal of the grid-connected switch is connected to the second terminal of a filter inductor, and the first terminal of the filter inductor is connected to the output terminal of the Buck-Boost circuit, with the three phases corresponding to the output terminals a, b, and c, respectively.

[0066] The first Buck-Boost circuit (as phase A in the three-phase power conversion circuit) includes a first switch S1, a second switch S2, a first inductor L1, a third switch S3, and a fourth switch S4. S1 and S2 are connected in series to form the first bridge arm, and S3 and S4 are connected in series to form the second bridge arm. The first end of the first inductor L1 is connected to the midpoint of the first bridge arm, and the second end of the first inductor L1 is connected to the midpoint of the second bridge arm. The first end of the second bridge arm serves as the output terminal a of the power conversion circuit, and the second end of the second bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfa are connected to the first end of the second bridge arm and the negative terminal m of the DC source, respectively.

[0067] The second Buck-Boost circuit (as phase B in the three-phase power conversion circuit) includes a fifth switch S5, a sixth switch S6, a second inductor L2, a seventh switch S7, and an eighth switch S8. S5 and S6 are connected in series to form the third bridge arm, and S7 and S8 are connected in series to form the fourth bridge arm. The first end of the second inductor L2 is connected to the midpoint of the third bridge arm, and the second end of the second inductor L2 is connected to the midpoint of the fourth bridge arm. The first end of the fourth bridge arm serves as the output terminal b of the power conversion circuit, and the second end of the fourth bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfb are connected to the first end of the fourth bridge arm and the negative terminal m of the DC source, respectively.

[0068] The third Buck-Boost circuit (as phase C in the three-phase power conversion circuit) includes the ninth switch S9, the tenth switch S10, the third inductor L3, the eleventh switch S11, and the twelfth switch S12. S9 and S10 are connected in series to form the fifth bridge arm, and S11 and S12 are connected in series to form the sixth bridge arm. The first end of the third inductor L3 is connected to the midpoint of the fifth bridge arm, and the second end of the third inductor L3 is connected to the midpoint of the sixth bridge arm. The first end of the sixth bridge arm serves as the output terminal b of the power conversion circuit, and the second end of the sixth bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfc are connected to the first end of the sixth bridge arm and the negative terminal m of the DC source, respectively.

[0069] The three-phase output terminals a, b, and c are connected to the negative terminal m of the DC source via corresponding AC-side capacitors Cfa, Cfb, and Cfc, respectively.

[0070] a, b, and c are connected to the first terminal of their respective AC switching devices via the corresponding filter inductor Lg. The second terminal of the AC switching device is connected to the three-phase power grid. For ease of explanation later, the AC switching device corresponding to a is K11, the AC switching device corresponding to b is K22, and the AC switching device corresponding to c is K33.

[0071] The inventors discovered in their research that the AC ports of power converters can be used in three-phase or single-phase applications. In related technologies, single-phase or three-phase power converters are generally developed according to the application scenarios of the AC ports. However, it is not possible to develop corresponding power converters for AC ports that are used in both single-phase and three-phase applications, which increases costs.

[0072] To address the aforementioned technical problems, a power converter based on the above embodiments is provided (see [reference]). Figure 2 This figure is a schematic diagram of another power converter provided in an embodiment of this application.

[0073] Another power converter provided in this application includes a three-phase power conversion circuit, a first switching device K1 and a second switching device K2. The first terminal of the first switching device K1 is connected to the positive terminal of the DC source, the second terminal of the first switching device K1 is connected to the first terminal of the second switching device K2, the first terminal of the second switching device K2 is connected to the neutral point N, and the second terminal of the second switching device is connected to any one of the output terminals a, b or c.

[0074] It should be noted that when filter inductors are set in a, b, and c respectively, the first terminal of the filter inductor connected to the second switching device can be connected to the corresponding output terminal or to the first terminal of the corresponding AC switching device. Figure 2An exemplary embodiment shows the second terminal of the second switching device K2 connected to the first terminal of the filter inductor corresponding to b, the first terminal of which is connected to b, and the second terminal of which is connected to the first terminal of the AC switching device K22. In another example, combined with... Figure 3 As shown, Figure 3 It is shown that the second terminal of the second switching device K2 is connected to the second terminal of the filter inductor corresponding to b, the first terminal of the filter inductor is connected to b, and the second terminal of the filter inductor is connected to the first terminal of the AC switching device K22.

[0075] by Figure 2 Taking the power converter shown as an example, when the AC port of the power converter is operating in three-phase mode (i.e., a three-phase power consumption scenario):

[0076] When the power converter is connected to the grid, K1 and K2 are both open, and K11, K22, and K33 are all closed, operating in a three-phase three-wire system. Figure 4 As shown.

[0077] When the power converter is off-grid, K1 is closed, K2 is open, and K11, K22, and K33 are all closed, operating in a three-phase four-wire system. Figure 5 As shown.

[0078] When the power converter operates in a three-phase four-wire system, the AC side output voltage Uxm of the power converter can be expressed as follows:

[0079]

[0080] Uxm represents the phase voltage amplitude on the AC side. ω represents phase, ω represents angular frequency, and t represents time.

[0081] by Figure 2 Taking the power converter shown as an example, when the AC port of the power converter is operating in single-phase mode (i.e., single-phase power consumption scenario):

[0082] (1) When K1 is closed and K2 is open, any two AC switching devices among K11, K22, and K33 are closed, operating in single-phase mode, such as... Figure 6 As shown. For example, when K11 and K22 are closed, the power converter is connected to a and b, and the power converter operates in split-phase mode.

[0083] (2) When a voltage is detected at output terminal a, i.e., the single-phase AC connection is at a and N, K2 and K11 are both closed, and K1, K22 and K33 are all open, the power converter operates in single-phase mode, such as Figure 7aAs shown; when voltage is detected at output terminal b, i.e., single-phase AC connection is between b and N, K1, K2, K11, K22, and K33 are all open, and an AC port connection error is reported; when voltage is detected at output terminal c, i.e., single-phase AC connection is between c and N, K2 and K33 are both closed, and K1, K11, and K22 are all open, the power converter operates in single-phase mode, as shown. Figure 7b As shown.

[0084] (3) When K1 is closed, K2 is open, K22 is closed, and K11 and K33 are open, the power converter operates in single-phase mode, such as... Figure 8 As shown.

[0085] Thus, the power converter provided in this application embodiment can switch between single-phase and three-phase modes of the AC port by controlling the closing and opening of K1, K2, K11, K22 and K33, thereby reducing costs and improving compatibility.

[0086] Furthermore, regarding the power converter provided in the above embodiments, see... Figure 9 The figure is a schematic diagram of another power converter provided in an embodiment of this application.

[0087] Another power converter provided in this application includes a three-phase power conversion circuit, a first switching device K1, a second switching device K2, and a third switching device K3. The first terminal of the first switching device K1 is connected to the positive terminal of a DC source. The second terminal of the first switching device K1 is connected to the first terminals of the second switching device K2 and the third switching device K3. The second terminal of the first switching device K1 is connected to the neutral point N through the load Rd. The second terminals of the second switching device K2 and the second terminals of the third switching device K3 are connected to the first terminals of any two corresponding filter inductors among a, b, and c. Figure 9 An example is shown where the first terminal of the filter inductor in a two-phase power conversion circuit is connected to its respective output terminal (b and c), and the second terminal of the filter inductor is connected to the first terminal of its respective AC switching device (K22 and K33). In another example, combined with... Figure 10 As shown, Figure 10 The second end of the filter inductor corresponding to the two-phase power conversion circuit is connected to its respective output terminal (b and c), and the first end of the filter inductor corresponding to the two-phase power conversion circuit is connected to the first end of its respective AC switching device (K22 and K33).

[0088] by Figure 9 Taking the power converter shown as an example, when the AC port of the power converter is operating in three-phase mode (i.e., a three-phase power consumption scenario):

[0089] When the power converter is connected to the grid, K1, K2, and K3 are all open, and K11, K22, and K33 are all closed, operating in a three-phase three-wire system. Figure 4 As shown.

[0090] When the power converter is off-grid, K1 is closed, K2 and K3 are both open, and K11, K22, and K33 are all closed, operating in a three-phase four-wire system. Figure 5 As shown.

[0091] by Figure 9 Taking the power converter shown as an example, when the AC port of the power converter is operating in single-phase mode (i.e., single-phase power consumption scenario):

[0092] (1) When K1 is closed, K2 and K3 are open, and any two phases of the AC switching devices in K11, K22, and K33 are closed, the power converter operates in split-phase mode. For example, if phases A and B are connected, then K11 and K22 are closed, such as... Figure 6 As shown.

[0093] Among them, split-phase mode means that the two-phase power conversion circuits operate in single-phase mode respectively.

[0094] (2) When a voltage is detected at output terminal a, i.e., the single-phase AC connection is between a and N, K2 and K11 are closed (or K3 and K11 are closed), and K1, K3 (or K2), K22 and K33 are all open, the power converter operates in single-phase mode, such as Figure 7a As shown; when a voltage is detected at output terminal b, i.e., the single-phase AC connection is between b and N, K3 and K22 are closed, and K1, K2, K11, and K33 are all open, the power converter operates in single-phase mode; when a voltage is detected at output terminal c, i.e., the single-phase AC connection is between c and N, K2 and K33 are closed, and K1, K3, K11, and K22 are all open, the power converter operates in single-phase mode, as shown. Figure 7b As shown.

[0095] (3) When K1 is closed, K2 and K3 are open, and any one of the AC switching devices in phases K11, K22, and K33 is closed, the power converter operates in single-phase mode. For example, if phase A is connected, then K11 is closed. Figure 8 As shown.

[0096] Thus, the power converter provided in this application embodiment can switch between single-phase and three-phase modes of the AC port by controlling the closing and opening of K1, K2, K3, K11, K22 and K33, thereby reducing costs and improving compatibility.

[0097] Based on the power converter provided in the above embodiments, the inventors further discovered in their research that when the power converter is operating in single-phase mode, since the waveform of the alternating current is a sine wave, it contains fundamental and harmonic components. These harmonic components may cause low-frequency voltage fluctuations (such as second harmonic low-frequency voltage fluctuations) on the DC side. These low-frequency voltage fluctuations may affect the components on the DC side (such as batteries, capacitors, etc.), such as causing the battery to heat up, reducing the lifespan of the capacitor, etc., and may further damage the components and increase the damage rate of the components.

[0098] Therefore, based on the power converter that can switch between single-phase and three-phase modes provided in the above embodiments, the embodiments of this application can control the power conversion circuit that is not operating in single-phase mode, so that the fluctuating current of the DC-side capacitor flows into the AC-side capacitor of the power conversion circuit that is not operating in single-phase mode. This prevents the voltage of the DC-side capacitor from being affected by the fluctuating current and generating low-frequency voltage fluctuations, thereby suppressing low-frequency voltage fluctuations and avoiding damage to DC-side components, thus reducing the component damage rate.

[0099] To enable those skilled in the art to better understand the present application, based on the content provided in the above embodiments, the technical solutions in the embodiments of the present application will be further described below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0100] See Figure 11 The figure is a schematic diagram of the structure of a power converter provided in an embodiment of this application.

[0101] Combination Figure 11 As shown, the inverter provided in this embodiment includes a controller 10 and a three-phase power conversion circuit 11. Each phase power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. For details, please refer to... Figures 2-3 The connections shown will not be elaborated further here.

[0102] The first terminals of the three-phase four-switch Buck-Boost circuit are connected in parallel to the DC-side capacitor, which is connected between the positive and negative terminals of the DC source. The voltage of the DC source is denoted by Uin. The second terminals of the three-phase four-switch Buck-Boost circuit are connected to the three AC phases of the power converter.

[0103] In the three-phase power conversion circuit 11, one or two phases operate in single-phase mode. The AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid, while the AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or power grid.

[0104] The controller 10 is used to control the power conversion circuit that is not operating in single-phase mode, so that the fluctuating current of the DC side capacitor flows into the AC side capacitor of the power conversion circuit that is not operating in single-phase mode.

[0105] Fluctuating current refers to the naturally occurring, fluctuating current that exists across the DC-side capacitor. This fluctuating current can cause low-frequency voltage fluctuations on the DC capacitor.

[0106] It should be noted that a certain current (which can be called the rated current) can exist across the DC-side capacitor. This rated current is the maximum allowable continuous operating current on the DC side. To improve efficiency, the DC-side current is generally the rated current. Correspondingly, the DC-side capacitor can also have a certain power (which can be called the rated power), which is used to balance the supply and demand of the power grid.

[0107] However, when the power inverter is operating in single-phase mode, there will be fluctuating current on the DC side, which will further cause low-frequency voltage fluctuations in the DC side capacitor. These low-frequency voltage fluctuations will affect the components on the DC side, so it is necessary to reduce or eliminate the low-frequency voltage fluctuations on the DC side.

[0108] It should be understood that, in the embodiments of this application, by controlling the power conversion circuit that is not operating in single-phase mode, the fluctuating current of the DC-side capacitor flows into the AC-side capacitor of the power conversion circuit that is not operating in single-phase mode, thereby preventing the voltage of the DC-side capacitor from being affected by the fluctuating current, suppressing low-frequency voltage fluctuations, and thus avoiding damage to DC-side components caused by low-frequency voltage fluctuations on the DC side, reducing the component damage rate.

[0109] It should be noted that the controller 10 provided in this application embodiment can also be used to control the switching action of each phase power conversion circuit in the three-phase power conversion circuit to realize power conversion or other functions, which will not be elaborated here.

[0110] Based on the power converters provided in the various embodiments described above, the closing methods of the switching devices and AC switching devices when the power converter operates in single-phase mode can be divided into two types. In order to make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the control methods of the power converter under the three closing methods of the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0111] Combination Figure 12 As shown, Figure 12 A power controller in a first closed-loop configuration is shown. The power converter may include a controller 10, which is used to control the components in the power converter described in any of the above embodiments, such as switching transistors, switching devices, AC switching devices, etc.

[0112] This application does not specifically limit the type of switching transistor, switching device, or AC switching device. For example, depending on actual efficiency, power density, and cost, one can choose a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), or a gallium nitride high electron mobility transistor (GaN-HEMT) with reverse conduction function. No specific limitation is made here.

[0113] Figure 12 The structure and connection relationships of the provided power converter can be found in [reference]. Figure 2 and Figure 9 The structure and connection relationships of the power converter shown are explained in detail in the above embodiments, and will not be repeated here.

[0114] For the first type of closure, please refer to [link / reference]. Figure 8 As shown, this means that any one phase of the three-phase power conversion circuit operates in single-phase mode, while the remaining two phases do not operate in single-phase mode. For ease of explanation, this is combined with... Figure 12 As shown, this embodiment of the application uses the example of K1 and K33 being closed, K2 (and K3), K11, and K22 being open, the C-phase power conversion circuit operating in single-phase mode, and the A-phase and B-phase circuits not operating in single-phase mode, as an example for illustrative purposes.

[0115] like Figure 12 As shown, S9, S10, S11 and S12 operate in single-phase mode. Controller 10 can control S1, S2, S3, S4, S5, S6, S7 and S8 to allow the fluctuating current of the DC side capacitor to flow into the AC side capacitor of phase A and / or phase B.

[0116] In one possible implementation, phase B is not working, and phase A works in any of the first, second, or third modes.

[0117] Phase B is not operating. When Phase A operates in the first mode, the two switches in the first bridge arm of Phase A are complementary switches, and they periodically switch on and off. In the second bridge arm of Phase A, one switch is normally on and the other is normally open, ensuring that the input voltage is greater than the output voltage. For example, in the first Buck-Boost circuit, S3 is normally on, S4 is normally open, and S1 and S2 are complementary switches, periodically switching on and off to allow the fluctuating current in the DC-side capacitor to flow into Cfa. In the second Buck-Boost circuit, S5, S6, S7, and S8 are all off.

[0118] Phase B is not operating. When phase A operates in the second mode, one switch in the first bridge arm of phase A is normally on and the other is normally open. The two switches in the second bridge arm of phase A are complementary switches. These two switches periodically switch to ensure the input voltage is lower than the output voltage. For example, in the first Buck-Boost circuit, S1 is normally on, S2 is normally open, and S3 and S4 are complementary switches. S3 and S4 periodically switch to allow the fluctuating current in the DC-side capacitor to flow into Cfa. In the second Buck-Boost circuit, S5, S6, S7, and S8 are all off.

[0119] Phase B is not operating. When Phase A operates in the third mode, the two switches in the first bridge arm of Phase A are complementary switches, and these two switches periodically switch on and off. Similarly, the two switches in the second bridge arm of Phase A are complementary switches, and these two switches periodically switch on and off. For example, in the first Buck-Boost circuit, S1 and S2 are complementary switches, as are S3 and S4. S1 and S2 switch periodically, and S3 and S4 switch periodically to allow the fluctuating current in the DC-side capacitor to flow into Cfa. In the second Buck-Boost circuit, S5, S6, S7, and S8 are all off.

[0120] Complementary switches refer to two switches in a circuit whose states are complements of each other, meaning the sum of their states is 1. Specifically, when one switch is in the ON (or OFF) state, the other switch is in the OFF (or OFF) state, and vice versa.

[0121] It should be noted that the implementation process of phase A not working and phase B working in any of the first, second, or third modes is similar to the implementation process of phase A working and phase B not working as described above. For relevant explanations, please refer to the explanation of phase A working and phase B not working, which will not be repeated here.

[0122] In another possible implementation, both phase A and phase B operate, and phase A and phase B operate in any combination of two of the first, second, or third modes.

[0123] Both phase A and phase B are working. When both phase A and phase B are working in the first mode, please refer to the implementation process of phase A working in the first mode in the above embodiments, which will not be repeated here.

[0124] Both phase A and phase B are working. When both phase A and phase B are working in the second mode, please refer to the implementation process of phase A working in the second mode in the above embodiments, which will not be repeated here.

[0125] Both phase A and phase B are working. When both phase A and phase B are working in the third mode, please refer to the implementation process of phase A working in the third mode in the above embodiments, which will not be repeated here.

[0126] Both phase A and phase B are operating. When phase A is operating in the first mode and phase B is operating in the second mode, S3 in the first Buck-Boost circuit is normally on, S4 is normally open, and S1 and S2 are complementary switches that periodically switch on and off. In the second Buck-Boost circuit, S5 is normally on, S6 is normally open, and S7 and S8 are complementary switches that periodically switch on and off. This allows the fluctuating current in the DC-side capacitor to flow into Cfa and Cfb, respectively.

[0127] Both phase A and phase B are operating. When phase A is operating in the second mode and phase B is operating in the first mode, S1 in the first Buck-Boost circuit is normally on, S2 is normally open, and S3 and S4 are complementary switches that periodically switch on and off. In the second Buck-Boost circuit, S7 is normally on, S8 is normally open, and S5 and S6 are complementary switches that periodically switch on and off. This allows the fluctuating current in the DC-side capacitor to flow into Cfa and Cfb, respectively.

[0128] It should be noted that when both phase A and phase B are working, phase A and phase B can direct the fluctuating current in the DC side capacitor into Cfa and Cfb respectively according to a preset ratio.

[0129] It should be understood that the embodiments of this application can control the power conversion circuit (phase A and / or phase B) that is not operating in single-phase mode, so that the fluctuating current of the DC side capacitor flows into the AC side capacitor (Cfa and / or Cfb) of the power conversion circuit that is not operating in single-phase mode, thereby suppressing the low-frequency voltage fluctuations on the DC side, avoiding damage to DC side components caused by the low-frequency voltage fluctuations on the DC side, and reducing the damage rate of components.

[0130] Combination Figure 13 As shown, Figure 13 A power controller in a second closed-loop configuration is shown, which may include controller 10.

[0131] Figure 13The structure and connection relationships of the provided power converter can be found in [reference]. Figure 2 and Figure 9 The structure and connection relationships of the power converter shown are explained in detail in the above embodiments, and will not be repeated here.

[0132] For the second type of closure, please refer to [link / reference]. Figure 6 , Figure 7a , Figure 7b As shown, any two phases of the three-phase power conversion circuit operate in single-phase mode, while the remaining phase does not operate in single-phase mode. For ease of explanation, this is combined with... Figure 13 As shown, this embodiment of the application uses the example where K1, K22, and K33 are closed, K2 (and K3) and K11 are both open, the power conversion circuits of phase B and phase C operate in single-phase mode, and phase A does not operate in single-phase mode, for illustrative purposes.

[0133] like Figure 13 As shown, S5, S6, S7, S8, S9, S10, S11 and S12 operate in single-phase mode. Controller 10 can control S1, S2, S3 and S4 to allow the fluctuating current of the DC side capacitor to flow into the AC side capacitor of phase A.

[0134] Phase A operates in any one of the first, second, or third modes.

[0135] When phases B and C operate in single-phase mode, phase A operates in the first mode. The implementation process of phase A operating in the first mode can be found in the above embodiments, and will not be repeated here.

[0136] When phases B and C operate in single-phase mode, phase A operates in the second mode. The implementation process of phase A operating in the second mode can be found in the above embodiments, and will not be repeated here.

[0137] When phases B and C operate in single-phase mode and phase A operates in the third mode, please refer to the implementation process of phase A operating in the third mode in the above embodiments, which will not be repeated here.

[0138] It should be understood that the embodiments of this application can control the power conversion circuit (phase A) that is not operating in single-phase mode, so that the fluctuating current across the DC side capacitor flows into the AC side capacitor (Cfa) of the power conversion circuit that is not operating in single-phase mode, thereby suppressing low-frequency voltage fluctuations on the DC side, avoiding damage to DC side components caused by low-frequency voltage fluctuations on the DC side, and reducing the damage rate of components.

[0139] Based on the power converter provided in the above embodiments, see [link to relevant documentation]. Figure 14This application also provides a control method for a power converter, which can be any of the power converters described in the above embodiments. The control method may include:

[0140] S1401: Controls one or two phases in a three-phase power conversion circuit to operate in single-phase mode.

[0141] In this circuit, the AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid, while the AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or power grid.

[0142] S1402: Control the power conversion circuit that is not operating in single-phase mode so that the fluctuating current of the DC side capacitor flows into the AC side capacitor of the power conversion circuit that is not operating in single-phase mode.

[0143] In this way, the fluctuating current on the DC side of the power converter flows into the AC side capacitor of the power conversion circuit that is not connected to the load or the power grid, thus avoiding damage to the DC side components caused by low-frequency voltage fluctuations on the DC side and reducing the component failure rate.

[0144] In one possible implementation, step S1402 includes: when two phases of the three-phase power conversion circuit are operating in single-phase mode, controlling the power conversion circuit that is not operating in single-phase mode to operate in any one of the first mode, second mode, or third mode.

[0145] In one possible implementation, step S1402 includes: when one phase of the three-phase power conversion circuit is operating in single-phase mode, controlling one phase of the two-phase power conversion circuit that is not operating in single-phase mode to operate in any one of the first mode, second mode, or third mode, and controlling the other phase of the two-phase power conversion circuit that is not operating in single-phase mode to not operate.

[0146] In one possible implementation, step S1402 includes: when one phase of the three-phase power conversion circuit is operating in single-phase mode, controlling the two-phase power conversion circuits that are not operating in single-phase mode to operate in any combination of two modes of the first mode, the second mode, or the third mode.

[0147] The control method of the power conversion circuit provided in this application embodiment has the same beneficial effects as the power converter provided in the above embodiments, and therefore will not be described again.

[0148] Based on the power converter and corresponding control method provided in the above embodiments, in order to more clearly explain how the fluctuating current flows from the two ends of the DC-side capacitor into the two ends of the AC-side capacitor of the power conversion circuit that is not operating in single-phase mode via a switching action, the following is combined with... Figures 15a-15d An example is provided.

[0149] Combination Figure 15a As shown, in this embodiment, the single-phase AC wiring is closed at a and N, K2 and K11 (or, K3 and K11 are closed), and K1, K3 (or K2), K22 and K33 are all open. At this time, phase B and phase C are working in single-phase mode, while phase A is not working in single-phase mode.

[0150] It should be noted that the embodiments of this application are based on... Figure 15a The power converter shown is illustrated by way of example, but is not limited to it. Figure 15a The power converter shown can also be the power converter illustrated in any of the foregoing embodiments. Figure 15a The power converter shown should not be used as a basis for limiting the scope of protection of this application.

[0151] In this embodiment of the application, it is assumed that the rated current is I. dc The rated voltage is U dc The fluctuating current is com >Ts, total current is dc >Ts, where dc >Ts=I dc + com >Ts, the triangular wave Us corresponding to the AC side capacitor Cfa, and the real-time voltage of the AC side capacitor is u. cfa .

[0152] The triangular wave is a wave with a waveform resembling a triangle, where the positive rise and negative decay times are equal, providing a 50% duty cycle. Within each cycle, the triangular wave linearly increases from a minimum to a maximum value, then linearly decreases back to a minimum. The direction of the hypotenuse can be either upward or downward, and the rise and fall times are equal.

[0153] In this embodiment, the triangular wave, as a periodic waveform, has a continuous linear slope that allows it to precisely control the on and off times of the power conversion circuit's switches. Specifically, by adjusting the relationship between the magnitude of the triangular wave and the modulated wave voltage, the on-time of the switch can be controlled, thereby achieving fine voltage regulation. The modulated wave voltage refers to the voltage obtained by modulating the real-time voltage of the AC-side capacitor.

[0154] In one possible implementation, combining Figure 15b As shown, assume S1 and S2 are complementary switches, S3 is normally on, and S4 is normally off. When there is a fluctuating current on the DC side... com >Ts, then the total current dc >Ts is greater than I dc ​​​​​​, and thus the DC-side capacitor will be affected by the fluctuating current, generating low-frequency voltage fluctuations. This low-frequency voltage fluctuation will have an impact on the components on the DC side, and even cause damage to the components on the DC side, increasing the damage rate of the components.

[0155] To solve this technical problem, in the embodiment of the present application, by controlling the conduction and cutoff of S1 and S2, the fluctuating current <i com >Ts is transferred to the AC-side capacitor Cfa of phase A.

[0156] Assume that the triangular wave corresponding to the AC-side capacitor Cfa is Figure 15b the shown Us, and the real-time voltage of the AC-side capacitor is u cfa , when u cfa ≥Us, S1 is turned on and S2 is turned off; when u cfa <Us, S1 is turned off and S2 is turned on, so that the fluctuating current <i com >Ts is transferred to the AC-side capacitor Cfa of phase A.

[0157] It should be understood that when the modulation wave voltage u m corresponding to the real-time voltage is greater than or equal to the triangular wave voltage, the controller can output a high-level signal, making S1 in the on state; when the modulation wave voltage is less than the triangular wave voltage, the controller can output a low-level signal, making S1 in the off state. That is, the switching of the high and low levels constitutes the PWM signal. Among them, the duty cycle of the PWM signal (i.e., the proportion of the high level) depends on the relative magnitudes of the triangular wave and the modulation wave voltage.

[0158] It should be noted that when S1 and S2 alternate in switching actions, at this time Udc > u cfa .

[0159] In this way, by comparing the magnitudes of the modulation wave voltage and the triangular wave voltage, PWM control can be achieved, and at the same time, the output voltage can be adjusted, the circuit efficiency can be improved, the stable control of the circuit can be achieved, and the electromagnetic interference can be reduced, etc.

[0160] In another possible implementation, as shown in Figure 15c , assume that S1 is always on, S2 is always off, and S3 and S4 are complementary switches. When there is a fluctuating current <i com >Ts on the DC side, then the total current <i dc >Ts is greater than I dc , and thus the DC-side capacitor will be affected by the fluctuating current, generating low-frequency voltage fluctuations. This low-frequency voltage fluctuation will have an impact on the components on the DC side, and even cause damage to the components on the DC side, increasing the damage rate of the components.

[0161] To solve this technical problem, in the embodiments of the present application, by controlling the on and off of S3 and S4, the fluctuating current <i com >Ts is transferred to the AC side capacitor Cfa of phase A.

[0162] Assume that the triangular wave corresponding to the AC side capacitor Cfa is Figure 15c the shown Us, and the real-time voltage of the AC side capacitor is u cfa . When u cfa ≥Us, S3 is turned on and S4 is turned off; when u cfa <Us, S3 is turned off and S4 is turned on, so that the fluctuating current <i com >Ts is transferred to the AC side capacitor Cfa of phase A.

[0163] It should be understood that when the modulation wave voltage is greater than or equal to the triangular wave voltage, the controller can output a high-level signal to make S3 in the on state; when the modulation wave voltage is less than the triangular wave voltage, the controller can output a low-level signal to make S3 in the off state. That is, the switching of the high and low levels constitutes the PWM signal. Among them, the duty cycle of the PWM signal (i.e., the proportion of the high level) depends on the relative magnitudes of the triangular wave and the modulation wave voltage.

[0164] It should be noted that when S3 and S4 alternately switch, at this time Udc < u cfa .

[0165] In another possible implementation, as shown in Figure 15d , assume that S1 and S2 are complementary switches, and S3 and S4 are complementary switches. When there is a fluctuating current <i com >Ts on the DC side, then the total current <i dc >Ts is greater than I dc . Furthermore, the DC side capacitor will be affected by the fluctuating current and generate low-frequency voltage fluctuations. These low-frequency voltage fluctuations will affect the components on the DC side and even cause damage to the components on the DC side, increasing the damage rate of the components.

[0166] To solve this technical problem, in the embodiments of the present application, by controlling the on and off of S1, S2, S3 and S4, the fluctuating current <i com >Ts is transferred to the AC side capacitor Cfa of phase A.

[0167] Assume that the triangular wave corresponding to the AC side capacitor Cfa is Figure 15d the shown Us, and the real-time voltage of the AC side capacitor is u cfa . In the first switching period, when u cfa ≥Us, S1 is turned on, S2 is turned off, and S3 and S4 do not act; when u cfa<When Us, S1 is turned off, S2 is turned on, and S3 and S4 do not act. In the second switching period, when u cfa ≥ Us, S3 is turned on, S4 is turned off, and S1 and S2 do not act; when u cfa < Us, S3 is turned off, S4 is turned on, and S1 and S2 do not act. Thus, by the actions of S1 and S2, S3 and S4 in different switching periods, the fluctuating current <i com > Ts is transferred to the AC-side capacitor Cfa of phase A.

[0168] It should be understood that when the modulating wave voltage is greater than or equal to the triangular wave voltage, the controller can output a high-level signal, making S1 and S3 in the on state; when the modulating wave voltage is less than the triangular wave voltage, the controller can output a low-level signal, making S1 and S3 in the off state. That is, the switching of high and low levels constitutes the PWM signal. Among them, the duty cycle of the PWM signal (i.e., the proportion of the high level) depends on the relative magnitudes of the triangular wave and the modulating wave voltage.

[0169] It should be noted that when S1 and S2 alternately switch, at this time Udc > u cfa ; when S3 and S4 alternately switch, at this time Udc < u cfa .

[0170] In a possible implementation manner, refer to Figure 16 , this figure is a schematic diagram of a control device provided by an embodiment of the present application.

[0171] The control device may include a memory 1611 and a processor 1612. The processor 1612 can be connected to the power converter and can drive the switches in each power conversion circuit in the power converter. As Figure 16 shown, the memory can be a random access memory (RAM), flash memory, read only memory (ROM), EPROM memory, non-volatile read only memory (Electronic Programmable ROM, EPROM), register, hard disk, removable disk, etc.

[0172] The memory 1611 can store computer instructions. When the computer instructions stored in the memory 1611 are executed by the processor 1612, the processor 1612 can be used to execute the control method. The memory 1611 can also store data, for example, information such as the preset ratio involved in the above embodiments.

[0173] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0174] This application also provides a readable storage medium for storing the methods provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0175] In the embodiments of this application, the terms "first" and "second" (if they exist) are used only as name identifiers and do not represent the order of first and second.

[0176] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.

[0177] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A power converter, characterized by, include: The controller and a three-phase power conversion circuit are included. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. A DC-side capacitor is connected in parallel between the positive and negative DC terminals of the three-phase power conversion circuit. The AC-side capacitor is connected between the AC side and the negative DC terminal of the power conversion circuit. One or two phases of the three-phase power conversion circuit operate in single-phase mode. The AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid. The AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or power grid. The controller is used to control the power conversion circuit that is not operating in single-phase mode, so that the fluctuating current of the DC-side capacitor flows into the AC-side capacitor of the power conversion circuit that is not operating in single-phase mode.

2. The power converter of claim 1, wherein, Each phase of the four-switch Buck-Boost circuit includes: a first switch, a second switch, a third switch, a fourth switch, and an inductor; The first and second switching transistors are connected in series to form a first bridge arm, and the two ends of the first bridge arm are respectively connected to the positive and negative terminals of the DC-side capacitor; the third and fourth switching transistors are connected in series to form a second bridge arm, the first end of the inductor is connected to the midpoint of the first bridge arm, and the second end of the inductor is connected to the midpoint of the second bridge arm; the first end of the second bridge arm serves as the output terminal of the power conversion circuit, the second end of the second bridge arm is connected to the negative terminal of the DC side, and the two ends of the AC-side capacitor are respectively connected to the first end of the second bridge arm and the negative terminal of the DC side.

3. The power converter of claim 2, wherein, When two phases of the three-phase power conversion circuit operate in single-phase mode, the controller controls the first and second switches in the power conversion circuit not operating in single-phase mode to operate complementaryly, and controls the third switch in the power conversion circuit not operating in single-phase mode to be normally on and the fourth switch to be normally off; or... The first switch in the power conversion circuit that is not operating in single-phase mode is controlled to be normally on and the second switch is controlled to be normally off. The third and fourth switches in the power conversion circuit that is not operating in single-phase mode are controlled to be complementary switches.

4. The power converter of claim 2, wherein, When one phase of the three-phase power conversion circuit operates in single-phase mode, the controller is used to control the first and second switches in at least one phase of the power conversion circuit not operating in single-phase mode to operate complementaryly, and to control the third switch in the power conversion circuit not operating in single-phase mode to be normally on and the fourth switch to be normally off; or... The first switch in at least one phase power conversion circuit that is not operating in single-phase mode is controlled to be normally on and the second switch is controlled to be normally off. The third and fourth switches in the power conversion circuit that is not operating in single-phase mode are controlled to be complementary switches.

5. The power converter of claim 2, wherein, Also includes: AC switching devices; The first end of the AC switching device is connected to the first end of the second bridge arm, and the second end of the AC switching device serves as the output end of the power conversion circuit.

6. The power converter according to claim 5, characterized in that, The power converter further includes: a first switching device and a second switching device; the first terminal of the first switching device is connected to the positive terminal of the DC-side capacitor, the second terminal of the first switching device is connected to the first terminal of the second switching device, and the second terminal of the second switching device is connected to the first terminal of the AC switching device of any one phase in the three-phase power conversion circuit.

7. The power converter according to claim 6, characterized in that, The power converter further includes a third switching device; the first end of the third switching device is connected to the second end of the first switching device, and the second end of the third switching device is connected to the first end of the AC switching device of any phase in the three-phase power conversion circuit; wherein the AC switching device connected to the second switching device is different from the AC switching device connected to the third switching device.

8. The power converter according to claim 6, characterized in that, Before controlling the power conversion circuit that is not operating in single-phase mode, the controller is further configured to: Control the first switching device to close, control the second switching device to open, and control the AC switching device of any one phase in the three-phase power conversion circuit to close; Alternatively, control the first switching device to close, control the second switching device to open, and control the AC switching devices of any two phases in the three-phase power conversion circuit to close. Alternatively, the first switching device can be controlled to open, the second switching device can be controlled to close, and either of the two AC switching devices that are not connected to the second switching device can be controlled to close.

9. The power converter according to claim 7, characterized in that, Before controlling the power conversion circuit that is not operating in single-phase mode, the controller is further configured to: Control the first switching device to close, control the second and third switching devices to open, and control the AC switching device of any one phase in the three-phase power conversion circuit to close; Alternatively, control the first switching device to close, control the second and third switching devices to open, and control the AC switching devices of any two phases in the three-phase power conversion circuit to close. Alternatively, control the first switching device to close, control the second or third switching device to close, or control an AC switching device that is not connected to the second or third switching device to close.

10. A control method for a power converter, characterized in that, The power converter includes a controller and a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit and an AC-side capacitor. A DC-side capacitor is connected in parallel between the positive and negative DC terminals of the three-phase power conversion circuit. The AC-side capacitor is connected between the AC side and the negative DC terminal of the power conversion circuit. One or two phases of the three-phase power conversion circuit operate in single-phase mode. The AC side of the power conversion circuit operating in single-phase mode is used to connect to a single-phase load or a single-phase power grid. The AC side of the power conversion circuit not operating in single-phase mode is not connected to a load or power grid. The control method includes: The power conversion circuit that is not operating in single-phase mode is controlled so that the fluctuating current of the DC-side capacitor flows into the AC-side capacitor of the power conversion circuit that is not operating in single-phase mode.

11. A control device, characterized in that, It includes a processor and a memory, the memory being used to store programs, instructions, or code, and the processor being used to execute the programs, instructions, or code in the memory to perform the control method as described in claim 10.

12. A computer-readable storage medium, characterized in that, The system contains a computer program that is loaded by a processor to execute the control method as described in claim 10.

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