Power converter

Abstract

Provided in the present application is a power converter, comprising a controller and a power conversion circuit; the controller is used for controlling the power conversion circuit to perform power conversion between a direct current and a three-phase alternating current; the controller is further used to: when the absolute value of the difference between an output indicator of the three-phase alternating current output by the power conversion circuit and a reference indicator exceeds a reference threshold, control an internal potential vector reference value corresponding to the output indicator of the three-phase alternating current output by the power conversion circuit that is less than the reference indicator to increase, and / or control an internal potential vector reference value corresponding to the output indicator of the three-phase alternating current output by the power conversion circuit that is greater than the reference indicator to decrease, such that the power converter has a capability of driving an unbalanced load.

Description

Power converter

[0001] This application claims priority to Chinese patent application No. 202510127713.2, filed with the State Intellectual Property Office of China on January 27, 2025, entitled "Power Converter", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of power electronics technology, and in particular to a power converter. Background Technology

[0003] Microgrids typically consist of distributed generation, electrical loads, energy storage devices, monitoring, protection, and automation systems, forming small-scale power supply and consumption systems capable of achieving basic internal power balance. When a microgrid operates independently, a certain proportion of the energy storage system needs to operate in voltage source mode (referred to as grid control) to establish and maintain the system's voltage and frequency levels. In off-grid commercial / industrial scenarios / microgrid scenarios, grid-connected energy storage converters act as the main power source to supply power to the loads, requiring the grid's three-phase voltage balance to meet load imbalance voltage requirements. Relevant standards impose certain requirements on grid imbalance during normal operation. With increasingly stringent load-carrying requirements for off-grid commercial / industrial scenarios or microgrid scenarios, power converters such as energy storage converters or photovoltaic inverters will be required to handle 100% unbalanced loads in off-grid conditions. Summary of the Invention

[0004] The power converter provided in this application can accurately identify three-phase unbalanced operating conditions on the AC side and effectively and safely respond to them, enabling the power converter to carry unbalanced loads.

[0005] In a first aspect, this application provides a power converter, including a controller and a three-phase three-wire power conversion circuit; the controller is used to control the three-phase three-wire power conversion circuit to perform power conversion between DC and three-phase AC; the controller is further used to, when the absolute value of the difference between the output index of the three-phase AC output by the three-phase three-wire power conversion circuit and the reference index exceeds a reference threshold, control the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase three-wire power conversion circuit that is less than the reference index to increase, and / or control the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase three-wire power conversion circuit that is greater than the reference index to decrease. The output index is the amplitude of one phase line voltage in the three-phase AC power supply, and the reference index is the average value of the three-phase line voltage amplitudes, a preset fixed reference amplitude, or the amplitude of the middle phase line voltage among the three-phase line voltage amplitudes; or, the output index is the difference between the phase of one phase line voltage in the three-phase AC power supply and the phase of the corresponding reference phase, and the reference index is one phase of the three-phase AC power supply when a balanced load is connected to the three-phase AC terminals of the three-phase three-wire power conversion circuit. The difference between the phase of the line voltage and the phase of the reference phase corresponding to one of the line voltages, or the average of the phase differences between each phase of the three-phase AC power and the reference phase corresponding to each phase of the AC power; wherein, the reference phase is any one of the line voltages of the three-phase AC power, or, the reference phase is a reference voltage other than the three-phase line voltages of the three-phase AC power that changes periodically with the same period, amplitude, and rate of change as any one of the line voltages of the three-phase AC power when a balanced load is connected to the three-phase AC terminals of the three-phase three-wire power conversion circuit.

[0006] In the technical solution provided in this application, the power converter can determine whether a three-phase unbalanced condition has occurred on the AC side of the power converter based on the change in the absolute value of the difference between the output index and the reference index of the three-phase AC power, such as the difference between the actual value and the rated value of various electrical parameters output by the power converter. The corresponding internal potential vector reference value is adjusted through a corresponding control strategy to achieve the purpose of balancing the three-phase AC power. Thus, the power converter can still output balanced three-phase AC power to the large power grid or micro power grid when carrying an unbalanced load.

[0007] It should be noted that when a power converter using a three-phase three-wire power conversion circuit is connected to a three-phase load on its AC side, such as a three-phase motor or power grid, the AC side of the power converter is generally in a three-phase balanced state. Connecting a single-phase load to the AC side of the power converter may cause three-phase imbalance, resulting in unequal amplitudes of the three-phase AC current. Therefore, the amplitude of the three-phase output line voltage of the power converter can be observed to determine whether an imbalance has occurred on the AC side. Under balanced three-phase AC operation, the amplitudes of the three-phase output line voltages are essentially equal. Therefore, any one of the three-phase output line voltage amplitudes or the average of the three-phase output line voltage amplitudes can be used as a reference indicator. When the amplitude of the three-phase output line voltage of the power converter differs significantly from this reference indicator, it can be considered that a three-phase imbalance has occurred on the AC side.

[0008] Under balanced three-phase AC operation, the phase differences of the three-phase output line voltages are sequentially equal. Therefore, the phase difference of the three-phase output line voltages can be used as an indicator of whether the three phases on the AC side are balanced. Ideally, the phase differences of the three-phase output line voltages are sequentially and uniformly 120° apart. Therefore, a reference phase can be set, i.e., a reference phase can be selected. This reference phase can be any of the three-phase output line voltages or any other preset phase. A reference voltage is selected, and like the other line voltages, its phase changes periodically with the same period, amplitude, and rate of change as when a balanced load is connected to the three-phase AC terminals of the power conversion circuit. The difference between the three-phase output line voltages and the reference phase remains constant under balanced three-phase conditions. This constant difference is the reference indicator. When the difference between the phase of any of the three-phase output line voltages and this reference phase deviates significantly from the reference indicator, three-phase imbalance on the AC side can be considered to have occurred. Alternatively, the phase of any one of the three-phase output line voltages can be selected as the reference phase. The reference index is the average value of the difference between the phase of the three-phase output line voltage and the phase of the line voltage. When the difference between the phase of the three-phase output line voltage and the average value deviates significantly from the reference index, it can be considered that a three-phase imbalance has occurred on the AC side.

[0009] In one embodiment, the controller is configured to, when the absolute value of the difference between the output index of the three-phase AC power output by the power conversion circuit and the reference index exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the power conversion circuit to increase. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

[0010] In one embodiment, the controller is configured to control the internal potential vector reference value corresponding to the output index of the three-phase AC power output by the power conversion circuit to decrease when the absolute value of the difference between the output index and the reference index exceeds the reference threshold. The larger the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the more the internal potential vector reference value corresponding to the output index decreases.

[0011] It should be understood that the greater the difference between the output index and the reference index in three-phase alternating current, the more serious the three-phase imbalance is, and the greater the adjustment is required to restore the three-phase alternating current to a balanced state as quickly as possible.

[0012] Secondly, this application provides a power converter, including a controller and a three-phase four-wire power conversion circuit; the controller is used to control the three-phase four-wire power conversion circuit to perform power conversion between DC and three-phase AC; the controller is further used to, when the absolute value of the difference between the output index and the reference index of the three-phase AC output by the three-phase four-wire power conversion circuit exceeds a reference threshold, control the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase four-wire power conversion circuit that is less than the reference index to increase, and / or control the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase four-wire power conversion circuit that is greater than the reference index to decrease; the output index is the phase voltage amplitude of one phase of the three-phase AC, and the reference index is the average value of the three phase voltage amplitudes of the three-phase AC or a preset fixed reference amplitude or a three-phase... The phase voltage amplitude is the phase voltage amplitude that is in the middle of the phase voltage amplitude; or, the output index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to the one phase voltage, and the reference index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to the one phase voltage when the three-phase AC terminals of the three-phase four-wire power conversion circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power and the respective reference phases of the three-phase AC power; wherein, the reference phase is any phase voltage in the three-phase AC power, or, the reference phase is a reference voltage other than the three phase voltages in the three-phase AC power that changes periodically with the same period, amplitude, and rate of change as any phase voltage in the three-phase AC power when the three-phase AC terminals of the three-phase four-wire power conversion circuit are connected to a balanced load. It should be noted that the AC side of a power converter using a three-phase four-wire power conversion circuit can be connected to both three-phase and single-phase loads. Therefore, the amplitude of the three-phase output phase voltages of the power converter can be observed to determine whether there is an imbalance on the AC side. Under balanced three-phase operation on the AC side, the amplitudes of the three-phase output phase voltages are basically equal. Therefore, any line voltage amplitude or the average of the three-phase output phase voltage amplitudes can be used as a reference indicator. When the amplitude of the three-phase output phase voltages of the power converter differs significantly from this reference indicator, it can be considered that a three-phase imbalance has occurred on the AC side.

[0013] Under balanced three-phase AC operation, the phase differences of the three-phase output phase voltages are sequentially equal. Therefore, the phase difference of the three-phase output phase voltages can be used as an indicator of whether the three phases on the AC side are balanced. In ideal conditions, the phase differences of the three-phase output phase voltages are sequentially and uniformly 120° apart. Therefore, a reference phase can be set, i.e., a reference phase is selected. This reference phase can be the phase of any line voltage of the three-phase output phase voltages, or any other phase besides the three-phase output phase voltages. This selected reference voltage, like the other phase voltages, undergoes periodic changes in phase with the same period, amplitude, and rate of change as when a balanced load is connected to the three-phase AC terminals of the power conversion circuit. The difference between the three-phase output phase voltages and the reference phase remains constant under balanced three-phase conditions. This constant difference is the reference indicator. When the difference between the phase of any three-phase output phase voltage and this reference phase deviates significantly from the reference indicator, a three-phase imbalance is considered to have occurred on the AC side. Alternatively, the phase of any one of the three-phase output phase voltages can be selected as the reference phase. The reference index is the average value of the difference between the phase of the three-phase output phase voltage and the phase of that phase voltage. When the difference between the phase of the three-phase output phase voltage and the average value deviates significantly from the reference index, it can be considered that a three-phase imbalance has occurred on the AC side.

[0014] In one embodiment, the controller is configured to, when the absolute value of the difference between the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit and the reference index exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index to increase. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

[0015] In one embodiment, the controller is configured to, when the absolute value of the difference between the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit and the reference index exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase four-wire power conversion circuit to decrease. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the decrease in the internal potential vector reference value corresponding to the output index.

[0016] It should be understood that the greater the difference between the output index and the reference index in three-phase alternating current, the more serious the three-phase imbalance is, and the greater the adjustment is required to restore the three-phase alternating current to a balanced state as quickly as possible.

[0017] Thirdly, this application provides a control method for a three-phase three-wire power conversion circuit, controlling the three-phase three-wire power conversion circuit to perform power conversion between DC and three-phase AC; and, when the absolute value of the difference between the output index and the reference index of the three-phase AC output by the three-phase three-wire power conversion circuit exceeds a reference threshold, the method controls the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase three-wire power conversion circuit that is less than the reference index to be increased, and / or controls the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase three-wire power conversion circuit that is greater than the reference index to be decreased; the output index is the amplitude of one phase line voltage in the three-phase AC, and the reference index is the average value of the three-phase line voltage amplitudes of the three-phase AC, or a preset fixed reference amplitude, or a value among the three-phase line voltage amplitudes. The amplitude of a single-phase line voltage with a moderate magnitude; or, the output index is the difference between the phase of one phase line voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase line voltage, wherein the reference index is the difference between the phase of one phase line voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase line voltage when the three-phase AC terminals of the three-phase three-wire power conversion circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power and the respective reference phases of the three-phase AC power; wherein, the reference phase is any single-phase line voltage in the three-phase AC power, or, the reference phase is any voltage other than the three-phase line voltages in the three-phase AC power, such as a reference voltage that periodically changes with the same period, amplitude, and rate of change when the three-phase AC power is connected to a balanced load at the three-phase AC terminals of the three-phase three-wire power conversion circuit.

[0018] In one implementation, when the absolute value of the difference between the output index of the three-phase AC power output from the three-phase three-wire power conversion circuit and the reference index exceeds a reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output from the three-phase three-wire power conversion circuit is increased. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

[0019] In one implementation, when the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase three-wire power conversion circuit exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase three-wire power conversion circuit is reduced. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the reduction in the internal potential vector reference value corresponding to the output index.

[0020] Fourthly, this application provides a control method for a three-phase four-wire power conversion circuit, controlling the three-phase four-wire power conversion circuit to perform power conversion between DC and three-phase AC; and, when the absolute value of the difference between the output index and the reference index of the three-phase AC output by the three-phase four-wire power conversion circuit exceeds a reference threshold, the method controls the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC output by the three-phase four-wire power conversion circuit to be increased, and / or controls the internal potential vector reference value corresponding to the output index that is greater than the reference index in the three-phase AC output by the three-phase four-wire power conversion circuit to be decreased; the output index is the phase voltage amplitude of one phase in the three-phase AC, and the reference index is the average value of the three phase voltage amplitudes of the three-phase AC, or a preset fixed reference amplitude, or the amplitude of the three phase voltage amplitudes. The output index is the phase voltage amplitude of the centrally located phase; or, the output index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase voltage, and the reference index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase voltage when the three-phase AC terminals of the three-phase four-wire power conversion circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power and the respective reference phases of the three-phase AC power; wherein, the reference phase is any phase voltage in the three-phase AC power, or, the reference phase is a reference voltage other than the three-phase phase voltages in the three-phase AC power that periodically changes with the same period, amplitude, and rate of change as any phase voltage in the three-phase AC power when the three-phase AC terminals of the three-phase four-wire power conversion circuit are connected to a balanced load.

[0021] In one implementation, when the absolute value of the difference between the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit and the reference index exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase four-wire power conversion circuit is increased. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

[0022] In one embodiment, when the absolute value of the difference between the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit and the reference index exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase four-wire power conversion circuit is reduced. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the reduction in the internal potential vector reference value corresponding to the output index.

[0023] It should be understood that the implementation and beneficial effects of the above two aspects of this application can be referenced from each other. Attached Figure Description

[0024] Figure 1 is a schematic diagram of an application scenario of a new energy power generation system provided in an embodiment of this application;

[0025] Figure 2 is a schematic diagram of the connection method between a three-phase three-wire power converter and a single-phase load and a three-phase load according to an embodiment of this application;

[0026] Figure 3 is a schematic diagram of the connection method between a three-phase four-wire power converter and a single-phase load and a three-phase load according to an embodiment of this application;

[0027] Figure 4 is a schematic diagram of a power conversion circuit control flow provided in an embodiment of this application. Detailed Implementation

[0028] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms "connected," "linked," and "connected" used herein to indicate electrical connection mean direct or indirect electrical connection.

[0030] In the following description, the terms "first," "second," etc., 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 with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0031] The technical solutions provided in this application can be applied to different application scenarios, especially to photovoltaic power generation or energy storage power supply scenarios such as industrial and commercial distributed power stations and large ground power stations.

[0032] Figure 1 illustrates an application scenario of the new energy power generation system provided in this application embodiment. The new energy power generation system provided in this application embodiment includes a DC source 200, which can be one or more photovoltaic strings. A photovoltaic string is formed by connecting one or more photovoltaic panels in series or parallel. The DC source 200 can also be one or more battery clusters, which are formed by connecting battery packs in series or parallel. The DC source 200 is used to transmit DC power to the power converter 100, which converts the DC power input from the DC source 200 into AC power and outputs it to the load. It should be understood that the load in a broad sense can be the power grid, electrical equipment, energy storage equipment, etc. The power converter 100 provided in this application embodiment can be connected to electrical equipment, energy storage equipment, etc., independently, or independently to the power grid, or simultaneously to the power grid, electrical equipment, and energy storage equipment, etc. In the application scenario of the power converter 100 shown in Figure 1, the output terminal of the power converter 100 is directly connected to the load and connected to the transformer through the AC bus AC Bus1. After being stepped up by the transformer, it is connected to the AC bus AC Bus2 and then connected to the main power grid.

[0033] The power converter 100 includes a controller 110 and a power conversion circuit 120. The DC bus in the power converter 100 receives DC power from the DC source 200, forming a DC voltage on the DC side of the power conversion circuit 120. The controller 110 controls the power conversion circuit 120 to convert the DC power on the DC side into AC power, which is then output to the power grid or load on the AC side. The power converter 100 can be a three-phase three-wire power converter or a three-phase four-wire power converter.

[0034] Figure 2 illustrates a specific connection method of a three-phase three-wire power converter for connecting a single-phase load and a three-phase load according to an embodiment of this application. The figure shows two three-phase three-wire power converters connected in parallel; in practical applications, there can be one unit or multiple units connected in parallel. It should be understood that a three-phase load is generally a balanced load. When the three-phase three-wire power converter is connected to a three-phase load, the A, B, and C lines connected to the converter output three-phase AC voltages respectively. The amplitudes of the three-phase AC voltages are equal, and their phases are uniformly 120° apart. However, when a single-phase load is connected to the three-phase three-wire power converter, as shown in the figure, the single-phase load is connected between lines B and C, while there is no load connected between lines A and B or between lines A and C. In this case, the three-phase three-wire power converter provides the line voltage between lines B and C to the single-phase load, while the other output line voltages are not connected to the single-phase load. The load condition of the three-phase three-wire power converter is an unbalanced load condition. Under normal circumstances, a three-phase three-wire power converter adjusts its output three-phase AC power according to the load voltage. Under unbalanced load conditions, continuing to adjust its output three-phase AC power in the original way will cause the output three-phase AC power of the three-phase three-wire power converter to be unbalanced. That is, the amplitude of the output three-phase AC power will be unequal, or the phase of the output three-phase AC power will be offset instead of being uniformly 120° out of phase, or both of the above situations will occur at the same time.

[0035] Similar to the aforementioned embodiments, Figure 3 illustrates a specific connection method for a three-phase four-wire power converter to connect a single-phase load and a three-phase load according to an embodiment of the application. The figure shows two three-phase four-wire power converters connected in parallel; in practical applications, there can be one unit or multiple units connected in parallel. It should be understood that a three-phase load is generally a balanced load. When the three-phase four-wire power converter is connected to a three-phase load, the A, B, C, and N lines connected to the converter output three-phase AC voltages respectively. The amplitudes of the three-phase AC voltages are equal, and their phases are uniformly 120° apart. However, when a single-phase load is connected to the three-phase four-wire power converter, as shown in the figure, the single-phase load is connected between the C and N lines, while there is no load connected between the A and N lines or between the B and N lines. In this case, the three-phase four-wire power converter provides the phase voltage between the C and N lines to the single-phase load, while the other output phases are not connected to a single-phase load. The load condition of the three-phase four-wire power converter is an unbalanced load condition.

[0036] In the aforementioned embodiments, due to the existence of unbalanced load conditions, it is necessary to adjust the control method of the three-phase AC output of the power converter in order to effectively cope with unbalanced load conditions.

[0037] In one embodiment, referring to FIG1, the power converter 100 includes a controller 110 and a power conversion circuit 120; the controller 110 is used to control the power conversion circuit 120 to perform power conversion between DC and three-phase AC. When three-phase imbalance occurs on the AC side of the power converter 100, the controller 110 can also improve the voltage amplitude imbalance and / or improve the voltage phase imbalance by adjusting the AC output of the power conversion circuit 120. Specifically, the controller 110 is also used to control the internal potential vector reference value corresponding to the output index of the three-phase AC output of the power conversion circuit 120 that is less than the reference index to increase, and / or control the internal potential vector reference value corresponding to the output index of the three-phase AC output of the power conversion circuit 120 that is greater than the reference index to decrease, when the absolute value of the difference between the output index and the reference index of the three-phase AC output of the power conversion circuit 120 exceeds the reference threshold. It should be understood that when the three phases of the power converter 100 are balanced on the AC side, the three-phase AC outputs of the power conversion circuit 120 have equal amplitudes and uniformly 120° phase differences. Therefore, the amplitude or phase of the three-phase AC outputs of the power conversion circuit 120 when balanced can be used as a reference indicator. When the amplitude or phase of the three-phase AC outputs of the power conversion circuit 120 deviates significantly from the reference indicator, it can be considered that the three-phase AC outputs of the power conversion circuit 120 are unbalanced. In this case, certain control measures are needed to reduce the unbalance. That is, if the output indicator of the three-phase AC outputs of the power conversion circuit 120 is less than the reference indicator, the internal potential vector reference value corresponding to that output indicator is increased, thereby increasing the value of that output indicator in the three-phase AC outputs of the power conversion circuit 120 to bring it closer to the reference indicator. Conversely, when the output indicator is greater than the reference indicator, the internal potential vector reference value corresponding to that output indicator is increased, thereby decreasing the value of that output indicator in the three-phase AC outputs of the power conversion circuit 120 to bring it closer to the reference indicator. These two control methods can be performed separately or simultaneously. When the difference between the output indicator and the reference indicator is less than a certain threshold, that is, when the absolute value of the difference between the output indicator and the reference indicator is less than the reference threshold, the three-phase AC power output by the power conversion circuit 120 can be considered balanced, and no further adjustments are needed.

[0038] In one embodiment, the power conversion circuit 120 adopts a three-phase three-wire power conversion circuit as shown in Figure 2; the output index is the amplitude of the three-phase output line voltage, and the reference index is the average value of the three-phase output line voltage amplitude or any one of the three-phase output line voltage amplitudes. As described in the previous embodiment, when the three phases on the AC side of the power converter 100 are balanced, the amplitudes of the three-phase AC line voltages output by the power conversion circuit 120 are equal. Specifically, the amplitudes of the three-phase line voltages output by the power conversion circuit 120 are equal, that is, the amplitudes of the line voltages between lines A and B, between lines A and C, and between lines B and C are equal. Therefore, using the average value of the three-phase output line voltage amplitude or any one of the three-phase output line voltage amplitudes as a reference index, and comparing the output index and the reference index, when the difference between their values ​​is large, that is, when the absolute value of the difference between any output index and the reference index is greater than the reference threshold, it can be considered that the three-phase AC power output by the power conversion circuit 120 is unbalanced. For example, assuming the three phases of the power converter 100 are balanced on the AC side, the three-phase AC line voltage amplitudes output by the power conversion circuit 120 are all around 380V, with a difference of less than 5V between them. At this time, if any phase line voltage amplitude is selected as a reference index, the value of the reference index is around 380V. If the line voltage amplitude between output index A and B is 400V and the reference threshold is 10V, then the output index is at least 15V larger than the reference index of 380V. The absolute value of the difference between the output index and the reference index exceeds the reference threshold. Therefore, the controller 110 will reduce the internal potential vector reference corresponding to the line voltage amplitude between output index A and B to control the reduction of the line voltage amplitude between output index A and B. As a result, the line voltage amplitude between output index A and B gradually approaches the reference index, and finally the three-phase AC power output by the power conversion circuit 120 is balanced. Similarly, using the average value of the three-phase output line voltage amplitude as a reference index, and still assuming that the three phases of the power converter 100 are balanced on the AC side, the three-phase AC line voltage amplitudes output by the power conversion circuit 120 are all around 380V, with a difference of less than 5V between them. The average value of the three-phase AC line voltage amplitudes output by the power conversion circuit 120 is approximately 380V. If the line voltage amplitude between output index A and B is 400V and the reference threshold is 10V, then the output index is 20V larger than the reference index of 380V. The absolute value of the difference between the output index and the reference index exceeds the reference threshold. Therefore, the controller 110 will reduce the internal potential vector reference corresponding to the line voltage amplitude between output index A and B to control the reduction of the line voltage amplitude between output index A and B. As a result, the line voltage amplitude between output index A and B gradually approaches the reference index, ultimately achieving three-phase AC power balance output by the power conversion circuit 120.Alternatively, based on practical experience, a fixed reference amplitude can be set as a reference index. This fixed reference amplitude can be equal to the amplitude of any of the aforementioned phase line voltages or the average value of the three phase line voltage amplitudes, or it can be other values.

[0039] In another embodiment, the power conversion circuit 120 still adopts the three-phase three-wire power conversion circuit shown in Figure 2; the difference between the three-phase output line voltage phase and the reference phase is selected as the output index, and the difference between the three-phase output line voltage phase and the reference phase when the three phases of the AC side of the power converter 100 are balanced is selected as the reference index; wherein, the reference index is the difference between the three-phase output line voltage phase and the reference phase when the three-phase AC terminals of the power conversion circuit 120 are connected to a balanced load, or, the reference index is the average value of the difference between the three-phase output line voltage phase and the reference phase when the three-phase AC terminals of the power conversion circuit 120 are connected to a balanced load, or the reference phase is a reference voltage phase other than the three-phase line voltage in the three-phase AC power that changes periodically with the same period, amplitude and rate of change as any phase line voltage in the three-phase AC power when the three-phase AC terminals of the three-phase three-wire power conversion circuit are connected to a balanced load. As described in the previous embodiment, when the three phases of the AC side of the power converter 100 are balanced, the phases of the line voltages of the three-phase AC power output by the power conversion circuit 120 are uniformly 120° apart. That is, the phases of the line voltages between lines A and B, between lines B and C, and between lines A and C are uniformly 120° apart in sequence. In other words, the phase difference of the three-phase output line voltages is relatively fixed. Therefore, a reference phase can be selected, and the difference between the three-phase output line voltage phase and the reference phase is also relatively fixed. The value of this difference when a balanced load is connected to the three-phase AC terminals of the power conversion circuit 120 is used as a reference index. If the difference between the three-phase output line voltage and the reference phase differs significantly from the reference index, that is, if the absolute value of the difference between the three-phase output line voltage and the reference phase and the reference index is greater than the reference threshold, then the three-phase AC power output by the power conversion circuit 120 can be considered unbalanced. For example, similarly, when the three phases of the AC side of the power converter 100 are balanced, the average value of the difference between the three-phase output line voltages and the reference phase of the power conversion circuit 120 is also relatively fixed. The average value of the difference between the three-phase output line voltages and the reference phase can also be used as a reference index. Alternatively, a manually set reference voltage can be selected. The phase change of this voltage is consistent with the phase changes of the line voltages between lines A and B, between lines B and C, and between lines A and C. Under three-phase balance conditions, the phase difference between this reference voltage and each phase remains constant. For example, it may lead the phase voltage between lines A and N by 10°, lag the phase voltage between lines B and N by 110°, and lag the phase voltage between lines C and N by 230°.

[0040] Furthermore, the reference phase in the aforementioned embodiment can be selected from one of the three-phase output line voltage phases. Thus, due to the principle described above, the line voltage phases between lines A and B, between lines B and C, and between lines A and C are sequentially and uniformly differing by 120°. Taking the line voltage phase between lines A and B as the reference phase, the three-phase output line voltage phases of the power conversion circuit 120 when connected to a balanced load—that is, the differences between the line voltage phases between lines A and B, between lines B and C, and between lines A and C and the reference phase—are 0°, 120°, and 240°, respectively. When the difference between the three-phase output line voltage phases of the power conversion circuit 120 and the reference phase deviates significantly from the aforementioned difference, that is, when the absolute value of the difference between the output index and the reference index exceeds the reference threshold, it can be considered that the three-phase AC power output by the power conversion circuit 120 is unbalanced. For example, if the reference threshold is 10°, and a balanced load is connected to the three-phase AC terminals of the power conversion circuit 120 at a certain moment, the line voltage phase between lines A and B is 90°. However, the actual line voltage phase between lines A and B output by the power conversion circuit 120 is 105°. In this case, the three-phase AC output by the power conversion circuit 120 is considered unbalanced. Since the output line voltage phase of 105° between lines A and B is larger than the reference value of 90°, the controller 110 will control the internal potential vector reference value corresponding to the line voltage phase between lines A and B to decrease. This means the line voltage phase between lines A and B output by the power conversion circuit 120 will shift to the left (phase decrease) to gradually bring the line voltage phase between lines A and B closer to the reference value, ultimately achieving three-phase AC balance output by the power conversion circuit 120.

[0041] It should be noted that the internal potential vector reference value mentioned in this application embodiment refers to the quantity output by the power conversion circuit 120 controlled by the controller 110. The output of the power conversion circuit 120 will change due to the influence of the power grid or load conditions after grid connection or load connection. In this application embodiment, the balance of the three-phase AC output of the power conversion circuit 120 is determined by the electrical parameters of the grid connection point (the position of AC Bus1 in Figure 1) after the power conversion circuit 120 is connected to the grid or load. The electrical parameters of the grid connection point after the power conversion circuit 120 is connected to the grid or load are improved by adjusting the internal potential vector reference value, so that the three-phase AC output of the power conversion circuit 120 reaches a balanced state at the grid connection point.

[0042] Referring again to Figure 3, in one embodiment, the power conversion circuit 120 is a three-phase four-wire power conversion circuit; the output index is the amplitude of the three-phase output phase voltage, and the reference index is the average value of the three-phase output phase voltage amplitude or any one of the three-phase output phase voltage amplitudes. Similar to the previous embodiment, when the three phases on the AC side of the power converter 100 are balanced, the amplitudes of the three-phase AC phase voltages output by the power conversion circuit 120 are equal. Specifically, the amplitudes of the three-phase phase voltages output by the power conversion circuit 120 are equal, that is, the phase voltage amplitudes between lines A and N, between lines B and N, and between lines C and N are equal. Therefore, using the average value of the three-phase output phase voltage amplitude or any one of the three-phase output phase voltage amplitudes as a reference index, and comparing the output index and the reference index, when the difference between their values ​​is large, that is, when the absolute value of the difference between any output index and the reference index is greater than a reference threshold, it can be considered that the three-phase AC power output by the power conversion circuit 120 is unbalanced. For example, assuming the three phases of the power converter 100 are balanced on the AC side, the three phase AC phase voltage amplitudes output by the power conversion circuit 120 are all 220V. At this time, any phase voltage amplitude is selected as a reference index, and the value of the reference index is 220V. If the phase voltage amplitude between the output index A and N lines is 250V and the reference threshold is 10V, then the output index is 30V larger than the reference index 220V. The absolute value of the difference between the output index and the reference index exceeds the reference threshold. Therefore, the controller 110 will reduce the internal potential vector reference corresponding to the phase voltage amplitude between the output index A and N lines to control the phase voltage amplitude between the output index A and N lines to decrease. As a result, the phase voltage amplitude between the output index A and N lines gradually approaches the reference index, and finally the three-phase AC power output by the power conversion circuit 120 is balanced.

[0043] In another embodiment, the power conversion circuit 120 still adopts the three-phase four-wire power conversion circuit shown in Figure 3; the difference between the three-phase output phase voltage phase and the reference phase is selected as the output index, and the difference between the three-phase output phase voltage phase and the reference phase when the three phases of the AC side of the power converter 100 are balanced is selected as the reference index; wherein, the reference index is the difference between the three-phase output phase voltage phase and the reference phase when the three-phase AC terminal of the power conversion circuit 120 is connected to the balanced load, or, the reference index is the average value of the difference between the three-phase output phase voltage phase and the reference phase when the three-phase AC terminal of the power conversion circuit 120 is connected to the balanced load, or the reference phase is a reference voltage phase other than the three-phase phase voltage in the three-phase AC power, which changes periodically with the same period, amplitude and rate of change as any phase voltage in the three-phase AC power when the three-phase AC terminal of the three-phase three-wire power conversion circuit is connected to the balanced load. As described in the previous embodiment, when the three phases of the AC side of the power converter 100 are balanced, the phases of the three-phase AC power output by the power conversion circuit 120 are uniformly 120° apart. That is, the phase voltage phases between lines A and N, between lines B and N, and between lines C and N are uniformly 120° apart. In other words, the phase difference of the three-phase output phase voltages is relatively fixed. Therefore, a reference phase can be selected, and the difference between the three-phase output phase voltage phases and the reference phase is also relatively fixed. This difference is used as a reference index when a balanced load is connected to the three-phase AC terminals of the power conversion circuit 120. If the difference between the three-phase output phase voltages and the reference phases differs significantly from the reference index, that is, if the absolute value of the difference between the three-phase output phase voltages and the reference phases and the reference index is greater than the reference threshold, then the three-phase AC power output by the power conversion circuit 120 can be considered unbalanced. For example, similarly, when the three phases of the AC side of the power converter 100 are balanced, the average value of the difference between the three-phase output phase voltages of the power conversion circuit 120 and the reference phase is also relatively fixed. The average value of the difference between the three-phase output phase voltages and the reference phase can also be used as a reference index. Alternatively, a manually set reference voltage can be selected. The phase change of this voltage is consistent with the phase change patterns of the phase voltages between lines A and N, B and N, and C and N. Under three-phase balance conditions, the phase difference between this reference voltage and each phase remains constant. For example, it may lead the phase voltage between lines A and N by 10°, lag the phase voltage between lines B and N by 110°, and lag the phase voltage between lines C and N by 230°.

[0044] Furthermore, the reference phase in the aforementioned embodiment can be selected from one of the three-phase output phase voltages. Thus, due to the principle described above, the phase voltage phases between lines A and N, between lines B and N, and between lines C and N are sequentially and uniformly differing by 120°. Taking the phase voltage phase between lines A and N as the reference phase, the three-phase output phase voltage phases of the power conversion circuit 120 when connected to a balanced load—that is, the phase voltage phases between lines A and N, between lines B and N, and between lines C and N—are 0°, 120°, and 240° respectively, compared to the reference phase. When the difference between the three-phase output phase voltage phases of the power conversion circuit 120 and the reference phase deviates significantly from the aforementioned difference, that is, when the absolute value of the difference between the output index and the reference index exceeds the reference threshold, it can be considered that the three-phase AC power output by the power conversion circuit 120 is unbalanced. For example, if the reference threshold is 10°, and a balanced load is connected to the three-phase AC terminals of the power conversion circuit 120 at a certain moment, the phase voltage phase between lines A and N is 90°. However, the actual phase voltage phase between lines A and N output by the power conversion circuit 120 is 105°. In this case, the three-phase AC output by the power conversion circuit 120 is considered unbalanced. Since the output specification of 105° phase voltage between lines A and N is larger than the reference specification of 90°, the controller 110 will control the internal potential vector reference value corresponding to the phase voltage phase between lines A and N to decrease. This means the phase voltage phase between lines A and N output by the power conversion circuit 120 will shift to the left (phase decrease) to gradually bring the phase voltage phase between lines A and N closer to the reference specification, ultimately achieving balance in the three-phase AC output by the power conversion circuit 120.

[0045] In one embodiment, the controller 110 is configured to control the internal potential vector reference value corresponding to the output index of the three-phase AC power output by the power conversion circuit 120 that is less than the reference index to increase when the absolute value of the difference between the output index and the reference index exceeds a reference threshold. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index. For example, the controller 110 originally sets the internal potential vector reference values ​​corresponding to the A, B, and C phase voltage phases of the three-phase AC power output by the power conversion circuit 120 to 120°, 240°, and 360°, respectively. When the three phases are balanced, the phases of the three-phase AC power output by the power conversion circuit 120 at the grid connection point are also 120°, 240°, and 360°, respectively. However, due to the influence of unbalanced load, the three-phase AC power output by the power conversion circuit 120 is unbalanced at the grid connection point. That is, the actual phases of the A, B, and C phase voltages at the grid connection point may be 100°, 240°, and 360°, respectively. It can be seen that the phase of the A phase voltage has shifted to the left (decreased). At this time, the reference value of the internal potential vector corresponding to the A phase voltage phase can be increased to shift the phase of the A phase voltage to the right (increase), so that the three-phase AC power output by the power conversion circuit 120 is in a balanced state at the grid connection point.

[0046] Similarly, when the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the controller 110 for the power conversion circuit 120 exceeds the reference threshold, the controller 110 controls the three-phase AC power output by the power conversion circuit 120 to reduce the internal potential vector reference value corresponding to the output index that is less than the reference index. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the more the internal potential vector reference value corresponding to the output index decreases, so that the three-phase AC power output by the power conversion circuit 120 is in a balanced state at the grid connection point.

[0047] This application also provides a control method for a power conversion circuit 120. The specific control flow of this control method is described below with reference to the control flowchart.

[0048] Referring to Figure 4, the first step is S101: determining whether the absolute value of the difference between the output indicator and the reference indicator exceeds the reference threshold. Here, both the output indicator and the reference indicator refer to the relevant indicators of the power conversion circuit 120. If yes, then step S102 is executed: determining whether the output indicator is greater than the reference indicator. If yes, then step S103 is executed: decreasing the internal potential vector reference value corresponding to the output indicator; if no, then step S104 is executed: determining whether the output indicator is less than the reference indicator; if yes, then step S105 is executed: increasing the internal potential vector reference value corresponding to the output indicator.

[0049] It should be noted that the foregoing embodiments are merely one possible condition judgment process. This process may be performed step-by-step in the order of the foregoing embodiments, or it may be performed simultaneously. For example, steps S101 and S102 can actually be performed simultaneously, comparing their magnitudes while calculating the absolute value of the difference between the output index and the reference index. This application does not impose specific limitations on this.

[0050] In addition, for details on how to select output indicators, reference indicators, and how to control the variation of the internal potential vector reference value, please refer to the embodiments related to the controller 110 controlling the power conversion circuit 120 in the previous embodiments.

[0051] The preferred embodiments disclosed above are merely illustrative of this application. The embodiments do not exhaustively describe all details, nor do they limit this application to the specific implementations described. Clearly, many modifications and variations can be made based on the embodiments of this application. These embodiments are selected and specifically described in this application to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application. This application is limited only by the claims and their full scope and equivalents.

Claims

1. A power converter, characterized in that, Includes the controller and a three-phase three-wire power conversion circuit; The controller is used to control the three-phase three-wire power conversion circuit to perform power conversion between DC and three-phase AC. The controller is further configured to, when the absolute value of the difference between the output index of the three-phase AC power output by the three-phase three-wire power conversion circuit and the reference index exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase three-wire power conversion circuit to increase, and / or control the internal potential vector reference value corresponding to the output index that is greater than the reference index in the three-phase AC power output by the three-phase three-wire power conversion circuit to decrease; The output index is the amplitude of one phase line voltage in the three-phase AC power, and the reference index is the average value of the three-phase line voltage amplitudes, a preset fixed reference amplitude, or the amplitude of the middle phase line voltage among the three-phase line voltage amplitudes; or The output index is the difference between the phase of one phase line voltage in the three-phase AC power supply and the phase of the reference phase corresponding to that phase line voltage. The reference index is the difference between the phase of one phase line voltage in the three-phase AC power supply and the phase of the reference phase corresponding to that phase line voltage when the three-phase AC terminals of the three-phase three-wire power conversion circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power supply and the respective reference phases of each phase of the AC power supply. The reference phase is any one phase line voltage in the three-phase AC power supply, or the reference phase is a reference voltage other than the three phase line voltages in the three-phase AC power supply that changes periodically with the same period, amplitude, and rate of change as any one phase line voltage in the three-phase AC power supply when the three-phase AC terminals of the three-phase three-wire power conversion circuit are connected to a balanced load.

2. The power converter according to claim 1, characterized in that, The controller is configured to, when the absolute value of the difference between the output index and the reference index of the three-phase AC power output from the three-phase three-wire power conversion circuit exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index to increase. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

3. The power converter according to claim 1, characterized in that, The controller is configured to, when the absolute value of the difference between the output index and the reference index of the three-phase AC power output from the three-phase three-wire power conversion circuit exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index to decrease. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the decrease in the internal potential vector reference value corresponding to the output index.

4. A power converter, characterized by, It includes a controller and a three-phase four-wire power conversion circuit; the controller is used to control the three-phase four-wire power conversion circuit to perform power conversion between DC and three-phase AC. The controller is further configured to, when the absolute value of the difference between the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit and the reference index exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit that is less than the reference index to be increased, and / or control the internal potential vector reference value corresponding to the output index of the three-phase AC power output by the three-phase four-wire power conversion circuit that is greater than the reference index to be decreased; The output index is the voltage amplitude of one phase of the three-phase AC power, and the reference index is the average value of the three-phase voltage amplitudes, a preset fixed reference amplitude, or the voltage amplitude of the phase with the middle value among the three-phase voltage amplitudes; or The output index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase voltage. The reference index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase voltage when the three-phase AC terminals of the three-phase four-wire power converter circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power and the respective reference phases of each phase of the AC power. The reference phase is any phase voltage in the three-phase AC power, or the reference phase is a reference voltage other than the three-phase phase voltages in the three-phase AC power that changes periodically with the same period, amplitude, and rate of change as any phase voltage in the three-phase AC power when the three-phase AC terminals of the three-phase four-wire power converter circuit are connected to a balanced load.

5. The power converter of claim 4, wherein, The controller is configured to, when the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase four-wire power conversion circuit exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index to increase. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

6. The power converter of claim 4, wherein, The controller is configured to, when the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase four-wire power conversion circuit exceeds the reference threshold, control the internal potential vector reference value corresponding to the output index that is less than the reference index to decrease. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the decrease in the internal potential vector reference value corresponding to the output index.

7. A method of controlling a three-phase three-wire power conversion circuit, characterized by, The three-phase three-wire power conversion circuit is controlled to perform power conversion between DC and three-phase AC; and when the absolute value of the difference between the output index of the three-phase AC output by the three-phase three-wire power conversion circuit and the reference index exceeds the reference threshold, the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase three-wire power conversion circuit that is less than the reference index is increased, and / or, the internal potential vector reference value corresponding to the output index of the three-phase AC output by the three-phase three-wire power conversion circuit that is greater than the reference index is decreased. The output index is the amplitude of one phase line voltage in the three-phase AC power, and the reference index is the average value of the three-phase line voltage amplitudes, a preset fixed reference amplitude, or the amplitude of the middle phase line voltage among the three-phase line voltage amplitudes; or The output index is the difference between the phase of one phase line voltage in the three-phase AC power supply and the phase of the reference phase corresponding to that phase line voltage. The reference index is the difference between the phase of one phase line voltage in the three-phase AC power supply and the phase of the reference phase corresponding to that phase line voltage when the three-phase AC terminals of the three-phase three-wire power conversion circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power supply and the respective reference phases of each phase of the AC power supply. The reference phase is any one phase line voltage in the three-phase AC power supply, or the reference phase is any voltage other than the three phase line voltages in the three-phase AC power supply, such as a reference voltage that periodically changes with the same period, amplitude, and rate of change when the three-phase AC power supply is connected to a balanced load at the three-phase AC terminals of the three-phase three-wire power conversion circuit.

8. The control method of a three-phase three-wire power conversion circuit according to claim 7, characterized by, When the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase three-wire power conversion circuit exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase three-wire power conversion circuit is increased. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

9. The three-phase three-wire power conversion circuit control method according to claim 7, characterized in that, When the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase three-wire power conversion circuit exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase three-wire power conversion circuit is reduced. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the reduction in the internal potential vector reference value corresponding to the output index.

10. A method of controlling a three-phase four-wire power conversion circuit, characterized by, The three-phase four-wire power conversion circuit is controlled to perform power conversion between DC and three-phase AC. Furthermore, when the absolute value of the difference between the output index of the three-phase AC output from the three-phase four-wire power conversion circuit and the reference index exceeds a reference threshold, the internal potential vector reference value corresponding to the output index of the three-phase AC output from the three-phase four-wire power conversion circuit that is less than the reference index is increased, and / or, the internal potential vector reference value corresponding to the output index of the three-phase AC output from the three-phase four-wire power conversion circuit that is greater than the reference index is decreased. The output index is the voltage amplitude of one phase of the three-phase AC power, and the reference index is the average value of the three-phase voltage amplitudes, a preset fixed reference amplitude, or the voltage amplitude of the phase with the middle value among the three-phase voltage amplitudes; or The output index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase voltage. The reference index is the difference between the phase of one phase voltage in the three-phase AC power and the phase of the reference phase corresponding to that phase voltage when the three-phase AC terminals of the three-phase four-wire power converter circuit are connected to a balanced load, or the average of the phase differences between each phase of the three-phase AC power and the respective reference phases of each phase of the AC power. The reference phase is any phase voltage in the three-phase AC power, or the reference phase is a reference voltage other than the three-phase phase voltages in the three-phase AC power that changes periodically with the same period, amplitude, and rate of change as any phase voltage in the three-phase AC power when the three-phase AC terminals of the three-phase four-wire power converter circuit are connected to a balanced load.

11. The method of claim 10, wherein, When the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase four-wire power conversion circuit exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase four-wire power conversion circuit is increased. The smaller the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the increase in the internal potential vector reference value corresponding to the output index.

12. The method of claim 10, wherein, When the absolute value of the difference between the output index and the reference index of the three-phase AC power output by the three-phase four-wire power conversion circuit exceeds the reference threshold, the internal potential vector reference value corresponding to the output index that is less than the reference index in the three-phase AC power output by the three-phase four-wire power conversion circuit is reduced. The greater the difference between the absolute value of the difference between the output index and the reference index and the reference threshold, the greater the reduction in the internal potential vector reference value corresponding to the output index.

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