Three-phase system and method of distributed control thereof

Abstract

A three-phase system and a distributed control method thereof. The three-phase system comprises: three-phase circuits, each phase circuit comprising at least one power conversion unit; at least three phase controllers corresponding to the control of each phase circuit respectively, each of the phase controllers comprising a communication interface, and the at least three phase controllers being communicatively connected to each other through the communication interface; wherein the phase controller of each phase circuit receives information sent by the phase controllers of the other two phase circuits through the communication interface, and adjusts the bridge arm voltage of the at least one power conversion unit in the phase circuit. The three-phase system and the distributed control method thereof solve the problems of three-phase current balance and three-phase direct current voltage stability through the coordination among the three phases. Through the present application, the three phases can be independently controlled, and the control flexibility is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a three-phase system and a distributed control method thereof. BACKGROUND

[0002] Three-phase combined converter refers to a three-phase converter combined by three single-phase systems. Cascade H-bridge (CHB) is a typical three-phase combined converter, which is widely used in the structure of medium and high voltage high power inverters. Cascade H-bridge topology can be applied to SVG (static var compensator), SST (solid state transformer), medium and high voltage energy storage inverters and other products.

[0003] There are two connection methods for three-phase cascade H-bridge, namely Y connection and Δ connection. The core control problem of three-phase combined converter is how to ensure the stability of three-phase DC voltage (i.e. DC-link voltage) and the balance of three-phase grid current when the three-phase DC side load is unbalanced.

[0004] The existing technology in the industry usually adopts centralized control method, that is, the three-phase average DC voltage is feedback controlled by a centralized controller, and on this basis, voltage balance control is added, so that each phase DC voltage tends to be the average value of three-phase voltage. Zero sequence injection method is generally used to balance the three-phase DC voltage, zero sequence current injection method is used for Δ connection system, and zero sequence voltage injection method is used for Y connection system.

[0005] However, the existing centralized control method has low reliability. Once the centralized controller fails or a phase circuit fails, the whole three-phase system stops working and cannot operate stably. SUMMARY

[0006] The purpose of the present application is to provide a three-phase system and a distributed control method thereof, which can solve one or more defects of the prior art.

[0007] In order to achieve the above purpose, the present application provides a three-phase system, characterized in that it comprises: a three-phase circuit, each phase circuit comprising at least one power conversion unit; at least three phase controllers corresponding to the control of each phase circuit, each phase controller comprising a communication interface and the at least three phase controllers being connected to each other in communication through the communication interface; wherein the phase controller of each phase circuit receives information sent by the phase controllers of the other two phase circuits through the communication interface, and adjusts the bridge arm voltage of the at least one power conversion unit in the phase circuit.

[0008] In an embodiment of the present application, the phase controller of each phase circuit receives active power information sent by the phase controllers of the other two phase circuits, and adjusts the bridge arm voltage of the at least one power conversion unit in the phase circuit according to the active power information of each phase circuit and the current phase information or the voltage phase information of the phase circuit.

[0009] In an embodiment of the present application, the three-phase system is a delta-connected three-phase system, and each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive a grid reactive current reference and active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a reactive current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current reference of the phase circuit according to the active current reference of the phase circuit, the reactive current reference of the phase circuit, and voltage phase information of the phase circuit; and a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output a modulation voltage reference of the phase circuit; wherein the modulation voltage references of the three-phase circuit are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

[0010] In an embodiment of the present application, the three-phase system is a delta-connected three-phase system, and each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current instruction of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; a DC voltage balance module configured to generate an AC current reference of the phase circuit according to the AC current instruction of the phase circuit and a zero sequence current; and a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output a modulation voltage reference of the phase circuit; wherein the modulation voltage references of the three-phase circuit are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

[0011] In an embodiment of the present application, each phase controller generates active power information reflecting the active power of the phase circuit according to voltage information reflecting the phase circuit, and receives active power information of the other two phase circuits, and generates the zero sequence current according to the active power information of each phase circuit and the voltage phase information of each phase circuit.

[0012] In an embodiment of the present application, the three-phase system is a Y-connected three-phase system, and each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit; a three-phase current balancing module configured to receive the active current reference of the phase circuit and active current references of other two phase circuits sent by phase controllers of the other two phase circuits, and output a balancing current reference of the phase circuit; an AC current command generation module configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, the balancing current reference of the phase circuit, and voltage phase information of the phase circuit; a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output an output voltage reference of the phase circuit; a DC voltage balancing module configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and a zero sequence voltage; and wherein the modulation voltage references of the three-phase circuit are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

[0013] In an embodiment of the present application, each phase controller generates active power information reflecting active power of the phase circuit according to voltage information reflecting the phase circuit, and receives active power information of other two phase circuits, and generates the zero sequence voltage according to the active power information of each phase circuit and current phase information of each phase circuit.

[0014] In an embodiment of the present application, each phase circuit comprises a plurality of power conversion units connected in series, and the plurality of power conversion units of each phase circuit are connected in series in communication with the corresponding phase controller to form a ring network.

[0015] In an embodiment of the present application, each phase circuit comprises a plurality of power conversion units, intra-phase communication between the plurality of power conversion units of each phase circuit adopts ring communication or bus type communication or star type communication, and inter-phase communication of the three-phase circuit adopts ring communication or bus type communication or star type communication.

[0016] To achieve the above object, the application further provides a three-phase system, characterized in that it comprises: three-phase circuits, each phase circuit comprising at least one power conversion unit; at least three phase controllers respectively corresponding to control each phase circuit; wherein each phase controller is used to generate active power information XA, XB, XC respectively reflecting the active power of the corresponding phase circuit according to voltage information reflecting the corresponding phase circuit; each phase controller is further used to receive active power information reflecting the active power of the other two phase circuits, and generate a zero sequence component according to the active power information XA, XB, XC reflecting the active power of each phase circuit and phase information YA, YB, YC reflecting the current phase or voltage phase of each phase circuit, wherein the zero sequence component = (XA×YA+XB×YB+XC×YC)×K0, wherein K0 is a proportional coefficient; each phase controller is further used to adjust the bridge arm voltage of each power conversion unit in the corresponding phase circuit according to the zero sequence component.

[0017] In another embodiment of the application, the three-phase system is a delta-connected three-phase system, the active power information of each phase circuit is the active current reference of each phase circuit, the phase information of each phase circuit is the voltage phase information of each phase circuit, and each phase controller generates the zero sequence current according to the active current reference reflecting the active power of the corresponding phase circuit and the active current reference reflecting the active power of the other two phase circuits received by the phase controller, and according to the active current reference of each phase circuit and the voltage phase information reflecting the voltage phase of each phase circuit.

[0018] In another embodiment of the application, each phase controller comprises: a DC voltage loop controller used to receive a DC voltage reference and a DC voltage feedback of the corresponding phase circuit and output an active current reference of the corresponding phase circuit; a three-phase current balance module used to receive the active current reference of the corresponding phase circuit and the active current reference of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the corresponding phase circuit; an AC current instruction generation module used to generate an AC current instruction of the corresponding phase circuit according to a grid reactive current reference, the balance current reference of the corresponding phase circuit, and the voltage phase information of the corresponding phase circuit; a DC voltage balance module used to generate an AC current reference of the corresponding phase circuit according to the AC current instruction of the corresponding phase circuit and a zero sequence current; and a current loop controller used to receive the AC current reference of the corresponding phase circuit and a current feedback of the corresponding phase circuit and output a modulation voltage reference of the corresponding phase circuit; wherein the modulation voltage references of the three-phase circuits are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage references.

[0019] In another embodiment of the present application, the three-phase system is a Y-connected three-phase system, the active power information of each phase circuit is an active current reference of the phase circuit, the phase information of each phase circuit is a current phase information of the phase circuit, and each phase controller generates the zero sequence voltage according to the active current reference reflecting the active power of the phase circuit and the current phase information reflecting the current phase of the phase circuit, and receives the active current reference reflecting the active power of the other two phase circuits.

[0020] In another embodiment of the present application, each phase controller comprises: a DC voltage loop controller, configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module, configured to receive the active current reference of the phase circuit and the active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an AC current instruction generation module, configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and a voltage phase information of the phase circuit; a current loop controller, configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output an output voltage reference of the phase circuit; and a DC voltage balance module, configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and a zero sequence voltage; wherein the modulation voltage references of the three-phase circuits are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

[0021] To achieve the above object, the present application further provides a distributed control method of a three-phase system, characterized in that the three-phase system comprises: a three-phase circuit, each phase circuit comprising at least one power conversion unit; and at least three phase controllers corresponding to each phase circuit respectively, each phase controller comprising a communication interface and the at least three phase controllers being connected to each other through the communication interface; wherein the distributed control method comprises:

[0022] when the DC side load of the three-phase system is unbalanced,

[0023] each phase controller generates active power information XA, XB and XC reflecting the active power of the phase circuit according to the voltage information reflecting the voltage of the phase circuit respectively;

[0024] The respective phase controller receives active power information of the other two phase circuits reflecting active power, and generates a zero sequence component according to the active power information XA, XB, XC reflecting active power of the respective phase circuit and phase information YA, YB, YC reflecting current phase or voltage phase of the respective phase circuit, wherein the zero sequence component = (XA×YA+XB×YB+XC×YC)×K0, wherein K0 is a proportional coefficient;

[0025] The respective phase controller adjusts the bridge arm voltage of the power conversion unit in the corresponding phase circuit according to the zero sequence component.

[0026] In another embodiment of the present application, the three-phase system is a delta-connected three-phase system, the active power information of each phase circuit is active current reference of each phase circuit, the phase information of each phase circuit is voltage phase information of each phase circuit, and each phase controller generates the zero sequence current according to the active current reference reflecting active power of the phase circuit and the active current reference reflecting active power of the other two phase circuits, according to the active current reference of the respective phase circuit and the voltage phase information reflecting the voltage phase of the respective phase circuit.

[0027] In another embodiment of the present application, each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and the active current reference of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current instruction of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; a DC voltage balance module configured to generate an AC current reference of the phase circuit according to the AC current instruction of the phase circuit and a zero sequence current; and a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output a modulation voltage reference of the phase circuit; wherein the modulation voltage references of the three-phase circuits are modulated to output the bridge arm voltage references of each phase circuit respectively, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

[0028] In another embodiment of the present application, the three-phase system is a Y-connected three-phase system, the active power information of each phase circuit is active current reference of each phase circuit, the phase information of each phase circuit is current phase information of each phase circuit, and each phase controller generates the zero sequence voltage according to the active current reference reflecting active power of the phase circuit and the active current reference reflecting active power of the other two phase circuits, according to the active current reference of the respective phase circuit and the current phase information reflecting the current phase of the respective phase circuit.

[0029] In yet another embodiment of the present application, each of the phase controllers comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit; a three-phase current balancing module configured to receive the active current reference of the phase circuit and active current references of other two phase circuits sent by phase controllers of the other two phase circuits and output a balancing current reference of the phase circuit; an AC current command generation module configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, the balancing current reference of the phase circuit and voltage phase information of the phase circuit; a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output an output voltage reference of the phase circuit; a DC voltage balancing module configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and a zero sequence voltage; wherein the modulation voltage references of the three-phase circuits are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

[0030] The three-phase system and the distributed control method thereof solve the problems of three-phase current balance and three-phase DC voltage stability through coordination among the three phases. Compared with the centralized control scheme, the single-point failure risk of the controller is reduced, and the three phases can be independently controlled, thereby improving the flexibility of control.

[0031] Additional aspects and advantages of the present application will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the description and examples thereof. BRIEF DESCRIPTION OF DRAWINGS

[0032] The foregoing and other features and advantages of the present application will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0033] Figure 1 Structure schematic diagram of the three-phase system of a preferred embodiment of the present application;

[0034] Figure 2 Circuit schematic diagram of the delta-connected three-phase system of the present application;

[0035] Figure 3A Schematic diagram of the first preferred embodiment of the distributed control method of the delta-connected three-phase system of the present application;

[0036] Figure 3B Schematic diagram of the second preferred embodiment of the distributed control method of the delta-connected three-phase system of the present application;

[0037] Figure 4 General block diagram of the distributed control method of the delta-connected three-phase system of the present application is shown.

[0038] Figure 5 Circuit diagram of the Y-connected three-phase system of the present application;

[0039] Figure 6 Schematic diagram of the distributed control method of the Y-connected three-phase system of the present application;

[0040] Figure 7 General block diagram showing the distributed control method of the Y-connected three-phase system of the present application;

[0041] Figure 8 Structural diagram of the three-phase system of another preferred embodiment of the present application, in which each phase circuit is formed by connecting a plurality of power conversion units in series;

[0042] Figure 9A Distributed control effect of the Δ-connected three-phase system of the present application;

[0043] Figure 9B Distributed control effect of the Y-connected three-phase system of the present application;

[0044] Figure 9C Effect of operating three-phase DC voltage at different values by the distributed control method of the present application. DETAILED DESCRIPTION

[0045] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations can be implemented in any

[0046] When introducing elements / components / etc. described and / or illustrated herein, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements / components unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including" and the like are

[0047] As Figure 1As shown, the three-phase system 100 of a preferred embodiment of the present application comprises three-phase circuits, for example, an A-phase circuit 11, a B-phase circuit 12 and a C-phase circuit 13, wherein each phase circuit can comprise at least one power conversion unit. In Figure 1 In the embodiment shown, each phase circuit comprises one power conversion unit, i.e. the A-phase circuit 11 has only one A-phase converter 111, the B-phase circuit 12 has only one B-phase converter 121, and the C-phase circuit 13 has only one C-phase converter 131. However, it is understood that in other embodiments, each phase circuit can comprise multiple power conversion units, which is not considered as a limitation to the present application.

[0048] The three-phase system 100 of the present application further comprises at least three phase controllers for respectively controlling each phase circuit, for example, the A-phase controller 10, the B-phase controller 20 and the C-phase controller 30 respectively controlling the A-phase circuit 11, the B-phase circuit 12 and the C-phase circuit 13. In the present application, each phase controller 10, 20, 30 comprises a communication interface, and these phase controllers 10, 20, 30 are communicatively connected to each other through the communication interfaces, for example, the A-phase controller 10 and the B-phase controller 20 can be communicatively connected through the communication interfaces to form a communication link L12 for communication coordination between the two, the B-phase controller 20 and the C-phase controller 30 can be communicatively connected through the communication interfaces to form a communication link L23 for communication coordination between the two, and the C-phase controller 30 and the A-phase controller 10 can be communicatively connected through the communication interfaces to form a communication link L31 for communication coordination between the two.

[0049] In the present application, the phase controller of each phase circuit can receive information sent by the phase controllers of the other two phase circuits through the communication interfaces, so as to adjust the bridge arm voltage of the power conversion unit in the phase circuit. For example, the phase controller of each phase circuit can receive active power information sent by the phase controllers of the other two phase circuits, and adjust the bridge arm voltage of the power conversion unit in the phase circuit according to the active power information of each phase circuit and the current phase information or voltage phase information of the phase circuit.

[0050] The three-phase system of the present application is distributedly controlled by using a three-phase distributed control architecture with communication coordination on the basis of three-phase completely decentralized control, i.e. each phase controller controls the respective phase converter, and communication coordination is used between the phase controllers to balance the three-phase grid current and stabilize the three-phase DC voltage.

[0051] In the present application, the above-mentioned three-phase distributed control architecture can be used for both delta-connected three-phase systems and Y-connected three-phase systems. Therefore, the specific content of the present application will be introduced below with respect to Figures 2-7 delta-connected three-phase systems and Y-connected three-phase systems as examples.

[0052] Distributed control of a delta-connected three-phase system:

[0053] like Figure 2 As shown, this illustrates the circuit of a typical combined delta-connected three-phase system according to the present invention. The delta-connected three-phase system is divided into three phases: AB, BC, and CA, each with an H-bridge rectifier circuit. Figure 2 In the middle, v gA v gB v gC For the three-phase power grid voltage, i gA i gB i gC For the three-phase power grid current, i AB i BC i CA V is the current of the three-phase converter. bAB v bBC v dCA V is the bridge arm voltage of the three-phase converter. dcAB v dcBC v dcCA For three-phase DC voltage, P AB P BC P CA This refers to the power of a three-phase load.

[0054] like Figure 3A As shown, this illustrates a first preferred embodiment (reactive current injection method) of the distributed control method for a delta-connected three-phase system according to the present invention. In this embodiment, each phase has its own DC voltage loop and current loop. The following detailed description uses phases AB as an example; the other two phases are similar. dcrAB As the DC voltage reference for phases AB, v dcAB The DC voltage feedback for phases AB is used, and after calculation, it becomes the input to a DC voltage loop controller, which can be, for example, a proportional-integral controller. The output of the DC voltage loop controller generates the active current reference for this phase, i. drAB This serves as the d-axis current reference for phases AB, i.e., the active current reference. Simultaneously, the active current reference for this phase is sent to the other two phases for generating the reactive current reference. The reactive current reference for this phase is... Among them, i qr As a reference for reactive current sent to the grid, this value is consistent for all three phases, while i drCA and i drBCActive current reference sent from CA phase and BC phase respectively. The generation of this reactive current reference is the principle of coordination among three phases: if one phase carries a resistive load, the other two phases can be equipped with certain proportion of capacitive and inductive load respectively to solve the problem of three-phase grid current imbalance. Further, according to the active current reference and the reactive current reference, the AC current reference is generated, i rAB = i drAB cos θ AB - i qrAB sin θ AB , where θ AB is the phase angle of AB phase grid voltage. i AB is the current feedback of AB phase converter. i AB and ir AB are the inputs of the current loop controller after operation. The current loop controller can be a proportional-resonant controller, for example. v gAB = v gA -v gB is the AB phase grid voltage, which is used as a feedforward to eliminate the influence of grid voltage change on current. v gAB and v rAB are the modulation voltage references of AB phase after operation of the current loop controller. The same method is used to generate v rBC and v rCA for the other two phases. The modulation voltage references of three phases are modulated to output the bridge arm voltage.

[0055] As can be seen, in the first preferred embodiment shown in Figure 3A , each phase controller in the delta-connected three-phase system can include: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit. A three-phase current balancing module configured to receive a grid reactive current reference and active current references of other two phase circuits sent by phase controllers of the other two phase circuits and output a reactive current reference of the phase circuit. An AC current command generation module configured to generate an AC current reference of the phase circuit according to the active current reference of the phase circuit, the reactive current reference of the phase circuit, and voltage phase information of the phase circuit. A current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output a modulation voltage reference of the phase circuit. The modulation voltage references of three phase circuits are modulated to output bridge arm voltage references of each phase circuit, and the bridge arm voltage of each phase circuit can be adjusted according to the bridge arm voltage reference. As shown in Figure 3B , a second embodiment (zero sequence current injection method) of the distributed control method of the delta-connected three-phase system is shown, which is similar to Figure 3AThe difference in the reactive current injection method shown lies in the implementation of the coordination part. The method for obtaining the three-phase active current reference is the same as in the first preferred embodiment, and will not be repeated here. The three-phase active current references are averaged to obtain the balance current reference for that phase, i.e. Then, based on the phase balance current reference, the phase information of the current phase, and the reactive current reference, an AC current command is generated, that is, Injecting zero-sequence current balances the three-phase DC voltages. The expression for the zero-sequence current is:

[0056]

[0057] Among them, i drAB The output of the DC voltage loop for phases AB is θ, which serves as the active current reference for phases AB and reflects the active power information of phases AB. AB This represents the grid voltage angle for phases AB, reflecting the phase information of the grid voltage for phases AB. The variables corresponding to the subscripts BC and CA have similar meanings to those for phases AB. Since the zero-sequence current circulates among the three phases but does not flow into the grid, it does not affect the balance of the three-phase grid current.

[0058] This shows that, Figure 3B In the second embodiment shown, each phase controller in the delta-connected three-phase system may include: a DC voltage loop controller, used to receive the DC voltage reference and DC voltage feedback of the phase circuit, and output the active current reference of the phase circuit; a three-phase current balancing module, used to receive the active current reference of the phase circuit and the active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output the balanced current reference of the phase circuit; an AC current command generation module, used to generate the AC current command of the phase circuit based on the grid reactive current reference, the balanced current reference of the phase circuit, and the voltage phase information of the phase circuit; a DC voltage balancing module, used to generate the AC current reference of the phase circuit based on the AC current command and the zero-sequence current; and a current loop controller, used to receive the AC current reference of the phase circuit and the current feedback of the phase circuit, and output the modulation voltage reference of the phase circuit. The modulation voltage references of the three-phase circuits are modulated and output as bridge arm voltage references for each phase circuit, and the bridge arm voltage of each phase circuit can be adjusted according to the bridge arm voltage references.

[0059] Furthermore, in this embodiment, each phase controller generates active power information reflecting the active power of its own phase circuit based on the voltage information of its own phase circuit, and receives active power information from the other two phase circuits. The zero-sequence current is generated based on the active power information reflecting each phase circuit and the voltage phase information of each phase circuit.

[0060] above Figure 3A and Figure 3BThe control effects of the two embodiments are equivalent. Both can make three-phase current balance and three-phase DC voltage stable.

[0061] Figure 4 A general block diagram of the distributed control of the delta-connected three-phase system of the present application is shown. Wherein i drAB , i drCA , i drBC , and i r0 are the quantities that need to be communicated and coordinated. The block diagram generalizes the two aforementioned embodiments, in which the delta-connected three-phase system comprises a DC voltage loop controller, a three-phase current balance module, an AC current reference generation module, a DC voltage balance module, and a current loop controller.

[0062] Distributed control of the wye-connected three-phase system:

[0063] Figure 5 A circuit of the wye-connected three-phase system of the present application is shown. In the figure, v gA , v gB , v gC are the three-phase grid voltages, i A , i B , i C are the three-phase grid currents, which are also the three-phase converter currents, v bA , v bB , v bC are the three-phase converter bridge arm voltages, v dcA , v dcB , v dcC are the three-phase DC voltages, and P A , P B , P C are the three-phase load powers.

[0064] Figure 6 A distributed control block diagram of the wye-connected three-phase system of the present application is shown. In this embodiment, each phase has its own DC voltage loop and current loop. The A phase is taken as an example for detailed description below, and the other two phases are similar. v dcrA is the DC voltage reference of the A phase, and v dcA is the DC voltage feedback of the A phase. Both are input to the DC voltage loop controller after operation, which can be a proportional-integral controller for example. The output of the DC voltage loop controller generates the active current reference i drA of the phase. Then, the active current references i drB , i drC of the other two phases are received to generate the balance current reference i The average of the three-phase active current reference is to make the three-phase current balanced. Further, according to the balanced current reference, the voltage phase information of the phase A and the reactive current reference, the alternating current reference i rA = i drComA cos θ A - o qr sin θ A , where θ A is the phase angle of the phase A grid voltage, reflecting the voltage phase information of the phase A. i A is the current feedback of the phase A converter. The alternating current reference of the phase A and the current feedback of the phase A converter are operated as the input of the current loop controller (Current Controller), which can be a proportional resonant controller, for example.v gA is the phase A grid voltage, which is injected into the output of the current loop controller as a feedforward to eliminate the influence of the grid voltage change on the current. In addition, the zero sequence voltage v b0 is injected to make the three-phase DC voltage balanced. The expression of the injected zero sequence voltage is:

[0065] v b0 = k0(i A i dr A+i B i drB +i C i drC )

[0066] where i A , i B , i C are the current feedbacks of the three phases, reflecting the phase information of the current of each phase, i drA , i drB , i drC are the DC voltage loop controller outputs of each phase, and i gM is a proportional coefficient, which can be a constant or can be taken according to the current amplitude, for example, the smaller the current amplitude, the larger the value of k0, and the preferred value formula of k0 is where V gM is the peak value of the grid voltage. It can be seen from the expression of the injected zero sequence voltage that the phase whose active power is large is closer to the phase of the current. When the three-phase current and the three-phase grid voltage are balanced, the injected zero sequence voltage makes the three-phase bridge arm voltage unbalanced, and the power absorbed by the bridge arm is unbalanced to cope with the imbalance of the DC side load power, thereby maintaining the stability of the DC voltage. Since the injected zero sequence voltage acts in the Y-connected three-phase system and does not generate zero sequence current, it does not affect the balance of the three-phase current. The output voltage reference v rAPand zero sequence voltage v b0 superimposed, finally generating the modulation voltage reference v rA , v rB , v rC , after subsequent modulation, outputting the bridge arm voltage.

[0067] Figure 7 A general block diagram of the distributed control of the Y-connected three-phase system of the present application is shown. Wherein i drA , i drB , i drC , and v b0 are the quantities that need to be communicated and coordinated. Wherein the Y-connected three-phase system comprises a DC voltage loop controller, a three-phase current balance module, an AC current reference generation module, a current loop controller, and a DC voltage balance module. The difference from the coordination unit of the delta-connected three-phase system is that the zero sequence voltage of the Y-connected three-phase system is added to the output of the current loop.

[0068] It can be seen that each phase controller of the Y-connected three-phase system of the present application can comprise: a DC voltage loop controller, configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit. A three-phase current balance module, configured to receive the active current reference of the phase circuit and active current references of other two phase circuits sent by phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit. An AC current reference generation module, configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit. A current loop controller, configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output an output voltage reference of the phase circuit. A DC voltage balance module, configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and a zero sequence voltage. Wherein the modulation voltage references of the three-phase circuit are respectively outputted as bridge arm voltage references of each phase circuit after modulation, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

[0069] In the present embodiment, each phase controller generates active power information reflecting the active power of the phase circuit according to voltage information reflecting the phase circuit, and receives active power information of other two phase circuits, and generates the zero sequence voltage according to the active power information reflecting each phase circuit and current phase information reflecting each phase circuit.

[0070] The above is the distributed control implementation for the case where each phase circuit has only one converter. However, it can be understood that, as Figure 8As shown, when each phase circuit 11, 12, 13 contains multiple power conversion units 111, 121, 121, i.e. formed by multiple converter units CELL1-CELLN in series, such as a three-phase cascaded H-bridge system, a controller implementation architecture as shown can be adopted. Figure 8 As shown, when each phase circuit 11, 12, 13 contains multiple power conversion units 111, 121, 121, i.e. formed by multiple converter units CELL1-CELLN in series, such as a three-phase cascaded H-bridge system, a controller implementation architecture as shown can be adopted.

[0071] As shown, when each phase circuit 11, 12, 13 contains multiple power conversion units 111, 121, 121, i.e. formed by multiple converter units CELL1-CELLN in series, such as a three-phase cascaded H-bridge system, a controller implementation architecture as shown can be adopted. Figure 8 As shown in the embodiment, the multiple converter units (i.e. power conversion units) of each phase circuit and the corresponding phase controller are connected in series in communication and form a ring network, and the multiple converter units within each phase circuit can adopt ring communication, and the phase controllers can also adopt ring communication. Of course, it can be understood that the intra-phase communication between the multiple power conversion units of each phase circuit can also adopt bus-type communication or star-type communication, and the inter-phase communication of the phase circuits can also adopt bus-type communication or star-type communication, which does not limit the present application.

[0072] The technical effects of the present application are as follows:

[0073] Figure 9A The distributed control effect of the delta-connected three-phase system of the present application is shown, in which the uppermost channel (Vdc) is the three-phase DC voltage, the middle channel (Igline) is the three-phase grid current, and the lowermost channel (Iphase) is the three-phase converter bridge arm current. L1, L2, and L3 represent the AB, BC, and CA three phases, respectively. The waveforms in the figure are obtained under the condition that the three-phase DC side loads are unbalanced, and the AB, BC, and CA three-phase DC side load currents are 3A, 1A, and 5A, respectively. Before 0.2s, three-phase completely independent distributed control is adopted, and it can be seen that the three-phase grid current and the three-phase converter grid current are both unbalanced, which is caused by the different three-phase load powers. The average value of the three-phase DC voltage is balanced, and the amplitude of the twice-frequency fluctuation is different. After 0.2s, the distributed control provided by the present application is adopted, and through coordinated control, the three-phase grid current is balanced, and at the same time, the three-phase DC voltage is also balanced, although the three-phase converter bridge arm current is still unbalanced. As long as the three-phase grid current is balanced, it meets the requirements of the grid, and therefore the method provided by the present application can meet the requirements of the grid.

[0074] Figure 9BThe distributed control effect of the Y-connected three-phase system of the present application is shown, in which the uppermost channel (Vdc) is the three-phase DC voltage, the middle channel (Ig) is the three-phase grid current, and the lowermost channel (Vb) is the three-phase converter leg voltage and its zero sequence voltage. L1, L2, L3 represent the AB, BC, and CA three phases respectively, and L4 represents the zero sequence voltage. Before 0.18s, the set working condition is DC load balance, and the system can be stable without the coordinated control of the present application, but after 0.18s, the working condition is set to three-phase DC side load imbalance, and the DC side currents are 3A, 2A, and 4A respectively. At this time, it can be seen that the three-phase DC voltage cannot be stable. After 0.2s, the distributed control provided by the present application is adopted, and through coordination and injection of the zero sequence voltage, it can be seen that the three-phase leg voltages are no longer balanced, and they act with the three-phase balanced grid current to generate unbalanced leg power to cope with the different load powers on the DC side, so as to make the three-phase DC voltage stable and balanced, and the three-phase grid current also balanced.

[0075] Since the three-phase DC voltage of the present application is controlled respectively, when the given values of the three-phase DC voltage are different, it can also work stably, which is difficult to achieve by centralized control, because the centralized DC voltage ring has only one, and it is difficult to give three different DC voltage references respectively. The three-phase system of the present application can work in the condition that the given values of the three-phase DC voltage are different in a distributed control manner, for example, the three-phase battery voltages are different in photovoltaic applications, and the effect is as shown in Figure 9C , in which the three-phase DC voltages can work at 1680V, 1580V, and 1480V respectively.

[0076] The present application further provides a three-phase system, which comprises: three-phase circuits, each phase circuit comprising at least one power conversion unit; and at least three phase controllers respectively corresponding to control each phase circuit. Each phase controller is configured to generate active power information XA, XB, XC reflecting the active power of the corresponding phase circuit according to voltage information reflecting the corresponding phase circuit. Each phase controller is further configured to receive active power information reflecting the active power of the other two phase circuits, and generate a zero sequence component according to the active power information XA, XB, XC reflecting the active power of each phase circuit and phase information YA, YB, YC reflecting the current phase or voltage phase of each phase circuit, wherein the zero sequence component = (XA×YA+XB×YB+XC×YC)×K0, wherein K0 is a proportional coefficient. Each phase controller is further configured to adjust the leg voltage of each power conversion unit in the corresponding phase circuit according to the zero sequence component.

[0077] Preferably, the three-phase system can be a delta-connected three-phase system as shown in Figure 2 , and as shown in Figure 4 , the active power information of each phase circuit can be the active current reference i drAB , idrBC drCA The phase information of each phase circuit can be the voltage phase information θ AB BC CA Each of the phase controllers can generate the zero sequence current i drAB drBC drCA based on the active current reference i AB BC CA of the respective phase circuit, and the voltage phase information θ r0 .

[0078] More specifically, each phase controller in the delta-connected three-phase system can include: a DC voltage loop controller configured to receive a DC voltage reference v dcrAB dcrBC dcrCA of the phase circuit, and a DC voltage feedback v dcAB dcBC dcCA of the phase circuit, and output an active current reference i drAB drAB drCA of the phase circuit; a three-phase current balancing module configured to receive the active current reference i drComAB drComBC drComCA of the phase circuit, and the active current references i qr drComAB drComBC drComCA of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balancing current reference i AB BC CA of the phase circuit; an AC current command generation module configured to generate an AC current command i rABP rBCP rCAP of the phase circuit based on a grid reactive current reference I rABP rBCP rCAP , the balancing current reference i r0 of the phase circuit, and the voltage phase information θ rAB rBC rCA ​​​​​​​​​​​​​​​​​​​​​​​​​​The current loop controller is used to receive the AC current reference i of this phase circuit. rAB i rBC i rCA and the current feedback i of the phase circuit AB i BC i CA And output the modulation voltage reference v of this phase circuit. rAB v rBC v rCA Among them, the modulation voltage reference v of the three-phase circuit rAB v rBC v rCA After modulation, the bridge arm voltage reference for each phase circuit is output, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

[0079] Preferably, the three-phase system can be as follows: Figure 5 The Y-connected three-phase system shown is as follows: Figure 7 As shown, the active power information for each phase circuit can be represented by the active current reference i for each phase circuit. drA i drB i drC The phase information of each phase circuit can be the current phase information i of each phase circuit. A i B i C Each phase controller can use the active current reference reflecting the active power of its own phase circuit, and receive active current references reflecting the active power of the other two phase circuits, and then use the active current references reflecting the active power of each phase circuit. drA i drB i drC and current phase information i reflecting the current phase of each phase circuit A i B i C To generate the zero-sequence voltage v b0 .

[0080] More specifically, each phase controller in the Y-connected three-phase system may include: a DC voltage loop controller for receiving a DC voltage reference v for that phase circuit. dcrA v dcrB v dcrC and DC voltage feedback v dc v dcB v dcC It outputs the active current reference i of the phase circuit. drA i drB i drC The three-phase current balancing module receives the active current reference of this phase circuit and the active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and outputs the balanced current reference i of this phase circuit.drComA i drComB i drComC The AC current command generation module is used to generate AC current based on a power grid reactive current reference I. qr The balancing current reference i of this phase circuit drComA i drComB i drComC and the voltage phase information θ of the phase circuit. A θ B θ C The AC current reference i for generating this phase circuit rA i rB i rC The current loop controller is used to receive the AC current reference i of this phase circuit. rA i rB i rC and the current feedback i of the phase circuit A i B i C And output the reference voltage v of this phase circuit. rAP v rBP v rCP DC voltage balancing module, used to balance the output voltage of this phase circuit based on the reference voltage V. rAP v rBP v rCP and zero-sequence voltage v b0 The modulation voltage reference v of this phase circuit is generated. rA v rB v rC Among them, the modulation voltage reference v of the three-phase circuit rA v rB v rC After modulation, the bridge arm voltage reference for each phase circuit is output, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

[0081] Accordingly, the present invention provides a distributed control method for a three-phase system, wherein the three-phase system includes: a three-phase circuit, each phase circuit including at least one power conversion unit; at least three phase controllers, each corresponding to control each phase circuit, each phase controller including a communication interface, and the at least three phase controllers communicating with each other through the communication interface. The distributed control method includes:

[0082] When the DC-side load of the three-phase system is unbalanced

[0083] Each phase controller generates active power information XA, XB, and XC, reflecting the active power of its respective phase circuit, based on the voltage information of that phase circuit.

[0084] The respective phase controller receives active power information of the other two phase circuits reflecting active power, and generates a zero sequence component according to the active power information XA, XB, XC reflecting active power of the respective phase circuit and phase information YA, YB, YC reflecting current phase or voltage phase of the respective phase circuit, wherein the zero sequence component = (XA×YA+XB×YB+XC×YC)×K0, wherein K0 is a proportional coefficient;

[0085] The respective phase controller adjusts the bridge arm voltage of the power conversion unit in the corresponding phase circuit according to the zero sequence component.

[0086] The three-phase system can be a delta-connected three-phase system, and the active power information of each phase circuit can be an active current reference of each phase circuit, and the phase information of each phase circuit can be voltage phase information of each phase circuit. Each phase controller can generate the zero sequence current according to the active current reference reflecting active power of the phase circuit and the active current reference reflecting active power of the other two phase circuits received by the other two phase controllers, according to the active current reference reflecting active power of the respective phase circuit and the voltage phase information reflecting the voltage phase of the respective phase circuit.

[0087] More specifically, each phase controller in the delta-connected three-phase system can include: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and the active current reference of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current instruction of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; a DC voltage balance module configured to generate an AC current reference of the phase circuit according to the AC current instruction of the phase circuit and a zero sequence current; and a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output a modulation voltage reference of the phase circuit; wherein the modulation voltage references of the three-phase circuits are modulated to output the bridge arm voltage references of each phase circuit respectively, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

[0088] The three-phase system can also be a Y-connected three-phase system, and the active power information of each phase circuit can be an active current reference of each phase circuit, and the phase information of each phase circuit can be current phase information of each phase circuit. Each phase controller can generate the zero sequence voltage according to the active current reference reflecting active power of the phase circuit and the active current reference reflecting active power of the other two phase circuits received by the other two phase controllers, according to the active current reference reflecting active power of the respective phase circuit and the current phase information reflecting the current phase of the respective phase circuit.

[0089] More specifically, each phase controller in the Y-connected three-phase system can include: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit; a three-phase current balancing module configured to receive the active current reference of the phase circuit and active current references of other two phase circuits sent by phase controllers of the other two phase circuits, and output a balancing current reference of the phase circuit; an AC current command generation module configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, the balancing current reference of the phase circuit, and voltage phase information of the phase circuit; a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output an output voltage reference of the phase circuit; a DC voltage balancing module configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and a zero sequence voltage; and wherein the modulation voltage references of the three phase circuits are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

[0090] In summary, the three-phase system and the distributed control method thereof solve the problems of three-phase current balancing and three-phase DC voltage stability through communication coordination among the three phases. Compared with the centralized control scheme, the single-point failure risk of the controller is reduced, and the three phases can be independently controlled, thereby improving the flexibility of control.

[0091] The exemplary embodiments of this application are specifically shown and described above. It is to be understood that the application is not limited to the disclosed embodiments, rather, the application is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A three-phase system, characterized in that, The application relates to a three-phase system, comprising: a three-phase circuit, each phase circuit comprising at least one power conversion unit; at least three phase controllers respectively corresponding to each phase circuit, each phase controller comprising a communication interface, and the at least three phase controllers being communicatively connected to each other through the communication interface; wherein the phase controller of each phase circuit receives information sent by the phase controllers of the other two phase circuits through the communication interface, and adjusts the bridge arm voltage of the at least one power conversion unit in the phase circuit, wherein each phase controller is configured to generate active power information XA, XB, XC reflecting the active power of the corresponding phase circuit according to voltage information reflecting the corresponding phase circuit; each phase controller is further configured to receive active power information of the other two phase circuits, and generate a zero sequence component according to the active power information XA, XB, XC reflecting the active power of each phase circuit and phase information YA, YB, YC reflecting the current phase or voltage phase of each phase circuit, wherein the zero sequence component=(XA*YA+XB*YB+XC*YC)*K0, wherein K0 is a proportional coefficient; each phase controller is further configured to adjust the bridge arm voltage of each power conversion unit in the corresponding phase circuit according to the zero sequence component.

2. The three-phase system of claim 1, wherein, The three-phase system is a delta-connected three-phase system, and each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current instruction of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; a DC voltage balance module configured to generate an AC current reference of the phase circuit according to the AC current instruction of the phase circuit and a zero sequence current; a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit, and output a modulation voltage reference of the phase circuit; wherein the modulation voltage reference of the three-phase circuit is modulated to output a bridge arm voltage reference of each phase circuit, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

3. The three-phase system of claim 2, wherein, Each phase controller generates active power information reflecting the active power of the corresponding phase circuit according to voltage information reflecting the corresponding phase circuit, receives active power information of the other two phase circuits, and generates the zero sequence current according to the active power information of each phase circuit and voltage phase information of each phase circuit.

4. The three-phase system of claim 1, wherein, The three-phase system is a Y-connected three-phase system, and each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current instruction of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; The AC current instruction generation module is configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, a balanced current reference of the phase circuit, and voltage phase information of the phase circuit; The current loop controller is configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output an output voltage reference of the phase circuit; The DC voltage balancing module is configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and a zero sequence voltage. The modulation voltage reference of the three-phase circuit is modulated to output a bridge arm voltage reference of each phase circuit, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

5. The three-phase system of claim 4, wherein, Each phase controller generates active power information reflecting the active power of the corresponding phase circuit according to voltage information reflecting the voltage of the corresponding phase circuit, receives active power information of the other two phase circuits, and generates the zero sequence voltage according to the active power information reflecting the active power of each phase circuit and phase information reflecting the current phase or voltage phase of each phase circuit.

6. The three-phase system according to any one of claims 1 to 5, characterized in that Each phase circuit includes a plurality of power conversion units, and the plurality of power conversion units are connected in series. The plurality of power conversion units of each phase circuit are connected in series with the corresponding phase controller to form a ring network.

7. The three-phase system of claim 1, wherein, Each phase circuit includes a plurality of power conversion units, and the inter-phase communication between the plurality of power conversion units of each phase circuit adopts ring communication or bus-type communication or star-type communication, and the inter-phase communication of the three-phase circuit adopts ring communication or bus-type communication or star-type communication.

8. A three-phase system, characterized by The three-phase system includes: Each phase circuit includes at least one power conversion unit; At least three phase controllers correspond to control each phase circuit; Each phase controller generates active power information XA, XB, XC reflecting the active power of the corresponding phase circuit according to voltage information reflecting the voltage of the corresponding phase circuit. Each phase controller also receives active power information of the other two phase circuits reflecting the active power, and generates a zero sequence component according to the active power information XA, XB, XC reflecting the active power of each phase circuit and phase information YA, YB, YC reflecting the current phase or voltage phase of each phase circuit, wherein The zero sequence component=(XA×YA+XB×YB+XC×YC)×K0, wherein K0 is a proportional coefficient. Each phase controller also adjusts the bridge arm voltage of each power conversion unit in the corresponding phase circuit according to the zero sequence component.

9. The three-phase system of claim 8, wherein, The three-phase system is a ∆-connected three-phase system, the active power information of each phase circuit is an active current reference of each phase circuit, the phase information of each phase circuit is voltage phase information of each phase circuit, each phase controller generates an active current reference reflecting the active power of the corresponding phase circuit according to the active current reference, receives active current references of the other two phase circuits reflecting the active power, and generates a zero sequence current according to the active current reference reflecting the active current of each phase circuit and voltage phase information reflecting the voltage phase of each phase circuit.

10. The three-phase system of claim 9, wherein, Each phase controller includes: The DC voltage loop controller is configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit. a three-phase current balance module configured to receive the active current reference of the phase circuit and the active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an alternating current instruction generation module configured to generate an alternating current reference of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; a direct current voltage balance module configured to generate an alternating current reference of the phase circuit according to the alternating current instruction of the phase circuit and the zero sequence current; a current loop controller configured to receive the alternating current reference of the phase circuit and a current feedback of the phase circuit, and output a modulation voltage reference of the phase circuit; wherein the modulation voltage references of the three-phase circuits are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

11. The three-phase system of claim 8, wherein, The three-phase system is a Y-connected three-phase system, the active power information of each phase circuit is an active current reference of each phase circuit, the phase information of each phase circuit is current phase information of each phase circuit, and each phase controller generates a zero sequence voltage according to the active current reference reflecting the active power of the phase circuit and the active current references reflecting the active power of the other two phase circuits.

12. The three-phase system of claim 11, wherein, Each phase controller comprises: a direct current voltage loop controller configured to receive a direct current voltage reference and a direct current voltage feedback of the phase circuit, and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and the active current references of the other two phase circuits sent by the phase controllers of the other two phase circuits, and output a balance current reference of the phase circuit; an alternating current instruction generation module configured to generate an alternating current reference of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and voltage phase information of the phase circuit; a current loop controller configured to receive the alternating current reference of the phase circuit and a current feedback of the phase circuit, and output an output voltage reference of the phase circuit; a direct current voltage balance module configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and the zero sequence voltage; wherein the modulation voltage references of the three-phase circuits are modulated to output bridge arm voltage references of each phase circuit respectively, and the bridge arm voltages of each phase circuit are adjusted according to the bridge arm voltage references.

13. A method of distributed control of a three-phase system, characterized by, The three-phase system comprises: three-phase circuits, each phase circuit comprising at least one power conversion unit; at least three phase controllers corresponding to control each phase circuit respectively, each phase controller comprising a communication interface, and the at least three phase controllers are connected to each other through the communication interface; wherein the distributed control method comprises: when the direct current side load of the three-phase system is unbalanced, each phase controller generates active power information XA, XB and XC reflecting the active power of the phase circuit according to voltage information reflecting the voltage of the phase circuit respectively; The active power information reflecting the active power of the other two phase circuits is received by each phase controller, and a zero sequence component is generated according to the active power information XA, XB, XC reflecting the active power of each phase circuit and the phase information YA, YB, YC reflecting the current phase or voltage phase of each phase circuit, wherein The zero sequence component = (XA×YA+XB×YB+XC×YC)×K0, wherein K0 is a proportional coefficient; The bridge arm voltage of each power conversion unit in the corresponding phase circuit is adjusted according to the zero sequence component by each phase controller.

14. The distributed control method of claim 13, wherein, The three-phase system is a ∆-connected three-phase system, the active power information of each phase circuit is the active current reference of each phase circuit, the phase information of each phase circuit is the voltage phase information of each phase circuit, and each phase controller generates a zero sequence current according to the active current reference reflecting the active power of the corresponding phase circuit and the active current reference reflecting the active power of the other two phase circuits received by the phase controller, according to the active current reference reflecting the active power of each phase circuit and the voltage phase information reflecting the voltage phase of each phase circuit.

15. The distributed control method of claim 14, wherein, Each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and the active current reference of the other two phase circuits sent by the phase controllers of the other two phase circuits and output a balance current reference of the phase circuit; an AC current instruction generation module configured to generate an AC current instruction of the phase circuit according to a grid reactive current reference, the balance current reference of the phase circuit, and the voltage phase information of the phase circuit; a DC voltage balance module configured to generate an AC current reference of the phase circuit according to the AC current instruction of the phase circuit and the zero sequence current; a current loop controller configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output a modulation voltage reference of the phase circuit; wherein the modulation voltage references of the three-phase circuits are modulated to output the bridge arm voltage references of each phase circuit respectively, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

16. The distributed control method of claim 13, wherein, The three-phase system is a Y-connected three-phase system, the active power information of each phase circuit is the active current reference of each phase circuit, the phase information of each phase circuit is the current phase information of each phase circuit, and each phase controller generates a zero sequence voltage according to the active current reference reflecting the active power of the corresponding phase circuit and the active current reference reflecting the active power of the other two phase circuits received by the phase controller, according to the active current reference reflecting the active power of each phase circuit and the current phase information reflecting the current phase of each phase circuit.

17. The distributed control method of claim 16, wherein, Each phase controller comprises: a DC voltage loop controller configured to receive a DC voltage reference and a DC voltage feedback of the phase circuit and output an active current reference of the phase circuit; a three-phase current balance module configured to receive the active current reference of the phase circuit and the active current reference of the other two phase circuits sent by the phase controllers of the other two phase circuits and output a balance current reference of the phase circuit; The AC current instruction generation module is configured to generate an AC current reference of the phase circuit according to a grid reactive current reference, a balanced current reference of the phase circuit, and voltage phase information of the phase circuit; The current loop controller is configured to receive the AC current reference of the phase circuit and a current feedback of the phase circuit and output an output voltage reference of the phase circuit; The DC voltage balancing module is configured to generate a modulation voltage reference of the phase circuit according to the output voltage reference of the phase circuit and the zero sequence voltage; The modulation voltage reference of the three-phase circuit is modulated to output a bridge arm voltage reference of each phase circuit, and the bridge arm voltage of each phase circuit is adjusted according to the bridge arm voltage reference.

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