Current balancing method and system of reconfiguration type vehicle-mounted charging system

Abstract

The invention relates to the technical field of vehicle-mounted charging, discloses a current balancing method and system of a reconfiguration type vehicle-mounted charging system, and provides a double-sequence decoupling independent regulation and control strategy for solving the problems of inductance imbalance, current asymmetry and direct current side voltage harmonic caused by motor winding multiplexing in an existing electric drive multiplexing scheme. Decomposing the three-phase unbalanced current into positive and negative sequence components, converting the positive and negative sequence components into a d-q coordinate system through coordinate transformation, eliminating inter-axis coupling through feedforward decoupling, and performing independent closed-loop control on the positive and negative sequence current; and carrying out Park inverse transformation superposition on the decoupled d-q reference voltage to generate a total control voltage so as to realize three-phase current equalization and unity power factor operation. According to the invention, negative-sequence harmonics are effectively suppressed, and the charging stability and efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of on-board charging technology, and in particular to a current balancing method and system for a reconfigurable on-board charging system. Background Technology

[0002] With the vigorous promotion of energy conservation, emission reduction, and the development plan for the new energy vehicle industry, electric vehicles have experienced rapid development due to their zero-emission driving advantages. Correspondingly, with the rapid increase in electric vehicles, charging issues have gradually become prominent. Therefore, based on the concept of charging-reuse, an electric drive reuse-type on-board charging system has been proposed. By reusing the motor windings, high-power inverter, and control circuit of the electric drive system, it can perform both driving and charging functions in a time-sharing manner, offering significant advantages in terms of cost, power level, and power density.

[0003] Existing methods typically reuse motor windings, but using multiplexed motor windings as filter inductors requires keeping the motor stationary, meaning the synthesized magnetomotive force (MOMF) should not cause rotation. Current system topologies based on multiphase permanent magnet synchronous motors primarily achieve this by changing the phase sequence of the motor windings to create a pulsating MOMF, thus keeping the motor stationary during charging. However, using all motor windings as AC-side filter inductors results in a limited output voltage regulation range, failing to meet the demands of low or high charging voltages.

[0004] In charging mode, the system's operating modes can be divided into two main categories: voltage source type and current source type. Compared with the current source type, the voltage source type has advantages such as simple structure, high energy storage efficiency, low loss, fast dynamic response, and convenient control; at the same time, it can meet the rated charging voltage requirements of electric vehicles. Therefore, the voltage source type has always been a focus of research and application.

[0005] Currently, common control methods for electric drive-reusable on-board charging systems include three categories: direct power control, model predictive control, and PI dual-loop control. Compared to the first two, the dual-loop control method transforms the three-phase AC current in the ABC coordinate system to the synchronous dq coordinate system, then decouples the dq-axis currents and controls them separately. By controlling and adjusting the q-axis current to 0, the system operates at unity power factor. This method has advantages such as simple control structure, fast dynamic response, and high current control accuracy. To ensure stable charging of the motor, a relatively stable DC output voltage is required. However, in practice, there are problems such as three-phase voltage imbalance and AC-side equivalent inductance imbalance caused by the motor's self-inductance and mutual inductance. These problems lead to AC-side current imbalance, which in turn causes harmonics in the DC-side output voltage, affecting charging stability.

[0006] In summary, existing solutions suffer from current imbalance caused by imbalanced equivalent inductance on the AC side and asymmetrical three-phase voltage when reusing components. Furthermore, existing control methods are mostly designed for ideal symmetrical operating conditions and are insufficient in suppressing negative sequence components and inter-axis coupling. They are unable to fundamentally solve the problems caused by current imbalance, such as DC side voltage harmonics, reduced charging efficiency, and decreased system stability, resulting in a decline in the operating performance of the on-board charging system. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is to overcome the current imbalance caused by the imbalance of equivalent inductance on the AC side and the asymmetry of three-phase voltage in the existing reconfigurable on-board charging system.

[0008] To address the aforementioned technical problems, this invention provides a current balancing method for a reconfigurable on-board charging system, comprising: The three-phase unbalanced current on the AC side of the reconfigurable on-board charging system is obtained, and the d-axis DC current and q-axis DC current in the dq coordinate system are obtained through coordinate transformation. Based on the voltage and current balance of each bridge arm in the six-phase voltage source inverter of the reconfigurable on-board charging system under different switching states, the first state equation of the reconfigurable on-board charging system in the three-phase stationary coordinate system is obtained, and the second state equation in the dq coordinate system is obtained through coordinate transformation. The three-phase unbalanced current on the AC side is represented as a set of symmetrical positive sequence components and a set of symmetrical negative sequence components, and the first three-phase current in the three-phase stationary coordinate system is obtained. Based on the static coordinate transformation matrix and the positive and negative sequence coordinate transformation matrix, the first three-phase current is transformed to obtain the second three-phase current of the AC side three-phase unbalanced current in the positive and negative sequence synchronous rotating dq coordinate system. Based on the difference in rotation direction between the positive-sequence dq rotating coordinate system and the negative-sequence dq rotating coordinate system, the second and third phase currents are decoupled using the dual-sequence decoupling independent control method. The third state equation of the reconfigurable on-board charging system in the dq rotating coordinate system is constructed to obtain the decoupled positive-sequence voltage component and the decoupled negative-sequence voltage component. Perform inverse Park transform on the decoupled positive-sequence voltage component and the decoupled negative-sequence voltage component respectively to obtain the positive-sequence voltage and negative-sequence voltage in the α-β coordinate system, and then superimpose them to obtain the total control voltage; The six-phase voltage source inverter is controlled by a drive signal generated from the total control voltage to achieve balance of the three-phase current on the AC side.

[0009] Preferably, the three-phase unbalanced current on the AC side of the on-board charging system is obtained, and the d-axis DC current and q-axis DC current in the dq coordinate system are obtained through coordinate transformation, including: Perform Clack transformation on the three-phase unbalanced current on the AC side of the on-board charging system to obtain the two-phase DC current in the α-β coordinate system; Perform Park transformation on the two-phase DC currents to obtain the d-axis DC current and q-axis DC current in the dq coordinate system; Among them, the voltage vector of the three-phase AC power grid connected to the AC side coincides with the d-axis of the dq coordinate system. The d-axis corresponds to the active component of the current, and the q-axis corresponds to the reactive component of the current.

[0010] Preferably, based on the voltage and current balance of each bridge arm in the six-phase voltage source inverter of the reconfigurable on-board charging system under different switching states, the first state equation of the reconfigurable on-board charging system in the three-phase stationary coordinate system is obtained, including: By using the input voltage of each phase to satisfy the equivalent voltage, resistor voltage drop, and AC side induced voltage of the corresponding six-phase voltage source inverter, a system voltage balance equation is constructed, expressed as: ; The sum of the charging current of the DC-side filter capacitor and the DC-side equivalent load current equals the current transferred from the AC side to the DC side through the six-phase voltage source inverter bridge arm. Therefore, the system current balance equation is constructed as follows: ; Combine the system voltage balance equation and the system current balance equation to form the first state equation; in, Indicates the equivalent inductance on the AC side. In the three-phase unbalanced current, the first Phase current, , Indicates the equivalent resistance on the AC side. Indicates the first Phase input voltage; Indicates the first The switching function of the phase bridge arm, Indicates the first The upper arm of the phase bridge arm is turned on and the lower arm is turned off. Indicates the first The upper bridge arm of the phase bridge arm is turned off, and the lower bridge arm is turned on; This refers to the DC-side filter capacitor. Indicates the DC side voltage. This indicates the equivalent load on the DC side.

[0011] Preferably, obtaining the second state equation in the dq coordinate system includes: The induced voltage based on the equivalent inductance on the AC side is equal to the d-axis input voltage minus the d-axis resistance voltage drop, minus the inverter bridge arm equivalent voltage, plus the q-axis coupling term. This constructs the d-axis voltage balance equation, which is expressed as: ; The induced voltage based on the equivalent inductance on the AC side is equal to the q-axis input voltage minus the q-axis resistance voltage drop, minus the inverter bridge arm equivalent voltage, and plus the d-axis coupling term. The q-axis voltage balance equation can be constructed as follows: ; Based on the relationship between the d-axis DC current, q-axis DC current, and DC-side voltage on the AC side, a formula for the DC-side voltage variation is constructed, expressed as: ; By combining the d-axis voltage balance equation, the q-axis voltage balance equation, and the DC-side voltage change equation, a second state equation is formed. in, and These represent the d-axis DC current and the q-axis DC current, respectively. and Let represent the d-axis equivalent switching function components and the q-axis equivalent switching function components, respectively. and These represent the d-axis voltage and the q-axis voltage, respectively. Indicates the equivalent resistance on the AC side. This represents the angular frequency of the external three-phase power grid voltage.

[0012] Preferably, the three-phase unbalanced current on the AC side is represented as a set of symmetrical positive-sequence components and a set of symmetrical negative-sequence components. The first three-phase current in the three-phase stationary coordinate system is obtained as follows: ; in, , and These represent the a-phase current, b-phase current, and c-phase current in the three-phase current, respectively. and These represent the magnitudes of the positive-sequence component and the negative-sequence component, respectively. Indicates the angular frequency of the external three-phase power grid voltage. Represents a time variable. and These represent the initial phase angles of the positive-sequence component and the negative-sequence component, respectively.

[0013] Preferably, the current balancing method for the reconfigurable on-board charging system, based on the static coordinate transformation matrix and the positive and negative sequence coordinate transformation matrices, performs coordinate transformation on the first three-phase current to obtain the second three-phase current of the AC side three-phase unbalanced current in the positive and negative sequence synchronously rotating dq coordinate system, expressed as: ; in, The static coordinate transformation matrix is ​​represented as follows: ; The ascending order transformation matrix is ​​represented as follows: ; and Let represent the positive sequence current components along the d-axis and q-axis in the dq rotating coordinate system, respectively. The ascending order transformation matrix is ​​represented as follows: ; and Let represent the negative-sequence current components along the d-axis and q-axis in the dq rotating coordinate system, respectively.

[0014] Preferably, based on the difference in rotation direction between the positive-sequence dq rotating coordinate system and the negative-sequence dq rotating coordinate system, the second and third phase currents are decoupled using a dual-sequence decoupling independent control method, and a third state equation for the reconfigurable on-board charging system in the dq rotating coordinate system is constructed, including: Based on the inductor-induced voltage, resistor voltage drop, rotating coupling term, and bridge arm neutral point positive-sequence voltage of the positive-sequence current component, a positive-sequence voltage balance expression is constructed, which is expressed as: ; Based on the inductor-induced voltage, resistor voltage drop, rotational coupling term, and bridge arm neutral point negative-sequence voltage of the negative-sequence current component, a negative-sequence voltage balance expression is constructed, which is expressed as: ; By combining the positive-sequence voltage balance expression and the negative-sequence voltage balance expression, the third state equation is formed. in, This represents the positive sequence voltage matrix, which includes the positive sequence voltages along the d-axis and the positive sequence voltages along the q-axis. This represents the positive sequence current component matrix, which includes the positive sequence current components along the d-axis and the positive sequence current components along the q-axis. A matrix representing the positive sequence voltages of the neutral points of each bridge arm; This represents the negative sequence voltage matrix, which includes the negative sequence voltages along the d-axis and the negative sequence voltages along the q-axis. This represents the negative sequence current component matrix, which includes the d-axis negative sequence current component and the q-axis negative sequence current component. A matrix representing the negative sequence voltages of the neutral points of each bridge arm; Indicates the equivalent inductance on the AC side. Indicates the equivalent resistance on the AC side. Represents the imaginary unit. This represents the angular frequency of the external three-phase power grid voltage.

[0015] This embodiment provides a reconfigurable on-board charging system, including: The six-phase voltage source inverter includes six parallel bridge arm branches, each of which includes an upper bridge arm and a lower bridge arm, and each bridge arm is equipped with a MOSFET. A six-phase permanent magnet synchronous motor includes: The first three-phase winding has one end connected to the three-phase output terminal of the external three-phase power grid, and the other end connected to the neutral point of the first, second and third bridge arm branches of the six-phase voltage source inverter. The second and third phase windings have one end connected to the three-phase output terminals of the external three-phase power grid, and the other end connected to the neutral points of the fourth, fifth and sixth bridge arm branches of the six-phase voltage source inverter. The filter capacitor is connected in parallel across the two ends of the six-phase voltage source inverter; The battery is connected at one end to the first contactor and at the other end to the second contactor. By adjusting the first and second contactors, it can be connected in parallel across the six-phase voltage source inverter or in parallel across the six-phase permanent magnet synchronous motor. The controller is connected to each MOSFET in the six-phase voltage source inverter. Using the current balancing method of the reconfigurable on-board charging system described above, it obtains the drive signal for controlling the six-phase voltage source inverter, thereby controlling the conduction state of each MOSFET and achieving the balance of the three-phase current on the AC side.

[0016] Preferably, when performing three-phase charging, the reconfigurable on-board charging system manifests as a three-phase rectifier unit and a DC-DC converter unit, including: The three-phase rectifier unit includes: Winding A in the first three-phase winding is connected at one end to phase a of the external three-phase power grid and at the other end to the neutral point of the second bridge arm branch in the six-phase voltage source inverter. Winding X in the second and third phase windings is connected at one end to phase b of the external three-phase power grid and at the other end to the neutral point of the first bridge arm branch in the six-phase voltage source inverter. The winding Y in the second and third phase windings is connected at one end to phase b of the external three-phase power grid and at the other end to the neutral point of the fourth bridge arm branch in the six-phase voltage source inverter. Winding B in the first three-phase winding is connected at one end to phase c of the external three-phase power grid and at the other end to the neutral point of the third bridge arm branch in the six-phase voltage source inverter. The filter capacitor is connected in parallel across the fourth bridge arm branch in the six-phase voltage source inverter. The DC-DC converter unit, with its reused filter capacitor, also includes: Winding C in the first three-phase winding is connected at one end to the positive terminal of the battery and at the other end to the neutral point of the fifth bridge arm branch in the six-phase voltage source inverter. Winding Z in the second and third phase windings is connected at one end to the negative terminal of the battery and at the other end to the neutral point of the sixth bridge arm branch in the six-phase voltage source inverter.

[0017] Preferably, when performing single-phase charging, the reconfigurable on-board charging system manifests as a single-phase rectifier unit and a DC-DC converter unit, including: A single-phase rectifier unit includes: Winding A in the first three-phase winding is connected at one end to a unidirectional power grid and at the other end to the neutral point of the first bridge arm branch in the six-phase voltage source inverter. The winding Y in the second and third phase windings is connected to the unidirectional power grid at one end and to the neutral point of the fourth bridge arm branch in the six-phase voltage source inverter at the other end. The filter capacitor is connected in parallel across the fourth bridge arm branch in the six-phase voltage source inverter. The DC-DC converter unit, with its reused filter capacitor, also includes: Winding C in the first three-phase winding is connected at one end to the positive terminal of the battery and at the other end to the neutral point of the fifth bridge arm branch in the six-phase voltage source inverter. Winding Z in the second and third phase windings is connected at one end to the negative terminal of the battery and at the other end to the neutral point of the sixth bridge arm branch in the six-phase voltage source inverter.

[0018] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: The current balancing method for reconfigurable on-board charging systems described in this invention addresses the current imbalance problem caused by inductance imbalance after reusing motor inductors in reconfigurable on-board charging systems. It achieves current balancing output through coordinate transformation, component decomposition, dual-sequence decoupling, and inverse coordinate transformation. Based on coordinate transformation, this invention converts the three-phase unbalanced current into d-axis and q-axis currents, transforming complex AC control into simple DC control, significantly reducing controller design difficulty and improving control response speed. Based on the opposite rotation directions of the positive and negative sequence dq coordinate systems, a third state equation is constructed to achieve dual-sequence decoupling, separating the positive and negative sequence components. These components can be independently controlled, avoiding mutual interference and achieving precise control of active, reactive, and harmonic components. Through the dual-sequence decoupling independent control method, the coupling terms between the d and q axes caused by coordinate system rotation are canceled, enabling independent control of the d and q axes. The d-axis current can be precisely set to 0 to achieve unity power factor operation, while the charging power is precisely adjusted to improve charging efficiency. This invention decomposes the three-phase unbalanced current into positive and negative sequence symmetrical components. Through closed-loop control of the negative sequence component, it precisely eliminates the negative sequence component, fundamentally solving the three-phase current asymmetry problem, reducing the grid-side harmonic distortion rate (THD), and further reducing the ripple of the DC-side output voltage. After obtaining the total control current, it is converted into a three-phase current command through inverse Clark transformation. Combined with negative sequence compensation, this ensures that the three-phase current output by the inverter satisfies a symmetrical relationship in amplitude and phase, achieving three-phase current balance on the AC side, improving grid compatibility, and meeting grid power quality standards.

[0019] The reconfigurable on-board charging system described in this invention reuses the windings of a six-phase permanent magnet synchronous motor as the charging-side inductor, eliminating the need for additional dedicated charging inductors, independent chargers, and other hardware, thus significantly simplifying the hardware structure of the on-board system. Simultaneously, it constructs a structure including an AC-DC converter in the preceding stage and a DC-DC converter in the following stage. By using the motor windings and power devices as DC-DC converters, the DC voltage output from the preceding stage can be further regulated, greatly expanding the voltage regulation range. Furthermore, connecting one phase of the motor winding to the neutral point of the three-phase AC power supply converts the system from a three-phase charging system to a single-phase charging system, increasing fault tolerance and further improving the system's adaptability to different power grid environments. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a flowchart of the current balancing method of the reconfigurable on-board charging system of the present invention; Figure 2This is a schematic diagram of coordinate transformation from three-phase unbalanced current to the dq coordinate system; Figure 3 This is the equivalent circuit diagram of a reconfigurable on-board charging system when performing three-phase charging. Figure 4 This is a block diagram of the control principle of the dual-sequence decoupling independent control method; Figure 5 This is a schematic diagram of positive and negative order rotation coordinate transformation; Figure 6 This is a current decoupling control block diagram based on the dual-sequence decoupling independent control method; Figure 7 This is a topology diagram of a reconfigurable on-board charging system; Figure 8 This is a topology diagram of a reconfigurable on-board charging system under three-phase charging mode; Figure 9 This is a topology diagram of a reconfigurable on-board charging system in single-phase charging mode; Figure 10 It is a magnetomotive force trajectory diagram during three-phase charging; Figure 11 It is a magnetomotive force trajectory diagram during single-phase charging; Figure 12 (a) is a schematic diagram of the DC-side output voltage and current before the addition of the dual-sequence decoupling independent control method; Figure 12 (b) is a schematic diagram of the voltage and current of phase a on the three-phase power grid side before the addition of the dual-sequence decoupling independent control method; Figure 12 (c) is a schematic diagram of the three-phase current on the three-phase power grid side before the addition of the dual-sequence decoupling independent control method; Figure 12 (d) is the harmonic analysis result of the a-phase current on the three-phase power grid side before the addition of the dual-sequence decoupling independent control method; Figure 13 (a) is a schematic diagram of the DC-side output voltage and current after the addition of the dual-sequence decoupling independent control method; Figure 13 (b) is a schematic diagram of the voltage and current of phase a on the three-phase power grid side after the addition of the dual-sequence decoupling independent control method; Figure 13 (c) is a schematic diagram of the three-phase current on the three-phase power grid side after the addition of the dual-sequence decoupling independent control method; Figure 13 (d) is the harmonic analysis result of the a-phase current on the three-phase power grid side after adding the dual-sequence decoupling independent control method; Figure 14 (a) is a schematic diagram of the AC side phase a voltage and AC side three-phase current without the dual-sequence decoupling independent control method; Figure 14 (b) is a schematic diagram of AC side phase a voltage, AC side phase a current, DC side voltage and DC side current without the dual-sequence decoupling independent control method; Figure 15(a) is a schematic diagram of the AC side phase a voltage and AC side three-phase current including the dual-sequence decoupling independent control method; Figure 15 (b) is a schematic diagram of the AC side phase a voltage, AC side phase a current, DC side voltage and DC side current including the dual-sequence decoupling independent control method. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0022] Reference Figure 1 The flowchart shown is a step diagram of the current balancing method of the reconfigurable on-board charging system of the present invention, and the specific steps are shown in S101 to S107.

[0023] S101: Obtain the three-phase unbalanced current on the AC side of the reconfigurable on-board charging system, and obtain the d-axis DC current and q-axis DC current in the dq coordinate system through coordinate transformation.

[0024] For electric drive reconfigurable on-board charging systems, the basic control strategy is to simplify calculations by transforming the three-phase AC power into two mutually perpendicular DC currents through coordinate transformation. (Refer to...) Figure 2 The diagram shows a coordinate transformation from three-phase unbalanced current to the dq coordinate system. The three-phase current and voltage can be transformed from the three-phase stationary coordinate system ABC to the two-phase stationary coordinate system α-β through the Clark transformation, and then transformed into the two-phase rotating coordinate system dq through the Park transformation.

[0025] The specific conversion steps include: S101-1: Perform Clack transformation on the three-phase unbalanced current on the AC side of the on-board charging system to obtain the two-phase DC current in the α-β coordinate system; The Clack transformation matrix is: ; S101-2: Perform Park transformation on the two-phase DC current to obtain the d-axis DC current and q-axis DC current in the dq coordinate system; The Park transformation matrix is: ; Among them, the voltage vector of the three-phase AC power grid connected to the AC side coincides with the d-axis of the dq coordinate system. The d-axis corresponds to the active component of the current, and the q-axis corresponds to the reactive component of the current.

[0026] S102: Based on the voltage and current balance of each bridge arm in the six-phase voltage source inverter of the reconfigurable on-board charging system under different switching states, the first state equation of the reconfigurable on-board charging system in the three-phase stationary coordinate system is obtained, and the second state equation in the dq coordinate system is obtained through coordinate transformation.

[0027] Reference Figure 3 The diagram shown is the equivalent circuit diagram of a reconfigurable on-board charging system during three-phase charging. To simplify calculations, a switching function is defined. , will the upper bridge arm Opening and lowering of the bridge arm Turn-off definition Define the upper arm as closed and the lower arm as open. There are eight switching states for the three-phase bridge arm, as shown in Table 1.

[0028] Table 1 Switching functions and their corresponding switching states

[0029] Therefore, the first state equation of the system in the three-phase stationary coordinate system and the second state equation in the dq coordinate system can be obtained, including: S102-1: Using the input voltage of each phase to satisfy the equivalent voltage, resistor voltage drop, and AC side induced voltage of the corresponding six-phase voltage source inverter, the system voltage balance relationship is constructed as follows: ; S102-2: The sum of the charging current of the DC-side filter capacitor and the DC-side equivalent load current equals the current transferred from the AC side to the DC side through the bridge arm of the six-phase voltage source inverter. The system current balance equation is then constructed as follows: ; S102-3: Combine the system voltage balance equation and the system current balance equation to form the first state equation; in, Indicates the equivalent inductance on the AC side. In the three-phase unbalanced current, the first Phase current, , Indicates the equivalent resistance on the AC side. Indicates the first Phase input voltage; Indicates the first The switching function of the phase bridge arm, Indicates the first The upper arm of the phase bridge arm is turned on and the lower arm is turned off. Indicates the first The upper bridge arm of the phase bridge arm is turned off, and the lower bridge arm is turned on; This refers to the DC-side filter capacitor. Indicates the DC side voltage. Indicates the equivalent load on the DC side; S102-4: Based on the equivalent inductance of the AC side, the induced voltage equals the d-axis input voltage minus the d-axis resistance voltage drop, minus the inverter bridge arm equivalent voltage, plus the q-axis coupling term, constructing the d-axis voltage balance relationship, expressed as: ; S102-5: Based on the equivalent inductance of the AC side, the induced voltage equals the q-axis input voltage minus the q-axis resistance voltage drop, minus the inverter bridge arm equivalent voltage, plus the d-axis coupling term. The q-axis voltage balance equation is constructed as follows: ; S102-6: Based on the relationship between the d-axis DC current, q-axis DC current, and DC-side voltage on the AC side, a formula for the DC-side voltage variation is constructed, expressed as: ; S102-7: Combine the d-axis voltage balance equation, the q-axis voltage balance equation, and the DC-side voltage change equation to form the second state equation; in, and These represent the d-axis DC current and the q-axis DC current, respectively. and Let represent the d-axis equivalent switching function components and the q-axis equivalent switching function components, respectively. and These represent the d-axis voltage and the q-axis voltage, respectively. Indicates the equivalent resistance on the AC side. This represents the angular frequency of the external three-phase power grid voltage.

[0030] According to the instantaneous reactive power theory, if the voltage vector of a three-phase AC power grid coincides with the d-axis of the dq coordinate system, then the d-axis represents the active component of the current, and the q-axis represents the reactive component of the current. Control and This allows adjustment of the rectifier's active and reactive power. Setting it to 0 achieves unity power factor operation. However, based on the second state equation, it can be found that there are coupling terms in the variables of the d and q axes, which will cause difficulties in the design of the controller.

[0031] Therefore, a feedforward decoupling control strategy is adopted for decoupling. Since the system in charging mode is a three-phase three-wire system, and the neutral line connected to the voltage neutral point is not activated, there is no zero-sequence current path. Therefore, the zero-sequence impedance can be considered infinite, meaning there is no zero-sequence current component in the system. Thus, when the AC current is asymmetrical, the current in the three-phase stationary coordinate system can be uniquely described as the superposition of a set of symmetrical positive-sequence components and a set of symmetrical negative-sequence components.

[0032] S103: The three-phase unbalanced current on the AC side is represented as a set of symmetrical positive-sequence components and a set of symmetrical negative-sequence components. The first three-phase current in the three-phase stationary coordinate system is obtained as follows: ; in, , and These represent the a-phase current, b-phase current, and c-phase current in the three-phase current, respectively. and These represent the magnitudes of the positive-sequence component and the negative-sequence component, respectively. Indicates the angular frequency of the external three-phase power grid voltage. Represents a time variable. and These represent the initial phase angles of the positive-sequence component and the negative-sequence component, respectively.

[0033] S104: Based on the static coordinate transformation matrix and the positive and negative sequence coordinate transformation matrix, the coordinate transformation of the first three-phase current is performed to obtain the second three-phase current of the AC side three-phase unbalanced current in the positive and negative sequence synchronous rotating dq coordinate system.

[0034] By simultaneously solving the Clark transformation matrix, the Park transformation matrix, and the first three-phase current, we can obtain the expression for the current under the condition of unbalanced AC current. This allows us to obtain the expressions for the AC three-phase current in the positive-sequence and negative-sequence dq synchronous rotating coordinate system, i.e., the second three-phase current, expressed as: ; in, The static coordinate transformation matrix is ​​represented as follows: ; The ascending order transformation matrix is ​​represented as follows: ; and Let represent the positive sequence current components along the d-axis and q-axis in the dq rotating coordinate system, respectively. The ascending order transformation matrix is ​​represented as follows: ; and Let represent the negative sequence current components along the d-axis and q-axis in the dq rotating coordinate system, respectively. , , and All of them are expressed as direct current.

[0035] If we ignore the AC side impedance and the losses of the switching transistor, and assume that the DC side voltage is constant, then according to the principle of power conservation, the expression for the DC side current is: ; As can be seen from the expression for DC-side current, under the condition of current asymmetry caused by inductance, the DC-side output current of the rectifier consists of a DC component and a negative-sequence AC component. If only the fundamental components of the input current and voltage are considered, the AC component in the DC current is a harmonic component of the second fundamental frequency. Furthermore, when the current is unbalanced, the negative-sequence component in the three-phase current will increase the harmonic content in the DC current and voltage output of the system, causing the THD of the DC-side current and voltage to rise.

[0036] Therefore, in order to reduce the impact of negative sequence current, a dual-sequence decoupling independent control method is adopted to separate the positive and negative sequences of the AC side current and then decouple and control the positive and negative sequence currents separately; refer to Figure 4 The diagram shown illustrates the control principle block diagram of the dual-sequence decoupled independent control method. Since the rotation directions of the dq rotating coordinate systems for the positive and negative sequences are different, coordinate transformation is required when considering the negative sequence component; refer to... Figure 5 The diagram shown illustrates the positive and negative coordinate transformations.

[0037] S105: Based on the difference in rotation direction between the positive-sequence dq rotating coordinate system and the negative-sequence dq rotating coordinate system, the second and third phase currents are decoupled using the dual-sequence decoupling independent control method. The third state equation of the reconfigurable on-board charging system in the dq rotating coordinate system is constructed, and the decoupled positive-sequence voltage components and decoupled negative-sequence voltage components are obtained, including: S105-1: Based on the inductor-induced voltage, resistor voltage drop, rotating coupling term, and bridge arm neutral point positive-sequence voltage of the positive-sequence current component, a positive-sequence voltage balance expression is constructed, expressed as: ; S105-2: Based on the inductor-induced voltage, resistor voltage drop, rotating coupling term, and bridge arm neutral point negative-sequence voltage of the negative-sequence current component, a negative-sequence voltage balance expression is constructed, expressed as: ; S105-3: Combine the positive-sequence voltage balance expression and the negative-sequence voltage balance expression to form the third state equation; in, This represents the positive sequence voltage matrix, which includes the positive sequence voltages along the d-axis and the positive sequence voltages along the q-axis. This represents the positive sequence current component matrix, which includes the positive sequence current components along the d-axis and the positive sequence current components along the q-axis. A matrix representing the positive sequence voltages of the neutral points of each bridge arm; This represents the negative sequence voltage matrix, which includes the negative sequence voltages along the d-axis and the negative sequence voltages along the q-axis. This represents the negative sequence current component matrix, which includes the d-axis negative sequence current component and the q-axis negative sequence current component. A matrix representing the negative sequence voltages of the neutral points of each bridge arm; Indicates the equivalent inductance on the AC side. Indicates the equivalent resistance on the AC side. Represents the imaginary unit. This represents the angular frequency of the external three-phase power grid voltage.

[0038] S106: Perform Park inverse transformation on the decoupled positive-sequence voltage component and the decoupled negative-sequence voltage component respectively to obtain the positive-sequence voltage and negative-sequence voltage in the α-β coordinate system, and superimpose them to obtain the total control voltage.

[0039] S107: Based on the total control voltage, a drive signal is generated to control the six-phase voltage source inverter, thereby achieving the balance of the three-phase current on the AC side.

[0040] Reference Figure 6 The diagram shows the current decoupling control block diagram based on the dual-sequence decoupling independent control method. Since the voltage in the α-β coordinate system is required for subsequent PWM control, the positive and negative sequence voltages in the α-β coordinate system need to be obtained through Park inverse transformation after decoupling. These are then added together to obtain the total voltage for subsequent control. Specifically, the actual three-phase currents... Decomposed into positive-sequence current and negative-sequence current, which are then transformed from three-phase stationary to two-phase rotating current respectively. Obtain the positive sequence dq current , and negative sequence dq current , For positive sequence current, based on the positive sequence reference current. With positive sequence d-axis current Difference, obtained through PI ; and Difference, obtained through PI For negative sequence currents, the negative sequence reference current... With negative sequence dq current , Difference, obtained through PI , Based on feedforward decoupling to eliminate inter-axis coupling, combined with coupling terms The positive-sequence q-axis current is coupled to the d-axis, and the positive-sequence d-axis current is coupled to the q-axis. These are then superimposed on the PI output to obtain... and Similarly, for negative sequence currents, the negative sequence q-axis current is coupled to the d-axis, and the negative sequence d-axis current is coupled to the q-axis, and then superimposed on the PI output to obtain... and ;right , , and Perform two-phase rotations to two-phase stationary coordinates respectively. After inverse transformation, obtain and The total control voltage is obtained by superimposing the values, which is then used to drive the six-phase voltage source inverter using PWM modulation.

[0041] This invention proposes a dual-sequence decoupling independent control method. By introducing a dynamic orthogonal decomposition mechanism, the time-domain characteristics of the three-phase current are decoupled into two independent orthogonal subspace components: a positive-sequence component and a negative-sequence component. Based on this, a dual-channel independent PI control system is constructed to eliminate the negative-sequence current and achieve the goal of three-phase current balance.

[0042] Based on the above embodiments, a reconfigurable on-board charging system is provided in this embodiment of the invention, referring to... Figure 7 The diagram shown is a topology diagram of a reconfigurable on-board charging system. The specific topology includes: The six-phase voltage source inverter includes six parallel bridge arm branches, each of which includes an upper bridge arm and a lower bridge arm, and each bridge arm is equipped with a MOSFET. A six-phase permanent magnet synchronous motor includes: The first three-phase winding has one end connected to the three-phase output terminal of the external three-phase power grid, and the other end connected to the neutral point of the first, second and third bridge arm branches of the six-phase voltage source inverter. The second and third phase windings have one end connected to the three-phase output terminals of the external three-phase power grid, and the other end connected to the neutral points of the fourth, fifth and sixth bridge arm branches of the six-phase voltage source inverter. The filter capacitor is connected in parallel across the two ends of the six-phase voltage source inverter; The battery is connected at one end to the first contactor and at the other end to the second contactor. By adjusting the first and second contactors, it can be connected in parallel across the six-phase voltage source inverter or in parallel across the six-phase permanent magnet synchronous motor. The controller is connected to each MOSFET in the six-phase voltage source inverter. Using the current balancing method of the reconfigurable on-board charging system described above, it obtains the drive signal for controlling the six-phase voltage source inverter, thereby controlling the conduction state of each MOSFET and achieving the balance of the three-phase current on the AC side.

[0043] Reference Figure 8 The diagram shows the topology of a reconfigurable on-board charging system in three-phase charging mode. In three-phase charging mode, the motor windings are reused as the AC-side filter inductor in the first half and the inductor in the second half. In this case, the reconfigurable on-board charging system consists of a three-phase rectifier unit and a DC-DC converter unit, including: The three-phase rectifier unit includes: Winding A in the first three-phase winding is connected at one end to phase a of the external three-phase power grid and at the other end to the neutral point of the second bridge arm branch in the six-phase voltage source inverter. Winding X in the second and third phase windings is connected at one end to phase b of the external three-phase power grid and at the other end to the neutral point of the first bridge arm branch in the six-phase voltage source inverter. The winding Y in the second and third phase windings is connected at one end to phase b of the external three-phase power grid and at the other end to the neutral point of the fourth bridge arm branch in the six-phase voltage source inverter. Winding B in the first three-phase winding is connected at one end to phase c of the external three-phase power grid and at the other end to the neutral point of the third bridge arm branch in the six-phase voltage source inverter. The filter capacitor is connected in parallel across the fourth bridge arm branch in the six-phase voltage source inverter. The DC-DC converter unit, with its reused filter capacitor, also includes: Winding C in the first three-phase winding is connected at one end to the positive terminal of the battery and at the other end to the neutral point of the fifth bridge arm branch in the six-phase voltage source inverter. Winding Z in the second and third phase windings is connected at one end to the negative terminal of the battery and at the other end to the neutral point of the sixth bridge arm branch in the six-phase voltage source inverter.

[0044] Reference Figure 9 The diagram shows the topology of a reconfigurable on-board charging system in single-phase charging mode. In single-phase charging mode, the single-phase charging circuit is composed of a winding connected to the power supply neutral point and a single-phase AC winding. In this case, the reconfigurable on-board charging system functions as a single-phase rectifier unit and a DC-DC converter unit, including: A single-phase rectifier unit includes: Winding A in the first three-phase winding is connected at one end to a unidirectional power grid and at the other end to the neutral point of the first bridge arm branch in the six-phase voltage source inverter. The winding Y in the second and third phase windings is connected to the unidirectional power grid at one end and to the neutral point of the fourth bridge arm branch in the six-phase voltage source inverter at the other end. The filter capacitor is connected in parallel across the fourth bridge arm branch in the six-phase voltage source inverter. The DC-DC converter unit, with its reused filter capacitor, also includes: Winding C in the first three-phase winding is connected at one end to the positive terminal of the battery and at the other end to the neutral point of the fifth bridge arm branch in the six-phase voltage source inverter. Winding Z in the second and third phase windings is connected at one end to the negative terminal of the battery and at the other end to the neutral point of the sixth bridge arm branch in the six-phase voltage source inverter.

[0045] In this embodiment, since the asymmetric six-phase permanent magnet synchronous motor is a high-order nonlinear time-varying system, the mathematical model in the natural coordinate system is too complex. Therefore, a vector space decoupling technique is introduced to transform the six-phase system into three subspaces: α-β, xy, and o1-o2 through a coordinate transformation matrix. The first and second rows form the fundamental wave plane α-β subspace of the dual three-phase motor, the third and fourth rows form the fifth harmonic wave plane xy subspace of the dual three-phase motor, and the fifth and sixth rows form the third harmonic wave plane o1-o2 subspace.

[0046] Wherein, the coordinate transformation matrix is: .

[0047] The fundamental reason for the rotation of the motor is that the alternating current flowing through the stator windings generates a magnetomotive force (MOF), which interacts with the stator permanent magnets to produce an electromagnetic torque. The MOF of a six-phase permanent magnet synchronous motor is the sum of the MOFs of the two sets of windings, that is: ; in, For the first set of windings ( , , The magnetomotive force of ) For the second set of windings ( , , The magnetomotive force of ).

[0048] Assuming the windings are perfectly symmetrical, we have: ; ; ; ; ; ;

[0049] in, The number of turns in the winding. , , , , , This represents the peak value of the six-phase winding current. Angular frequency, , , , , and The phase of the current in each phase winding.

[0050] Reference Figure 10The image shown is a magnetomotive force trajectory diagram during three-phase charging; refer to... Figure 11 The diagram shows the magnetomotive force trajectory during single-phase charging. In three-phase charging, although the combined magnetomotive force F still tends to cause the motor to rotate, the magnetomotive force F2 of the second winding is a constant. That is, when the electromagnetic torque generated by the current in the DC-DC converter winding can cancel the electromagnetic torque generated by the current in the AC winding, the motor will be fixed in a certain position. In single-phase charging, the combined magnetomotive force F generated by the system is itself a pulsating magnetomotive force, which will not cause the motor to rotate, verifying the rationality of the reconfigurable on-board charging system topology of this invention.

[0051] The reconfigurable on-board charging system described in this invention reuses the windings of a six-phase permanent magnet synchronous motor as the charging-side inductor, eliminating the need for additional dedicated charging inductors, independent chargers, and other hardware, thus significantly simplifying the hardware structure of the on-board system. Simultaneously, it constructs a structure including an AC-DC converter in the preceding stage and a DC-DC converter in the following stage. By using the motor windings and power devices as DC-DC converters, the DC voltage output from the preceding stage can be further regulated, greatly expanding the voltage regulation range. Furthermore, connecting one phase of the motor winding to the neutral point of the three-phase AC power supply converts the system from a three-phase charging system to a single-phase charging system, increasing fault tolerance and further improving the system's adaptability to different power grid environments.

[0052] In this embodiment, a charging system model with AC-side inductance imbalance was built based on MATLAB, and the simulation parameters were set as follows: peak grid-side voltage. The inductance values ​​L of phases a and b a L b =5mH; c-phase inductance value L c =3mH; DC-side capacitor C=3000μF; DC-side equivalent load resistance R L =15Ω; DC output voltage setpoint u dc-ref =600V.

[0053] Reference Figure 12 As shown in (a), this is a schematic diagram of the DC-side output voltage and current before the addition of the dual-sequence decoupling independent control method; refer to Figure 12 As shown in (b), this is a schematic diagram of the voltage and current of phase a on the three-phase grid side before the addition of the dual-sequence decoupling independent control method; refer to Figure 12 As shown in (c), this is a schematic diagram of the three-phase current on the three-phase grid side before the addition of the dual-sequence decoupling independent control method; refer to Figure 12 Figure (d) shows the harmonic analysis results of the a-phase current on the three-phase power grid side before the addition of the dual-sequence decoupling independent control method. (Refer to...) Figure 13 As shown in (a), this is a schematic diagram of the DC-side output voltage and current after incorporating the dual-sequence decoupling independent control method; refer to Figure 13 As shown in (b), this is a schematic diagram of the voltage and current of phase a on the three-phase power grid side after incorporating the dual-sequence decoupling independent control method; refer to Figure 13 As shown in (c), this is a schematic diagram of the three-phase current on the three-phase power grid side after incorporating the dual-sequence decoupling independent control method; refer to Figure 13 As shown in (d), this is the result of harmonic analysis of phase a current on the three-phase power grid side after adding the dual-sequence decoupling independent control method.

[0054] Figure 12 and Figure 13 The simulation results of the vector control strategy before and after incorporating the dual-sequence decoupling independent control method show that, under inductor imbalance, the ripple of the output voltage and current using only PI control is approximately 0.3%. Although the voltage and current of phase a on the grid side are in phase, satisfying the requirement of unit power operation, the three-phase currents become unbalanced, with differences in peak values; the three-phase harmonics increase, with harmonics of phases a, b, and c being 3.81%, 3.94%, and 4.18%, respectively. After adopting the dual-sequence decoupling independent control method, the ripple of the output voltage and current decreases to approximately 0.21%, the waveform of the three-phase current on the grid side improves, and the peak values ​​are basically the same; the three-phase harmonics are significantly reduced, with harmonics of phases a, b, and c being 1.61%, 1.73%, and 2.12%, respectively.

[0055] For ease of analysis, this embodiment uses the concept of unbalance to measure the difference in three-phase currents, and the calculation formula is as follows: Positive-order imbalance is expressed as: ; Negative order imbalance is expressed as: ; in, This represents the root-mean-square value of the positive-sequence component of the three-phase voltage. This represents the root mean square value of the negative sequence component of the three-phase voltage. , , These are the three-phase voltage or current values. .

[0056] Therefore, calculations show that the positive-sequence current imbalance is 6.2% and the negative-sequence current imbalance is 4% without the dual-sequence decoupling independent control method. With the dual-sequence decoupling independent control method, the positive-sequence current imbalance is 2.89% and the negative-sequence current imbalance is 1%. This invention achieves three-phase current balance on the AC side.

[0057] This embodiment also conducted experimental verification for actual inductance imbalance. The experimental results before and after adding the dual-sequence decoupling independent control method are as follows: Figure 14 and Figure 15 As shown. (Refer to...) Figure 14 As shown in (a), this is a schematic diagram of the AC side phase a voltage and AC side three-phase current without the dual-sequence decoupling independent control method; refer to Figure 14 As shown in (b), this is a schematic diagram of the AC side phase a voltage, AC side phase a current, DC side voltage, and DC side current without the dual-sequence decoupling independent control method; refer to Figure 15 As shown in (a), this is a schematic diagram of the AC side phase a voltage and AC side three-phase current including the dual-sequence decoupling independent control method; refer to Figure 15 As shown in (b), this is a schematic diagram of the AC side phase a voltage, AC side phase a current, DC side voltage, and DC side current, including the dual-sequence decoupling independent control method. Figure 14 and Figure 15 It can be seen that, under the condition of three-phase inductance imbalance, without the addition of the dual-sequence decoupling independent control method, the system can ensure that the phase current and phase voltage of AC side a are in phase, meet the unity power factor operation, and the DC side output voltage and current are stable with small fluctuations, meeting the requirements for voltage stability during charging. However, it was also found that the amplitudes of the three-phase currents on the AC side are different under this condition. Based on the formula, the positive and negative sequence imbalance degrees of the three-phase currents are 10.98% and 7.3%, respectively. The THDs of the three-phase currents are 5.19%, 5.99%, and 3.47%, respectively. After adding the dual-sequence decoupling independent control method, the positive and negative sequence imbalance degrees of the three-phase currents on the AC side are 7.69% and 5.19%, respectively. The THDs of the three-phase currents are 4.95%, 3.43%, and 3.36%, respectively. Comparing the two results, it can be found that the imbalance degree of the three-phase current is greatly reduced after adding the dual-sequence decoupling independent control method, and the harmonics of the AC side current are significantly reduced, and the waveform is improved. This verifies the effectiveness of the control method of the present invention.

[0058] The current balancing method for reconfigurable on-board charging systems described in this invention addresses the current imbalance problem caused by inductance imbalance after reusing motor inductors in reconfigurable on-board charging systems. It achieves current balancing output through coordinate transformation, component decomposition, dual-sequence decoupling, and inverse coordinate transformation. Based on coordinate transformation, this invention converts the three-phase unbalanced current into d-axis and q-axis currents, transforming complex AC control into simple DC control, significantly reducing controller design difficulty and improving control response speed. Based on the opposite rotation directions of the positive and negative sequence dq coordinate systems, a third state equation is constructed to achieve dual-sequence decoupling, separating the positive and negative sequence components. These components can be independently controlled, avoiding mutual interference and achieving precise control of active, reactive, and harmonic components. Through the dual-sequence decoupling independent control method, the coupling terms between the d and q axes caused by coordinate system rotation are canceled, enabling independent control of the d and q axes. The d-axis current can be precisely set to 0 to achieve unity power factor operation, while the charging power is precisely adjusted to improve charging efficiency. This invention decomposes the three-phase unbalanced current into positive and negative sequence symmetrical components. Through closed-loop control of the negative sequence component, it precisely eliminates the negative sequence component, fundamentally solving the three-phase current asymmetry problem, reducing the grid-side harmonic distortion rate (THD), and further reducing the ripple of the DC-side output voltage. After obtaining the total control current, it is converted into a three-phase current command through inverse Clark transformation. Combined with negative sequence compensation, this ensures that the three-phase current output by the inverter satisfies a symmetrical relationship in amplitude and phase, achieving three-phase current balance on the AC side, improving grid compatibility, and meeting grid power quality standards.

[0059] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0060] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0061] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0062] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0063] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A current balancing method for a reconfigurable on-board charging system, characterized in that, include: The three-phase unbalanced current on the AC side of the reconfigurable on-board charging system is obtained, and the d-axis DC current and q-axis DC current in the dq coordinate system are obtained through coordinate transformation. Based on the voltage and current balance of each bridge arm in the six-phase voltage source inverter of the reconfigurable on-board charging system under different switching states, the first state equation of the reconfigurable on-board charging system in the three-phase stationary coordinate system is obtained, and the second state equation in the dq coordinate system is obtained through coordinate transformation. The three-phase unbalanced current on the AC side is represented as a set of symmetrical positive sequence components and a set of symmetrical negative sequence components, and the first three-phase current in the three-phase stationary coordinate system is obtained. Based on the static coordinate transformation matrix and the positive and negative sequence coordinate transformation matrix, the first three-phase current is transformed to obtain the second three-phase current of the AC side three-phase unbalanced current in the positive and negative sequence synchronous rotating dq coordinate system. Based on the difference in rotation direction between the positive-sequence dq rotating coordinate system and the negative-sequence dq rotating coordinate system, the second and third phase currents are decoupled using the dual-sequence decoupling independent control method. The third state equation of the reconfigurable on-board charging system in the dq rotating coordinate system is constructed to obtain the decoupled positive-sequence voltage component and the decoupled negative-sequence voltage component. Perform inverse Park transform on the decoupled positive-sequence voltage component and the decoupled negative-sequence voltage component respectively to obtain the positive-sequence voltage and negative-sequence voltage in the α-β coordinate system, and then superimpose them to obtain the total control voltage; The six-phase voltage source inverter is controlled by a drive signal generated from the total control voltage to achieve balance of the three-phase current on the AC side.

2. The current balancing method for the reconfigurable on-board charging system according to claim 1, characterized in that, The three-phase unbalanced current on the AC side of the on-board charging system is obtained. Through coordinate transformation, the d-axis DC current and q-axis DC current in the dq coordinate system are obtained, including: Perform Clack transformation on the three-phase unbalanced current on the AC side of the on-board charging system to obtain the two-phase DC current in the α-β coordinate system; Perform Park transformation on the two-phase DC currents to obtain the d-axis DC current and q-axis DC current in the dq coordinate system; Among them, the voltage vector of the three-phase AC power grid connected to the AC side coincides with the d-axis of the dq coordinate system. The d-axis corresponds to the active component of the current, and the q-axis corresponds to the reactive component of the current.

3. The current balancing method for the reconfigurable on-board charging system according to claim 1, characterized in that, Based on the voltage and current balance of each bridge arm in the six-phase voltage source inverter of the reconfigurable on-board charging system under different switching states, the first state equation of the reconfigurable on-board charging system in the three-phase stationary coordinate system is obtained, including: By using the input voltage of each phase to satisfy the equivalent voltage, resistor voltage drop, and AC side induced voltage of the corresponding six-phase voltage source inverter, a system voltage balance equation is constructed, expressed as: ； The sum of the charging current of the DC-side filter capacitor and the DC-side equivalent load current equals the current transferred from the AC side to the DC side through the six-phase voltage source inverter bridge arm. Therefore, the system current balance equation is constructed as follows: ； Combine the system voltage balance equation and the system current balance equation to form the first state equation; in, Indicates the equivalent inductance on the AC side. In the three-phase unbalanced current, the first Phase current, , Indicates the equivalent resistance on the AC side. Indicates the first Phase input voltage; Indicates the first The switching function of the phase bridge arm, Indicates the first The upper arm of the phase bridge arm is turned on and the lower arm is turned off. Indicates the first The upper bridge arm of the phase bridge arm is turned off, and the lower bridge arm is turned on; This refers to the DC-side filter capacitor. Indicates the DC side voltage. This indicates the equivalent load on the DC side.

4. The current balancing method for the reconfigurable on-board charging system according to claim 2, characterized in that, Obtain the second state equation in the dq coordinate system, including: The induced voltage based on the equivalent inductance on the AC side is equal to the d-axis input voltage minus the d-axis resistance voltage drop, minus the inverter bridge arm equivalent voltage, plus the q-axis coupling term. This constructs the d-axis voltage balance equation, which is expressed as: ; The induced voltage based on the equivalent inductance on the AC side is equal to the q-axis input voltage minus the q-axis resistance voltage drop, minus the inverter bridge arm equivalent voltage, and plus the d-axis coupling term. The q-axis voltage balance equation can be constructed as follows: ; Based on the relationship between the d-axis DC current, q-axis DC current, and DC-side voltage on the AC side, a formula for the DC-side voltage variation is constructed, expressed as: ; By combining the d-axis voltage balance equation, the q-axis voltage balance equation, and the DC-side voltage change equation, a second state equation is formed. in, and These represent the d-axis DC current and the q-axis DC current, respectively. and Let represent the d-axis equivalent switching function components and the q-axis equivalent switching function components, respectively. and These represent the d-axis voltage and the q-axis voltage, respectively. Indicates the equivalent resistance on the AC side. This indicates the angular frequency of the external three-phase power grid voltage.

5. The current balancing method for the reconfigurable on-board charging system according to claim 1, characterized in that, The three-phase unbalanced current on the AC side is represented as a set of symmetrical positive-sequence components and a set of symmetrical negative-sequence components. The first three-phase current in the three-phase stationary coordinate system is obtained as follows: ； in, , and These represent the a-phase current, b-phase current, and c-phase current in the three-phase current, respectively. and These represent the magnitudes of the positive-sequence component and the negative-sequence component, respectively. Indicates the angular frequency of the external three-phase power grid voltage. Represents a time variable. and These represent the initial phase angles of the positive-sequence component and the negative-sequence component, respectively.

6. The current balancing method for a reconfigurable on-board charging system according to claim 5, characterized in that, The current balancing method for a reconfigurable on-board charging system, based on a static coordinate transformation matrix and positive-sequence and negative-sequence coordinate transformation matrices, performs coordinate transformation on the first three-phase current to obtain the second three-phase current of the AC side three-phase unbalanced current in the positive- and negative-sequence synchronously rotating dq coordinate system, expressed as: ； in, The static coordinate transformation matrix is ​​represented as follows: ; The ascending order transformation matrix is ​​represented as follows: ; and Let represent the positive sequence current components along the d-axis and q-axis in the dq rotating coordinate system, respectively. The ascending order transformation matrix is ​​represented as follows: ; and Let represent the negative-sequence current components along the d-axis and q-axis in the dq rotating coordinate system, respectively.

7. The current balancing method for a reconfigurable on-board charging system according to claim 1, characterized in that, Based on the difference in rotation direction between the positive-sequence dq rotating coordinate system and the negative-sequence dq rotating coordinate system, the second and third phase currents are decoupled using a dual-sequence decoupling independent control method. This leads to the construction of the third state equation of the reconfigurable on-board charging system in the dq rotating coordinate system, including: Based on the inductor-induced voltage, resistor voltage drop, rotating coupling term, and bridge arm neutral point positive-sequence voltage of the positive-sequence current component, a positive-sequence voltage balance expression is constructed, which is expressed as: ； Based on the inductor-induced voltage, resistor voltage drop, rotational coupling term, and bridge arm neutral point negative-sequence voltage of the negative-sequence current component, a negative-sequence voltage balance expression is constructed, which is expressed as: ； By combining the positive-sequence voltage balance expression and the negative-sequence voltage balance expression, the third state equation is formed. in, This represents the positive sequence voltage matrix, which includes the positive sequence voltages along the d-axis and the positive sequence voltages along the q-axis. This represents the positive sequence current component matrix, which includes the positive sequence current components along the d-axis and the positive sequence current components along the q-axis. A matrix representing the positive sequence voltages of the neutral points of each bridge arm; This represents the negative sequence voltage matrix, which includes the negative sequence voltages along the d-axis and the negative sequence voltages along the q-axis. This represents the negative sequence current component matrix, which includes the d-axis negative sequence current component and the q-axis negative sequence current component. A matrix representing the negative sequence voltages of the neutral points of each bridge arm; Indicates the equivalent inductance on the AC side. Indicates the equivalent resistance on the AC side. Represents the imaginary unit. This indicates the angular frequency of the external three-phase power grid voltage.

8. A reconfigurable on-board charging system, characterized in that, include: The six-phase voltage source inverter includes six parallel bridge arm branches, each of which includes an upper bridge arm and a lower bridge arm, and each bridge arm is equipped with a MOSFET. A six-phase permanent magnet synchronous motor includes: The first three-phase winding has one end connected to the three-phase output terminal of the external three-phase power grid, and the other end connected to the neutral point of the first, second and third bridge arm branches of the six-phase voltage source inverter. The second and third phase windings have one end connected to the three-phase output terminals of the external three-phase power grid, and the other end connected to the neutral points of the fourth, fifth and sixth bridge arm branches of the six-phase voltage source inverter. The filter capacitor is connected in parallel across the two ends of the six-phase voltage source inverter; The battery is connected at one end to the first contactor and at the other end to the second contactor. By adjusting the first and second contactors, it can be connected in parallel across the six-phase voltage source inverter or in parallel across the six-phase permanent magnet synchronous motor. The controller is connected to each MOSFET in the six-phase voltage source inverter. Using the current balancing method of the reconfigurable on-board charging system as described in any one of claims 1 to 7, the controller obtains the drive signal for controlling the six-phase voltage source inverter, thereby controlling the conduction state of each MOSFET and achieving the balance of the three-phase current on the AC side.

9. The reconfigurable on-board charging system according to claim 8, characterized in that, When performing three-phase charging, the reconfigurable on-board charging system consists of a three-phase rectifier unit and a DC-DC converter unit, including: The three-phase rectifier unit includes: Winding A in the first three-phase winding is connected at one end to phase a of the external three-phase power grid and at the other end to the neutral point of the second bridge arm branch in the six-phase voltage source inverter. Winding X in the second and third phase windings is connected at one end to phase b of the external three-phase power grid and at the other end to the neutral point of the first bridge arm branch in the six-phase voltage source inverter. The winding Y in the second and third phase windings is connected at one end to phase b of the external three-phase power grid and at the other end to the neutral point of the fourth bridge arm branch in the six-phase voltage source inverter. Winding B in the first three-phase winding is connected at one end to phase c of the external three-phase power grid and at the other end to the neutral point of the third bridge arm branch in the six-phase voltage source inverter. The filter capacitor is connected in parallel across the fourth bridge arm branch in the six-phase voltage source inverter. The DC-DC converter unit, with its reused filter capacitor, also includes: Winding C in the first three-phase winding is connected at one end to the positive terminal of the battery and at the other end to the neutral point of the fifth bridge arm branch in the six-phase voltage source inverter. Winding Z in the second and third phase windings is connected at one end to the negative terminal of the battery and at the other end to the neutral point of the sixth bridge arm branch in the six-phase voltage source inverter.

10. The reconfigurable on-board charging system according to claim 8, characterized in that, When performing single-phase charging, the reconfigurable on-board charging system consists of a single-phase rectifier unit and a DC-DC converter unit, including: A single-phase rectifier unit includes: Winding A in the first three-phase winding is connected at one end to a unidirectional power grid and at the other end to the neutral point of the first bridge arm branch in the six-phase voltage source inverter. The winding Y in the second and third phase windings is connected to the unidirectional power grid at one end and to the neutral point of the fourth bridge arm branch in the six-phase voltage source inverter at the other end. The filter capacitor is connected in parallel across the fourth bridge arm branch in the six-phase voltage source inverter. The DC-DC converter unit, with its reused filter capacitor, also includes: Winding C in the first three-phase winding is connected at one end to the positive terminal of the battery and at the other end to the neutral point of the fifth bridge arm branch in the six-phase voltage source inverter. Winding Z in the second and third phase windings is connected at one end to the negative terminal of the battery and at the other end to the neutral point of the sixth bridge arm branch in the six-phase voltage source inverter.

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