A bidirectional charge-discharge topology with unbalanced load and control method

Abstract

This invention proposes a bidirectional charging and discharging topology and control method capable of handling unbalanced loads, relating to the field of electric vehicle charging technology. The topology includes an LCL filter, a front-stage AC-DC converter, and a rear-stage DC-DC isolation converter. One side of the LCL filter is connected to the front-stage AC-DC converter, and the other side is connected to the load or the grid side. The LCL filter is used to suppress switching harmonics generated by the front-stage AC-DC converter. The front-stage AC-DC converter is connected to the rear-stage DC-DC isolation converter, which is used for bidirectional energy conversion between the AC port and the DC output side of the front-stage AC-DC converter in grid-connected or off-grid operation modes. The rear-stage DC-DC isolation converter is connected to an energy storage battery, and is used for bidirectional isolated transmission between the DC output side of the front-stage AC-DC converter and the energy storage battery. This application helps improve the operational stability and output voltage / current quality of the bidirectional charging and discharging topology.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle charging technology, and in particular to a bidirectional charging and discharging topology and control method capable of carrying unbalanced loads. Background Technology

[0002] The global energy crisis and environmental pollution have spurred the development of the electric vehicle (EV) industry worldwide. The ever-increasing number of EVs presents both significant challenges and opportunities for the construction and development of power systems. On the one hand, the large number of EVs connecting to the grid for centralized charging as new loads, if not properly managed and guided, can lead to increased peak electricity demand on the grid, overloading the grid and increasing the difficulty of peak regulation, placing immense pressure on grid planning and construction. On the other hand, the current power system's vigorous development of new energy generation is characterized by strong intermittency and randomness, with power generation heavily influenced by the natural environment. EVs, as mobile energy storage devices, can serve as system backup capacity, providing ancillary services to the grid, promoting the integration of new energy sources, enhancing system frequency stability, and achieving vehicle-grid convergence.

[0003] Chinese Patent CN120863408A discloses a bidirectional feedback virtual synchronous charging and discharging system and method for electric vehicles, relating to the field of virtual synchronous motor technology. The system includes: monitoring the state parameters of the vehicle-side battery and transmitting them to a virtual synchronous control module and a bidirectional feedback module; transmitting the battery state parameters to the power grid; optimizing the grid's scheduling and load distribution strategies based on the battery state parameters; monitoring the grid's operating status in real time; calculating and generating corresponding control signals based on the monitoring results and sending them to the bidirectional feedback module; and adjusting the charging and discharging behavior of the electric vehicle after receiving the grid's control signals. However, the above solution does not consider the connection of three-phase four-wire unbalanced loads and neutral point potential control when the electric vehicle is used as an AC power source to supply power to external loads. This makes it difficult to guarantee the output voltage and current quality and system operational stability under single-phase or severely unbalanced load conditions. Therefore, it is essential to provide a bidirectional charging and discharging topology and control method capable of handling unbalanced loads to improve the operational stability and output voltage / current quality of the bidirectional charging and discharging topology. Summary of the Invention

[0004] In view of this, the present invention proposes a bidirectional charging and discharging topology and control method capable of carrying unbalanced loads.

[0005] This invention provides a bidirectional charge-discharge topology capable of handling unbalanced loads, comprising an LCL filter, a front-stage AC-DC converter, and a rear-stage DC-DC isolation converter, wherein... One side of the LCL filter is connected to the preceding AC-DC converter, and the other side of the LCL filter is connected to the load or the power grid. The LCL filter is used to suppress the switching harmonics generated by the preceding AC-DC converter, so as to reduce the harmonic impact of the switching harmonics on the power grid or the load. The front-stage AC-DC converter is connected to the rear-stage DC-DC isolation converter. The front-stage AC-DC converter is used to perform bidirectional energy conversion between the AC port of the front-stage AC-DC converter and the DC output side of the front-stage AC-DC converter in grid-connected or off-grid operation mode, so as to maintain the voltage / current stability of the AC side under unbalanced load conditions. The subsequent DC-DC isolation converter is connected to the energy storage battery. The subsequent DC-DC isolation converter is used to perform bidirectional isolation transmission between the DC output side of the preceding AC-DC converter and the energy storage battery, so as to manage the energy of the energy storage battery according to the charging or discharging conditions.

[0006] Based on the above technical solution, preferably, the LCL filter includes inductors La1, La2, Lb1, Lb2, Lc1, Lc2, capacitors Ca1, Cb1, and Cc1, wherein, The common terminal of inductors La1 and La2 is connected to one end of capacitor Ca1, and the other end of inductor La1 is connected to the pre-amplifier AC-DC converter. The other end of inductor La2 is connected to resistor Ra. The common terminal of inductors Lb1 and Lb2 is connected to one end of capacitor Cb1, and the other end of inductor Lb1 is connected to the pre-amplifier AC-DC converter. The other end of inductor Lb2 is connected to resistor Rb. The common terminal of inductors Lc1 and Lc2 is connected to one end of capacitor Cc1, and the other end of inductor Lc1 is connected to the pre-amplifier AC-DC converter. The other end of inductor Lc2 is connected to resistor Rc. The other end of capacitor Ca1 is connected to the other ends of capacitors Cb1 and Cc1 respectively.

[0007] Based on the above technical solutions, preferably, the front-end AC-DC converter includes high-frequency switching transistors Va1, Va2, Vb1, Vb2, Vc1, Vc2, Vn1, Vn2, capacitors C1 and C2, and inductor Ln1, wherein... The common terminal of the high-frequency switching transistors Va1 and Va2 is connected to the LCL filter. The common terminal of the high-frequency switching transistors Vb1 and Vb2 is connected to the LCL filter. The common terminal of the high-frequency switching transistors Vc1 and Vc2 is connected to the LCL filter. The common terminal of the high-frequency switching transistors Va1, Vb1, Vc1, and Vn1 is connected to one end of the subsequent DC-DC isolation converter and one end of the capacitor C1, respectively. The common terminal of the high-frequency switching transistors Va2, Vb2, Vc2, and Vn2 is connected to one end of the subsequent DC-DC isolation converter and one end of the capacitor C2, respectively. The common terminal of the high-frequency switching transistors Vn1 and Vn2 is connected to the other end of the capacitor C1, the other end of the capacitor C2, and one end of the inductor Ln1, respectively. The other end of the inductor Ln1 is connected to the load or the power grid side.

[0008] More preferably, the subsequent DC-DC isolated converter includes a primary-side full-bridge converter unit, an energy transfer unit, a secondary-side full-bridge converter unit, and an energy management unit, wherein... The primary-side full-bridge converter unit is connected to the front-stage AC-DC converter and the energy transfer unit respectively. The primary-side full-bridge converter unit is used to convert the DC voltage output from the DC output side of the front-stage AC-DC converter into a high-frequency AC voltage. The energy transfer unit is connected to the secondary-side full-bridge converter unit, and the energy transfer unit is used to provide electrical isolation and transmission between the primary-side full-bridge converter unit and the secondary-side full-bridge converter unit; The secondary-side full-bridge converter is connected to the energy management unit, and the secondary-side full-bridge converter is used to convert the high-frequency AC voltage output by the energy transfer unit into the target DC voltage.

[0009] More preferably, the primary-side full-bridge converter unit includes switches S1A, S2A, S3A, S4A, S1B, S2B, S3B, and S4B, wherein... The common terminal of the switching transistors S1A and S2A is connected to the energy transfer unit. The first common terminal of the switching transistors S1B and S3B is connected to the other end of the switching transistor S1A and the front-end AC-DC converter, respectively. The first common terminal of the switching transistors S2B and S4B is connected to the other end of the switching transistor S4A and the front-end AC-DC converter, respectively. The common terminal of the switching transistors S3A and S4A is connected to the energy transfer unit. The common terminal of the switching transistors S1B and S2B is connected to the energy transfer unit. The common terminal of the switching transistors S3B and S4B is connected to the energy transfer unit.

[0010] More preferably, the energy transfer unit includes inductor Lf1, inductor Lf2, capacitor CV1, capacitor CV2, capacitor CF1, capacitor CF2, high-frequency isolation transformer T11, and high-frequency isolation transformer T12, wherein, One end of capacitor CV1 is connected to the common terminal of switching transistors S1A and S2A through inductor Lf1. The other end of capacitor CV1 is connected to the first input terminal of high-frequency isolation transformer T11. The second input terminal of high-frequency isolation transformer T11 is connected to the common terminal of switching transistors S3A and S4A. The first output terminal of high-frequency isolation transformer T11 is connected to the secondary-side full-bridge converter unit through capacitor CF1. The second output terminal of high-frequency isolation transformer T11 is connected to the secondary-side full-bridge converter unit. One end of capacitor CV2 is connected to the common terminal of switching transistors S1B and S2B through inductor Lf2. The other end of capacitor CV2 is connected to the first input terminal of high-frequency isolation transformer T12. The second input terminal of high-frequency isolation transformer T12 is connected to the common terminal of switching transistors S3B and S4B. The first output terminal of high-frequency isolation transformer T12 is connected to the secondary-side full-bridge converter unit through capacitor CF2. The second output terminal of high-frequency isolation transformer T12 is connected to the secondary-side full-bridge converter unit.

[0011] More preferably, the secondary-side full-bridge converter unit includes switches S5A, S6A, S7A, S8A, S5B, S6B, S7B, and S8B, wherein... The common terminal of the switching transistors S5A and S6A is connected to the energy transfer unit; the common terminal of the switching transistors S7A and S8A is connected to the energy transfer unit; the common terminal of the switching transistors S5A and S7A is connected to the energy management unit; and the common terminal of the switching transistors S6A and S8A is connected to the energy management unit. The common terminal of the switching transistors S5B and S6B is connected to the energy transfer unit, the common terminal of the switching transistors S7B and S8B is connected to the energy transfer unit, the common terminal of the switching transistors S5B and S7B is connected to the energy management unit, and the common terminal of the switching transistors S6B and S8B is connected to the energy management unit.

[0012] More preferably, the energy management unit includes switch S1, switch S2, switch S3, and an energy storage battery, wherein, One end of switch S1 is connected to the common terminal of the energy storage battery and the switching transistors S5A and S7A respectively. The other end of switch S1 is connected to one end of switch S2 and the common terminal of the switching transistors S5B and S7B respectively. The other end of switch S2 is connected to one end of switch S3 and the common terminal of the switching transistors S6A and S8A respectively. The other end of switch S3 is connected to the common terminal of the energy storage battery and the switching transistors S6B and S8B respectively.

[0013] A second aspect of this application provides a control method for a bidirectional charge-discharge topology capable of carrying an unbalanced load, the control method comprising: Obtain the electrical parameters of the front-end AC-DC converter, wherein the electrical parameters include the three-phase output voltage, filter inductor current, grid-side voltage, DC bus voltage, and energy storage battery voltage; Based on the off-grid command, the grid-connected command, and the contactor status of the off-grid and grid-connected side circuits, determine the current operating mode of the bidirectional charging and discharging topology, wherein the operating mode includes any one of the off-grid inverter mode, the grid-connected inverter mode, and the grid-connected rectification mode. In the off-grid inverter mode or grid-connected inverter mode, the front-end AC-DC converter is controlled to perform inverter energy transfer between the energy storage battery and the grid side or load. In the grid-connected rectification mode, the front-stage AC-DC converter is controlled to perform rectified energy transmission between the grid side and the DC bus, wherein the DC bus is the DC bus formed by the DC output side of the front-stage AC-DC converter; The control system enables bidirectional isolation energy transfer between the DC output side of the preceding AC-DC converter and the energy storage battery, and manages the energy of the energy storage battery according to the charging or discharging conditions.

[0014] More preferably, the method further includes: In the off-grid inverter mode and the grid-connected inverter mode, the downstream DC-DC isolation converter is in a forward operating state, using the voltage of the energy storage battery as the input voltage and the DC bus voltage of the upstream AC-DC converter as the output voltage. In the grid-connected rectification mode, the downstream DC-DC isolation converter operates in reverse, using the DC bus voltage of the upstream AC-DC converter as the input voltage and the energy storage battery voltage as the output voltage.

[0015] The bidirectional charging and discharging topology and control method capable of handling unbalanced loads provided by this invention have the following advantages over existing technologies: (1) By setting an LCL filter between the front-end AC-DC converter and the grid / load, the switching harmonics generated by the front-end AC-DC converter are effectively suppressed, the harmonic interference to the grid side or load side is reduced, and the power quality requirements of the grid / consumer side are met. The front-end AC-DC converter has bidirectional energy conversion capability. In grid-connected or off-grid mode, it can actively adjust the AC side voltage and current to compensate for three-phase unbalanced or single-phase unbalanced loads. Thus, the AC side voltage / current can still be kept stable and symmetrical when the load is unbalanced. At the same time, through the rear-end DC-DC isolation converter, bidirectional energy transmission between the front-end DC bus and the energy storage battery can be realized. It can be flexibly controlled according to the charging or discharging conditions, and the battery can be accurately charged and discharged to improve the battery utilization rate. It provides electrical isolation between the energy storage battery and the grid / load side for the isolation structure, thereby improving the operational stability and output voltage / current quality of the bidirectional charging and discharging topology and reducing the risk of fault propagation.

[0016] (2) By collecting off-grid commands, grid-connected commands and contactor status, the system can automatically determine whether it is in off-grid inverter, grid-connected inverter or grid-connected rectification mode, realize intelligent switching of the topology between the three operating conditions, improve the system's adaptability and flexibility to different application scenarios, and perform closed-loop control based on electrical parameters such as three-phase output voltage, filter inductor current and grid voltage. It can accurately adjust the inverter side in off-grid inverter and grid-connected inverter modes, and maintain the stability of AC side voltage / current and power quality when the load is unbalanced or the operating conditions change. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a bidirectional charge-discharge topology capable of carrying an unbalanced load provided by the present invention; Figure 2 The internal operating logic framework diagram corresponding to the bidirectional charging and discharging topology provided by the present invention; Figure 3 The off-grid inverter mode control block diagram corresponding to the bidirectional charging and discharging topology provided by the present invention; Figure 4 The grid-connected inverter mode control block diagram corresponding to the bidirectional charging and discharging topology provided by this invention; Figure 5 A control block diagram of the grid-connected rectification mode corresponding to the bidirectional charging and discharging topology provided by the present invention; Figure 6 A schematic diagram of the phase-shift buck-boost waveform provided by this invention; Figure 7 The algorithm control block diagram of the downstream DC-DC isolation converter provided by the present invention.

[0019] Explanation of reference numerals in the attached diagram: 1. LCL filter; 2. Pre-stage AC-DC converter; 3. Post-stage DC-DC isolation converter. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention discloses a bidirectional charge-discharge topology capable of handling unbalanced loads, with reference to... Figure 1 and Figure 2 The aforementioned bidirectional charging and discharging topology includes an LCL filter 1, a front-stage AC-DC converter 2, and a rear-stage DC-DC isolation converter 3, wherein... One side of LCL filter 1 is connected to the preceding AC-DC converter 2, and the other side of LCL filter 1 is connected to the load or the power grid. LCL filter 1 is used to suppress the switching harmonics generated by the preceding AC-DC converter 2 in order to reduce the harmonic impact of the switching harmonics on the power grid or the load.

[0022] Furthermore, the LCL filter 1 includes inductors La1, La2, Lb1, Lb2, Lc1, Lc2, capacitors Ca1, Cb1, and Cc1, wherein... The common terminal of inductors La1 and La2 is connected to one end of capacitor Ca1. The other end of inductor La1 is connected to the pre-amplifier AC-DC converter 2. The other end of inductor La2 is connected to resistor Ra. The common terminal of inductors Lb1 and Lb2 is connected to one end of capacitor Cb1. The other end of inductor Lb1 is connected to the pre-amplifier AC-DC converter 2. The other end of inductor Lb2 is connected to resistor Rb. The common terminal of inductors Lc1 and Lc2 is connected to one end of capacitor Cc1. The other end of inductor Lc1 is connected to the pre-amplifier AC-DC converter 2. The other end of inductor Lc2 is connected to resistor Rc. The other end of capacitor Ca1 is connected to the other ends of capacitors Cb1 and Cc1 respectively.

[0023] In this embodiment, the design of LCL filter 1 mainly considers the single harmonic and total harmonic content in accordance with national standards, the inductor current ripple on the inverter side, and reduces the inductor core loss, switching loss, and reactive power introduced by the filter capacitor on the inverter side. When designing the closed loop, the system is transformed from a three-phase abc stationary coordinate system to a two-phase dq stationary coordinate system for control, and a simple PI regulator can effectively eliminate steady-state errors.

[0024] L1 represents the inverter-side inductance of LCL filter 1, i.e., the inductance value of each phase. The lower / upper limit of the inverter-side inductance value, calculated based on factors such as ripple and voltage distortion, can be expressed as: in, This indicates the lower limit of the inductance value on the inverter side. This indicates the upper limit of the inductance value on the inverter side. The ripple factor is typically chosen to be between 0.2 and 0.3. T represents the carrier period, and I represents the effective value of the rated current. Indicates the grid voltage. Represents the angular frequency of the grid voltage. This represents the ratio of the effective voltage values, typically 0.05.

[0025] exist Figure 1In this example, capacitors Ca1, Cb1, and Cc1 have the same capacitance value. Considering the reactive power introduced by the filter capacitor C, the larger the capacitance of the filter capacitor, the larger the current flowing through the inductor L1 and the switching transistor, and the greater the switching conduction loss. The ratio of the reactive power introduced by the filter capacitor C to the rated active power output of the grid-connected inverter is defined as λc, which is generally chosen to be around 0.02. Po This indicates the output power of one of the phases.

[0026] Grid-connected current of a certain phase i Regarding the bridge arm output voltage The transfer function is: in, This represents the transfer function of LCL filter 1 from the output voltage of the bridge arm to the grid current. s Represents the complex frequency domain variables in the Laplace transform. Indicates grid-connected current. This indicates the inverter-side inductance of LCL filter 1. This indicates the grid-side inductance of LCL filter 1. This represents the resonant angular frequency of LCL filter 1.

[0027] After selecting the inverter-side inductor and filter capacitor, the grid-side inductor value L2 is designed according to standard constraints, and the modulation wave angle frequency, initial phase value, and frequency of the SPWM modulation method are set. The triangular carrier amplitude, modulation ratio, and other related parameters are set, and the Fourier transform expansion is used for calculation. The spectrum was used to determine the main harmonic frequencies. The number of times and the amplitude. Then, according to the filtered grid-connected current... The proportion of harmonics in the rated grid-connected current ,make The grid-side inductance L2 is obtained as follows:

[0028] The front-stage AC-DC converter 2 is connected to the rear-stage DC-DC isolation converter 3. The front-stage AC-DC converter 2 is used to perform bidirectional energy conversion between the AC port of the front-stage AC-DC converter 2 and the DC output side of the front-stage AC-DC converter 2 in grid-connected or off-grid operation mode, so as to maintain the voltage / current stability of the AC side under unbalanced load conditions.

[0029] Furthermore, the front-end AC-DC converter 2 includes high-frequency switching transistors Va1, Va2, Vb1, Vb2, Vc1, Vc2, Vn1, Vn2, capacitors C1 and C2, and inductor Ln1, wherein, The common terminal of high-frequency switching transistors Va1 and Va2 is connected to LCL filter 1. The common terminal of high-frequency switching transistors Vb1 and Vb2 is connected to LCL filter 1. The common terminal of high-frequency switching transistors Vc1 and Vc2 is connected to LCL filter 1. The common terminal of high-frequency switching transistors Va1, Vb1, Vc1, and Vn1 is connected to one end of the subsequent DC-DC isolation converter 3 and capacitor C1, respectively. The common terminal of high-frequency switching transistors Va2, Vb2, Vc2, and Vn2 is connected to one end of the subsequent DC-DC isolation converter 3 and capacitor C2, respectively. The common terminal of high-frequency switching transistors Vn1 and Vn2 is connected to the other end of capacitor C1, the other end of capacitor C2, and one end of inductor Ln1, respectively. The other end of inductor Ln1 is connected to the load or the mains.

[0030] In this embodiment, the front-end AC-DC converter uses two-level SiC transistors as high-frequency switches, with a switching frequency of 40kHz. A full-bridge structure is adopted, and its control logic is as follows:

[0031] In off-grid inverter mode, the front-end employs quasi-proportional resonant control in the voltage outer loop and PI control in the current inner loop. The quasi-proportional resonant controller eliminates the need for coordinate transformation and decoupling control, directly controlling sinusoidal quantities in the three-phase stationary coordinate system. While simplifying the control system, compared to traditional PI controllers, the quasi-proportional resonant controller enhances the system's anti-interference capability and robustness. The transfer function of the quasi-proportional resonant controller is:

[0032] in, k p This represents the proportionality coefficient. k r Represents the resonance coefficient. ω c Indicates the cutoff angular frequency; ω 0 represents the fundamental angular frequency. k p Affects the overall gain of the controller. k r The gain that affects the resonance peak ω c Affecting Xie Zhenfeng's frequency band bandwidth This indicates the resonant frequency.

[0033] While quasi-PR control is used in the outer voltage loop to improve the inverter's voltage tracking performance, a PI controller is used in the inner current loop to improve system response speed and anti-interference capability. The modulation strategy employs SPWM modulation, in which a sinusoidal AC voltage reference is compared with a high-frequency triangular carrier wave in real time. A high-level output is triggered when the sinusoidal AC voltage reference is greater than the high-frequency triangular carrier wave, and a low-level output is triggered when the sinusoidal AC voltage reference is less than the high-frequency triangular carrier wave. This can be implemented in the DSP through the EPWM module, using the value of CMPA and the counter TBCTR for real-time comparison. The off-grid inverter mode control block diagram is shown below. Figure 3 As shown, the specific process is as follows:

[0034] Step 1: Obtain the three-phase output voltage V ao , V bo , V co The modulation signal is obtained by passing the signal through a quasi-proportional resonant controller and a PI controller, respectively. V am , V bm , V cm .

[0035] Step Two: V am , V bm , V cm After passing through the voltage equalization controller, the zero-sequence voltage is obtained. V n Then, the modulation signal is obtained through a proportional resonant controller. V nm .

[0036] Step 3: V am , V bm , V cm , V nm The PWM wave is obtained through SPWM modulation, which in turn controls the inverter.

[0037] In this embodiment, the control structure of the three-phase four-wire front-end AC-DC converter 2 (inverter) in off-grid inverter mode includes a three-phase voltage outer loop-current inner loop dual closed-loop control unit, a zero-sequence voltage equalization control unit, and an SPWM modulation unit, etc.

[0038] For phase A: Set the voltage... V refa Actual voltage of phase A at inverter output terminalV ao The voltage error signal obtained from the comparison is input into the phase A quasi-proportional resonant controller, which outputs the phase A current reference value. ;Will With the actual current of the filter inductor I aL In comparison, the obtained current error is fed into the A-phase PI controller, and the PI controller outputs the A-phase modulation signal component. V am .

[0039] For phase B: voltage given V refb With actual voltage V bo The error signal is compared, and the current reference value is obtained by the B-phase quasi-proportional resonant controller. Then, with the current of the filter inductor I bL The B-phase modulated signal component is obtained by comparison using the B-phase PI controller. V bm .

[0040] For phase C: voltage given V refc With actual voltage V co The error signal is compared, and the current reference value is obtained by the C-phase quasi-proportional resonant controller. Then, combined with the current of the filter inductor. I cL The C-phase modulated signal component is obtained by comparison with the C-phase PI controller. V cm .

[0041] Through the cascaded control of the voltage outer loop and the current inner loop, the amplitude and waveform of the three-phase output voltage can be precisely adjusted, and the ripple and peak value of the filter inductor current can be limited.

[0042] The three-phase voltage modulation wave is sent to the voltage equalization controller, which outputs a zero-sequence voltage command based on the voltage imbalance across the split DC capacitor. V n .

[0043] Zero-sequence voltage command V n The error signal obtained by comparing with the zero-sequence voltage reference value (usually taken as 0) is input to the proportional resonant controller, and finally obtains the modulation signal for controlling the fourth bridge arm, thereby achieving voltage balance of the split capacitor and stability of the neutral point potential under unbalanced load or single-phase / two-phase load conditions.

[0044] modulated signal V am ,V bm , V cm 、V nm The signal is fed into the SPWM modulation unit, which generates a corresponding PWM pulse sequence based on the comparison result between the modulation signal and the carrier signal. The PWM pulse sequence serves as the drive signal for each phase arm switch and the neutral arm switch in the three-phase four-wire inverter, thereby controlling the inverter's output voltage.

[0045] In grid-connected inverter mode, a current inner loop structure based on the dq coordinate system is adopted. Phase-locked loop (PLL) control is used to acquire the grid phase, accurately detecting the phase angle and frequency of the grid voltage in real time. This phase is used as the phase angle for coordinate transformation during the control process. The core objective of the inverter mode is to inject a controllable, high-quality sinusoidal current into the grid; therefore, only the inductor current is controlled. The control block diagram for grid-connected inverter mode is shown below. Figure 4 As shown, the specific process is as follows:

[0046] Step 1: Obtain the three-phase output voltage V o Inductor current I L Grid voltage V g Grid voltage V g The reference phase is obtained through a phase-locked loop controller. The three-phase output voltage Vo and inductor current IL are obtained through coordinate transformation based on the reference phase. V od , V oq , I Ld , I Lq .

[0047] Step Two: I Ld , I Lq Obtained through the PI controller V d , V q The modulation signal is then obtained through inverse coordinate transformation. V am , V bm , V cm .

[0048] Step 3: V am , V bm ,V cm The PWM wave is obtained through SPWM modulation, which in turn controls the inverter.

[0049] In this embodiment, the control structure of the front-end three-phase four-wire AC-DC converter in grid-connected inverter mode mainly includes: a phase-locked loop module, a coordinate transformation module, a current dual closed-loop regulation module, a dq / abc coordinate inverse transformation module, an SPWM modulation module, and a three-phase four-wire inverter unit.

[0050] grid voltage V g The input phase-locked loop (PLL) module detects and locks onto the grid voltage, outputting a reference phase that is in phase and frequency with the grid voltage. θ g Electrical reference phase θ g This serves as a reference phase for subsequent abc / dq and dq / abc coordinate transformations.

[0051] Acquisition of three-phase filter inductor current I L and in the reference phase θ g Performing an abc / dq coordinate transformation in a synchronous rotating coordinate system yields the d-axis and q-axis components of the current. I Ld and I Lq ; Simultaneously collect three-phase output voltage V o In the same reference phase θ g Perform an abc / dq coordinate transformation to obtain the voltage components. V od and V oq .

[0052] Give active current With actual d-axis current I Ld In comparison, the obtained current error signal is sent to the d-axis PI controller, and the PI controller outputs an adjustment amount, which is compared with the d-axis voltage component. V od The commands are superimposed to obtain the d-axis control voltage command. V d ; Give reactive current (Typically set to 0) and the actual q-axis current I Lq In comparison, the obtained error signal is sent to the q-axis PI controller, and the PI controller outputs an adjustment amount, which is compared with the q-axis voltage component.I Lq The commands are superimposed to obtain the q-axis control voltage command. V q .

[0053] Through the above-mentioned dual closed-loop control of d / q axis current, the active and reactive currents can be adjusted independently during grid-connected operation, thereby achieving decoupled control of grid-connected active and reactive power.

[0054] The obtained d-axis and q-axis control voltage commands V d , V q In reference phase θ g Perform an inverse dq / abc coordinate transformation to obtain the three-phase modulated signal. V am , V bm , V cm The three-phase modulation signal is sent to the SPWM modulation module, and after being compared with the carrier wave, it generates PWM pulse signals for each arm of the three-phase four-wire inverter.

[0055] The PWM pulse signal output by the SPWM modulation module is used to drive the various power switching devices of the three-phase four-wire inverter, thereby controlling the inverter's output voltage and current waveforms to match the grid current and grid voltage. V g It operates at the same frequency and phase, and its amplitude is adjustable, meeting the requirements for grid-connected inverter operation and power regulation.

[0056] In grid-connected rectification mode, a voltage outer loop-current inner loop structure based on the dq coordinate system is adopted. The DC voltage outer loop, after being controlled by a PI controller, serves as the d-axis reference value for the current loop, while the q-axis reference value is 0. The control block diagram for grid-connected rectification mode is shown below. Figure 5 As shown, the specific process is as follows:

[0057] Step 1: Obtain the three-phase output voltage V o Inductor current I L Grid voltage V g Bus voltage V dc Grid voltage V g The reference phase is obtained through a phase-locked loop controller. The three-phase output voltage Vo and inductor current IL are obtained through coordinate transformation based on the reference phase. V od , V oq , ILd , I Lq .

[0058] Step 2: Bus voltage V dc The reference value of the d-axis current is obtained through a PI controller. I Ld , I Lq Obtained through the PI controller V d , V q The modulation signal is then obtained through inverse coordinate transformation. V am , V bm , V cm .

[0059] Step 3: V am , V bm , V cm The PWM wave is obtained through SPWM modulation, which then controls the inverter.

[0060] In this embodiment, the control structure of the front-end three-phase four-wire AC-DC converter in grid-connected rectification mode mainly includes: a phase-locked loop module, an abc / dq coordinate transformation module, a DC bus voltage outer loop-current inner loop dual closed-loop control module, a dq / abc coordinate inverse transformation module, and an SPWM modulation module, etc.

[0061] grid voltage V g The input phase-locked loop (PLL) module detects and locks onto the grid voltage, outputting a reference phase that is in phase and frequency with the grid voltage. θ g This serves as the reference phase for subsequent abc / dq and dq / abc coordinate transformations.

[0062] Collect three-phase output voltage V o In the reference phase θ g The d-axis component of the voltage in the synchronous rotating coordinate system is obtained through the abc / dq coordinate transformation module. V od and q-axis components V oq ; Acquisition of three-phase filter inductor current I L In the same reference phase θg The d-axis and q-axis components of the current are obtained through the abc / dq coordinate transformation module. I Ld , I Lq .

[0063] DC bus voltage setpoint V dcref With actual DC bus voltage V dc In comparison, the obtained voltage error signal is sent to the PI controller, and the PI controller outputs the d-axis current reference value. I Ld_ref By adjusting the outer voltage loop, the DC bus voltage is stabilized near the preset reference value.

[0064] The d-axis current reference value given by the voltage outer loop I Ld_ref With actual d-axis current I Ld In comparison, the obtained current error is fed into the d-axis PI controller, and the adjustment amount output by the PI controller is compared with the voltage component. V od The two are superimposed to obtain the d-axis control voltage command. V d ; Compare the q-axis current reference value (usually set to 0) with the actual q-axis current. I Lq In comparison, the obtained current error is fed into the q-axis PI controller, and the adjustment amount output by the PI controller is compared with the voltage component. V oq The two are superimposed to obtain the q-axis control voltage command. V q Through the aforementioned d / q-axis current inner loop control, decoupled regulation of the active and reactive components of the grid-connected current is achieved. The d-axis current is used to regulate the DC bus voltage, while the q-axis current is controlled to zero to achieve unity power factor operation.

[0065] The obtained d-axis and q-axis control voltage commands V d , V q In reference phase θ g Perform an inverse dq / abc coordinate transformation to obtain the corresponding three-phase modulation signal. V am , V bm , V cm The three-phase modulation signal is sent to the SPWM modulation module, and after being compared with the carrier wave, it generates PWM pulse signals for each arm of the three-phase four-wire inverter.

[0066] The PWM pulses output by the SPWM module are used to drive the various power switching devices in the three-phase four-wire inverter, thereby controlling the inverter to operate in rectification mode, so that the grid-connected current is in phase and frequency with the grid voltage, and the DC bus voltage is stabilized by adjusting the d-axis current.

[0067] The downstream DC-DC isolation converter 3 is connected to the energy storage battery. The downstream DC-DC isolation converter 3 is used to perform bidirectional isolation transmission between the DC output side of the upstream AC-DC converter 2 and the energy storage battery, so as to manage the energy of the energy storage battery according to the charging or discharging conditions.

[0068] The subsequent DC-DC isolated converter 3 includes a primary-side full-bridge converter unit, an energy transfer unit, a secondary-side full-bridge converter unit, and an energy management unit. The primary-side full-bridge converter unit is connected to the front-stage AC-DC converter 2 and the energy transfer unit respectively. The primary-side full-bridge converter unit is used to convert the DC voltage output from the DC output side of the front-stage AC-DC converter 2 into a high-frequency AC voltage. The primary-side full-bridge converter unit includes switches S1A, S2A, S3A, S4A, S1B, S2B, S3B, and S4B, wherein... The common terminal of switching transistors S1A and S2A is connected to the energy transfer unit. The first common terminal of switching transistors S1B and S3B is connected to the other end of switching transistor S1A and the front-end AC-DC converter 2, respectively. The first common terminal of switching transistors S2B and S4B is connected to the other end of switching transistor S4A and the front-end AC-DC converter 2, respectively. The common terminal of switching transistors S3A and S4A is connected to the energy transfer unit. The common terminal of switching transistors S1B and S2B is connected to the energy transfer unit. The common terminal of switching transistors S3B and S4B is connected to the energy transfer unit.

[0069] The energy transfer unit is connected to the secondary-side full-bridge converter unit. The energy transfer unit is used to provide electrical isolation and transmission between the primary-side full-bridge converter unit and the secondary-side full-bridge converter unit. The energy transfer unit includes inductors Lf1 and Lf2, capacitors CV1 and CV2, capacitors CF1 and CF2, a high-frequency isolation transformer T11, and a high-frequency isolation transformer T12. One end of capacitor CV1 is connected to the common terminal of switching transistors S1A and S2A through inductor Lf1. The other end of capacitor CV1 is connected to the first input terminal of high-frequency isolation transformer T11. The second input terminal of high-frequency isolation transformer T11 is connected to the common terminal of switching transistors S3A and S4A. The first output terminal of high-frequency isolation transformer T11 is connected to the secondary-side full-bridge converter unit through capacitor CF1. The second output terminal of high-frequency isolation transformer T11 is connected to the secondary-side full-bridge converter unit. One end of capacitor CV2 is connected to the common terminal of switching transistors S1B and S2B through inductor Lf2. The other end of capacitor CV2 is connected to the first input terminal of high-frequency isolation transformer T12. The second input terminal of high-frequency isolation transformer T12 is connected to the common terminal of switching transistors S3B and S4B. The first output terminal of high-frequency isolation transformer T12 is connected to the secondary-side full-bridge converter unit through capacitor CF2. The second output terminal of high-frequency isolation transformer T12 is connected to the secondary-side full-bridge converter unit.

[0070] The secondary-side full-bridge converter unit is connected to the energy management unit. The secondary-side full-bridge converter unit is used to convert the high-frequency AC voltage output by the energy transfer unit into the target DC voltage.

[0071] The secondary-side full-bridge converter unit includes switches S5A, S6A, S7A, S8A, S5B, S6B, S7B, and S8B. The common terminal of switching transistors S5A and S6A is connected to the energy transfer unit, the common terminal of switching transistors S7A and S8A is connected to the energy transfer unit, the common terminal of switching transistors S5A and S7A is connected to the energy management unit, and the common terminal of switching transistors S6A and S8A is connected to the energy management unit. The common terminal of switching transistors S5B and S6B is connected to the energy transfer unit, the common terminal of switching transistors S7B and S8B is connected to the energy transfer unit, the common terminal of switching transistors S5B and S7B is connected to the energy management unit, and the common terminal of switching transistors S6B and S8B is connected to the energy management unit.

[0072] The energy management unit includes switch S1, switch S2, switch S3, and an energy storage battery. One end of switch S1 is connected to the common terminal of the energy storage battery and switching transistors S5A and S7A respectively. The other end of switch S1 is connected to one end of switch S2 and the common terminal of switching transistors S5B and S7B respectively. The other end of switch S2 is connected to one end of switch S3 and the common terminal of switching transistors S6A and S8A respectively. The other end of switch S3 is connected to the common terminal of the energy storage battery and switching transistors S6B and S8B respectively.

[0073] In this embodiment, the downstream DC-DC isolation converter 3 employs TPS control, a control method offering greater flexibility. Power flow is achieved by controlling the primary side's inward phase shift angle D1, the secondary side's inward phase shift angle D2, and the primary and secondary sides' outward phase shift angles Dw. This optimizes converter performance by achieving an ultra-wide soft-switching range, minimum current stress, and reduced return power.

[0074] like Figure 6 As shown, Figure 6 S1B to S8B are Figure 1 The switching transistor number of the downstream DC-DC isolation converter 3 in the overall hardware topology diagram, U ab U cd The waveforms before and after phase shift are shown.

[0075] Please see Figure 7 , Figure 7 This is the algorithm control block diagram for the subsequent DC-DC isolation converter 3. The specific control process is the output voltage U. 2ref The error between the output voltage U2 and the input voltage U2 is used as the input to the PI controller. V The PI output and output current I2 determine the converter's transmission power P, and the per-unit transmission power P0* is obtained through calculation. The voltage conversion ratio K and power are calculated in real time. The input is fed into a multi-objective optimized modulation strategy to determine the current power range of the transmitted power. Then, Dw, D1, and D2 are calculated, and the phase shift angle is written into the DSP phase register to achieve output voltage stabilization and power flow. The formula is as follows:

[0076] Among them, U 2ref U1 represents the output reference voltage, U2 represents the input voltage, U2 represents the output voltage, I2 represents the output current, n represents the transformation ratio of the primary and secondary sides, D1 represents the inward phase shift angle of the primary side, D2 represents the inward phase shift angle of the secondary side, Dw represents the outward phase shift angle of the primary and secondary sides, K represents the voltage conversion ratio, and P represents the transmission power.

[0077] In both off-grid and grid-connected modes, it operates in the forward direction, with the battery voltage as the input voltage U1 and the bus voltage as the output voltage U2. In rectifier mode, it operates in the reverse direction, with the bus voltage as the input voltage U1 and the battery voltage as the output voltage U2.

[0078] In this embodiment, by setting an LCL filter 1 between the front-end AC-DC converter 2 and the grid / load, the switching harmonics generated by the front-end AC-DC converter 2 are effectively suppressed, reducing harmonic interference to the grid side or load side, and meeting the power quality requirements of the grid-connected / consumer side. Furthermore, the front-end AC-DC converter 2 has bidirectional energy conversion capability, and can actively adjust the AC side voltage and current in grid-connected or off-grid modes to compensate for three-phase unbalanced or single-phase unbalanced loads. Thus, it can still maintain the stability and symmetry of AC side voltage / current when the load is unbalanced. At the same time, through the rear-end DC-DC isolation converter 3, bidirectional energy transfer between the front-end DC bus and the energy storage battery is realized. It can be flexibly controlled according to the charging or discharging conditions, and precise charge and discharge management of the battery can be performed to improve battery utilization. It provides electrical isolation between the energy storage battery and the grid / load side for the isolated structure, thereby improving the operational stability and output voltage / current quality of the bidirectional charge and discharge topology and reducing the risk of fault propagation.

[0079] Please refer to it again. Figure 2 In one example, the control method of the bidirectional charging and discharging topology capable of carrying unbalanced loads according to the present invention comprises two main modules: a power conversion part and a control and human-machine interaction part.

[0080] The power conversion section consists of a front-end AC-DC converter circuit, a rear-end bidirectional isolated DC-DC converter circuit, and a battery, among other components: Load / Grid Side: One end of the AC side of the system can be connected to an external three-phase four-wire power grid, or connected to an independent load via a contactor, to achieve grid-connected operation or off-grid power supply operation.

[0081] Pre-conversion circuit: The load / grid side is connected to the pre-conversion AC-DC converter circuit via corresponding switches. The pre-conversion circuit is used to realize bidirectional energy conversion between the AC side and the DC bus, and to complete the rectification or inversion function in different operating modes.

[0082] DC bus: The DC output side of the front-stage AC-DC converter circuit forms the DC bus, which is used as the input or output bus of the subsequent DC-DC isolation converter 3 to realize the collection and distribution of energy within the system.

[0083] The subsequent conversion circuit: The DC bus is connected to the subsequent DC-DC isolation converter 3. The subsequent DC-DC isolation converter 3 is used to perform bidirectional isolated energy transfer between the DC bus and the energy storage battery, so as to realize the charging and discharging control of the battery.

[0084] Energy storage battery: The other end of the subsequent DC-DC isolation converter 3 is connected to an energy storage battery for storing and releasing energy from the grid / load.

[0085] Sampling circuits are set at the front-end and rear-end conversion circuits respectively: the front-end sampling circuit is used to collect signals such as grid voltage, grid current, inverter output voltage, and DC bus voltage and current; the rear-end sampling circuit is used to collect signals such as battery voltage, battery current, and input / output voltage and current of the rear-end DC-DC isolation converter 3, providing real-time feedback for the control strategy.

[0086] The control section mainly includes front-end main control DSP, back-end main control DSP, and external control digital tube units. Front-end main control DSP: The front-end main control DSP is electrically connected to the front-end sampling circuit. It is used to receive sampling signals such as AC side voltage and current and DC bus voltage and current. According to the current working mode and control strategy, it generates the drive control quantity of the front-end AC-DC converter 2 to realize the operation functions such as grid-connected inverter, off-grid inverter or grid-connected rectification.

[0087] Post-stage main control DSP: The post-stage main control DSP is electrically connected to the post-stage sampling circuit. It is used to receive the battery terminal voltage, current and relevant electrical parameters of the post-stage DC-DC isolation converter 3. Based on the battery charging and discharging requirements, SOC status and system upper control commands, it generates the phase shift control quantity of the post-stage DC-DC isolation converter 3 to realize the charging and discharging management of the energy storage battery.

[0088] Communication between DSPs: The front-end main control DSP and the back-end main control DSP achieve bidirectional data interaction through a communication interface, which is used to transmit operating mode commands, power setpoints, voltage and current limits and fault status information, thereby realizing the coordinated control and operation status coordination of the front and back-end power conversion units.

[0089] External control digital tube and host control interface: The external control digital tube (or external control panel / host computer) is connected to the back-end main control DSP via communication. It is used to issue external control commands such as operating mode selection and power / voltage setting, and to display system operating parameters and fault information. The back-end main control DSP adjusts the local control strategy according to the external control commands, and at the same time transmits relevant instructions and status information to the front-end main control DSP to realize the unified and coordinated control of the entire bidirectional charging and discharging system.

[0090] and Figure 1 The main parameters of the corresponding test instance are shown in Table 1.

[0091] Table 1 Based on the above method, this application discloses a control method for a bidirectional charge-discharge topology capable of carrying an unbalanced load. The control method includes: Obtain the electrical parameters of the front-end AC-DC converter 2, including the three-phase output voltage, filter inductor current, grid-side voltage, DC bus voltage, and energy storage battery voltage. Based on the off-grid command, grid-connected command, and the contactor status of the off-grid and grid-connected side circuits, determine the current operating mode of the bidirectional charging and discharging topology. The operating mode includes any one of the following: off-grid inverter mode, grid-connected inverter mode, and grid-connected rectification mode. In off-grid inverter mode or grid-connected inverter mode, the front-end AC-DC converter 2 is controlled to transfer inverter energy between the energy storage battery and the grid side or load. In grid-connected rectification mode, the front-end AC-DC converter 2 is controlled to transfer rectified energy between the grid side and the DC bus. The DC bus is the DC bus formed by the DC output side of the front-end AC-DC converter 2. The control unit 3 enables bidirectional isolation energy transfer between the DC output side of the control unit 2 and the energy storage battery, and manages the energy of the energy storage battery according to the charging or discharging conditions.

[0092] The method also includes: In both off-grid inverter mode and grid-connected inverter mode, the downstream DC-DC isolation converter 3 operates in the forward direction, using the voltage of the energy storage battery as the input voltage and the DC bus voltage of the upstream AC-DC converter 2 as the output voltage. In grid-connected rectification mode, the downstream DC-DC isolation converter 3 operates in reverse, using the DC bus voltage of the upstream AC-DC converter 2 as the input voltage and the energy storage battery voltage as the output voltage.

[0093] In this embodiment, by collecting off-grid commands, grid-connected commands, and contactor status, the system automatically determines whether it is currently in off-grid inverter, grid-connected inverter, or grid-connected rectification mode, enabling intelligent switching of the topology between the three operating conditions and improving the system's adaptability and flexibility to different application scenarios (power supply, grid-connected power generation, and charging). Closed-loop control is performed based on electrical parameters such as three-phase output voltage, filter inductor current, and grid voltage, precisely adjusting the inverter side in both off-grid and grid-connected inverter modes. Even with load imbalance and changing operating conditions, the system maintains the stability of AC side voltage / current and power quality. In off-grid / grid-connected inverter modes, the system enables the energy storage battery to discharge to the grid or load side and the grid to provide reverse energy feedback to the energy storage. In grid-connected rectification mode, the grid provides rectified power to the DC bus, creating stable DC bus conditions for subsequent energy storage charging and improving overall energy utilization efficiency. By monitoring the energy storage battery voltage and controlling the subsequent DC-DC isolation converter 3 for bidirectional energy transfer, appropriate voltage and current characteristics can be set according to charging / discharging conditions. It enables precise control over the battery charging and discharging process, avoiding overcharging and over-discharging, and improving battery life and safety.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A bidirectional charge-discharge topology capable of handling unbalanced loads, characterized in that, It includes an LCL filter (1), a front-stage AC-DC converter (2), and a rear-stage DC-DC isolation converter (3), wherein, One side of the LCL filter (1) is connected to the front-stage AC-DC converter (2), and the other side of the LCL filter (1) is connected to the load or the power grid. The LCL filter (1) is used to suppress the switching harmonics generated by the front-stage AC-DC converter in order to reduce the harmonic impact of the switching harmonics on the power grid or the load. The front-stage AC-DC converter (2) is connected to the rear-stage DC-DC isolation converter (3). The front-stage AC-DC converter (2) is used to perform bidirectional energy conversion between the AC port of the front-stage AC-DC converter and the DC output side of the front-stage AC-DC converter in grid-connected operation mode or off-grid operation mode, so as to maintain the voltage / current stability of the AC side under unbalanced load conditions. The subsequent DC-DC isolation converter (3) is connected to the energy storage battery. The subsequent DC-DC isolation converter (3) is used to perform bidirectional isolation transmission between the DC output side of the preceding AC-DC converter and the energy storage battery, so as to manage the energy of the energy storage battery according to the charging or discharging conditions.

2. The bidirectional charge-discharge topology capable of handling unbalanced loads as described in claim 1, characterized in that, The LCL filter (1) includes inductors La1, La2, Lb1, Lb2, Lc1, Lc2, capacitors Ca1, Cb1, and Cc1, wherein... The common terminal of inductor La1 and inductor La2 is connected to one end of capacitor Ca1. The other end of inductor La1 is connected to the front-end AC-DC converter (2). The other end of inductor La2 is connected to resistor Ra. The common terminal of inductor Lb1 and inductor Lb2 is connected to one end of capacitor Cb1. The other end of inductor Lb1 is connected to the front-end AC-DC converter (2). The other end of inductor Lb2 is connected to resistor Rb. The common terminal of inductor Lc1 and inductor Lc2 is connected to one end of capacitor Cc1. The other end of inductor Lc1 is connected to the front-end AC-DC converter (2). The other end of inductor Lc2 is connected to resistor Rc. The other end of capacitor Ca1 is connected to the other ends of capacitors Cb1 and Cc1 respectively.

3. The bidirectional charge-discharge topology capable of handling unbalanced loads as described in claim 1, characterized in that, The pre-amplifier AC-DC converter (2) includes high-frequency switching transistors Va1, Va2, Vb1, Vb2, Vc1, Vc2, Vn1, Vn2, capacitors C1 and C2, and inductor Ln1, wherein, The common terminal of the high-frequency switching transistors Va1 and Va2 is connected to the LCL filter (1). The common terminal of the high-frequency switching transistors Vb1 and Vb2 is connected to the LCL filter (1). The common terminal of the high-frequency switching transistors Vc1 and Vc2 is connected to the LCL filter (1). The common terminals of the high-frequency switching transistors Va1, Vb1, Vc1, and Vn1 are respectively connected to the subsequent DC-DC isolation converter. The common terminal of the high-frequency switch (Va2), the high-frequency switch (Vb2), the high-frequency switch (Vc2) and the high-frequency switch (Vn2) is connected to one end of the subsequent DC-DC isolation converter (3) and the capacitor (C2), respectively. The common terminal of the high-frequency switch (Vn1) and the high-frequency switch (Vn2) is connected to the other end of the capacitor (C1), the other end of the capacitor (C2) and one end of the inductor (Ln1), respectively. The other end of the inductor (Ln1) is connected to the load or the power grid side.

4. The bidirectional charge-discharge topology capable of handling unbalanced loads as described in claim 1, characterized in that, The subsequent DC-DC isolated converter (3) includes a primary-side full-bridge converter unit, an energy transfer unit, a secondary-side full-bridge converter unit, and an energy management unit, wherein, The primary-side full-bridge converter unit is connected to the front-stage AC-DC converter (2) and the energy transfer unit respectively. The primary-side full-bridge converter unit is used to convert the DC voltage output from the DC output side of the front-stage AC-DC converter into a high-frequency AC voltage. The energy transfer unit is connected to the secondary-side full-bridge converter unit, and the energy transfer unit is used to provide electrical isolation and transmission between the primary-side full-bridge converter unit and the secondary-side full-bridge converter unit; The secondary-side full-bridge converter is connected to the energy management unit, and the secondary-side full-bridge converter is used to convert the high-frequency AC voltage output by the energy transfer unit into the target DC voltage.

5. A bidirectional charge-discharge topology capable of carrying an unbalanced load as described in claim 4, characterized in that, The primary-side full-bridge converter unit includes switches S1A, S2A, S3A, S4A, S1B, S2B, S3B, and S4B, wherein... The common terminal of the switching transistors S1A and S2A is connected to the energy transfer unit. The first common terminal of the switching transistors S1B and S3B is connected to the other end of the switching transistor S1A and the front-end AC-DC converter (2), respectively. The first common terminal of the switching transistors S2B and S4B is connected to the other end of the switching transistor S4A and the front-end AC-DC converter (2), respectively. The common terminal of the switching transistors S3A and S4A is connected to the energy transfer unit. The common terminal of the switching transistors S1B and S2B is connected to the energy transfer unit. The common terminal of the switching transistors S3B and S4B is connected to the energy transfer unit.

6. A bidirectional charge-discharge topology capable of carrying an unbalanced load as described in claim 5, characterized in that, The energy transfer unit includes inductors Lf1 and Lf2, capacitors CV1 and CV2, capacitors CF1 and CF2, a high-frequency isolation transformer T11, and a high-frequency isolation transformer T12. One end of capacitor CV1 is connected to the common terminal of switching transistors S1A and S2A through inductor Lf1. The other end of capacitor CV1 is connected to the first input terminal of high-frequency isolation transformer T11. The second input terminal of high-frequency isolation transformer T11 is connected to the common terminal of switching transistors S3A and S4A. The first output terminal of high-frequency isolation transformer T11 is connected to the secondary-side full-bridge converter unit through capacitor CF1. The second output terminal of high-frequency isolation transformer T11 is connected to the secondary-side full-bridge converter unit. One end of capacitor CV2 is connected to the common terminal of switching transistors S1B and S2B through inductor Lf2. The other end of capacitor CV2 is connected to the first input terminal of high-frequency isolation transformer T12. The second input terminal of high-frequency isolation transformer T12 is connected to the common terminal of switching transistors S3B and S4B. The first output terminal of high-frequency isolation transformer T12 is connected to the secondary-side full-bridge converter unit through capacitor CF2. The second output terminal of high-frequency isolation transformer T12 is connected to the secondary-side full-bridge converter unit.

7. A bidirectional charge-discharge topology capable of carrying an unbalanced load as described in claim 4, characterized in that, The secondary-side full-bridge converter unit includes switches S5A, S6A, S7A, S8A, S5B, S6B, S7B, and S8B, wherein... The common terminal of the switching transistors S5A and S6A is connected to the energy transfer unit; the common terminal of the switching transistors S7A and S8A is connected to the energy transfer unit; the common terminal of the switching transistors S5A and S7A is connected to the energy management unit; and the common terminal of the switching transistors S6A and S8A is connected to the energy management unit. The common terminal of the switching transistors S5B and S6B is connected to the energy transfer unit, the common terminal of the switching transistors S7B and S8B is connected to the energy transfer unit, the common terminal of the switching transistors S5B and S7B is connected to the energy management unit, and the common terminal of the switching transistors S6B and S8B is connected to the energy management unit.

8. A bidirectional charge-discharge topology capable of carrying an unbalanced load as described in claim 7, characterized in that, The energy management unit includes switch S1, switch S2, switch S3, and an energy storage battery, wherein... One end of switch S1 is connected to the common terminal of the energy storage battery and the switching transistors S5A and S7A respectively. The other end of switch S1 is connected to one end of switch S2 and the common terminal of the switching transistors S5B and S7B respectively. The other end of switch S2 is connected to one end of switch S3 and the common terminal of the switching transistors S6A and S8A respectively. The other end of switch S3 is connected to the common terminal of the energy storage battery and the switching transistors S6B and S8B respectively.

9. A control method for a bidirectional charge-discharge topology capable of handling unbalanced loads, operating based on the bidirectional charge-discharge topology of any one of claims 1-8, characterized in that, The control method includes: Obtain the electrical parameters of the front-end AC-DC converter (2), wherein the electrical parameters include the three-phase output voltage, the filter inductor current, the grid side voltage, the DC bus voltage, and the energy storage battery voltage; Based on the off-grid command, the grid-connected command, and the contactor status of the off-grid and grid-connected side circuits, determine the current operating mode of the bidirectional charging and discharging topology, wherein the operating mode includes any one of the off-grid inverter mode, the grid-connected inverter mode, and the grid-connected rectification mode. In the off-grid inverter mode or grid-connected inverter mode, the front-end AC-DC converter (2) is controlled to perform inverter energy transfer between the energy storage battery and the grid side or load; In the grid-connected rectification mode, the front-stage AC-DC converter (2) is controlled to perform rectified energy transmission between the grid side and the DC bus, wherein the DC bus is the DC bus formed by the DC output side of the front-stage AC-DC converter (2); The control stage DC-DC isolation converter (3) performs bidirectional isolation energy transfer between the DC output side of the front stage AC-DC converter (2) and the energy storage battery, and performs energy management of the energy storage battery according to the charging or discharging conditions.

10. The control method for a bidirectional charging and discharging topology capable of handling unbalanced loads as described in claim 9, characterized in that, The method further includes: In the off-grid inverter mode and the grid-connected inverter mode, the downstream DC-DC isolation converter (3) is in a positive working state, using the voltage of the energy storage battery as the input voltage and the DC bus voltage of the upstream AC-DC converter (2) as the output voltage. In the grid-connected rectification mode, the downstream DC-DC isolation converter (3) is in reverse operation, using the DC bus voltage of the upstream AC-DC converter (2) as the input voltage and the energy storage battery voltage as the output voltage.

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