Topological structure of photovoltaic energy storage composite grid-connected converter device and its control method

Abstract

The present invention belongs to the technical field of power electronic converters, and discloses a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device topology structure and its control method, wherein the topology structure includes a three-phase dual active bridge, a DC / AC inverter circuit, and a DC / DC bidirectional Boost and Buck circuit. This topology has four ports, including three DC ports and one AC port, to achieve flexible power exchange between the power grid, photovoltaics, and energy storage. The control method adopts the optimal pulse width synchronous modulation method to ensure that the current stress is minimized, and controls the power flow by adjusting the voltage phase difference. The power flow of the AC / DC circuit adopts direct voltage control and hybrid current control based on proportional resonance. The present invention reuses the three-phase dual active bridge topology to achieve grid connection and photovoltaic and energy storage combination, improve the reliability of the device, and protect the safety of the device. It provides an efficient solution for the flexible interaction of the power grid, photovoltaics, and energy storage systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and more specifically, relates to a topological structure of a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device and a control method thereof. Background Art

[0002] Renewable energy generation is often connected to the grid as distributed power sources, characterized by volatility and intermittency. Coupled with new energy vehicle (NEV) loads, the output of renewable energy generation differs significantly from the changing trends of electricity loads, making power forecasting challenging. The power flow distribution in distribution networks is fluctuating, making traditional distribution network control methods inadequate. Therefore, building intelligent, interconnected power grids based on DC microgrids will be a future trend for integrating large amounts of renewable energy, distributed energy storage systems, and corresponding converters into the grid. The core of building a DC microgrid lies in the design of isolated bidirectional DC converters. Three-phase dual-active bridge circuits, with their high specific power density and minimal input and output current ripple, are increasingly becoming a dominant approach in isolated bidirectional DC converter designs. To mitigate power fluctuations caused by renewable energy generation and ensure reliable power supply and safe operation, energy storage devices must be integrated to enable grid-connected devices to achieve peak, frequency, and voltage regulation. Therefore, the use of a multi-port AC / DC / DC converter structure and its control method to flexibly regulate power flows between photovoltaics, energy storage, and the grid will effectively improve system operational stability.

[0003] In existing technologies, the simultaneous connection of photovoltaics and energy storage to the grid requires the introduction of multiple power electronic converter modules, which brings problems of large size and high cost. At the same time, existing control methods are difficult to stabilize the output voltage and current of the energy storage device and the grid-connected current, which can easily lead to excessive DC voltage and threaten the safety of the device. In terms of control implantation, the control of the energy storage device is difficult to integrate into the existing grid-connected converter control, making the composite energy storage control difficult to promote. Summary of the Invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device topology structure and its control method, aiming to solve the problem that the current photovoltaic energy storage grid-connected converter is difficult to stabilize the output voltage and current of the energy storage device and the grid current, and the energy storage device control is difficult to integrate into the existing grid-connected converter control.

[0005] To achieve the above object, a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device topology is provided, which includes a three-phase dual active bridge circuit, a DC / AC inverter circuit and a set of DC / DC chopper circuits;

[0006] The topology structure of the four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device includes four ports: DC port 1, DC port 2, DC port 3 and AC port;

[0007] Among the four ports, DC port 1 can be connected to an external photovoltaic matrix or supercapacitor, DC port 2 can be connected to an external photovoltaic matrix, DC port 3 can be connected to an external battery, and the AC port is connected to the power grid;

[0008] The four ports are: DC port 1 is connected to the AC port via a DC / AC inverter circuit composed of a three-phase bridge circuit C1 and an LLCL filter; DC port 1 is connected to DC port 2 via a three-phase dual active bridge circuit of a three-phase five-winding transformer with a zigzag connection; DC port 2 is connected to DC port 3 via a set of DC / DC chopper circuits composed of a three-phase bridge circuit C2, a secondary winding of a zigzag transformer, a filter inductor LB, and a filter capacitor CB;

[0009] Furthermore, the three-phase dual active bridge circuit includes:

[0010] The three-phase bridge circuit C1 and the three-phase bridge circuit C2 are configured at different DC ports;

[0011] A three-phase five-winding transformer with a zigzag connection is connected to the outputs of the three-phase bridge circuits C1 and C2;

[0012] DC port 1 and DC port 2, wherein DC port 1 is connected to a photovoltaic array or a supercapacitor and includes a filter capacitor Cdc1; DC port 2 is connected to a photovoltaic array and includes a filter capacitor Cdc2;

[0013] The three-phase bridge circuits C1 and C2 are composed of six MOSFET switches respectively, which are configured on the primary and secondary sides of the transformer to achieve current conversion and modulation.

[0014] Furthermore, each MOSFET switch tube of the three-phase bridge circuits C1 and C2 is connected to a corresponding winding of the transformer via a corresponding filter inductor and filter capacitor to optimize current quality and reduce harmonics.

[0015] Furthermore, the DC / AC inverter circuit includes:

[0016] A three-phase bridge circuit C1 is connected to DC port 1;

[0017] An LLCL filter is connected to the output of the three-phase bridge circuit C1 to further filter and stabilize the output current to the grid;

[0018] The three-phase H-bridge includes six MOSFET switches configured in the three-phase bridge circuit C1 to control the current inversion;

[0019] The DC port 1 is connected to an LLCL filter via a three-phase H-bridge to achieve high-efficiency current conversion and output.

[0020] Furthermore, the DC / DC chopper circuit includes:

[0021] The voltage conversion between DC port 2 and DC port 3 is achieved through three Buck circuits or Boost circuits;

[0022] Each Buck or Boost circuit contains a MOSFET switch, a diode, a secondary winding of a zigzag transformer, a filter inductor, and a filter capacitor to achieve effective voltage reduction or boosting;

[0023] By controlling the on and off of the MOSFET switch tube, the current passing through the secondary winding of the zigzag transformer is regulated, thereby adjusting the output voltage and current of the DC port 3, thereby achieving effective energy conversion and management.

[0024] The present invention also provides a method for controlling a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter, comprising the following steps:

[0025] (a) Using a photovoltaic maximum power tracker and the conductance increment method, the photovoltaic array is ensured to operate at the maximum power point, and the voltage at the maximum power point is set to the voltage reference value V2ref of DC port 2;

[0026] (b) calculating the difference between the voltage reference value V2ref and the actual voltage V2 of the DC port 2 using a first subtractor;

[0027] (c) processing the difference through a first proportional-integral controller to obtain a reference deviation of the shift phase D3;

[0028] (d) using a second subtractor to calculate the sum of the phase shift reference value D3*, the reference deviation, and the phase difference between the primary and secondary sides of the transformer to obtain the phase shift D3;

[0029] (e) Calculating the output power Po of DC port 2 through the transmission power generator;

[0030] (f) Calculate the voltage transformation ratio M between the primary and secondary sides of the transformer using the voltage transformation ratio generator;

[0031] (g) Using the global optimal modulation strategy controller, based on the transmission power Po and the voltage transformation ratio M, with the goal of minimizing the global current stress, the duty cycle Dc* and the shift ratio D3* of the switching device are determined;

[0032] (h) Convert the above control signal into a PWM signal to control the switching devices in the three-phase bridge circuits C1 and C2.

[0033] Furthermore, the method includes calculating a difference between a duty cycle reference value Dc* and an actual duty cycle Dc of the switching device using a third subtractor, and processing the difference through a second proportional-integral controller to adjust the actual duty cycle of the switching device.

[0034] Further, the method includes using a first adder and a second adder to calculate the switching device duty cycles Dc1 and Dc2 of the three-phase bridge circuits C1 and C2, respectively, based on the switching device duty cycle Dc and the respective voltage reference values Urefp and Urefs.

[0035] Furthermore, a synchronous pulse width modulator is used to convert the phase shift ratio D3, the duty ratio Dc1 of the switching devices of the three-phase bridge circuit C1, and the duty ratio Dc2 of the switching devices of the three-phase bridge circuit C2 into PWM signals for all the switching devices.

[0036] Furthermore, it includes using a phase-locked loop controller to synchronize the three-phase voltage on the grid side to calculate the grid angular frequency wt, and generating a three-phase cosine signal related to this frequency through a cosine generator for generating and adjusting the three-phase current reference value.

[0037] Compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0038] First, the present invention provides a topology and control method for a four-port, high-frequency, isolated photovoltaic energy storage hybrid grid-connected converter. Utilizing a multi-winding, high-frequency transformer structure, this device achieves electrical isolation while offering significant advantages such as a reduced component count and minimal switching ripple. While simultaneously implementing DC / DC conversion, one bridge achieves three-phase AC grid connection, while the other bridge realizes DC port integration. This topology offers the advantages of active support, high efficiency, and low cost, while enabling combined photovoltaic and energy storage integration.

[0039] The present invention provides a topological structure of a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device and its control method. By reusing switching devices, the photovoltaic array outputs maximum power and transmits it to the power grid through an AC / DC inverter circuit. At the same time, the output power of the energy storage device is controlled, enabling the device to output or absorb stable AC power over a period of time.

[0040] The present invention has good economic efficiency, and the modulation current output by the energy storage control can be extended to any grid-connected converter adopting current loop control, which shows that the present invention has good promotion and universality.

[0041] The present invention can maintain unbiased voltage control of the energy storage device, accurately control the output AC voltage and current, and simultaneously avoid overvoltage at the high-voltage DC port, thereby improving the reliability and stability of the control system.

[0042] Second, the present invention mainly addresses the following technical problems in the prior art:

[0043] 1. Power quality issues: In existing technologies, photovoltaic power generation systems and other renewable energy systems often face power quality issues during grid-connected operations, such as voltage fluctuations and frequency instability, which will affect the stability of the power grid and the effective use of electricity.

[0044] 2. Energy efficiency: Traditional grid-connected systems often fail to effectively utilize various energy sources, especially in scenarios where photovoltaic and energy storage equipment work together. The lack of effective management and optimization strategies leads to energy waste.

[0045] 3. System complexity and cost: Existing solutions often require multiple independent systems to handle power quality and energy management, which not only increases system complexity but also increases costs.

[0046] 4. Response speed and control accuracy: Existing technologies have limitations in terms of rapid response to grid demand and precise control, especially in high-load and highly volatile grid environments.

[0047] Significant technological advancements achieved:

[0048] To address the above issues, the present invention provides a four-port high-frequency isolated photovoltaic-energy storage composite grid-connected converter device, and achieves the following technological advancements through an innovative control strategy:

[0049] 1. Improve power quality: By integrating photovoltaic maximum power point tracking with advanced voltage and power control strategies, the present invention significantly improves the power quality in grid-connected operation, including stabilizing voltage and reducing grid fluctuations.

[0050] 2. Optimized energy management: The four-port design of the present invention makes the energy conversion between photovoltaic power generation and energy storage equipment more efficient, optimizes energy distribution through intelligent control strategies, improves energy utilization efficiency, and reduces energy loss.

[0051] 3. System integration and cost-effectiveness: By integrating multiple functions into a single device, the present invention simplifies the system architecture, reduces the need for additional equipment and overall installation costs, and also reduces operation and maintenance complexity.

[0052] 4. Improve response speed and control accuracy: The synchronous pulse width modulation technology and proportional integral control strategy adopted in the present invention improve the response speed and control accuracy to grid changes, especially when the grid load changes rapidly, and can quickly and stably output.

[0053] The present invention not only solves multiple technical problems in the prior art, but also achieves significant technological progress through innovative technical solutions, making grid-connected operations more efficient and stable, while also providing a solid foundation for the development of future smart grid technologies.

[0054] Third, as auxiliary evidence for the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0055] The technical solution of the present invention fills the technical gaps in the industry at home and abroad: the present invention provides a four-port high-frequency isolated photovoltaic-energy storage composite grid-connected converter device, which optimizes the existing photovoltaic grid-connected converter topology. This topology utilizes a multi-winding high-frequency transformer structure to achieve DC / DC conversion while one bridge achieves three-phase AC grid connection and the other bridge achieves DC port combination. Its four ports are respectively connected to photovoltaic panels, energy-type energy storage elements, power-type energy storage elements and the power grid, and have the capabilities of maximum power tracking, charge and discharge control, and grid power fluctuation smoothing. The topology realizes the joint access of light and storage while having the advantages of active support, high efficiency and low cost, and is particularly suitable for small and medium-power distributed photovoltaic grid-connected scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a circuit topology diagram of a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device provided by an embodiment of the present invention;

[0057] Figure 2 This is a control block diagram of a three-phase dual-active bridge circuit control unit provided by an embodiment of the present invention;

[0058] Figure 3 This is a control block diagram of a DC / AC inverter circuit control unit provided by an embodiment of the present invention;

[0059] Figure 4 This is a waveform diagram of the voltage and current output on the AC side of a DC / AC inverter circuit provided by an embodiment of the present invention;

[0060] Figure 5 This is a diagram showing the battery voltage and current output waveforms of a DC / AC inverter circuit provided by an embodiment of the present invention;

[0061] Figure 6 This is a waveform diagram of the voltage output at DC port 1 and DC port 2 of the three-phase dual active bridge circuit provided by an embodiment of the present invention;

[0062] Figure 7 This is a waveform diagram of the primary and secondary voltage outputs of a three-phase dual-active bridge circuit zigzag transformer provided by an embodiment of the present invention;

[0063] Figure 8 This is a waveform diagram of photovoltaic array power output under maximum power point tracking control provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0064] This invention addresses the complex multi-port energy management, low conversion efficiency, and poor system reliability issues inherent in existing grid-connected photovoltaic energy storage systems. Traditional systems often employ a single topology, making it difficult to achieve efficient energy exchange between photovoltaics, energy storage, and the grid, resulting in overall low system efficiency. Furthermore, existing technologies lack flexibility and precision in multi-port energy management and power flow control, which can easily lead to system instability and equipment damage.

[0065] By introducing a four-port, high-frequency, isolated photovoltaic energy storage composite grid-connected converter, the present invention achieves flexible multi-port energy management and efficient conversion. The device utilizes a three-phase dual-active bridge topology, a DC / AC three-phase inverter circuit topology, and a DC / DC bidirectional boost and buck circuit topology to ensure efficient energy flow between photovoltaics, energy storage, and the grid. The use of a high-frequency isolation transformer not only improves energy conversion efficiency but also enhances system safety and isolation, resolving the issues of low conversion efficiency and poor reliability found in existing technologies.

[0066] In terms of control methods, the present invention utilizes optimal pulse-width synchronous modulation (PWM) and a hybrid current control structure to achieve precise control of power flow at each port. Optimal pulse-width synchronous modulation (PWM) controls the direction and magnitude of power flow by adjusting the sign and magnitude of the voltage phase difference across the transformer, while minimizing global current stress and improving overall system efficiency and equipment lifespan. The hybrid current control structure combines direct voltage control with proportional resonant control to ensure stable operation of the AC / DC circuit and high-quality grid connection, resolving the issues of inaccurate control and unstable system operation found in existing technologies.

[0067] This invention represents a significant technological advancement in the design and control of grid-connected photovoltaic energy storage systems. Through its innovative topology and advanced control methods, it significantly improves the system's energy conversion efficiency and operational reliability, enabling flexible and precise multi-port energy management. This approach holds significant application value and promises broad market prospects.

[0068] like Figures 1 to 3As shown, an embodiment of the present invention discloses a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device topology structure and control method thereof, belonging to the technical field of power electronic converters. Its topology structure includes: a three-phase dual-active bridge topology composed of a three-phase bridge circuit C1 and a three-phase bridge circuit C2, a DC / AC three-phase inverter circuit topology composed of the three-phase bridge circuit C1, and three DC / DC bidirectional Boost and Buck circuit topologies composed of the three-phase bridge circuit C2. The four ports of this topology are three DC ports and one AC port, wherein the AC port of the inverter circuit is connected to the grid through an LLCL filter, DC port 1 is connected to a photovoltaic or supercapacitor, and is connected to DC port 2 through the three-phase bridge circuit C1, a zigzag transformer, and the three-phase bridge circuit C2. DC port 2 is also connected to a photovoltaic, and is connected to DC port 3 through three DC / DC bidirectional Boost and Buck circuit topologies, and DC port 3 is connected to a battery. The control method is as follows: using the optimal pulse width synchronous modulation method to control the direction and magnitude of power flow by adjusting the sign and magnitude of the voltage phase difference on both sides of the transformer while ensuring the minimum global current stress; using direct voltage control and a hybrid current control structure based on proportional resonance control to control the power flow of the AC / DC circuit; the present invention realizes the grid connection of the converter and the combination of photovoltaic and energy storage by reusing the three-phase dual active bridge topology structure, and can realize flexible power exchange between the power grid, energy storage and photovoltaic through the four-port dual active bridge circuit, and can protect the safety of device components and improve the reliability of the device.

[0069] The four-port, high-frequency, isolated photovoltaic energy storage hybrid grid-connected converter device of this invention combines a three-phase dual active bridge topology, a DC / AC three-phase inverter circuit topology, and three DC / DC bidirectional boost and buck circuit topologies to achieve flexible energy exchange between photovoltaics, supercapacitors, and batteries. The four ports are connected to different DC and AC power sources, and a high-frequency isolation transformer is used for power transmission and conversion, ensuring efficient energy management in all operating conditions.

[0070] In terms of control methods, this invention employs optimal pulse-width synchronous modulation. By adjusting the sign and magnitude of the voltage phase difference across the transformer, the direction and magnitude of power flow are controlled, while minimizing global current stress, improving system efficiency and equipment lifespan. Furthermore, the system combines direct voltage control with a hybrid current control structure based on proportional resonant control to precisely regulate power flow in the AC / DC circuit, ensuring high quality and stability of the grid-connected current.

[0071] The device's operating process includes three main parts: first, the energy from photovoltaics or supercapacitors is converted through DC port 1 and three-phase bridge circuit C1, then transferred to three-phase bridge circuit C2 through a transformer, and finally transmitted to DC port 2. Second, three DC / DC bidirectional boost and buck circuit topologies realize bidirectional energy conversion between DC port 2 and DC port 3, managing the charging and discharging of the battery. Finally, the DC energy is converted into AC energy through the three-phase bridge circuit C1 and connected to the grid through the LLCL filter, ensuring the stable operation of the power grid.

[0072] In summary, this invention, through its innovative topology and advanced control methods, achieves efficient, reliable, and flexible operation of a photovoltaic energy storage system. Compared to existing technologies, this invention significantly improves energy conversion efficiency and system reliability, ensures stable and controllable energy flow between various ports, and enhances the overall performance and application value of the photovoltaic power station.

[0073] As an optimization solution of an embodiment of the present invention, a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device topology structure and control method thereof include: a three-phase dual active bridge circuit, a DC / AC inverter circuit and a set of DC / DC chopper circuits;

[0074] The topology structure of the four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device includes four ports: DC port 1, DC port 2, DC port 3 and AC port;

[0075] Among the four ports, DC port 1 can be connected to an external photovoltaic matrix or supercapacitor, DC port 2 can be connected to an external photovoltaic matrix, DC port 3 can be connected to an external battery, and the AC port is connected to the power grid;

[0076] The four ports are: DC port 1 is connected to the AC port via a DC / AC inverter circuit composed of a three-phase bridge circuit C1 and an LLCL filter; DC port 1 is connected to DC port 2 via a three-phase dual active bridge circuit of a three-phase five-winding transformer with a zigzag connection; DC port 2 is connected to DC port 3 via a set of DC / DC chopper circuits composed of a three-phase bridge circuit C2, a secondary winding of a zigzag transformer, a filter inductor LB, and a filter capacitor CB;

[0077] The three-phase dual-active bridge circuit includes a three-phase bridge circuit C1, a three-phase bridge circuit C2 and a three-phase five-winding transformer with a zigzag connection;

[0078] The three-phase dual active bridge circuit includes two DC ports: DC port 1 and DC port 2;

[0079] The DC port 1 of the three-phase dual active bridge circuit includes a filter capacitor Cdc1 connected to a photovoltaic array or a supercapacitor; the DC port 2 includes a filter capacitor Cdc2 connected to a photovoltaic array.

[0080] The three-phase bridge circuit C1 connects the DC port 1 to the primary side of the three-phase zigzag transformer via a three-phase H-bridge; the three-phase H-bridge includes six MOSFET switch tubes (Q11 to Q16); the switch tubes Q11 and Q12 form a phase a bridge arm, the source of Q11 is connected to the drain of Q12, and are connected to the primary side a phase winding of the zigzag transformer via corresponding filter inductor L1 and filter capacitor C1, the drain of Q11 is connected to the positive electrode of the DC port 1, and the source of Q12 is connected to the negative electrode of the DC port 1; the switch tubes Q13 and Q14 form a phase b bridge arm, Q13 The source of Q13 is connected to the drain of Q14, and is connected to the primary b-phase winding of the zigzag transformer through the corresponding filter inductor L1 and filter capacitor C1. The drain of Q13 is connected to the positive electrode of DC port 1, and the source of Q14 is connected to the negative electrode of DC port 1. The switch tubes Q15 and Q16 form the c-phase bridge arm. The source of Q15 is connected to the drain of Q16, and is connected to the primary c-phase winding of the zigzag transformer through the corresponding filter inductor L1 and filter capacitor C1. The drain of Q15 is connected to the positive electrode of DC port 1, and the source of Q16 is connected to the negative electrode of DC port 1.

[0081] The three-phase bridge circuit C2 connects the secondary side of the three-phase zigzag transformer to the DC port 2 via a three-phase H-bridge; the three-phase H-bridge includes six MOSFET switches (Q21 to Q26); the switches Q21 and Q22 form a bridge arm of phase a, the source of Q21 is connected to the drain of Q22, and are also connected to the secondary side a winding of the zigzag transformer, the drain of Q21 is connected to the positive electrode of the DC port 2, and the source of Q22 is connected to the negative electrode of the DC port 2; the switches Q23 and Q24 form a bridge arm of phase a. The source of Q23 is connected to the drain of Q24, and is also connected to the secondary b-phase winding of the zigzag transformer. The drain of Q23 is connected to the positive electrode of DC port 2, and the source of Q24 is connected to the negative electrode of DC port 2. The switching tubes Q25 and Q26 form the c-phase bridge arm, the source of Q25 is connected to the drain of Q26, and is also connected to the secondary c-phase winding of the zigzag transformer. The drain of Q25 is connected to the positive electrode of DC port 2, and the source of Q26 is connected to the negative electrode of DC port 2.

[0082] The DC / AC inverter circuit includes a three-phase bridge circuit C1 and an LLCL filter;

[0083] The three-phase bridge circuit C1 connects the DC port 1 to the LLCL filter via a three-phase H-bridge; the three-phase H-bridge includes six MOSFET switches (Q11 to Q16); the switches Q11 and Q12 form a phase a bridge arm, the source of Q11 is connected to the drain of Q12, and is also connected to the corresponding filter inductor L1, the drain of Q11 is connected to the positive electrode of the DC port 1, and the source of Q12 is connected to the negative electrode of the DC port 1; the switches Q13 and Q14 are connected to the positive electrode of the DC port 1. The b-phase bridge arm is formed, with the source of Q13 connected to the drain of Q14 and to the corresponding filter inductor L1. The drain of Q13 is connected to the positive electrode of DC port 1, and the source of Q14 is connected to the negative electrode of DC port 1. The switch tubes Q15 and Q16 form the c-phase bridge arm, with the source of Q15 connected to the drain of Q16 and to the corresponding filter inductor L1. The drain of Q15 is connected to the positive electrode of DC port 1, and the source of Q16 is connected to the negative electrode of DC port 1.

[0084] The other end of the LLCL filter filter inductor L1 is connected to the filter inductor L2 and the filter capacitor C1 respectively, wherein the other end of the filter inductor L2 is connected to the power grid, and the other end of the filter capacitor C1 is connected to the filter inductor L1σ, and the other ends of each filter inductor L1σ are connected to each other.

[0085] The DC / DC chopper circuit includes three Buck circuits or Boost circuits; DC port 2 and DC port 3 are connected through the DC / DC chopper circuit;

[0086] When the Buck circuit is running, the i-th Buck circuit among the three Buck circuits consists of a MOSFET switch tube, a diode, a secondary winding L2σ of a zigzag transformer, a filter inductor LB and a filter capacitor CB, i = 1, 2, 3;

[0087] In the Buck circuit, the switch tube Q21 and the diode D22 form the PV1 bridge arm, the cathode of D22 is connected to the source of Q21 and to the secondary winding L2σ of the zigzag transformer corresponding to PV1, the drain of Q21 is connected to the positive electrode of DC port 2, and the positive electrode of D22 is connected to the negative electrode of DC port 2; the switch tube Q23 and the diode D24 form the PV2 bridge arm, the cathode of D24 is connected to the source of Q23 and to the secondary winding L2σ of the zigzag transformer corresponding to PV2, the drain of Q23 is connected to the positive electrode of DC port 2, and the positive electrode of D24 is connected to the negative electrode of DC port 2; the switch tube Q25 and the diode D26 form the PV3 bridge arm, the cathode of D26 is connected to the source of Q25 and to the secondary winding L2σ of the zigzag transformer corresponding to PV3, the drain of Q25 is connected to the positive electrode of DC port 2, and the positive electrode of D26 is connected to the negative electrode of DC port 2;

[0088] When the boost circuit is running, the i-th boost circuit among the three boost circuits consists of a MOSFET switch tube, a diode, a secondary winding L2σ of a zigzag transformer, a filter inductor LB and a filter capacitor CB, i = 1, 2, 3;

[0089] In the Boost circuit, the switch tube Q22 and the diode D21 form the PV1 bridge arm, the positive electrode of D21 is connected to the drain of Q22 and to the secondary winding L2σ of the zigzag transformer corresponding to PV1, the source of Q22 is connected to the negative electrode of DC port 2, and the negative electrode of D21 is connected to the positive electrode of DC port 2; the switch tube Q24 and the diode D23 form the PV2 bridge arm, the positive electrode of D23 is connected to the drain of Q24 and to the secondary winding L2σ of the zigzag transformer corresponding to PV2, the source of Q24 is connected to the negative electrode of DC port 2, and the negative electrode of D23 is connected to the positive electrode of DC port 2; the switch tube Q26 and the diode D25 form the PV3 bridge arm, the positive electrode of D25 is connected to the drain of Q26 and to the secondary winding L2σ of the zigzag transformer corresponding to PV3, the source of Q26 is connected to the negative electrode of DC port 2, and the negative electrode of D25 is connected to the positive electrode of DC port 2;

[0090] The other end of the secondary winding L2σ of the zigzag transformer is connected to one end of the filter inductor LB, the other end of the filter inductor LB is connected to the filter capacitor CB, the other end of the filter capacitor CB is connected to the negative electrode of the DC port 2, and the two ends of the filter capacitor CB are connected to the DC port 3 and connected to the battery.

[0091] The three-phase dual active bridge circuit realizes power flow between the DC port 1 and the DC port 2 through the three-phase dual active bridge circuit control unit.

[0092] The three-phase dual active bridge circuit control unit takes global current stress minimization as the goal, and generates a PWM signal to control the primary and secondary three-phase MOSFET switches by combining the DC port 2 voltage, the DC port 2 voltage reference value, the transformer ratio, the DC port 2 output current, the primary and secondary reference voltages using DC voltage control, DC port 2 power control, global current stress minimization control, and synchronous pulse width modulation control;

[0093] The DC / AC inverter circuit realizes power flow between the DC port 1 and the AC port through a DC / AC inverter circuit control unit.

[0094] The DC / AC inverter circuit control unit is used to generate a primary-secondary side reference voltage by combining the three-phase voltage on the grid side, the three-phase current on the grid side, the DC port 1 voltage, the DC port 1 voltage reference value, the DC port 3 current, and the DC port 3 current reference value, using a phase-locked loop controller, DC voltage control, and AC current control to provide a PWM signal for the three-phase dual active bridge circuit control unit to control the primary-secondary three-phase MOSFET switch tube.

[0095] A four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device according to claim 1, characterized in that the three-phase dual active bridge circuit control unit includes:

[0096] The photovoltaic maximum power tracker is used to combine the voltage Vpv and current Ipv of the photovoltaic array through the conductance increment method to make the photovoltaic array operate at the maximum power point, and use the voltage at the maximum power point as the DC port 2 voltage reference value V2ref;

[0097] A first subtractor is configured to subtract the DC port 2 voltage reference value V2ref from the DC port 2 voltage V2 to obtain a DC voltage difference;

[0098] A first proportional-integral controller is used to calculate the DC voltage difference by proportional calculation and integral calculation to obtain a value as a deviation from the reference value D3;

[0099] The second subtractor is used to subtract the phase shift reference value D3* from the phase shift reference value D3 and the primary-secondary phase difference caused by the zigzag transformer to obtain the phase shift reference value D3;

[0100] A transmission power generator, configured to multiply the DC port 2 voltage V2 by the DC port 2 output current I2 to obtain the transmission power Po of the three-phase dual active bridge;

[0101] A voltage transformation ratio generator is used to multiply the DC port 2 voltage V2 by the transformer transformation ratio N and then divide the result by the DC port 1 voltage V1 to obtain the transformer primary-to-secondary voltage transformation ratio M;

[0102] The global optimal modulation strategy controller is used to combine the transmission power Po with the voltage transformation ratio M, with the goal of minimizing the global current stress, and use the global optimal modulation strategy algorithm to determine the circuit operating mode, and output the duty cycle reference value Dc* of the switching devices of the three-phase bridge circuit C1 and the three-phase bridge circuit C2, as well as the shift ratio reference value D3* of the corresponding bridge arms of the three-phase bridge circuit C1 and the three-phase bridge circuit C2;

[0103] a third subtractor, configured to subtract the switching device duty cycle reference value Dc* from the switching device duty cycle Dc to obtain a duty cycle difference;

[0104] A second proportional-integral controller is used to calculate the duty cycle difference by proportional calculation and integral calculation to obtain a value as the duty cycle Dc of the switching device;

[0105] A first adder is configured to add the duty cycle Dc of the switching device to the primary voltage reference value Urefp to obtain the duty cycle Dc1 of the switching device of the three-phase bridge circuit C1;

[0106] A second adder is configured to add the switching device duty cycle Dc and the secondary voltage reference value Urefs to obtain the switching device duty cycle Dc2 of the three-phase bridge circuit C2;

[0107] a synchronous pulse width modulator, configured to convert the phase shift ratio D3, the duty cycle Dc1 of the switching devices in the three-phase bridge circuit C1, the duty cycle Dc2 of the switching devices in the three-phase bridge circuit C2, and the sawtooth wave into PWM signals for all the switching devices in the three-phase dual active bridge circuit;

[0108] A four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device according to claim 1, characterized in that the DC / AC inverter circuit control unit includes:

[0109] a fourth subtractor, configured to subtract the DC port 1 voltage reference value 800 from the DC port 1 voltage V1 to obtain a DC voltage difference;

[0110] a third proportional-integral controller, configured to calculate the DC voltage difference by proportional calculation and integral calculation and obtain a value as a DC current reference amplitude Iref;

[0111] A phase-locked loop controller is used to obtain an angular frequency wt by phase-locking calculation using the three-phase voltage on the grid side;

[0112] a third adder, configured to add the grid angular frequency wt and the phase value;

[0113] A cosine generator, used for generating corresponding three-phase cosine signals;

[0114] A three-phase current reference value generator is used to multiply the three-phase cosine signal and the current reference value amplitude to obtain the three-phase current reference value;

[0115] a fifth subtractor, configured to subtract the three-phase current reference value from the grid-side three-phase current Iabc to obtain a three-phase current deviation value;

[0116] The proportional resonant controller calculates the three-phase current deviation value through proportional calculation and resonant loop calculation, and the resulting value is used as the three-phase voltage reference value;

[0117] a sixth subtractor, configured to subtract the three-phase voltage Vabc on the grid side from the three-phase voltage reference value to obtain a three-phase voltage deviation value;

[0118] A primary side reference voltage generator is used to obtain a primary side voltage reference value Urefp by dividing the three-phase voltage deviation value, the DC port 1 voltage reference value, and the DC utilization factor;

[0119] a seventh subtractor, configured to subtract the battery voltage from the corresponding maximum charging voltage to obtain a voltage deviation value of the DC port 3;

[0120] a fourth proportional-integral controller, configured to calculate the value obtained by adding the voltage deviation value of the DC port 3 through proportional calculation and integral calculation as a reference value for the battery charging current;

[0121] an eighth subtractor, configured to subtract the battery current from a battery charging current reference value to obtain a battery charging current deviation value;

[0122] The fifth proportional-integral controller is used to calculate the value obtained by adding the battery charging current deviation value through proportional calculation and integral calculation as the secondary side voltage reference value Urefs.

[0123] The present invention builds a simulation model of a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device on the MATLAB / Simulink simulation experimental platform. The DC port 1 voltage reference value is 800V, and the capacitor C at the DC port 1 is 1. dc1 =10mF, three-phase bridge circuit C1 uses a total of 6 IGBTs, and the switching frequency of each IGBT is 36kHz; three-phase bridge circuit C1 is connected to the grid through an LLCL filter, where the converter-side inductor L1 = 50μH, the grid-side inductor L2 = 1mH, the branch inductor L3 = 3.26μH, and the branch capacitor C1 = 6μF; the grid phase-to-phase voltage is 380V, the frequency is 50Hz, and the initial phase of phase A is 0; the zigzag transformer ratio is 2; three-phase bridge circuit C2 uses a total of 6 IGBTs, and the switching frequency of each IGBT is 36kHz; the DC port 2 voltage reference value is 400V, and the DC port 2 capacitor C dc1 =1mF; the photovoltaic array light intensity is 1000, the temperature set value is 25, the maximum power point output power is about 1.5kW; the filter inductor L B =50μH, filter capacitor C B =1mF; the battery voltage is 200V; the simulation results are as follows Figures 4 to 8 shown.

[0124] Figure 4 These are the voltage and current output waveforms on the AC side of the DC / AC inverter circuit provided by an embodiment of the present invention; the voltage waveform amplitude is approximately 660V, and the current waveform amplitude is approximately 25A.

[0125] Figure 5The figure shows the battery voltage and current output waveforms of the DC / AC inverter circuit provided by an embodiment of the present invention. The figure shows the battery charging state, with a charging voltage of 224V and a charging current of approximately 20A. The battery's charge and discharge states can be switched.

[0126] Figure 6 The following are the output waveforms of the DC port 1 voltage and the DC port 2 voltage of the three-phase dual-active bridge circuit provided by an embodiment of the present invention. The DC port 1 voltage is controlled at approximately 800 V, while the DC port 2 voltage is controlled at approximately 400 V. There is no significant fluctuation in either voltage.

[0127] Figure 7 This is the output waveform of the primary and secondary voltages of the three-phase dual-active bridge circuit zigzag transformer provided by an embodiment of the present invention. Observing the graph, it can be seen that its output waveform is stable, and the secondary voltage phase leads the primary voltage phase. Since the working principle of the three-phase dual-active bridge circuit is similar to the conclusion that the voltage phase determines the active power in the inductive line transmission of the power system, the graph shows that the active power flow at this moment is from the secondary side to the primary side. It should be noted that the power flow shown in this figure is only a special case, and the actual power flow and magnitude can be adjusted according to the desired control link.

[0128] Figure 8 This is the power output waveform of the photovoltaic array under maximum power point tracking (MPPT) control provided by an embodiment of the present invention. Using the conductance increment method to implement MPPT, it can be seen that the photovoltaic array reaches its maximum operating point at approximately 25ms and stabilizes at that point, demonstrating good stability and dynamic performance.

[0129] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device topology, characterized in that: The topology includes a three-phase dual active bridge circuit, a DC / AC inverter circuit and a set of DC / DC chopper circuits; The topology structure of the four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device includes four ports: DC port 1, DC port 2, DC port 3 and AC port; Among the four ports, DC port 1 can be connected to an external photovoltaic matrix or supercapacitor, DC port 2 can be connected to an external photovoltaic matrix, DC port 3 can be connected to an external battery, and the AC port is connected to the power grid; The four ports are connected to the AC port via a DC / AC inverter circuit composed of a three-phase bridge circuit C1 and an LLCL filter; the DC port 1 is connected to the DC port 2 via a three-phase dual active bridge circuit of a three-phase five-winding transformer with a zigzag connection; the DC port 2 is connected to the AC port via a set of DC / DC chopper circuits composed of a three-phase bridge circuit C2, a secondary winding of a zigzag transformer and a filter inductor L. B and filter capacitor C B Connected to DC port 3; The three-phase dual active bridge circuit includes: The three-phase bridge circuit C1 and the three-phase bridge circuit C2 are configured at different DC ports; A three-phase five-winding transformer with a zigzag connection is connected to the outputs of the three-phase bridge circuit C1 and the three-phase bridge circuit C2; DC port 1 and DC port 2, wherein DC port 1 is connected to a photovoltaic array or a supercapacitor and includes a filter capacitor Cdc1; DC port 2 is connected to a photovoltaic array and includes a filter capacitor Cdc2; The three-phase bridge circuit C1 and the three-phase bridge circuit C2 are respectively composed of six MOSFET switch tubes, which are configured on the primary side and the secondary side of the transformer to achieve current conversion and modulation.

2. The topological structure according to claim 1, characterized in that Each MOSFET switch tube of the three-phase bridge circuit C1 and the three-phase bridge circuit C2 is connected to a corresponding winding of the transformer through a corresponding filter inductor and filter capacitor to optimize the quality of the current and reduce harmonics.

3. The topological structure according to claim 1, wherein: The DC / AC inverter circuit includes: A three-phase bridge circuit C1 is connected to DC port 1; An LLCL filter is connected to the output of the three-phase bridge circuit C1 to further filter and stabilize the output current to the grid; The three-phase H-bridge includes six MOSFET switches configured in the three-phase bridge circuit C1 to control the current inversion; The DC port 1 is connected to an LLCL filter via a three-phase H-bridge to achieve high-efficiency current conversion and output.

4. The topological structure according to claim 1, wherein: The DC / DC chopper circuit includes: The voltage conversion between DC port 2 and DC port 3 is achieved through three Buck circuits or Boost circuits; Each Buck or Boost circuit contains a MOSFET switch, a diode, a secondary winding of a zigzag transformer, a filter inductor, and a filter capacitor to achieve effective voltage reduction or boosting; By controlling the on and off of the MOSFET switch tube, the current passing through the secondary winding of the zigzag transformer is regulated, thereby adjusting the output voltage and current of the DC port 3, thereby achieving effective energy conversion and management.

5. A method for controlling a four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter having the topology structure of the four-port high-frequency isolated photovoltaic energy storage composite grid-connected converter device according to any one of claims 1 to 4, characterized in that: The following steps are involved: (a) Using a photovoltaic maximum power tracker and the conductance increment method, the photovoltaic array is ensured to operate at the maximum power point, and the voltage at the maximum power point is set to the voltage reference value V2ref of DC port 2; (b) calculating the difference between the voltage reference value V2ref and the actual voltage V2 of the DC port 2 using a first subtractor; (c) processing the difference through a first proportional-integral controller to obtain a reference deviation of the shift phase D3; (d) using a second subtractor to calculate the sum of the phase shift reference value D3*, the reference deviation, and the phase difference between the primary and secondary sides of the transformer to obtain the phase shift D3; (e) Calculating the output power Po of DC port 2 through the transmission power generator; (f) Calculate the voltage transformation ratio M between the primary and secondary sides of the transformer using the voltage transformation ratio generator; (g) Using the global optimal modulation strategy controller, based on the transmission power Po and the voltage transformation ratio M, with the goal of minimizing the global current stress, the duty cycle Dc* and the shift ratio D3* of the switching device are determined; (h) Converting the control signal into a PWM signal to control the switching devices in the three-phase bridge circuit C1 and the three-phase bridge circuit C2.

6. The method according to claim 5, characterized in that The method includes calculating the difference between the duty cycle reference value Dc* and the actual duty cycle Dc of the switching device by using a third subtractor, and processing the difference by a second proportional integral controller to adjust the actual duty cycle of the switching device.

7. The method according to claim 5, characterized in that This includes using a first adder and a second adder to calculate the switching device duty cycles Dc1 and Dc2 of the three-phase bridge circuit C1 and the three-phase bridge circuit C2, respectively, based on the switching device duty cycle Dc and the respective voltage reference values Urefp and Urefs.

8. The method according to claim 5, characterized in that The method includes using a synchronous pulse width modulator to convert the shift ratio D3, the duty ratio Dc1 of the switching devices of the three-phase bridge circuit C1, and the duty ratio Dc2 of the switching devices of the three-phase bridge circuit C2 into PWM signals of all the switching devices.

9. The method according to claim 5, characterized in that The method includes using a phase-locked loop controller to synchronize the three-phase voltages on the grid side to calculate the grid angular frequency wt, and generating a three-phase cosine signal related to this frequency through a cosine generator for generating and adjusting the three-phase current reference value.

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