Inverter feedback battery charging and discharging system

Abstract

The utility model discloses an inverter feedback type battery charging and discharging system, comprising a battery pack, a DC / DC conversion unit, a DC / AC conversion unit, an LCL filter unit, a thyristor switching unit, a DSP control core unit, a human-machine interface and an LCD monitoring unit; the battery pack, the DC / DC conversion unit, the DC / AC conversion unit, the LCL filter unit and the thyristor switching unit are connected in sequence; the DSP control core unit sends a PWM signal to drive the DC / DC conversion unit and the DC / AC conversion unit; the human-machine interface and the LCD monitoring unit are bidirectionally interconnected with the DSP control core unit; the battery pack and the thyristor switching unit are respectively connected with the DSP control core unit. By adopting a grid-connected discharge circuit structure, using a full-bridge soft switch DC / DC converter, a fuzzy PID control circuit, a three-phase full-bridge inverter circuit, a PID control circuit based on a BP neural network, and an improved second-order generalized integrator to design a phase-locked loop PLL and a frequency-locked loop FLL, energy feedback to the power grid is realized, the voltage and constant current discharge current are continuously adjustable, and the capacity of the battery pack is accurately measured.

Description

Technical Field

[0001] The utility model relates to the field of charge and discharge control technology, in particular to an inverter feedback type battery charge and discharge system. Background Art

[0002] Battery discharge test is a necessary means to detect battery capacity, deal with plate active material condensation and prevent early battery failure. The main discharge methods are resistance energy dissipation discharge and grid-connected discharge. Resistance energy dissipation discharge is very easy to cause energy waste and produce poor dynamic response; grid-connected discharge is an important means to realize energy feedback to the grid and create benefits for the grid and users. Based on the above research background and significance, the key needs of extending battery life and improving the reliability of DC operating power supply are fully considered. The grid-connected discharge circuit structure should be used to detect the battery, and the grid-connected discharge circuit structure should be optimized and improved to meet the relevant requirements of the power industry. Utility Model Content

[0003] In view of this, the utility model aims to address the deficiencies in the prior art, and its main purpose is to provide an inverter feedback battery charging and discharging system, which adopts a grid-connected discharge circuit structure and utilizes a full-bridge soft-switching DC / DC converter, a fuzzy PID control circuit, a three-phase full-bridge inverter circuit, a PID control circuit based on a BP neural network, an improved second-order generalized integrator to design a phase-locked loop PLL and a frequency-locked loop FLL to achieve energy feedback to the grid, with continuously adjustable voltage, continuously adjustable constant current discharge current, and accurate measurement of the battery pack capacity.

[0004] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0005] An inverter feedback battery charging and discharging system, which includes a battery pack for providing direct current power to the system, a DC / DC conversion unit for converting the direct current of the battery pack into direct current suitable for subsequent circuits, a DC / AC conversion unit for converting direct current into alternating current for grid connection or driving other alternating current loads, an LCL filter unit for filtering high-frequency harmonics generated by the DC / AC conversion unit to ensure the purity of the output current and improve the quality of electric energy, a thyristor switching unit for controlling the on and off of alternating current to meet the needs of the grid, a control logic unit responsible for the control logic of the entire system and receiving sampling and human-computer interaction signals, generating PWM signals to control the DC / DC conversion unit and the DC / AC converter The DSP control core unit is used to control the switch state of the switching unit, adjust the output power, respond to system changes in real time and issue control instructions, and the human-machine interface and LCD monitoring unit are used to provide a user interface, display system status and parameters, and allow users to monitor and adjust system operation; the battery pack, DC / DC conversion unit, DC / AC conversion unit, LCL filter unit and thyristor switching unit are connected in sequence; the DSP control core unit sends a PWM signal to drive the DC / DC conversion unit and the DC / AC conversion unit; the human-machine interface and LCD monitoring unit are bidirectionally interconnected with the DSP control core unit; the battery pack and the thyristor switching unit are respectively connected to the DSP control core unit.

[0006] As a preferred solution: the DSP control core unit is a DSP controller TMS320F2808.

[0007] As a preferred solution: the LCL filter unit is an LCL filter with a speed attenuation of -60dB / dec.

[0008] As a preferred solution: the DC / DC conversion unit is a full-bridge soft-switching DC / DC converter that can reduce switching losses and improve efficiency during the switching process, and its circuit structure includes: main switch tubes S1, S2, S3 and S4 for controlling the on and off of current; a high-frequency transformer TR for changing the voltage; rectifier diodes D1, D2, D3 and D4 for converting AC power into DC power; a buffer circuit composed of Q1, Q2, C1, C2, L2 and D5 for absorbing the energy impact generated during switching; a clamping capacitor C1 for limiting the voltage peak and protecting the circuit; a resonant capacitor C2 for cooperating with an inductor to achieve energy resonance transmission; coupling inductors L1 and L2 for connecting different circuit parts and transferring energy; a leakage inductance L1 of the transformer. lk and the magnetizing inductance L m and output filter capacitor C o; The coupled inductor L2 is part of the buffer circuit, and L1 is part of the LCL filter unit; the main switch tubes Q1-Q4 control the current flow to the transformer TR; the rectifier diodes D1-D4 convert the AC power output by the transformer into DC power; the capacitors and inductors in the buffer circuit absorb and release energy to reduce the impact during switching; the clamping capacitor and the resonant capacitor work together to ensure the stability of the circuit; the coupled inductor L and the LC filter circuit further purify the current; the leakage inductance and the excitation inductance are the characteristics of the transformer and affect the performance of the circuit; the output filter capacitor C smoothes the output current.

[0009] As a preferred solution: it also includes a fuzzy PID control circuit, which includes: a sensor S for monitoring and collecting actual current, a PID regulator for adjusting the output according to the current difference to reduce the error, and a PWM modulator for adjusting the switching time of the switching device according to the output of the PID regulator to control the current size; the sensor S monitors the discharge current of the battery pack and compares it with the set reference current I dcc-ref The difference is compared and sent to the PID regulator to calculate the amount that needs to be adjusted. The PWM modulator adjusts the switching time of the switching device according to the output of the PID regulator to form a control signal to maintain current stability.

[0010] As a preferred solution: the DC / AC conversion unit is a three-phase full-bridge inverter circuit in a control mode of voltage source input and current source output.

[0011] As a preferred solution: it also includes a PID control circuit based on a BP neural network, which includes a PID controller and a BP neural network, wherein the k of the PID controller p , k i , k d The parameters are directly adjusted by the BP neural network in real time, and the controlled object is closed-loop controlled; the BP neural network can output the best k according to the error performance function p , k i , k d .

[0012] As a preferred solution, it also includes designing a phase-locked loop (PLL) by improving a second-order generalized integrator.

[0013] As a preferred solution: it also includes a frequency locked loop FLL which can obtain power grid frequency information accurately in real time.

[0014] Compared with the prior art, the utility model has obvious advantages and beneficial effects. Specifically, it can be seen from the above technical scheme that the system is composed of two power units, DC / DC and DC / AC, an auxiliary power supply, an input and output detection protection circuit and the like. The control link using TI's DSP controller TMS320F2808 as the core completes the work of sampling data calculation, PWM signal generation, phase locking and data exchange with the human-machine interface. During the discharge process, the system three-phase voltage, inverter three-phase current, battery voltage, battery discharge current, discharge time, discharge capacity ampere-hours and other data can be automatically recorded and displayed in real time through an LCD liquid crystal.

[0015] Through the design and development of a large-capacity grid-connected inverter feedback battery discharge system, the system is composed of INV-DC220V-20A active inverter feedback modules in parallel. The module adopts DSP digital control technology and high-frequency soft switching technology. The inverter has a built-in CPU and an independent LCD display. Its DC input and AC output are completely electrically isolated, meeting the relevant requirements of the power industry.

[0016] In order to more clearly illustrate the structural features and effects of the present invention, it is described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the system structure of the utility model;

[0018] Figure 2 This is a schematic diagram of the circuit structure of a full-bridge soft-switching DC / DC converter of the utility model;

[0019] Figure 3 This is a schematic diagram of the constant current discharge control algorithm of the battery pack of the present utility model;

[0020] Figure 4 This is a schematic diagram of the converter circuit structure under fuzzy PID control of the utility model;

[0021] Figure 5 It is a schematic diagram of the topological structure of the three-phase full-bridge grid-connected inverter of the utility model;

[0022] Figure 6 This is a schematic diagram of the control structure of the three-phase full-bridge grid-connected inverter of the utility model;

[0023] Figure 7 This is a schematic diagram of the structure of the BP neural network combined with PID control of the utility model;

[0024] Figure 8 The utility model is a schematic diagram of the control structure of the grid-connected inverter based on the phase-locked loop and the frequency-locked loop. DETAILED DESCRIPTION

[0025] The utility model Figures 1 to 8 As shown, an inverter feedback battery charging and discharging system includes a battery pack for providing direct current power to the system, a DC / DC conversion unit for converting the direct current of the battery pack into direct current suitable for subsequent circuits, a DC / AC conversion unit for converting direct current into alternating current for grid connection or driving other alternating current loads, an LCL filter unit for filtering high-frequency harmonics generated by the DC / AC conversion unit to ensure the purity of the output current and improve the quality of electric energy, a thyristor switching unit for controlling the on and off of alternating current to meet the needs of the grid, a DSP control core unit responsible for the control logic of the entire system and receiving sampling and human-machine interaction signals, generating PWM signals to control the switching states of the DC / DC conversion unit and the DC / AC conversion unit, adjusting the output power, responding to system changes in real time and issuing control instructions, and a human-machine interface and LCD monitoring unit for providing a user interface, displaying system status and parameters, and allowing users to monitor and adjust system operation; wherein,

[0026] The battery pack, DC / DC conversion unit, DC / AC conversion unit, LCL filter unit and thyristor switching unit are connected in sequence; the DSP control core unit sends a PWM signal to drive the DC / DC conversion unit and the DC / AC conversion unit; the human-machine interface and LCD monitoring unit are bidirectionally interconnected with the DSP control core unit; the battery pack and thyristor switching unit are respectively connected to the DSP control core unit. The DSP control core unit is a DSP controller TMS320F2808.

[0027] In order to reduce the control difficulty and save costs, reduce the loss of the drive circuit and increase the service life of the battery, the team members designed a new full-bridge soft-switching DC / DC converter based on the full-bridge DC / DC converter structure and added an auxiliary network to the rear side of the rectifier bridge. This converter can realize soft switching of all switching devices and improve the working efficiency of the converter.

[0028] The full-bridge soft-switching DC / DC converter includes: main switch tubes S1, S2, S3 and S4 for controlling the on and off of current; a high-frequency transformer TR for changing the voltage; rectifier diodes D1, D2, D3 and D4 for converting AC power into DC power; a buffer circuit composed of Q1, Q2, C1, C2, L2 and D5 for absorbing the energy impact generated during switching; a clamping capacitor C1 for limiting the voltage peak and protecting the circuit; a resonant capacitor C2 for cooperating with an inductor to achieve energy resonance transmission; coupled inductors L1 and L2 for connecting different circuit parts and transferring energy; and a leakage inductor L1 of the transformer. lk and the magnetizing inductance L m and output filter capacitor C o; The coupled inductor L2 is part of the buffer circuit, and L1 is part of the LCL filter unit; the main switch tubes Q1-Q4 control the current flow to the transformer TR; the rectifier diodes D1-D4 convert the AC power output by the transformer into DC power; the capacitors and inductors in the buffer circuit absorb and release energy to reduce the impact during switching; the clamping capacitor and the resonant capacitor work together to ensure the stability of the circuit; the coupled inductor L and the LC filter circuit further purify the current; the leakage inductance and the excitation inductance are the characteristics of the transformer and affect the performance of the circuit; the output filter capacitor C smoothes the output current.

[0029] The constant current discharge in the discharge system designed in this paper is realized by current single-loop control. By collecting the actual battery discharge current I b , and compare it with the set discharge reference current I dcc-ref The difference is sent to the PID regulator and then enters the PWM modulation link to form a control signal. Figure 3 shown.

[0030] Considering that the traditional PID controller is a typical linear control method based on the linear model, but the converter itself is a typical nonlinear system, the PID controller only performs parameter design for a certain operating point of the converter. For the unexpected operating point, although the PID controller can often make the converter enter a steady state and maintain stability, its dynamic process is obviously affected by the operating conditions. The occurrence of disturbances will lead to worse system dynamic behavior quality, which is specifically manifested as larger overshoot and more severe oscillation. When the dynamic quality of the converter deteriorates to a certain extent, it is not only not conducive to the stability of the system, but may even cause the switching device to exceed its allowable voltage level due to excessive overshoot or oscillation, eventually causing the entire system to be damaged.

[0031] In view of the shortcomings of traditional PID controller, the team members combined fuzzy control with traditional PID control, aiming to make the gain parameters of PID controller adaptively adjusted with the operating point of the system, so that the system can achieve optimal operation at the unexpected operating point. The structural block diagram of fuzzy PID controller is shown in the figure. Figure 4 shown.

[0032] like Figure 4 As shown in the figure, the designed fuzzy PID controller is based on the traditional PID controller. The PID controller is used as the control object of the fuzzy controller, and the system status information output by the sensor is used as the input of the fuzzy controller. The gain coefficient of the PID controller is refreshed after fuzzy reasoning to achieve adaptive adjustment. The PID controller uses the system status information output by the sensor and the gain coefficient output by the fuzzy controller to perform compensation calculation, and then adjust the behavior of the system.

[0033] The fuzzy PID control circuit includes: a sensor S for monitoring and collecting actual current, a PID regulator for adjusting the output according to the current difference to reduce the error, and a PWM modulator for adjusting the switching time of the switching device according to the output of the PID regulator to control the current size; the sensor S monitors the discharge current of the battery pack and compares it with the set reference current I dcc-ref The difference is compared and sent to the PID regulator to calculate the amount that needs to be adjusted. The PWM modulator adjusts the switching time of the switching device according to the output of the PID regulator to form a control signal to maintain current stability.

[0034] The system selects a three-phase full-bridge inverter circuit with a voltage source input and a current source output control mode, such as Figure 5 To ensure good attenuation performance in the high frequency band, this study uses an LCL filter with an attenuation rate of -60dB / dec in the filtering process.

[0035] In view of the problem that the fixed parameters of the traditional PID controller are difficult to achieve ideal control effects on nonlinear systems, the BP neural network is combined with PID control, and the appropriate PID parameters are output in real time through the BP learning algorithm, which can effectively improve the response speed and tracking accuracy of the discharge system. The inverter feedback battery charging and discharging system is also equipped with a PID control circuit based on the BP neural network, which includes a PID controller and a BP neural network, wherein the k of the PID controller p , k i , k d The parameters are directly adjusted by the BP neural network in real time, and the controlled object is closed-loop controlled; the BP neural network can output the best k according to the error performance function p , k i , k d The structural diagram of BP neural network combined with PID control is as follows: Figure 7 shown.

[0036] In order to fully consider the actual needs of battery grid-connected discharge, it is decided to adopt a voltage-oriented vector control strategy. This control strategy is based on direct current control and uses a three-phase synchronous phase-locked loop to achieve the orientation of the grid-side voltage vector. Its control structure is as follows: Figure 6 As shown. In order to solve the problems of grid voltage and current distortion, grid frequency deviation and power quality degradation, the team members used an improved second-order generalized integrator to design a phase-locked loop (PLL) and added a frequency-locked loop (FLL) to obtain grid frequency information in real time and accurately. This solution can improve the adaptability of the discharge system to grid frequency changes, suppress grid-connected current harmonics, and improve the system response speed. When the grid voltage and frequency fluctuate severely, it can ensure that the module function is not damaged and improve the system steady-state performance. Its control structure is as follows: Figure 8 shown.

[0037] The improved second-order generalized integrator design phase-locked loop (PLL) has the following functions:

[0038] 1. Frequency Lock: The main function of the PLL is to lock the frequency of the input signal. The improved second-order generalized integrator can track the grid frequency more accurately and maintain lock even when the grid conditions change.

[0039] 2. Phase lock: In addition to frequency, PLL can also lock the phase of the input signal. This means that the AC power generated by the inverter can be in phase with the grid voltage, thus achieving efficient power exchange.

[0040] 3. Harmonic suppression: Improved PLL design can reduce the harmonic content in the inverter output and improve the power quality. This is essential for meeting grid standards and reducing electromagnetic interference to other equipment.

[0041] 4. Improve system response speed: When the grid frequency changes, the improved second-order generalized integrator can be adjusted quickly, so that the output frequency of the inverter can quickly adapt to the changes in the grid frequency, thereby improving the response speed of the entire system.

[0042] 5. Enhanced system stability: Improved designs may include better damping and stability characteristics, helping to reduce system oscillations and improve long-term operational stability.

[0043] 6. Adapt to grid voltage fluctuations: When the grid voltage fluctuates, the improved PLL can maintain accurate frequency tracking, ensure the stable operation of the inverter, and avoid equipment damage caused by frequency deviation.

[0044] 7. Improve system dynamic performance: The improved second-order generalized integrator design can optimize the dynamic performance of the PLL, such as increasing the capture range and shortening the lock time, so that the inverter can adapt to changes in grid conditions more quickly.

[0045] 8. Assisting other control strategies: As a key part of the grid interface inverter (GI), PLL can assist in implementing more advanced control strategies such as reactive power control and harmonic compensation.

[0046] 9. Improve the overall performance of grid-connected inverters: By improving the PLL design, the comprehensive performance of the inverter in grid-connected applications can be improved, including efficiency, reliability and adaptability to grid changes.

[0047] When designing inverters and grid-connected systems, PLL is a key component that directly affects the performance and power quality of the system. By using an improved second-order generalized integrator, the performance of the PLL can be significantly improved, thereby improving the performance of the entire grid-connected inverter system.

[0048] A frequency-locked loop (FLL) is a special type of phase-locked loop (PLL) whose main function is to lock the frequency of the input signal instead of the phase. Here are some key features of an FLL:

[0049] 1. Frequency tracking: FLL is able to accurately track and lock to the frequency of the input signal and remain locked even if the signal frequency changes.

[0050] 2. Frequency detection: It can detect the frequency of the input signal and provide accurate frequency information, which is very useful for systems that require frequency feedback.

[0051] 3. Frequency Lock: Once the frequency is detected, the FLL can lock to that frequency and maintain a stable internal clock or output signal that is synchronized with the frequency of the input signal.

[0052] 4. Low Phase Noise: FLLs typically have lower phase noise, which makes them useful in applications that require a low-noise frequency source.

[0053] 5. Fast locking capability: Some FLL designs have fast locking characteristics and can respond quickly to changes in the input signal frequency.

[0054] 6. Frequency stability: FLL can provide stable frequency output, and can keep the output frequency stable even if the amplitude of the input signal changes.

[0055] 7. Anti-interference ability: Since FLLs focus on frequency locking, they have better suppression ability for noise and interference in the input signal.

[0056] 8. Versatility: FLL can be used in a variety of applications, including frequency synthesizers, clock recovery, data communications, and power systems.

[0057] 9. Collaborative work with PLL: FLL can be used in conjunction with PLL to provide more comprehensive frequency and phase locking capabilities, such as in grid synchronization applications.

[0058] 10. Frequency correction: FLL can be used to correct the frequency deviation of the input signal to ensure that the output signal is consistent with the expected frequency.

[0059] Frequency-locked loops (FLLs) are particularly important in power system and inverter design because they can help the system adapt to fluctuations in grid frequency and maintain a stable output frequency, thereby improving power quality and overall system performance.

[0060] Through the research and design of large-capacity grid-connected inverter feedback battery discharge system, this system can meet the following requirements:

[0061] 1. Battery pack discharge test with multi-voltage discharge function, the voltage is continuously adjustable.

[0062] 2. It has the function of constant current discharge of battery pack: the constant current discharge current is continuously adjustable and the capacity of battery pack can be accurately measured.

[0063] 3. It has the function of pausing and modifying parameters during the discharge process: During the discharge process, you can manually pause the discharge and modify the discharge setting parameters (lower limit voltage, discharge current, discharge time, etc.), and you can continue discharging without terminating the test.

[0064] 4. The DC input and AC output are completely electrically isolated, and no external isolation transformer is required to meet the requirements of the power inverter in the integrated power supply design.

[0065] 5. When the grid voltage frequency fluctuates severely or there is a power outage, the module automatically shuts down and stops feedback to protect the module from damage and respond quickly.

[0066] 6. Wide operating voltage range, compatible with 220V and 110V systems, actual operating voltage can be from 90VDC to 250VDC.

[0067] After the system design and commissioning were completed, the designed discharge system was used to conduct verification charge and discharge tests on 68 groups of station batteries and 148 groups of communication batteries, and the technical transformation project of 12 substation batteries was completed. After promotion and application, the energy saving can be about 868,800 kW·h per year, a total of 364,869 yuan / year. The test results are shown in Table 1.

[0068] Table 1 Test results

[0069]

[0070] Combined with the effect of the developed system after promotion and application, it can be known that it has the advantages of environmental protection and energy saving, and can effectively feed back most of the output energy of the battery pack to the power grid without pollution, saving most of the energy. In addition, after the team members assembled and debugged the entire system, the system was made small in size and light in weight, and there was no need to use bulky resistor boxes and cooling equipment, which effectively saved space.

[0071] The design focus of the utility model is that the system is composed of two power units, DC / DC and DC / AC, an auxiliary power supply, an input and output detection protection circuit and other parts, and uses TI's DSP controller TMS320F2808 as the core control link to complete the sampling data calculation, PWM signal generation, phase locking and data exchange with the human-machine interface. During the discharge process, the system three-phase voltage, inverter three-phase current, battery voltage, battery discharge current, discharge time, discharge capacity ampere-hours and other data can be automatically recorded and displayed in real time through the LCD liquid crystal.

[0072] Through the design and development of a large-capacity grid-connected inverter feedback battery discharge system, the system is composed of INV-DC220V-20A active inverter feedback modules in parallel. The module adopts DSP digital control technology and high-frequency soft switching technology. The inverter has a built-in CPU and an independent LCD display. Its DC input and AC output are completely electrically isolated, meeting the relevant requirements of the power industry.

[0073] It is an important means to realize the return of energy to the grid and create benefits for the grid and users. Based on the above research background and significance, and taking into full consideration the key needs of extending the battery life and improving the reliability of the DC operating power supply, the grid-connected discharge circuit structure should be used to detect the battery, and the grid-connected discharge circuit structure should be optimized and improved to meet the relevant requirements of the power industry. The DC input and AC output are completely electrically isolated to meet the relevant requirements of the power industry.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An inverter feedback battery charging and discharging system, characterized in that: It includes a battery pack for providing DC power to the system, a DC / DC conversion unit for converting the DC power of the battery pack into DC power suitable for subsequent circuits, a DC / AC conversion unit for converting DC power into AC power for grid connection or driving other AC loads, an LCL filter unit for filtering high-frequency harmonics generated by the DC / AC conversion unit to ensure the purity of the output current and improve the quality of power, a thyristor switching unit for controlling the on and off of AC power to meet the needs of the power grid, and a control logic unit for the entire system, which receives sampling and human-computer interaction signals, generates PWM signals to control the switching states of the DC / DC conversion unit and the DC / AC conversion unit. A DSP control core unit that adjusts output power, responds to system changes in real time and issues control instructions, as well as a human-machine interface and LCD monitoring unit that provide a user interface, display system status and parameters, and allow users to monitor and adjust system operation; the battery pack, DC / DC conversion unit, DC / AC conversion unit, LCL filter unit and thyristor switching unit are connected in sequence; the DSP control core unit sends a PWM signal to drive the DC / DC conversion unit and the DC / AC conversion unit; the human-machine interface and LCD monitoring unit are bidirectionally interconnected with the DSP control core unit; the battery pack and thyristor switching unit are respectively connected to the DSP control core unit.

2. The inverter feedback battery charging and discharging system according to claim 1 is characterized in that: The DSP control core unit is a DSP controller TMS320F2808.

3. The inverter feedback battery charging and discharging system according to claim 1 is characterized in that: The LCL filter unit is an LCL filter with a speed attenuation of -60dB / dec.

4. The inverter feedback battery charging and discharging system according to claim 1 is characterized in that: The DC / DC conversion unit is a full-bridge soft-switching DC / DC converter that can reduce switching losses and improve efficiency during the switching process. Its circuit structure includes: main switch tubes S1, S2, S3 and S4 for controlling the on and off of current; a high-frequency transformer TR for changing the voltage; rectifier diodes D1, D2, D3 and D4 for converting AC power into DC power; a buffer circuit composed of Q1, Q2, C1, C2, L2 and D5 for absorbing the energy impact generated during switching; a clamping capacitor C1 for limiting the voltage peak and protecting the circuit; a resonant capacitor C2 for cooperating with an inductor to achieve energy resonance transmission; coupling inductors L1 and L2 for connecting different circuit parts and transferring energy; and a leakage inductor L1 of the transformer. lk and the magnetizing inductance L m and output filter capacitor C o ; The coupled inductor L2 is part of the buffer circuit, and L1 is part of the LCL filter unit; the main switch tubes Q1-Q4 control the current flow to the transformer TR; the rectifier diodes D1-D4 convert the AC power output by the transformer into DC power; the capacitors and inductors in the buffer circuit absorb and release energy to reduce the impact during switching; the clamping capacitor and the resonant capacitor work together to ensure the stability of the circuit; the coupled inductor L and the LC filter circuit further purify the current; the leakage inductance and the excitation inductance are the characteristics of the transformer and affect the performance of the circuit; the output filter capacitor C smoothes the output current.

5. The inverter feedback battery charging and discharging system according to claim 4 is characterized in that: The fuzzy PID control circuit includes: a sensor S for monitoring and collecting actual current, a PID regulator for adjusting the output according to the current difference to reduce the error, and a PWM modulator for adjusting the switching time of the switching device according to the output of the PID regulator to control the current size; the sensor S monitors the discharge current of the battery pack and compares it with the set reference current I dcc-ref The difference is compared and sent to the PID regulator to calculate the amount that needs to be adjusted. The PWM modulator adjusts the switching time of the switching device according to the output of the PID regulator to form a control signal to maintain current stability.

6. The inverter feedback battery charging and discharging system according to claim 1 is characterized in that: The DC / AC conversion unit is a three-phase full-bridge inverter circuit in a control mode of voltage source input and current source output.

7. The inverter feedback battery charging and discharging system according to claim 6 is characterized in that: The invention also includes a PID control circuit based on a BP neural network, which includes a PID controller and a BP neural network, wherein the k of the PID controller is p , k i , k d The parameters are directly adjusted by the BP neural network in real time, and the controlled object is closed-loop controlled; the BP neural network can output the best k according to the error performance function p , k i , k d .

8. The inverter feedback battery charging and discharging system according to claim 6 is characterized in that: It also includes an improved second-order generalized integrator to design a phase-locked loop (PLL).

9. The inverter feedback battery charging and discharging system according to claim 8 is characterized in that: It also includes a frequency locked loop FLL which can obtain grid frequency information accurately and in real time.

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