Transformer-free direct current to alternating current conversion device and method based on battery dynamic access

Abstract

The invention discloses a transformer-free direct current to alternating current conversion device and method based on battery dynamic access, and belongs to the technical field of power electronics. The device comprises a battery pack module (1), a switch array module (8), a control module (2), a polarity switching module (7), a filtering module (3), a compensation module (4) and a protection module (5). The battery pack module (1) is formed by connecting a plurality of small battery packs in series, and each small battery pack is formed by connecting a plurality of single batteries in series. And the control module (2) dynamically controls the connection and disconnection of the battery modules through the switch array module (8) according to a target output voltage waveform, controls the polarity of the output voltage of the connected battery module group through the polarity switching module (7), and synthesizes the output voltage approximate to the target voltage waveform. The filtering module (3) and the compensation module (4) are used for improving waveform quality. The protection module (5) monitors the state of the battery and takes protection measures. Low-frequency control is adopted, high-frequency switching loss is avoided, conversion efficiency is improved, control complexity is reduced, and the method has the advantages of being good in power grid compatibility and cost advantage, low in electromagnetic interference, longer in battery life and the like.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics technology, and more specifically, relates to a transformerless DC to AC conversion device and method based on dynamic battery access, which can be used to efficiently convert low-voltage DC power into AC power, and is particularly suitable for solar power generation, wind power generation, electric vehicles, energy storage systems, uninterruptible power supplies (UPS), and microgrids. Background Art

[0002] Traditional DC-AC conversion technologies, such as inverters, usually rely on complex switching circuits and high-frequency modulation technologies, such as pulse width modulation (PWM). These technologies generate a lot of switching losses, conduction losses, and magnetic component losses in the process of converting DC to AC, resulting in reduced conversion efficiency. Especially in the case of low input voltage, such as when using a single battery as a power source, the room for efficiency improvement is very limited due to the need for a boost circuit.

[0003] Existing technical solutions mainly improve conversion efficiency by optimizing switching devices, improving modulation strategies, and adopting resonant technology. For example, high-efficiency topologies such as LLC resonant converters are widely used in DC-AC conversion. However, in the application scenario of ultra-low input voltage, the efficiency improvement of these technologies is still limited.

[0004] In addition, although transformerless DC-AC conversion solutions can reduce size and weight, they usually have problems such as common-mode noise and leakage current, and corresponding measures need to be taken to meet grid standards.

[0005] In the prior art, the technical solution closest to the present invention is the solution of using a multi-level inverter (MLI), such as a modular multi-level converter (MMC). However, the existing multi-level inverter solution usually uses high-frequency switching technology, which is complex to control and has high switching losses. In addition, for the medium and high voltage direct hanging technology, although the efficiency is high, it directly connects the high voltage to the power grid, which has safety risks and high equipment costs.

[0006] In view of the above problems existing in the prior art, this application cites and analyzes the following background technology documents:

[0007] 1. Patent literature:

[0008] US6480397B1 (2002) - "Transformerless DC-to-AC power conversion." This patent proposes a transformerless DC-AC converter that uses multiple battery cells connected in series and a switch network to synthesize an AC waveform by controlling the on and off of the switches. However, the solution does not detail how to control the access and polarity switching of the battery, how to deal with the battery balancing problem, and the number of switching devices used is relatively large. In addition, the patent does not consider how to optimize the quality of the output waveform and how to reduce electromagnetic interference.

[0009] US7414867B2(2008)-"Modular multilevel inverter." This patent describes the basic structure and control method of a modular multilevel inverter (MMC). Although MMC can achieve high-efficiency and high-quality waveform output, its control is complex and costly. It is mainly used in fields such as high-voltage DC transmission and is not suitable for low-voltage applications. It has high voltage withstand requirements for switching devices and is difficult to apply to low-cost single-cell battery application scenarios. EP2387158A1(2011)-"Control method for a modular multi-level converter." This patent proposes a control method for MMC, focusing on controlling the balance of sub-module capacitor voltages. However, this method is still based on high-frequency PWM control, has high switching losses, and has high control complexity. For low-voltage application scenarios, this method has poor control complexity and cost-effectiveness.

[0010] CN103840577A(2014)-"A grid-connected inverter and its control method" This Chinese patent proposes a grid-connected inverter and its control method, which reduces switching losses through an improved control strategy. However, the patent still uses the traditional PWM control method, and its efficiency improvement is limited for low-voltage application scenarios.

[0011] 2. Non-patent literature:

[0012] RW Erickson, D. Maksimovic, "Fundamentals of Power Electronics," 2nd ed., Springer, 2001. This book is a classic textbook in the field of power electronics, which introduces in detail the topology, working principle and control method of various DC-AC converters. The book points out that the traditional inverter based on high-frequency PWM has the problem of high switching loss, which limits its efficiency in low-voltage applications. The various topologies and control methods mentioned in the book provide a theoretical basis for the innovation of the present invention, but do not directly provide a transformer-free DC to AC conversion solution for direct access to batteries with low-voltage input.

[0013] S. Kouro et al., "Recent advances and industrial applications of multilevel converters," in IEEE Transactions on Industrial Electronics, vol. 57, no. 8, pp. 2553-2580, Aug. 2010, doi: 10.1109 / TIE.2010.2049719. This review article details the latest advances and industrial applications of multilevel inverters (MLI), including various topologies, modulation strategies, and control methods. The article points out that although MLI has many advantages, its control complexity and cost remain a challenge. For low-voltage applications, MLI is not cost-effective and the control complexity is too high.

[0014] M.Saeedifard and R.Iravani,"Dynamic performance of a modularmultilevel back-to-back HVDC system,"in IEEE Transactions on Power Delivery,vol.25,no.4,pp.2903-2912,Oct.2010,doi:10.1109 / TPWRD.2010.2050787.This paper studies the dynamic performance of modular multilevel back-to-back HVDC transmission system. The literature shows that although MMC technology has advantages in the field of HVDC transmission, its control system is very complex and needs to deal with a large number of sub-module voltage balancing and circulating current suppression problems. This further shows that MMC technology is not suitable for low-voltage application scenarios.

[0015] The above literature shows that the existing transformerless DC-AC conversion technology mainly has the following problems and shortcomings:

[0016] High-frequency switching losses: Most solutions use high-frequency PWM control, which leads to higher switching losses and limits the efficiency improvement, especially under low-voltage input conditions.

[0017] Complex control: The control algorithms of solutions such as multi-level inverters are complex and require coordination of the switching states of each power unit and voltage balancing control.

[0018] Low efficiency at low voltage input: Existing technologies have limited efficiency improvements for low voltage input, especially when the input voltage is the voltage of a single cell.

[0019] High cost: High-frequency switching devices, SiC devices and complex control systems lead to high costs.

[0020] Safety hazards: Although medium and high voltage direct hanging technology is highly efficient, it directly connects high voltage to the power grid, which poses a safety hazard.

[0021] Battery balancing problem: Existing solutions rarely consider battery balancing problems, and battery inconsistency will affect the performance and life of the system.

[0022] Electromagnetic interference (EMI) problem: High-frequency switching will produce more serious electromagnetic interference, which requires additional filtering circuits to suppress, increasing system cost and complexity.

[0023] The technical problem to be solved by the present invention is: how to use single cells as power sources to achieve efficient, reliable, and low-cost DC to AC conversion, and output AC that complies with various power grid standards, such as but not limited to 220V / 50Hz, 110V / 60Hz or other voltage / frequency standards, while meeting the requirements of power grid standards, reducing costs and safety hazards, and effectively suppressing electromagnetic interference. Summary of the invention

[0024] In order to solve the above problems existing in the prior art, the present invention proposes a transformerless DC to AC conversion device and method based on dynamic battery access, which directly synthesizes an approximate sinusoidal waveform by dynamically controlling the access number and polarity of the battery modules, thereby avoiding the loss caused by high-frequency switching and achieving higher conversion efficiency.

[0025] 1. Technical issues to be resolved

[0026] The technical problem to be solved by the present invention is to provide a transformerless DC to AC conversion device and method based on dynamic battery access, so as to overcome the problems of low efficiency, complex control, difficulty in meeting grid standards, high cost, potential safety hazards and serious electromagnetic interference in the prior art of low-voltage DC to AC conversion, and to achieve efficient, reliable, low-cost, safer and low-electromagnetic interference DC to AC conversion.

[0027] (II) Technical solution

[0028] The technical solution provided by the present invention is as follows:

[0029] A transformerless DC to AC conversion device based on dynamic battery access, characterized by comprising:

[0030] Battery pack module: It is composed of multiple battery groups connected in series. Each battery group is composed of multiple single cells connected in series. The battery pack module is divided into multiple battery modules with different voltage outputs.

[0031] Switch array module: used to control the connection and disconnection of each battery module in the battery pack module;

[0032] Polarity switching module: used to control the output voltage polarity of the connected battery module group;

[0033] Control module: used to control the switch array module and the polarity switching module, and control the connection and disconnection of each battery module and the polarity of the output voltage of the connected battery module group according to the target output voltage waveform, amplitude and frequency in each cycle according to the preset timing and logic, so as to synthesize an output voltage that approximates the target voltage waveform;

[0034] Filter module: used to filter the voltage waveform output by the control module to reduce the harmonic content;

[0035] Compensation module: optional, used to compensate the filtered voltage waveform to further improve the waveform quality;

[0036] Protection module: used to monitor the status of the battery pack module and take protective measures when abnormal conditions occur.

[0037] Furthermore, the switch array module includes a plurality of switch units, each of which controls the connection and disconnection of one or more battery modules, and the switch units include but are not limited to:

[0038] Unidirectional switch: It is composed of one or more unidirectional switch devices connected in series, such as MOSFET, IGBT, etc.

[0039] Bidirectional switch: It is composed of two unidirectional switch devices connected in reverse parallel, or it is composed of bidirectional switch devices, such as Triac.

[0040] Furthermore, the polarity switching module includes one or more polarity switching switches for changing the output voltage polarity of the connected battery module group, and the polarity switching switches include but are not limited to:

[0041] H-bridge circuit: An H-bridge circuit consisting of four switching devices;

[0042] Double Pole Double Throw Switch (DPDT): A mechanical or solid state double pole double throw switch.

[0043] Furthermore, the control module controls the connection and disconnection of each battery module and the polarity of the output voltage of each battery module in each cycle according to the preset timing and logic according to the target output voltage waveform, so as to synthesize an output voltage that approximates the target voltage waveform. The target output voltage waveform includes but is not limited to a sine wave, a square wave, etc., the frequency of the target output voltage includes but is not limited to 50Hz, 60Hz or direct current, and the amplitude of the target output voltage includes but is not limited to 220V, 110V or any voltage value required by the user.

[0044] Furthermore, the control frequency adopted by the control module is 10 times lower than the target output voltage frequency.

[0045] Furthermore, the control module is implemented using a digital signal processor (DSP), a field programmable gate array (FPGA), a microcontroller (MCU) or an application specific integrated circuit (ASIC).

[0046] Furthermore, the filtering module adopts an L-type, LC-type, π-type or multiple low-pass filter.

[0047] Furthermore, the compensation module adopts a digital control method to generate a compensation signal by comparing the deviation between the real-time waveform of the output voltage and the target waveform, and adjusts the timing of connecting, disconnecting or polarity switching of the battery module according to the compensation signal to compensate for the waveform distortion.

[0048] Furthermore, the compensation module compensates for the deviation of the voltage amplitude by adjusting the time or number of battery modules connected.

[0049] Furthermore, the protection module includes a battery management system (BMS) for monitoring the voltage, current and temperature of each battery group and achieving battery balancing.

[0050] Furthermore, the protection module also includes one or more of an overvoltage protection circuit, an undervoltage protection circuit, an overcurrent protection circuit, a short circuit protection circuit and an overtemperature protection circuit.

[0051] Furthermore, the protection module also includes an active common-mode suppression circuit for reducing common-mode noise.

[0052] A transformerless DC to AC conversion method based on dynamic battery access, characterized in that it comprises the following steps: 1. Battery grouping: connect multiple single cells in series to form a battery group, then connect multiple battery groups in series to form a battery module, and divide the battery module into multiple battery modules with different voltage outputs; 2. Dynamic access and polarity control: According to the waveform, amplitude and frequency of the target output voltage, in each cycle, the switch array module controls the access and disconnection of each battery module, and the polarity of the output voltage of the connected battery module group is controlled by the polarity switching module to synthesize an output voltage that approximates the target voltage waveform; 3. Waveform filtering: Filter the synthesized output voltage waveform to reduce the harmonic content; 4. Waveform compensation: Optionally, the filtered voltage waveform is compensated to further improve the waveform quality; 5. Protection and management: Monitor the status of the battery pack module and take protective measures when abnormal conditions occur.

[0053] Furthermore, in step 2, the target output voltage waveform includes but is not limited to a sine wave, a square wave, etc., the frequency of the target output voltage includes but is not limited to 50 Hz, 60 Hz or direct current, and the amplitude of the target output voltage includes but is not limited to 220 V, 110 V or any voltage value required by the user.

[0054] Furthermore, in step 2, when the target output voltage is a sine wave, the number and polarity of the battery modules to be connected are determined according to the instantaneous voltage value of the sine wave.

[0055] Furthermore, in step 3, L-type, LC-type, π-type or multiple low-pass filters are used for filtering.

[0056] Furthermore, in step 4, a digital control method is used to generate a compensation signal by comparing the deviation between the real-time waveform of the output voltage and the target waveform, and adjust the timing of connecting, disconnecting or polarity switching of the battery module according to the compensation signal to compensate for the waveform distortion.

[0057] Furthermore, in step 4, the voltage amplitude deviation is compensated by adjusting the time or number of battery modules connected.

[0058] Furthermore, in step 5, the state of the battery pack module includes the voltage, current and temperature of each battery group, and protective measures are taken when overvoltage, undervoltage, overcurrent, short circuit or overtemperature occurs.

[0059] Furthermore, in step 5, a battery management system (BMS) is used to achieve battery balancing.

[0060] Furthermore, in step 5, an active common-mode suppression circuit is used to reduce common-mode noise.

[0061] (III) Beneficial effects.

[0062] The transformerless DC to AC conversion device and method based on dynamic battery access provided by the present invention has the following beneficial effects compared with the prior art:

[0063] 1. High efficiency: The present invention directly synthesizes an approximate target waveform by dynamically controlling the access and polarity of the battery module, thereby avoiding the high-frequency switching loss in traditional DC-AC conversion technology. In theory, higher conversion efficiency can be achieved, especially in the case of low voltage input.

[0064] 2. Low control complexity: The present invention adopts a low-frequency control strategy, and the control frequency is much lower than the switching frequency of traditional PWM technology, which greatly reduces the control difficulty and the complexity of the control circuit.

[0065] 3. High reliability: The present invention adopts a modular design, and both the battery pack module and the control module can work independently, thereby improving the reliability and maintainability of the system.

[0066] 4. Good grid compatibility: The present invention can effectively reduce the harmonic content and common-mode noise of the output voltage by adopting technologies such as multiple filtering, dynamic waveform compensation and active common-mode suppression, and meet the requirements of various grid standards.

[0067] 5. Cost advantage: The present invention does not require a transformer, which reduces the volume, weight and cost of the system. At the same time, low-frequency switching reduces the performance requirements for switching devices, and lower-cost switching devices can be used.

[0068] 6. High flexibility: The amplitude and frequency of the output voltage can be dynamically adjusted according to demand, suitable for a variety of application scenarios.

[0069] 7. Higher safety: Compared with medium and high voltage direct hanging technology, the present invention has lower working voltage and higher safety.

[0070] 8. Low electromagnetic interference: Due to the use of low-frequency switching, the electromagnetic interference generated by the present invention is much lower than that of the traditional high-frequency PWM solution, which is beneficial to improving the electromagnetic compatibility of the system.

[0071] 9. Longer battery life: By precisely controlling the connection and disconnection of each battery module, the battery usage can be optimized, overcharging and over-discharging can be avoided, and the battery life can be extended. DETAILED DESCRIPTION

[0072] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0073] Implementation Case 1

[0074] like Figure 1As shown, this embodiment provides a transformerless DC to AC conversion device based on dynamic battery access, including a battery pack module 1, a switch array module 8, a control module 2, a polarity switching module 7, a filtering module 3, a compensation module 4 and a protection module 5.

[0075] like Figure 2 As shown, the battery pack module 1 is composed of a plurality of battery groups connected in series, and each battery group is composed of a plurality of single cells connected in series to provide a certain voltage output. The battery pack module 1 is divided into 4 battery modules, and each battery module contains a plurality of battery groups, which can provide a certain voltage output. The single cells here can be various types of single cells such as lithium-ion batteries, nickel-metal hydride batteries, and lead-acid batteries, and their nominal voltages can be selected according to actual application requirements, such as 3.2V, 3.7V, 1.2V, 2V, etc.

[0076] The switch array module 8 is used to control the connection and disconnection of each battery module in the battery pack module 1. In this embodiment, the switch array module 8 adopts Figure 5 The implementation shown is composed of multiple one-way switches, each of which controls the connection and disconnection of a battery module.

[0077] The polarity switching module 7 is used to control the polarity of the output voltage of each battery module. Figure 6 The H-bridge circuit shown is implemented.

[0078] The control module 2 is implemented using FPGA and is used to control the on and off of each switch in the switch array module 8 and the state of the polarity switching module 7. The control module 2 controls the connection and disconnection of each battery module and the polarity of the output voltage of each battery module according to the target output voltage waveform (such as 220V / 50Hz sine wave, 110V / 60Hz sine wave, or other voltage / frequency standards) in each cycle according to the preset timing and logic.

[0079] like Figure 3 As shown, taking the output sine wave as an example, in the positive half cycle of the sine wave, starting from 0, the control module 2 controls the switch array module 8 to increase the number of connected battery modules one by one, and controls the output positive polarity voltage through the H-bridge circuit until it approaches the peak of the sine wave. At the peak of the sine wave, all battery modules are connected and the output voltage reaches the maximum value. In the second half cycle of the sine wave, the control module 2 reduces the number of connected battery modules one by one and maintains the output positive polarity voltage until 0. In the negative half cycle, similar operations are performed, but the output negative polarity voltage is controlled by the H-bridge circuit. In this way, an output voltage that approximates a sine wave can be synthesized, such as Figure 4 shown.

[0080] The control module 2 adopts a low-frequency control strategy, and its control frequency is much lower than 10 times the target output voltage frequency. For example, when outputting 50Hz AC power, the control frequency of the control module 2 can be set to 100Hz or lower, or even the same as the output frequency, i.e. 50Hz. This greatly reduces the control difficulty and the complexity of the control circuit.

[0081] The filter module 3 uses multiple LC low-pass filters to filter the voltage waveform output by the control module 2 to reduce the harmonic content.

[0082] The compensation module 4 is digitally controlled and implemented by DSP. The compensation module 4 dynamically adjusts the connection and disconnection and polarity of the battery module according to the deviation between the real-time waveform of the output voltage and the target waveform to compensate for the waveform distortion and further improve the waveform quality. For example, when it is detected that the output voltage amplitude is low, the compensation module 4 can control to increase the connection time of a battery module to increase the amplitude of the output voltage.

[0083] The protection module 5 includes a battery management system (BMS) and an active common mode suppression circuit. The BMS is used to monitor the voltage, current and temperature of each battery group and achieve battery balancing to prevent overcharging, overdischarging and overheating. The active common mode suppression circuit is used to reduce common mode noise. The protection module 5 also includes an overvoltage protection circuit, an undervoltage protection circuit, an overcurrent protection circuit and a short circuit protection circuit to ensure safe and reliable operation of the system.

[0084] Application scenarios:

[0085] Application scenario 1: Solar power generation and energy storage system Solar power generation and energy storage system.

[0086] In this application scenario, the battery pack module 1 is composed of a solar panel and an energy storage battery. The solar panel charges the energy storage battery during the day, and converts the excess electrical energy into alternating current through the device of the present invention for use by users or into the power grid. At night or in rainy weather, the energy storage battery is used as a power source and converted into alternating current through the device of the present invention to provide users with a continuous power supply. The device of the present invention can intelligently control the connection and disconnection of the battery module according to the sunshine conditions and load requirements, optimize the system efficiency, and extend the battery life. At the same time, the device of the present invention can achieve seamless switching between the grid-connected and off-grid modes, thereby improving the reliability of power supply.

[0087] Application scenario 2: Home energy storage system

[0088] In this application scenario, the battery pack module 1 is composed of energy storage batteries, such as lithium-ion battery packs. During periods of low electricity prices, the device of the present invention converts the AC power of the power grid into DC power to charge the energy storage battery; during periods of peak electricity prices, the device of the present invention converts the DC power of the energy storage battery into AC power to power household loads, thereby reducing the user's electricity costs. The device of the present invention can automatically switch between charging and discharging according to the user's settings to achieve the function of "peak shaving and valley filling". At the same time, the device of the present invention can also be used as a backup power source for the home, providing users with a continuous power supply when the power grid is out of power.

[0089] Application scenario three: UPS (uninterruptible power supply system).

[0090] In this application scenario, the battery pack module 1 is composed of energy storage batteries. When the power grid is supplying power normally, the device of the present invention converts the AC power of the power grid into DC power to charge the energy storage battery, and at the same time provides a stable AC power supply for the load; when the power grid is out of power, the device of the present invention converts the DC power of the energy storage battery into AC power to provide an uninterrupted power supply to the load, ensuring the normal operation of important equipment. The device of the present invention can achieve rapid switching at the millisecond level to ensure the continuity of power supply. At the same time, because the device of the present invention adopts low-frequency control, it has higher reliability and longer life, and is more suitable for application scenarios with extremely high reliability requirements, such as data centers, hospitals, etc.

[0091] Implementation case 2.

[0092] This embodiment provides a transformerless DC to AC conversion method based on dynamic battery access, including the following steps:

[0093] 1. Battery grouping: connect multiple single cells in series to form a battery group to provide a certain voltage output, and then connect multiple battery groups in series to form a battery module to provide a higher voltage output. Divide the battery module into 4 battery modules, each of which provides a certain voltage output.

[0094] 2. Dynamic access and polarity control: According to the target output voltage waveform (such as 220V / 50Hz sine wave, 110V / 60Hz sine wave, or other voltage / frequency standards), in each cycle, the switch array module controls the access and disconnection of each battery module, and the polarity of the output voltage of the connected battery module group is controlled by the polarity switching module to synthesize an output voltage that approximates the target voltage waveform. The specific control timing is as follows Figure 3 shown.

[0095] 3. Waveform filtering: Multiple LC low-pass filters are used to filter the synthesized output voltage waveform to reduce the harmonic content.

[0096] 4. Waveform compensation: Digital control is used to dynamically adjust the connection and disconnection of the battery module and the polarity according to the deviation between the real-time waveform of the output voltage and the target waveform to compensate for the waveform distortion. For example, when the output voltage amplitude is detected to be low, the connection time of a battery module can be controlled to increase the amplitude of the output voltage.

[0097] 5. Protection and management: BMS is used to monitor the status of battery pack modules, achieve battery balancing, and prevent overcharging, over-discharging, and over-temperature. Active common-mode suppression circuits are used to reduce common-mode noise. Multiple protection measures such as overvoltage protection circuits, undervoltage protection circuits, overcurrent protection circuits, and short-circuit protection circuits are used to ensure safe and reliable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 The structure block diagram of the transformerless DC to AC conversion device based on dynamic battery access of the present invention.

[0102] Figure 2 It is a schematic structural diagram of the battery pack module of the present invention.

[0103] Figure 3 It is a schematic diagram of the timing of dynamic access control of the battery module of the present invention.

[0104] Figure 4 Schematic diagram of output voltage waveform of the present invention.

[0105] Figure 5 The figure is a schematic diagram of a specific implementation of the switch array module of the present invention.

[0106] Figure 6 It is a schematic diagram of a specific implementation method of the polarity switching module of the present invention.

Claims

1. A transformerless DC to AC conversion device based on dynamic battery access, characterized in that: include: * A battery pack module (1), which is composed of a plurality of battery groups connected in series, each battery group being composed of a plurality of single cells connected in series, and the battery pack module is divided into a plurality of battery modules having different voltage outputs; * a switch array module (8), used to control the connection and disconnection of each battery module in the battery pack module (1); * a polarity switching module (7), used to control the output voltage polarity of the connected battery module group; * a control module (2) for controlling the switch array module (8) and the polarity switching module (7) to control the connection and disconnection of each battery module and the polarity of the output voltage of the connected battery module group according to the target output voltage waveform, amplitude and frequency, in each cycle and in accordance with a preset timing and logic, so as to synthesize an output voltage that approximates the target voltage waveform; * A filtering module (3), used for filtering the voltage waveform output by the control module (2) to reduce harmonic content; * a compensation module (4), optionally used to compensate the filtered voltage waveform to further improve the waveform quality; * A protection module (5) is used to monitor the status of the battery pack module (1) and take protective measures when an abnormal situation occurs.

2. The device according to claim 1, characterized in that The switch array module (8) comprises a plurality of switch units, each of which controls the connection and disconnection of one or more battery modules. The switch units include but are not limited to: * Unidirectional switch: It is composed of one or more unidirectional switch devices connected in series, such as MOSFET, IGBT, etc.; * Bidirectional switch: It is composed of two unidirectional switch devices connected in reverse parallel, or it is composed of bidirectional switch devices, such as Triac, etc.

3. The device according to claim 1, characterized in that The polarity switching module (7) comprises one or more polarity switching switches for changing the output voltage polarity of the connected battery module group, and the polarity switching switches include but are not limited to: * H-bridge circuit: An H-bridge circuit consisting of four switching devices; * Double-pole double-throw switch (DPDT): A mechanical or solid-state double-pole double-throw switch.

4. The device according to claim 1, characterized in that The control module (2) controls the connection and disconnection of each battery module and the polarity of the output voltage of each battery module according to the target output voltage waveform in each cycle according to the preset timing and logic, so as to synthesize an output voltage that approximates the target voltage waveform. The target output voltage waveform includes but is not limited to a sine wave, a square wave, etc. The frequency of the target output voltage includes but is not limited to 50Hz, 60Hz or direct current, and the amplitude of the target output voltage includes but is not limited to 220V, 110V or any voltage value required by the user. The control module is implemented using a digital signal processor (DSP), a field programmable gate array (FPGA), a microcontroller (MCU) or an application specific integrated circuit (ASIC).

5. An electronic device, comprising: * Memory; * Processor; as well as * a computer program stored in said memory and executable on said processor, It is characterized in that when the processor executes the computer program, the method according to any one of claims 13-22 is implemented.

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