Single-phase isolated battery energy storage system, control method and soc equalization method

Abstract

The application discloses a single-phase isolated battery energy storage system, a control method and an SOC equalization method. The system comprises a first battery unit, a second battery unit, first to twelfth switch tubes, a first transformer, a second transformer, a first inductor, a second inductor, first to fourth capacitors and an alternating-current output port. The ninth switch tube, the tenth switch tube, the first capacitor and the second capacitor are sequentially connected in series to form an upper half-bridge circuit, the eleventh switch tube, the twelfth switch tube, the third capacitor and the fourth capacitor are sequentially connected in series to form a lower half-bridge circuit, the lower end of the upper half-bridge circuit is connected with the upper end of the lower half-bridge circuit, and the negative electrode of the second capacitor is connected with the negative electrode of the third capacitor. Through the application, the conversion of electric energy from direct current to alternating current and the electrical isolation between input and output are simultaneously completed, so that the system volume and weight are effectively reduced. The application can also realize the SOC equalization between the battery units, and is favorable for improving the conversion efficiency.

Description

Technical Field

[0001] This application relates to the field of power converter technology, and in particular to a single-phase isolated battery energy storage system, control method, and SOC equalization method. Background Technology

[0002] Energy storage systems, as key devices for balancing electricity supply and demand, improving grid stability, and enhancing the absorption capacity of renewable energy, are fundamentally about enabling rapid and controllable bidirectional power flow between energy storage units (typically DC-based batteries, supercapacitors, etc.) and the AC grid. This power interface not only needs to meet the power factor correction, low current harmonics, electrical isolation, and safety specifications required by grid connection standards, but also faces increasingly stringent engineering challenges in terms of efficiency, power density, cost, and reliability.

[0003] To achieve the above functions, the industry generally adopts a two-stage or multi-stage power conversion architecture. Although such multi-stage architectures are technically mature and offer relatively independent control, their inherent drawbacks limit further improvements in overall system performance:

[0004] First, the energy needs to go through two or more complete power conversion processes. Each stage has conduction losses, switching losses, and magnetic component losses, making it difficult for the overall system efficiency to break through the bottleneck. The losses are even more significant under partial load conditions.

[0005] Secondly, multi-stage structures typically require one or more large-capacity intermediate DC bus capacitors to decouple the power between the preceding and following stages, buffer secondary power pulsations, and maintain voltage stability. These electrolytic capacitors are not only bulky and expensive, but their lifespan is often shorter than that of other core components in the system, becoming a weak link affecting the overall reliability and service life of the device.

[0006] In addition, multiple power stages and their corresponding control circuits and heat dissipation mechanisms increase the complexity, size and manufacturing cost of the system, which is not conducive to achieving high power density and compact design. Summary of the Invention

[0007] This application provides a single-phase isolated battery energy storage system, a control method, and a SOC balancing method to enable low-voltage energy storage units to generate single-phase AC voltage through unipolar power conversion, with the energy storage and the grid isolated by a high-frequency transformer; and to achieve SOC balancing among battery units, thereby improving conversion efficiency.

[0008] The embodiments of this application adopt the following technical solutions:

[0009] In a first aspect, embodiments of this application provide a single-phase isolated battery energy storage system, including a first battery unit, a second battery unit, first to twelfth switching transistors, a first transformer, a second transformer, a first inductor, a second inductor, first to fourth capacitors, and an AC output port;

[0010] The ninth switch, the tenth switch, the first capacitor, and the second capacitor are connected in series to form the upper half-bridge circuit, and the eleventh switch, the twelfth switch, the third capacitor, and the fourth capacitor are connected in series to form the lower half-bridge circuit.

[0011] The lower end of the upper half-bridge circuit is connected to the upper end of the lower half-bridge circuit, and the negative terminal of the second capacitor is connected to the negative terminal of the third capacitor.

[0012] The positive terminal of the first battery cell is connected to the upper end of the first switching transistor, and the negative terminal is connected to the lower end of the fourth switching transistor. The lower end of the first switching transistor is connected to the upper end of the second switching transistor and then connected to one end of the primary winding of the first transformer. The lower end of the third switching transistor is connected to the upper end of the fourth switching transistor and then connected to the other end of the primary winding of the first transformer.

[0013] The positive terminal of the second battery unit is connected to the upper end of the fifth switch tube, and the negative terminal is connected to the lower end of the sixth switch tube. The lower end of the fifth switch tube is connected to the upper end of the sixth switch tube and then connected to one end of the primary winding of the second transformer. The lower end of the seventh switch tube is connected to the upper end of the eighth switch tube and then connected to the other end of the primary winding of the second transformer.

[0014] One end of the secondary winding of the first transformer is connected to the first inductor and then to the lower end of the ninth switch and the upper end of the tenth switch, and the other end is connected to the negative terminal of the first capacitor; one end of the secondary winding of the second transformer is connected to the second inductor and then to the lower end of the eleventh switch and the upper end of the twelfth switch, and the other end is connected to the negative terminal of the third capacitor.

[0015] The positive terminal of the first capacitor is connected to the upper terminal of the AC output port, and the negative terminal of the fourth capacitor is connected to the lower terminal of the AC output port.

[0016] In some embodiments, the first to fourth switches are connected in series to form a first full-bridge inverter circuit, and the fifth to eighth switches are connected in series to form a second full-bridge inverter circuit.

[0017] In some embodiments, the first transformer and the second transformer are high-frequency transformers, and their primary windings are respectively connected to the midpoint of the bridge arm of the corresponding full-bridge inverter circuit to achieve electrical isolation between the DC side and the AC side and high-frequency energy transfer.

[0018] In some embodiments, the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are electrolytic capacitors or film capacitors, used to stabilize the midpoint voltage of the corresponding half-bridge circuit.

[0019] In some embodiments, the first inductor L1 and the second inductor L2 are buffer inductors of the circuit, used to generate a current waveform for power transfer to adapt to the voltage difference between the input and output.

[0020] Secondly, embodiments of this application also provide a control method based on the single-phase isolated battery energy storage system described in the first aspect, wherein the positive terminal of the first capacitor is the positive terminal of the upper half-bridge arm output voltage, the negative terminal of the second capacitor is the negative terminal of the upper half-bridge arm output voltage, the positive terminal of the fourth capacitor is the positive terminal of the lower half-bridge arm output voltage, and the negative terminal of the third capacitor is the negative terminal of the lower half-bridge arm output voltage. The AC output voltage of the circuit is differentially synthesized from the upper half-bridge arm output voltage and the lower half-bridge arm output voltage, and satisfies:

[0021] The upper half-bridge arm output voltage is a sinusoidal voltage with DC bias;

[0022] The lower half-bridge arm output voltage is a sinusoidal voltage with DC bias;

[0023] The upper half-bridge arm output voltage and the lower half-bridge arm output voltage have the same amplitude and DC bias, and the AC sinusoidal components have the same frequency and a phase difference of half a cycle.

[0024] The AC output voltage of the circuit contains only a sinusoidal AC component and does not include DC bias.

[0025] Thirdly, embodiments of this application also provide a SOC balancing method based on the single-phase isolated battery energy storage system described in the first aspect, comprising the following steps:

[0026] Step 1: Superimpose an equal voltage component ΔU1, which has the same frequency and phase as the output current, onto the sinusoidal AC component of the upper half-bridge arm output voltage;

[0027] Step 2: Superimpose a balanced voltage component ΔU2, which has the same amplitude and phase as ΔU1, onto the sinusoidal AC component of the lower half-bridge arm output voltage;

[0028] Step 3: The equalized voltage component superimposed on the upper half-bridge arm and the output current generate active power ΔP, and the equalized voltage component superimposed on the lower half-bridge arm and the output current generate active power -ΔP. The SOC balance between the first battery cell and the second battery cell is achieved through this power difference.

[0029] In some embodiments, the calculation of the equalization voltage components ΔU1 and ΔU2 is based on the deviation between the first battery cell SOC1 and the second battery cell SOC2, i.e., ΔSOC = SOC_1 - SOC_2, and ΔU1 = ΔU2.

[0030] In some embodiments, the balanced voltage component is superimposed on the output voltage command value U generated by the power outer loop and the current loop.ref The voltage difference between the sampled voltage and the voltage is used to generate a phase shift angle through PR control in order to maintain a constant output voltage of the system.

[0031] In some embodiments, the amplitude of the equalization voltage component is determined by the product of the proportional coefficient K and the SOC deviation value ΔSOC, i.e., ΔU_1=K×ΔSOC, so as to achieve dynamic adjustment of the SOC deviation.

[0032] The at least one technical solution adopted in this application embodiment can achieve the following beneficial effects: a single-phase isolated battery energy storage system includes a first battery unit, a second battery unit, first to twelfth switching transistors, a first transformer, a second transformer, a first inductor, a second inductor, first to fourth capacitors, and an AC output port; a ninth switching transistor, a tenth switching transistor, the first capacitor, and the second capacitor are connected in series to form an upper half-bridge circuit, and an eleventh switching transistor, a twelfth switching transistor, the third capacitor, and the fourth capacitor are connected in series to form a lower half-bridge circuit; the lower end of the upper half-bridge circuit is connected to the upper end of the lower half-bridge circuit, and the negative terminal of the second capacitor is connected to the negative terminal of the third capacitor; the positive terminal of the first battery unit is connected to the upper end of the first switching transistor, and the negative terminal is connected to the lower end of the fourth switching transistor; the lower end of the first switching transistor is connected to the upper end of the second switching transistor and then connected to one end of the primary winding of the first transformer. The lower end of the third switch is connected to the upper end of the fourth switch and then to the other end of the primary winding of the first transformer; the positive terminal of the second battery unit is connected to the upper end of the fifth switch and the negative terminal is connected to the lower end of the sixth switch. The lower end of the fifth switch and the upper end of the sixth switch are connected to one end of the primary winding of the second transformer. The lower end of the seventh switch and the upper end of the eighth switch are connected to the other end of the primary winding of the second transformer. One end of the secondary winding of the first transformer is connected to the first inductor and then to the lower end of the ninth switch and the upper end of the tenth switch. The other end is connected to the negative terminal of the first capacitor. One end of the secondary winding of the second transformer is connected to the second inductor and then to the lower end of the eleventh switch and the upper end of the twelfth switch. The other end is connected to the negative terminal of the third capacitor. The positive terminal of the first capacitor is connected to the upper terminal of the AC output port, and the negative terminal of the fourth capacitor is connected to the lower terminal of the AC output port. The aforementioned system is based on an innovative single-stage high-frequency isolation topology. Specifically, it uses a single high-frequency power conversion stage to simultaneously convert the power form from DC to AC and achieve electrical isolation between the input and output. This effectively reduces system size and weight while increasing inverter power density. Simultaneously, it avoids the drawback of two-stage or multi-stage architectures where a stable intermediate DC bus is required between stages. This enhances the overall reliability and lifespan of the system and reduces the risk of failure due to capacitor aging and drying. Attached Figure Description

[0033] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0034] Figure 1 This is a schematic diagram of the overall topology of the single-phase isolated battery energy storage system in the embodiments of this application;

[0035] Figure 2 This is a schematic diagram of the overall control of a single-phase isolated battery energy storage system in an embodiment of this application;

[0036] Figure 3 This is a schematic diagram of the SOC balancing method for a single-phase isolated battery energy storage system in an embodiment of this application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] A single-stage, single-phase boost inverter topology with a magnetically coupled energy storage inductor in the inverter bridge is disclosed in related technologies. This topology has advantages such as single-stage boost power conversion, high power density, high conversion efficiency, bidirectional power flow, low output waveform distortion, high reliability under overload and short circuit conditions, and low cost. However, its advantages are only significant in boost inverter applications with small to medium power, single phase, and large input voltage variation range. It also highly depends on precise control algorithms and highly consistent magnetic components. When handling high power or expanding to three-phase systems, it may face significant challenges in terms of magnetic components, current sharing, and control complexity, making it difficult to meet the comprehensive requirements of energy storage for high efficiency, high power density, and reliable operation.

[0039] Therefore, given the limitations of existing multi-stage power conversion architectures in terms of efficiency, power density, cost, and reliability, there is an urgent need to research simpler and more efficient power conversion solutions. This application provides a novel topology that integrates voltage conversion, electrical isolation, and grid-connected control into a single-stage power conversion stage. This significantly reduces system losses, the number of components, and the size of the component, while improving power density and reliability, ultimately lowering the total lifecycle cost. It possesses significant technological value and market implications.

[0040] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0041] This application provides a single-phase isolated battery energy storage system, such as... Figure 1 The diagram shows the overall topology of a single-phase isolated battery energy storage system according to an embodiment of this application. It includes a first battery unit, a second battery unit, first to twelfth switching transistors, a first transformer, a second transformer, a first inductor, a second inductor, first to fourth capacitors, and an AC output port. A ninth switching transistor, a tenth switching transistor, the first capacitor, and the second capacitor are connected in series to form an upper half-bridge circuit. An eleventh switching transistor, a twelfth switching transistor, the third capacitor, and the fourth capacitor are connected in series to form a lower half-bridge circuit. The lower end of the upper half-bridge circuit is connected to the upper end of the lower half-bridge circuit, and the negative terminal of the second capacitor is connected to the negative terminal of the third capacitor. The positive terminal of the first battery unit is connected to the upper end of the first switching transistor, and the negative terminal is connected to the lower end of the fourth switching transistor. The lower end of the first switching transistor is connected to the upper end of the second switching transistor and then connected to one end of the primary winding of the first transformer. The third switching transistor... The lower end of the first switching transistor is connected to the upper end of the fourth switching transistor and then to the other end of the primary winding of the first transformer; the positive terminal of the second battery unit is connected to the upper end of the fifth switching transistor, and the negative terminal is connected to the lower end of the sixth switching transistor. The lower end of the fifth switching transistor and the upper end of the sixth switching transistor are connected to one end of the primary winding of the second transformer. The lower end of the seventh switching transistor and the upper end of the eighth switching transistor are connected to the other end of the primary winding of the second transformer. One end of the secondary winding of the first transformer is connected to the first inductor and then to the lower end of the ninth switching transistor and the upper end of the tenth switching transistor. The other end is connected to the negative terminal of the first capacitor. One end of the secondary winding of the second transformer is connected to the second inductor and then to the lower end of the eleventh switching transistor and the upper end of the twelfth switching transistor. The other end is connected to the negative terminal of the third capacitor. The positive terminal of the first capacitor is connected to the upper terminal of the AC output port, and the negative terminal of the fourth capacitor is connected to the lower terminal of the AC output port.

[0042] like Figure 1 As shown, the single-phase isolated battery energy storage system in this embodiment specifically includes a first battery unit, a second battery unit, and first to twelfth switching transistors (Q1-Q2). 12 The system consists of a first transformer, a second transformer, a first inductor L1, a second inductor L2, first to fourth capacitors (C1-C4), and an AC output port. Switches Q1-Q4 and Q5-Q8 form two full-bridge circuits, with the DC side of each circuit connected to the first and second battery cells, respectively. The midpoints of the two arms of each full-bridge circuit are connected to the primary winding of the high-frequency transformer, achieving electrical isolation and energy transfer between the DC and AC sides under high-frequency conditions.

[0043] In addition, the AC side is composed of switching transistors Q9-Q1 respectively. 10 Capacitors C1 and C2 and switching transistor Q 11 -Q 12Two identical and symmetrical half-bridge circuits, consisting of capacitors C3 and C4, are designated as the upper and lower half-bridges. The capacitors in each half-bridge circuit are used to stabilize the midpoint voltage. A half-bridge circuit structure is further employed to achieve AC power modulation. Compared to a full-bridge topology, the half-bridge structure requires fewer main power switches, greatly simplifying the AC main circuit and its supporting systems, thus offering competitive advantages in cost, size, and long-term operational stability.

[0044] One end of the secondary winding of the first transformer is connected to L1, and then the lower end of Q9 is connected to Q. 10 The upper end is connected to the negative terminal of C1, and the other end is connected to the negative terminal of C1; one end of the secondary winding of the second transformer is connected to L2 and then to Q. 11 The lower end of Q 12 The upper end of C1 is connected to the positive terminal of C3, and the other end is connected to the positive terminal of C4. The positive terminal of C1 is connected to the upper terminal of the AC port, and the positive terminal of C4 is connected to the lower terminal of the AC port. The upper half-bridge arm output voltage V is connected to the positive terminal of C1. p The positive terminal of C2 and the negative terminal of C2 are the upper half-bridge arm output voltage V. p The negative terminal of C4 is used as the negative terminal, and the positive terminal of C4 is used as the output voltage of the lower half-bridge arm, V. n The positive terminal of C3 and the negative terminal of C3 are the lower half-bridge arm output voltage V. n The negative terminal will result in the AC output voltage v of the circuit. ac It is synthesized by the differential mode of the output voltage of the upper half-bridge arm and the output voltage of the lower half-bridge arm, that is... , where v p and v n Both are sine waves with DC bias, and v ac It is a sine wave without DC bias.

[0045] In one embodiment of this application, the first to fourth switches are connected in series to form a first full-bridge inverter circuit, and the fifth to eighth switches are connected in series to form a second full-bridge inverter circuit.

[0046] The basic components of a full-bridge inverter circuit include: four power switching devices (usually MOSFETs or IGBTs) connected in parallel with four freewheeling diodes, forming an H-type bridge circuit. Specifically, the connection method of the full-bridge inverter circuit is as follows: the four switching devices are divided into two pairs of complementary working bridge arms; the DC power supply is connected to both ends of the bridge arm, and the AC output is taken from the midpoint of the bridge arm and connected across the load.

[0047] In one embodiment of this application, the first transformer and the second transformer are high-frequency transformers, and their primary windings are respectively connected to the midpoint of the bridge arm of the corresponding full-bridge inverter circuit to achieve electrical isolation between the DC side and the AC side and high-frequency energy transfer.

[0048] A high-frequency transformer is a transformer with an operating frequency exceeding 10kHz, primarily used in high-frequency switching power supplies, inverters, and other applications. It achieves voltage transformation and electrical isolation through electromagnetic induction. Its core characteristics include: Operating frequency range: typically above 10kHz, reaching up to several hundred MHz, far exceeding that of traditional low-frequency transformers (50 / 60Hz). Electrical isolation between the DC and AC sides and high-frequency energy transfer are achieved through the first and second transformers.

[0049] In one embodiment of this application, the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are electrolytic capacitors or film capacitors, used to stabilize the midpoint voltage of the corresponding half-bridge circuit.

[0050] An electrolytic capacitor is a polarized capacitor. Its positive electrode uses a metal foil, with an oxide film closely attached to the metal serving as the dielectric. The cathode is composed of conductive materials and an electrolyte. Electrolytic capacitors are characterized by high capacitance density per unit volume, with typical capacitance ranging from 1μF to 47mF. They can operate at hundreds of volts of DC, making them commonly used in applications requiring large-capacity energy storage, such as power supply filtering and energy storage.

[0051] Film capacitors are capacitors that use a plastic film as the dielectric. They are constructed by winding a metal foil or metallized vapor-deposited layer onto the plastic film to form a cylindrical shape. Film capacitors have advantages such as non-polarity, high insulation resistance, excellent frequency characteristics, and low dielectric loss. They are suitable for high-frequency and low-frequency circuits, such as analog signal coupling and power supply noise bypass. Their capacitance range is typically from 3pF to 0.1μF, and they have strong voltage withstand capability.

[0052] In one embodiment of this application, the first inductor L1 and the second inductor L2 are buffer inductors of the circuit, used to generate a current waveform for power transfer to adapt to the voltage difference between the input and output.

[0053] The high-frequency filter inductor is an inductor component mainly used in high-frequency circuits to perform filtering functions.

[0054] This application embodiment also provides a control method for the single-phase isolated battery energy storage system, wherein the positive terminal of the first capacitor is the positive terminal of the upper half-bridge arm output voltage, the negative terminal of the second capacitor is the negative terminal of the upper half-bridge arm output voltage, the positive terminal of the fourth capacitor is the positive terminal of the lower half-bridge arm output voltage, and the negative terminal of the third capacitor is the negative terminal of the lower half-bridge arm output voltage. The AC output voltage of the circuit is differentially synthesized from the upper half-bridge arm output voltage and the lower half-bridge arm output voltage, and satisfies the following: the upper half-bridge arm output voltage is a sinusoidal voltage with DC bias; the lower half-bridge arm output voltage is a sinusoidal voltage with DC bias; the upper half-bridge arm output voltage and the lower half-bridge arm output voltage have the same amplitude and DC bias, the AC sinusoidal components have the same frequency, and the phase difference is half a cycle; the AC output voltage of the circuit only contains the sinusoidal AC component and does not contain DC bias.

[0055] Specifically, the upper half-bridge arm output voltage is a sinusoidal voltage with DC bias. The lower half-bridge arm output voltage is also a sinusoidal voltage with DC bias. The upper and lower half-bridge arm output voltages have the same DC bias amplitude, the same frequency of their AC sinusoidal components, and a phase difference of half a cycle. The circuit's AC output voltage is a differential-mode synthesis of the upper and lower half-bridge arm output voltages, which does not include DC bias and only contains the sinusoidal AC component.

[0056] like Figure 3 As shown in the embodiments of this application, a SOC equalization method based on the single-phase isolated battery energy storage system is also provided, including the following steps:

[0057] Step 310: Superimpose an equal voltage component ΔU1 with the same frequency and phase as the output current onto the sinusoidal AC component of the upper half-bridge arm output voltage;

[0058] Step 320: Superimpose an equal voltage component ΔU2, which has the same amplitude and phase as ΔU1, onto the sinusoidal AC component of the lower half-bridge arm output voltage;

[0059] Step 330: The equalization voltage component superimposed on the upper half-bridge arm and the output current generate active power ΔP, and the equalization voltage component superimposed on the lower half-bridge arm and the output current generate active power -ΔP. The SOC balance between the first battery cell and the second battery cell is achieved through this power difference.

[0060] Based on the single-stage DC-AC conversion function, by changing the modulation voltage of the half-bridge to achieve differentiated output of DC-side power, the SOC balancing function of the battery cells can be realized. This avoids excessive differences in the state of charge of battery cells during long-term operation due to parameter differences, thereby improving the safety and reliability of the system.

[0061] In one embodiment of this application, the calculation of the equalization voltage components ΔU1 and ΔU2 is based on the deviation between the first battery cell SOC1 and the second battery cell SOC2, i.e., ΔSOC = SOC_1 - SOC_2, and ΔU1 = ΔU2.

[0062] In one embodiment of this application, the equalization voltage component is superimposed on the output voltage command value U generated by the power outer loop and the current loop. ref The voltage difference between the sampled voltage and the voltage is used to generate a phase shift angle through PR control in order to maintain a constant output voltage of the system.

[0063] In one embodiment of this application, the amplitude of the equalization voltage component is determined by the product of the proportional coefficient K and the SOC deviation value ΔSOC, i.e., ΔU_1=K×ΔSOC, so as to realize the dynamic adjustment of the SOC deviation.

[0064] like Figure 2 As shown, the circuit can operate in a battery SOC balancing mode by superimposing a balancing voltage component ΔU1, which is in phase with the output current frequency, onto the sinusoidal AC component vp of the upper half-bridge arm output voltage, and superimposing a balancing voltage component ΔU2, which is in phase with the output current frequency, onto the sinusoidal AC component of the lower half-bridge arm output voltage. Figure 2 Since ∆SOC = (SOC_1 + SOC_2) / 2, the equalization voltage components ΔU1 = ΔU2 of the upper and lower bridge arms are superimposed on the output voltage command value Uref generated by the power outer loop and current loop. The difference between this value and the sampled voltage is then used to generate the phase shift angle through PR control. At this time, the overall output voltage vac of the battery energy storage system remains unchanged. The equalization voltage components superimposed on the output voltages of the upper and lower bridge arms generate active power ΔP and -ΔP with the output current I, respectively. This power difference can be used to balance the SOC between the first and second battery cells.

[0065] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A single-phase isolated battery energy storage system, characterized in that, It includes a first battery cell, a second battery cell, first to twelfth switching transistors, a first transformer, a second transformer, a first inductor, a second inductor, first to fourth capacitors, and an AC output port; The ninth switch, the tenth switch, the first capacitor, and the second capacitor are connected in series to form the upper half-bridge circuit, and the eleventh switch, the twelfth switch, the third capacitor, and the fourth capacitor are connected in series to form the lower half-bridge circuit. The lower end of the upper half-bridge circuit is connected to the upper end of the lower half-bridge circuit, and the negative terminal of the second capacitor is connected to the negative terminal of the third capacitor. The positive terminal of the first battery cell is connected to the upper end of the first switching transistor, and the negative terminal is connected to the lower end of the fourth switching transistor. The lower end of the first switching transistor is connected to the upper end of the second switching transistor and then connected to one end of the primary winding of the first transformer. The lower end of the third switching transistor is connected to the upper end of the fourth switching transistor and then connected to the other end of the primary winding of the first transformer. The positive terminal of the second battery unit is connected to the upper end of the fifth switch tube, and the negative terminal is connected to the lower end of the sixth switch tube. The lower end of the fifth switch tube is connected to the upper end of the sixth switch tube and then connected to one end of the primary winding of the second transformer. The lower end of the seventh switch tube is connected to the upper end of the eighth switch tube and then connected to the other end of the primary winding of the second transformer. One end of the secondary winding of the first transformer is connected to the first inductor and then to the lower end of the ninth switch and the upper end of the tenth switch, and the other end is connected to the negative terminal of the first capacitor; one end of the secondary winding of the second transformer is connected to the second inductor and then to the lower end of the eleventh switch and the upper end of the twelfth switch, and the other end is connected to the negative terminal of the third capacitor. The positive terminal of the first capacitor is connected to the upper terminal of the AC output port, and the negative terminal of the fourth capacitor is connected to the lower terminal of the AC output port.

2. The single-phase isolated battery energy storage system according to claim 1, characterized in that, The first to fourth switches are connected in series to form a first full-bridge inverter circuit, and the fifth to eighth switches are connected in series to form a second full-bridge inverter circuit.

3. The single-phase isolated battery energy storage system according to claim 1, characterized in that, The first and second transformers are high-frequency transformers, and their primary windings are respectively connected to the midpoint of the bridge arm of the corresponding full-bridge inverter circuit to achieve electrical isolation between the DC side and the AC side and high-frequency energy transfer.

4. The single-phase isolated battery energy storage system according to claim 1, characterized in that, The first, second, third, and fourth capacitors are electrolytic capacitors or film capacitors, used to stabilize the midpoint voltage of the corresponding half-bridge circuit.

5. The single-phase isolated battery energy storage system according to claim 1, characterized in that, The first inductor and the second inductor are buffer inductors of the circuit, used to generate a current waveform that transmits power to adapt to the voltage difference between the input and output.

6. A control method for a single-phase isolated battery energy storage system as described in claim 1, characterized in that, With the positive terminal of the first capacitor as the positive terminal of the upper half-bridge arm output voltage and the negative terminal of the second capacitor as the negative terminal of the upper half-bridge arm output voltage, and with the positive terminal of the fourth capacitor as the positive terminal of the lower half-bridge arm output voltage and the negative terminal of the third capacitor as the negative terminal of the lower half-bridge arm output voltage, the AC output voltage of the circuit is differentially synthesized from the upper half-bridge arm output voltage and the lower half-bridge arm output voltage, and satisfies the following: The upper half-bridge arm output voltage is a sinusoidal voltage with DC bias; The lower half-bridge arm output voltage is a sinusoidal voltage with DC bias; The upper half-bridge arm output voltage and the lower half-bridge arm output voltage have the same amplitude and DC bias, and the AC sinusoidal components have the same frequency and a phase difference of half a cycle. The AC output voltage of the circuit contains only a sinusoidal AC component and does not include DC bias.

7. A SOC equalization method based on the single-phase isolated battery energy storage system of claim 1, characterized in that, Includes the following steps: Step 1: Superimpose an equal voltage component ΔU1, which has the same frequency and phase as the output current, onto the sinusoidal AC component of the upper half-bridge arm output voltage; Step 2: Superimpose a balanced voltage component ΔU2, which has the same amplitude and phase as ΔU1, onto the sinusoidal AC component of the lower half-bridge arm output voltage; Step 3: The equalization voltage component superimposed on the upper half-bridge arm and the output current generate active power ΔP, and the equalization voltage component superimposed on the lower half-bridge arm and the output current generate active power -ΔP. The SOC balance between the first battery cell and the second battery cell is achieved through the power difference between the active power ΔP and the active power -ΔP.

8. The SOC equalization method according to claim 7, characterized in that, The calculation of the equal voltage components ΔU1 and ΔU2 is based on the deviation between the first battery cell SOC1 and the second battery cell SOC2, i.e., ΔSOC = SOC1 - SOC2, and ΔU1 = ΔU2.

9. The SOC equalization method according to claim 7, characterized in that, The equalized voltage component is superimposed on the output voltage command value Uref generated by the power outer loop and the current loop. After the difference is calculated with the sampled voltage, the phase shift angle is generated by PR control to maintain the system's external output voltage unchanged.

10. The SOC equalization method according to claim 7, characterized in that, The amplitude of the equalization voltage component is determined by the product of the proportional coefficient K and the SOC deviation value ΔSOC, i.e., ΔU_1=K×ΔSOC, so as to realize the dynamic adjustment of SOC deviation.

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