High-voltage hybrid energy storage device of cascaded full-bridge MMC and charging and discharging control method of high-voltage hybrid energy storage device

Abstract

The invention relates to a cascaded full-bridge MMC high-voltage hybrid energy storage device and a charging and discharging control method thereof.The cascaded full-bridge MMC high-voltage hybrid energy storage device comprises a grid-connected side circuit, a direct-current side switch, a discharging circuit and an energy storage side circuit, the grid-connected side circuit comprises a cascaded full-bridge MMC converter and an electric reactor, and the energy storage side circuit comprises an energy storage half-bridge power unit and an energy storage battery; one end of the cascaded full-bridge MMC converter is connected in series with a reactor and then is connected to a three-phase alternating current bus, and the other end of the cascaded full-bridge MMC converter is connected in series with a direct current side switch and then is connected in parallel with a discharge circuit; the discharge circuit comprises a discharge switch and a discharge resistor, and the discharge switch and the discharge resistor are connected in series; the energy storage half-bridge power unit is connected with an energy storage battery in parallel; the discharging circuit is connected with an energy storage side circuit in parallel; according to the invention, the power output capability, the energy density and the service life are improved, the direct current utilization rate of energy storage is improved, the circulating current is reduced, and the direct current loss of equipment is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage hybrid energy storage, and in particular to a cascade full-bridge MMC high-voltage hybrid energy storage device and a charge and discharge control method thereof. Background Art

[0002] At the beginning of 2024, the total installed capacity of photovoltaic, solar power generation systems and wind power generation systems in the country's renewable energy power generation reached 1.516 billion kilowatts, accounting for 51.9% of the country's total installed power generation capacity. The proportion of new energy is gradually increasing. Affected by natural and environmental factors such as light and wind, renewable energy is unstable. Energy storage systems are a good solution, especially high-voltage hybrid energy storage, which has instant response and flexible control, and can improve the safety and reliability of the power grid; for the energy storage system of MMC positive and negative DC multi-module multi-level bidirectional DC-DC converter, the DC current PI control of the DC voltage outer loop plus the DC inductor single current loop is generally adopted, but there is little research on the problem that the DC current utilization rate of the energy storage is reduced due to the circulating current of the DC-DC converter half-bridge control. Summary of the invention

[0003] The present invention provides a high-voltage hybrid energy storage device of a cascade full-bridge MMC and a charge and discharge control method thereof. The grid-connected side is composed of an MMC structure based on a cascade full-bridge, and the energy storage side is composed of a hybrid energy storage of a multi-module multi-level half-bridge bidirectional DC-DC converter. Not only is the output waveform quality higher, but the step voltage of the output voltage is also reduced, so that the power output capacity, energy density and life are all improved. In view of the problem that the circulating current in the half-bridge control of the DC-DC converter will lead to a decrease in the utilization rate of the DC current of the energy storage, the present invention proposes a DC voltage outer loop control method with DC-DC converter modulation degree feedback, which improves the utilization rate of the DC current of the energy storage, reduces the circulating current, and reduces the DC loss of the equipment.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A high-voltage hybrid energy storage device of a cascade full-bridge MMC, comprising a grid-connected side circuit, a DC side switch, a discharge circuit and an energy storage side circuit, wherein the grid-connected side circuit comprises a cascaded full-bridge MMC converter and a reactor, and the energy storage side circuit comprises an energy storage half-bridge power unit and an energy storage battery;

[0006] One end of the cascade full-bridge MMC converter is connected in series with a reactor and then connected to a three-phase AC bus, and the other end of the cascade full-bridge MMC converter is connected in series with a DC side switch and then connected in parallel with a discharge circuit;

[0007] The discharge circuit comprises a discharge switch and a discharge resistor, wherein the discharge switch and the discharge resistor are connected in series;

[0008] The energy storage half-bridge power unit is an energy storage DC-DC cascade half-bridge power unit, which is connected in parallel with an energy storage battery. The discharge circuit is connected in parallel with the energy storage side circuit. The energy storage battery includes a supercapacitor battery stack and a chemical battery stack. The supercapacitor battery stack is connected in parallel with the chemical battery stack.

[0009] Furthermore, the cascade full-bridge MMC converter includes a three-phase upper bridge arm and a three-phase lower bridge arm, each phase bridge arm is connected to an inductor, each phase bridge arm is composed of a number of MMC power units connected in series, the MMC power unit includes an H-bridge inverter composed of four insulated gate bipolar transistors IGBT, a DC side capacitor and a DC side resistor, and the H-bridge inverter, DC side capacitor and DC side resistor constitute a parallel circuit; as the voltage level on the grid side increases, the number of MMC power units increases, and the star points of each phase MMC power units are connected in series to form the positive and negative poles of the rectifier side of the MMC.

[0010] Furthermore, the supercapacitor battery stack is composed of a plurality of supercapacitor cells connected in series, and the chemical battery stack is composed of a plurality of lithium battery cells connected in series.

[0011] Furthermore, the energy storage half-bridge power unit includes two insulated gate bipolar transistors IGBTs, a DC capacitor and a DC resistor. The two insulated gate bipolar transistors IGBTs are connected in series and then connected in parallel to the DC capacitor and the DC resistor.

[0012] Furthermore, it also includes a discharge resistor, a fuse and an inductor on the energy storage side. After the energy storage board bridge power unit is connected in series with the inductor and the fuse, the discharge resistor on the energy storage side and the energy storage battery are connected in parallel.

[0013] A charge and discharge control method for a cascade full-bridge MMC high-voltage hybrid energy storage device includes the following contents:

[0014] 1) Pre-charging control before equipment operation: When the equipment is powered on for the first time after long-term storage, after the MMC converter is ready, if the total DC voltage of the energy storage side circuit is lower than the limit, the pre-charging control is started. If the total DC voltage of the energy storage side circuit is higher than the limit, the pre-charging process ends.

[0015] 2) Discharge control after the equipment stops: After the equipment stops or when the MMC converter of the cascade full-bridge fails, the DC side switch is first disconnected to separate the MMC converter side from the energy storage side circuit. The energy storage side circuit is only connected to the charging circuit. When the total DC voltage of the energy storage side circuit is higher than the limit, discharge control is entered. When the total DC voltage of the energy storage side circuit is lower than the limit, the discharge process ends.

[0016] 3) Energy storage side circuit charge and discharge control during equipment operation: The output voltage of the DC bus is controlled by the cascaded full-bridge MMC converter, and the charging or discharging current is controlled by the energy storage side circuit. The DC voltage given values ​​of the positive and negative DC buses and the feedback value of the modulation wave of the DC-DC cascaded half-bridge power unit of the energy storage side circuit are given. The calculated values ​​of these two items are used as the given values ​​of the DC voltage, and the DC voltage detection value is used as the feedback value. The difference between the two is subjected to PI operation, and after limiting processing, it is output to the energy storage side circuit energy storage half-bridge power unit as the input of its DC current control PI.

[0017] Furthermore, the pre-charging control before the device is operated specifically includes the following steps:

[0018] 1) After the grid-connected MMC converter is ready, determine whether the total DC voltage of the energy storage circuit is lower than the limit. If it is lower than the limit, enter pre-charging control;

[0019] 2) The MMC converter transmits the pre-charge control instruction to the DC side control of the energy storage side circuit;

[0020] 3) The DC side of the energy storage circuit controls the energy storage half-bridge power unit, turns on its upper bridge arm, and charges the energy storage circuit;

[0021] 4) If the total voltage on the DC side of the energy storage circuit is higher than the limit, the pre-charging process ends, the energy storage half-bridge power unit turns off the upper bridge arm, and enters the normal working mode;

[0022] 5) The pre-charging process ends.

[0023] Furthermore, the discharge control after the device stops specifically includes the following steps:

[0024] 1) After the equipment stops or the MMC converter of the cascade full-bridge fails, the DC side switch is disconnected first. After the grid-connected MMC converter is separated from the energy storage side circuit, it is determined whether the total DC side voltage of the energy storage side circuit is higher than the limit value. If it is greater than the limit value, discharge control is entered;

[0025] 2) The MMC converter transmits the discharge control instruction to the DC side control of the energy storage side circuit;

[0026] 3) The DC side of the energy storage side circuit controls the energy storage half-bridge power unit, turns on its upper bridge arm, and discharges the energy storage side circuit. The released energy is mainly consumed in the discharge resistor of the discharge circuit;

[0027] 4) If the total voltage on the DC side of the energy storage circuit is lower than the limit, the discharge process ends and the energy storage half-bridge unit turns off the upper bridge arm;

[0028] 5) The discharge process ends.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The grid-connected side is composed of an MMC structure based on a cascaded H-bridge, and the energy storage side is composed of a hybrid energy storage of a cascaded half-bridge bidirectional DC-DC converter. It can be directly connected to the medium and high voltage power grid without a step-up transformer, and is suitable for applications in high voltage and high power situations. The AC side has a large number of output voltage levels and low harmonic content. The cascaded H-bridge structure has a stronger ability to regulate the DC voltage. The units all adopt a modular design, which is conducive to integrated production;

[0031] 2) The energy storage battery of the hybrid energy storage side circuit is cascaded to reduce the contradiction between the low voltage of the energy storage unit and the high voltage of the application, so that the system can adapt to the requirements of high-voltage applications. This topology has small voltage and current stress of the switching device under the same power level conditions, and has obvious advantages in high-voltage and high-power bidirectional power conversion occasions;

[0032] 3) The grid-connected side and the energy storage side are connected and disconnected through the DC side switch to realize the independent charging and discharging process of the energy storage side circuit without affecting the grid-connected side;

[0033] 4) The charge and discharge control method of the device solves the problem that the commonly used charge and discharge control logic cannot fully utilize the DC current of the energy storage side circuit. When the lower bridge arm of the DCDC is turned on, a large circulating current is generated, which adjusts the target value and output of the DC bus voltage, reduces the circulating component of the DC current, and improves the efficiency of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a topological structure diagram of the hybrid energy storage system of the device described in the present invention.

[0035] Figure 2 It is a schematic diagram of the structure of the MMC power unit of the present invention.

[0036] Figure 3 It is a schematic diagram of the structure of the energy storage half-bridge power unit of the present invention.

[0037] Figure 4 It is a schematic diagram of the energy storage side circuit structure of the present invention.

[0038] Figure 5 It is a schematic diagram of the DC side connection structure of the energy storage side circuit of the present invention.

[0039] Figure 6 It is a pre-charging control flow chart of the energy storage side circuit described in the present invention.

[0040] Figure 7 It is a discharge control flow chart of the energy storage side circuit of the present invention.

[0041] Figure 8It is a schematic diagram of the MMC DC voltage control principle of the present invention.

[0042] Fig. 9 It is a schematic diagram of direct current of the conventional MMC control method of the present invention.

[0043] Fig.10 It is a DC current schematic diagram of the MMC improved DC voltage control method of the present invention.

[0044] Fig.11 It is a schematic diagram of PI control of charging and discharging DC current during operation of the energy storage side circuit described in the present invention. DETAILED DESCRIPTION

[0045] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0046] See Figure 1 , is a topological structure diagram of the hybrid energy storage system of the device of the present invention. The present invention is a high-voltage hybrid energy storage device of cascade full-bridge MMC, including a grid-connected side circuit, DC side switches Q1 and Q2, a discharge circuit, an energy storage side discharge resistor, a fuse FU1, an inductor L1 and an energy storage side circuit, the grid-connected side circuit includes a cascaded full-bridge MMC converter and a reactor, and the energy storage side circuit includes an energy storage half-bridge power unit and an energy storage battery; the voltage level of the power grid is different, and the unit level of the device is different. As the voltage level of the grid-connected side circuit increases, the power unit level of the device increases, and the star points of each phase MMC power unit are connected in series to form the positive and negative poles of the rectifier side of the MMC.

[0047] The advantages of supercapacitors are higher power density and cycle life. The advantage of chemical energy storage is high energy density. The combination of the two makes full use of their complementary characteristics, and the power output capacity, energy density and life of the system are improved. Due to the above advantages, hybrid energy storage is suitable for high-voltage power grid reactive power without compensation, grid voltage sag control, frequency modulation, wind / solar energy storage power station peak shaving and valley filling, etc. In high-voltage and high-power application scenarios, two-level VSC or three-level NPC topologies have problems such as high technical difficulty, poor output waveform caused by low switching frequency, and high harmonic content. Therefore, devices based on MMC-modular multi-level converter topology technology, due to sampling PWM control and a large number of units in each bridge arm, not only have higher output waveform quality, but also reduced step voltage of the output voltage.

[0048] One end of the cascade full-bridge MMC converter is connected to a three-phase AC bus after being connected in series with a reactor. The cascade full-bridge MMC converter is a six-phase cascade full-bridge MMC converter, and the other end is connected in series with DC side switches Q1 and Q2 and then connected in parallel with a discharge circuit. The positive electrode of the cascade full-bridge MMC converter is connected to the DC reactor and then connected to the positive electrode of the energy storage side circuit, and the negative electrode is connected to the negative electrode of the energy storage side circuit, and the discharge circuit is connected in parallel with the energy storage side circuit.

[0049] The discharge circuit comprises a discharge switch and a discharge resistor, wherein the discharge switch and the discharge resistor are connected in series;

[0050] The energy storage half-bridge power unit is an energy storage DC-DC cascade half-bridge power unit, connected in parallel with the energy storage battery, and the discharge circuit is connected in parallel with the energy storage side circuit. Figure 5 , the energy storage board bridge power unit is connected in series with the inductor and the fuse FU1, and then connected in parallel with the energy storage side discharge resistor and the energy storage battery. The energy storage battery includes a supercapacitor battery stack and a chemical battery stack. The supercapacitor battery stack is connected in parallel with the chemical battery stack. The energy storage battery is generally composed of battery clusters in series. The supercapacitor battery stack is composed of multiple supercapacitor monomers in series, and the chemical battery stack is composed of multiple lithium battery monomers in series. The voltage of the hybrid energy storage component monomers (supercapacitor monomers, lithium battery monomers, etc.) is relatively low. Usually, multiple monomers or components are required to be connected in series to form an energy storage component group PACK to meet the requirements of high-voltage applications. Each phase of the energy storage side circuit is composed of multiple units in cascade. Figure 4 , each phase can be controlled independently.

[0051] The cascade full-bridge MMC converter includes a three-phase upper bridge arm and a three-phase lower bridge arm, each phase bridge arm is connected to a reactor, and each phase bridge arm is composed of a number of MMC power units connected in series. Although the half-bridge power unit has a low cost, the DC voltage regulation capability of the half-bridge power unit is poor compared to the full-bridge power unit, and when the DC bus fails, such as a short circuit, the fault cannot be crossed, which may cause irreversible damage to the equipment. Therefore, the device adopts a full-bridge power unit to form the converter side of the MMC. Figure 2 The MMC power unit includes an H-bridge inverter composed of four insulated gate bipolar transistors IGBT, a DC side capacitor and a DC side resistor R, and the H-bridge inverter, the DC side capacitor and the DC side resistor R form a parallel circuit; as the voltage level on the grid side increases, the number of MMC power units increases, and the star points of each phase of the MMC power unit are connected in series to form the positive and negative poles of the rectifier side of the MMC.

[0052] See Figure 3 The energy storage half-bridge power unit includes two insulated gate bipolar transistors IGBT, a DC capacitor and a DC resistor R. The two insulated gate bipolar transistors IGBT are connected in series and then connected in parallel to the DC capacitor and the DC resistor R.

[0053] A charging and discharging control method for a cascade full-bridge MMC high-voltage hybrid energy storage device, wherein the device charging includes two parts: charging of the MMC converter side of the cascade full-bridge and charging of the energy storage side circuit. First, the charging of the MMC converter side of the cascade full-bridge must be completed, and then the MMC converter of the cascade full-bridge enters the operating state, and then the DC voltage output by the MMC side is controlled to charge the energy storage side, and at the same time, the energy storage side circuit is also synchronously charged and controlled, including the following contents:

[0054] 1. Pre-charging control before the equipment is operated, including the MMC converter and energy storage circuit of the cascaded full bridge, and pre-charging control of the energy storage circuit of the equipment (non-operating state). When the equipment is powered on for the first time after long-term storage, there is no voltage and energy storage on the DC side of the energy storage circuit, so pre-charging is required. The pre-charging steps are as follows: Figure 6 As shown;

[0055] (1) After the grid-connected MMC converter is ready, determine whether the total DC voltage of the energy storage circuit is lower than the limit. If it is lower than the limit, enter pre-charging control;

[0056] (2) The MMC converter transmits the pre-charge control instruction to the DC side control of the energy storage side circuit;

[0057] (3) The DC side of the energy storage side circuit controls the energy storage half-bridge power unit, turns on its upper bridge arm, and charges the energy storage part of the energy storage side circuit;

[0058] (4) If the total voltage on the DC side of the energy storage circuit is higher than the limit, the pre-charging process ends, the energy storage half-bridge power unit turns off the upper bridge arm, and enters the normal working mode;

[0059] (5) The pre-charging process ends.

[0060] Since there is a large-capacity energy storage device on the DC side of the device, such as Figure 4 When the device is powered on, the energy storage side circuit will be charged. Only after it has been detected that the over-capacity part and the chemical energy storage part can work normally will it enter the normal working state. This process is the charging process when the device is powered on (during abnormal working).

[0061] 2. Discharge control after the equipment stops is the discharge control of the energy storage side of the equipment (non-operating state), which mainly refers to the energy storage part of the energy storage side circuit. After the equipment stops or when the MMC converter of the cascade full bridge fails, the stored electricity of the energy storage side circuit needs to be completely discharged. When discharging, it is necessary to first disconnect the positive and negative switches on the DC side of the energy storage side circuit to separate the MMC converter side from the energy storage side circuit. The energy storage side circuit is only connected to the charging circuit. The discharge control flow chart of the energy storage side circuit is shown in Figure 7 ;

[0062] (1) After the equipment stops or the MMC converter of the cascaded full-bridge fails, first disconnect the DC side switches Q1 and Q2. After the grid-connected MMC converter is separated from the energy storage side circuit, determine whether the total DC side voltage of the energy storage side circuit is higher than the limit value. If it is greater than the limit value, enter the discharge control;

[0063] (2) The MMC converter transmits the discharge control instruction to the DC side control of the energy storage side circuit;

[0064] (3) The DC side of the energy storage circuit controls the energy storage half-bridge power unit, turns on its upper bridge arm, and discharges the energy storage part of the energy storage circuit. The released energy is mainly consumed in the discharge resistor of the discharge circuit.

[0065] (4) If the total voltage on the DC side of the energy storage circuit is lower than the limit, the discharge process ends and the energy storage half-bridge unit turns off the upper bridge arm;

[0066] (5) The discharge process ends.

[0067] The equipment needs to be fully discharged before transportation and maintenance to ensure the safety of the equipment and maintenance personnel. The discharge function of the equipment also needs to discharge the energy storage side circuit under special working conditions, such as when the MMC side fails. This is the discharge process when the equipment is working abnormally.

[0068] 3. Energy storage side charging and discharging control during equipment operation:

[0069] The control of the device consists of two parts, namely, the MMC converter of the cascaded full bridge and the energy storage cascaded half-bridge power unit of the energy storage side circuit. The fast charging or discharging control of the device is controlled by the MMC converter of the cascaded full bridge to control the output voltage of the DC bus, and the energy storage side circuit controls the charging or discharging current, that is, the DC voltage control on the MMC converter side of the cascaded full bridge and the DC current control on the energy storage side circuit, which require coordinated control of these two parts; the DC current PI control with a DC voltage outer loop plus a DC inductor single current loop is commonly used now, but the DC-DC converter half-bridge control has a problem of circulating current that will lead to a reduction in the utilization rate of the DC current of the energy storage; the conventional charging and discharging control-single current loop DC current PI control cannot fully utilize the current of the energy storage side circuit, and there will be a large circulating current when the DCDC lower bridge arm of the energy storage half-bridge power unit is turned on, adjusting the target value and output of the DC bus voltage, reducing the circulating component of the DC current, and improving the efficiency of the entire system; the control method is as follows Figure 8 As shown, it is mainly divided into two parts:

[0070] (1) Calculation of positive and negative DC bus voltage settings, mainly setting the DC voltage settings (target values) of the positive and negative DC buses and the feedback value of the current modulation wave on the energy storage side. The calculated values ​​of these two items are used as the DC voltage settings;

[0071] (2) Positive and negative DC bus voltage feedback calculation, detected by high-voltage voltage sensor;

[0072] The difference between the two is processed by PI operation and output to the energy storage control part after limiting processing as the input part of its DC current control. The control effect is compared as follows: Fig. 9 , 10 As shown, the light color is the instantaneous value of the current, and the dark color is the average value of the current. Fig.10 The DC current schematic diagram of the DC voltage control method, that is, the control algorithm taking into account the DCDC modulation ratio, increases the DC current average value from 150A to about 200A;

[0073] The main contents of the DC current control method of the energy storage side circuit are:

[0074] like Fig.11 As shown, the main control on the MMC converter side calculates the DC current target value Idc_Ref, the energy storage side detects the feedback of the DC current, and performs PI control operation. The PI result is output to each energy storage half-bridge power unit on the energy storage side after limiting processing.

[0075] When the equipment is compensating for the active power demand of the grid side or the load, such as the grid voltage sag control equipment containing energy storage, it is necessary to perform fast or slow charging and discharging control. A DC voltage and current control method with DCDC side modulation feedback is proposed to more efficiently utilize the stored energy.

[0076] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A high-voltage hybrid energy storage device of a cascade full-bridge MMC, characterized in that: It includes a grid-connected side circuit, a DC side switch, a discharge circuit and an energy storage side circuit, wherein the grid-connected side circuit includes a cascaded full-bridge MMC converter and a reactor, and the energy storage side circuit includes an energy storage half-bridge power unit and an energy storage battery; One end of the cascade full-bridge MMC converter is connected in series with a reactor and then connected to a three-phase AC bus, and the other end of the cascade full-bridge MMC converter is connected in series with a DC side switch and then connected in parallel with a discharge circuit; The discharge circuit comprises a discharge switch and a discharge resistor, wherein the discharge switch and the discharge resistor are connected in series; The energy storage half-bridge power unit is an energy storage DC-DC cascade half-bridge power unit, which is connected in parallel with an energy storage battery. The discharge circuit is connected in parallel with the energy storage side circuit. The energy storage battery includes a supercapacitor battery stack and a chemical battery stack. The supercapacitor battery stack is connected in parallel with the chemical battery stack.

2. A high-voltage hybrid energy storage device of a cascade full-bridge MMC according to claim 1, characterized in that: The cascade full-bridge MMC converter includes a three-phase upper bridge arm and a three-phase lower bridge arm, each phase bridge arm is connected to a reactor, each phase bridge arm is composed of a plurality of MMC power units connected in series, the MMC power unit includes an H-bridge inverter composed of four insulated gate bipolar transistors IGBTs, a DC side capacitor and a DC side resistor, and the H-bridge inverter, the DC side capacitor and the DC side resistor form a parallel circuit; as the voltage level of the grid-connected side increases, the number of MMC power units increases, and the star points of each phase MMC power units are connected in series to form the positive and negative poles of the rectifier side of the MMC.

3. A high-voltage hybrid energy storage device of a cascade full-bridge MMC according to claim 1, characterized in that: The supercapacitor battery stack is composed of a plurality of supercapacitor cells connected in series, and the chemical battery stack is composed of a plurality of lithium battery cells connected in series.

4. A high-voltage hybrid energy storage device of a cascade full-bridge MMC according to claim 1, characterized in that: The energy storage half-bridge power unit comprises two insulated gate bipolar transistors IGBTs, a DC capacitor and a DC resistor. The two insulated gate bipolar transistors IGBTs are connected in series and then connected in parallel to the DC capacitor and the DC resistor.

5. A high-voltage hybrid energy storage device of a cascade full-bridge MMC according to claim 1, characterized in that: It also includes a discharge resistor, a fuse and an inductor on the energy storage side. The energy storage board bridge power unit is connected in series with the inductor and the fuse, and then connected in parallel with the discharge resistor and the energy storage battery on the energy storage side.

6. A charge and discharge control method for a cascade full-bridge MMC high-voltage hybrid energy storage device according to any one of claims 1 to 5, characterized in that: It includes the following: 1) Pre-charging control before equipment operation: When the equipment is powered on for the first time after long-term storage, after the MMC converter is ready, if the total DC voltage of the energy storage side circuit is lower than the limit, the pre-charging control is started. If the total DC voltage of the energy storage side circuit is higher than the limit, the pre-charging process ends. 2) Discharge control after the equipment stops: After the equipment stops or when the MMC converter of the cascade full-bridge fails, the DC side switch is first disconnected to separate the MMC converter side from the energy storage side circuit. The energy storage side circuit is only connected to the charging circuit. When the total DC voltage of the energy storage side circuit is higher than the limit, discharge control is entered. When the total DC voltage of the energy storage side circuit is lower than the limit, the discharge process ends. 3) Energy storage side circuit charge and discharge control during equipment operation: The output voltage of the DC bus is controlled by the cascaded full-bridge MMC converter, and the charging or discharging current is controlled by the energy storage side circuit. The DC voltage given values ​​of the positive and negative DC buses and the feedback value of the modulation wave of the DC-DC cascaded half-bridge power unit of the energy storage side circuit are given. The calculated values ​​of these two items are used as the given values ​​of the DC voltage, and the DC voltage detection value is used as the feedback value. The difference between the two is subjected to PI operation, and after limiting processing, it is output to the energy storage side circuit energy storage half-bridge power unit as the input of its DC current control PI.

7. The charge and discharge control method of a cascade full-bridge MMC high-voltage hybrid energy storage device according to claim 6, characterized in that: The pre-charging control before the operation of the device specifically includes the following steps: 1) After the grid-connected MMC converter is ready, determine whether the total DC voltage of the energy storage circuit is lower than the limit. If it is lower than the limit, enter pre-charging control; 2) The MMC converter transmits the pre-charge control instruction to the DC side control of the energy storage side circuit; 3) The DC side of the energy storage circuit controls the energy storage half-bridge power unit, turns on its upper bridge arm, and charges the energy storage circuit; 4) If the total voltage on the DC side of the energy storage circuit is higher than the limit, the pre-charging process ends, the energy storage half-bridge power unit turns off the upper bridge arm, and enters the normal working mode; 5) The pre-charging process ends.

8. The charge and discharge control method of a cascade full-bridge MMC high-voltage hybrid energy storage device according to claim 6, characterized in that: The discharge control after the device stops specifically includes the following steps: 1) After the equipment stops or the MMC converter of the cascade full-bridge fails, the DC side switch is disconnected first. After the grid-connected MMC converter is separated from the energy storage side circuit, it is determined whether the total DC side voltage of the energy storage side circuit is higher than the limit value. If it is greater than the limit value, discharge control is entered; 2) The MMC converter transmits the discharge control instruction to the DC side control of the energy storage side circuit; 3) The DC side of the energy storage side circuit controls the energy storage half-bridge power unit, turns on its upper bridge arm, and discharges the energy storage side circuit. The released energy is mainly consumed in the discharge resistor of the discharge circuit; 4) If the total voltage on the DC side of the energy storage circuit is lower than the limit, the discharge process ends and the energy storage half-bridge unit turns off the upper bridge arm; 5) The discharge process ends.

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