Isolation type energy storage direct current power conversion system, control method thereof and related device

Abstract

The invention belongs to a direct-current power conversion system, and aims to solve the technical problems that an existing direct-current power conversion system faces common bus-to-ground short-circuit impact current and lacks equalization management on the state of a battery module, and a whole machine needs to be shut down when an individual battery module or a corresponding BMS (Battery Management System) breaks down. The isolation type energy storage direct current power conversion system comprises a direct current access single-phase full bridge, a single-phase transformer, Nm battery side single-phase full bridges and Nm relay switches K1, the direct current access single-phase full bridge is connected with the two ends of the secondary side of the single-phase transformer and is connected with the positive electrode and the negative electrode of a common direct current bus outside a battery energy storage system, and the Nm battery side single-phase full bridges are connected with the relay switches K1. The battery side single-phase full bridges are connected with the two ends of the primary side of the single-phase transformer, the alternating-current sides of the Nm battery side single-phase full bridges are connected in series to form a cascade full bridge, and a relay switch K1 is connected between the alternating-current side end E1 and the alternating-current side end E1 of the direct-current access single-phase full bridge.

Description

Technical Field

[0001] The present application relates to a DC power conversion system, and specifically to an isolated energy storage DC power conversion system and a control method and related devices thereof. Background Art

[0002] In an integrated system or microgrid with a common low-voltage DC bus and a battery energy storage system, the battery cluster in the battery energy storage system is mostly composed of multiple battery modules connected in series or in parallel. The battery cluster is connected to the DC power conversion system (PCS) in the battery energy storage system, and the charging or discharging power of the battery cluster is controlled by the DC PCS.

[0003] However, the existing DC PCS faces the following problems in control: 1. In order to reduce losses and make the design compact, DC PCS generally uses non-isolated step-up or step-down converters. When a short circuit occurs to the ground on the common bus, if the battery energy storage system does not have a fast DC circuit breaker, the battery module will generate a short-term huge current, posing a safety hazard. 2. Due to the differences between battery modules, the charging and discharging depth of the battery energy storage system is limited by a few battery modules that are fully charged or discharged first, which has a short board effect and reduces the actual utilization rate of the battery energy storage system. Therefore, it is necessary to balance the battery module status. 3. When an individual battery module or the battery management system (BMS) corresponding to an individual battery module fails, the entire battery energy storage system needs to be shut down. Summary of the invention

[0004] The present application aims to solve the technical problems faced by existing DC power conversion systems, such as short-circuit impact current of the common bus to the ground, lack of balanced management of the battery module status, and the need to shut down the entire system due to failure of individual battery modules or corresponding BMS, and to provide an isolated energy storage DC power conversion system, a control method thereof, and related devices.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions: In the first aspect, the present application proposes an isolated energy storage DC power conversion system, including a DC access single-phase full-bridge, a single-phase transformer, Nm battery-side single-phase full-bridges and Nm relay switches K1; Nm is the number of battery modules; The DC-access single-phase full-bridge includes four power semiconductor relay switches, namely power semiconductor relay switch QB1 to power semiconductor relay switch QB4; wherein, an AC side terminal D1 is formed between the power semiconductor relay switch QB1 and the power semiconductor relay switch QB2, and an AC side terminal D2 is formed between the power semiconductor relay switch QB3 and the power semiconductor relay switch QB4; the DC side positive pole of the DC-access single-phase full-bridge is recorded as the DC side positive terminal D3, and the DC side negative pole is recorded as the DC side negative terminal D4, and the DC side positive terminal D3 and the DC side negative terminal D4 are respectively connected to the positive pole and the negative pole of the common DC bus outside the battery energy storage system; the AC side terminal D1 and the AC side terminal D2 are respectively connected to the two ends of the secondary side of the single-phase transformer; The battery-side single-phase full bridge includes four power semiconductor relay switches, namely power semiconductor relay switch Q1 to power semiconductor relay switch Q4; wherein, an AC side terminal E1 is formed between the power semiconductor relay switch Q1 and the power semiconductor relay switch Q2, and an AC side terminal E2 is formed between the power semiconductor relay switch Q3 and the power semiconductor relay switch Q4; the DC side positive pole of the battery-side single-phase full bridge is recorded as the DC side positive terminal E3, and the DC side negative pole is recorded as the DC side negative terminal E4, and the DC side positive terminal E3 and the DC side negative terminal E4 are respectively connected to the positive pole and negative pole of a battery module; the AC sides of Nm battery-side single-phase full bridges are connected in series to form a cascade full bridge; and the AC side terminal E1 of the first battery-side single-phase full bridge and the AC side terminal E2 of the Nm-th battery-side single-phase full bridge are respectively connected to the two ends of the primary side of the single-phase transformer; Two ends of the relay switch K1 are connected to the AC side end E1 and the AC side end E2 respectively.

[0006] In a second aspect, the present application proposes a control method for the above-mentioned isolated energy storage DC power conversion system, characterized in that it includes: Control the battery-side single-phase full-bridge and the DC-access single-phase full-bridge to be in square wave working state, so that the isolated energy storage DC power conversion system is in single-phase shift control mode; Alternatively, a portion of the battery-side single-phase full-bridge is controlled to be in a zero-level working state, another portion of the battery-side single-phase full-bridge is controlled to be in a square wave working state, and the DC-access single-phase full-bridge is controlled to be in a PWM working state, so that the isolated energy storage DC power conversion system is in a phase-shift plus PWM working state; Alternatively, the relay switch K1 corresponding to a battery-side single-phase full-bridge is controlled to be disconnected, the remaining battery-side single-phase full-bridge is in a square wave working state, and the DC-access single-phase full-bridge is in a PWM working state, so that the isolated energy storage DC power conversion system is in a phase-shift plus PWM working state.

[0007] In a third aspect, the present application proposes an electronic device, comprising: a memory, and one or more processors; the memory is coupled to the processor; wherein the memory stores computer program code, the computer program code includes computer instructions, and when the computer instructions are executed by the processor, the electronic device executes the steps of the control method of the above-mentioned isolated energy storage DC power conversion system.

[0008] In a fourth aspect, the present application proposes a computer-readable storage medium, in which a computer program is stored. When the computer program is executed by a processor, the steps of the control method of the above-mentioned isolated energy storage DC power conversion system are implemented.

[0009] Compared with the prior art, this application has the following beneficial effects: The present application proposes an isolated energy storage DC power conversion system, including a DC access single-phase full bridge, a single-phase transformer, Nm battery-side single-phase full bridges and Nm relay switches K1. The DC access single-phase full bridge connects the two ends of the secondary side of the single-phase transformer and connects the positive and negative poles of the public DC bus outside the battery energy storage system. The battery-side single-phase full bridge connects the two ends of the primary side of the single-phase transformer, and the AC sides of the Nm battery-side single-phase full bridges are connected in series to form a cascade full bridge. The relay switch K1 is connected between the AC side terminal E1 and the AC side terminal E2 of the DC access single-phase full bridge. The present application realizes the soft switching of the switching device while realizing the electrical isolation of the battery module from the public DC bus, ensuring the system efficiency and low electromagnetic interference, and using modular topology and a novel control method to realize the SOC balancing control of the battery module.

[0010] The present application also proposes a control method for an isolated energy storage DC power conversion system, an electronic device and a computer storage medium, which have all the advantages of the above-mentioned isolated energy storage DC power conversion system. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 A schematic diagram of an isolated energy storage DC power conversion system for the present application; Figure 2 A schematic diagram of a single-phase full bridge on the battery side; Figure 3 A schematic diagram of a single-phase full bridge for DC access; Figure 4 The DC access single-phase full-bridge duty cycle in the embodiment of the present application is Follow Schematic diagram of the changes; Figure 5 The lower limit LLimitZVS of the soft switch value range of the phase shift angle dp during discharge in the embodiment of the present application is Schematic diagram of the changes; Figure 6 This is a schematic diagram of the working waveforms of various components when there are 8 battery modules and corresponding battery-side single-phase full-bridges in the embodiment of the present application, one of which is in a bypass state and the single-phase transformer ratio is set according to the DC voltage ratio when there is no bypass; Figure 7 It is a flow chart of realizing SOC balancing control of a battery module through a zero-level pipeline in an embodiment of the present application; Figure 8 This is a schematic diagram of the hysteresis loop judgment process of the extreme difference size sign Sign_LD in the embodiment of the present application; Fig. 9 It is a schematic diagram of the inference process of the zero-level pipeline operation sign Sign_ZPP of the battery module in the embodiment of the present application; Fig.10 A schematic diagram of a process for calculating the number of zero-level cycles of a single-phase full-bridge on the battery side corresponding to an active battery module in an embodiment of the present application; Fig.11 This is a flow chart of the zero-level pipeline processing of the single-phase full-bridge on the battery side of the active battery module in the embodiment of the present application. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0014] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0015] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0016] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invented product is usually placed when used. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0017] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0018] In the description of the embodiments of the present application, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0019] In the integrated system or microgrid architecture that includes a public low-voltage DC bus and battery energy storage equipment, the battery energy storage system plays a vital role. It can not only store excess electricity, but also release electricity when demand increases, thereby ensuring the stable operation of the battery energy storage system and optimizing energy utilization. The battery energy storage equipment is usually composed of multiple battery modules, which are carefully combined in series and parallel to form a larger-scale, higher-capacity battery cluster. This design is intended to improve the overall energy density, power output capability, and system reliability and flexibility of the battery energy storage system. The battery cluster is not directly connected to the grid or load, but is interfaced through a DC power conversion system (DC PCS). The DC PCS is the core control unit of the battery energy storage system, which is responsible for monitoring the status of the battery cluster (such as voltage, current, temperature, etc.), and intelligently adjusts the charging or discharging power of the battery cluster according to the operating requirements of the battery energy storage system and the health of the battery. When there is surplus power in the battery energy storage system, the DC PCS will guide the battery cluster to absorb this power at an appropriate rate and convert it into chemical energy for storage; when the battery energy storage system is short of power or the demand is peak, the DC PCS will control the battery cluster to discharge and convert the stored chemical energy back into electrical energy to supply the grid or directly meet the load demand. In this way, the DC PCS not only achieves efficient energy management and scheduling, but also effectively balances the supply and demand relationship, enhancing the stability and self-sufficiency of the entire integrated system or microgrid.

[0020] In the above battery energy storage system: 1. In order to reduce losses and make the design compact, DC PCS generally uses non-isolated boost converters or buck converters. When a short circuit occurs to the ground on the common bus, if the battery energy storage device does not have a fast DC circuit breaker, the energy storage battery will generate a short-term huge current, which poses a safety hazard. However, the DC circuit breaker will bring a significant increase in cost, and the isolated converter is suitable for dealing with short-circuit faults, which is worth considering. 2. Due to the differences between batteries, the depth of charge and discharge of the battery energy storage system is limited by a few batteries that are fully charged or discharged first, which has a short board effect and reduces the actual utilization rate of the battery energy storage system. For this reason, the ability to balance the status of the battery module is required. 3. When an individual battery or the battery management system corresponding to an individual battery fails, the energy storage device must be shut down. A more advanced solution can consider stopping the faulty module from working alone and bypassing it from the battery cluster, while other modules continue to work so that the whole machine continues to operate.

[0021] For example, the Chinese invention patent with publication number CN115622201B, the Chinese invention patent application with publication number CN116345643A, and the Chinese invention patent application with publication number CN116316971A all proposed an isolated DC conversion system with a balancing bus. Each battery module in the battery energy storage system is connected to the balancing bus through an isolated bidirectional DC converter submodule. The isolated bidirectional DC converter submodule only processes a part of the module power used to balance the battery module state, and the balancing bus and the external port can transmit power through a boost converter, or they can be not connected to the outside world. In this type of solution, compared with the charging and discharging power, only a small power converter is used for balancing. If the battery module bypass is considered, the bypass component can be integrated in the isolated bidirectional DC converter submodule. However, this solution requires an additional converter in addition to the DC PCS, resulting in an increase in the level and a more complex system. The Chinese invention patent application with publication number CN117913949A adds a low-voltage DC converter to the balanced bus voltage, and the output of the low-voltage DC converter is connected in series with the original battery cluster, so that the final series total voltage is increased and controllable. The Chinese invention patent application with publication number CN116031979A proposes that each battery cell is connected to the balanced bus through a balanced submodule to achieve the goal of balanced control at the battery cell level. The hardware basis of the control strategy proposed in the Chinese invention patent application with publication number CN116111619A is a modular isolated CLLC bidirectional converter output parallel system (CLLC is a specific circuit topology structure), the input of each CLLC bidirectional converter is connected to a battery module, the CLLC bidirectional converter bears all the charging and discharging power, the battery module is completely isolated from the main bus, the power switching device can realize soft switching, the device loss and interference are low, but the number of CLLC bidirectional converters is equal to the number of battery modules, the total number of transformers and the number of LC resonant networks are large (LC resonant network is a circuit structure composed of inductance (L) and capacitance (C)), which is not conducive to system integration. In addition, there are papers proposing three-port and four-port active bridge DC-DC (Direct Current to Direct Current). If this type of solution is used for energy storage DC PCS, each port can be connected to a battery module to achieve balanced control of the battery module status. However, the power decoupling control of such CLLC bidirectional converters with more than three ports is very complicated, and the core high-power multi-winding medium and high-frequency transformers are difficult to develop. If the same number of transformers as battery modules are used, the number of transformers will increase, and the cost will be difficult to control to an ideal level.

[0022] Based on the above situation, the present application proposes an isolated energy storage DC power conversion system and its control method and related devices. The present application is described in detail below in conjunction with the embodiments and drawings.

[0023] like Figure 1 As shown, it is a schematic diagram of an isolated energy storage DC power conversion system of the present application, which may include: a DC access single-phase full-bridge, a single-phase transformer, Nm battery-side single-phase full-bridges and Nm relay switches K1; Nm is the number of battery modules. Figure 1 Y represents the common DC bus outside the battery energy storage system, and X1 to XNm represent Nm battery modules.

[0024] The DC-connected single-phase full-bridge includes four power semiconductor relay switches, namely power semiconductor relay switch QB1 to power semiconductor relay switch QB4; wherein, an AC side terminal D1 is formed between power semiconductor relay switch QB1 and power semiconductor relay switch QB2, and an AC side terminal D2 is formed between power semiconductor relay switch QB3 and power semiconductor relay switch QB4; the DC side positive pole of the DC-connected single-phase full-bridge is recorded as the DC side positive terminal D3, and the DC side negative pole is recorded as the DC side negative terminal D4, and the DC side positive terminal D3 and the DC side negative terminal D4 are respectively connected to the positive pole and negative pole of the public DC bus outside the battery energy storage system; the AC side terminal D1 and the AC side terminal D2 are respectively connected to the two ends of the secondary side of the single-phase transformer. The DC-connected single-phase full-bridge is composed of four power semiconductor relay switches, and the conversion between DC and AC is achieved by controlling the conduction or disconnection of these power semiconductor relay switches. The DC side positive terminal D3 and the DC side negative terminal D4 are respectively connected to the positive and negative poles of the public DC bus outside the battery energy storage system, realizing the connection with the DC grid. The single-phase transformer plays the role of electrical isolation and voltage conversion, transferring the AC power generated by the DC single-phase full-bridge to the battery side, while achieving voltage matching.

[0025] The battery-side single-phase full bridge includes four power semiconductor relay switches, namely power semiconductor relay switch Q1 to power semiconductor relay switch Q4; wherein, an AC side terminal E1 is formed between the power semiconductor relay switch Q1 and the power semiconductor relay switch Q2, and an AC side terminal E2 is formed between the power semiconductor relay switch Q3 and the power semiconductor relay switch Q4; the DC side positive pole of the battery-side single-phase full bridge is recorded as the DC side positive terminal E3, and the DC side negative pole is recorded as the DC side negative terminal E4, and the DC side positive terminal E3 and the DC side negative terminal E4 are respectively connected to the positive pole and negative pole of a battery module; the AC sides of Nm battery-side single-phase full bridges are connected in series to form a cascade full bridge; and the AC side terminal E1 of the first battery-side single-phase full bridge and the AC side terminal E2 of the Nmth battery-side single-phase full bridge are respectively connected to the two ends of the primary side of the single-phase transformer. Each battery-side single-phase full bridge also includes four power semiconductor relay switches, which are used to convert the DC power of the battery module into AC power, or vice versa. The AC sides of Nm battery-side single-phase full bridges are connected in series to form a cascade full bridge. This structure can improve the voltage level and power handling capacity of the system. The AC side terminal E1 of the first battery-side single-phase full bridge and the AC side terminal E2 of the Nm-th battery-side single-phase full bridge are respectively connected to the two ends of the primary side of the single-phase transformer to form a closed AC circuit.

[0026] The two ends of the relay switch K1 are respectively connected to the AC side terminal E1 and the AC side terminal E2, and are used to cut off or connect the circuit between the AC side terminal E1 and the AC side terminal E2 when needed, so as to control the working state of the whole system.

[0027] like Figure 2 As shown, it is a schematic diagram of a single-phase full bridge on the battery side, wherein the power semiconductor relay switch Q1 to the power semiconductor relay switch Q4 are not limited to the type of switch device. Taking the use of power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as an example, the connection is the same as the traditional single-phase full bridge structure, and the source of the power semiconductor relay switch Q1 is connected to the drain of the power semiconductor relay switch Q2, and is connected to the AC side terminal E1. The source of the power semiconductor relay switch Q3 is connected to the drain of the power semiconductor relay switch Q4, and is connected to the AC side terminal E2. The drain of the power semiconductor relay switch Q1 is connected to the drain of the power semiconductor relay switch Q3, and is connected to the DC side positive terminal E3. The source of the power semiconductor relay switch Q2 is connected to the source of the power semiconductor relay switch Q4, and is connected to the DC side negative terminal E4. The two ends of the relay switch K1 are respectively connected to the AC side terminal E1 and the AC side terminal E2. It should be noted that two capacitors can be connected in parallel to the source of the power semiconductor relay switch Q1 and the circuit where the power semiconductor relay switch Q2 is located, and the two capacitors can be connected in series.

[0028] The DC positive terminal E3 and the DC negative terminal E4 of each battery-side single-phase full bridge are respectively connected to the positive and negative poles of the battery module. The AC side terminal E1 of the first battery-side single-phase full bridge is connected to the AC side terminal E2 of the second battery-side single-phase full bridge, and the AC side terminal E1 of the second battery-side single-phase full bridge is connected to the AC side terminal E2 of the third battery-side single-phase full bridge, and so on, so that the AC sides of all Nm battery-side single-phase full bridges are connected in series to form a cascade full bridge. The AC side terminal E1 of the first battery-side single-phase full bridge and the AC side terminal E2 of the Nmth battery-side single-phase full bridge are retained and become the 1st and 2nd ends of the cascade full bridge. The 1st and 2nd ends of the medium and high frequency single-phase transformer are respectively connected to the 1st and 2nd ends of the DC-connected single-phase full bridge cascade full bridge, and the 3rd and 4th ends of the medium and high frequency single-phase transformer are respectively connected to the AC side terminal D1 and the AC side terminal D2 of the DC-connected single-phase bridge, and the 1st and 3rd ends of the single-phase transformer are the same-named ends. The DC side positive terminal D3 and the DC side negative terminal D4 of the DC access single-phase full-bridge are respectively connected to the positive pole and the negative pole of the common DC bus outside the battery energy storage system.

[0029] like Figure 3 As shown, it is a schematic diagram of a single-phase full bridge connected to a DC circuit. The power semiconductor relay switches QB1 to QB4 are not limited to the type of switch devices used. Taking the power semiconductor switch device as an example, the power MOSFET is used. The connection is the same as the traditional single-phase full bridge. The source of the power semiconductor relay switch QB1 is connected to the drain of the power semiconductor relay switch QB2, and is connected to the AC side terminal D1. The source of the power semiconductor relay switch QB3 is connected to the drain of the power semiconductor relay switch QB4, and is connected to the AC side terminal D2. The drain of the power semiconductor relay switch QB1 is connected to the drain of the power semiconductor relay switch QB3, and is connected to the DC side positive terminal D3. The source of the power semiconductor relay switch QB2 is connected to the source of the power semiconductor relay switch QB4, and is connected to the DC side negative terminal D4. It should be noted that a capacitor can be connected in parallel to the source of the power semiconductor relay switch QB3 and the line where the power semiconductor relay switch QB4 is located.

[0030] Each battery side single-phase full bridge has three working states: (1) The first working state of the single-phase full bridge on the battery side is the square wave working state: The corresponding relay switch K1 remains turned on, the power semiconductor relay switch Q1 and the power semiconductor relay switch Q4 are turned on or off at the same time, the power semiconductor relay switch Q2 and the power semiconductor relay switch Q3 are turned on or off at the same time, the switching states of the power semiconductor relay switch Q1 and the power semiconductor relay switch Q2 are complementary, and the switching states of the power semiconductor relay switch Q3 and the power semiconductor relay switch Q4 are complementary.

[0031] Ts represents the switching cycle time of the power semiconductor relay switch. Each power semiconductor device switches from off to on and from on to off once in a switching cycle. Ignoring the conversion time, the on time and the off time both account for 50% of Ts. The voltage between the AC side terminal E1 and the AC side terminal E2 of the j-th battery side single-phase full bridge at time t is The waveform is a voltage square wave in which the positive level and the negative level each occupy half of the time within Ts. The voltage drop of the power semiconductor device is not considered, and the absolute value of the level is equal to the The battery module voltage Vm_j is calculated, and the start time of a switching cycle of the single-phase full-bridge on the battery side is recorded as tm0.

[0032]

[0033] in, Indicates the serial number of the single-phase full bridge on the battery side, .

[0034] (2) The second working state of the single-phase full bridge on the battery side is the zero-level working state: There are two redundant states, both of which keep the relay switch K1 turned on. The first redundant state is: the power semiconductor relay switch Q1 and the power semiconductor relay switch Q3 are turned on, and the power semiconductor relay switch Q2 and the power semiconductor relay switch Q4 are turned off. The second redundant state is: the power semiconductor relay switch Q2 and the power semiconductor relay switch Q4 are turned on, and the power semiconductor relay switch Q1 and the power semiconductor relay switch Q3 are turned off.

[0035] (3) The third working state of the single-phase full bridge on the battery side is the relay switch bypass state: In this state, the power semiconductor relay switch Q1 , the power semiconductor relay switch Q2 , the power semiconductor relay switch Q3 , and the power semiconductor relay switch Q4 are all kept off, and the relay switch K1 is turned on.

[0036] When the battery side single-phase full bridge is in zero-level working state or relay switch bypass state, if the voltage drop of the switch device is not considered, the voltage between the AC side terminal E1 and the AC side terminal E2 of the jth battery side single-phase full bridge at time t is is equal to zero, that is:

[0037] There are two working states for DC access single-phase full bridge: (1) The first working state of the DC-connected single-phase full-bridge is the square wave working state: The power semiconductor relay switch QB1 and the power semiconductor relay switch QB4 are turned on or off at the same time, the power semiconductor relay switch QB2 and the power semiconductor relay switch QB3 are turned on or off at the same time, the switching states of the power semiconductor relay switch QB1 and the power semiconductor relay switch QB2 are complementary, and the switching states of the power semiconductor relay switch QB3 and the power semiconductor relay switch QB4 are complementary. The switching cycle time of the power semiconductor switch device of the DC-connected single-phase full-bridge is also Ts. Each power semiconductor relay switch switches from off to on and from on to off once within one Ts. Ignoring the conversion time, the on-time and off-time both account for 50% of Ts. At this time, the voltage between the AC side terminal D1 and the AC side terminal D2 of the DC-connected single-phase full-bridge at time t is The waveform is a voltage square wave in which the positive level and the negative level each occupy half of the time during the switching cycle. The voltage drop of the switching device is not considered, and the absolute value of the level is equal to the common DC bus voltage. .

[0038] (2) The second working state of the DC-connected single-phase full-bridge is the PWM working state: Each switching cycle is divided into the first half cycle and the second half cycle. The first half cycle is divided into the first sub-cycle and the second sub-cycle in chronological order. Assuming that the ratio of the pulse time width to Ts / 2 is d, the first half cycle is the positive level pulse time tp1, which is equal to the product of d and Ts / 2. During this time, the power semiconductor relay switch QB1 and the power semiconductor relay switch QB4 are turned on, and the power semiconductor relay switch QB2 and the power semiconductor relay switch QB3 are turned off. The second half cycle is the zero level time tp0, which is equal to the product of (1-d) and Ts / 2. During this time, the power semiconductor relay switch QB2 and the power semiconductor relay switch QB4 are turned on, and the power semiconductor relay switch QB1 and the power semiconductor relay switch QB3 are turned off. Equal to 0. The above ignores the voltage drop on the switching device.

[0039]

[0040] The second half cycle is also divided into the third sub-cycle and the fourth sub-cycle in chronological order. The first half cycle is the negative level pulse time tn1, which is equal to the product dTs / 2 of d and Ts / 2. During this time, the power semiconductor relay switch QB2 and the power semiconductor relay switch QB3 are turned on, and the power semiconductor relay switch QB1 and the power semiconductor relay switch QB4 are turned off. The second half cycle is the zero level time tn0, which is equal to the product of (1-d) and Ts / 2 (1-d)Ts / 2. During this time, the power semiconductor relay switch QB1 and the power semiconductor relay switch QB3 are turned on, and the power semiconductor relay switch QB2 and the power semiconductor relay switch QB4 are turned off. is equal to 0.

[0041]

[0042] Assume that the start time of a switching cycle of a DC-connected single-phase full-bridge is tB0, which is also the start time of the first half cycle. Within a switching cycle, the dividing points of each time period are set as , and .

[0043]

[0044] Considering that most battery energy storage systems use lithium iron phosphate batteries, and there is a long period of voltage change flat period during the charging and discharging process of lithium iron phosphate batteries, the transformation ratio Nt of the single-phase transformer can be configured according to the ratio of the total average module voltage during the voltage flat period when all battery modules are charged and discharged at rated power to the rated common bus voltage.

[0045] When the jth battery module is charged at rated power, the voltage of the battery module during the steady period is Vmrc_j, and when the jth battery module is discharged at rated power, the voltage of the battery module during the steady period is Vmrd_j. Then the transformation ratio of the single-phase transformer is:

[0046] In some embodiments of the present application, a single-phase transformer may integrate an equivalent series inductor Lk to facilitate the battery-side single-phase full-bridge to cooperate with the DC-access single-phase full-bridge to operate in a dual active bridge (DAB) manner.

[0047] Correspondingly, the overall working modes of the isolated energy storage DC power conversion system can be three: Working mode 1: single phase shift control mode.

[0048] When all battery modules do not have any bypass or zero level, all battery-side single-phase full bridges select the first working state, i.e., the square wave working state. The working waveforms of the power semiconductor relay switches are synchronized. The switching cycle time is Ts. The starting time of a switching cycle time is tm0. The voltage V12_sum(t) between the 1st and 2nd terminals of the cascaded full bridge at time t is:

[0049] At the same time, the DC-connected single-phase full-bridge also works in a square wave working state, with a switching cycle time of Ts, and the starting time of a switching cycle time is tB0.

[0050] The time difference of the battery-side single-phase full-bridge tm0 leading the DC access single-phase bridge tB0 is set to tp, and the half-cycle normalized phase shift angle of the overall phase shift control of the isolated energy storage DC power conversion system is dp:

[0051] Assuming the discharge direction is the positive power direction, the overall battery side power PDAB of the isolated energy storage DC power conversion system is:

[0052] Wherein, Lk is the inductance value of the equivalent series inductor integrated in the single-phase transformer on one side of the single-phase full-bridge on the battery side.

[0053] Since the switch states are exactly the same, the average current iavg of all battery modules is equal to:

[0054] This average current iavg has nothing to do with the state of the battery module, and the charge change of each battery module is equal in the same time.

[0055] The principle of the isolated energy storage DC power conversion system working mode 1 is similar to the single-phase shift control of the traditional DAB (Dual ActiveBridge). Assume that the current of the inductor Lk is iLk, and assume that the dead time of the upper and lower tubes of all bridge converters is small enough, and the parasitic output capacitance of the switching device is small enough. Under the definition of the current power direction, as long as the zero-crossing point of the battery-side single-phase full-bridge voltage V12_j(t) is ahead of the zero-crossing point of the iLk trapezoidal current, and the zero-crossing point of the iLk trapezoidal current is ahead of the DC-connected single-phase bridge voltage , then all switching devices can achieve zero voltage turn-on and eliminate the reverse recovery loss of the anti-parallel diode.

[0056] Working mode two: comprehensive phase shift control mode.

[0057] When Nb battery-side full bridges are in a zero-level working state, and the remaining Nm-Nb battery-side single-phase full bridges are in a square wave working state, the DC-connected single-phase full bridge selects the second working state, namely, the PWM working state. Among them, 1<Nb<Nm.

[0058] The switching waveforms of all single-phase full-bridges on the battery side in square wave working state are synchronized. The switching cycle time is Ts. The starting time of a switching cycle time is tm0. Ignoring the voltage drop of the switching device, the voltage between the 1st and 2nd terminals of the cascaded full bridge at time t is yes:

[0059] Among them, x is the serial number of the battery side single-phase full-bridge in the square wave working state, and Vm_x is the battery side single-phase full-bridge voltage in the xth square wave working state.

[0060] At the same time, the DC access single-phase full-bridge is in PWM working state, the switching cycle time is Ts, and the starting time of a switching cycle time is tB0.

[0061] Assume that the center time of the positive level of the single-phase full-bridge on the battery side is tmc, the center time of the positive level of the single-phase full-bridge connected to the DC is tBc, and the relationship between the center time of the positive level of the single-phase full-bridge on the battery side and the cycle start time is:

[0062] The time difference between tmc and tBc is set to tpc, and the half-cycle normalized phase shift angle of the overall phase shift control of the converter is dpc. Generally, dpc is less than 0.5.

[0063]

[0064] Through Fourier series analysis and calculation, the DC access power Po1 and Po3 of the switching cycle fundamental wave and the third harmonic are obtained:

[0065] Among them, Fp1 is the fundamental power factor and Fp3 is the third harmonic power factor.

[0066]

[0067] Among them, the fundamental power is the main component of the power, but when the phase shift angle is small (such as dpc=0.1 or 0.2), only considering the fundamental power, the total power error will be more obvious, and the third harmonic power should be added to the total power. At this time, under most conditions, when the phase shift angle is small, the total power relative error is below 0.1, and when the phase shift angle is large, the total power relative error drops to below 0.01.

[0068] From the fundamental wave analysis, when the iLk fundamental wave lags behind the V12_sum(t) fundamental wave, the iLk fundamental wave leads If the fundamental angle is greater than the angle corresponding to half of the zero-level time, full soft switching can be achieved. Based on this, the relationship between the DC access single-phase full-bridge duty cycle d and the equivalent voltage transformation ratio can be obtained:

[0069] in, is the equivalent voltage transformation ratio.

[0070] Since zero level does not transfer power, the zero level time of equal power Too long will increase the peak value of the current waveform, so the zero level time should be limited. As an example, the following can be used:

[0071] like Figure 4 As shown, the DC access single-phase full-bridge duty cycle in this embodiment Follow Schematic diagram of the changes.

[0072] At this time, the limit of the phase shift angle dp mentioned above can be simplified. The lower limit of the soft switching value range of the phase shift angle dp during discharge is :

[0073] like Figure 5 As shown, it is the lower limit of the soft switching value range of the phase shift angle dp during discharge. Follow Kv Schematic diagram of the changes.

[0074] The above soft switching conditions are calculated by fundamental wave analysis under discharge. The calculation method under charging conditions is similar and will not be repeated here.

[0075] Assume that there are 8 battery modules and corresponding single-phase full-bridges on the battery side, one of which is in bypass state, and the single-phase transformer ratio is set according to the DC voltage ratio when there is no bypass. The working waveforms of each component are as follows: Figure 6 It should be noted that Figure 6 It is a steady-state waveform drawn by taking a heavier load discharge as an example after conversion according to the single-phase transformer ratio. Figure 6 The first waveform from top to bottom is the waveform of the power semiconductor relay switch Q1 and the power semiconductor relay switch Q4 in the battery side single-phase full-bridge in square wave working state, and the power semiconductor relay switch QB1 and the power semiconductor relay switch QB3 in the DC access single-phase full-bridge in PWM working state; the second waveform is the voltage V12_sum(t) between the 1st and 2nd ends of the cascaded full bridge in all the battery side single-phase full bridges in square wave working state at time t, and the sum of the voltages between the AC side ends D1 and the AC side ends D2 of all the DC access single-phase full bridges in square wave working state at time t The third waveform diagram is the waveform diagram of the current iLk of the equivalent series inductor; the fourth waveform diagram is the waveform diagram of the DC end current i_in of the single-phase full-bridge on the battery side in the square wave working state, and the DC access single-phase full-bridge DC end current i_out.

[0076] In the first waveform diagram, the high level of the waveform is on, and the low level is off. The specific values ​​are meaningless. The power semiconductor relay switch Q1 and the power semiconductor relay switch Q4 are turned on or off at the same time. The switch state of the undrawn power semiconductor relay switch Q2 is opposite to that of the power semiconductor relay switch Q1, and the switch state of the power semiconductor relay switch Q3 is opposite to that of the power semiconductor relay switch Q4. During discharge, the switch state waveform phase of the power semiconductor relay switch QB1 lags behind that of Q1 and the power semiconductor relay switch Q4, and the phase difference does not exceed 1 / 4 of the switching cycle. The power semiconductor relay switch QB3 lags behind the power semiconductor relay switch QB1 phase, and the phase difference is between 1 / 2 and 3 / 4 of the switching cycle. The switch state of the undrawn power semiconductor relay switch QB2 is opposite to that of the power semiconductor relay switch QB1, and the switch state of the power semiconductor relay switch QB4 is opposite to that of the power semiconductor relay switch QB3. Due to the above switch state settings, in the second waveform diagram, V12_sum(t) is a square wave. It is a symmetrical step waveform. Two steps appear in sequence in the half switching cycle after the rising edge of V12_sum(t). The rising edge of V12_sum(t) and the falling edge of V12_sum(t) are followed by two V12_sum(t) and The difference between the two acts on the equivalent series inductance Lk to produce the waveform change of iLk in the third waveform. Through appropriate switching signal design, the zero crossing point of iLk from negative to positive can be delayed from the rising edge of V12_sum(t) but ahead of the rising edge of V12_sum(t) within half a switching cycle. The rising edge of iLk makes the zero crossing point of iLk from positive to negative lag behind the falling edge of V12_sum(t) but ahead of This allows all switching devices to be turned on at zero voltage and eliminates the reverse recovery loss of the anti-parallel diode.

[0077] In some embodiments of the present application, the SOC (State of Charge) balancing control of the battery module can also be implemented through a zero-level pipeline. Specifically, the following method can be called for control according to a fixed period. For example, the following control method can be executed once in each switching cycle of the single-phase full-bridge on the battery side, such as Figure 7 As shown, it is a schematic diagram of the process of realizing SOC balancing control of a battery module through a zero-level pipeline, which may include: (1) Determine whether the switching cycle count value PC of the battery-side single-phase full-bridge is 0. If so, execute step (2); otherwise, execute step (8); (2) Set the zero-level pipeline processing flag of the single-phase full-bridge on the battery side to 0; (3) Calculating the SOC range of the battery module; the SOC range is equal to the difference between the maximum SOC value and the minimum SOC value; (4) Determine whether the SOC range is greater than a preset SOC range upper threshold. If so, set the range size flag Sign_LD to 1 and execute step (5); otherwise, determine whether the SOC range is less than a preset SOC range lower threshold. If so, reset the range size flag Sign_LD to 0 and execute step (5); otherwise, execute step (5); Figure 8 As shown, this is a schematic diagram of the hysteresis judgment process of the range size sign Sign_LD; (Step (4) here corresponds to Figure 7 Subprocess 1 in . ) (5) Determine whether the range size flag Sign_LD is set to 1. If so, execute step (6); otherwise, execute step (8); (6) Determine whether it is currently in a discharge state. If so, calculate the SOC difference between each battery module and the battery module with the maximum SOC to obtain a set of first SOC differences; otherwise, calculate the SOC difference between each battery module and the battery module with the minimum SOC to obtain a set of second SOC differences; determine the battery module corresponding to the first SOC difference and the second SOC difference that is greater than the preset SOC extreme value lower threshold, record it as an active battery module, and record the other battery modules as inactive battery modules, and record the number of active battery modules as Nsb, so that the battery side single-phase full bridge corresponding to the active battery module participates in active state balancing, performs zero-level pipeline operation, sets the flag Sign_ZPP participating in the zero-level pipeline operation to 1, and sets the flag Sign_ZPP participating in the zero-level pipeline operation to 0 for the inactive battery module; it should be noted that the SOC of the battery module with the minimum SOC and the SOC of the battery module with the maximum SOC are obtained within the same sampling time; Fig. 9 As shown, it is a schematic diagram of the inference process of the zero-level pipeline operation sign Sign_ZPP of the battery module; (step (6) here corresponds to Figure 7 Subprocess 2 in . ) (7) Determine whether Nsb is equal to 1. If so, execute step (8); otherwise, execute steps (7-1) to (7-7): (7-1) Calculate the sum of the first SOC difference and the second SOC difference of the active battery module, denoted as Sum_Dsox; (7-2) Calculate the number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to each active battery module according to the following formula:

[0078] in, Indicates the serial number The number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to the active battery module, Indicates The first SOC difference or the second SOC difference of the active battery module is represented by Npp, which represents the total number of switching cycles in one working cycle of the zero-level pipeline, and n represents the sequence number of the active battery module in all battery modules. , j1 represents the sequence number of the first main battery module among all battery modules, j2 represents the sequence number of the second main battery module among all battery modules, and jNsb represents the sequence number of the Nsbth main battery module among all battery modules; Nz_n is rounded to the nearest integer according to the rounding rule; (7-3) Calculate the sum of Nz_n of all active battery modules, denoted as Sum_Nz; (7-4) Determine whether Sum_Nz is greater than Npp. If so, execute step (7-5). Otherwise, execute step (7-6). (7-5) Find the Sum_Nz-Npp active battery modules with the smallest Dsoxn value in the active battery modules, record them as small active battery modules, reduce Nz_n of the battery-side single-phase full bridge corresponding to the small active battery modules by 1, and execute step (8); (7-6) Determine whether Sum_Nz is less than Npp. If so, execute step (7-7); otherwise, execute step (8); (7-7) Find the Npp-Sum_Nz active battery modules with the largest Dsoxn value in the active battery modules, record them as large active battery modules, add 1 to the Nz_n of the battery-side single-phase full bridge corresponding to the large active battery module, and execute step (8); Fig.10 As shown, it is a flow chart of calculating the number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to the active battery module; (Step (7) corresponds to Figure 7 Subprocess 3 in . ) (8) Determine whether the extreme difference size flag Sign_LD is set to 1. If so, execute step (9). Otherwise, make all battery-side single-phase full bridges in square wave working state, and then complete one SOC balancing control; (9) Determine whether Nsb is equal to 1. If so, the battery side single-phase full bridge corresponding to the main battery module is in a zero-level working state, and the battery side single-phase full bridge corresponding to the non-main battery module is in a square wave working state, and execute step (10); otherwise, execute steps (9-1) to (9-8): (9-1) Determine whether the switching cycle count value PC of the single-phase full-bridge on the battery side satisfies:

[0079] in, is the number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to the main battery module with serial number j1; If yes, execute step (9-2); otherwise, execute step (9-3); (9-2) Make the battery-side single-phase full-bridge corresponding to the main battery module with serial number j1 in a zero-level working state, and make the battery-side single-phase full-bridge corresponding to other main battery modules in a square-wave working state, and execute step (10); (9-3) Set the variable m=2; the variable m indicates the size of the PC to be judged for the mth time, which is used to determine which battery side single-phase full bridge is in the zero-level working state corresponding to the PC; (9-4) Determine whether m≤Nsb holds. If so, execute step (9-5). Otherwise, execute step (9-8). (9-5) Determine whether the switching cycle count value PC of the single-phase full-bridge on the battery side satisfies the following formula:

[0080] If yes, execute step (9-6); otherwise, execute step (9-7); (9-6) Make the battery side single-phase full bridge corresponding to the active battery module with serial number jm in zero-level working state, and make the battery side single-phase full bridge corresponding to other active battery modules in square wave working state, and execute step (10); (9-7) Set m+1 and return to step (9-4); (9-8) Report counting failure and execute step (10); like Fig.11 As shown, it is a flow chart of the zero-level pipeline processing of the single-phase full-bridge on the battery side of the active battery module; it should be noted that after step (9-3), for Nsb>1, there must be an m value in the interval [2, Nsb], so that the formula in step (9-5) is valid, otherwise it indicates that there is a problem in the calculation, and an error can be reported accordingly, and step (9) is terminated; (step (9) here corresponds to Figure 7 Subprocess 4 in . ) (10) Increase the switching cycle count value PC of the single-phase full-bridge on the battery side by 1; (11) Determine whether the switching cycle count value PC of the single-phase full-bridge on the battery side satisfies:

[0081] If so, the switching cycle count value PC of the single-phase full-bridge on the battery side is assigned to 0, and an SOC balancing control is completed; otherwise, an SOC balancing control is completed.

[0082] An embodiment of the present application also provides an electronic device, which may include one or more processors, a memory, and a communication interface.

[0083] The memory, the communication interface and the processor are coupled, for example, the memory, the communication interface and the processor may be coupled together via a bus.

[0084] The communication interface is used for data transmission with other devices. The memory stores computer program code. The computer program code includes computer instructions. When the computer instructions are executed by the processor, the electronic device executes the steps of the control method of the above-mentioned isolated energy storage DC power conversion system.

[0085] Wherein, the processor can be a processor or a controller, for example, a central processing unit (CPU), a general processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. It can implement or execute various exemplary logic boxes, modules and circuits described in conjunction with the present disclosure. The processor can also be a combination that implements a computing function, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, and the like. The processor can be used to support electronic devices to execute the method steps provided in the above embodiments. Wherein, the bus can be a peripheral component interconnect standard (PCI) bus or an extended industry standard architecture (EISA) bus, etc. The above bus can be divided into an address bus, a data bus, a control bus, etc.

[0086] The computer-readable storage medium provided in the embodiments of the present application performs various exemplary logic blocks, modules and circuits described in conjunction with the present disclosure. The processor may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc. The processor may be used to support an electronic device in executing the method steps provided in the above embodiments.

[0087] The bus may be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. The above bus may be divided into an address bus, a data bus, a control bus, etc.

[0088] The machine-readable storage medium stores a computer program, and when the computer program is executed by the processor, the steps of the control method of the above-mentioned isolated energy storage DC power conversion system are implemented.

[0089] The computer-readable storage medium involved in the present application includes random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the technical field.

[0090] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An isolated energy storage DC power conversion system, characterized in that: It includes a DC access single-phase full-bridge, a single-phase transformer, Nm battery-side single-phase full-bridges and Nm relay switches K1; Nm is the number of battery modules; The DC-access single-phase full-bridge includes four power semiconductor relay switches, namely power semiconductor relay switch QB1 to power semiconductor relay switch QB4; wherein, an AC side terminal D1 is formed between the power semiconductor relay switch QB1 and the power semiconductor relay switch QB2, and an AC side terminal D2 is formed between the power semiconductor relay switch QB3 and the power semiconductor relay switch QB4; the DC side positive pole of the DC-access single-phase full-bridge is recorded as the DC side positive terminal D3, and the DC side negative pole is recorded as the DC side negative terminal D4, and the DC side positive terminal D3 and the DC side negative terminal D4 are respectively connected to the positive pole and the negative pole of the common DC bus outside the battery energy storage system; the AC side terminal D1 and the AC side terminal D2 are respectively connected to the two ends of the secondary side of the single-phase transformer; The battery-side single-phase full bridge includes four power semiconductor relay switches, namely power semiconductor relay switch Q1 to power semiconductor relay switch Q4; wherein, an AC side terminal E1 is formed between the power semiconductor relay switch Q1 and the power semiconductor relay switch Q2, and an AC side terminal E2 is formed between the power semiconductor relay switch Q3 and the power semiconductor relay switch Q4; the DC side positive pole of the battery-side single-phase full bridge is recorded as the DC side positive terminal E3, and the DC side negative pole is recorded as the DC side negative terminal E4, and the DC side positive terminal E3 and the DC side negative terminal E4 are respectively connected to the positive pole and the negative pole of a battery module; the AC sides of Nm battery-side single-phase full bridges are connected in series to form a cascade full bridge; and the AC side terminal E1 of the first battery-side single-phase full bridge and the AC side terminal E2 of the Nm-th battery-side single-phase full bridge are respectively connected to the two ends of the primary side of the single-phase transformer; Two ends of the relay switch K1 are connected to the AC side end E1 and the AC side end E1 respectively.

2. The isolated energy storage DC power conversion system according to claim 1, characterized in that: The single-phase transformer is located on one side of the battery-side single-phase full-bridge and is integrated with an equivalent series inductor.

3. A control method for the isolated energy storage DC power conversion system according to claim 1 or 2, characterized in that: include: Control the battery-side single-phase full-bridge and the DC-access single-phase full-bridge to be in square wave working state, so that the isolated energy storage DC power conversion system is in single-phase shift control mode; Alternatively, a portion of the battery-side single-phase full-bridge is controlled to be in a zero-level working state, another portion of the battery-side single-phase full-bridge is controlled to be in a square wave working state, and the DC-access single-phase full-bridge is controlled to be in a PWM working state, so that the isolated energy storage DC power conversion system is in a phase-shift plus PWM working state; Alternatively, the relay switch K1 corresponding to a battery-side single-phase full-bridge is controlled to be disconnected, the remaining battery-side single-phase full-bridge is in a square wave working state, and the DC-access single-phase full-bridge is in a PWM working state, so that the isolated energy storage DC power conversion system is in a phase-shift plus PWM working state.

4. The control method of the isolated energy storage DC power conversion system according to claim 3 is characterized in that: The method for controlling the battery-side single-phase full-bridge to be in a square wave working state comprises: Keep the corresponding relay switch K1 turned on, the power semiconductor relay switch Q1 and the power semiconductor relay switch Q4 turned on or off at the same time, and the power semiconductor relay switch Q2 and the power semiconductor relay switch Q3 turned on or off at the same time; and the switching states of the power semiconductor relay switch Q1 and the power semiconductor relay switch Q2 are complementary, and the switching states of the power semiconductor relay switch Q3 and the power semiconductor relay switch Q4 are complementary; No. The AC side terminal E1 and the AC side terminal E2 of the battery side single-phase full bridge are connected. Voltage at the moment for: Wherein, j represents the serial number of the single-phase full bridge on the battery side, , Indicates Battery module voltage, Indicates the start time of a switching cycle of the single-phase full-bridge on the battery side. Indicates the switching cycle time of the power semiconductor relay switch.

5. The control method of the isolated energy storage DC power conversion system according to claim 3, characterized in that: The method for controlling the battery-side single-phase full-bridge to be in a zero-level working state comprises: Keep the corresponding relay switch K1 turned on, the power semiconductor relay switch Q1 and the power semiconductor relay switch Q3 turned on at the same time, and the power semiconductor relay switch Q2 and the power semiconductor relay switch Q4 turned off at the same time; Alternatively, the power semiconductor relay switch Q2 and the power semiconductor relay switch Q4 are turned on at the same time, and the power semiconductor relay switch Q1 and the power semiconductor relay switch Q3 are turned off at the same time; The voltage between the AC side terminal E1 and the AC side terminal E2 of the j-th battery side single-phase full bridge at time t is zero.

6. The control method of the isolated energy storage DC power conversion system according to claim 3, characterized in that: The method for controlling a DC-connected single-phase full-bridge to be in a square wave working state comprises: Make the power semiconductor relay switch QB1 and the power semiconductor relay switch QB4 turned on or off at the same time, and the power semiconductor relay switch QB2 and the power semiconductor relay switch QB3 turned on or off at the same time; and the switching states of the power semiconductor relay switch QB1 and the power semiconductor relay switch QB2 are complementary, and the switching states of the power semiconductor relay switch QB3 and the power semiconductor relay switch QB4 are complementary.

7. The control method of the isolated energy storage DC power conversion system according to claim 3, characterized in that: The method for controlling a DC-connected single-phase full-bridge to be in a PWM working state comprises: Define that the switching cycle of the power semiconductor relay switch includes a first half cycle and a second half cycle, and the first half cycle includes a first sub-cycle and a second sub-cycle, and the second half cycle includes a third sub-cycle and a fourth sub-cycle; The voltage between the AC side terminal D1 and the AC side terminal D2 of the DC-connected single-phase full bridge at time t for: in, represents the common DC bus voltage, Indicates the start time of a switching cycle of a single-phase full-bridge connected to DC. Indicates the start time of the second sub-cycle of the DC access single-phase full-bridge. Indicates the start time of the third sub-cycle of the DC access single-phase full-bridge. Indicates the start time of the fourth sub-cycle of the DC access single-phase full-bridge.

8. The control method of the isolated energy storage DC power conversion system according to claim 3, characterized in that: Also includes: Controlling the transformation ratio of a single-phase transformer satisfy: in, Indicates When a battery module is charged at rated power, the voltage of the battery module during the plateau period is Indicates The plateau voltage of the battery module when the battery module is discharged at rated power.

9. The control method of the isolated energy storage DC power conversion system according to claim 3, characterized in that: It also includes the SOC balancing control of the battery module through the zero-level pipeline: (1) Determine whether the switching cycle count value PC of the battery-side single-phase full-bridge is 0. If so, execute step (2); otherwise, execute step (8); (2) Set the zero-level pipeline processing flag of the single-phase full-bridge on the battery side to 0; (3) Calculating the SOC range of the battery module; the SOC range is equal to the difference between the maximum SOC value and the minimum SOC value; (4) Determine whether the SOC range is greater than a preset SOC range upper threshold. If so, set the range size flag Sign_LD to 1 and execute step (5); otherwise, determine whether the SOC range is less than a preset SOC range lower threshold. If so, reset the range size flag Sign_LD to 0 and execute step (5); otherwise, directly execute step (5); (5) Determine whether the range size flag Sign_LD is set to 1. If so, execute step (6); otherwise, execute step (8); (6) Determine whether the battery is currently in a discharging state. If so, calculate the SOC difference between each battery module and the battery module with the maximum SOC to obtain a set of first SOC differences; Otherwise, the SOC differences between each battery module and the battery module with the minimum SOC are calculated respectively to obtain a set of second SOC differences; Determine the battery module corresponding to the first SOC difference and the second SOC difference that is greater than the preset SOC extreme value lower threshold, record it as the active battery module, record the other battery modules as the inactive battery modules, and record the number of active battery modules as Nsb, so that the battery-side single-phase full bridge corresponding to the active battery module participates in active state balancing, performs zero-level pipeline operation, sets the zero-level pipeline operation flag Sign_ZPP to 1, and sets the zero-level pipeline operation flag Sign_ZPP of the inactive battery module to 0; (7) Determine whether Nsb is equal to 1. If so, execute step (8); otherwise, execute steps (7-1) to (7-7): (7-1) Calculate the sum of the first SOC difference and the second SOC difference of the active battery module, denoted as Sum_Dsox; (7-2) Calculate the number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to each active battery module according to the following formula: in, Indicates the serial number The number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to the active battery module, Indicates The first SOC difference or the second SOC difference of the active battery module is represented by Npp, which represents the total number of switching cycles in one working cycle of the zero-level pipeline, and n represents the sequence number of the active battery module in all battery modules. , j1 represents the sequence number of the first main battery module among all battery modules, j2 represents the sequence number of the second main battery module among all battery modules, and jNsb represents the sequence number of the Nsbth main battery module among all battery modules; Nz_n is rounded to the nearest integer according to the rounding rule; (7-3) Calculate the sum of Nz_n of all active battery modules, denoted as Sum_Nz; (7-4) Determine whether Sum_Nz is greater than Npp. If so, execute step (7-5). Otherwise, execute step (7-6). (7-5) Find the Sum_Nz-Npp active battery modules with the smallest Dsoxn value in the active battery modules, record them as small active battery modules, reduce Nz_n of the battery-side single-phase full bridge corresponding to the small active battery modules by 1, and execute step (8); (7-6) Determine whether Sum_Nz is less than Npp. If so, execute step (7-7); otherwise, execute step (8); (7-7) Find the Npp-Sum_Nz active battery modules with the largest Dsoxn value in the active battery modules, record them as large active battery modules, add 1 to the Nz_n of the battery-side single-phase full bridge corresponding to the large active battery module, and execute step (8); (8) Determine whether the extreme difference size flag Sign_LD is set to 1. If so, execute step (9). Otherwise, make all battery-side single-phase full bridges in square wave working state, and then complete one SOC balancing control; (9) Determine whether Nsb is equal to 1. If so, the battery side single-phase full bridge corresponding to the main battery module is in a zero-level working state, and the battery side single-phase full bridge corresponding to the non-main battery module is in a square wave working state, and execute step (10); otherwise, execute steps (9-1) to (9-8): (9-1) Determine whether the switching cycle count value PC of the single-phase full-bridge on the battery side satisfies: in, For serial number The number of zero-level cycles of the single-phase full-bridge on the battery side corresponding to the main battery module; If yes, execute step (9-2); otherwise, execute step (9-3); (9-2) Make the sequence number The battery side single-phase full bridge corresponding to the main battery module is in a zero-level working state, and the battery side single-phase full bridge corresponding to other main battery modules is in a square wave working state, and step (10) is executed; (9-3) Make the variable ; (9-4) Judgment Is it true? If so, execute step (9-5); otherwise, execute step (9-8); (9-5) Determine whether the switching cycle count value PC of the single-phase full-bridge on the battery side satisfies the following formula: If yes, execute step (9-6); otherwise, execute step (9-7); (9-6) Make the battery side single-phase full bridge corresponding to the active battery module with serial number jm in zero-level working state, and make the battery side single-phase full bridge corresponding to other active battery modules in square wave working state, and execute step (10); (9-7) Set m+1 and return to step (9-4); (9-8) Report counting failure and execute step (10); (10) Increase the switching cycle count value PC of the single-phase full-bridge on the battery side by 1; (11) Determine whether the switching cycle count value PC of the single-phase full-bridge on the battery side satisfies: If so, the switching cycle count value PC of the single-phase full-bridge on the battery side is assigned to 0, and an SOC balancing control is completed; otherwise, an SOC balancing control is completed.

10. An electronic device, characterized in that: include: A memory, one or more processors; the memory is coupled to the processor; wherein the memory stores computer program code, the computer program code includes computer instructions, and when the computer instructions are executed by the processor, the electronic device executes the steps of the control method of the isolated energy storage DC power conversion system as described in any one of claims 3 to 9.

11. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the control method of the isolated energy storage DC power conversion system as described in any one of claims 3 to 9 are implemented.

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