Battery boost type high voltage direct-mounted energy storage conversion system and control method

Abstract

The present invention discloses a battery boost type high voltage direct hanging energy storage conversion system and control method, which belongs to the field of power electronic energy storage technology, including phase A, phase B, and phase C, each phase is composed of multiple power units connected in series, each power unit is the same, and includes an AC output H-bridge conversion circuit, a DC bus capacitor, multiple BAT modules and a bypass switch, the BAT module is connected in parallel on the DC capacitor side, the positive pole of each BAT module is connected to a bypass switch K1, and a bypass switch K2 is connected across the two bridge arms of each AC H-bridge conversion circuit, and a BAT module includes a battery pack and a battery boost circuit. When the present invention detects a system fault or a superior dispatching instruction, within the allowable bypass level range, the battery boost controller or the main controller can issue an instruction to disconnect the power electronic switch tube, so that the faulty module is cut out of the power circuit, and bypass protection at the battery module level and the unit level can be realized, thereby improving the system reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic energy storage, and in particular to a battery boost type high voltage direct-mounted energy storage conversion system and a control method. Background Art

[0002] At present, the battery side of the energy storage system outputs multiple cells in clusters. A certain number of cells are connected in series to form a battery module, and the battery modules are connected in series again to form a battery PACK. Finally, the battery PACK is connected in series to form a battery cluster and connected to the DC bus voltage. This solution is limited by high-voltage insulation protection and creepage distance issues. Modules cannot be connected in series indefinitely. The DC voltage is mainly below 1500V. The inverter side needs to be equipped with a 10kV / 35kV transformer to be connected to the grid. This grid-connected method is inefficient and costly.

[0003] High-voltage direct-mounted energy storage systems can be connected to the grid without a transformer. They are divided into two structures: MMC and chain. The chain structure is simple and has lower cost, so it is widely used. However, the DC side still maintains a battery cluster structure. One is that the battery cluster is directly connected to the DC bus, and the other is that a DC / DC circuit is added between the DC bus and the battery cluster for buck-boost control, which is more conducive to battery charge and discharge management. Both of the above structures require high battery consistency, and the inability to accurately monitor the battery cell layer also makes maintenance difficult.

[0004] In the prior art, a Chinese patent with application number 202110443465.4 discloses an energy storage system, a balanced control method for an energy storage system, and a photovoltaic power generation system. Each power conversion branch of the energy storage system includes a power conversion circuit, or each power conversion branch includes at least two power conversion circuits connected in series. The second end of each power conversion circuit is connected to at least one battery cluster; each battery cluster includes at least two energy storage modules connected in series, and each energy storage module includes a DC / DC conversion circuit and a battery pack; the output end of each battery pack is connected to the input end of the corresponding DC / DC conversion circuit, and the output end of each DC / DC conversion circuit is connected in parallel to the balancing bus, and the controller controls each DC / DC conversion circuit to balance the power of each battery pack in the battery cluster. However, this patent has no bypass protection. When a unit module fails, the faulty module cannot be cut out of the main circuit, reducing the reliability of the system.

[0005] The Chinese patent application number 202311399829.9 discloses a high-voltage direct-mounted power electronic battery PACK circuit system and control method. The circuit system includes multiple groups of direct-mounted power electronic battery PACK circuits connected in series. Each group of direct-mounted power electronic battery PACK circuits includes three power electronic battery PACK main circuits, namely phase A, phase B, and phase C; each power electronic battery PACK main circuit includes a bidirectional DC-DC circuit, an H-bridge conversion circuit, and an ECO switch circuit. The bypass switch added by the patent can improve the redundancy and reliability of the system, but if a single battery cell is damaged, the entire battery cluster will fail, resulting in reduced efficiency of the battery cluster, inability to accurately detect the battery cell layer, and difficulty in maintaining the battery cluster.

[0006] The Chinese patent application number 201910697341.1 discloses a high-voltage direct-mounted energy storage device, including

[0007] In summary: A-phase H-bridge power module, B-phase H-bridge power module and C-phase H-bridge power module connected to A-phase, B-phase and C-phase lines respectively, each including more than two cascaded H-bridge power modules, and A-phase, B-phase and C-phase lines adopt star connection mode; DC side capacitor, a DC side capacitor is connected in parallel to the DC side of each H-bridge power module; battery and super capacitor, respectively as energy storage element and power storage element; and isolated three-port active bridge converter, one side of which is connected to one side of the capacitor, and the other side is connected to the battery and super capacitor at the same time. However, this topology increases the complexity of the battery side control algorithm and reduces the control stability of the system. Summary of the invention

[0008] The present invention aims to solve the above-mentioned problems existing in the high-voltage direct-mounted energy storage system in the prior art, and proposes a battery boost type high-voltage direct-mounted energy storage converter system and a control method.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0010] The battery boost type high voltage direct-mounted energy storage conversion system includes phase A, phase B and phase C. Each phase is composed of multiple power units connected in series. Each power unit is the same and includes an AC output H-bridge conversion circuit, a DC bus capacitor, multiple BAT modules and a bypass switch. The BAT module is connected in parallel on the DC capacitor side. The positive pole of each BAT module is connected to a bypass switch K1. A bypass switch K2 is connected across the two bridge arms of each AC H-bridge conversion circuit. A BAT module includes a battery pack and a battery boost circuit.

[0011] Furthermore, each AC output H-bridge conversion circuit includes switches T1, T2, T3, and T4, switches T1 and T2 form a bridge arm, and switches T3 and T4 form a bridge arm; the three-phase circuits of phase A, phase B, and phase C are connected in a star connection or a triangle connection; when a star connection is adopted, the midpoints of the bridge arms of switches T1 and T2 in the first-stage power module are respectively connected to the filter inductors La, Lb, and Lc on the main circuit, and the inductors La, Lb, and Lc are then connected to the A phase, B phase, and C phase of the power grid, and the midpoints of the bridge arms of switches T3 and T4 in the first-stage power module are connected to the switches T1 and T4 of the H-bridge conversion circuit in the second-stage power module. The midpoint of the bridge arm of T2 is connected end to end; the midpoints of the bridge arms of switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase A, phase B and phase C are connected to each other; when a triangle connection is adopted, the connection method of the first few power modules is consistent with the star connection, the difference is that the midpoints of the bridge arms of switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase A are connected to phase B of the AC power grid, the midpoints of the bridge arms of switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase B are connected to phase C of the power grid, and the midpoints of the bridge arms of switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase C are connected to phase A of the power grid.

[0012] Furthermore, the battery boost circuit includes a filter capacitor, two H-bridge conversion circuits, a transformer, resonant inductors Lr1, Lr2, Lm, and resonant capacitors Cr1 and Cr2; the filter capacitor is connected across the battery pack, the primary side H-bridge of the transformer includes switches S1, S2, S3, and S4, the midpoint of the bridge arm formed by switches S1 and S2 is connected to the resonant inductor Lr1, the midpoint of the bridge arm formed by switches S3 and S4 is connected to the resonant capacitor Cr1, and the resonant inductor Lm is the transformer reactance; the transformer ratio is 1:N, the secondary side H-bridge of the transformer includes switches S5, S6, S7, and S8, the midpoint of the bridge arm formed by switches S5 and S6 is connected to the resonant inductor Lr2, and the midpoint of the bridge arm formed by switches S7 and S8 is connected to the resonant capacitor Cr2.

[0013] Furthermore, the battery boost circuit is connected to a battery boost controller, and the battery boost controller is used to collect the battery status of each battery cell, the battery current, the module output current, the bridge arm voltages on both sides of the transformer, and the primary and secondary side currents of the transformer, and perform closed-loop control based on the current reference value output by the SOC balancing control between the BAT modules of the charge and discharge operation mode, control the output of the driving signal of the H-bridge switch tube in the battery boost circuit to the isolation drive module, and finally output the driving signal through the isolation drive module.

[0014] Furthermore, the power module is connected to a main controller, which is used to collect the voltage and current of the common DC capacitor, the voltage and current of the inverter output, the relevant information transmitted by the battery boost controller, and the battery information transmitted by the battery management system BMS, and then combine the different operating instructions given by the host computer or the upper-level dispatcher to perform closed-loop control and superimpose the SOC balanced control output on the modulation information of each phase and each unit. The final modulation signal is modulated by phase-shifted PWM, and the drive signal of the switch tube in the AC H bridge of the output unit is isolated through the drive board. It is also used to determine whether the bypass requirements are met based on the collected battery pack fault information, the battery boost circuit fault information and the unit fault information, and control the corresponding BAT module bypass switch K1 to act through the bypass controller to realize the BAT module bypass function, and control the control unit bypass switch K2 to act to realize the unit bypass function.

[0015] Based on the above-mentioned battery boost type high voltage direct-mounted energy storage conversion system, the present invention also provides a control method for the battery boost type high voltage direct-mounted energy storage conversion system, wherein the unit level and BAT module level bypass control process of the battery boost type high voltage direct-mounted energy storage system includes:

[0016] Step 1: The main controller detects whether the battery pack voltage is less than or equal to the minimum allowable operating voltage of the battery cell, whether the battery pack SOC is less than or equal to the minimum allowable operating SOC of the battery cell, and whether the battery boost main circuit reports a fault. If one of the three conditions is met, jump to step 2, otherwise jump to step 3;

[0017] Step 2, lock the switch drive of the battery boost circuit, disconnect all the switches of the H bridge in the battery boost circuit, disconnect one of the bypass switches K1, so that the corresponding BAT module is bypassed; if multiple BAT modules need to be bypassed, disconnect the corresponding bypass switches; the main controller determines whether the battery bypass level exceeds the set threshold, if it exceeds the allowable bypass level, jump to step 4, otherwise, run step 3;

[0018] Step 3: The battery boost circuit operates normally, the BAT module bypass switch K1 is closed, the power unit AC H-bridge conversion circuit operates in the inverter / rectifier mode, and outputs a stable AC voltage. Continue to determine whether the battery pack voltage is less than or equal to the minimum allowable operating voltage of the battery cell, whether the battery pack SOC is less than or equal to the minimum allowable operating SOC of the battery cell, and whether the battery boost main circuit reports a fault. If one of the three conditions is met, jump to step 2, otherwise continue to step 3; while running step 3, if the superior has a scheduling instruction or the unit main circuit fails, jump to step 4, otherwise continue to step 3;

[0019] Step 4: The main controller blocks the switches in the unit AC H-bridge and the H-bridge switches in all BAT modules. All BAT modules and the unit AC H-bridge stop working. The unit bypass switch K2 is closed to enter the unit bypass state.

[0020] Furthermore, the current control method between BAT modules of the battery boost type high-voltage direct-mounted energy storage system unit includes: collecting the voltage value of the common DC bus capacitor, subtracting it from the reference voltage and inputting it into the PI loop, collecting the battery current Ibat in the BAT module, taking its sign and multiplying it with the output of the voltage PI loop as the negative input of the current loop, calculating the root mean square value of Ibat as another negative input of the current loop, and summing the two negative inputs with the given value of the battery current and sending them to the PI link output fs as the final modulation signal, which drives the H-bridge switch tube of the battery boost circuit after modulation.

[0021] Furthermore, the grid-connected control method of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the three-phase voltages ea, eb, and ec for phase locking and positive and negative sequence separation to obtain the positive sequence voltage e+, negative sequence voltage e-, positive sequence angle θ+, and negative sequence angle θ-; the three-phase currents ia, ib, and ic are subjected to PACK transformation to obtain the feedback Id+, Iq+, Id-, and Iq-, and then the positive and negative sequence are decoupled and controlled respectively, and the output modulation signal is obtained by the inverse pack transformation, and the inter-phase and intra-phase SOC balance control output signals are superimposed with the current inner loop output modulation signal to realize the SOC balance control of the system inter-phase and intra-phase energy storage elements.

[0022] Furthermore, the SOC balancing control method between BAT modules of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the battery state of charge of each BAT module of the unit, performing mean calculation to obtain the average state of charge of each BAT module of the unit, subtracting the state of charge of each BAT module from the average state of charge, and obtaining the correction amount of the charging and discharging current of each BAT module through a balancing coefficient, which is passed to the target optimization calculation module to obtain the battery current given value of each BAT module.

[0023] Furthermore, the SOC balancing control method within each phase of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the state of charge of all unit battery modules of the u phase, v phase, and w phase, performing average calculation to obtain the average state of charge of the u, v, and w phases, respectively, subtracting the SOC of each unit battery module of the u, v, and w phases from the average SOC of each phase, and finally calculating the balancing voltage to be injected into each unit according to the three-phase current and the grid angle; the three-phase inter-phase SOC balancing control method of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the SOC of all batteries in the u, v, and w phases to obtain the average state of charge SOCu, SOCv, and SOCw of the u, v, and w phases, and then obtaining the average state of charge SOCd of the three-phase chain converter energy storage system through average calculation, subtracting SOCu, SOCv, and SOCw from SOCd and injecting them into the phase of the zero-sequence voltage, and obtaining the three-phase zero-sequence voltage to be injected through a phase-to-phase balancing coefficient and a limiting module.

[0024] In summary, the present invention has the following advantages:

[0025] 1. The battery boost type high voltage direct hanging energy storage system provided by the present invention can boost the battery pack to a high voltage by connecting fewer cells in series, and then achieve greater power and capacity by connecting the battery boost modules in parallel. This solution not only does not require high consistency of the cells, but also can realize status detection and management of a single cell;

[0026] 2. The bypass control method of the battery boost type high voltage direct-mounted energy storage system provided by the present invention can detect a system fault or a superior dispatching instruction, and within the allowable bypass level range, the battery boost controller or the main controller can issue an instruction to disconnect the power electronic switch tube, and at the same time, the bypass controller issues an instruction to control the bypass switches K11~K1n to be disconnected or K2 to be closed, so that the faulty module is cut out of the power circuit, and bypass protection at the battery module level and unit level can be realized. This process can be controlled at the us level to ensure the continuous stability of the output voltage, will not affect the operation of other modules, and can improve the system reliability;

[0027] 3. The charge state balancing control method between phases, within phases, and at the BAT module level provided by the present invention realizes active charge state balancing control between phases, within phases, and between battery packs (BAT modules) through closed-loop charge state control at different levels and a software control algorithm, without the need for additional hardware loops. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the topological structure of a battery boost type high voltage direct-mounted energy storage converter system;

[0029] Figure 2 It is a structural schematic diagram of a battery boost type high voltage direct-mounted energy storage conversion system with a triangle connection between the three phases.

[0030] Figure 3 It is the topology and control structure diagram of the battery boost circuit system.

[0031] Figure 4 It is the topology and control structure diagram of the power unit.

[0032] Figure 5 It is a diagram of the unit-level and BAT module-level bypass control strategy for a battery boost-type high-voltage direct-mounted energy storage system.

[0033] Figure 6 It is a grid-connected control block diagram of a battery boost type high voltage direct-mounted energy storage system.

[0034] Figure 7 It is a block diagram of SOC balancing control between BAT modules of a battery boost type high voltage direct-mounted energy storage system unit.

[0035] Figure 8 It is a block diagram of SOC balancing control within each phase of a battery boost type high voltage direct-mounted energy storage system.

[0036] Fig. 9 It is a block diagram of the three-phase interphase SOC balancing control of a battery boost type high voltage direct-mounted energy storage system.

[0037] Fig.10 It is a schematic diagram of the SOC balancing control results between unit BAT modules.

[0038] Fig.11 It is a schematic diagram of the SOC balancing control results within each phase.

[0039] Fig.12 It is a schematic diagram of the three-phase interphase SOC balancing control results. DETAILED DESCRIPTION

[0040] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments and drawings. It should be understood by those skilled in the art that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0041] Example 1

[0042] The battery boost type high voltage direct hanging energy storage conversion system of the present invention is as follows Figure 1 As shown, it includes phase A, phase B, and phase C. Each phase is composed of multiple power units in series. Each power unit is composed of an AC output H-bridge conversion circuit, a DC bus capacitor, and multiple BAT modules in parallel. A BAT module includes a battery pack and a battery boost circuit.

[0043] like Figure 3The topological structure diagram of the battery boost circuit system shown in FIG. 1 shows a battery boost circuit including a filter capacitor Cbat, two H bridges, a transformer, resonant inductors Lr1, Lr2, Lm, resonant capacitors Cr1, Cr2, and a bypass switch K1. The filter capacitor Cbat is connected across the battery pack to filter out high-frequency ripple current. The H bridge on the primary side of the transformer is composed of switches S1, S2, S3, and S4. Switches S1 and S2 form a bridge arm, and the midpoint of the bridge arm is connected to the resonant inductor Lr1. Switches S3 and S4 form a bridge arm, and the midpoint of the bridge arm is connected to the resonant capacitor Cr1. Lm is the transformer reactance. The transformer ratio is 1:N, which is responsible for boosting during discharge and reducing voltage during charging. The H bridge on the secondary side of the transformer is composed of switches S5, S6, S7, and S8. Switches S5 and S6 form a bridge arm, and the midpoint of the bridge arm is connected to the resonant inductor Lr2. Switches S7 and S8 form a bridge arm, and the midpoint of the bridge arm is connected to the resonant capacitor Cr2.

[0044] like Figure 4 The topological structure diagram of the power unit shown in FIG. 1 shows that the power unit includes multiple BAT modules, an AC H-bridge conversion circuit, a DC bus capacitor Cdc, and bypass switches K11~K1n and K2. The BAT modules are connected in parallel on the DC capacitor side, and the bypass switches K11~K1n are connected to the positive pole of each BAT module; the AC H-bridge conversion circuit is composed of switches T1, T2, T3, and T4. Switches T1 and T2 form a bridge arm, switches T3 and T4 form a bridge arm, and the bypass switch K2 is connected between the two bridge arms.

[0045] The midpoints of the bridge arms of switches T1 and T2 of the first-stage power modules of phases A, B and C are respectively connected to the filter inductors La, Lb and Lc on the main circuit, and the inductors La, Lb and Lc are then connected to phases A, B and C of the power grid; the midpoints of the bridge arms of switches T3 and T4 of the first-stage power modules of phases A, B and C are connected to the midpoints of the bridge arms of switches T1 and T2 of the second-stage power modules, thus connecting end to end, and the midpoints of the bridge arms of switches T3 and T4 of the last stage of phases A, B and C are connected to each other to form a star connection.

[0046] In addition, in practical applications, the three-phase circuits can also be connected in a triangle, such as Figure 2As shown. The AC output H-bridge conversion circuit includes switches T1, T2, T3, and T4; the midpoints of the bridge arms of switches T1 and T2 in the first-stage power modules of phase A, phase B, and phase C are respectively connected to the filter inductors La, Lb, and Lc on the main circuit, and the inductors La, Lb, and Lc are then connected to the A phase, B phase, and C phase of the power grid; the midpoints of the bridge arms of switches T3 and T4 in the first-stage power modules of phase A, phase B, and phase C are connected to the midpoints of the bridge arms of switches T1 and T2 in the H-bridge conversion circuit in the second-stage power module, so as to be connected end to end; the midpoints of the bridge arms of switches T3 and T4 in the H-bridge conversion circuit in the last-stage power module of phase A are connected to the B phase of the AC power grid, the midpoints of the bridge arms of switches T3 and T4 in the last-stage power module of phase B are connected to the C phase of the power grid, and the midpoints of the bridge arms of switches T3 and T4 in the last-stage power module of phase C are connected to the A phase of the power grid, forming a triangle connection.

[0047] like Figure 3 As shown in the control structure diagram of the battery boost circuit system, the battery boost controller uses a high-speed and stable FPGA as the control chip to achieve high-frequency control of the battery boost circuit. The battery boost controller contains a variety of external interfaces and has powerful computing capabilities. By collecting the battery status such as SOC, voltage, temperature, battery current Ibat, module output current Iout, bridge arm voltage U1, bridge arm voltage U2, transformer primary side current I1 and transformer secondary side current I2 of each battery cell, closed-loop control is performed according to the charge and discharge operation mode and combined with the current reference value of the SOC balance control output between the unit BAT modules, and the drive signal of the output switch tube S1~S8 is controlled to the isolation drive module, and finally the drive signal PWMn and PWMz (including dead time) are output through the isolation drive module. The battery boost controller also communicates with the main controller, and the communication content includes fault information, battery information, etc.

[0048] The control structure diagram of the power unit is as follows: Figure 4As shown, the main controller control chip includes ARM, FPGA, and 3568, among which ARM is responsible for control algorithms, data processing, etc., FPGA is responsible for wave management and data transmission, and 3568 is responsible for communication and data transmission. By collecting the voltage Vdc and current Idc of the common DC capacitor, the voltage Unb and current Inb of the inverter output, the relevant information transmitted by the battery boost controller, and the battery information transmitted by the BMS, combined with different operating instructions given by the host computer or the upper scheduling, such as constant voltage, constant current, constant power, high and low wear and other working modes, closed-loop control is performed and the SOC balanced control output is superimposed on the modulation information of each phase and each unit. The final modulation signal is modulated by phase-shift PWM, and the drive signal PWMb (including dead time) of the output switch tube T1~T4 is isolated through the driver board. The main controller determines whether the bypass requirement is met based on the collected battery pack fault information, battery boost circuit fault information and unit fault information. If bypass is required, it will send a command to the bypass controller. After receiving the command, the bypass controller controls the corresponding bypass switch (K11, ..., k1n, K2) to realize the bypass function. BMS-1 ​​also communicates with the external EMS to transmit the battery status and various information to the upper-level energy management system to facilitate energy scheduling.

[0049] The switch tubes S1~S8 and T1~T4 can be IGBT, MOSFET, SiC, etc., and can be a single tube or multiple tubes connected in parallel to form a switch group. Switches K1 and K2 include but are not limited to contactors, circuit breakers, power electronic switches, etc.

[0050] Example 2

[0051] Based on the battery boost type high voltage direct-mounted energy storage converter system described in Example 1, this embodiment also proposes a unit-level and BAT module-level bypass control method for the battery boost type high voltage direct-mounted energy storage system, such as Figure 5 As shown, the specific steps are as follows:

[0052] Step 1: The main controller detects whether the battery pack voltage Ubattery is less than or equal to UL (the minimum allowable operating voltage of the battery cell), whether the battery pack state of charge (SOC) is less than or equal to SOCL (the minimum allowable operating SOC of the battery cell), and whether the battery boost main circuit reports a fault. If one of the three conditions is met, jump to step 2, otherwise jump to step 3;

[0053] Step 2: Lock the switch S1~S8 drive of the battery boost circuit, all switches S1~S8 are turned off, one of the bypass switches K11~K1n is turned off, and a BAT module is bypassed. If multiple BAT modules need to be bypassed, turn off the corresponding bypass switch. The main control determines whether the battery bypass level exceeds the set threshold. If it exceeds the allowable bypass level, jump to step 4, otherwise, run step 3.

[0054] Step 3: The battery boost circuit operates normally, the BAT module bypass switch is closed, the power unit AC H-bridge conversion circuit operates in the inverter / rectifier mode, and outputs a stable AC voltage. Continue to determine whether the battery pack voltage Ubattery is less than or equal to UL (the minimum allowable operating voltage of the battery cell), whether the battery pack SOC is less than or equal to SOCL (the minimum allowable operating SOC of the battery cell), and whether the battery boost main circuit reports a fault. If one of the three conditions is met, jump to step 2, otherwise continue to step 3; while running step 3, if the superior has a scheduling instruction or the unit main circuit fails, jump to step 4, otherwise continue to step 3.

[0055] Step 4: The controller blocks switches T1~T4 and the H-bridge switches in all BAT modules, all BAT modules and unit AC H-bridges stop working, and closes the unit bypass switch K2 to enter the unit bypass state.

[0056] The current control between the BAT modules of the battery boost type high voltage direct-mounted energy storage system unit is as follows: the voltage value Vdc of the common DC bus capacitor Cdc is collected, subtracted from the reference voltage Vdc*, and then input into the PI loop. The battery current Ibat in the BAT module is collected, its sign is taken and multiplied with the output of the voltage PI loop as the negative input of the current loop, and the root mean square value of Ibat is calculated as another negative input of the current loop. The two negative inputs are summed with the given value of the battery current and sent to the PI link output fs as the final modulation signal, which drives the H-bridge switch tube of the battery boost circuit after modulation.

[0057] The grid-connected control method of battery boost type high voltage direct-mounted energy storage system is as follows Figure 6 As shown, idref* and iqref* are the d-axis and q-axis current reference values ​​output by the outer loop control, idref*- and iqref*- are the negative-sequence reference values, and the voltages ea, eb, and ec are collected for phase locking and positive- and negative-sequence separation to obtain the positive-sequence voltage e+, negative-sequence voltage e-, positive-sequence angle θ+, and negative-sequence angle θ-. The three-phase currents ia, ib, and ic are transformed by PACK to obtain the feedback Id+, Iq+, Id-, and Iq-, and then the positive and negative sequence decoupling control is performed respectively. The control obtains the output modulation signal through the inverse pack transformation, and the inter-phase and intra-phase SOC balance control output signals are superimposed on the current inner loop output modulation signal to realize the SOC balance control of the system inter-phase and intra-phase energy storage elements.

[0058] Battery boost type high voltage direct hanging energy storage system unit BAT module SOC balance control Figure 7As shown: By collecting the battery state of charge SOCj of each BAT module of the unit, the average state of charge SOCbat of each BAT module of the unit is obtained by average calculation, and the state of charge of each BAT module is subtracted from the average state of charge. After a balancing coefficient kp is used to obtain the correction amount DIbatj of the charging and discharging current of each BAT module, it is passed to a target optimization calculation module (taking into account the battery pack temperature, SOC, impedance, etc.) to obtain the battery current given value Ibat* of each BAT module.

[0059] The SOC balancing control in each phase of the battery boost type high voltage direct-mounted energy storage system is as follows Figure 8 As shown: by collecting the state of charge SOCdui of all unit battery modules of phase u, the state of charge SOCdvi of all battery modules of phase v, and the state of charge SOCdwi of all batteries of phase w, the average value SOCu of the state of charge of phase u, the average value SOCv of the state of charge of phase v, and the average value SOCw of the state of charge of phase w are obtained respectively, and the SOC of each unit battery module of phase u, v, and w is subtracted from the average value of the SOC of each phase respectively. Finally, the balancing voltage DVuli, DVvli, and DVwli that needs to be injected into each unit are calculated according to the three-phase current and the grid angle.

[0060] Battery boost type high voltage direct hanging energy storage system three-phase interphase SOC balancing control Fig. 9 As shown: By collecting the SOC of all batteries in phases u, v, and w, the average state of charge SOCu, SOCv, and SOCw of phases u, v, and w are calculated, and then the average state of charge SOCd of the three-phase chain converter energy storage system is calculated. SOCu, SOCv, and SOCw are injected into the phase of the zero-sequence voltage after subtracting them from SOCd respectively, and the three-phase zero-sequence voltages DVup, DVvp, and DVwp that need to be injected are obtained through a phase-to-phase balancing coefficient and a limiting module.

[0061] The simulation diagram of battery SOC balancing results of battery boost type high voltage direct hanging energy storage system is as follows Figures 10-12 The simulation parameters are set as 3 BAT modules per unit and three units per phase.

[0062] Fig.10 It is a schematic diagram of the SOC balancing control results between unit BAT modules. It can be seen from the figure that the initial SOCs of the three modules BAT1, BAT2 and BAT3 are different. Under the SOC balancing control between unit BAT modules, the SOCs of the three module battery packs gradually tend to be the same, which verifies the effectiveness of the SOC balancing control between unit BAT modules.

[0063] Fig.11It is a schematic diagram of the SOC balancing control results within each phase. It can be seen from the figure that the initial SOCs of the three units U1, U2, and U3 of phase U are different. Under the action of the intra-phase SOC balancing control, the SOCs of the three unit battery packs gradually tend to be the same, verifying the effectiveness of the intra-phase SOC balancing control.

[0064] Fig.12 It is a schematic diagram of the three-phase interphase SOC balancing control results. It can be seen from the figure that the initial SOCs of the three units of U phase, V phase and W phase are different. Under the action of the three-phase interphase SOC balancing control, the SOCs of the three-phase battery pack gradually tend to be the same, which verifies the effectiveness of the three-phase interphase SOC balancing control.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A control method for a battery boost type high voltage direct-mounted energy storage converter system, characterized in that: The battery boost type high voltage direct-mounted energy storage conversion system includes phase A, phase B, and phase C. Each phase is composed of multiple power units connected in series. Each power unit is the same and includes an AC output H-bridge conversion circuit, a DC bus capacitor, multiple BAT modules and a bypass switch. The BAT module is connected in parallel on the DC capacitor side. The positive pole of each BAT module is connected to a bypass switch K1. A bypass switch K2 is connected across the two bridge arms of each AC H-bridge conversion circuit. A BAT module includes a battery pack and a battery boost circuit. The unit-level and BAT module-level bypass control process of the battery boost high-voltage direct-mounted energy storage system includes: Step 1: The main controller detects whether the battery pack voltage is less than or equal to the minimum allowable operating voltage of the battery cell, whether the battery pack SOC is less than or equal to the minimum allowable operating SOC of the battery cell, and whether the battery boost main circuit reports a fault. If one of the three conditions is met, jump to step 2, otherwise jump to step 3; Step 2, lock the switch drive of the battery boost circuit, disconnect all the switches of the H bridge in the battery boost circuit, disconnect one of the bypass switches K1, so that the corresponding BAT module is bypassed; if multiple BAT modules need to be bypassed, disconnect the corresponding bypass switches; the main controller determines whether the battery bypass level exceeds the set threshold, if it exceeds the allowable bypass level, jump to step 4, otherwise, run step 3; Step 3: The battery boost circuit operates normally, the BAT module bypass switch K1 is closed, the power unit AC H-bridge conversion circuit operates in the inverter / rectifier mode, and outputs a stable AC voltage. Continue to determine whether the battery pack voltage is less than or equal to the minimum allowable operating voltage of the battery cell, whether the battery pack SOC is less than or equal to the minimum allowable operating SOC of the battery cell, and whether the battery boost main circuit reports a fault. If one of the three conditions is met, jump to step 2, otherwise continue to step 3; while running step 3, if the superior has a scheduling instruction or the unit main circuit fails, jump to step 4, otherwise continue to step 3; Step 4: The main controller blocks the switches in the unit AC H-bridge and the H-bridge switches in all BAT modules. All BAT modules and the unit AC H-bridge stop working. The unit bypass switch K2 is closed to enter the unit bypass state.

2. The control method of the battery boost type high voltage direct-mounted energy storage converter system according to claim 1 is characterized in that: Each AC output H-bridge conversion circuit includes switches T1, T2, T3, and T4. Switches T1 and T2 form a bridge arm, and switches T3 and T4 form a bridge arm. The three-phase circuits of phase A, phase B, and phase C are connected in star connection or triangle connection. When the star connection is adopted, the midpoints of the bridge arms of switches T1 and T2 in the first-stage power module are respectively connected to the filter inductors La, Lb, and Lc on the main circuit, and the inductors La, Lb, and Lc are then connected to the A phase, B phase, and C phase of the power grid. The midpoints of the bridge arms of switches T3 and T4 in the first-stage power module are connected to the switches T1 and T2 bridge arms of the H-bridge conversion circuit in the second-stage power module. The midpoints of the arms of the switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase A, phase B and phase C are connected end to end; the midpoints of the arms of the switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase A are connected to phase B of the AC power grid, the midpoints of the arms of the switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase B are connected to phase C of the power grid, and the midpoints of the arms of the switches T3 and T4 of the H-bridge conversion circuit in the last power module of phase C are connected to phase A of the power grid.

3. The control method of the battery boost type high voltage direct-mounted energy storage conversion system according to claim 1 is characterized in that: The battery boost circuit includes a filter capacitor, two H-bridge conversion circuits, a transformer, resonant inductors Lr1, Lr2, Lm, and resonant capacitors Cr1 and Cr2; the filter capacitor is connected across the battery pack, the primary side H-bridge of the transformer includes switches S1, S2, S3, and S4, the midpoint of the bridge arm formed by switches S1 and S2 is connected to the resonant inductor Lr1, the midpoint of the bridge arm formed by switches S3 and S4 is connected to the resonant capacitor Cr1, and the resonant inductor Lm is the transformer reactance; the transformer ratio is 1:N, the secondary side H-bridge of the transformer includes switches S5, S6, S7, and S8, the midpoint of the bridge arm formed by switches S5 and S6 is connected to the resonant inductor Lr2, and the midpoint of the bridge arm formed by switches S7 and S8 is connected to the resonant capacitor Cr2.

4. The control method of the battery boost type high voltage direct-mounted energy storage conversion system according to claim 3 is characterized in that: The battery boost circuit is connected to a battery boost controller, which is used to collect the battery status of each battery cell, the battery current, the module output current, the bridge arm voltages on both sides of the transformer, and the primary and secondary currents of the transformer, and perform closed-loop control according to the current reference value output by the SOC balancing control between the BAT modules of the charge and discharge operation mode, control the output of the driving signal of the H-bridge switch tube in the battery boost circuit to the isolation drive module, and finally output the driving signal through the isolation drive module.

5. The control method of the battery boost type high voltage direct-mounted energy storage converter system according to claim 2 is characterized in that: The power module is connected to the main controller, which is used to collect the voltage and current of the common DC capacitor, the voltage and current of the inverter output, the relevant information transmitted by the battery boost controller, and the battery information transmitted by the battery management system BMS, and then combined with different operating instructions given by the host computer or the upper dispatcher, to perform closed-loop control and superimpose the SOC balanced control output on the modulation information of each phase and each unit. The final modulation signal is modulated by phase-shift PWM, and the drive signal of the switch tube in the AC H bridge of the output unit is isolated through the drive board. It is also used to determine whether the bypass requirements are met based on the collected battery pack fault information, battery boost circuit fault information and unit fault information, and control the corresponding BAT module bypass switch K1 to act through the bypass controller to realize the BAT module bypass function, and control the control unit bypass switch K2 to act to realize the unit bypass function.

6. The control method of the battery boost type high voltage direct-mounted energy storage converter system according to claim 1, characterized in that: The current control method between BAT modules of a battery boost type high voltage direct-mounted energy storage system unit includes: collecting the voltage value of the common DC bus capacitor, subtracting it from the reference voltage and inputting it into the PI loop, collecting the battery current Ibat in the BAT module, taking its sign and multiplying it with the output of the voltage PI loop as the negative input of the current loop, calculating the root mean square value of Ibat as another negative input of the current loop, summing the two negative inputs with the given value of the battery current and sending them to the PI link output fs as the final modulation signal, which drives the H-bridge switch tube of the battery boost circuit after modulation.

7. The control method of the battery boost type high voltage direct-mounted energy storage converter system according to claim 1, characterized in that: The grid-connected control method of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the three-phase voltages ea, eb, and ec for phase locking and positive and negative sequence separation to obtain the positive sequence voltage e+, negative sequence voltage e-, positive sequence angle θ+, and negative sequence angle θ-; the three-phase currents ia, ib, and ic are subjected to PACK transformation to obtain the feedback Id+, Iq+, Id-, and Iq-, and then the positive and negative sequence are decoupled and controlled respectively, and the output modulation signal is obtained by the inverse pack transformation, and the inter-phase and intra-phase SOC balance control output signals are superimposed with the current inner loop output modulation signal to realize the SOC balance control of the system inter-phase and intra-phase energy storage elements.

8. The control method of the battery boost type high voltage direct-mounted energy storage converter system according to claim 1, characterized in that: The SOC balancing control method between BAT modules of a battery boost type high voltage direct-mounted energy storage system includes: collecting the battery state of charge of each BAT module of the unit, performing mean calculation to obtain the average state of charge of each BAT module of the unit, subtracting the state of charge of each BAT module from the average state of charge, and obtaining a correction amount of the charge and discharge current of each BAT module through a balancing coefficient, which is then transmitted to a target optimization calculation module to obtain a given value of the battery current of each BAT module.

9. The control method of the battery boost type high voltage direct-mounted energy storage converter system according to claim 1, characterized in that: The SOC balancing control method within each phase of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the state of charge of all unit battery modules of the u phase, v phase, and w phase, performing average calculation to obtain the average state of charge of the u, v, and w phases, respectively, subtracting the SOC of each unit battery module of the u, v, and w phases from the average SOC of each phase, and finally calculating the balancing voltage to be injected into each unit according to the three-phase current and the grid angle; the three-phase interphase SOC balancing control method of the battery boost type high-voltage direct-mounted energy storage system includes: collecting the SOC of all batteries in the u, v, and w phases to calculate the average state of charge SOCu, SOCv, and SOCw of the u, v, and w phases, and then calculating the average state of charge SOCd of the three-phase chain converter energy storage system by average calculation, subtracting SOCu, SOCv, and SOCw from SOCd and injecting them into the phase of the zero-sequence voltage, and obtaining the three-phase zero-sequence voltage to be injected through an interphase balancing coefficient and a limiting module.

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