Control circuit of an energy storage system and energy storage system

Abstract

A control circuit of an energy storage system, characterized in that it comprises: a cell module (10), a control module (20), and a commutation module (30); wherein the cell module (10), the control module (20), and the commutation module (30) are sequentially connected to one another; wherein the cell module (10) comprises n modularized cell control units (11); each modularized cell control unit (11) comprises a cell, a first switch, and a second switch; the cell and the first switch are connected in series, and the cell connected in series and the first switch are connected in parallel with the second switch; the n is a positive integer;wherein the first switch of a first cell control unit (11) of the n modularized cell control units (11) and the second switch of the first cell control unit (11) of the n modularized cell control units (11) are connected to each other to serve as the first end of the cell module (10); the first switch of an nth cell control unit (11) of the n modularized cell control units (11) and the second switch of the nth cell control unit (11) of the n modularized cell control units (11) are connected to each other to serve as the second end of the cell module (10); the commutation module (30) comprises a first commutation switch (Kb), a second commutation switch (Kc), a third commutation switch (Kd), a fourth commutation switch (Ke), and a filter unit (31); the filter unit (31) comprises a first end, a second end, and a third end;the first end of the cell module (10) is connected to a first end of the first commutation switch (Kb) and a first end of the third commutation switch (Kd); a second end of the first commutation switch (Kb) is connected to the first end of the filter unit (31); a second end of the third commutation switch (Kd) is connected to the third end of the filter unit (31); the second end of the cell module (10) is connected to a first end of the second commutation switch (Kc) and a first end of the fourth commutation switch (Ke); the second commutation switch (Kc) is connected to the first end of the filter unit (31); a second end of the fourth commutation switch (Ke) is connected to the third end of the filter unit (31); an AC network is connected between the second end of the filter unit (31) and the third end of the filter unit (31);wherein the control module (20) is communicatively connected to the modularized cell control units (11) and the commutation module (30); the control module (20) is configured to control the first commutation switch (Kb), the second commutation switch (Kc), the third commutation switch (Kd), and the fourth commutation switch (Ke) so that they are switched on or off.

Description

Technical FieldThe present application relates to the technical field of power supply circuits, particularly a control circuit of an energy storage system and an energy storage system.Prior ArtIn the related technology, the lithium battery energy storage system is mainly composed of the battery system and the power conversion system (PCS). PCS mainly realizes the mutual conversion between the DC battery voltage and the AC grid voltage by power electronic technology. PCS can control the charging and discharging of the battery system and can convert AC and DC current and can directly power AC loads when no grid is present. The battery system is composed of 15s or 16s cells connected in series to modules, and then the modules are connected in series to packs, and then a plurality of packs are connected in series to battery clusters until they are arrayed to a required high voltage and then interact with the AC power supply via the PCS for power exchange. There is a slave control unit of the battery management system (BMS) in the battery module or pack and a master control unit of the BMS in the battery cluster to manage the battery system.However, as the capacity and size of the cells become larger and larger, the individual cells are large and heavy, and when they are then connected in series to form modules, the modules become large and weigh several hundred pounds, making assembly and operation difficult. Moreover, due to the high cost for BMS and PCS, there is a disadvantage that the PCS volume is large, the cost for the power storage system is high, and the new and old batteries cannot be mixed.Content of the Present ApplicationThe present application provides a control circuit of an energy storage system and an energy storage system, with which the size of a PCS can be reduced, the cost can be lowered, the utilization efficiency of the energy storage system can be improved, and the yield can be increased.In a first aspect, the present disclosure provides a control circuit of an energy storage system, comprising: a cell module, a control module, and a commutation module; wherein the cell module, the control module, and the commutation module are sequentially connected to each other;wherein the cell module comprises n modularized cell control units; each modularized cell control unit comprises a cell, a first switch, and a second switch; the cell and the first switch are connected in series with each other, and the series-connected cell and the first switch are connected in parallel with the second switch; the n is a positive integer;wherein the first switch of a first cell control unit of the n modularized cell control units and the second switch of the first cell control unit of the n modularized cell control units are connected to each other to serve as a first end of the cell module; the first switch of an n-th cell control unit of the n modularized cell control units and the second switch of the n-th cell control unit of the n modularized cell control units are connected to each other to serve as a second end of the cell module;the commutation module comprises a first commutation switch, a second commutation switch, a third commutation switch, a fourth commutation switch, and a filter unit; the filter unit comprises a first end, a second end, and a third end; the first end of the cell module is connected to a first end of the first commutation switch and a first end of the third commutation switch; a second end of the first commutation switch is connected to the first end of the filter unit; a second end of the third commutation switch is connected to the third end of the filter unit; the second end of the cell module is connected to a first end of the second commutation switch and a first end of the fourth commutation switch; the second commutation switch is connected to the first end of the filter unit; a second end of the fourth commutation switch is connected to the third end of the filter unit; an AC power network connected between the second end of the filter unit and the third end of the filter unit;wherein the control module is communicatively connected to the modularized cell control units and the commutation module; the control module is configured to control the first commutation switch, the second commutation switch, the third commutation switch, and the fourth commutation switch to be turned on or off.In a second aspect, the present disclosure provides a control method of an energy storage system, comprising:detecting an AC mains voltage;calculating a phase angle between the AC grid voltage and a circuit voltage based on the AC grid voltage and a voltage of a series circuit of cells;determining an operating mode of the energy storage system; wherein the operating mode comprises a discharging mode and a charging mode;performing a close cut operation by a control module following a first preset control strategy in response to the energy storage system being in the charging mode and the phase angle between the AC grid voltage and the circuit voltage satisfying a preset condition; andperforming the close-cut operation by the control module by following a second preset control strategy in response to the energy storage system being in the discharging mode and the phase angle between the AC grid voltage and the circuit voltage satisfying the preset condition.In a third aspect, the present disclosure provides an energy storage system comprising: n-stage, series-connected, modularized cell control units; wherein each modular cell control unit comprises an external terminal end, a cell, a temperature sensing circuit, a cell microcontroller module, a cell voltage sensing circuit, a communication circuit, and a switch switching module; the n is a positive integer; wherein the cell is electrically connected to the external terminal end via the switch switching module; the switch switching module is configured to control whether the cell is connected to the energy storage system; wherein the temperature sensing circuit is electrically connected to the cell microcontroller module; the temperature sensing circuit is configured to sense a temperature of the cell and transmit the temperature to the cell microcontroller module; wherein the cell voltage sensing circuit is connected in series between the cell and the cell micro-control module; the cell voltage sensing circuit is configured to sense a voltage of the cell and transmit the voltage to the cell micro-control module; wherein the communication circuit is communicatively connected to the cell micro-control module; the communication circuit is configured to perform an information interaction between the modularized cell control unit and a master control unit; wherein the cell micro-control module is remotely electrically connected to the switch switching module; the cell micro-control module is configured to control the switch switching module based on the temperature, the voltage, and / or the information interaction with the master control unit.Positive effect:In the present disclosure, the control circuit and the cell are integrated into one module to form the energy storage system. The product can be modularized and standardized, so that assembly and wiring can be easily performed. The energy storage system may be formed by omitting a separate BMS and a separate PCS, therefore the energy storage system may be small and have relatively low overall cost. A bus capacitor in the conventional PCS is omitted, so that the size is reduced. A filter does not need to be large unlike the conventional PCS, thereby further reducing cost and size. The control circuit may bypass a defective cell without interfering with normal operation of the energy storage system, thereby improving load on the energy storage system and increasing yield. Since a high voltage cell is used first in discharging and a low voltage cell is used first in charging, an additional BMS for controlling the cells is not required, therefore, the cost for the BMS can be reduced. The cell may be connected in series in the system circuit based on a particular algorithm, and new cells and original cells may be used in combination, such that the usage rate of the energy storage system is improved and yield is increased.In the present disclosure, the unitized cell control unit is arranged. The temperature sensing circuit is configured to sense the temperature of the cell, and the cell voltage sensing circuit is configured to sense the voltage of the cell. The temperature and voltage are then sent to the cell microcontroller module. The cell microcontroller transmits the temperature and voltage to the master controller via the communication circuit. The master control unit sends commands to the cell microcontroller module based on the information of the individual modules. The cell microcontroller controls the switch switching module to control the cell to connect to or disconnect from the energy storage system based on the commands. In the present embodiment, the control unit of the cell can be modularized to form the power storage system without the need to arrange a battery management system or a PCS. Therefore, the assembly can be easily performed and the cost can be reduced. Therefore, the present disclosure solves the technical problem that the PCS is large, the cost of the energy storage system is high, and the new cell cannot be used in combination with the original cells.BRIEF DESCRIPTION OF THE DRAWINGFIG. 1 is a circuit diagram of a control circuit of an energy storage system according to some embodiments of the present disclosure. FIG. 2 is another circuit diagram of a control circuit of an energy storage system according to some embodiments of the present disclosure. FIG. 3 is a flowchart of conversion between an alternating current and a direct current according to some embodiments of the present disclosure. FIG. 4 is a flow diagram of an algorithm for closing and cutting cells according to some embodiments of the present disclosure. FIG. 5 is a schematic view of a voltage waveform according to some embodiments of the present disclosure. FIG. 6 is a waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 7 is another waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 8 is another waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 9 is another waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 10 is a topological diagram of a three-phase energy storage system in accordance with some embodiments of the present disclosure. FIG. 11 is waveforms of voltages of the three-phase power storage system according to some embodiments of the present disclosure. FIG. 12 is a schematic structural view of a modularized cell control unit according to some embodiments of the present disclosure. FIG. 13 is a circuit diagram of the modularized cell control unit according to some embodiments of the present disclosure. FIG. 14 is a flowchart of a control method of the energy storage system according to some embodiments of the present disclosure. FIG. 15 is a schematic structural view of an energy storage system according to some embodiments of the present disclosure. FIG. 16 is a schematic structural view of another energy storage system according to some embodiments of the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTSFIG. 1 is a circuit diagram of a control circuit of an energy storage system according to some embodiments of the present disclosure. As shown in FIG. 1, the present embodiment provides a control circuit of an energy storage system. The control circuit of the energy storage system includes: a cell module 10, a control module 20, and a commutation module 30. the cell module 10, the control module 20, and the commutation module 30 are sequentially connected to each other. The cell module 10 includes n modularized cell control units 11. Each modularized cell control unit 11 includes a cell, a first switch, and a second switch. The cell and the first switch are connected in series with each other, and the series-connected cell and the first switch are connected in parallel with the second switch. The n is a positive integer; wherein the first switch (i.e., first first switch) of a first cell control unit 11 of the n modularized cell control units 11 and the second switch (i.e., first second switch) of the first cell control unit 11 of the n modularized cell control units 11 are connected to each other to serve as a first end of the cell module 10; the first switch (i.e., n-th first switch) of an n-th cell control unit 11 of the n modularized cell control units 11 and the second switch (i.e., n-th second switch) of the n-th cell control unit 11 of the n modularized cell control units 11 are connected to each other to serve as a second end of the cell module 10. Commutation module 30 includes a first commutation switch Kb, a second commutation switch Kc, a third commutation switch Kd, a fourth commutation switch Ke, and a filter unit 31. Filter unit 31 includes a first end 311, a second end 312, and a third end 313. The first end of the cell module 10 is connected to a first end of the first commutation switch Kb and a first end of the third commutation switch Kd. A second end of the first commutation switch Kb is connected to the first end 311 of the filter unit 31. A second end of the third commutation switch Kd is connected to the third end 313 of the filter unit 31. The second end of the cell module 10 is connected to a first end of the second commutation switch Kc and a first end of the fourth commutation switch Ke. The second commutation switch Kc is connected to the first end 311 of the filter unit 31. A second end of the fourth commutation switch Ke is connected to the third end 313 of the filter unit 31. An alternating current network is connected between the second end 312 of the filter unit 31 and the third end 313 of the filter unit 31. The control module 20 is communicatively connected to the modularized cell control units 11 and the commutation module 30. The control module 20 is configured to control the first commutation switch Kb, the second commutation switch Kc, the third commutation switch Kd, and the fourth commutation switch Ke to be turned on or off.Specifically, the cell module 10 includes n unit modularized cells 11. The cell may be a module of any combination of cells. A B- of a modularized cell control unit 11 is connected to a B+ of a subsequent cell control unit 11, and a B+ of the modularized cell control unit 11 is connected to a B- of a previous cell control unit 11. A B+ of a cell control unit 11 at the starting end is connected to the commutation unit, and a B- of a cell control unit 11 at the terminating end is connected to the commutation module 30. When an energy storage system is formed and connected to the grid, the number of modularized cells is limited by the voltage of the grid. Taking a 230V network as an example, the number of modularized cells connected in series is: 230V×1.1×1.414 / 2.5V=144. Therefore, the 230V network system requires at least 144 modularized cell control units 11 that must be connected in series with each other.The control module 20 exchanges information with the modularized cell control units 11 via fiber optic communication. The control module 20 controls the first commutation switch Kb, the second commutation switch Kc, the third commutation switch Kd, and the fourth commutation switch Ke via an optical fiber to be turned on or off. A control module 20 may communicate with another control module 20 via the fiber optic. In some embodiments, the control module 20 may interact with external mobile devices such as cellular phones and computers via Bluetooth, 5G, or WIFI modules.The commutation module 30 includes a commutation control unit and the filter unit 31. The filter unit 31 is configured to smooth and filter a stepped wave of the cell. The commutation control unit may include four power switching transistors. The filter unit 31 may include an LC filter device. The filter unit 31 may be constituted by any combination of LC, LCL and other filter circuits according to requirements. FIG. 1 exemplarily shows that the filter unit 31 includes an inductor L and a capacitor C. The inductor L and the capacitor C form an AC output filter circuit to allow a smoother AC output voltage. The first commutation switch Kb, the second commutation switch Kc, the third commutation switch Kd, the fourth commutation switch Ke, the n first switches, and the n second switches are high-power switching devices of the same type. The high-power switching device can withstand high voltages and can be switched on and off by insulated driving. The high-power switching device may be, for example, a MOSFET, IGBT, SCR, SiC, or GaN.An operation principle of the energy storage system is as follows. The modularized cell control unit 11 detects a temperature and a voltage of the respective cell, and transmits the temperature and the voltage to an external control board via the optical fiber communication. The external control board sends commands to each modularized electric cell unit 11 via optical fiber communication, according to certain algorithms and based on the data collected from each cell and a state of the power network, so that the corresponding first switch K 1 and the second switch K 1 aare controlled to be turned on or off to determine whether or not the corresponding cell is connected in series in the power storage system.An operating principle of bypassing a failed cell is as follows. When a cell fails, the corresponding unitized cell control unit 11 turns off the first switch K 1 connected in series with the failed cell and turns on the second switch K 1 aconnected in parallel with the failed cell. In this way, the failed cell is bypassed and normal operation of the system is not impaired. In this case, the modularized cell control unit 11 quickly flashes an LED to inform the personnel that the corresponding cell has failed, and the failed cell can be replaced in time.In the present disclosure, the control circuit and the cell are integrated into one module to form the energy storage system. The product can be modularized and standardized, so that assembly and wiring can be easily performed. The energy storage system may be formed by omitting a separate BMS and a separate PCS, therefore the energy storage system may be small and have relatively low overall cost. A bus capacitor in the conventional PCS is omitted, so that the size is reduced. A filter does not need to be large unlike the conventional PCS, thereby further reducing cost and size. The control circuit may bypass a defective cell without interfering with normal operation of the energy storage system, thereby improving load on the energy storage system and increasing yield. Since a high voltage cell is used first in discharging and a low voltage cell is used first in charging, an additional BMS for controlling the cells is not required, therefore, the cost for the BMS can be reduced. The cell may be connected in series in the system circuit based on a particular algorithm, and new cells and original cells may be used in combination, such that the usage rate of the energy storage system is improved and yield is increased. Therefore, the present disclosure solves the technical problem that the PCS is large, the cost of the energy storage system is high, and the new cell cannot be used in combination with the original cells.FIG. 2 is another circuit diagram of a control circuit of an energy storage system according to some embodiments of the present disclosure. As shown in FIG. 2, the modularized cell control unit 11 further includes a cell sensing chip 111. The control module 20 further includes a main controller 21. The cell sensing chips 111 are configured to detect voltages and temperatures of the n cells and transmit the voltages and temperatures to the main controller 21. The main controller 21 is communicatively connected to the first commutation switch Kb, the second commutation switch Kc, the third commutation switch Kd, and the fourth commutation switch Ke. The main controller 21 is configured to analyze and calculate the received voltages and temperatures, and control the n first switches, the n second switches, the first commutation switch Kb, the second commutation switch Kc, the third commutation switch Kd, and the fourth commutation switch Ke to be turned on or off.Specifically, the cell sensing chip 111 may be a micro controller unit (MCU). The MCU is substantially configured to sense the voltage and temperature of the respective cell. The main controller 21 detects a total voltage of the cell module 10 to dynamically monitor the total voltage of the cell module 10. The main controller 21 generates a certain control timing according to the data of the total voltage to achieve conversion from AC to DC and conversion from DC to AC by controlling the switches that are turned on and off. The main controller 21 controls the n first switches and the n second switches to be turned on and off, and performs data analysis and algorithm calculation. The main controller 21 may be a single MCU, which may simplify the circuit structure and reduce the cost; or may include a plurality of MCUs, which may increase the data processing rate and improve the operation efficiency.Still referring to FIG. 2, the commutation module 30 further includes a voltage sensing unit 32 and a current sensing unit 33. a first end of the voltage sensing unit 32 is connected to an eleventh end of the main controller 21, and a second end of the voltage sensing unit 32 is connected to a tenth end of the main controller 21. A third end of the voltage sensing unit 32 is connected to the second end 312 of the filter unit 31, and a fourth end of the voltage sensing unit 32 is connected to the third end 313 of the filter unit 31. A first end of the current detection unit 33 is connected to a twelfth end 12 of the main controller 21. A second end of the current detection unit 33 is connected to the second end 312 of the filter unit 31.FIG. 3 is a flowchart of conversion between an alternating current and a direct current according to some embodiments of the present disclosure. As shown in FIG. 3, an operation principle of the control circuit of the energy storage system is as follows.1). 1) 1). The control circuit receives a power request command from a user. The power demand command may be an active power P & a reactive power Q; or an active power P & a power factor.2). The modularized cell controller senses the voltage and temperature of the cell and uploads the voltage and temperature to the control module.3). The line voltage Vs is detected, and a magnitude and a phase of the line voltage Vs are calculated.4). An amplitude and a phase angle δ of the voltage Vi of the series circuit of the cells are calculated as follows: P=3Vs×Vi×sinδ / jWL; Q=3Vs×(Vs-Vi×conδ / jWL). The phase angle δ is an angle between the line voltage Vs and the voltage Vi of the series circuit of the cells.5). A sinusoidal half wave of Vi is divided into 288 equal parts, and a peak voltage at a time of nT is Vi×sin (180×nT / 288).6). When the line voltage Vs and the phase angle δ satisfy preset conditions, closing and cutting are performed at the unitized cell control unit. The sum of the voltages of the modularized cell control units that are closed and cut must be close to Vi×sin(180×nT / 288).It should be noted that various algorithms are available for closing and cutting the modularized cells. In one example, the close cut algorithm is that in a charging process, a cell is first charged with a low voltage and in a discharging process, a cell is first discharged with a high voltage, in a charging mode, a peak voltage of Vi×sin90=Vi is reached at a time of 144T, the voltages of the cells are added from a low voltage to a high voltage until a sum is reached that is approximately equal to Vi. Subsequently, the control units send commands to the modularized cell units to turn on the corresponding switches K1 and turn off the corresponding switches K1a. In this case, all of these cells are connected in series with the system circuit, and the switches K1a of the remaining cells are turned on and the switches K1 of the remaining cells are turned off. In this case, the voltage of the entire system circuit is approximately equal to Vi. In this manner, a stepped sinusoidal half wave is formed between time 1T and time 288T. A commutation operation is performed on a second sinusoidal half wave to obtain the stepped sinusoidal waveform. In addition, the stepped sine waveform is processed by LC filtering to obtain a smooth sine wave.FIG. 4 is a flow diagram of an algorithm for closing and cutting cells according to some embodiments of the present disclosure. As shown in FIG. 4, a concept of closing and cutting cells is as follows: in the charging process, the cell having the low voltage is first charged; in the discharging process, the cell having the high voltage is first discharged.When the energy storage system is in the charging mode, the control module 20 orders the voltages of the cells in the modularized cell control units from a low value to a high value. When the line voltage Vs and the phase angle δ meet preset conditions, the modularized cell control units are closed and cut. The voltages of the cells are added from the low voltage to the high voltage until the sum is approximately Vi×sin(180×nT / 288). In addition, the modularized cells are closed and cut into the circuit.When the energy storage system is in the discharge mode, the control module 20 orders the voltages of the cells in the modularized cell control units from the high value to the low value. When the line voltage Vs and the phase angle δ meet preset conditions, the modularized cell control units are closed and cut. The voltages of the cells are added from the high voltage to the low voltage until the sum is approximately Vi×sin(180×nT / 288). In addition, the modularized cells are closed and cut into the circuit.FIG. 5 is a schematic view of a voltage waveform according to some embodiments of the present disclosure. FIG. 5 exemplarily shows the voltage waveforms when the cells are closed and cut in a single phase energy storage system.FIG. 6 is a waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 7 is another waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 8 is another waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. FIG. 9 is another waveform of inductive reactive power and capacitive reactive power, in accordance with some embodiments of the present disclosure. As shown in FIGS. 6, 7, 8, and 9, the energy storage system is controlled by commands of the user to operate in a rectification mode or an inverter mode and to operate with the reactive inductive power or the reactive capacitive power. The control module 20 calculates the Vi and the δ value according to the commands, and the waveforms of the reactive inductive power and the reactive capacitive power in the rectifier mode and the inverter mode are illustrated in FIGS. 6, 7, 8, and 9. FIG. 10 is a topological diagram of a three-phase energy storage system in accordance with some embodiments of the present disclosure. FIG. 11 is waveforms of voltages of the three-phase power storage system according to some embodiments of the present disclosure. As shown in FIGS. 10 and 11, the three-phase power storage system functions as follows. The three-phase power storage system includes an A-phase unit, a B-phase unit, and a C-phase unit. An N conductor of the A-phase unit, an N conductor of the B-phase unit, and an N conductor of the C-phase unit are connected to each other. The ignition cables of the three phase units correspond to the three-phase ignition cables R, S, and T of the three-phase grid. The A-phase unit is a main control unit, and the control module 20 of the A-phase unit communicates with the other two phases via optical fiber communication. The main control unit controls the B-phase unit and the C-phase unit to have a phase angle of 120 degrees in sequence. Each phase is connected in series with the corresponding cells to form a circuit that follows the functional principle of the single-phase energy storage system.FIG. 12 is a schematic structural view of a modularized cell control unit according to some embodiments of the present disclosure. As shown in FIG. 12, the modularized cell control unit further includes: a temperature detection circuit 112, a power supply circuit 113, a cell voltage detection circuit 114, a display circuit 115, and a communication circuit 116. A first end of the temperature detection circuit 112 is connected to the power supply circuit 113. A second end of the temperature sensing circuit 112 is connected to a first end 1 of the cell sensing chip 111. A third end of the temperature sensing circuit 112 is connected to a second end 2 of the cell sensing chip 111. A fourth end of the temperature sensing circuit 112 is connected to a third end 3 of the cell sensing chip 111. A fifth end of the temperature sensing circuit 112 is grounded (GND). A first end of the power supply circuit 113 is connected to a positive electrode of the cell. A second end of the power supply circuit 113 is connected to the cell voltage detection circuit 114. A first end of the cell voltage detection circuit 114 is connected to a ninth end 9 of the cell sensing chip 111. A second end of the cell voltage detection circuit 114 is connected to the positive electrode of the cell. A third end of the cell voltage detection circuit 114 is connected to a negative electrode of the cell. A first end of the display circuit 115 is connected to an eighth end 8 of the cell sensing chip 111. A second end of the display circuit 115 is connected to a fourth end 4 of the cell sensing chip 111. A first end of the communication circuit 116 is connected to a sixth end 6 and a seventh end 7 of the cell sensing chip 111. A second end of the communication circuit 116 is communicatively connected to an external control unit.In particular, the cell is of high capacity, large size, and large weight. The cell sensing chip 111 may be an MCU, and the first switch K 1 is connected in series with the cell. The first switch K 1 is controlled to be turned on and off by the MCU. The cell and the first switch K1 are connected in series with each other and also connected in parallel with the second switch K1a. The second switch K 1 ais controlled to be turned on and off by the MCU. The MCU is configured to receive the temperature of the cell detected by the temperature detection circuit 112 and the voltage of the cell detected by the cell voltage detection circuit 114, and transmit the received data to a cell-level control board (cell control board) via optical fiber communication. The cell-level control board may be communicatively connected to the control module 20 to upload data and receive commands. The first switch K 1 and the second switch K 1 aare controlled to be turned on and off according to commands received from the cell-level control board. The MCU controls the display circuit 115 to illuminate or not illuminate depending on the temperature and voltage of the cell.The temperature sensing circuit 112 is configured to sense the temperature of the cell and transmit it to the MCU. The power supply circuit 113 receives the power directly from the cell and then converts it to a voltage of 5 V or 3.3 V required by the MCU and other circuits. The cell voltage detection circuit 114 detects the voltage of the cell and sends it to the MCU. The display circuit 115 is configured to display the operating state of the modularized cell control unit. When the display circuit 115 is normally lit, the unitized cell control unit operates normally. When the display circuit 115 blinks, the unitized cell controller has failed. The communication circuit 116 includes an optical fiber port and an optical fiber communication chip and is configured to exchange information with the control module 20. The cell-level control board may be disposed on a side of the cell or on a front side of an electrode. The location of the control board is determined based on the actual circumstances, so that the control board and the cell are configured in a one-piece structure to achieve modularity.FIG. 13 is a circuit diagram of the modularized cell control unit according to some embodiments of the present disclosure. As shown in FIG. 13, the temperature detection circuit includes: a negative temperature coefficient (NTC) thermistor, a first resistor R 1, a second resistor R 2, and a first capacitor C 1. A first end of the NTC thermistor is connected to a first end of the first resistor R 1 and a first end of the second resistor R 2. A second end of the first resistor R 1 is connected to the power supply circuit 113. A second end of the second resistor R 2 is connected to the first end 1 of the cell sensing chip 111. The first capacitor C 1 is connected between the second end 2 and the third end 3 of the cell sensing chip 111. A second end of the NTC thermistor is connected to a second end of the first capacitor C 1 and is then grounded (GND).Specifically, the NTC thermistor is attached to the cell. The NTC thermistor, the first resistor R 1, the second resistor R 2, the first capacitor C 1, and the power supply together form the temperature detection circuit, which detects the temperature of the cell and sends the temperature to the MCU.A resistance value of the NTC thermistor decreases with increasing temperature.As shown in FIG. 13, the cell voltage detection circuit includes: an operational amplifier U 4; a fifth resistor R 5; a sixth resistor R 6; and a seventh resistor R 7. A first end of the operational amplifier U 4 is connected to a first end of the seventh resistor R 7. A second end of the seventh resistor R 7 is connected to the ninth end 9 of the cell sensing chip 111. A second end of the operational amplifier U 4 is connected to a first end of the fifth resistor R 5. A second end of the fifth resistor R 5 is connected to the positive electrode of the cell. A third end 3 of the operational amplifier U 4 is connected to a first end of the sixth resistor R 6. A second end of the sixth resistor R 6 is connected to the negative electrode of the cell.Specifically, the operational amplifier U 4, the fifth resistor R 5, the sixth resistor R 6, and the seventh resistor R 7 together constitute the cell voltage detection circuit that detects the voltage of the cell and sends the voltage to the MCU.As shown in FIG. 13, the display circuit includes: an eighth resistor R 8; and a light emitting diode D 1. A first end of the eighth resistor R 8 is connected to the eighth end 8 of the cell sensing chip 111. A second end of the eighth resistor R 2 is connected to an anode of the light emitting diode D 1. A cathode of the light emitting diode D 1 is connected to the fourth end 4 of the cell sensing chip 111.In particular, the light emitting diode D 1 is configured to indicate the operating state of the modularized cell control unit. When the light emitting diode D 1 emits light, it is indicated that the modularized cell control unit is operating normally. When the light emitting diode D 1 flashes, it is indicated that the modularized cell control unit is not functioning properly.As shown in FIG. 13, the modularized cell control unit further includes: an isolation driver, a third resistor R 3, and a fourth resistor R 4. A first end of the isolation driver is connected to a control end of the first switch K 1, and a second end of the isolation driver is connected to a first end of the fourth resistor R 4. A second end of the fourth resistor R 4 is connected to the third end 3 of the cell sensing chip 111. A first end of the third resistor R 3 is connected to a control end of the second switch K 1 a. A second end of the third resistor R 3 is connected to the second end 2 of the cell sensing chip 111.In some embodiments, the isolation driver includes a transformer or an optocoupler.In particular, a high voltage portion of the circuit includes the cell and a low voltage portion of the circuit includes the cell sensing chip. Therefore, the insulation drive must be arranged between the high-voltage part and the low-voltage part. The transformer or optocoupler is configured to isolate the control circuit from the main circuit to prevent heavy electricity in the main circuit from interfering with weak electrical signals in the control circuit. The optocoupler insulation is substantially designed such that it prevents interference from electrical connections, in particular interference between the low-voltage control circuit and the external high-voltage circuit. The transformer isolation is essentially designed to isolate dangerous voltages to ensure safe operation of the circuit.FIG. 14 is a flowchart of a control method of the energy storage system according to some embodiments of the present disclosure. The present disclosure further provides a control method for an energy storage system. The control method includes the following operations.In a process S 110, a mains AC voltage is detected.In an operation S 120, a phase angle between the grid voltage and the circuit voltage is calculated based on the grid AC voltage and the voltage of the series circuit of the cells.In a process S 130, an operating mode of the energy storage system is determined, wherein the operating mode comprises the discharging mode and the charging mode.In operation S 140, when the energy storage system is in the charging mode and the phase angle between the line voltage and the circuit voltage satisfies the preset conditions, the control module performs a close-cut operation by following a first preset control strategy.In operation S 150, when the energy storage system is in the discharging mode and the phase angle satisfies the preset conditions, the control module performs the close-cut operation by following a second preset control strategy.Specifically, a power request command is received from the user. The power demand command may be an active power P & a reactive power Q; or an active power P & a power factor. The modularized cell control unit detects the voltage and temperature of the cell and transmits the voltage and temperature to the control module. The line voltage Vs is detected, and a magnitude and a phase of the line voltage Vs are calculated. An amplitude and a phase angle δ of the voltage Vi of the series circuit of the cells are calculated as follows: P=3Vs×Vi×sinδ / jWL; Q=3Vs×(Vs-Vi×conδ / jWL). The phase angle δ is an angle between the line voltage Vs and the voltage Vi of the series circuit of the cells. A sinusoidal half wave of the Vi is divided into 288 equal parts, and a peak voltage at a time of nT is Vi×sin (180×nT / 288). When the grid voltage Vs and the phase angle δ satisfy preset conditions, closing and cutting are performed at the modularized cell control unit. The sum of the voltages of the modularized cell control units that are closed and cut must be close to Vi×sin(180×nT / 288).When the energy storage system is in the charging mode, the control module orders the voltages of the cells in the modularized cell control units from a low value to a high value. When the line voltage Vs and the phase angle δ meet preset conditions, the modularized cell control units are closed and cut. The voltages of the cells are added from the low voltage to the high voltage until the sum is approximately Vi×sin(180×nT / 288). In addition, the modularized cells are closed and cut into the circuit.When the energy storage system is in the discharge mode, the control module orders the voltages of the cells in the modularized cell control units from the high value to the low value. When the line voltage Vs and the phase angle δ meet preset conditions, the modularized cell control units are closed and cut. The voltages of the cells are added from the high voltage to the low voltage until the sum is approximately Vi×sin(180×nT / 288). In addition, the modularized cells are closed and cut into the circuit.The control method of the energy storage system provided in the present embodiment is applied to the control circuit of the energy storage system, similar technical principles are applied, and similar technical effects are produced, which are not repeated here.FIG. 15 is a schematic structural view of an energy storage system according to some embodiments of the present disclosure. As shown in FIG. 15, the power storage system includes: n-stage, series-connected, modularized cell control units 51. the modular cell control unit 51 includes an external terminal end 511, a cell 512, a temperature sensing circuit 112, a cell micro control module 514, a cell voltage sensing circuit 114, a communication circuit 116, and a switch switching module 517. The n is a positive integer.The cell 512 is electrically connected to the external terminal end 511 via the switch switching module 517. The switch switching module 517 is configured to control whether the cell 512 is connected to the energy storage system.The temperature sensing circuit 112 is electrically connected to the cell microcontroller 514. The temperature sensing circuit 112 is configured to sense the temperature of the cell 512 and send the temperature to the cell microcontroller 514.The cell voltage sensing circuit 114 is connected in series between the cell 512 and the cell microcontroller 514. The cell voltage sensing circuit 114 is configured to sense the voltage of the cell 512 and send the voltage to the cell microcontroller 514.The communication circuit 116 is communicatively connected to the cell microcontroller 514. The communication circuit 116 is configured to perform information interaction between the modularized cell control unit 51 and a master control unit. The cell microcontroller 514 is remotely electrically connected to the switch switch module 517. The cell microcontroller module 514 is configured to control the switch switching module 517 based on the temperature, voltage, and / or information interaction with the master controller.The communication circuit 116 may include the fiber optic connector and the fiber optic communication chip. The functional principle of the modularized cell control unit 51 is as follows. The temperature sensing circuit 112 senses the temperature of the cell 512 and sends the temperature to the cell microcontroller 514. The cell voltage detection circuit 114 detects the voltage of the cell 512 and sends the voltage to the cell microcontroller 514. The cell microcontroller 514 transmits the received temperature and voltage of the cell 512 to the master controller via the communication circuit 116. The higher-level control unit sends commands to the cell microcontroller 514 via the communication circuit 116, which commands are based on the information of the individual modules and the state of the power network and on a preset control strategy. The cell microcontroller module 514 receives the commands and controls the switch switching module 517 to perform an appropriate operation in accordance with the commands to control the cell 512 to be connected in series in the energy storage system or disconnected from the energy storage system.In the present disclosure, the unitized cell control unit 51 is arranged. The temperature sensing circuit 112 is configured to sense the temperature of the cell 512 and the cell voltage sensing circuit 114 is configured to sense the voltage of the cell 512. The temperature and voltage are then sent to the cell microcontroller 514. The cell micro-control module 514 transmits the temperature and the voltage to the master control unit via the communication circuit 116. The master controller sends commands to the cell microcontroller 514 based on the information of the individual modules. The cell microcontroller module 514 controls the switch switching module 517 to connect or disconnect the cell 512 from the energy storage system based on the commands. In the present embodiment, the control unit of the cell 512 may be modularized to form the energy storage system without the need to arrange a battery management system or a PCS. Therefore, the assembly can be easily performed and the cost can be reduced.As shown in FIG. 13 based on the above embodiments, in some embodiments, the external terminal end 511 includes a positive electrode terminal end B+ and a negative electrode terminal end B-. The negative electrode terminal end B- is electrically connected to the negative electrode of the cell 512.The switch switching module 517 includes a first switch K 1 and a second switch K 1 a. The first switch K 1 is connected in series between the positive electrode and the positive electrode terminal end B+ of the cell 512. The second switch K1a is connected in series between the positive electrode terminal end B+ and the negative electrode terminal end B-.As further shown in FIG. 13, in some embodiments, the first switch K 1 and / or the second switch K 1 aincludes a MOS transistor.Specifically, the cell microcontroller 514 sends a drive signal according to commands sent from the master controller to turn off or on the MOS transistors in the first switch K 1 and the second switch K 1 ato further control the cell 512 to be connected to or disconnected from the energy storage system. For example, the MOS transistor in the first switch K1 is turned on, and the positive electrode terminal end B+ is connected to the positive electrode of the cell 512. The MOS transistor in the second switch K1a is turned off, the negative electrode terminal end B- is connected to the negative electrode of the cell 512, and in this case, the cell 512 is connected to the power storage system. In another example, the MOS transistor in the first switch K 1 is turned off, the positive electrode terminal end B+ is separated from the positive electrode of the cell 512. The MOS transistor in the second switch K1a is turned on, and the negative electrode terminal end B- is connected to the positive electrode terminal end B+. In this case, the cell 512 is disconnected from the energy storage system.In the present embodiment, by disposing the first switch K 1 and the second switch K 1 ain the switch switching module 517, the external terminal end 511 can be connected to and disconnected from the positive electrode and the negative electrode of the cell 512 by turning on and off the MOS transistors, respectively. In this way, the cell 512 is controlled to connect to or disconnect from the energy storage system, which allows for more convenient operation of the energy storage system.As shown in FIG. 13, a power supply voltage 17 supplies a voltage to an NTC resistor NTC1 via the first resistor R1. The NTC resistor NTC 1 detects the temperature of the cell and sends the temperature to the cell microcontroller module via the second resistor R 2. The first capacitor C 1 is configured to filter out high frequency noise induced from a power source or the circuit board.In the present embodiment, by arranging the NTC resistor NTC 1, the first resistor R 1, and the second resistor R 2 in the temperature detection circuit 112, the temperature of the cell is detected and sent to the cell microcontroller module. In this way, the cell microcontroller module and the higher-level control unit may control the cell based on the temperature. The first resistor R 1 and the second resistor R 2 may prevent the current in the circuit from becoming too large, thereby improving safety of the energy storage system.As shown in FIG. 13, in some embodiments, the energy storage system includes the following in addition to the above embodiments.A power supply circuit 113 is disposed and electrically connected to the cell. The power supply circuit 113 is configured to provide a power supply voltage to the modularized cell control unit.Specifically, the power supply circuit 113 directly receives power from the cell and converts the power into a voltage required by the modularized cell control unit. By way of example, the voltage required by the modularized cell control unit may be 5V or 3.3V.In the present embodiment, the power supply circuit 113 supplies power to the modularized cell control unit. Since the power supply circuit 113 has a simple structure and a flexible design, the modularized cell control unit can be easily assembled and operated.As shown in FIG. 13, in some embodiments, the cell microcontroller module includes, in addition to the above embodiments, a microcontroller chip U 2, an isolation driver circuit U 3, the third resistor R 3, and the fourth resistor R 4. In one embodiment, microcontroller chip U2 is the same as cell scan chip 111 described above.The microcontroller chip U2 includes a first drive signal pin and a second drive signal pin. The third resistor R3 is connected in series between the first drive signal pin and the control end of the second switch K1a. The isolation driver circuit U3 and the fourth resistor R4 are connected in series between the second driver signal pin and the control end of the first switch K1.Specifically, the microcontroller chip U 2 outputs a first drive signal via the first drive signal pin to drive the second switch K 1 ato be turned on or off. The microcontroller chip U2 outputs a second drive signal via the second drive signal pin to drive the first switch K1 to be turned on or off. Since the MOS transistors in the first switch K1 and the second switch K1a have a high operating frequency and a high input impedance, the MOS transistors can be easily disturbed. Therefore, the isolation driving circuit U3 is arranged to achieve isolation between the main circuit and the control circuit, so that the MOS transistors have high anti-interference ability and the power level circuit is prevented from disturbing the driving signal. The third resistor R 3 and the fourth resistor R 4 are configured to prevent the current from becoming too large and damaging the circuit.In the present embodiment, by the arrangement of the microcontroller chip U 2, the isolation driving circuit U 3, the third resistor R 3, and the fourth resistor R 4 in the cell microcontroller module, the first switch K 1 and the second switch K 1 acan be controlled. In this way, the chip is securely and effectively controlled to be connected to or disconnected from the energy storage system, so that the module can be easily assembled and operated.As shown in FIG. 13, the cell voltage detection circuit includes an operational amplifier U 4, a fifth resistor R 5, a sixth resistor R 6, and a seventh resistor R 7. A voltage signal at the positive electrode of the cell is input to the operational amplifier U4 through the fifth resistor R5. A voltage signal at the negative electrode of the cell is fed to the operational amplifier U4 through the sixth resistor R6. In this way, a voltage difference is generated, i.e. voltages at the two ends of the cell. The voltage is amplified by the operational amplifier U4 and input to the cell microcontroller module through the seventh resistor R7.In the present embodiment, by arranging the operational amplifier U 4, the fifth resistor R 5, the sixth resistor R 6, and the seventh resistor R 7 in the cell voltage detection circuit 114, the voltage of the cell is detected and sent to the cell microcontroller module. In this way, the cell microcontroller module and the higher-level control unit may control the cell based on the voltage. The fifth resistor R 5, the sixth resistor R 6, and the seventh resistor R 7 are configured to prevent the current in the circuit from becoming too large and damaging the operational amplifier U 4, thereby improving safety of the power storage system.As shown in FIG. 13, in some embodiments, the energy storage system includes, in addition to the above embodiments: an eighth resistor R8 and a display light module D1'. The eighth resistor R8 and the indicator light module D1' are connected in series between the cell microcontroller module and a ground terminal. The display light module D1' is configured to display a state of the modularized cell control unit.The display light module D1' may include a light emitting diode or an incandescent lamp.Specifically, the cell micro-control module controls the display light module D1' based on the temperature and voltage of the cell to display the operation state of the modularized cell control unit. When the indicator light lights up, the modular cell control unit operates normally. When the indicator light flashes, there is a malfunction of the modularized cell control unit. The eighth resistor R 8 is configured to prevent the current from becoming excessively large.In the present embodiment, the eighth resistor R 8 and the display light module D 1 are arranged to display the operation state of the modularized cell control unit, the structure is simple, and the user can easily understand the operation state of each modularized cell control unit. When a fault occurs, the user is able to discover the faulty structure in time, so that the faulty structure can be found and repaired.In addition to the above embodiments, the temperature sensing circuit 112, the cell microcontroller module 514, the cell voltage sensing circuit 114, the communication circuit 116, and the switch switching module 517 are disposed on a cell control board 10'.Specifically, the temperature detection circuit 112, the cell microcontroller module 514, the cell voltage detection circuit 114, the communication circuit 116, and the switch switching module 517 are integrated into the cell control board 10'. In this way, circuit design is simplified, circuit size is reduced, and cost is lowered. Depending on the actual situation, the cell control board 10' may be disposed on a side or a front side of the cell, and the cell control board 10' and the cell may be integrated to form a one-piece structure so that the cell control unit is modularized.In the present embodiment, by the arrangement of the cell control board 10', the temperature detection circuit 112, the cell micro control module 514, the cell voltage detection circuit 114, the communication circuit 116, and the switch switching module 517 are integrated into the cell control board 10'. In this way, the size of the circuit is reduced and the cost is effectively lowered. Moreover, the cell control board 10' and the cell form an integral and one-piece structure, and the energy storage system can be more conveniently assembled and operated.FIG. 16 is a schematic structural view of another energy storage system according to some embodiments of the present disclosure. As shown in FIG. 16, the energy storage system includes the following in addition to the above embodiments.A superordinate control unit 2' is arranged.A commutation module 3' comprises a first commutation switch Kb, a second commutation switch Kc, a third commutation switch Kd, a fourth commutation switch Ke, and a filter unit 30'. The filter unit 30' includes a filter input end, a filter output end, and a common end. The first commutation switch Kb is connected in series between the positive electrode of the modularized cell control unit 1' of a stage 1 and the filter input end. The second commutation switch Kc is connected in series between the negative electrode of the modularized cell control unit 1' of a stage n and the filter input side. The third commutation switch Kd is connected in series between the positive electrode of the modularized stage 1 cell control unit 1' and the common end. The fourth commutation switch Ke is connected in series between the negative electrode of the modularized n-stage cell control unit 1' and the common end. The filter output end and the common end serve as an output end of the commutation module 3'.The upper control unit 2' is configured to control a state of the first commutation switch Kb, the second commutation switch Kc, the third commutation switch Kd, and the fourth commutation switch Ke to convert the direct current of the modularized cell control unit 1' into alternating current.In one embodiment, the master control unit 2' is the same as the control module 20 described above.As shown in FIG. 16, in some embodiments, the filter unit 30' includes a first filter inductor L and a first filter capacitor C.As shown in FIG. 16, in some embodiments, the n-stage modularized cell control units are connected in series to form the modularized cell unit. A positive electrode terminal end B+ of the modularized Stage 1 cell controller is electrically connected to the commutation module 3'. A negative electrode terminal end B- of the modularized stage 1 cell control unit is electrically connected to a positive electrode terminal end B+ of the modularized stage 2 cell control unit. In the remaining modularized cell control units, a positive electrode terminal end B+ of the modularized cell control unit of a certain stage is connected to a negative electrode terminal end B- of the modularized cell control unit of a stage before the certain stage in sequence. A negative electrode terminal end B of the unitized cell control unit of stage n is electrically connected to the commutation module 3'.As shown in FIG. 16, the master control unit 2' in some embodiments includes a main control chip 20', a first communication unit 21', and a second communication unit 22.In particular, the higher-order control unit 2' interacts with the modularized cell control unit 1' via the first communication unit 21' and controls the switches in the commutation module 3' via the second communication unit 22' in order to switch them on or off. Commutation module 3' is configured to commutate the sinusoidal half-wave voltage. The filter unit 30' is configured to smooth and filter the stepped waveform of the cell. The higher-level control unit 2' can also exchange information with mobile devices via Bluetooth or 5G or a WIFI module. By way of example, the mobile devices can be a mobile telephone or a computer, etc.When the energy storage system is connected to the grid, the number of modularized cell control units is limited by the voltage of the grid. Taking the grid with a voltage of 230 V as an example, the number of modularized cell controllers is n=230×1.1×1.414 / 2.5=144, and therefore at least 144 modularized cell controllers 1' must be connected in series to form the 230 V grid system.As shown in FIG. 16, in some embodiments, the energy storage system further includes the following in addition to the above embodiments.A current detection unit 4' is electrically connected to the master control unit 2'. The current detection unit 4' is configured to detect a current at the filter output end and to send the current to the upper control unit 2'.A voltage sensing unit 5' is electrically connected to the master control unit 2'. The voltage sensing unit 5' is configured to sense a voltage at the output end of the commutation module 3' and to send the voltage to the master control unit 2'.In particular, the voltage sensing unit 5' is configured to phase lock the line voltage. The current detection unit 4' is configured to detect the current of the system and to turn off the switches in the commutation module 3' when the current exceeds a preset threshold value.An operation principle of the energy storage system in the present embodiment is as follows.S110', the system is turned on.S120', a power request command is received from the user. The power demand command includes an active power command and a reactive power command; or includes an active power command and a power factor command.S130', the unitized cell control unit 1' detects the voltage and temperature of the cell and uploads the voltage and temperature to the upper-level control unit 2'.S140', the line voltage Vs is detected, and an amplitude and a phase of the line voltage Vs are calculated.S150', an amplitude and a phase angle δ of the series connection of the voltage Vi of the n-stage modularized cell control unit 1' is calculated. The calculation is performed according to the following formula:P stands for the active power, Q for the reactive power, and L for a filter inductance.S160', a sinusoidal half wave of the series connection of the voltage Vi of the n-stage modularized cell control unit 1' is divided into 288 equal parts, and a peak voltage at time nT is Vi×sin (180×nT / 288).S170', a close cut operation is performed on the modularized cell control unit 1' when the phase angle δ of the line voltage satisfies preset conditions. The sum of the voltages of the modularized cell control units 1' that are closed and cut must be close to the peak voltage.In the present embodiment, by the arrangement of the current detection unit 4' and the voltage sensing unit 5', the line voltage and the output current at the filter output are detected, so that the voltage calculation can be easily performed when the modularized cell control unit 1' is closed, and the safety of the system circuit is improved.In the present embodiment, the master control unit 2' and the commutation module 3' are arranged to convert the DC current of the modularized cell control unit into AC current. In the present embodiment, the PCS can be omitted, i.e., the cost and size of the system are reduced.It should be noted that various algorithms are available for closing and cutting the modularized cell controller. In one example, the close cut algorithm is that in a charging process, a cell with a low voltage is first charged and in a discharging process, a cell with a high voltage is first discharged. However, the present disclosure is limited thereto.In addition to the above embodiments, as shown in FIG. 5, the voltage waveform is commutated to be a complete sinusoidal waveform.For example, in the charging mode at time 144T, the peak voltage Vp is: Vp=Vi×sin90=Vi. The voltages of the cells of the n-stage modularized cell control units 1' are added from a low voltage to a high voltage until the sum of the voltages of m cells approximately equals the peak voltage. The master control unit 2' sends commands to the m modularized cell control units 1' involved in the sum calculation to turn on the corresponding first switches K1 and turn off the corresponding second switches K1a. In this case, the m cells are connected in series to the energy storage system. Moreover, the master control unit 2' sends commands to the remaining n-m modularized cell control units 1' to turn off the corresponding first switches K1 and turn on the corresponding second switches K1a. In this case, the n-m cells are disconnected from the energy storage system. In this case, the voltage of the entire system circuit is approximately equal to Vi. In this manner, a stepped sinusoidal half wave is formed between time 1T and time 288T. A commutation operation is performed on a second sinusoidal half wave to obtain the stepped sinusoidal waveform. In addition, the stepped sine waveform is processed by the filter unit 30' to obtain a smooth sine wave.As shown in FIG. 6, the system is in the discharging mode when the line voltage has a phase angle δ=0 and the series circuit voltage Vi of the n-stage modularized cell control units 1' is greater than the line voltage Vs, and a system output is a purely active power output. As shown in Fig. 7, the system is in the charging mode when the line voltage has the phase angle δ=0 and the series voltage Vi of the n-stage modularized cell control units 1' is less than the line voltage Vs, and the system output is a purely active power output. As shown in Fig. 8, the system is in the discharging mode when the line voltage has a phase angle δ<0 and the series connection Vi of the n-stage modularized cell control units 1' is larger than the line voltage Vs, and the system output is an active power and inductive reactive power output. As shown in Fig. 9, the system is in the discharging mode when the line voltage has a phase angle δ>0 and the series connection Vi of the n-stage modularized cell control units 1' is larger than the line voltage Vs, and the system output is an active power and capacitive reactive power output.Note that the operation mode of the energy storage system and the type of reactive power may be determined according to requirements. The operating mode of the energy storage system includes a rectifier mode and an inversion mode. The type of reactive power of the energy storage system comprises the inductive reactive power and the capacitive reactive power.An operating principle for bypassing a failed cell is as follows. When a cell fails, a corresponding cell microcontroller module 14 turns off the corresponding first switch K1 of the modularized cell control unit 1' and turns on the corresponding second switch K1a of the modularized cell control unit 1'. In this way, the failed cell is bypassed and normal operation of the system is not impaired. In this case, the cell micro-control module 14 controls the display light module D1 to blink to indicate that the corresponding modularized cell control unit 1' has failed.In the present embodiment, in the closing and cutting algorithm, the low voltage cell is first charged during the charging operation and the high voltage cell is first discharged during the discharging operation, so that the battery management system is not needed to control the cell and the cost of the energy storage system is reduced. When a single cell has failed, the cell micro-control module 14 also controls the first switch K1 of the modularized cell control unit 1' to be turned off and controls the second switch K1a of the modularized cell control unit 1' to be turned on. In addition, the cell micro-control module 14 controls the display light module D 1 to send a reminder to the user. In this way, normal operation of the system is impaired and system errors can be quickly found and corrected.As illustrated in FIG. 10, the power storage system outputs three-phase alternating current.The n-stage modularized cell control units 1' connected in series, the higher-order control unit 2, and the commutation module 3' are connected to each other to form a single-phase AC output module of the energy storage system.The alternating currents output from the three-phase AC output module have a phase angle of 120 degrees between two alternating currents each.As shown in FIG. 10, the master control unit 2 in some embodiments further includes a third communication unit 23.The three-phase AC output module is an A-phase AC output module, a B-phase AC output module, and a C-phase AC output module.Specifically, the neutral wires N of the AC output modules of all phases are connected to each other. The extinguishing wire L of the AC output module of each phase is connected to the three-phase extinguishing wires (R wire, S wire, and L wire) of the three-phase mesh, respectively. The master control unit 2 in the AC output module of the A phase serves as a main control unit and communicates with the AC output modules of the other two phases via the third communication unit 23 to control the AC output modules of the other two phases to have a phase angle of 120 degrees one after another.In the present embodiment, the n-stage modularized cell control units 1 connected in series, the higher-order control unit 2, and the commutation module 3 are connected to each other to form a single-phase AC output module of the energy storage system. The energy storage system outputs three-phase alternating currents for connection to the power grid. In the present embodiment, the three-phase output power storage system may be formed by omitting the battery management system and the PCS. The energy storage system can be easily assembled and operated, and the cost of the energy storage system is reduced

Claims

A control circuit of an energy storage system, characterized by comprising: a cell module (10), a control module (20), and a commutation module (30); wherein the cell module (10), the control module (20), and the commutation module (30) are sequentially connected to each other; wherein the cell module (10) comprises n modularized cell control units (11); each modularized cell control unit (11) comprises a cell, a first switch, and a second switch; the cell and the first switch are connected to each other in series, and the series-connected cell and the first switch are connected in parallel to the second switch; the n is a positive integer; wherein the first switch of a first cell control unit (11) of the n modularized cell control units (11) and the second switch of the first cell control unit (11) of the n modularized cell control units (11) are connected to each other to serve as a first end of the cell module (10); the first switch of an nth cell control unit (11) of the n modularized cell control units (11) and the second switch of the nth cell control unit (11) of the n modularized cell control units (11) are connected to each other to serve as a second end of the cell module (10); the commutation module (30) comprises a first commutation switch (Kb), a second commutation switch (Kc), a third commutation switch (Kd), a fourth commutation switch (Ke), and a filter unit (31); the filter unit (31) comprises a first end, a second end, and a third end; the first end of the cell module (10) is connected to a first end of the first commutation switch (Kb) and a first end of the third commutation switch (Kd); a second end of the first commutation switch (Kb) is connected to the first end of the filter unit (31); a second end of the third commutation switch (Kd) is connected to the third end of the filter unit (31); the second end of the cell module (10) is connected to a first end of the second commutation switch (Kc) and a first end of the fourth commutation switch (Ke); the second commutation switch (Kc) is connected to the first end of the filter unit (31); a second end of the fourth commutation switch (Ke) is connected to the third end of the filter unit (31); an AC power network is connected between the second end of the filter unit (31) and the third end of the filter unit (31); wherein the control module (20) is communicatively connected to the modularized cell control units (11) and the commutation module (30); the control module (20) is configured to control the first commutation switch (Kb), the second commutation switch (Kc), the third commutation switch (Kd), and the fourth commutation switch (Ke) to be turned on or off.The control circuit of claim 1, wherein each modularized cell controller (11) further comprises a cell sense chip (111); the control module (20) further comprises a main controller (21); wherein the cell sense chips (111) from the n modularized cell controller (11) are communicatively connected to the n cells and the main controller (21); the cell sense chips (111) are configured to sense voltages and temperatures of the n cells and transmit the voltages and temperatures to the main controller (21); wherein the main controller (21) is communicatively connected to the first commutation switch (Kb), the second commutation switch (Kc), the third commutation switch (Ke), and the fourth commutation switch (Ke); the main controller (21) is configured to analyze and calculate the received voltages and temperatures and control the n first switches, the n second switches, the first commutation switch (Kb), the second commutation switch (Kc), the third commutation switch (Kd), and the fourth commutation switch (Ke) to be turned on or off.The control circuit of claim 2, wherein the commutation module (30) further comprises a voltage sensing unit (32) and a current sensing unit (33); wherein a first end of the voltage sensing unit (32) is connected to an eleventh end of the main controller (21) and a second end of the voltage sensing unit (32) is connected to a tenth end of the main controller (21); a third end of the voltage sensing unit (32) is connected to the second end of the filter unit (31), and a fourth end of the voltage sensing unit (32) is connected to the third end of the filter unit (31); wherein a first end of the current sensing unit (33) is connected to a twelfth end of the main controller (21); a second end of the current sensing unit (33) is connected to the second end of the filter unit (31).The control circuit of claim 2, wherein each unitized cell control unit (11) further comprises a temperature detection circuit (112), a power supply circuit (113), a cell voltage detection circuit (114), a display circuit (115), and a communication circuit (116); wherein a first end of the temperature detection circuit (112) is connected to the power supply circuit (113); a second end of the temperature detection circuit (112) is connected to a first end of the cell sensing chip (111); a third end of the temperature detection circuit (112) is connected to a second end of the cell sensing chip (111); a fourth end of the temperature detection circuit (112) is connected to a third end of the cell sensing chip (111); a fifth end of the temperature detection circuit (112) is grounded; wherein a first end of the power supply circuit (113) is connected to a positive electrode of the cell; a second end of the power supply circuit (113) is connected to the cell voltage detection circuit (114); wherein a first end of the cell voltage detection circuit (114) is connected to a ninth end of the cell sensing chip (111); a second end of the cell voltage detection circuit (114) is connected to the positive electrode of the cell; a third end of the cell voltage detection circuit (114) is connected to a negative electrode of the cell, wherein a first end of the display circuit (115) is connected to an eighth end of the cell sensing chip (111); a second end of the display circuit (115) is connected to a fourth end of the cell sensing chip (111); a first end of the communication circuit (116) being connected to a sixth end and a seventh end of the cell sensing chip (111); a second end of the communication circuit (116) being communicatively connected to an external control unit.The control circuit of claim 4, wherein the temperature sensing circuit (112) comprises a negative temperature coefficient (NTC) thermistor, a first resistor (R1), a second resistor (R2), and a first capacitor (C1); wherein a first end of the NTC thermistor is connected to a first end of the first resistor (R1) and a first end of the second resistor (R2); a second end of the first resistor (R1) is connected to the power supply circuit (113); a second end of the second resistor (R2) is connected to the first end of the cell sensing chip (111); the first capacitor (C1) is connected between the second end and the third end of the cell sensing chip (111); a second end of the NTC thermistor is connected to a second end of the first capacitor (C1) and then grounded.The control circuit of claim 4, wherein the cell voltage sensing circuit (114) comprises an operational amplifier (U4), a fifth resistor (R5), a sixth resistor (R6), and a seventh resistor (R7); wherein a first end of the operational amplifier (U4) is connected to a first end of the seventh resistor (R7); a second end of the seventh resistor (R7) is connected to the ninth end of the cell sensing chip (111); a second end of the operational amplifier (U4) is connected to a first end of the fifth resistor (R5); a second end of the fifth resistor (R5) is connected to the positive electrode of the cell; a third end of the operational amplifier (U4) is connected to a first end of the sixth resistor (R6); a second end of the sixth resistor (R6) is connected to the negative electrode of the cell.The control circuit of claim 4, wherein the display circuit (115) comprises an eighth resistor (R8) and a light emitting diode (D1); wherein a first end of the eighth resistor (R8) is connected to the eighth end of the cell sensing chip (111); a second end of the eighth resistor (R8) is connected to an anode of the light emitting diode (D1); a cathode of the light emitting diode (D1) is connected to the fourth end of the cell sensing chip (111).The control circuit of any one of claims 4 to 7, wherein each modularized cell control unit (11) further comprises an isolation driver, a third resistor (R3), and a fourth resistor (R4); wherein a first end of the isolation driver is connected to a control end of the first switch, and a second end of the isolation driver is connected to a first end of the fourth resistor (R4); a second end of the fourth resistor (R4) is connected to the third end of the cell sensing chip (111); a first end of the third resistor (R3) is connected to a control end of the second switch; a second end of the third resistor (R3) is connected to the second end of the cell sensing chip (111).The control circuit of claim 8, wherein the isolation driver comprises a transformer or an optocoupler.The control circuit of any of claims 1 to 7, wherein the control module (20) interacts with external mobile devices via Bluetooth, 5G or WIFI modules.An energy storage system characterized by comprising: n-stage, series-connected, modularized cell control units (51); wherein each modular cell control unit (51) comprises an external terminal end (511), a cell (512), a temperature sensing circuit (112), a cell microcontroller module (514), a cell voltage sensing circuit (114), a communication circuit (116), and a switch switching module (517); the n is a positive integer; wherein the cell (512) is electrically connected to the external terminal end (511) via the switch switching module (517); the switch switching module (517) is configured to control whether the cell (512) is connected to the energy storage system; wherein the temperature sensing circuit (112) is electrically connected to the cell microcontroller module (514); the temperature sensing circuit (112) is configured to sense a temperature of the cell (512) and transmit the temperature to the cell microcontrol module (514); wherein the cell voltage sensing circuit (114) is connected in series between the cell (512) and the cell microcontrol module (514); the cell voltage sensing circuit (114) is configured to sense a voltage of the cell (512) and transmit the voltage to the cell microcontrol module (514); wherein the communication circuit (116) is communicatively connected to the cell microcontrol module (514); the communication circuit (116) is configured to perform an information interaction between the modularized cell control unit (51) and a master control unit (2'); wherein the cell microcontrol module (514) is further electrically connected to the switch switching module (517); the cell micro-control module (514) is configured to control the switch switching module (517) based on the temperature, the voltage, and / or the information interaction with the master control unit (2').The energy storage system of claim 11, wherein the external terminal end (511) comprises a positive electrode terminal end (B+) and a negative electrode terminal end (B-); the negative electrode terminal end (B-) is electrically connected to a negative electrode of the cell (512); the switch switching module (517) comprises a first switch (K1) and a second switch (K1a); the first switch (K1) is connected in series between a positive electrode and the positive electrode terminal end (B+) of the cell (512); the second switch (K1a) is connected in series between the positive electrode terminal end (B+) and the negative electrode terminal end (B-).The energy storage system according to claim 12, wherein the first switch (K1) and / or the second switch (K1a) comprise a MOS tube.The energy storage system of claim 11, wherein the temperature sensing circuit (112) comprises a negative temperature coefficient (NTC) resistor (NTC1), a first resistor (R1), a second resistor (R2), and a first capacitor (C1); wherein a first end of the NTC resistor (NTC1) is electrically connected to a first end of the first resistor (R1), and a second end of the first resistor (R1) is electrically connected to a power supply voltage; a first end of the second resistor (R2) is electrically connected to the first end of the first resistor (R1), a second end of the second resistor (R2) is electrically connected to the cell microcontroller (514); the first capacitor (C1) is electrically connected to the first end of the first resistor (R1), the first capacitor (C1) is electrically connected to the second end of the NTC resistor (NTC1), and the second end of the NTC resistor (NTC1) is grounded.The energy storage system of claim 14, further comprising: a power supply circuit (113) electrically connected to the cell (512); wherein the power supply circuit (113) is configured to provide the power supply voltage to the modularized cell control unit (51).The energy storage system of claim 12, wherein the cell microcontroller module (514) comprises a microcontroller chip (U2), an isolation driver circuit (U3), the third resistor (R3), and the fourth resistor (R4); wherein the microcontroller chip (U2) comprises a first driver signal pin and a second driver signal pin; the third resistor (R3) is connected in series between the first driver signal pin and a control end of the second switch (K1a); the isolation driver circuit (U3) and the fourth resistor (R4) are connected in series between the second driver signal pin and a control end of the first switch (K1).The energy storage system of claim 12, wherein the cell voltage sensing circuit (114) comprises an operational amplifier (U4), a fifth resistor (R5), a sixth resistor (R6), and a seventh resistor (R7); wherein the fifth resistor (R5) is connected in series between the positive electrode of the cell (512) and a first input end of the operational amplifier (U4), the sixth resistor (R6) is connected in series between the negative electrode of the cell (512) and a second input end of the operational amplifier (U4), and the seventh resistor (R7) is connected in series between an output end of the operational amplifier (U4) and the cell microcontroller (514).The energy storage system of claim 11, further comprising: an eighth resistor (R8) and a display light module (D1'); wherein the eighth resistor (R8) and the display light module (D1') are connected in series between the cell microcontroller module (514) and a ground terminal; the display light module (D1') is configured to display a state of the modularized cell control unit (51).The energy storage system of any of claims 11 to 18, further comprising: a cell control board (10'); wherein the temperature sensing circuit (112), the cell microcontroller module (514), the cell voltage sensing circuit (114), the communication circuit (116), and the switch switching module (517) are disposed on the cell control board (10').The energy storage system according to any one of claims 11 to 18, further comprising: the master control unit (2'); and a commutation module (3') comprising: a first commutation switch (Kb), a second commutation switch (Kc), a third commutation switch (Kd), a fourth commutation switch (Ke), and a filter unit (30'); wherein the filter unit (30') comprises a filter input end, a filter output end, and a common end; the first commutation switch (Kb) is connected in series between a positive electrode of the unitized cell control unit (51) of a stage 1 and the filter input end; the second commutation switch (Kc) is connected in series between a negative electrode of the unitized cell control unit (51) of a stage n and the filter input side; the third commutation switch (Kd) is connected in series between the positive electrode of the stage 1 modularized cell control unit (51) and the common end; the fourth commutation switch (Ke) is connected in series between the negative electrode of the stage n modularized cell control unit (51) and the common end; the filter output end and the common end serve as an output end of the commutation module (3'); wherein the upper control unit (2') is configured to control a state of the first commutation switch (Kb), the second commutation switch (Kc), the third commutation switch (Kd), and the fourth commutation switch (Ke) to convert direct currents of the modularized cell control units (51) into alternating currents.The energy storage system of claim 20, further comprising: a current sensing unit (4') electrically connected to the master control unit (2'); wherein the current sensing unit (4') is configured to sense a current at the filter output end and to send the current to the master control unit (2'); and a voltage sensing unit (5') electrically connected to the master control unit (2'); wherein the voltage sensing unit (5') is configured to sense a voltage at the output end of the commutation module (3') and to send the voltage to the master control unit (2').The energy storage system of claim 20, wherein the energy storage system outputs three-phase alternating current; wherein the n-stage modularized cell control units (51) connected in series, the master control unit (2'), and the commutation module (3') are connected to each other to form a single-phase alternating current output module of the energy storage system; wherein the alternating currents output from the three-phase alternating current output module have a phase angle of 120 degrees between each two alternating currents.

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