Energy storage system and battery equalization method

Abstract

The application discloses a kind of energy storage systems and battery equalization method, energy storage system includes: controller, N battery modules, grid-connected inductance and alternating current power supply;Controller is connected with N battery modules, host computer respectively;N battery modules are connected in series;First battery module is sequentially connected with Nth battery module through grid-connected inductance, alternating current power supply;Battery module includes electronic switch;Controller is used to detect the battery parameter of battery module, and according to battery parameter control electronic switch's on-off, to control the charge-discharge state of battery module, realizes the active equalization of N battery modules.The application realizes the flexible adjustment and independent control of the internal battery cell of battery module by controlling the on-off of electronic switch, can carry out energy conversion and storage to single battery cell, solves the overcharge and overdischarge problem caused by the inconsistent attenuation of battery cell, improves the safety and reliability of energy storage system, simultaneously has fault tolerance ability, significantly improves the overall performance and life of energy storage system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage systems, in particular to an energy storage system and a battery equalization method. BACKGROUND

[0002] The current battery and power electronic-based energy storage technology is developing rapidly, and the direct current side of the energy storage system uses multiple battery modules or clusters for series and parallel connection. During use, the attenuation speed of each battery module is inconsistent due to the influence of temperature, large current charging and discharging, etc., therefore, a battery management system is needed for battery equalization control. In extreme cases, the rapid decline of a single or several battery cells can easily lead to overcharging and overdischarging, which poses a serious safety hazard.

[0003] However, the current battery modules and internal battery cells all use fixed welding methods, which cannot adjust the connection and disconnection of the battery cells inside the battery module, and once a battery cell fails, it will cause a systematic failure. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide an energy storage system and a battery equalization method, which can flexibly adjust the connection and disconnection of the battery cells inside the battery module, and intelligently realize independent control of the energy conversion and energy storage of individual battery cells, and fault tolerance.

[0005] In order to solve the above problems, the present application is implemented according to the following scheme:

[0006] An energy storage system is provided, comprising a controller, N battery modules, a grid-connected inductor and an alternating current power supply;

[0007] The controller is connected with the N battery modules and an upper computer respectively; the N battery modules are connected in series; a first battery module is connected with an Nth battery module through the grid-connected inductor and the alternating current power supply in turn;

[0008] The battery module comprises an electronic switch; the controller is used for detecting battery parameters of the battery module, and controlling the on-off of the electronic switch according to the battery parameters, so as to control the charging and discharging state of the battery module and realize active equalization of the N battery modules.

[0009] Compared with the prior art, the energy storage system has the following advantages: by controlling the on-off of the electronic switch in the battery module, flexible adjustment and independent control of the battery cells inside the battery module are realized, and the energy conversion and storage of individual battery cells can be intelligently performed, effectively solving the problems of overcharging and overdischarging caused by inconsistent battery cell attenuation, improving the safety and reliability of the energy storage system, and at the same time, having fault tolerance capability, which significantly improves the overall performance and service life of the energy storage system.

[0010] Optionally, the battery module further comprises N temperature sensors and a cooling plate; the temperature sensors are connected with the battery module; the N battery modules are connected with the cooling plate.

[0011] Optionally, the battery module comprises a cell and a power unit; the cell is connected with the power unit and the temperature sensor;

[0012] The N power units comprised by the N battery modules are connected in series; the power units comprised by the first battery module are connected in sequence through the grid-connected inductor and the AC power supply to the power units comprised by the Nth battery module.

[0013] Optionally, the power unit comprises a fuse, a capacitor, a shunt and the electronic switch;

[0014] The electronic switch comprises a power unit electronic switch, a full-bridge circuit and a module bypass switch;

[0015] The cell is connected with the fuse and the shunt; the fuse is connected with the power unit electronic switch; the capacitor is connected with the power unit electronic switch, the full-bridge circuit and the shunt; the full-bridge circuit is connected with the module bypass switch;

[0016] The N module bypass switches comprised by the N power units are connected in series; the module bypass switches comprised by the first power unit are connected in sequence through the grid-connected inductor and the AC power supply to the module bypass switches comprised by the Nth power unit.

[0017] Optionally, the full-bridge circuit comprises a first bridge arm and a second bridge arm connected in parallel; the capacitor is connected with the first bridge arm and the second bridge arm in parallel; the module bypass switch is connected with the midpoint of the first bridge arm and the midpoint of the second bridge arm.

[0018] Optionally, the first bridge arm comprises a first switch and a second switch connected in series; the second bridge arm comprises a third switch and a fourth switch connected in series;

[0019] The capacitor is connected with the first end of the first switch, the second end of the second switch, the first end of the third switch and the second end of the fourth switch; the module bypass switch is connected with the second end of the first switch, the first end of the second switch, the second end of the third switch and the first end of the fourth switch.

[0020] Optionally, the power unit electronic switch, the module bypass switch, the first switch, the second switch, the third switch and the fourth switch are all semiconductor switches;

[0021] The controller is configured to control the switching states of the power unit electronic switch, the module bypass switch, the first switch, the second switch, the third switch and the fourth switch according to the battery parameters; the switching states of the first switch and the fourth switch are the same, the switching states of the second switch and the third switch are the same, the switching states of the first switch and the second switch are opposite, and the switching states of the third switch and the fourth switch are opposite.

[0022] Optionally, the controller comprises a processor and a memory, and the memory stores at least one instruction, at least one program, a code set or an instruction set, which is loaded and executed by the processor.

[0023] A battery balancing method is also provided, which is applied to N battery modules included in the energy storage system, and comprises

[0024] Obtaining battery parameters of the battery modules, wherein the battery parameters comprise output voltages, current directions and cell states of charge;

[0025] Determining a control type according to the current directions;

[0026] According to the cell states of charge and the control type, the N battery modules are sorted to obtain N battery modules in sequence;

[0027] According to the output voltages, the number of cells is determined, which is the number of battery modules to be controlled in the N battery modules in sequence;

[0028] According to the number of cells, the first several battery modules in the N battery modules in sequence are selected as the battery modules to be controlled;

[0029] According to the control type, the opening and closing states of the power unit electronic switch, the module bypass switch, the first switch, the second switch, the third switch and the fourth switch of the battery modules to be controlled are controlled, so that the battery modules to be controlled are put into or cut off from the energy storage system, and the N battery modules of the energy storage system are balanced.

[0030] Optionally, the number of times that the battery modules to be controlled are put into or cut off from the energy storage system within a preset time period is limited to one time. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The whole frame of the energy storage system of the present application is shown in Figure 1 ;

[0032] Figure 2 The whole frame of the energy storage system of the present application is shown in Figure 2 ;

[0033] Figure 3 Circuit diagram of the battery module of the present application;

[0034] Figure 4 Partial circuit diagram of the energy storage system of the present application;

[0035] Figure 5 Flow of the battery equalization method of the present application Figure 1 ;

[0036] Figure 6 Flow of the battery equalization method of the present application Figure 2 ;

[0037] Figure 7 Signal modulation schematic diagram of the energy storage system of the present application including 6 battery modules in a cycle;

[0038] Figure 8 SOC value of the battery cell of the energy storage system of the present application including 6 battery modules;

[0039] Figure 9 Signal modulation schematic diagram of the energy storage system of the present application including 6 battery modules after sorting.

[0040] The reference signs are explained as follows: 1, controller; 2, battery module; 201, battery cell; 202, power unit; 3, grid-connected inductor; 4, alternating current power supply; 5, upper computer; 6, temperature sensor; 7, cooling plate. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, and it should be understood that the preferred embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0042] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present application. It should be appreciated that the present application can be practiced in a variety of ways, and that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting save for in the claims. The use of the terms "first", "second", "third", etc. are not intended to denote a particular order or sequence, but are used to distinguish one element from another. The use of the term "a" or "an" is intended to denote one or more, unless specified otherwise.

[0043] Reference Signs List, 1, controller; 2, battery module; 201, battery cell; 202, power unit; 3, grid-connected inductor; 4, alternating current power supply; 5, upper computer; 6, temperature sensor; 7, cooling plate. Figure 1As shown, the present application provides an energy storage system, comprising: a controller 1, N battery modules 2, a grid-connected inductor 3 and an alternating current power supply 4; the controller 1 is connected with the N battery modules 2 and an upper computer 5 respectively; the alternating current power supply 4 is used to provide alternating current power supply for the energy storage system; the N battery modules 2 are connected in series; the first battery module 2 is connected with the Nth battery module 2 through the grid-connected inductor 3 and the alternating current power supply 4 in turn; the battery module 2 comprises an electronic switch; the controller 1 is used to detect the battery parameters of the battery module 2, and control the on-off of the electronic switch according to the battery parameters, so as to control the charging and discharging state of the battery module, realize the active balancing among the N battery modules 2, and the staff can check the battery parameters through the upper computer 5.

[0044] As shown in the drawings, Figure 2 As shown in an embodiment of the present application, the energy storage system further comprises N temperature sensors 6 and a cooling plate 7; the temperature sensor 6 is connected with the battery module 2; the N battery modules 2 are connected with the cooling plate 7, specifically, the battery module 2 is placed on the cooling plate 7, and the cooling plate 7 is used to input external cooling liquid.

[0045] The energy storage system further comprises a plurality of smoke sensors and a fire-fighting interface, and the control module is connected with the temperature sensor 6, the smoke sensor, the cooling plate 7 and the fire-fighting interface; the fire-fighting interface is used to input external fire extinguishing agent; the smoke sensor is used to obtain the concentration values of CO2, CO, H2 and other gases in the energy storage system and send them to the controller 1; when the concentration values of CO2, CO, H2 and other gases exceed the preset concentration, it means that the energy storage system may have a fire phenomenon, the controller 1 controls the fire-fighting interface to open, so that the external fire extinguishing agent enters the energy storage system to extinguish the fire of the energy storage system, thereby avoiding more serious problems and affecting the normal operation of the energy storage system.

[0046] As shown in the drawings, Figures 3-4 As shown in an embodiment of the present application, the battery module 2 comprises a battery cell 201 and a power unit 202; the battery cell 201 is connected with the power unit 202 and the temperature sensor 6; the temperature sensor 6 is used to obtain the temperature of the battery cell 201 in real time and send it to the controller 1; when the temperature of the battery cell 201 exceeds the preset temperature, the controller 1 controls the interface of the cooling plate 7 which inputs the cooling liquid to open, so that the external cooling liquid enters the cooling plate 7, and then the battery module 2 placed on the cooling plate 7 is cooled, which plays a cooling role on the battery module 2; the N power units 202 included in the N battery modules 2 are connected in series; the power unit 202 included in the first battery module 2 is connected with the power unit 202 included in the Nth battery module 2 through the grid-connected inductor 3 and the alternating current power supply 4 in turn, that is, the first power unit 202 is connected with the Nth power unit 202 through the grid-connected inductor 3 and the alternating current power supply 4 in turn.

[0047] The power unit 202 includes a fuse F, a capacitor C, a shunt R and an electronic switch; the electronic switch includes a power unit electronic switch Q5, a full-bridge circuit and a module bypass switch S; the battery cell 201 is connected with the fuse F and the shunt R; the fuse F is connected with the power unit electronic switch Q5; the capacitor C is connected with the power unit electronic switch Q5, the full-bridge circuit and the shunt R; the full-bridge circuit is connected with the module bypass switch S.

[0048] The power unit electronic switch Q5 is used to realize the connection and disconnection between the battery cell 201 inside the battery module 2 and the power unit 202; when the power unit electronic switch Q5 is turned on, the battery cell 201 inside the battery module 2 is connected with the power unit 202; when the power unit electronic switch Q5 is turned off, the battery cell 201 inside the battery module 2 is disconnected with the power unit 202.

[0049] The module bypass switch S is used to disconnect the faulty battery module 2 when a fault occurs inside the battery module 2, so as to ensure that the battery modules 2 without faults in the energy storage system can normally operate; the module bypass switch S is usually in an open circuit state, that is, the module bypass switch S is usually in an off state; when the power unit 202 or the battery cell 201 inside the battery module 2 fails, the module bypass switch S is closed (at this time, the module bypass switch S is in an on state), so as to ensure that the battery modules 2 without faults in the energy storage system can normally operate; and through the module bypass switch S, the battery cell 201 inside the battery module 2 can be flexibly adjusted and independently controlled, the energy conversion and storage of a single battery cell 201 can be intelligently performed, the overcharging and overdischarging problems caused by inconsistent attenuation of the battery cells 201 can be effectively solved, the safety and reliability of the energy storage system are improved, the energy storage system has fault tolerance capability, and the overall performance and service life of the energy storage system are significantly improved.

[0050] Figure 4 N is the number of battery modules 2 in the energy storage system, that is, N is the number of battery cells 201 in the energy storage system, that is, N is the number of power units 202 in the energy storage system; Figure 4 The connection relationship between the N battery modules 2 is shown, that is, the connection relationship between the N power units 202 is shown; the N module bypass switches S included in the N power units 202 are connected in series, that is, Figure 4 the first module bypass switch S1 is connected with the Nth module bypass switch SN through the second module bypass switch S2, …, in sequence; the module bypass switch S included in the first power unit 202 is connected with the module bypass switch S included in the Nth power unit 202 through the grid-connected inductor 3 and the alternating current power supply 4 in sequence, that is, the first module bypass switch S1 is connected with the Nth module bypass switch SN through the grid-connected inductor 3 and the alternating current power supply 4 in sequence.

[0051] The full-bridge circuit includes a first bridge arm and a second bridge arm in parallel; a capacitor C is connected in parallel with the first bridge arm and the second bridge arm; a module bypass switch S is connected with the midpoint of the first bridge arm and the midpoint of the second bridge arm; wherein the first bridge arm includes a first switch Q1 and a second switch Q2 in series; the second bridge arm includes a third switch Q3 and a fourth switch Q4 in series; the capacitor C is connected with the first end of the first switch Q1, the second end of the second switch Q2, the first end of the third switch Q3, and the second end of the fourth switch Q4; the module bypass switch S is connected with the second end of the first switch Q1, the first end of the second switch Q2, the second end of the third switch Q3, and the first end of the fourth switch Q4; the power unit electronic switch Q5, the module bypass switch S, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 are all semiconductor switches.

[0052] The controller 1 is configured to control the switching states of the power unit electronic switch Q5, the module bypass switch S, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 according to the battery parameters; the switching states of the first switch Q1 and the fourth switch Q4 are the same, the switching states of the second switch Q2 and the third switch Q3 are the same, the switching states of the first switch Q1 and the second switch Q2 are opposite, and the switching states of the third switch Q3 and the fourth switch Q4 are opposite.

[0053] The controller 1 controls the switching states of the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 to realize the charging and discharging state conversion of the battery cell 201, so that Figure 3 The single battery module 2 shown in the figure is used to explain the charging and discharging state conversion of the battery cell 201 in detail:

[0054] The power unit electronic switch Q5 is used to realize the connection and disconnection between the battery cell 201 inside the battery module 2 and the power unit 202; when the power unit electronic switch Q5 is in the on state (the power unit electronic switch Q5 is closed), the battery cell 201 inside the battery module 2 is connected with the power unit 202; when the power unit electronic switch Q5 is in the off state (the power unit electronic switch Q5 is opened), the battery cell 201 inside the battery module 2 is disconnected with the power unit 202; therefore, no matter whether the battery cell 201 is in the charging state or the discharging state, the power unit electronic switch Q5 needs to be in the on state.

[0055] When the first switch Q1 and the fourth switch Q4 are in the on state (the first switch Q1 and the fourth switch Q4 are closed), the second switch Q2 and the third switch Q3 are in the off state (the second switch Q2 and the third switch Q3 are opened), and U ab1 =U c =U b , i dc =-i o , the battery cell 201 is in the charging state;

[0056] When the first switch Q1 and the fourth switch Q4 are in an off state (the first switch Q1 and the fourth switch Q4 are open), the second switch Q2 and the third switch Q3 are in an on state (the second switch Q2 and the third switch Q3 are closed), and U ab1 = U c = U b , i dc = -i o , the battery cell 201 is in a charging state.

[0057] When the first switch Q1 and the fourth switch Q4 are in an on state (the first switch Q1 and the fourth switch Q4 are closed), the second switch Q2 and the third switch Q3 are in an off state (the second switch Q2 and the third switch Q3 are open), and -U ab1 = U c = U b , i dc = i o , the battery cell 201 is in a discharging state.

[0058] When the first switch Q1 and the fourth switch Q4 are in an off state (the first switch Q1 and the fourth switch Q4 are open), the second switch Q2 and the third switch Q3 are in an on state (the second switch Q2 and the third switch Q3 are closed), and -U ab1 = U c = U b , i dc = i o , the battery cell 201 is in a discharging state.

[0059] The controller 1 includes a processor and a memory. The memory stores at least one instruction, at least one program, a code set, or an instruction set, which is loaded and executed by the processor.

[0060] The processor can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or the like.

[0061] The memory can be used to store the computer program or module, the processor runs or executes the computer program or module stored in the memory, and calls the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, an application required by at least one function, and the like; and the data storage area can store data created according to the use of the mobile phone and the like. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, for example, a hard disk, a memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0062] The application realizes multifunctional information fusion and modular integration of the battery cell 201 and the power unit 202 and the battery module 2 in the energy storage system through the controller 1, reduces the integration difficulty and maintenance cost of the energy storage system, and the prior art separates the battery, the converter (power unit 202), the battery management system and the safety pipe (temperature, smoke), which leads to high integration difficulty of the energy storage system and high requirements for technicians and maintenance personnel.

[0063] The application realizes automatic switching of the battery cell 201 by using high-frequency power electronic semiconductor switches (control power unit electronic switches Q5, module bypass switches S, first switches Q1, second switches Q2, third switches Q3 and fourth switches Q4), realizes flexible interconnection of the battery cell 201 and energy storage and conversion of the battery cell 201, samples the voltage, current and temperature of the battery cell 201 through the power unit 202, actively balances the battery cell 201 and realizes two-in-one of power conversion, fully utilizes the energy of each battery cell 201 and reduces over-provisioning of the battery of the energy storage system.

[0064] The energy storage system of the application realizes real-time monitoring of the voltage, current and temperature of each battery cell 201 under the charging, discharging and standing state of the battery cell 201 in the energy storage system, flexible connection of each battery cell 201 and the power unit 202 through the fuse F and the power unit electronic switch Q5, closing of the module bypass switch S when the power unit 202 or the battery cell 201 fails, continuous operation of other battery cells 201 (battery modules 2) in the energy storage system, hard connection between the battery modules 2 in the conventional energy storage system and disconnection of the failed battery module 2.

[0065] Referring to Figures 5-6 The application further provides a battery balancing method applied to the N battery modules included in the energy storage system, and the method comprises the following steps:

[0066] S1: Obtain the battery parameters of the battery module. The battery parameters include output voltage, current direction and cell state of charge. The cell state of charge includes the cell SOC value, which is calculated as: cell SOC value = (remaining cell capacity / cell rated capacity) * 100%.

[0067] This invention maps the cell's State of Charge (SOC) value by sampling the cell's open-circuit voltage after disconnecting the power unit electronic switch Q5 (in the off state). For example, when the cell's highest open-circuit voltage is 3.6V, its corresponding SOC value is 100%; 3.5V corresponds to 95%; 3.4V to 90%; 3.3V to 85%; 3.2V to 80%; and 3.1V to [missing value]. The SOC value of a battery cell can be obtained based on its open-circuit voltage. Specifically, an open-circuit voltage of 3.0V corresponds to a SOC value of 70%, 2.9V to 65%, 2.85V to 60%, 2.8V to 55%, 2.75V to 45%, 2.7V to 35%, 2.65V to 25%, 2.6V to 10%, and 2.55V to 0%.

[0068] S2: Determine the control type based on the current direction, where the current direction is... Figure 4 Middle I b The direction of the current, according to I b Size determines its flow direction; when I b When I > 0, the current direction is positive, and the battery cells of the battery module are discharged at this time; that is, the control type at this time is the discharge type. b When the current is less than 0, the current direction is reversed. At this time, the battery cells of the battery module are charged, and the control type at this time is the charging type.

[0069] S3: Sort the N battery modules according to their state of charge and control type to obtain a sorted list of N battery modules, specifically:

[0070] When the control type is discharge type, the cell with more remaining power has a longer discharge time, and the cell with less remaining power has a shorter discharge time. That is, the cell with a larger SOC value is put into the energy storage system first, and the cell with a smaller SOC value is removed from the energy storage system. Therefore, when the control type is discharge type, the N battery modules are sorted from largest to smallest according to the SOC value of the cells corresponding to the battery modules.

[0071] When the control type is the charging type, the charging time of the battery cell with less remaining power is long, and the charging time of the battery cell with more remaining power is short, that is, the battery cell with a small SOC value is first put into the energy storage system, and the battery cell with a large SOC value is cut off from the energy storage system, so when the control type is the charging type, the N battery modules are sorted from small to large according to the respective SOC values of the battery modules.

[0072] S4: determining the number of battery cells according to the output voltage, the output voltage being Figure 4 the output voltage of the full-bridge circuit in each power unit in the energy storage system ab1 , U ab2 ,..., U abN , U ab , and the total output voltage of all power units in the energy storage system being

[0073]

[0074] The energy storage system uses battery modules (battery cells) as the smallest cascaded unit, and each energy storage system usually contains dozens to hundreds of battery cells, so the step wave is used to directly approximate the modulation wave by instantaneous level superposition, and the switching frequency is less than pulse width modulation (PWM), which can significantly reduce the switching loss of high-frequency power electronic semiconductors. The on-resistance of low-voltage power electronic semiconductor devices is extremely low, usually 1-2 milliohms, so the conduction loss is very small.

[0075] Referring to Figure 7 , a signal modulation schematic diagram of an energy storage system including six battery modules in a cycle is given, that is, a signal modulation schematic diagram of an energy storage system including six power units is given; the output voltage U abi of a single full-bridge circuit is +U b , -U b , and the maximum output of six power units in cascade is 12 levels, and the range of the 12 levels is -6U b to +6U b .

[0076] According to the modulation wave in Figure 7 , the number k of battery cells (power units) put in each cycle can be calculated as

[0077]

[0078] wherein k is the number of battery cells put in the current cycle, round(x) represents taking the integer closest to x, abs(x) represents taking the absolute value of x, and the value of k satisfies 0≤k≤N; isFigure 7 the peak value of the sinusoidal modulation wave, the plateau value of the staircase wave. Figure 7 The peak value of the sinusoidal modulation wave is divided by the plateau value of the staircase wave, and the number of steps of the staircase wave is obtained, that is, the number of battery cells required to be put into the energy storage system.

[0079] S5: According to the number of battery cells, select the first several battery modules from the sequentially sorted N battery modules as the to-be-controlled battery modules.

[0080] If the number of battery cells in the current period is the same as that in the last period, it is necessary to determine whether the SOC value corresponding to the to-be-controlled battery module is within the cutoff range, and the cutoff range is the battery cell discharge termination SOC value, such as the SOC value corresponding to the open-circuit voltage of 2.6V is 10% as the cutoff range. Controlling the SOC value of the battery cell within the cutoff range can protect the battery cell and prevent the battery cell from being damaged due to over-discharge; if the SOC value corresponding to the to-be-controlled battery module is within the cutoff range, the pulse of the power unit is kept unchanged; if the SOC value corresponding to the to-be-controlled battery module is not within the cutoff range, according to the current direction of the power unit, the switching states of the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 of the full-bridge circuit in the partial power unit are controlled, specifically, the on state and the off state are interchanged.

[0081] If the number of battery cells in the current period is different from that in the last period, according to the current direction and the control type, the battery modules that need to be put into or cut off are determined, specifically, if the to-be-controlled battery module is the battery module to be put into in the current period, the battery module put into in the last period is not the battery module to be cut off in the current period as the to-be-controlled battery module, for example, the energy storage system in the last period put in the first battery module, the second battery module, and the third battery module, and the battery module to be put into in the current period is the first battery module and the second battery module, and then the battery module to be cut off in the current period is the third battery module.

[0082] Since the SOC value of the battery cell changes at a second level, the battery cell based on the SOC value sorting may change within a few seconds, which will cause some battery cells to be frequently put in and cut off during the charging and discharging process. Therefore, in an embodiment of the present application, the number of times that the to-be-controlled battery module is put into the energy storage system or cut off from the energy storage system within a predetermined time period is limited to one time.

[0083] S6: According to the control type, control the opening and closing states of the power unit electronic switch Q5, the module bypass switch S, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 of the to-be-controlled battery module, so as to put the to-be-controlled battery module into the energy storage system or cut it off from the energy storage system, and balance the N battery modules of the energy storage system.

[0084] The application realizes the balance among multiple battery modules according to the SOC values of each battery cell, and the power unit adopts the nearest level modulation strategy; in the case of poor consistency of battery cell capacity, active balancing control of each battery cell can be easily realized, while the conventional carrier phase-shift modulation strategy needs to adjust the modulation wave of each power unit, and the control process is much more complicated, and the existing active balancing control of battery cell needs auxiliary circuit, which will bring additional energy loss, while the application can realize the investment or removal operation of each battery cell without additional auxiliary circuit, so as to realize the active balancing of the battery module.

[0085] The application provides the condition for online measurement of open circuit voltage of the battery cell, because the battery cell in the battery module can be flexibly connected or disconnected with the AC circuit, while the battery module of the conventional energy storage system is hard connected, and the online measurement of open circuit voltage of the battery module cannot be realized, so that the SOC value of the battery cell of each battery module can be accurately obtained by online measurement of the open circuit voltage of the battery cell in the battery module.

[0086] Next, the charging process of the single-phase 6 battery modules shown in Figure 7 will be taken as an example to specifically explain the working principle of the battery balancing method of the energy storage system.

[0087] Referring to Figures 8-9 , Figure 8 B1, B2,..., B6 in the formula respectively represent the SOC values of the battery cells of the 6 battery modules, the controller disconnects Q1-Q5 (low-voltage MOSFET as power switch tube) of the power module, and the 6 battery cells are allowed to stand for a period of time, then the open circuit voltage of each battery cell is tested, and the SOC value (remaining power of the battery cell) of each battery module is estimated according to the open circuit voltage of the 6 battery cells.

[0088] In the charging state, that is, the control type is the charging type, each battery module is arranged in the order from small to large according to the SOC value of the battery cell, and the open circuit voltage corresponding to each battery cell is denoted as U bi , and the required charging power of each battery cell is P bi ; referring to Table 1 and Table 2, Table 1 shows the result before sorting, and Table 2 shows the result after sorting.

[0089] Table 1: Result before sorting

[0090]

[0091] Table 2: Result after sorting

[0092]

[0093] Referring to Figure 9As shown, the signal modulation of each power module in the charging process is arranged according to the SOC of each battery cell. As can be seen from the figure, the lower the SOC value of the battery cell, the longer the power unit is turned on, and the more power is supplied to the battery cell. After a period of time, the SOC values of the battery cells are basically consistent.

[0094] Thereafter, in order to ensure that the SOC values of the battery cells of each battery module reach 100% at the same time, the signal modulation of the battery cells of each battery module needs to be round-robin modulated, for example, the signal modulation of the battery cells of each battery module is arranged in the order of SM1, SM2, SM3, SM4, SM5 and SM6. Figure 7 The signal modulation shown is the initial state, and the second round of signal modulation is arranged in the order of SM6, SM1, SM2, SM3, SM4 and SM5, and the third round of signal modulation is arranged in the order of SM5, SM6, SM1, SM2, SM3 and SM4. The above process is repeated until the SOC values of the battery cells of each battery module reach 100%.

[0095] In the charging process, if the power unit corresponding to SM3 fails or the SOC value of the battery cell corresponding to SM3 reaches 100% first, the module bypass switch S of the power unit corresponding to SM3 is closed. At the same time, the power unit electronic switch Q5 connected to the power unit and the battery cell is disconnected, and the remaining five battery cells continue to be charged according to the signal modulation shown in Figure 7 The signal modulation shown in the figure continues to charge, but one set of modulation signals is reduced.

[0096] In the discharging process of the battery, the SOC of each battery cell is arranged in the order from large to small, and the signal modulation process is the same as the above principle, which will not be described here.

[0097] The above is only a preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An energy storage system, characterized in that, include: Controller, N battery modules, grid-connected inductor, and AC power supply; The controller is connected to N battery modules and a host computer respectively; the N battery modules are connected in series; the first battery module is connected to the Nth battery module in sequence through the grid-connected inductor and the AC power supply; The battery module includes an electronic switch; the controller is used to detect the battery parameters of the battery module, determine the on / off time of the electronic switch according to the battery parameters, and control the on / off time of the electronic switch to control the charging and discharging state of the battery module, thereby achieving active balancing of N battery modules. It also includes N temperature sensors and a cooling plate; the temperature sensors are connected to the battery module; the N battery modules are connected to the cooling plate; It also includes multiple smoke sensors and fire extinguishing interfaces. The controller is connected to the smoke sensors and the fire extinguishing interfaces respectively. The smoke sensors are used to detect gas concentration. When the gas concentration exceeds a preset concentration, the controller controls the fire extinguishing interfaces to open. The battery module includes a battery cell and a power unit; the battery cell is connected to the power unit and the temperature sensor; the temperature sensor is used to detect the temperature of the battery cell, and the battery parameters include the state of charge of the battery cell; the charging and discharging current of the battery module is controlled according to the temperature of the battery cell and the state of charge of the battery cell. The N battery modules each contain N power units connected in series; the power units of the first battery module are connected to the power units of the Nth battery module in sequence through the grid-connected inductor and the AC power supply. The power unit includes a fuse, a capacitor, a shunt, and the electronic switch; The electronic switch includes a power unit electronic switch, a full-bridge circuit, and a module bypass switch; The battery cell is connected to the fuse and the shunt; the fuse is connected to the power unit electronic switch; the capacitor is connected to the power unit electronic switch, the full-bridge circuit, and the shunt; the full-bridge circuit is connected to the module bypass switch. The N power units each include N module bypass switches connected in series; the module bypass switch of the first power unit is connected to the module bypass switch of the Nth power unit in sequence through the grid-connected inductor and the AC power supply.

2. The energy storage system according to claim 1, characterized in that, The full-bridge circuit includes a first bridge arm and a second bridge arm connected in parallel; the capacitor is connected in parallel with the first bridge arm and the second bridge arm; the module bypass switch is connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm.

3. The energy storage system according to claim 2, characterized in that, The first bridge arm includes a first switch and a second switch connected in series; the second bridge arm includes a third switch and a fourth switch connected in series. The capacitor is connected to the first terminal of the first switch, the second terminal of the second switch, the first terminal of the third switch, and the second terminal of the fourth switch; the module bypass switch is connected to the second terminal of the first switch, the first terminal of the second switch, the second terminal of the third switch, and the first terminal of the fourth switch.

4. An energy storage system according to claim 3, characterized in that, The power unit electronic switch, the module bypass switch, the first switch, the second switch, the third switch, and the fourth switch are all semiconductor switches; The controller is used to control the switching states of the power unit electronic switch, the module bypass switch, the first switch, the second switch, the third switch, and the fourth switch according to the battery parameters; the first switch and the fourth switch have the same switching state, the second switch and the third switch have the same switching state, the first switch and the second switch have opposite switching states, and the third switch and the fourth switch have opposite switching states.

5. An energy storage system according to claim 4, characterized in that, The controller includes a processor and a memory, the memory storing at least one instruction, at least one program, code set, or instruction set, the at least one instruction, at least one program, code set, or instruction set being loaded and executed by the processor.

6. A battery balancing method, applied to the energy storage system according to claims 1-5, wherein the energy storage system comprises N battery modules, characterized in that, The method includes the following steps: Obtain the battery parameters of the battery module, including output voltage, current direction and cell state of charge; The control type is determined based on the current direction; Based on the cell state of charge and the control type, the N battery modules are sorted to obtain N battery modules in sequence. The number of battery cells is determined based on the output voltage, where the number of battery cells is the number of battery modules to be controlled among N battery modules arranged in sequence. Based on the number of battery cells, select the first few battery modules from the N battery modules arranged in sequence as the battery modules to be controlled. According to the control type, the opening and closing states of the power unit electronic switch, module bypass switch, first switch, second switch, third switch and fourth switch of the battery module to be controlled are controlled so that the battery module to be controlled is put into the energy storage system or is cut out from the energy storage system, thereby balancing the N battery modules of the energy storage system.

7. The battery balancing method according to claim 6, characterized in that, The number of times the battery module to be controlled can be put into or removed from the energy storage system within a preset time period is limited to once.

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