Energy storage system and battery equalization method

Abstract

The invention discloses an energy storage system and a battery equalization method. The energy storage system comprises a controller, N battery modules, a grid-connected inductor and an alternating current power supply, the controller is respectively connected with the N battery modules and the upper computer; the N battery modules are connected in series; the first battery module is connected with the Nth battery module through a grid-connected inductor and an alternating current power supply in sequence; the battery module comprises an electronic switch; the controller is used for detecting battery parameters of the battery modules and controlling on-off of the electronic switches according to the battery parameters so as to control the charging and discharging states of the battery modules, and active equalization of the N battery modules is achieved. By controlling the on-off of the electronic switch, flexible adjustment and independent management and control of the battery cells in the battery module are realized, energy conversion and storage can be performed on the single battery cell, the problem of over-charging and over-discharging caused by inconsistent attenuation of the battery cells is solved, the safety and reliability of the energy storage system are improved, and meanwhile, the energy storage system has the fault-tolerant capability and is suitable for popularization and application. The overall performance and the service life of the energy storage system are obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and in particular to an energy storage system and a battery balancing method. Background Art

[0002] At present, energy storage technology based on batteries and power electronics is developing rapidly. The DC side of the energy storage system uses multiple battery modules or clusters in series and parallel. During use, due to the influence of temperature, high current charging and discharging, etc., the decay speed of each battery module is inconsistent. Therefore, a battery management system is needed to perform battery balancing control. In extreme cases, the rapid decrease in the capacity of a single or several cells can easily lead to overcharging and over-discharging, posing serious safety hazards.

[0003] However, currently the battery modules and internal cells are all fixedly welded, and the connection and disconnection of the cells inside the battery module cannot be adjusted. Once a cell fails, it will cause a systemic failure. Summary of the invention

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

[0005] In order to solve the above problems, the present invention is implemented according to the following scheme: Provided is an energy storage system, comprising: a controller, N battery modules, a grid-connected inductor and an AC power supply; The controller is connected to N battery modules and the host computer respectively; the N battery modules are connected in series; the first battery module is connected to the Nth battery module through the grid-connected inductor and the AC power supply in sequence; The battery module includes an electronic switch; the controller is used to detect battery parameters of the battery module and control the on and off of the electronic switch according to the battery parameters to control the charge and discharge state of the battery module and achieve active balancing of N battery modules.

[0006] Compared with the prior art, the beneficial effects of an energy storage system of the present invention are as follows: by controlling the on and off of the electronic switch in the battery module, flexible adjustment and independent control of the battery cells inside the battery module are achieved, and the energy conversion and storage of a single battery cell can be intelligently performed, effectively solving the overcharge and over-discharge problems caused by inconsistent battery cell attenuation, improving the safety and reliability of the energy storage system, and at the same time having fault tolerance capabilities, significantly improving the overall performance and life of the energy storage system.

[0007] Optionally, it also includes N temperature sensors and a cooling plate; the temperature sensor is connected to the battery module; and the N battery modules are connected to the cooling plate.

[0008] Optionally, 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 N power units respectively included in the N battery modules are connected in series; the power unit included in the first battery module is connected to the power unit included in the Nth battery module through the grid-connected inductor and the AC power supply in sequence.

[0009] Optionally, 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 module bypass switches respectively included in the N power units are connected in series; the module bypass switch included in the first power unit is connected to the module bypass switch included in the Nth power unit through the grid-connected inductor and the AC power supply in sequence.

[0010] Optionally, 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; and the module bypass switch is connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm.

[0011] Optionally, 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 a first end of the first switch, a second end of the second switch, a first end of the third switch, and a second end of the fourth switch; the module bypass switch is connected to a second end of the first switch, a first end of the second switch, a second end of the third switch, and a first end of the fourth switch.

[0012] 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; 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 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.

[0013] Optionally, the controller includes a processor and a memory, wherein the memory stores at least one instruction, at least one program, code set or instruction set, and the at least one instruction, at least one program, code set or instruction set is loaded and executed by the processor.

[0014] A battery balancing method is also provided, which is applied to the N battery modules included in the energy storage system, including: Obtaining battery parameters of the battery module, wherein the battery parameters include output voltage, current direction, and battery cell charge state; Determining a control type according to the current direction; Sorting the N battery modules according to the battery cell charge state and the control type to obtain N battery modules that are sequentially sorted; Determine the number of battery cells according to the output voltage, where the number of battery cells is the number of battery modules to be controlled in the N battery modules arranged in sequence; According to the number of battery cells, the first several battery modules are selected 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, the module bypass switch, the first switch, the second switch, the third switch and the 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 removed from the energy storage system to balance the N battery modules of the energy storage system.

[0015] Optionally, the number of times the battery module to be controlled is put into the energy storage system or removed from the energy storage system within a preset time period is limited to once. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The overall frame of the energy storage system of the present invention Figure 1 ; Figure 2 The overall frame of the energy storage system of the present invention Figure 2 ; Figure 3 is a circuit diagram of a battery module of the present invention; Figure 4 It is a partial circuit diagram of the energy storage system of the present invention; Figure 5 The process of the battery balancing method of the present invention is as follows Figure 1 ; Figure 6 The process of the battery balancing method of the present invention is as follows Figure 2 ; Figure 7 The energy storage system of the present invention includes 6 battery modules in one cycle. Figure 8The energy storage system of the present invention includes a battery cell SOC value of 6 battery modules; Fig. 9 A partial circuit diagram of an energy storage system of the present invention including 6 battery modules; Fig.10 The energy storage system of the present invention includes 6 battery modules after being sorted.

[0017] Explanation of the reference numerals: 1. controller; 2. battery module; 201. battery cell; 202. power unit; 3. grid-connected inductor; 4. AC power supply; 5. host computer; 6. temperature sensor; 7. cooling plate. DETAILED DESCRIPTION

[0018] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0019] When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0020] See also Figure 1 As shown, the present invention provides an energy storage system, including: a controller 1, N battery modules 2, a grid-connected inductor 3 and an AC power supply 4; the controller 1 is connected to the N battery modules 2 and a host computer 5 respectively; the AC power supply 4 is used to provide AC power for the energy storage system; the N battery modules 2 are connected in series; the first battery module 2 is connected to the Nth battery module 2 through the grid-connected inductor 3 and the AC power supply 4 in turn; the battery module 2 includes an electronic switch; the controller 1 is used to detect the battery parameters of the battery module 2, and control the on and off of the electronic switch according to the battery parameters to control the charge and discharge state of the battery module, and realize active balance between the N battery modules 2, and the staff can view the battery parameters through the host computer 5.

[0021] See also Figure 2 As shown, in one embodiment of the present invention, the energy storage system also includes N temperature sensors 6 and a cooling plate 7; the temperature sensor 6 is connected to the battery module 2; the N battery modules 2 are connected to 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 coolant.

[0022] The energy storage system also includes multiple smoke sensors and fire interfaces. The control module is connected to the temperature sensor 6, the smoke sensor, the cooling plate 7, and the fire interface; the fire interface is used to input external fire extinguishing agents; the smoke sensor is used to obtain the concentration values ​​of gases such as CO2, CO, H2 in the energy storage system and send them to the controller 1. When the concentration values ​​of gases such as CO2, CO, H2 exceed the preset concentration, it means that there may be a fire in the energy storage system. The controller 1 controls the fire interface to open so that the external fire extinguishing agent enters the energy storage system to extinguish the fire in the energy storage system, thereby avoiding more serious problems and affecting the normal operation of the energy storage system.

[0023] See also Figure 3-4 As shown, in one embodiment of the present invention, the battery module 2 includes a battery cell 201 and a power unit 202; the battery cell 201 is connected to the power unit 202 and a 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 input coolant interface of the cooling plate 7 to open so that the external coolant enters the cooling plate 7, thereby cooling the battery module 2 placed on the cooling plate 7, and cooling the battery module 2. At the same time, the controller 1 also controls the current of the battery cell 201 for charging and discharging according to the temperature of the battery cell 201 to extend the service life of the battery cell 201; the N power units 202 respectively included in the N battery modules 2 are connected in series; the power unit 202 included in the first battery module 2 is connected to the power unit 202 included in the Nth battery module 2 through the grid-connected inductor 3 and the AC power supply 4 in turn, that is, the first power unit 202 is connected to the Nth power unit 202 through the grid-connected inductor 3 and the AC power supply 4 in turn.

[0024] 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 to the fuse F and the shunt R; the fuse F is connected to the power unit electronic switch Q5; the capacitor C is connected to the power unit electronic switch Q5, the full-bridge circuit and the shunt R; the full-bridge circuit is connected to the module bypass switch S.

[0025] The power unit electronic switch Q5 is used to realize the connection and disconnection between the internal battery cell 201 of the battery module 2 and the power unit 202. When the power unit electronic switch Q5 is turned on, the internal battery cell 201 of the battery module 2 and the power unit 202 are connected. When the power unit electronic switch Q5 is turned off, the internal battery cell 201 of the battery module 2 and the power unit 202 are disconnected.

[0026] 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 that have not failed in the energy storage system can operate normally. The module bypass switch S is usually in an open circuit state, that is, the module bypass switch S is usually in a closed state. When a power unit 202 or a battery cell 201 in the battery module 2 fails, the module bypass switch S is closed (the module bypass switch S is in an open state at this time) to ensure that the battery modules 2 that have not failed in the energy storage system can operate normally. In addition, the module bypass switch S can also realize flexible adjustment and independent control of the battery cells 201 inside the battery module 2, and can intelligently perform energy conversion and storage of a single battery cell 201, effectively solving the overcharge and over-discharge problems caused by inconsistent attenuation of the battery cells 201, improving the safety and reliability of the energy storage system, and at the same time having fault tolerance, which significantly improves the overall performance and life of the energy storage system.

[0027] Figure 4 Where 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 power units 202 respectively include N module bypass switches S connected in series, that is, Figure 4 The first module bypass switch S1 is connected to the Nth module bypass switch SN in sequence through the second module bypass switch S2, ...; the module bypass switch S included in the first power unit 202 is connected to the module bypass switch S included in the Nth power unit 202 in sequence through the grid-connected inductor 3 and the AC power supply 4, that is, the first module bypass switch S1 is connected to the Nth module bypass switch SN in sequence through the grid-connected inductor 3 and the AC power supply 4.

[0028] The full-bridge circuit includes a first bridge arm and a second bridge arm connected 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 to 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 connected in series; the second bridge arm includes a third switch Q3 and a fourth switch Q4 connected in series; the capacitor C is connected to a first end of the first switch Q1, a second end of the second switch Q2, a first end of the third switch Q3, and a second end of the fourth switch Q4; the module bypass switch S is connected to a second end of the first switch Q1, a first end of the second switch Q2, a second end of the third switch Q3, and a 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.

[0029] The controller 1 is used 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.

[0030] The controller 1 realizes the charge and discharge state conversion of the battery cell 201 by controlling the switch states of the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4. Figure 3 The single battery module 2 shown provides a detailed description of the charge and discharge state conversion of the battery cell 201: Because 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 to the power unit 202, and when the power unit electronic switch Q5 is in the off state (the power unit electronic switch Q5 is open), the battery cell 201 inside the battery module 2 is disconnected from the power unit 202; therefore, regardless of whether the battery cell 201 is in the charging state or the discharging state, the power unit electronic switch Q5 must be in the on state.

[0031] 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 open), and U ab1 =U c =U b ,i dc = -i o When , the battery cell 201 is in a charging state; When the first switch Q1 and the fourth switch Q4 are in the off state (the first switch Q1 and the fourth switch Q4 are open), the second switch Q2 and the third switch Q3 are in the on state (the second switch Q2 and the third switch Q3 are closed), and U ab1 =U c =U b ,i dc = -i o When , the battery cell 201 is in a charging state; 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 open), and -U ab1 =U c =U b ,idc =i o When , the battery cell 201 is in a discharging state; When the first switch Q1 and the fourth switch Q4 are in the off state (the first switch Q1 and the fourth switch Q4 are open), the second switch Q2 and the third switch Q3 are in the 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.

[0032] The controller 1 comprises a processor and a memory, wherein at least one instruction, at least one program, a code set or an instruction set is stored in the memory, and the at least one instruction, at least one program, a code set or an instruction set is loaded and executed by the processor.

[0033] The processor can be a central processing unit (CPU), or 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, etc.

[0034] The memory can be used to store the computer program or module, and 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, at least one application required for a function, etc.; the data storage area can store data created according to the use of the mobile phone, etc. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (SmartMedia Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0035] The present invention controls the battery cell 201, the power unit 202, and the battery module 2 through the controller 1 to achieve multifunctional information fusion and modular integration within the energy storage system, reducing the integration difficulty and maintenance cost of the energy storage system. However, the prior art separates the battery, the converter (power unit 202), the battery management system, and the safety tube (temperature, smoke), making the integration of the energy storage system difficult and requiring high technical and maintenance personnel.

[0036] The present invention realizes automatic switching of the battery cell 201 by adopting high-frequency power electronic semiconductor switches (control power unit electronic switch Q5, module bypass switch S, first switch Q1, second switch Q2, third switch Q3, fourth switch Q4), which not only realizes flexible interconnection of the battery cell 201 level, but also realizes energy storage and conversion of the battery cell 201. Since the power unit 202 needs to sample the voltage, current, temperature, etc. of the battery cell 201, the present invention can achieve active balancing of the battery cell 201 and power conversion in one, which can make full use of the energy of each battery cell 201 and reduce battery over-allocation of the energy storage system.

[0037] In the energy storage system of the present invention, when the internal battery cells 201 are being charged, discharged, or at rest, the controller 1 monitors the voltage, current, and temperature of each battery cell 201 in real time. Each battery cell 201 is flexibly connected to the power unit 202 via a fuse F and a power unit electronic switch Q5. When a power unit 202 or battery cell 201 fails, the module bypass switch S is closed to ensure that other battery cells 201 (battery modules 2) in the energy storage system continue to operate. In conventional energy storage systems, the battery modules 2 are hard-connected, and a failed battery module 2 cannot be disconnected.

[0038] See also Figure 5-6 As shown, the present invention also provides a battery balancing method, which is applied to N battery modules included in the above energy storage system, including: S1: Obtain battery parameters of the battery module. The battery parameters include output voltage, current direction and battery cell state of charge. The battery cell state of charge includes the battery cell SOC value, which is calculated by the formula: battery cell SOC value = (battery cell remaining power / battery cell rated capacity) * 100%.

[0039] The present invention maps the SOC value of the battery cell by disconnecting the power unit electronic switch Q5 in the power unit (in the off state) and sampling the open circuit voltage of the battery cell; for example, when the highest open circuit voltage value of the battery cell voltage is 3.6V, its corresponding SOC value is 100%, the open circuit voltage of 3.5V corresponds to the SOC value of 95%, the open circuit voltage of 3.4V corresponds to the SOC value of 90%, the open circuit voltage of 3.3V corresponds to the SOC value of 85%, the open circuit voltage of 3.2V corresponds to the SOC value of 80%, and the open circuit voltage of 3.1V corresponds to the SOC value of 75%, 3.0V open circuit voltage corresponds to SOC value of 70%, 2.9V open circuit voltage corresponds to SOC value of 65%, 2.85V open circuit voltage corresponds to SOC value of 60%, 2.8V open circuit voltage corresponds to SOC value of 55%, 2.75V open circuit voltage corresponds to SOC value of 45%, 2.7V open circuit voltage corresponds to SOC value of 35%, 2.65V open circuit voltage corresponds to SOC value of 25%, 2.6V open circuit voltage corresponds to SOC value of 10%, 2.55V open circuit voltage corresponds to SOC value of 0%. According to the open circuit voltage of the battery cell, the SOC value of the battery cell can be obtained.

[0040] S2: Determine the control type according to the current direction. The current direction is Figure 4 Middle I b The direction of the current is determined by I b The size determines its flow direction; when I b >0, the current direction is positive, and the battery cells of the battery module are put into discharge, that is, the control type at this time is the discharge type; when I b When <0, the current direction is reverse, and the battery cells of the battery module are charged at this time, that is, the control type at this time is the charging type.

[0041] S3: sorting the N battery modules according to the state of charge of the battery cells and the control type to obtain N battery modules sorted in sequence, specifically: When the control type is the discharge type, the battery cells with more remaining power have a longer discharge time, and the battery cells with less remaining power have a shorter discharge time, that is, the battery cells with a large battery SOC value are first put into the energy storage system, and the battery cells with a small battery SOC value are removed from the energy storage system. Therefore, when the control type is the discharge type, the N battery modules are sorted from large to small according to the battery cell SOC values ​​corresponding to each battery module; When the control type is charging type, the battery cells with less remaining power take a long time to charge, and the battery cells with more remaining power take a short time to charge, that is, the battery cells with smaller SOC values ​​are first put into the energy storage system, and the battery cells with larger SOC values ​​are removed from the energy storage system. Therefore, when the control type is charging type, the N battery modules are sorted from small to large according to the battery cell SOC values ​​corresponding to the battery modules.

[0042] S4: Determine the number of battery cells according to the output voltage. The number of battery cells is the number of battery modules to be controlled in the N battery modules arranged in sequence. The output voltage is Figure 4 The output voltage U of the full bridge circuit in each power unit ab1 , U ab2 , ..., U abN , U ab is the total output voltage of all power units cascaded in the energy storage system, satisfying the following equation:

[0043] The energy storage system uses battery modules (battery cells) as the smallest cascade unit. Each energy storage system usually contains dozens or hundreds of battery cells. Therefore, a step wave is used to directly approximate the modulation wave through instantaneous level superposition. The number of switching times 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 their conduction loss is very small.

[0044] See also Figure 7 As shown, a schematic diagram of signal modulation of an energy storage system including 6 battery modules in one cycle is given, that is, a schematic diagram of signal modulation of an energy storage system including 6 power units is shown; the output voltage U of a single full-bridge circuit abi +U b , -U b These 2 levels, and 6 power units can output a maximum of 12 levels after cascading, and the range of these 12 levels is -6U b Up to +6U b .

[0045] according to Figure 7 The modulation wave in can calculate the number of cells (power units) put into use in each cycle k as

[0046] Where k is the number of cells put into use in the current cycle, round(x) means taking the integer closest to x, abs(x) means taking the absolute value of x, and the value of k satisfies 0≤k≤N; for Figure 7 The peak value of the sinusoidal modulation wave, for Figure 7 The platform value of the step wave. The peak value of the sinusoidal modulation wave is divided by the platform value of the step wave to get the number of steps of the step wave, that is, the number of cells that need to be invested in the energy storage system.

[0047] S5: According to the number of battery cells, select the first several battery modules from the N battery modules arranged in sequence as the battery modules to be controlled.

[0048] If the number of battery cells in the current cycle is the same as the number of battery cells in the previous cycle, it is necessary to determine whether the SOC value corresponding to the battery module to be controlled is within the cut-off range. The cut-off range is the SOC value at the end of battery cell discharge. For example, the SOC value corresponding to the 2.6V open circuit voltage is 10% as the cut-off range. Controlling the battery cell SOC value within the cut-off range can protect the battery cell and prevent the battery cell from being damaged by over-discharge. If the SOC value corresponding to the battery module to be controlled is within the cut-off range, the pulse of the power unit is kept unchanged. If the SOC value corresponding to the battery module to be controlled is not within the cut-off range, 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 some power units are controlled according to the current direction of the power unit, specifically, the on state and the off state are interchanged.

[0049] If the number of battery cells in the current cycle is different from the number of battery cells in the previous cycle, the battery modules that need to be put into operation or removed are determined based on the current direction and control type. Specifically, if the above-mentioned battery module to be controlled is the battery module to be put into operation in the current week, the battery modules put into operation in the previous cycle that are not the same as the battery modules to be put into operation in the current week are used as the battery modules to be removed in the current week. For example, the energy storage system in the previous cycle put into operation the 1st battery module, the 2nd battery module, and the 3rd battery module, and the battery modules to be put into operation in the current week are the 1st battery module and the 2nd battery module, then the battery module to be removed in the current week is the 3rd battery module.

[0050] Since the SOC value of the battery cell changes in seconds, the battery cells sorted based on the SOC value may change within a few seconds, which will cause some battery cells to be frequently switched on and off during the charging and discharging process. Therefore, in one embodiment of the present invention, the number of times the battery module to be controlled is added to the energy storage system or removed from the energy storage system within a preset time period is limited to once.

[0051] S6: According to the control type, 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 battery module to be controlled are controlled so that the battery module to be controlled is put into the energy storage system or removed from the energy storage system to balance the N battery modules of the energy storage system.

[0052] The present invention adopts a nearest level modulation strategy for the power unit according to the SOC value of each battery cell to achieve balance among multiple battery modules; in the case of poor consistency in battery cell capacity, it is easy to achieve active balancing control of each battery cell, while the conventional carrier phase shift modulation strategy requires adjustment of the modulation wave of each power unit, and the control process will be much more complicated. In addition, the existing active balancing control of battery cells requires auxiliary circuits, which will cause additional energy loss. The present invention does not require additional auxiliary circuits and can implement the operation of putting in or removing each battery cell to achieve active balancing of the battery module.

[0053] Because the battery cells inside the battery module of the present invention can be flexibly connected or disconnected from the AC circuit, conditions are provided for online measurement of the open circuit voltage of the battery cells. However, the battery modules of conventional energy storage systems are hard-connected and online measurement of the open circuit voltage of the battery modules cannot be achieved. Therefore, the present invention can accurately obtain the battery cell SOC value of each battery module by online measuring the open circuit voltage of the battery cells in the battery module.

[0054] Next, Figure 7 The charging process of the single-phase six battery modules shown is taken as an example to specifically illustrate the working principle of the battery balancing method executed by the energy storage system.

[0055] See also Figure 8-9 As shown, Figure 8 B1, B2, ..., B6 refer to the SOC values ​​of the cells of the six battery modules respectively. The controller disconnects Q1~Q5 of the power module (low-voltage MOSFET is used as the power switch tube), lets the six cells stand for a period of time, and then tests the open-circuit voltage of each cell. Based on the open-circuit voltage of the six cells, the SOC value (remaining battery capacity) of each battery module is estimated.

[0056] In the charging state, that is, the control type is the charging type, the battery modules are arranged in ascending order according to the SOC value of the battery cell, and the open circuit voltage corresponding to each battery cell is recorded as U bi , the charging power required for each battery cell is P bi ; See Table 1 and Table 2, Table 1 shows the results before sorting, and Table 2 shows the results after sorting.

[0057] Table 1 Results before sorting

[0058] Table 2 Sorting results

[0059] See also Fig.10As shown in the figure, after the SOC of each battery cell is sorted, the signal modulation sorting of each power module in the charging process is sorted. It can be seen from the figure that the lower the SOC value of the battery cell, the longer the power unit is turned on, and the more electric energy is charged to the battery cell. After a period of time, the SOC values ​​of each battery cell are basically consistent.

[0060] After that, in order to ensure that the SOC value of the battery cells of each battery module reaches 100% at the same time, it is necessary to perform round-robin modulation on the battery cell signal modulation of each battery module, for example, Figure 7 The signal modulation shown is the initial state, so the second round of signal modulation sequence is: SM6, SM1, SM2, SM3, SM4, SM5, and the third round of signal modulation sequence is: SM5, SM6, SM1, SM2, SM3, SM4. Repeat this cycle until the SOC value of the battery cells of each battery module reaches 100%.

[0061] During the charging process, if the power unit corresponding to SM3 fails or the SOC value of the battery cell reaches 100% first, the module bypass switch S of the power unit corresponding to SM3 is directly closed. At the same time, the power unit electronic switch Q5 connecting the corresponding power unit and the battery cell is disconnected, and the remaining 5 batteries continue to follow Figure 7 The signal modulation shown continues charging, but the modulation signal is reduced by one group.

[0062] During the battery discharge process, the SOC of each cell is arranged in order from large to small, and the signal modulation process is the same as the above principle, which will not be repeated here.

[0063] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should 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 the host computer respectively; the N battery modules are connected in series; the first battery module is connected to the Nth battery module through the grid-connected inductor and the AC power supply in sequence; The battery module includes an electronic switch; the controller is used to detect battery parameters of the battery module and control the on and off of the electronic switch according to the battery parameters to control the charge and discharge state of the battery module and realize active balancing of N battery modules; It also includes N temperature sensors and a cooling plate; the temperature sensor is connected to the battery module; and the N battery modules are connected to the cooling plate.

2. An energy storage system according to claim 1, characterized in that: 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 N power units respectively included in the N battery modules are connected in series; the power unit included in the first battery module is connected to the power unit included in the Nth battery module through the grid-connected inductor and the AC power supply in sequence.

3. An energy storage system according to claim 2, characterized in that: 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 module bypass switches respectively included in the N power units are connected in series; the module bypass switch included in the first power unit is connected to the module bypass switch included in the Nth power unit through the grid-connected inductor and the AC power supply in sequence.

4. An energy storage system according to claim 3, 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; and the module bypass switch is connected with the midpoint of the first bridge arm and the midpoint of the second bridge arm.

5. An energy storage system according to claim 4, 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 a first end of the first switch, a second end of the second switch, a first end of the third switch, and a second end of the fourth switch; the module bypass switch is connected to a second end of the first switch, a first end of the second switch, a second end of the third switch, and a first end of the fourth switch.

6. An energy storage system according to claim 5, 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 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.

7. An energy storage system according to claim 6, characterized in that: The controller includes a processor and a memory, wherein the memory stores at least one instruction, at least one program, code set or instruction set, and the at least one instruction, at least one program, code set or instruction set is loaded and executed by the processor.

8. A battery balancing method, applied to the energy storage system according to claims 1-7, wherein the energy storage system comprises N battery modules, characterized in that: The method comprises the following steps: Obtaining battery parameters of the battery module, wherein the battery parameters include output voltage, current direction, and battery cell charge state; Determining a control type according to the current direction; Sorting the N battery modules according to the battery cell charge state and the control type to obtain N battery modules that are sequentially sorted; Determine the number of battery cells according to the output voltage, where the number of battery cells is the number of battery modules to be controlled among the N battery modules arranged in sequence; According to the number of battery cells, the first several battery modules are selected 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, the module bypass switch, the first switch, the second switch, the third switch and the 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 removed from the energy storage system to balance the N battery modules of the energy storage system.

9. A battery equalization method according to claim 8, characterized in that: The number of times the battery module to be controlled is put into the energy storage system or removed from the energy storage system within a preset time period is limited to once.

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