Comprehensive safety assurance method for batteries in high-voltage direct-mounted energy storage equipment

Abstract

The present invention provides a comprehensive battery safety assurance method for high-voltage, direct-mounted energy storage equipment, relating to the field of power system transmission and distribution technology, comprising: Step S1: constructing a secondary battery cluster with insulation resistance against strong electromagnetic transient faults; Step S2: After the secondary battery cluster is constructed, setting a cascade energy storage unit protection method that suppresses overvoltage and lightning strikes; Step S3: Based on the secondary battery cluster and cascade energy storage unit protection method, setting a multi-condition fault protection control strategy and state machine suitable for high-voltage, direct-mounted energy storage systems. The present invention can proactively select stable operation, reactive power support, or safe shutdown based on internal faults and external impacts, thereby safely increasing the system's available capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission and distribution of electric power systems, and in particular to a comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment. Background Art

[0002] In an environment where renewable energy is connected to the grid on a large scale, the configuration of large-capacity energy storage systems can improve the efficiency of the power system and help the system structure further transform towards clean energy.

[0003] High-voltage direct-mounted energy storage technology greatly simplifies the construction complexity of large-scale power plants. This topology is based on three units, each composed of several submodules. Each submodule includes four fully controlled switching transistors, a filter capacitor, a filter inductor, and a battery cluster. The structure of high-voltage direct-mounted energy storage devices is relatively simple, making it easy to load control strategies. Its high scalability also makes it easy to interact with the grid. The output level of the cascaded converter can be adjusted directly based on the grid-side status. The system voltage level and output harmonic content can be effectively controlled by increasing the number of modules.

[0004] When high-voltage direct-mounted energy storage systems are applied, they may face extreme working conditions such as lightning strikes and large current shocks, which may lead to overcharging and damage of battery clusters, causing fires and explosions. It is necessary to introduce system anti-shock control strategies and strong insulation capability hardware design to improve the reliability of high-voltage direct-mounted energy storage systems. If the high-voltage direct-mounted energy storage system has multi-level safety protection measures for control, equipment, and sub-components, it can greatly improve the system's ability to work smoothly in various extreme working conditions and fault conditions, and further improve the system's grid-connected output capacity.

[0005] Electromagnetic transient faults can be primarily categorized into three types based on their time scale: microseconds, hundreds of milliseconds, and seconds. Lightning strikes are microsecond-scale overvoltage transient electromagnetic faults, grid-side overcurrent surges are hundreds of millisecond-scale overcurrent transient electromagnetic faults, and the post-fault disturbance stabilization process is a second-scale transient fault. Current battery energy storage systems, from the battery to the equipment level, have largely failed to consider the impact of multi-timescale electromagnetic transient shocks and their solutions during the design phase. The equipment's ability to withstand high-rate overloads of current and voltage is weak, and the system's tolerance to lightning strikes and short-term, extremely high-rate conditions is poor. This not only prevents energy transmission or storage, but also makes it prone to serious safety hazards caused by system overloads. Therefore, to ensure stable system operation under multiple operating conditions, it is necessary to improve the overload tolerance and insulation capabilities of the system's internal battery cells and introduce an operating strategy with protective capabilities.

[0006] In addition, due to the high integration of the high-voltage direct-hanging system, when facing multi-time-scale electromagnetic transient shocks and the maximum overload directly acts on the sub-unit, it is necessary to prevent overvoltage shocks caused by battery circuit breakage, which in turn causes insulation failure.

[0007] High-voltage, direct-mounted energy storage systems enable grid interaction and support the power system, offering high scalability and integration. However, as system capacity increases, the resulting increase in the number of battery cells increases, which can lead to system safety issues and reduce reliability. Ensuring that the system remains operational safely under various shocks, particularly strong electromagnetic transients, is a pressing issue in the research and application of high-voltage, direct-mounted energy storage systems. Summary of the Invention

[0008] In response to the deficiencies in the prior art, the present invention provides a comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment.

[0009] According to a comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment provided by the present invention, the scheme is as follows:

[0010] In a first aspect, a comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment is provided, the method comprising:

[0011] Step S1: constructing a secondary battery cluster with insulation resistance against strong electromagnetic transient faults;

[0012] Step S2: After the secondary battery cluster is constructed, a cascade energy storage unit protection mode is set to suppress overvoltage and lightning strike operations;

[0013] Step S3: On the basis of the protection method of the secondary battery cluster and the cascade energy storage unit, a multi-operating condition fault protection control strategy and its state machine applicable to the high-voltage direct-mounted energy storage system are set.

[0014] Preferably, the secondary battery cluster comprises: a cover plate, a pole, a secondary battery, a shell, a connecting piece and a current collector;

[0015] The pole, secondary battery, adapter and current collector are all located in the shell, and the cover plate is located on the upper side of the shell;

[0016] The adapter is connected to the cover plate, the pole and the current collector respectively.

[0017] Preferably, the adapter comprises: an overload protection portion, a pole connection portion, a cover plate connection portion, and a current collector connection portion;

[0018] Wherein, the pole connecting portion is connected to the pole, the current collector connecting portion is connected to the current collector, and the cover plate connecting portion is connected to the cover plate;

[0019] The overload protection unit comprises a first overload protection unit and a second overload protection unit;

[0020] During normal use, the second overload protection portion is connected to the pole connection portion and the current collector connection portion, and the first overload protection portion is in contact with the second overload protection portion;

[0021] The secondary battery forms a circuit through the positive electrode post-positive electrode post connection part-positive electrode second overload protection part-positive electrode current collector connection part-secondary battery-negative electrode current collector connection part-negative electrode second overload protection part-negative electrode post connection part-negative electrode post; wherein the left side of the first overload protection part is fixed to the electrode post connection part, and the right side is in contact with the current collector connection part but not fixed.

[0022] Preferably, the first overload protection portion comprises: an upper metal sheet and a lower metal sheet;

[0023] Among them, the part facing the cover plate has a low thermal expansion coefficient, and the part facing the secondary battery has a high thermal expansion coefficient; when lightning strikes and strong electromagnetic transient shocks occur, the second overload protection part generates heat, causing the first overload protection part to deform due to heat, and the right end rises and overlaps with the cover plate connection part; thus forming a circuit of positive pole-positive pole connection part-second positive pole overload protection part-cover plate-negative pole second overload protection part-negative pole connection part-negative pole, ensuring the normal use of the module and cutting off the circuit of the secondary battery at the same time.

[0024] The cascade energy storage unit protection method for suppressing overvoltage and lightning strike operations in step S2 includes:

[0025] Step S2.1: Conduct voltage impulse tests on the cells in the secondary battery cluster and the arrester installed outside the battery cluster, and obtain a curve showing the relationship between the impulse discharge voltage and the corresponding discharge time, i.e., the volt-second characteristic;

[0026] Step S2.2: Compare the lightning arrester and the secondary battery cluster insulation volt-second characteristics, confirm that the lightning arrester volt-second characteristics are always lower than the battery module insulation volt-second characteristics, and determine the lightning arrester parameters based on the determined volt-second characteristic range;

[0027] Step S2.3: The energy storage unit of the high-voltage direct-mounted energy storage equipment is connected to the grid using three phases. Each phase subunit has multiple energy storage units, and a grid-connected reactor is introduced between the subunit and the grid connection point. After confirming the selection of the lightning arrester, a passive protector is installed between the energy storage subunit and the grid-connected reactor.

[0028] Step S2.4: According to the different grounding methods of the energy storage unit, a lightning arrester is installed inside each phase of the energy storage unit.

[0029] Preferably, the step S2.4 includes:

[0030] The energy storage system adopts three-phase grid-connected design, including phases A, B and C. For Y-type grounded energy storage units, a lightning arrester is installed at the neutral point, and lightning arresters are installed in the first three submodules of phases A, B and C close to the grid-connected reactor. For delta-grounded energy storage units, lightning arresters are installed in the first three submodules of phases A, B and C close to the grid-connected reactor and the three submodules farthest from the grid-connected reactor.

[0031] Preferably, the multi-operating-condition fault protection control strategy and its state machine applicable to the high-voltage direct-mounted energy storage system in step S3 are a millisecond-to-second time-scale protection method proposed based on the microsecond-level protection of secondary battery clusters with insulation resistance to strong electromagnetic transient faults and the nanosecond-level protection of cascaded energy storage units that suppress lightning impulses and switching impulse overvoltages. This control strategy is proposed for an energy storage system architecture based on a cascade of H-bridge converters and includes the following steps:

[0032] Step S3.1: Determine the system operating status and disturbance impact;

[0033] Step S3.2: Based on the different circuit states and the instructions of the state machine, the next required circuit state and the driving signal of the main switch are obtained. Based on the changes in electromagnetic transient impact and working state requirements, the working state of the working modules is redistributed to maintain the stable operation capability of the system under various fault conditions.

[0034] By real-time monitoring of the working conditions, that is, controlling the driving signals of the submodules, the submodules complete the working state transformation based on the set state machine in each working state experienced during the switching process.

[0035] In a second aspect, a secondary battery is provided, comprising: a positive electrode sheet, a separator, and a negative electrode sheet;

[0036] The positive electrode sheet includes a composite current collector, an electrode active material layer, and a safety coating disposed between the current collector and the electrode active material layer. The impedance of the safety coating increases rapidly at high temperatures.

[0037] The safety coating comprises a phase change material, a conductive agent and a binder. Based on the total weight of the safety coating, the weight percentage of the phase change material is 5wt% to 80wt%, the weight percentage of the conductive agent is 20wt% to 50wt%, and the weight percentage of the binder is 10wt% to 50wt%.

[0038] Preferably, the phase change material is selected from at least one of paraffin, fatty acid, fatty alcohol and polyol.

[0039] In a third aspect, a method for preparing a secondary battery is provided, the method comprising:

[0040] Preparation steps of the positive electrode sheet: paraffin wax, conductive graphite SP, and polyvinylidene fluoride PVDF are mixed in a set ratio with N-methyl-2-pyrrolidone NMP as solvent, and then coated on both surfaces of the metal current collector. After drying, a safety coating is obtained;

[0041] Then, a set ratio of positive electrode active material and polyvinylidene fluoride (PVDF) is mixed evenly with N-methyl-2-pyrrolidone (NMP) as a solvent, and then coated on the safety coating of the current collector prepared according to the above method, and dried to obtain a positive electrode active material layer;

[0042] The current collector with the safety coating and the positive electrode active material layer is then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions, and the current collector is connected to form a secondary battery positive electrode sheet;

[0043] The negative electrode sheet preparation steps are as follows: active material graphite, conductive graphite SP, carboxymethyl cellulose CMC, and styrene-butadiene rubber emulsion SBR are added to the solvent deionized water in a predetermined mass ratio and mixed evenly to form an anode slurry; the anode slurry is coated on the surface of the negative electrode metal collector copper foil and dried, and then trimmed, cut into pieces, and striped, and dried under vacuum conditions, and the current collector is connected to form the secondary battery negative electrode sheet;

[0044] The electrolyte preparation step is as follows: ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a predetermined volume ratio to obtain an EC / DEC mixed solvent, and then lithium hexafluorophosphate (LiPF6) is dissolved in the mixed solvent to obtain an electrolyte;

[0045] Secondary battery preparation steps: Use polypropylene film as the separator, stack the positive electrode sheet, separator and negative electrode sheet in order, wind them into a battery cell, inject electrolyte, and obtain a secondary battery through vacuum packaging, standing, formation and shaping processes.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The present invention is applicable to high-voltage direct-mounted energy storage equipment subjected to strong electromagnetic transient impacts. When subjected to high voltage or lightning strikes, the second overload protection generates high temperature under the action of high current, and the high temperature is transmitted to the first overload protection. One end of the first overload protection portion is fixedly connected to the pole connection portion, so the deformation caused by high-temperature expansion accumulates on the other end, causing warping toward the upper end and then overlapping the cover plate connection portion. The overload protection portions of the positive and negative poles both undergo the aforementioned warping deformation, thereby establishing a circuit between the positive and negative poles and the cover plate, thereby avoiding the impact of lightning strikes and high voltage on the electrode assembly.

[0048] 2. The safety coating in the battery cell of the present invention is no different from the prior art in normal use. However, when the battery is subjected to a high voltage shock, the battery generates heat and the internal temperature rises. As the temperature rises, the phase change material undergoes a phase change, and the resistance of the safety coating increases rapidly, blocking the electron path, thereby protecting the battery.

[0049] 3. The present invention can actively select stable operation, reactive power support or safe cut-out according to the difference between internal faults and external impacts, thereby achieving the purpose of safely improving the available capacity of the system.

[0050] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0052] Figure 1 The invention is a secondary battery cluster suitable for high-voltage direct-mounted energy storage systems and has insulation resistance against strong electromagnetic transient faults;

[0053] Figure 2 It is a battery thermal induction adapter suitable for high-voltage direct-mounted energy storage systems of the present invention;

[0054] Figure 3 This is a secondary battery cluster battery adapter connection method suitable for high-voltage direct-mounted energy storage systems of the present invention;

[0055] Figure 4 The invention is a bimetallic strip structure for an overload protection part of a high-voltage direct-mounted energy storage system;

[0056] Figure 5 The present invention is a method for comparing the volt-second characteristics of lightning arresters and battery modules applicable to high-voltage direct-mounted energy storage systems;

[0057] Figure 6a and Figure 6b The invention provides a Y-type connection energy storage unit protection method applicable to a high-voltage direct-mounted energy storage system;

[0058] Figure 7 The invention is a multi-operating-condition fault protection control strategy and its state machine applicable to a high-voltage direct-mounted energy storage system;

[0059] Figures 8a-8b The current direction of the submodules of the high-voltage direct-mounted energy storage system is divided into positive and negative directions respectively;

[0060] Figures 9a to 9j This is the multi-condition fault protection control strategy for high-voltage direct-mounted energy storage systems and the working conditions of the corresponding submodules of its state machine. Figures 9a to 9j They are V1 to V10 respectively.

[0061] Figure numerals: 1. cover plate; 2. shell; 3. adapter; 4. overload protection part; 5. pole connection part; 6. cover plate connection part; 7. current collector connection part; 8. first overload protection part; 9. second overload protection part; 10. upper metal sheet; 11. lower metal sheet. DETAILED DESCRIPTION

[0062] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0063] The embodiment of the present invention provides a comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment. In order to ensure the reliability of the system under external overvoltage impact conditions, the present invention needs to analyze the mechanical energy characteristics of electromagnetic transient faults, design a MOA configuration method for microsecond-level lightning overvoltage electromagnetic transient faults, design a battery cluster with insulation resistance to strong electromagnetic transient faults for hundred-millisecond-level overload electromagnetic transient faults, and design a system disturbance stabilization control and protection strategy after a second-level fault. From batteries and equipment to upper-level control logic, the time scale covers microseconds, hundred-milliseconds to seconds, with simple control, flexible and expandable structure, and can also achieve tolerance to extreme working conditions. Reference Figure 1 and Figure 2 As shown, the method specifically includes:

[0064] Step S1: constructing a secondary battery cluster with insulation resistance against strong electromagnetic transient faults;

[0065] Step S2: After the secondary battery cluster is constructed, a cascade energy storage unit protection mode is set to suppress overvoltage and lightning strike operations;

[0066] Step S3: On the basis of the protection method of the secondary battery cluster and the cascade energy storage unit, a multi-operating condition fault protection control strategy and its state machine applicable to the high-voltage direct-mounted energy storage system are set.

[0067] Specifically, a secondary battery cluster includes a cover plate 1, a terminal, a secondary battery, a housing 2, an adapter 3, and a current collector. The terminal, secondary battery, adapter, and current collector are all located within the housing, with the cover plate located on the upper side. The adapter is connected to the cover plate, terminal, and current collector, respectively. The bare cell of a secondary battery is called a JS (secondary battery) and consists of a cathode active material, an anode active material, and a current collector. The portion of the current collector exposed outside the bare cell (Jelly Roll) is called the tab, which is connected to the adapter.

[0068] Reference Figure 2 and Figure 3 As shown, the adapter includes: an overload protection part 4, a pole connecting part 5, a cover connecting part 6, and a current collector connecting part 7; wherein the pole connecting part is connected to the pole, the current collector connecting part is connected to the current collector, and the cover connecting part is connected to the cover;

[0069] The overload protection part 4 includes a first overload protection part 8 and a second overload protection part 9; in normal use, the second overload protection part connects the pole connection part and the current collector connection part, and the first overload protection part contacts the second overload protection part;

[0070] The secondary battery forms a circuit through the positive electrode post-positive electrode post connection part-positive electrode second overload protection part-positive electrode current collector connection part-secondary battery-negative electrode current collector connection part-negative electrode second overload protection part-negative electrode post connection part-negative electrode post; wherein the left side of the first overload protection part is fixed to the electrode post connection part, and the right side is in contact with the current collector connection part but not fixed.

[0071] Reference Figure 4 As shown, the first overload protection part also includes: an upper metal sheet 10 and a lower metal sheet 11; wherein, the portion facing the cover plate has a low thermal expansion coefficient, and the portion facing the secondary battery has a high thermal expansion coefficient; when lightning strikes and strong electromagnetic transient shocks occur, the second overload protection part generates heat, causing the first overload protection part to deform due to heat, and the right end rises and overlaps with the cover plate connection part; thereby forming a circuit of positive pole-positive pole connection part-second positive pole overload protection part-cover plate-negative pole second overload protection part-negative pole connection part-negative pole, ensuring the normal use of the module, while cutting off the circuit of the secondary battery, avoiding the impact on the secondary battery.

[0072] The secondary battery used in the present invention includes: a positive electrode plate, a separator and a negative electrode plate; wherein the positive electrode plate includes a composite current collector, an electrode active material layer and a safety coating arranged between the current collector and the electrode active material layer, and the impedance of the safety coating increases rapidly at high temperature.

[0073] The safety coating comprises a phase change material, a conductive agent, and a binder. Based on the total weight of the safety coating, the phase change material accounts for 5 to 80 weight percent, the conductive agent accounts for 20 to 50 weight percent, and the binder accounts for 10 to 50 weight percent. The phase change material is selected from at least one of paraffin, fatty acids, fatty alcohols, and polyols.

[0074] The preparation method of the secondary battery specifically includes:

[0075] The positive electrode sheet preparation steps are as follows: paraffin wax, conductive graphite (SP), and polyvinylidene fluoride (PVDF) (30wt%: 25wt%: 55wt%) are mixed in N-methyl-2-pyrrolidone (NMP) as a solvent, and then coated on both surfaces of the metal current collector. The mixture is then dried at 85°C to obtain a safety coating. Next, 95wt% of the positive electrode active material, 2wt% of SP, and 3wt% of PVDF are mixed in NMP (N-methylpyrrolidone) as a solvent, and then coated on the safety coating of the current collector prepared in the above manner. The mixture is then dried at 60°C to obtain a positive electrode active material layer. The current collector with the safety coating and positive electrode active material layer is then cold-pressed, trimmed, cut, and slit. The mixture is then dried under vacuum at 60°C for 16 hours, and the tabs are welded to produce a secondary battery positive electrode sheet that meets the requirements.

[0076] Preparation steps of negative electrode sheet: add active material graphite, conductive graphite SP, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR in a mass ratio of 95.5:2.0:1.0:1.5 to solvent deionized water and mix evenly to form anode slurry; apply the anode slurry on the surface of the negative electrode metal collector copper foil and dry it at 60°C, then trim, cut and strip it, and then dry it under vacuum conditions at 60°C for 4 hours, weld the pole ears, and make a secondary battery negative electrode sheet that meets the requirements.

[0077] The electrolyte preparation steps are as follows: ethylene carbonate EC and diethyl carbonate DEC are mixed in a volume ratio of 5:5 to obtain an EC / DEC mixed solvent, and then lithium salt LiPF6 is dissolved in the mixed solvent to obtain a solution with a concentration of 1M to obtain the electrolyte.

[0078] Secondary battery preparation steps: Using a 16μm polypropylene film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The sheets are then wound into a bare cell. Electrolyte is then injected, and the cells undergo vacuum packaging, resting, formation, and shaping to create a secondary battery.

[0079] Fully charge the secondary battery at 1P power to the charge cut-off voltage, then stop charging. Then, continue charging at 1P constant current until the battery reaches 1.5 times the charge cut-off voltage or after 1 hour.

[0080] Furthermore, the cascade energy storage unit protection method mentioned in the above step S2 for suppressing overvoltage and lightning operation is provided, with reference to Figure 5 、 6a , 6b, including:

[0081] Step S2.1: Conduct voltage surge tests on the cells in the secondary battery cluster and the arresters installed outside the battery cluster, and obtain Figure 5 The relationship curve between the impulse discharge voltage U and the corresponding discharge time t is shown, that is, the volt-second characteristic.

[0082] Step S2.2: Compare the arrester and secondary battery cluster insulation volt-second characteristics to confirm that the arrester volt-second characteristic is always lower than the battery module insulation volt-second characteristic. Figure 5 As shown, the arrester parameters are determined based on the determined volt-second characteristic interval.

[0083] Step S2.3: The energy storage unit of the high-voltage direct-mounted energy storage equipment is connected to the grid using three phases. Each phase subunit has multiple energy storage units, and a grid-connected reactor is introduced between the subunit and the grid connection point. After confirming the lightning arrester selection, a passive protective device is installed between the energy storage subunit and the grid-connected reactor. The energy storage system is connected to the grid using three phases, including phases A, B, and C. A lightning arrester is installed between phases A and A grid-connected reactors, between phases B and B grid-connected reactors, and between phases C and C grid-connected reactors. A lightning arrester module is installed at the energy storage unit busbar. Specifically, the lightning arrester is installed at the energy storage unit busbar.

[0084] Step S2.4: Lightning arresters are installed inside each phase of the energy storage unit according to the different grounding methods of the energy storage unit. For a Y-type grounded energy storage unit, a lightning arrester is installed at the neutral point, and lightning arresters are installed in the first three submodules of phases A, B, and C close to the grid-connected reactor. For a delta-type grounded energy storage unit, lightning arresters are installed in the first three submodules of phases A, B, and C close to the grid-connected reactor and the three submodules farthest from the grid-connected reactor.

[0085] The multi-operating-condition fault protection control strategy and its state machine applicable to the high-voltage direct-mounted energy storage system in the aforementioned step S3 are a millisecond-to-second timescale protection method based on the microsecond-level protection of secondary battery clusters with insulation resistance to strong electromagnetic transient faults and the nanosecond-level protection of cascaded energy storage units that suppress lightning surges and switching surge overvoltages. This control strategy is proposed for an energy storage system architecture based on a cascade of H-bridge converters and includes the following steps:

[0086] Step S3.1: Determine the system operating status and disturbance impact;

[0087] Step S3.2: Based on the different circuit states and the instructions of the state machine, the next required circuit state and the driving signal of the main switch are obtained. Based on the changes in electromagnetic transient impact and working state requirements, the working state of the working modules is redistributed to maintain the stable operation capability of the system under various fault conditions.

[0088] By real-time monitoring of the working conditions, that is, controlling the driving signals of the submodules, the submodules complete the working state transformation based on the set state machine in each working state experienced during the switching process.

[0089] For the multi-condition fault protection control strategy and state machine state switching applicable to high-voltage direct-mounted energy storage systems, Figure 7 As shown in the figure, V1 and V10 are in the cut-out state, V2, V3, V8, and V9 are in the reactive power support state, V4 and V6 are in the charging state, and V5 and V7 are in the discharging state. To ensure that transient overcharge does not affect battery module performance, the control strategy prohibits direct switching between charge and discharge states. Charge and discharge transitions must be performed through the reactive power support or cut-out state. All other states can be switched between each other.

[0090] like Figures 8a-8b As shown, the high-voltage direct-mounted energy storage system circuit is divided into forward current state and reverse current state, which is convenient for subsequent research and explanation.

[0091] In the submodule, Q1-Q4 represent the H-bridge converter arm switches within the module. Q5 is the battery circuit breaker. L is the battery-side filter inductor, C is the battery-side filter capacitor, and Eb is the battery potential. i+ and i- denote the module current flow direction: i+ indicates forward current flow and i- indicates reverse current flow.

[0092] V1: The system is subjected to a strong electromagnetic transient impact. The current flows through the submodule in the forward direction, turning on the switch tubes Q2 and Q4, isolating the unit, and allowing the impact to pass through the AC bus directly to the ground through the MOA.

[0093] V1-V2: The submodule is subjected to a small electromagnetic transient disturbance, turning off the switch tube Q4 and turning on the switch tube Q3. The current flows through the capacitor in the forward direction, causing the capacitor to be in a charging state. The battery side is disconnected by the battery circuit breaker Q5 to achieve isolation.

[0094] V2-V4: The system is operating in a steady state. The energy storage system is not full and enters a steady-state charging state. The battery circuit breaker Q5 is turned on to start charging the submodule batteries.

[0095] V4-V10: The system is subjected to a strong electromagnetic transient shock. The current flows in the reverse direction through the submodule, disconnecting the battery circuit breaker Q5 and turning on the switches Q1 and Q3, isolating the unit. This causes the shock to pass directly through the AC busbar and be grounded directly through the MOA.

[0096] V10-V8: The submodule is subjected to a small electromagnetic transient disturbance, turning off the switch tube Q3 and turning on the switch tube Q4. The current flows through the capacitor in the forward direction, causing the capacitor to be in a charging state. The battery side is disconnected by the battery circuit breaker Q5 to achieve isolation.

[0097] V8-V6: The system is operating in a steady state. The energy storage system capacity is not full, and it enters a steady-state charging state. The battery circuit breaker Q5 is turned on to start charging the submodule batteries.

[0098] V6-V10-V9: The submodule's charge and discharge status changes. First, module isolation is completed, and then commutation is completed. That is, the state machine first reaches V10 from V6 state, disconnects the battery circuit breaker Q5, turns off the switch tube Q4 and turns on the switch tube Q3, isolates the submodule to protect the submodule's safety, and then turns off the switch tube Q1 and turns on the switch tube Q2 to complete the commutation. The current flows in the opposite direction through the capacitor, putting the capacitor in a discharged state.

[0099] V9-V7: The system operates in a steady state. The energy storage system has a certain amount of power and enters a steady-state discharge state. The battery circuit breaker Q5 is turned on, and the submodule battery begins to discharge.

[0100] V7-V1-V3: Current reverses. First, module isolation is completed, and then commutation is completed. That is, the state machine reaches V1 from V6 state, disconnects the battery circuit breaker Q5, turns off the switch tube Q3 and turns on the switch tube Q4, isolates the sub-module to protect the sub-module safety, and then turns off the switch tube Q2 and turns on the switch tube Q1 to complete the commutation. The current flows in the opposite direction through the capacitor, putting the capacitor in a discharged state.

[0101] V3-V5: The system operates in a steady state. The energy storage system has a certain amount of power and enters a steady-state discharge state. The battery circuit breaker Q5 is turned on, and the submodule battery begins to discharge.

[0102] The multi-condition fault protection control strategy applicable to high-voltage direct-mounted energy storage systems and the working conditions of the corresponding submodules of its state machine are as follows: Figures 9a to 9j shown.

[0103] Next, the present invention will be described in more detail.

[0104] The present invention provides a comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment. The energy storage system subunits use secondary battery clusters with insulation resistance to strong electromagnetic transient faults, and are equipped with a cascade energy storage unit protection method that suppresses overvoltage and lightning strike operations. The control strategy uses a multi-operating condition fault protection control strategy and its state machine suitable for high-voltage direct-mounted energy storage systems.

[0105] A secondary battery cluster with insulation resistance against strong electromagnetic transient faults features two adapters between the tab and the post of each battery cell, one for each positive and negative pole. One end of the adapter is connected to the post and the other to the tab. The adapter is also designed with two overload protection components. The second overload protection component is connected to the post or tab, and the first overload protection component contacts the second overload protection component. When subjected to external high voltage and lightning strikes, the second overload protection component first generates heat, which then transfers heat to the first overload protection component, causing one end of the first overload protection component to deform, warp, and overlap with the cover plate connection, thereby eliminating the effects of the high voltage and lightning strike. The phase change material in the battery cell safety coating actually serves two purposes: it serves as a PTC (Positive Temperature Coefficient) matrix and as a filler, increasing the adhesion between the current collector and the active material, primarily acting as a PTC matrix. However, when the battery is subjected to a high voltage shock, the battery generates heat and the internal temperature rises. As the temperature rises, the phase change material undergoes a phase change, the resistance of the safety coating increases rapidly, the conductive network is almost completely isolated, and the current approaches zero, thereby protecting the electrochemical device using the safety coating.

[0106] The protection method for cascaded energy storage units to suppress lightning impulses and switching impulse overvoltages is: first, set an overvoltage passive protector between the energy storage subunit and the grid-connected reactor; second, set a lightning arrester at the energy storage unit busbar; finally, for Y-type grounded energy storage units, set lightning arresters at the neutral point and the first three submodules of each phase close to the grid-connected reactor; for delta-grounded energy storage units, set lightning arresters at the first three submodules and the last three submodules of each phase respectively; finally, when selecting the lightning arrester parameters, the insulation volt-second characteristics of the lightning arrester and the secondary battery cluster are compared with each other, and it is ensured that the insulation volt-second characteristic of each battery module in the secondary battery cluster is always higher than the lightning arrester inter-second characteristic. This method reasonably sets the lightning arrester according to the overvoltage propagation path, overvoltage distribution and capacity rise effect characteristics of the cascade energy storage unit. It can provide a modular energy storage unit protection method without changing the existing cascade energy storage unit structure, and effectively suppress the lightning impulse and operation impulse overvoltage of the cascade energy storage unit, especially the steep slope impulse overvoltage.

[0107] The voltage passive protector installed between the energy storage subunit and the grid-connected reactor can protect the energy storage system from various overvoltages (operation overvoltage, lightning overvoltage, resonance overvoltage, etc.) and ensure battery safety. The main parameters of the voltage passive protector are: (1) Voltage protection level: 8kV and below; (2) Response time: <1ns; (3) Energy absorption capacity: not less than 2000J; (4) Working environment: temperature (-40℃ ~ +85℃); (5) No external power supply required, passive operation, no energy consumption; (6) Circuit breaker when not working, does not affect the original system function; (7) Multi-level protection, failure rate less than 0.0001%; ​​(8) Maintenance-free.

[0108] The multi-condition fault protection control strategy and state machine for high-voltage direct-mounted energy storage systems include the following steps:

[0109] Step 1: Determine the submodule output status based on system impact and fault status.

[0110] Step 2: According to different circuit states and in accordance with the instructions of the state machine, the next required circuit state and the driving signal of the main switch tube are obtained.

[0111] For the multi-condition fault protection control strategy and its state machine applicable to high-voltage direct-mounted energy storage system, the state switching is as follows: Figure 7 As shown, where:

[0112] like Figures 8a-8b As shown in the figure, the submodule circuit of the single-phase high-voltage direct-mounted energy storage system is divided into positive current state and negative current state. The multi-condition fault protection control strategy applicable to the high-voltage direct-mounted energy storage system and the corresponding submodule working conditions of its state machine are shown in the figure. Figures 9a to 9j As shown, it is convenient for the subsequent research description.

[0113] V1: Switch tubes Q2 and Q4 are turned on, switch tubes Q1 and Q3 are turned off, the battery circuit breaker is disconnected, and the bus current flows in the forward direction.

[0114] V2: Switch tubes Q2 and Q3 are turned on, switch tubes Q1 and Q4 are turned off, the battery circuit breaker is disconnected, and the bus current flows in the forward direction.

[0115] V3: Switch tubes Q1 and Q4 are turned on, switch tubes Q2 and Q3 are turned off, the battery circuit breaker is disconnected, and the bus current flows in the forward direction.

[0116] V4: Switch tubes Q2 and Q3 are turned on, switch tubes Q1 and Q4 are turned off, the battery circuit breaker is turned on, and the bus current flows in the forward direction.

[0117] V5: Switch tubes Q1 and Q4 are turned on, switch tubes Q2 and Q3 are turned off, the battery circuit breaker is turned on, and the bus current flows in the forward direction.

[0118] V6: Switch tubes Q1 and Q4 are turned on, switch tubes Q2 and Q3 are turned off, the battery circuit breaker is turned on, and the bus current flows in the reverse direction.

[0119] V7: Switch tubes Q2 and Q3 are turned on, switch tubes Q1 and Q4 are turned off, the battery circuit breaker is turned on, and the bus current flows in the reverse direction.

[0120] V8: Switch tubes Q1 and Q4 are turned on, switch tubes Q2 and Q3 are turned off, the battery circuit breaker is disconnected, and the bus current flows in the reverse direction.

[0121] V9: Switch tubes Q2 and Q3 are turned on, switch tubes Q1 and Q4 are turned off, the battery circuit breaker is disconnected, and the bus current flows in the reverse direction.

[0122] V10: Switch tubes Q1 and Q3 are turned on, switch tubes Q2 and Q4 are turned off, the battery circuit breaker is disconnected, and the bus current flows in the reverse direction.

[0123] This embodiment of the present invention provides a comprehensive battery safety assurance method for high-voltage, direct-mounted energy storage equipment. This method enables smooth operating state switching under various impact conditions, providing strong electromagnetic transient impact protection for submodule components. Because the subunit control signals are independent of each other, the present invention is applicable not only to high-voltage, direct-mounted systems but also to MMCs.

[0124] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0125] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A comprehensive battery safety assurance method for high-voltage direct-mounted energy storage equipment, characterized in that: include: Step S1: constructing a secondary battery cluster with insulation resistance against strong electromagnetic transient faults; Step S2: After the secondary battery cluster is constructed, a cascade energy storage unit protection method is set to suppress overvoltage and lightning strike operations; Step S3: Based on the protection method of the secondary battery cluster and the cascade energy storage unit, a multi-operating condition fault protection control strategy and its state machine applicable to the high-voltage direct-mounted energy storage system are set; The secondary battery cluster includes: a cover plate, a pole, a secondary battery, a shell, a connecting piece and a current collector; The pole, secondary battery, adapter and current collector are all located in the shell, and the cover plate is located on the upper side of the shell; The adapter is respectively connected to the cover plate, the pole and the current collector; The adapter includes: an overload protection part, a pole connection part, a cover plate connection part, and a current collector connection part; Wherein, the pole connecting portion is connected to the pole, the current collector connecting portion is connected to the current collector, and the cover plate connecting portion is connected to the cover plate; The overload protection unit includes a first overload protection unit and a second overload protection unit; During normal use, the second overload protection portion is connected to the pole connection portion and the current collector connection portion, and the first overload protection portion is in contact with the second overload protection portion; The secondary battery forms a circuit through the positive electrode post-positive electrode post connection part-positive electrode second overload protection part-positive electrode current collector connection part-secondary battery-negative electrode current collector connection part-negative electrode second overload protection part-negative electrode post connection part-negative electrode post; wherein the left side of the first overload protection part is fixed to the electrode post connection part, and the right side is in contact with the current collector connection part but not fixed; The first overload protection part includes: an upper metal sheet and a lower metal sheet; Among them, the part facing the cover plate has a low thermal expansion coefficient, and the part facing the secondary battery has a high thermal expansion coefficient; when lightning strikes and strong electromagnetic transient shocks occur, the second overload protection part generates heat, causing the first overload protection part to deform due to heat, and the right end rises and overlaps with the cover plate connection part; thus forming a circuit of positive pole-positive pole connection part-second positive pole overload protection part-cover plate-negative pole second overload protection part-negative pole connection part-negative pole, ensuring the normal use of the module and cutting off the circuit of the secondary battery at the same time.

2. The battery comprehensive safety assurance method for high-voltage direct-mounted energy storage equipment according to claim 1 is characterized in that: The cascade energy storage unit protection method for suppressing overvoltage and lightning strike operations in step S2 includes: Step S2.1: Conduct voltage impulse tests on the cells in the secondary battery cluster and the arrester installed outside the battery cluster, and obtain a curve showing the relationship between the impulse discharge voltage and the corresponding discharge time, i.e., the volt-second characteristic; Step S2.2: Compare the lightning arrester and the secondary battery cluster insulation volt-second characteristics, confirm that the lightning arrester volt-second characteristics are always lower than the battery module insulation volt-second characteristics, and determine the lightning arrester parameters based on the determined volt-second characteristic range; Step S2.3: The energy storage unit of the high-voltage direct-mounted energy storage equipment is connected to the grid using three phases. Each phase subunit has multiple energy storage units, and a grid-connected reactor is introduced between the subunit and the grid connection point. After confirming the selection of the lightning arrester, a passive protector is installed between the energy storage subunit and the grid-connected reactor. Step S2.4: According to the different grounding methods of the energy storage unit, a lightning arrester is installed inside each phase of the energy storage unit.

3. The battery comprehensive safety assurance method for high-voltage direct-mounted energy storage equipment according to claim 2 is characterized in that: The step S2.4 includes: The energy storage system adopts three-phase grid-connected design, including phases A, B and C. For Y-type grounded energy storage units, a lightning arrester is installed at the neutral point, and lightning arresters are installed in the first three submodules of phases A, B and C close to the grid-connected reactor. For delta-grounded energy storage units, lightning arresters are installed in the first three submodules of phases A, B and C close to the grid-connected reactor and the three submodules farthest from the grid-connected reactor.

4. The battery comprehensive safety assurance method for high-voltage direct-mounted energy storage equipment according to claim 1 is characterized in that: The multi-operating-condition fault protection control strategy and its state machine applicable to the high-voltage direct-mounted energy storage system in step S3 are a millisecond-to-second timescale protection method based on the microsecond-level protection of secondary battery clusters with insulation resistance to strong electromagnetic transient faults and the nanosecond-level protection of cascaded energy storage units that suppress lightning surges and switching surge overvoltages. This control strategy is proposed for an energy storage system architecture based on a cascaded H-bridge converter, and includes the following steps: Step S3.1: Determine the system operating status and disturbance impact; Step S3.2: Based on the different circuit states and the instructions of the state machine, the next required circuit state and the driving signal of the main switch are obtained. Based on the changes in electromagnetic transient impact and working state requirements, the working state of the working modules is redistributed to maintain the stable operation capability of the system under various fault conditions. By real-time monitoring of the working conditions, that is, controlling the driving signals of the submodules, the submodules complete the working state transformation based on the set state machine in each working state experienced during the switching process.

5. A secondary battery, based on the battery comprehensive safety assurance method of high-voltage direct-mounted energy storage equipment according to any one of claims 2 to 4, characterized in that: The secondary battery comprises: a positive electrode sheet, a separator and a negative electrode sheet; The positive electrode sheet includes a composite current collector, an electrode active material layer, and a safety coating disposed between the current collector and the electrode active material layer. The impedance of the safety coating increases rapidly at high temperatures. The safety coating comprises a phase change material, a conductive agent and a binder. Based on the total weight of the safety coating, the weight percentage of the phase change material is 5wt% to 80wt%, the weight percentage of the conductive agent is 20wt% to 50wt%, and the weight percentage of the binder is 10wt% to 50wt%.

6. The secondary battery according to claim 5, characterized in that The phase change material is selected from at least one of paraffin, fatty acid, fatty alcohol and polyol.

7. A method for preparing a secondary battery, based on the secondary battery according to claim 6, characterized in that: include: Preparation steps of the positive electrode sheet: paraffin wax, SP, and PVDF are mixed in a set ratio with N-methyl-2-pyrrolidone (NMP) as solvent, and then coated on both surfaces of the metal current collector. After drying, a safety coating is obtained; Then, the positive electrode active material and PVDF in a set ratio are mixed evenly with NMP as solvent, and then coated on the safety coating of the current collector prepared according to the above method, and dried to obtain the positive electrode active material layer; The current collector with the safety coating and the positive electrode active material layer is then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions and connected to the tabs to form the positive electrode sheet of the secondary battery; The steps for preparing the negative electrode sheet are as follows: active materials graphite, SP, CMC, and SBR are added to the solvent deionized water in a set mass ratio and mixed evenly to form an anode slurry; the anode slurry is coated on the surface of the negative electrode metal collector copper foil and dried, and then trimmed, cut, and striped, and dried under vacuum conditions, and the tabs are connected to form the secondary battery negative electrode sheet; Electrolyte preparation steps: EC and DEC are mixed in a set volume ratio to obtain an EC / DEC mixed solvent, and then lithium salt LiPF6 is dissolved in the mixed solvent to obtain an electrolyte; Secondary battery preparation steps: Use polypropylene film as the separator, stack the positive electrode sheet, separator and negative electrode sheet in order, wind them into a battery cell, inject electrolyte, and obtain a secondary battery through vacuum packaging, standing, formation and shaping processes.

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