Method and system for detecting health state of storage battery for direct current system of transformer substation

Abstract

The invention provides a method and system for detecting the health state of a storage battery for a transformer substation direct current system, and the method comprises the steps: obtaining first state data which comprises an access switch state of a battery pack, a closed-loop switch state between direct current buses, a voltage increment state of the battery pack, and a current increment state of the battery pack; determining the operation condition of the storage battery according to the first state data; according to the operation condition, collecting operation data including the boost rate, the charge increment, the charging duration and the discharging duration of the storage battery, calculating a health characteristic value HF of the storage battery under the corresponding condition according to the operation data, and obtaining second state data including the voltage V, the internal resistance R, the temperature T and the health characteristic value HF of the storage battery, and the SOH value diagnosis model generates an SOH value for determining the health state of the storage battery according to the second state data. The health state of the storage battery can be judged from multiple angles by combining the operation condition of the storage battery in the direct-current circuit, and the detection accuracy of the health state of the storage battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery health status detection, and in particular to a method and system for detecting the health status of a battery for a DC system of a substation. Background Art

[0002] Substations are the central neurons of the power grid, and the safe and stable operation of the power grid is closely related to substations. The DC system of the substation is responsible for providing power supply for protection, automatic devices, control, signals, etc. Once a fault occurs in the DC system of the substation, it may cause the relay protection and automatic devices in the substation to lose power, and the circuit breaker cannot trip to isolate the fault, thereby causing a series of dangerous consequences such as the upper power supply tripping or even the decoupling of the power grid. As the core power supply equipment of the DC system of the substation, the healthy operation level of the battery is of great significance to ensuring the safety and reliability of the power grid.

[0003] Due to long-term online operation, batteries will inevitably have defects such as aging, disconnection of the plate connection bridge, chemical deposition, and sulfation. Due to the characteristics of the battery itself, its failure evolution often presents a "cliff-like" characteristic. The battery running with a problem will suddenly have a positive and negative electrode disconnection (open circuit). The battery pack of the substation is composed of multiple lead-acid (lithium iron phosphate) batteries in series. If any battery is disconnected, the voltage of the entire battery pack will become zero, the DC system of the substation will fail, and then it will cause a huge hidden danger to the operation of the power grid. Therefore, defect monitoring, early warning and fault handling measures for substation batteries are particularly important. Summary of the invention

[0004] In view of this, the problem to be solved by the present invention is to provide a method and system for detecting the health status of batteries for a substation DC system, which can judge the health status of the battery from multiple angles in combination with operating conditions and improve the accuracy of battery health status detection.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method and system for detecting the health status of a battery for a DC system of a substation, comprising a plurality of DC circuits for providing DC power to the DC system of the substation, wherein the DC circuits include a charger connected to a corresponding DC bus, wherein an output end of the charger is connected in parallel to a battery group, wherein the battery group is composed of a plurality of batteries connected in series; Determine the battery operating condition, obtain first state data including the access switch state of the battery pack, the closing switch state between the DC buses, the voltage increment state of the battery pack, and the current increment state of the battery pack, and determine the operating condition of the battery according to the first state data; Calculate the SOH value of the storage battery. According to the operating conditions, collect the operating data including the battery supercharging rate, charge increment, charging duration, and discharging duration. Calculate the health feature value HF of the battery under the corresponding operating conditions based on the operating data. Obtain the second state data including the battery voltage V, internal resistance R, temperature T, and health feature value HF. The SOH value diagnosis model generates the SOH value for determining the health state of the battery based on the second state data.

[0006] Further, the operating conditions include static power supply A where the charger is normally powered and the battery pack operates stably, AC failure B where the charger fails and the battery pack discharges, AC recovery C where the charger resumes power supply and the battery pack charges, capacity verification discharge D where the charger is normally powered and the battery pack is taken out of operation and in the test state, and capacity verification charge E where the charger is normally powered and the battery pack is reconnected and charges.

[0007] Further, determining the operating conditions of the battery pack includes: data collection, obtaining the current state data of the battery pack; Operating condition matching, matching the state data with the corresponding state data of static power supply A, AC failure B, AC recovery C, capacity verification discharge D, and capacity verification charge E respectively. If it matches successfully with one of them, output the successfully matched operating condition; if all matches fail, output the operating condition of abnormal power supply F, and jump to the data collection step.

[0008] Further, the health feature value of the battery under static power supply A The calculation formula is: , where t （n）charge represents the total charging duration of the nth battery when the floating charge voltage of the battery pack increases by x, and t （n）discharge represents the total discharging duration of the nth battery when the floating charge voltage of the battery pack decreases by x, and x represents a non - negative value.

[0009] Further, the health feature value of the battery under AC failure B The calculation formula is: , where Δt represents the sampling time interval, and Δu （n） represents the change value of the voltage drop of the nth battery within the Δt interval; The health feature value of the battery under AC recovery C The calculation formula is: , , , , Among them, t sum represents the total duration of AC restoration, t CI represents the duration of the constant current stage, t CV represents the duration of the constant voltage stage, Q0 is the nominal battery capacity, U m is the floating charge voltage reference value of the battery, u （n） is the voltage of the nth battery, N is the number of batteries in the battery pack, v1 represents the voltage of the battery at the start of charging, and v2 represents the voltage of the battery at the end of charging.

[0010] Furthermore, the health characteristic values of the battery under the nuclear capacity discharge D and nuclear capacity charge E 、 The calculation formula is: , , Among them, t （n）discharge represents the discharge time of the nth battery, t （n）charge represents the charging duration of the nth battery.

[0011] Furthermore, the SOH value diagnosis model is constructed based on the Gaussian process regression algorithm and corresponds one-to-one with the operating conditions.

[0012] A power supply protection system for batteries in a substation DC system, including a power supply unit that outputs direct current, a diagnosis unit that determines whether the batteries in the power supply unit are below the SOH threshold, a protection unit that removes the batteries below the SOH threshold from the circuit, and an early warning unit that reminds of the position of the defective batteries below the SOH threshold; The power supply unit includes several DC circuits that output direct current; the diagnosis unit includes a working condition module that detects the working state of the battery pack, a diagnosis module that calculates the SOH value of each battery in the battery pack and determines whether it is below the SOH threshold.

[0013] Furthermore, the DC circuit includes a first circuit and a second circuit with exactly the same circuit structure. The first circuit includes a first charger and a first battery pack. The first charger and the first battery pack are respectively connected to one end of a first switch, a second switch, and a third switch, and the other end of the third switch is connected to the first DC bus; The second circuit includes a second charger, a second battery pack, a fourth switch, a fifth switch, and a sixth switch. The output end of the second circuit is connected to the second DC bus, and a seventh switch is connected in series between the first DC bus and the second DC bus.

[0014] Further, the protection unit includes an isolation circuit for removing the storage battery. The isolation circuit includes a plurality of relay switches corresponding to the storage batteries one by one. The positive pin of the relay switch is connected to the positive electrode of the storage battery, and the negative pin of the relay switch is connected to the negative electrode of the storage battery.

[0015] The advantages and positive effects of the present invention are: By determining the operating characteristics of the battery pack, collecting the corresponding first state data according to the operating characteristics, and then calculating the health characteristic value HF of the storage battery in the battery pack. The SOH value diagnostic model corresponding to the operating characteristics generates the SOH value based on the voltage V, internal resistance R, temperature T, and health characteristic value HF of the storage battery. Whether there is a defect in the storage battery is judged according to the SOH value of the storage battery. The above method can judge the health state of the storage battery from multiple angles in combination with the operating conditions, and improve the accuracy of the health state detection of the storage battery. Description of the Drawings

[0016] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention. In the drawings: Figure 1 is a flowchart of a method for detecting the health state of a storage battery for a substation DC system according to the present invention; Figure 2 is a schematic diagram of calculating the health characteristic value HF of the storage battery in a method for detecting the health state of a storage battery for a substation DC system according to the present invention; Figure 3 is a schematic diagram of calculating the SOH estimated value in a method for detecting the health state of a storage battery for a substation DC system according to the present invention; Figure 4 is a system diagram of a power supply protection system for a storage battery for a substation DC system according to the present invention; Figure 5 is a DC circuit diagram of a power supply protection system for a storage battery for a substation DC system according to the present invention; Figure 6 is an isolation circuit diagram in a power supply protection system for a storage battery for a substation DC system according to the present invention. Detailed Embodiments

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0019] The present invention provides a method for detecting the health state of a battery used in a substation DC system. As Figure 5 shown, it includes a DC circuit that powers the substation DC system. The DC circuit includes a charger that converts 220V AC power in the power grid into 220V DC power and a battery pack composed of a plurality of batteries connected in series. The output terminal of the charger is connected to the DC bus, and the output terminal of the charger is connected in parallel with the battery pack. There are several DC buses for transmitting DC power in the substation DC system, and each DC bus is separately connected to the corresponding electrical equipment. An embodiment of the present application is that there are two DC buses in the substation DC system, namely the first DC bus and the second DC bus, and the first DC bus and the second DC bus respectively correspond to the first circuit and the second circuit for outputting DC power.

[0020] An embodiment of the present application is that the first DC bus corresponds to the first circuit. When the first circuit is operating, the charger converts the AC power in the power grid into DC power and then supplies power to the first DC bus, and the battery pack is the backup power supply; when there is a power grid fault, the charger fails, and the battery pack supplies power to the first DC bus.

[0021] As Figure 1 and Figure 2 shown, the method for detecting the health state includes: determining the battery operating conditions, obtaining first state data including the access switch state of the battery pack, the loop closing switch state between the DC buses, the voltage increment state of the battery pack, and the current increment state of the battery pack, and determining the operating conditions of the battery based on the first state data.

[0022] The access switch status includes Pos1 = 0 or 1: when the battery pack is connected, Pos1 = 1; when the battery pack is not connected, Pos1 = 0. The closed-loop switch status includes Pos2 = 0 or 1: when the connection switch between the two DC buses is closed, Pos2 = 1; when the connection switch between the two DC buses is open, Pos2 = 0. The voltage increment status includes State_Voltage = -1 or 0 or 1: when the battery pack is charging, the voltage increment is positive, State_Voltage = 1; when the battery pack is in a regulated voltage state or used as a backup power source, the voltage increment is zero, State_Voltage = 0; when the battery pack is discharging, the voltage increment is negative, State_Voltage = -1. The current increment status includes State_Current = -1, 0, 1: when the battery pack is charging, the current flows from the charger to the battery pack, State_Current = 1; when the battery pack is discharging, the current flows from the battery pack to the DC bus, State_Current = -1; when the battery pack is isolated, there is no current flowing between the battery pack and the charger (or DC bus), State_Current = 0.

[0023] The operating conditions include static power supply A, AC failure B, AC recovery C, capacitive discharge D, and capacitive charge E. Different operating conditions correspond to different first state data, and the operating conditions of the battery pack in the DC circuit are determined by matching the first state data.

[0024] When the DC circuit is in the static power supply A state, the charger outputs current normally, and the battery pack is used for voltage regulation or as a backup power source. The first state data is: , When the DC circuit is in the AC failure B state, the AC input of the charger is abnormal, resulting in the charger being unable to output, and the battery pack discharges. The first state data is: , When the DC circuit is in the AC recovery C state, the charger outputs DC power normally, and the battery pack is charged. The first state data is: , When the DC circuit is in the capacitive discharge D state, the charger outputs DC power normally, and the battery pack is not connected to the DC circuit and discharges at a constant current alone (the battery pack discharges at a constant current for the load in the substation DC system). The first state data is: , When the DC circuit is in the capacitive charge E state, the charger outputs DC power normally, and the battery pack is connected to the DC circuit and charged. The first state data is: , Determining the operating conditions of the battery pack includes: data acquisition to obtain the current first state data of the battery pack; operating condition matching, matching the first state data with the first state data corresponding to static power supply A, AC failure B, AC recovery C, capacity verification discharge D, and capacity verification charge E respectively. If a match is successful with one of them, the successfully matched operating condition is output; if all matches fail, the operating condition of abnormal power supply F is output. Abnormal power supply F indicates that the charger or battery is currently in an abnormal operating state, and the data acquisition step needs to be re-executed until the current operating condition of the battery is determined.

[0025] Calculate the SOH value of the battery. According to the operating conditions, collect operating data including the battery boost rate, charge increment, charge duration, and discharge duration. Calculate the health characteristic value HF of the battery under the corresponding operating conditions based on the operating data. Obtain the second state data including the battery voltage V, internal resistance R, temperature T, and health characteristic value HF. The SOH value diagnosis model generates the SOH value for determining the health state of the battery based on the second state data.

[0026] Under static power supply A, based on existing experience, there is a significant correlation between the time required for the battery to charge / discharge to cause a fixed change in voltage and the SOH value of the battery. Therefore, the operating data includes the total charge duration and total discharge duration of the battery, and the health characteristic value HF of the battery can be calculated. The process of collecting the operating data is as follows: adjust the floating charge voltage setting value (charging voltage of the battery pack) of the charger up and down. The voltage values for increasing and decreasing the charging voltage are both x, and the battery pack is made to perform short-term charge and discharge. Health characteristic value under static power supply The calculation formula is: , where t （n）charge represents the total charge duration of the nth battery when the charging voltage of the charger increases by x, and t （n）discharge represents the total discharge duration of the nth battery when the charging voltage of the charger decreases by x, and x represents a non-negative value.

[0027] Under AC failure B, after the AC system loses voltage (after the power grid cannot provide alternating current for the charger), the battery pack discharges at a constant current with the same current as the charger output current under static power supply A. The battery pack starts to decline from the static floating charge voltage. Affected by the uncertain power grid fault time, the discharge process time is difficult to measure. At the same discharge time interval, the higher the battery health degree, the smaller the battery voltage drop. Therefore, the operating data includes the voltage drop change rate of the battery. The collection process is as follows: collect the voltage change value of the battery at fixed time intervals. Health characteristic value under AC failure The calculation formula is: , where Δt represents the sampling time interval, and Δu（n） It represents the change value of the voltage drop of the nth section of the battery within the Δt interval. Δt is set by the operator's experience. To ensure the accuracy of the characteristic indicators, Δt is recommended to take a fixed duration, such as 15 minutes.

[0028] When the AC is restored at C, after the grid AC fault is restored, the charger recharges the battery pack. Due to the different lengths of the grid fault time, there will be differences in the remaining power in the battery pack. Therefore, the charging method of the battery pack may be constant current first and then constant voltage, or it may be constant voltage throughout the process.

[0029] During constant current charging, the larger the area of the differential curve between the battery charge and the battery voltage, the better the charge storage performance of the battery, and thus the larger the SOH value of the battery; during constant voltage charging, the closer the charging voltage of the battery is to the equalizing charge voltage of the battery pack, the larger the SOH value of the battery.

[0030] However, in actual situations, if the AC failure time at B is short and the power loss of the battery is low, there is no constant current charging stage. Therefore, to generate the SOH value of the battery more accurately, the operating data includes the constant current charging duration, the constant voltage charging duration, and the total charging duration, and the health characteristic value at AC restoration C The calculation formula is: , , , , where: t sum represents the total duration of AC restoration, t CI represents the constant current charging duration, t CV represents the constant voltage charging duration. Q0 is the nominal charge of the battery, U m is the floating charge voltage reference value of the battery, u （n） is the voltage of the nth section of the battery, N is the number of batteries in the battery pack, v1 represents the starting charging voltage of the battery, and v2 represents the ending charging voltage of the battery.

[0031] During capacity verification discharge at D, the battery pack is disconnected from the DC circuit and a separate discharge experiment is conducted (i.e., connecting the battery pack to the tester). During the experiment, the battery pack discharges from the floating charge voltage at a constant current to the cut-off voltage. The longer the discharge time of the battery, the higher the SOH value. Therefore, the discharge time of each battery is collected separately. The health characteristic value during capacity verification discharge at D The calculation formula is: , where, t （n）discharge represents the discharge time of the nth section of the battery.

[0032] During the capacity test charging E, after verifying that the voltages of all the storage batteries in the battery pack are normal, the battery pack is reconnected to the DC circuit. The charger charges the battery pack. As the voltages of all the storage batteries in the battery pack rise to the floating charge voltage, the shorter the charging time of the storage battery, the higher the SOH value. Therefore, the charging duration of each storage battery is collected separately. The health characteristic value is calculated by the formula: , where t （n）charge represents the charging duration of the nth storage battery.

[0034] To improve the calculation accuracy of the SOH value, continuously detect the state variables Pos1, Pos2, State_Voltage, and State_Current, and determine whether there is a change in the state variables. If not, adjust the sampling time of the second state data according to the current operating condition to continuously update the SOH value of the storage battery; if yes, immediately collect the first state data to update the operating condition, and collect the second state data according to the operating condition to update the SOH value of the storage battery.

[0035] An embodiment of this application is as follows: Operating condition A is the long-term state in the actual operation of the substation DC system, and the second state data is collected once every 1 hour; in operating condition B, the second state data is collected once every 15 minutes; in operating conditions C, D, and E, the second state data includes the whole process of the operating condition.

[0036] As Figure 3 shown, the input of the SOH value diagnosis model is the second state data, and the output is the SOH value. When training the SOH value diagnosis model, separately collect the second state data and the corresponding SOH values under different operating conditions, and separately train the SOH value diagnosis model corresponding to the operating condition according to the collected data to obtain the SOH value diagnosis models corresponding to different operating conditions, so as to realize the multi-angle judgment of the health state of the storage battery while ensuring the accuracy of the judgment. An embodiment of this application is as follows: Build the SOH value diagnosis model based on the Gaussian process regression algorithm (GPR). The SOH value diagnosis models for static power supply A, AC failure B, AC recovery C, capacity test discharge D, and capacity test charging E are model 1, model 2, model 3, model 4, and model 5 respectively.

[0037] When calculating the SOH value of a storage battery, according to the operating conditions of the battery pack where the storage battery is located, the SOH value diagnosis model corresponding to the operating conditions is retrieved. The SOH value diagnosis model receives the second state data and outputs the SOH value of the storage battery. The second state data of all the storage batteries in the battery pack are input into the SOH value diagnosis model in sequence, and the SOH value of each storage battery in the battery pack is output. Whether there are defective storage batteries in the battery pack is determined according to the SOH value. If the SOH value of a storage battery is lower than the SOH threshold, it needs to be removed in time (that is: every time the SOH value is updated, the action of judging the health status and whether to remove is executed).

[0038] A substation DC battery pack power supply protection system, as Figure 4 shown, includes a substation system (corresponding to the substation DC system) and a power supply protection system. The power supply protection system is connected to the substation DC system through a DC bus. The power supply protection system includes a power supply unit that outputs direct current, a diagnosis unit that judges whether there are defective storage batteries in the power supply unit, a protection unit that removes the defective storage batteries from the circuit, and a warning unit that reminds the location of the defective storage batteries.

[0039] The power supply unit includes a DC circuit whose output terminal is connected to the DC bus. The DC circuit supplies power to the substation DC system through the DC bus. The DC circuit includes a charger that converts alternating current into direct current and a battery pack composed of a plurality of storage batteries connected in series. The output terminal of the charger is connected to the DC bus, and the output terminal of the charger is connected in parallel with the battery pack. When the power supply circuit operates, the charger outputs direct current to supply power to the substation DC system, and the battery pack plays a voltage stabilizing role or serves as a backup power source. When the power grid or the charger fails, the battery pack supplies power to the substation DC system alone.

[0040] An embodiment of the present application is: as Figure 5 shown, the DC circuit includes a first circuit and a second circuit with exactly the same circuit structure. The first circuit includes a first charger and a first battery pack. The first charger and the first battery pack are respectively connected to one end of a third switch K3 through a first switch K1 and a second switch K2 (corresponding to the access switch of the battery pack). The other end of the third switch K3 is connected to the first DC bus. When the third switch K3 is closed, the first circuit starts to supply power. When the first power supply circuit operates normally, the first switch K1 and the second switch K2 are closed at the same time. When the power grid or the first charger fails, the first switch K1 is opened. When the first battery pack fails, the second switch K2 is opened. The second circuit includes a second charger, a second battery pack, a fourth switch K4, a fifth switch K5 and a sixth switch K6. The output terminal of the second circuit is connected to the second DC bus.

[0041] A seventh switch K7 is provided between the first DC bus and the second DC bus. The seventh switch K7 corresponds to the closing switch between the DC buses. Before the battery pack performs capacity verification discharge D, the seventh switch K7 is closed to close the loop of the two DC buses, and then the connection between the battery pack and the corresponding DC circuit is disconnected to perform the capacity verification discharge D.

[0042] The power supply diagnosis unit includes a working condition module for detecting the working state of the battery pack and a diagnosis module for judging whether the health state of each storage battery in the battery pack meets the threshold. The working condition module determines the operating condition of the battery pack based on the first state data of the battery pack and outputs a working condition feedback. The working condition data includes the state of the second switch K2 or the fifth switch K5, the state of the seventh switch K7, the voltage increment data of the battery pack, and the current increment data of the battery pack. The working condition feedback of the battery pack includes: static operation during the separate power supply process of the charger, AC failure during the charger power supply failure process, AC recovery during the charger power supply recovery process, capacity verification discharge during the battery capacity verification process, capacity verification charge during the process of connecting to the system after the verification is completed, and abnormal operation not belonging to any of the above processes.

[0043] The diagnosis module receives the working condition feedback, collects the operation data of the battery pack based on the working condition feedback, and calculates the health characteristic value HF of each storage battery in the battery pack under the corresponding working condition. The diagnosis module includes an SOH value diagnosis model corresponding to the operating condition. The SOH value diagnosis model receives the health characteristic value HF, voltage V, internal resistance R, and temperature T of the storage battery under the corresponding working condition, outputs the SOH value representing the health state of the storage battery, and judges whether there are defects based on the SOH value of each storage battery.

[0044] The protection unit receives the position information of the storage battery with an SOH value lower than the SOH threshold, eliminates the low-SOH storage battery based on the position information, and feeds back the protection result. As Figure 6 shown, the protection unit includes an isolation circuit for eliminating the storage battery. The isolation circuit includes a number of relay switches corresponding to the storage batteries one by one. The positive pin of the relay switch is connected to the positive electrode of the storage battery, and the negative pin of the relay switch is connected to the negative electrode of the storage battery. The working process of the isolation circuit is that the protection unit controls the corresponding relay switch to conduct according to the position information, and the positive and negative electrodes of the corresponding storage battery are short-circuited to complete the isolation of the storage battery.

[0045] As Figure 5As shown in the figure, normally closed first relay switch KM1 and second relay switch KM2 are respectively provided at the power supply output ends of the first battery pack and the second battery pack, and normally open third relay switch KM3 is provided between the first DC bus and the second DC bus. An embodiment of the present application is as follows: when the voltage of the battery pack drops significantly due to the removal of multiple batteries with SOH lower than the threshold value in the first battery pack, or when the first battery pack voltage is lower than the limit safety voltage due to a long-term AC power failure, and the electrical energy provided by the first battery pack cannot meet the normal operation of the substation relay protection and automatic devices, control the first relay switch KM1 to disconnect and the third relay switch KM3 to close, and the first DC bus and the second DC bus operate in a closed loop. Use the second charger and the second battery pack to carry the entire DC load of the substation, which can extend the power supply duration and gain time for emergency repair.

[0046] The warning unit receives the protection result and location information and issues a text warning reminder. An embodiment of the present application is as follows: when the staff receives the text warning reminder of "the health status of the nth battery in the Nth battery pack is lower than the threshold value and has been taken out of service", the staff goes to the location of the nth battery to replace the battery and reconnects the battery to the Nth battery pack.

[0047] The above has described the embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equal changes and improvements made according to the scope of the present invention should still fall within the scope covered by this patent.

Claims

1. A method for detecting the health state of a storage battery used in a substation DC system, characterized in that, It includes several DC circuits that provide direct current for the DC system of the substation. The DC circuits include battery chargers connected to the corresponding DC buses. The output terminals of the battery chargers are connected in parallel to a battery bank, and the battery bank is formed by connecting several storage batteries in series. Determine the working conditions of the storage batteries, obtain first status data including the access switch status of the battery bank, the loop closing switch status between the DC buses, the voltage increment status of the battery bank, and the current increment status of the battery bank, and determine the operating conditions of the storage batteries based on the first status data. Calculate the SOH value of the storage batteries. Based on the operating conditions, collect operating data including the boosting rate of the storage batteries, the charge increment, the charging duration, and the discharging duration. Calculate the health feature value HF of the storage batteries under the corresponding operating conditions based on the operating data. Obtain second status data including the voltage V, internal resistance R, temperature T, and health feature value HF of the storage batteries. The SOH value diagnosis model generates the SOH value for determining the health status of the storage batteries based on the second status data.

2. The method for detecting the health state of a storage battery used in a substation DC system according to claim 1, characterized in that, The operating conditions include static power supply A where the battery charger supplies power normally and the battery bank operates stably, AC failure B where the battery charger fails and the battery bank discharges, AC recovery C where the battery charger resumes power supply and charges the battery bank, capacity verification discharge D where the battery charger supplies power normally and the battery bank is taken out of operation and is in the test state, and capacity verification charge E where the battery charger supplies power normally and the battery bank is reconnected and charged.

3. The method for detecting the health state of a storage battery for a substation DC system according to claim 2, characterized in that, Determining the operating conditions of the battery bank includes: data collection, obtaining the current first status data of the battery bank. Operating condition matching: Match the first status data with the corresponding first status data of static power supply A, AC failure B, AC recovery C, capacity verification discharge D, and capacity verification charge E respectively. If a match is successful with one of them, output the successful matching operating condition. If all matches fail, output the operating condition of abnormal power supply F and jump to the data collection step.

4. The method for detecting the health state of a storage battery for a substation DC system according to claim 1, characterized in that, The health characteristic value of the battery under the static power supply A The calculation formula is as follows: ， where t （n）charge represents the total charging duration of the nth battery when the floating charge voltage of the battery pack increases by x, and t （n）discharge represents the total discharging duration of the nth battery when the floating charge voltage of the battery pack decreases by x, and x represents a non-negative value.

5. The method for detecting the health state of a storage battery used in a substation DC system according to claim 1, wherein The health characteristic value of the battery under AC failure B The calculation formula is as follows: ， where Δt represents the sampling time interval, and Δu （n） represents the change value of the voltage drop of the nth battery cell within the Δt interval; The healthy characteristic value of the battery under the AC restoration C The calculation formula is as follows: ， ， ， ， Among them, t sum represents the total duration of the AC restoration process, t CI represents the duration of the constant current stage, t CV represents the duration of the constant voltage stage, Q0 is the nominal power of the storage battery, U m is the floating charge voltage reference value of the storage battery, u （n） is the voltage of the nth storage battery, N is the number of storage batteries in the battery pack, v1 represents the voltage of the storage battery at the start of charging, and v2 represents the voltage of the storage battery at the end of charging.

6. The method for detecting the health state of a battery for a substation DC system according to claim 1, wherein, The health characteristic values of the battery under the nuclear capacity discharge D and the nuclear capacity charge E and The calculation formulas are respectively as follows: ， ， where t （n）discharge represents the discharge duration of the nth battery cell, and t （n）charge represents the charging duration of the nth battery cell.

7. A method for detecting the health state of a storage battery for a substation DC system according to claim 1, characterized in that, The SOH value diagnosis model is constructed based on the Gaussian process regression algorithm and corresponds one-to-one with the operating conditions.

8. A power supply protection system for a battery in a substation DC system, according to the method for detecting the health state of a battery in a substation DC system described in any one of claims 1-7, characterized in that, It includes a power supply unit that outputs direct current, a diagnosis unit that determines whether the storage batteries in the power supply unit are below the SOH threshold, a protection unit that removes the storage batteries below the SOH threshold from the battery bank, and a warning unit that reminds the location of the defective storage batteries below the SOH threshold. The power supply unit includes several DC circuits that output direct current. The diagnosis unit includes a working condition module that detects the working state of the battery bank, a diagnosis module that calculates the SOH value of each storage battery in the battery bank and determines whether it is below the SOH threshold.

9. The power supply protection system for a storage battery used in a substation DC system according to claim 8, characterized in that, The DC circuit includes a first circuit and a second circuit with exactly the same circuit structure. The first circuit includes a first battery charger and a first battery bank. The first battery charger and the first battery bank are respectively connected to one end of a first switch, a second switch, and a third switch through the first switch and the second switch. The other end of the third switch is connected to the first DC bus. The second circuit includes a second battery charger, a second battery bank, a fourth switch, a fifth switch, and a sixth switch. The output terminal of the second circuit is connected to the second DC bus. A seventh switch is connected in series between the first DC bus and the second DC bus.

10. The power supply protection system for a storage battery used in a substation DC system according to claim 8, characterized in that, The protection unit includes an isolation circuit for removing the storage battery. The isolation circuit includes a number of relay switches corresponding to the storage batteries one by one. The positive pin of the relay switch is connected to the positive electrode of the storage battery, and the negative pin of the relay switch is connected to the negative electrode of the storage battery.

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