Energy management method and system of network construction type energy storage system

Abstract

The invention relates to an energy management method and system for a network-forming type energy storage system, and belongs to the technical field of energy storage system control. According to the method, SOC correction is carried out on the energy storage system with SOC offset, specifically, the energy storage system triggering SOC offset early warning in the optimal maintenance time period is charged with the charging power of the system in the time period until the SOC is calibrated to 100%, and after calibration is finished, SOC operation of the system is limited to be not lower than the discharging boundary value of the system and not exceed the charging boundary value of the system. Controlling the SOC of the energy storage system to run to the boundary so as to avoid the SOC offset phenomenon when the battery is not fully charged and not emptied for a long time; the SOC operation of the energy storage system which does not trigger the SOC offset early warning in the optimal maintenance period is limited to be greater than the discharging threshold value and smaller than the charging threshold value, the discharging threshold value is greater than the discharging boundary value, and the charging threshold value is smaller than the charging boundary value; therefore, the problem that the energy storage system loses the network construction capability due to the fact that the SOC of the energy storage system runs to the boundary and the energy storage converter is converted to the standby state according to the BMS instruction is avoided.

Description

Technical Field

[0001] The present invention relates to an energy management method and system for a grid-forming energy storage system, belonging to the technical field of energy storage system control. Background Art

[0002] With the high proportion of new energy connected to the power grid system, due to the natural uncertainty of new energy power generation, the new power grid requires that the energy storage system equipment connected has the function of grid-forming support and needs to have the voltage source function when off-grid.

[0003] At present, the energy management schemes of grid-forming energy storage systems all follow the schemes of grid-connected energy storage systems, that is, only based on the information uploaded by the battery and BMS (Battery Management System), power limiting, charging and discharging prohibition, and the state of charge (SOC) value of the battery are used for energy management operations. There are the following two problems:

[0004] 1) The energy management of the conventional energy storage system controls the SOC of the charging state of the energy storage system to run to the boundary, that is, the battery is fully charged. The energy storage converter will switch to standby according to the BMS instruction, thus losing the grid-forming ability. If the power grid loses power at this time, the busbar in the grid will overvoltage and shut down;

[0005] The energy management of the conventional energy storage system controls the SOC of the discharging state of the energy storage system to run to the boundary, that is, the battery is emptied. The energy storage converter will switch to standby according to the BMS instruction, thus losing the grid-forming ability. If the power grid loses power at this time, the busbar in the grid will undervoltage and shut down.

[0006] 2) And restricting the operation of the energy storage system battery within a certain range for a long time, that is, restricting the SOC of the energy storage system to run less than the charging boundary value and greater than the discharging boundary value, that is, the battery is not fully charged and not emptied for a long time, the SOC offset phenomenon will occur, that is, a SOC step occurs near the boundary, resulting in over- and under-voltage faults of the energy storage system battery and shutting down, thus losing the grid-forming ability.

[0007] In summary, once the grid-forming energy storage system loses its grid-forming ability, and if the power grid loses power at this time, it will cause the busbar in the grid to shut down. Summary of the Invention

[0008] The purpose of the present invention is to provide an energy management method for a grid-forming energy storage system to solve the problem that the existing energy management of the grid-forming energy storage system loses the grid-forming ability under the charging condition; and to provide another energy management method for a grid-forming energy storage system to solve the problem that the existing energy management of the grid-forming energy storage system loses the grid-forming ability under the discharging condition; and to provide an energy management system for a grid-forming energy storage system to solve the problem that the existing energy management of the grid-forming energy storage system loses the grid-forming ability under the charging condition or to solve the problem that the existing energy management of the grid-forming energy storage system loses the grid-forming ability under the discharging condition.

[0009] To achieve the above object, the solution of the present invention includes:

[0010] An energy management method for a network-forming energy storage system of the present invention includes the following steps:

[0011] During the optimal maintenance period, the energy storage system that triggers the SOC offset warning is charged at the charging power of the system during this period. Under the constraint of the allowable charging current or allowable charging power, it is charged until the SOC is calibrated to 100%. After that, the SOC operation of the system is restricted not to be lower than its discharge boundary value and not to exceed its charging boundary value;

[0012] Restrict the SOC operation of the energy storage system that does not trigger the SOC offset warning during the optimal maintenance period to be greater than its discharge threshold value and less than its charging threshold value. The discharge threshold value is greater than the discharge boundary value, and the charging threshold value is less than the charging boundary value;

[0013] The period when the load within the network-forming network is greater than zero and the power consumption of the systems within the network-forming network is the smallest during the maintenance time is used as the optimal maintenance period. The maintenance time is obtained based on the rated capacity of the energy storage system and the current charging power of the system.

[0014] Further, the condition for triggering the SOC offset warning is that the charging warning value of the single-cell voltage of the energy storage system is less than or equal to the charging threshold value.

[0015] Further, the calculation formulas for the charging warning value and the charging threshold value are as follows:

[0016]

[0017] A U-i-charge-threshold =(SOC max -k×(1 - SOC max ))×100%

[0018] In the formula, A U-i-charge is the charging warning value of the single-cell voltage of the i-th energy storage system, A U-i-charge-threshold is the charging warning threshold value of the i-th energy storage system as the charging threshold value, U i-SOC is the available voltage of the single cell of the i-th energy storage system, U i-max is the highest voltage of the current single cell of the i-th energy storage system, U i-j is the voltage of the j-th single cell of the i-th energy storage system, m is the total number of single cells in the i-th energy storage system, i ∈ [1, n], SOC max is the charging boundary value of the i-th energy storage system, k = 1 indicates triggering the SOC offset warning, k = 0 indicates not triggering the SOC offset warning, and the i-th energy storage system is used as the energy storage system.

[0019] Further, the discharge threshold value is the discharge warning threshold value A of the i-th energy storage system U-i-discharge-threshold , and its calculation formula is as follows:

[0020] A U-i-discharge-threshold =(SOC min +j×SOC min )×100%

[0021] In the formula, SOC min is the discharge boundary value of the i-th energy storage system, and j = 1 indicates triggering the SOC offset warning, while j = 0 indicates not triggering the SOC offset warning.

[0022] Further, the calculation formulas for the discharge boundary value and the charge boundary value are as follows:

[0023]

[0024] In the formula, SOC min is the discharge boundary value of the i-th energy storage system, SOC max is the charge boundary value of the i-th energy storage system, W BESS-j is the rated capacity of the i-th energy storage system, j is the j-th energy storage system among the i energy storage systems, i ∈ [1, n], P load-max is the maximum load power required for the energy storage system to support grid connection, t load is the maximum load operation time, and P power-max is the total power generation of the energy storage system.

[0025] Further, it further includes the following steps:

[0026] Restrict the SOC operation of the energy storage system that does not trigger the SOC offset warning to be not lower than its discharge boundary value and not exceed its charge boundary value.

[0027] An energy management method for a grid-connected energy storage system according to the present invention includes the following steps:

[0028] During the optimal maintenance period, the energy storage system that triggers the SOC offset warning discharges at the discharge power of the system during this period. Under the constraint of the allowable discharge current or allowable discharge power, it discharges until the SOC is calibrated to 0%, and then restricts the SOC operation of the system to be not lower than its discharge boundary value and not exceed its charge boundary value;

[0029] Restrict the SOC operation of the energy storage system that does not trigger the SOC offset warning outside the optimal maintenance period to be greater than its discharge threshold value and less than its charge threshold value. The discharge threshold value is greater than the discharge boundary value, and the charge threshold value is less than the charge boundary value;

[0030] The time period corresponding to zero load within the network-forming network and the minimum system power consumption within the network-forming network during the maintenance time is used as the optimal maintenance time period, and the maintenance time is obtained based on the rated capacity of the energy storage system and the current discharge power of the system.

[0031] Further, the condition for triggering the SOC deviation warning is that the discharge warning value of the single-cell voltage of the energy storage system is greater than or equal to the discharge threshold value.

[0032] Further, the calculation formulas for the discharge warning value and the discharge threshold value are as follows:

[0033]

[0034] A U-i-discharge-threshold =(SOC min +j×SOC min )×100%

[0035] In the formula, A U-i-discharge is the discharge warning value of the single-cell voltage of the i-th energy storage system, A U-i-discharge-threshold is the discharge warning threshold value of the i-th energy storage system as the discharge threshold value, U i-SOC is the available voltage of the single cell of the i-th energy storage system, U i-min is the lowest voltage of the current single cell of the i-th energy storage system, U i-j is the voltage of the j-th single cell of the i-th energy storage system, m is the total number of single cells in the i-th energy storage system, i∈[1,n], SOC min is the discharge boundary value of the i-th energy storage system, j = 1 indicates triggering the SOC deviation warning, j = 0 indicates not triggering the SOC deviation warning, and the i-th energy storage system is used as the energy storage system.

[0036] Further, the charging threshold value is the charging threshold warning value A U-i-charge-threshold of the i-th energy storage system, and its calculation formula is as follows:

[0037] A U-i-charge-threshold =(SOC max -k×(1-SOC max ))×100%

[0038] In the formula, SOC max is the charging boundary value of the i-th energy storage system, k = 1 indicates triggering the SOC deviation warning, and k = 0 indicates not triggering the SOC deviation warning.

[0039] Further, the calculation formulas for the discharge boundary value and the charging boundary value are as follows:

[0040]

[0041] In the formula, SOC minis the discharge boundary value of the i-th energy storage system, SOC max is the charging boundary value of the i-th energy storage system, W BESS-j is the rated capacity of the i-th energy storage system, j is the j-th energy storage system among the i energy storage systems, i ∈ [1, n], P load-max is the maximum load power required for the energy storage system to support grid connection, t load is the maximum load operation time, P power-max is the total power generation of the energy storage system.

[0042] Furthermore, the following steps are also included:

[0043] Restrict the SOC operation of the energy storage system that has not triggered the SOC offset warning to be not lower than its discharge boundary value and not exceed its charging boundary value.

[0044] An energy management system for a grid-forming energy storage system of the present invention includes a processor, and the processor executes a computer program to implement the steps of the energy management method of the grid-forming energy storage system as described above.

[0045] Advantages of the present invention:

[0046] The present invention is a pioneering invention that provides an energy management method for a grid-forming energy storage system. Under the charging condition, by correcting the SOC of the energy storage system with SOC offset, specifically, the energy storage system that triggers the SOC offset warning within the optimal maintenance period is charged at the charging power of the system during this period. Under the constraint of the allowable charging current or allowable charging power, it is charged until the SOC is calibrated to 100%. After the calibration is completed, restrict the SOC operation of the system to be not lower than its discharge boundary value and not exceed its charging boundary value, and control the SOC operation of the energy storage system to the boundary to avoid the SOC offset phenomenon of the battery under long-term non-full and non-empty states, thereby avoiding the loss of the grid-forming ability of the energy storage system. Also, restrict the SOC operation of the energy storage system that does not trigger the SOC offset warning within the optimal maintenance period to be greater than its discharge threshold value and less than its charging threshold value. The discharge threshold value is greater than the discharge boundary value, and the charging threshold value is less than the charging boundary value, that is, control the SOC operation of the energy storage system to be less than the charging boundary value and greater than the discharge boundary value to avoid the loss of the grid-forming ability of the energy storage system caused by the SOC operation of the energy storage system reaching the boundary and the energy storage converter turning to standby according to the BMS instruction.

[0047] The present invention is a pioneering invention and also provides an energy management method for a network-forming energy storage system. Under the discharging condition, the SOC of the energy storage system with SOC offset is corrected. Specifically, the energy storage system that triggers the SOC offset warning within the optimal maintenance period discharges at the discharging power of the system during this period. Under the constraint of the allowable discharging current or allowable discharging power, it discharges until the SOC is calibrated to 0%. After calibration, the SOC operation of the system is restricted not to be lower than its discharging boundary value and not to exceed its charging boundary value, controlling the SOC operation of the energy storage system to the boundary to avoid the SOC offset phenomenon of the battery under the condition of long-term non-full charge and non-empty discharge, and further avoiding the loss of the network-forming ability of the energy storage system. The SOC operation of the energy storage system that does not trigger the SOC offset warning within the optimal maintenance period is also restricted to be greater than its discharging threshold value and less than its charging threshold value. The discharging threshold value is greater than the discharging boundary value, and the charging threshold value is less than the charging boundary value, that is, controlling the SOC operation of the energy storage system to be less than the charging boundary value and greater than the discharging boundary value to avoid the loss of the network-forming ability of the energy storage system caused by the energy storage converter turning to standby according to the BMS instruction when the SOC operation of the energy storage system reaches the boundary. Description of the Drawings

[0048] Figure 1 is the topology diagram of the network-forming microgrid system;

[0049] Figure 2 is the flowchart of the energy management method of the network-forming energy storage system;

[0050] Figure 3 is the topology diagram of the network-forming AC microgrid system;

[0051] Figure 4 is the topology diagram of the network-forming DC microgrid system. Detailed Embodiments

[0052] To solve the problems in the background art, an energy management method for a network-forming energy storage system of the present invention controls the SOC operation of the energy storage system to the boundary for a period of time and controls the SOC operation of the energy storage system within the boundary for a period of time, and timely calibrates the SOC offset to avoid the loss of the network-forming ability of the network-forming energy storage system.

[0053] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0054] Embodiment 1 of an energy management method for a network-forming energy storage system:

[0055] An energy management method for a network-forming energy storage system includes the following steps:

[0056] The energy storage system that triggers the SOC offset warning during the optimal maintenance period is charged at the charging power of the system during this period. Under the constraints of the allowed charging current or allowed charging power, it is charged until the SOC is calibrated to 100%, realizing the calibration of the SOC. After the calibration is completed, the SOC operation of the system is restricted to not be lower than its discharge boundary value and not exceed its charging boundary value, controlling the SOC operation of the energy storage system to the boundary to avoid the SOC offset phenomenon of the battery under the condition of long-term non-full charge and non-empty discharge, and further avoiding the loss of the grid-forming ability of the energy storage system.

[0057] It also restricts the SOC operation of the energy storage system that does not trigger the SOC offset warning during the optimal maintenance period to be greater than its discharge threshold value and less than its charging threshold value. The discharge threshold value is greater than the discharge boundary value, and the charging threshold value is less than the charging boundary value, that is, controlling the SOC operation of the energy storage system to be less than the charging boundary value and greater than the discharge boundary value, so as to avoid the loss of the grid-forming ability of the energy storage system caused by the SOC operation of the energy storage system reaching the boundary and the energy storage converter turning to standby according to the BMS instruction.

[0058] Among them, to reduce the impact of the calibration of the SOC under the charging condition on the grid, the period when the load in the grid-forming grid is greater than zero and the power consumption of the grid-forming grid system is the smallest during the maintenance time is used as the optimal maintenance period, and the maintenance time is obtained according to the rated capacity of the energy storage system and the current charging power of the system.

[0059] Among them, the charging boundary value and the discharge boundary value can be set according to experience or requirements; the discharge threshold value and the charging threshold value can be set according to experience or requirements.

[0060] Specifically, the condition for triggering the SOC offset warning is that the charging warning value of the single battery voltage of the energy storage system is less than or equal to the charging threshold value. Of course, the condition for triggering the SOC offset warning can also be set according to experience.

[0061] Among them, the charging warning value can be set according to experience or requirements.

[0062] Specifically, the calculation formula for the charging warning value is as follows:

[0063]

[0064] The calculation formula for the charging threshold value is as follows:

[0065] A U-i-charge-threshold =(SOC max -k×(1-SOC max ))×100%

[0066] In the formula, A U-i-charge is the charging warning value of the single battery voltage of the i-th energy storage system, A U-i-charge-thresholdis the charging warning threshold value of the i-th energy storage system as the charging threshold value, U i-SOC is the available voltage of the single cell of the i-th energy storage system, U i-max is the highest voltage of the current single cell of the i-th energy storage system, U i-j is the voltage of the j-th single cell of the i-th energy storage system, m is the total number of single cells in the i-th energy storage system, i ∈ [1, n], SOC max is the charging boundary value of the i-th energy storage system, k = 1 indicates triggering the SOC offset warning, k = 0 indicates not triggering the SOC offset warning, and the i-th energy storage system is used as an energy storage system.

[0067] Specifically, the calculation formula for the discharge threshold value is as follows:

[0068] A U-i-discharge-threshold =(SOC min +j×SOC min )×100%

[0069] In the formula, A U-i-discharge-threshold is the discharge warning threshold value of the i-th energy storage system as the discharge threshold value, SOC min is the discharge boundary value of the i-th energy storage system, j = 1 indicates triggering the SOC offset warning, j = 0 indicates not triggering the SOC offset warning.

[0070] Specifically, the calculation formulas for the discharge boundary value and the charging boundary value are as follows:

[0071]

[0072] In the formula, SOC min is the discharge boundary value of the i-th energy storage system, SOC max is the charging boundary value of the i-th energy storage system, W BESS-j is the rated capacity of the i-th energy storage system, j is the j-th energy storage system in the i-th energy storage system, i ∈ [1, n], P load-max is the maximum load power required for the energy storage system to support grid connection, t load is the maximum load operation time, P power-max is the total power generation of the energy storage system.

[0073] As another implementation, an energy management method for a grid-connected energy storage system includes the following steps:

[0074] The energy storage system that triggers the SOC offset warning during the optimal maintenance period is charged at the charging power of the system during this period. Under the constraints of the allowed charging current or the allowed charging power, it is charged until the SOC is calibrated to 100%, achieving the calibration of the SOC. After the calibration is completed, the SOC operation of the system is restricted to be not lower than its discharge boundary value and not exceed its charging boundary value, controlling the SOC operation of the energy storage system to the boundary to avoid the occurrence of SOC offset phenomena when the battery is not fully charged and not fully discharged for a long time, and further avoiding the loss of grid-forming ability of the energy storage system;

[0075] It also restricts the SOC operation of the energy storage system that triggers the SOC offset warning outside the optimal maintenance period to be greater than its discharge threshold value and less than its charging threshold value. The discharge threshold value is greater than the discharge boundary value, and the charging threshold value is less than the charging boundary value, that is, controlling the SOC operation of the energy storage system to be less than the charging boundary value and greater than the discharge boundary value to avoid the loss of grid-forming ability of the energy storage system caused by the energy storage converter turning to standby according to the BMS instruction when the SOC operation of the energy storage system reaches the boundary;

[0076] It also restricts the SOC operation of the energy storage system that does not trigger the SOC offset warning to be not lower than its discharge boundary value and not exceed its charging boundary value.

[0077] Among them, to reduce the impact of the calibration of the SOC under the charging condition on the network, the period when the network load in the grid-forming network is greater than zero and the power consumption of the system in the grid-forming network is the smallest during the maintenance time is used as the optimal maintenance period, and the maintenance time is obtained according to the rated capacity of the energy storage system and the current charging power of the system.

[0078] Among them, the condition for triggering the SOC offset warning is that the charging warning value of the single-cell voltage of the energy storage system is less than or equal to the charging threshold value.

[0079] Embodiment 2 of an energy management method for a grid-forming energy storage system:

[0080] An energy management method for a grid-forming energy storage system includes the following steps:

[0081] The energy storage system that triggers the SOC offset warning during the optimal maintenance period discharges at the discharge power of the system during this period. Under the constraints of the allowed discharge current or the allowed discharge power, it discharges until the SOC is calibrated to 0%, achieving the calibration of the SOC. After the calibration is completed, the SOC operation of the system is restricted to be not lower than its discharge boundary value and not exceed its charging boundary value, controlling the SOC operation of the energy storage system to the boundary to avoid the occurrence of SOC offset phenomena when the battery is not fully charged and not fully discharged for a long time, and further avoiding the loss of grid-forming ability of the energy storage system;

[0082] It also restricts the SOC operation of the energy storage system that does not trigger the SOC offset warning during the optimal maintenance period to be greater than its discharge threshold value and less than its charge threshold value. The discharge threshold value is greater than the discharge boundary value, and the charge threshold value is less than the charge boundary value. That is, it controls the SOC operation of the energy storage system to be less than the charge boundary value and greater than the discharge boundary value to avoid the SOC of the energy storage system running to the boundary, which may cause the energy storage converter to switch to standby according to the BMS instruction and result in the loss of grid-forming ability of the energy storage system.

[0083] Among them, to reduce the impact of SOC calibration under the discharge condition on the grid, the period when the in-grid load of the grid-forming is zero and the power consumption of the in-grid system is the smallest during the maintenance time is used as the optimal maintenance period. The maintenance time is obtained based on the rated capacity of the energy storage system and its current discharge power.

[0084] Among them, the charge boundary value and the discharge boundary value can be set according to experience or requirements; the discharge threshold value and the charge threshold value can be set according to experience or requirements.

[0085] Specifically, the condition for triggering the SOC offset warning is that the discharge warning value of the single battery voltage of the energy storage system is greater than or equal to the discharge threshold value.

[0086] Among them, the discharge warning value can be set according to experience or requirements.

[0087] Specifically, the calculation formula for the discharge warning value is as follows:

[0088]

[0089] The calculation formula for the discharge threshold value is as follows:

[0090] A U-i-discharge-threshold =(SOC min +j×SOC min )×100%

[0091] In the formula, A U-i-discharge is the discharge warning value of the single battery voltage of the i-th energy storage system, A U-i-discharge-threshold is the discharge warning threshold value of the i-th energy storage system as the discharge threshold value, U i-SOC is the available voltage of the single battery of the i-th energy storage system, U i-min is the lowest voltage of the current single battery of the i-th energy storage system, U i-j is the voltage of the j-th single battery of the i-th energy storage system, m is the total number of single batteries in the i-th energy storage system, i∈[1,n], SOC min is the discharge boundary value of the i-th energy storage system, j = 1 indicates triggering the SOC offset warning, j = 0 indicates not triggering the SOC offset warning, and the i-th energy storage system is used as the energy storage system.

[0092] Specifically, the calculation formula for the charging threshold value is as follows:

[0093] A U-i-charge-threshold = (SOC max - k × (1 - SOC max )) × 100%

[0094] In the formula, A U-i-charge-threshold is the charging threshold warning value of the i-th energy storage system serving as the charging threshold value, SOC max is the charging boundary value of the i-th energy storage system, k = 1 indicates triggering the SOC offset warning, and k = 0 indicates not triggering the SOC offset warning.

[0095] Specifically, the calculation formulas for the discharge boundary value and the charging boundary value are as follows:

[0096]

[0097] In the formula, SOC min is the discharge boundary value of the i-th energy storage system, SOC max is the charging boundary value of the i-th energy storage system, W BESS-j is the rated capacity of the i-th energy storage system, j is the j-th energy storage system among the i energy storage systems, i ∈ [1, n], P load-max is the maximum load power required for the energy storage system to support grid formation, t load is the maximum load operation time, P power-max is the total power generation of the energy storage system.

[0098] As another implementation method, an energy management method for a grid-forming energy storage system includes the following steps:

[0099] The energy storage system that triggers the SOC offset warning during the optimal maintenance period discharges at the discharge power of the system during this period. Under the constraint of the allowable discharge current or allowable discharge power, it discharges until the SOC is calibrated to 0%, achieving the calibration of the SOC; after the calibration is completed, the SOC operation of the system is restricted not to be lower than its discharge boundary value and not to exceed its charging boundary value, controlling the SOC operation of the energy storage system to the boundary to avoid the SOC offset phenomenon when the battery is not fully charged and not fully discharged for a long time, and further avoiding the loss of the grid-forming ability of the energy storage system;

[0100] It also restricts the SOC operation of the energy storage system that does not trigger the SOC offset warning during the optimal maintenance period to be greater than its discharge threshold value and less than its charging threshold value. The discharge threshold value is greater than the discharge boundary value, and the charging threshold value is less than the charging boundary value, that is, controlling the SOC operation of the energy storage system to be less than the charging boundary value and greater than the discharge boundary value to avoid the loss of the grid-forming ability of the energy storage system caused by the SOC operation of the energy storage system reaching the boundary and the energy storage converter turning to standby according to the BMS instruction;

[0101] It also restricts the SOC operation of the energy storage system that has not triggered the SOC offset warning to be not lower than its discharge boundary value and not exceed its charge boundary value.

[0102] Among them, to reduce the impact of SOC calibration under the discharge condition on the grid, the period when the load in the grid-forming grid is zero and the power consumption of the system in the grid-forming grid is the minimum during the maintenance time is used as the optimal maintenance period, and the maintenance time is obtained according to the rated capacity of the energy storage system and the current discharge power of the system.

[0103] Among them, the condition for triggering the SOC offset warning is that the discharge warning value of the single-cell voltage of the energy storage system is greater than or equal to the discharge threshold value.

[0104] Embodiment 3 of an energy management method for a grid-forming energy storage system:

[0105] An energy management method for a grid-forming energy storage system includes an energy management method under the charging condition and an energy management method under the discharging condition. The energy management method under the charging condition has been described in detail in Embodiment 1 of an energy management method for a grid-forming energy storage system, and will not be elaborated here; the energy management method under the discharging condition has been described in detail in Embodiment 2 of an energy management method for a grid-forming energy storage system, and will not be elaborated here.

[0106] Specifically, an energy management method for a grid-forming energy storage system performs energy management functions and state of charge accuracy warnings according to the constraints of the BMS battery single-cell voltage, SOC, and allowable charge and discharge current / power. When a warning is generated, the operating state information of the equipment in the grid-forming grid is screened to determine the optimal maintenance period for battery SOC correction. When not maintained, it switches to the energy management in the warning state, and after the maintenance is completed, it switches to the normal energy management state, solving the problem that the energy storage system loses its grid-forming ability due to the operation of the energy storage system to the boundary and SOC offset.

[0107] Specifically, as Figure 2 shown, normal energy management is performed on the energy storage system that has not triggered the state of charge accuracy warning (also known as SOC offset warning or SOC accuracy deviation warning), state of charge correction is performed on the energy storage system that has triggered the state of charge accuracy warning and is in the optimal maintenance period, and normal energy management is performed after the correction is completed. Warning state energy management is performed on the energy storage system that has triggered the state of charge accuracy warning but is not in the optimal maintenance period.

[0108] Among them, the method for the state of charge accuracy warning is as follows:

[0109] The number of energy storage system devices in the grid-forming grid is n, where n ≥ 1.

[0110] Assume that the number of single cells of the battery of the i-th energy storage system device is m i , m i≥1, perform state-of-charge accuracy early warnings on n energy storage system devices respectively. Taking the i-th energy storage system device as an example, the following steps are specifically executed:

[0111] Step 1: Calculate the charge and discharge early warning values of the battery cell voltage. Assume that the voltage of the j-th battery cell of the i-th device is U i-j .

[0112] Then the charge early warning value A of the i-th battery cell voltage U-i-charge , and the charge early warning value is calculated based on the maximum value of the cell voltage and the difference between the average battery voltage. The calculation formula is as follows:

[0113]

[0114] Then the discharge early warning value A of the i-th battery cell voltage U-i-discharge , and the discharge early warning value is calculated based on the average value of the battery voltage and the minimum value of the cell voltage. The calculation formula is as follows:

[0115]

[0116] The definitions of each variable in the formula are as follows:

[0117] U i-SOC : The available voltage of the battery cell, that is, the voltage difference corresponding to the battery cell at SOC100% and SOC0%;

[0118] U i-max : The current highest voltage of the battery cell;

[0119] U i-min : The current lowest voltage of the battery cell.

[0120] Step 2: Calculate the boundary values for the normal energy management operation of the i-th energy storage system. Assume that the rated capacity of the i-th energy storage device in the system is W BESS-i , the maximum load power required for grid connection support in the system is P load-max , the maximum load operation time is t load , the total power generation is P power-max , the maximum discharge time is t power-max , then the charging power range of the in-grid devices is [0, P power-max , the reserved charging power is [0, P power-max × t load , the discharge power range is [0, P load-max , and the reserved discharge power is [0, P power-max × t load .

[0121] The charging boundary value SOC of the i-th device max is calculated as follows:

[0122]

[0123] The SOC of the discharge boundary value of the i-th unit min The calculation is as follows:

[0124]

[0125] The energy storage system operates within this range to ensure the ability to form a grid at all times.

[0126] Step 3: Calculate the charge and discharge warning threshold values of the i-th unit.

[0127] The charge warning threshold value A of the i-th unit U-i-charge-threshold The calculation is as follows:

[0128] A U-i-charge-threshold =(SOC max -ΔSOC charge )×100%

[0129] The discharge warning threshold value A of the i-th unit U-i-discharge-threshold The calculation is as follows:

[0130] A U-i-discharge-threshold =(SOC min +ΔSOC discharge )×100%

[0131] In the formula, ΔSOC charge and ΔSOC discharge are the charge and discharge warning threshold hysteresis control values, which prevent the warning value from reaching the charge and discharge boundary values described in Step 2 during the operation of the energy storage system, resulting in charge prohibition / discharge prohibition and the energy storage system losing the ability to form a grid.

[0132] Among them:

[0133] ΔSOC charge =k×(1 - SOC max )

[0134] ΔSOC discharge =j×SOC min

[0135] In the formula, k = 1 indicates that a warning is triggered. When k takes the value of 1, it means that the system still has the ability to meet 100% of the energy demand of the charging equipment to form a grid when the warning occurs. k = 0 indicates that no warning is triggered; j = 1 indicates that a warning is triggered. When j takes the value of 1, it means that the system still has the ability to meet 100% of the energy demand of the discharging equipment to form a grid when the warning occurs. j = 0 indicates that no warning is triggered.

[0136] Step 4: Compare the charge and discharge warning values of the battery cell voltage with the threshold values to generate warning alerts.

[0137] When A U-i-charge ≤ A U-i-charge-threshold , an SOC accuracy deviation warning (SOC offset warning) is generated;

[0138] Or when A U-i-discharge ≥ A U-i-discharge-threshold , an SOC accuracy deviation warning is generated.

[0139] Among them, the method for determining the optimal maintenance period is as follows:

[0140] Assume that t (in hours) corresponds to the time of the day, t ∈ [0, 23], and every D days is used as a maintenance cycle. Determine the maintenance time t BESS-check-i of the i-th energy storage system, and the calculation method is as follows:

[0141]

[0142] In the formula, P BESS-check-i is the charge / discharge power when the i-th energy storage system corrects the SOC during the maintenance period, and it is divided into two working conditions according to the load and distributed generation in the grid-connected network.

[0143] Working condition 1:

[0144] When the load in the grid-connected network is greater than zero, select the SOC correction method with the energy storage system fully charged. Calculate the minimum power consumption W BESS-check-i of the equipment in the grid-connected network during the continuous t bus-charge-min period every day within the D-day cycle, as follows:

[0145]

[0146] In the formula, P(t) is the net power, which is the difference between the distributed generation power and the load power. Select the period corresponding to the minimum value of W bus-charge-min as the maintenance period of the D + 1 cycle.

[0147] Working condition 2:

[0148] When the load in the grid-connected network is zero, that is, there are only distributed generation equipment and energy storage system equipment in the grid-connected network, select the SOC correction method with the energy storage system emptied. Calculate the minimum discharge power consumption W BESS-check-i of the equipment in the grid-connected network during the continuous t bus-charge-min period every day within the D-day cycle, as follows:

[0149]

[0150] In the formula, P(t) is the power of the distributed generation equipment. Select the period corresponding to the minimum value of W bus-charge-min as the maintenance period of the D + 1-day cycle.

[0151] Among them, the method for correcting the battery SOC is as follows:

[0152] According to the determined optimal maintenance period, perform the following steps for SOC calibration.

[0153] Step 1:

[0154] Assume that there are x energy storage systems triggering warnings within a cycle, x ∈ [0, n]. The energy storage system that triggers the warning first performs SOC correction.

[0155] Under Condition 1, for the energy storage device that needs to be corrected, within the optimal maintenance period, charge at a power of P BESS-check-i Under the constraint of the allowed charging current / power, charge until charging is prohibited, complete the SOC calibration to 100%, and then switch to the normal energy management state.

[0156] Under Condition 2, within the optimal maintenance period, for the energy storage device that needs to be corrected, discharge at a power of P BESS-check-i Under the constraint of the allowed discharge current / power, discharge until it is emptied and the SOC is calibrated to 0%, and then switch to the normal energy management state.

[0157] Step 2:

[0158] In the next optimal maintenance period, perform SOC correction on the second energy storage system that triggers the warning, using the same method as in the previous step until the SOC correction of the xth energy storage system warning is completed.

[0159] Among them, the energy management method in the warning state is: if the ith energy storage system triggers a warning but has not entered the SOC correction operation (SOC calibration operation) during the maintenance period, switch to the energy management in the warning state, that is, limit the SOC operating range to (A U-i-discharge-threshold , A U-i-charge-threshold ).

[0160] Among them, the energy management method in the non-warning state is: limit the SOC operating range to [SOC min , SOC max .

[0161] The network-forming microgrid system to which the above energy management strategy of the network-forming energy storage system is applied, as Figure 3 shown, includes energy storage system equipment, load equipment, and distributed generation equipment connected in parallel to the AC bus, or as Figure 4 shown, includes energy storage system equipment, load equipment, and distributed generation equipment connected in parallel to the DC bus.

[0162] The energy management method of the network-forming energy storage system of the present invention is applied to such as Figure 1The shown network-forming microgrid system, which includes a common AC / DC bus, an energy storage converter, a battery, a load, and distributed generation equipment.

[0163] An embodiment of an energy management system for a network-forming energy storage system:

[0164] An energy management system for a network-forming energy storage system, including a processor that executes a computer program to implement the steps of an energy management method for a network-forming energy storage system. Among them, the energy management method for a network-forming energy storage system has been described in detail in Embodiment 1 of the energy management method for a network-forming energy storage system, Embodiment 2 of the energy management method for a network-forming energy storage system, and Embodiment 3 of the energy management method for a network-forming energy storage system, and will not be elaborated here.

Claims

1. An energy management method for a grid-type energy storage system, characterized in that: The steps include: The energy storage system that triggers the SOC deviation warning during the optimal maintenance period is charged with the charging power of the system during the period, and is charged until the SOC is calibrated to 100% under the constraints of the allowed charging current or allowed charging power, and then the SOC of the system is restricted to operate not less than its discharge boundary value and not more than its charging boundary value; The SOC of the energy storage system that does not trigger the SOC deviation warning within the optimal maintenance period is restricted to be greater than its discharge threshold value and less than its charge threshold value, the discharge threshold value is greater than the discharge boundary value, and the charge threshold value is less than the charge boundary value; The time period when the load in the network is greater than zero and the power consumption of the system in the network is the minimum during the maintenance time is taken as the optimal maintenance period. The maintenance time is obtained according to the rated capacity of the energy storage system and the current charging power of the system.

2. The energy management method of the grid-type energy storage system according to claim 1, characterized in that: The condition for triggering the SOC deviation warning is that the charging warning value of the single battery voltage of the energy storage system is less than or equal to the charging threshold value.

3. The energy management method of the grid-type energy storage system according to claim 2, characterized in that: The calculation formulas for the charging warning value and the charging threshold value are as follows: A U-i-charge-threshold =(SOC max -k×(1-SOC max ))×100% In the formula, A U-i-charge is the charging warning value of the single battery voltage of the i-th energy storage system, A U-i-charge-threshold is the charging warning threshold value of the i-th energy storage system as the charging threshold value, U i-SOC is the available voltage of the single battery of the i-th energy storage system, U i-max is the highest voltage of the current single battery in the i-th energy storage system, U i-j is the voltage of the jth battery in the i-th energy storage system, m is the total number of batteries in the i-th energy storage system, i∈[1,n], SOC max is the charging boundary value of the i-th energy storage system, k=1 indicates that the SOC deviation warning is triggered, k=0 indicates that the SOC deviation warning is not triggered, and the i-th energy storage system is used as the energy storage system.

4. The energy management method of the grid-type energy storage system according to claim 3, characterized in that: The discharge threshold value is the discharge warning threshold value A of the i-th energy storage system. U-i-discharge-threshold , and its calculation formula is as follows: A U-i-discharge-threshold =(SOC min +j×SOC min )×100% In the formula, SOC min is the discharge boundary value of the i-th energy storage system, j=1 indicates that the SOC deviation warning is triggered, and j=0 indicates that the SOC deviation warning is not triggered.

5. The energy management method of a grid-type energy storage system according to any one of claims 1 to 4, characterized in that: The calculation formulas for the discharge boundary value and the charge boundary value are as follows: In the formula, SOC min is the discharge boundary value of the i-th energy storage system, SOC max is the charging boundary value of the i-th energy storage system, W BESS-j is the rated capacity of the i-th energy storage system, j is the j-th energy storage system among the i-th energy storage system, i∈[1,n], P load-max is the maximum load power that the energy storage system requires the grid to support, t load is the maximum load operation time, P power-max is the total power generation of the energy storage system.

6. The energy management method of a grid-type energy storage system according to any one of claims 1 to 4, characterized in that: The following steps are also included: The SOC of the energy storage system that has not triggered the SOC deviation warning is restricted to run not lower than its discharge boundary value and not higher than its charge boundary value.

7. An energy management method for a grid-type energy storage system, characterized in that: The steps include: The energy storage system that triggers the SOC deviation warning during the optimal maintenance period discharges at the discharge power of the system during the period, and discharges until the SOC is calibrated to 0% under the constraints of the allowed discharge current or allowed discharge power, and then limits the SOC operation of the system to not be lower than its discharge boundary value and not exceed its charge boundary value; The SOC of the energy storage system that does not trigger the SOC deviation warning within the optimal maintenance period is restricted to be greater than its discharge threshold value and less than its charge threshold value, the discharge threshold value is greater than the discharge boundary value, and the charge threshold value is less than the charge boundary value; The optimal maintenance period is the time period when the load in the network is zero and the power consumption of the system in the network is the minimum during the maintenance time. The maintenance time is obtained according to the rated capacity of the energy storage system and the current discharge power of the system.

8. The energy management method of the grid-type energy storage system according to claim 7, characterized in that: The condition for triggering the SOC deviation warning is that the discharge warning value of the single battery voltage of the energy storage system is greater than or equal to the discharge threshold value.

9. The energy management method of the grid-type energy storage system according to claim 8, characterized in that: The calculation formulas for the discharge warning value and the discharge threshold value are as follows: A U-i-discharge-threshold =(SOC min +j×SOC min )×100% In the formula, A U-i-discharge is the discharge warning value of the single battery voltage of the i-th energy storage system, A U-i-discharge-threshold is the discharge warning threshold value of the i-th energy storage system as the discharge threshold value, U i-SOC is the available voltage of the single battery of the i-th energy storage system, U i-min is the lowest voltage of the current single battery of the i-th energy storage system, U i-j is the voltage of the jth battery in the i-th energy storage system, m is the total number of batteries in the i-th energy storage system, i∈[1,n], SOC min is the discharge boundary value of the i-th energy storage system, j=1 indicates that the SOC deviation warning is triggered, j=0 indicates that the SOC deviation warning is not triggered, and the i-th energy storage system is used as the energy storage system.

10. The energy management method of the grid-type energy storage system according to claim 9, characterized in that: The charging threshold value is the charging threshold warning value A of the i-th energy storage system. U-i-charge-threshold , and its calculation formula is as follows: A U-i-charge-threshold =(SOC max -k×(1-SOC max ))×100% In the formula, SOC max is the charging boundary value of the i-th energy storage system, k=1 indicates that the SOC deviation warning is triggered, and k=0 indicates that the SOC deviation warning is not triggered.

11. The energy management method of a grid-type energy storage system according to any one of claims 7 to 10, characterized in that: The calculation formulas for the discharge boundary value and the charge boundary value are as follows: In the formula, SOC min is the discharge boundary value of the i-th energy storage system, SOC max is the charging boundary value of the i-th energy storage system, W BESS-j is the rated capacity of the i-th energy storage system, j is the j-th energy storage system among the i-th energy storage system, i∈[1,n], P load-max is the maximum load power that the energy storage system requires the grid to support, t load is the maximum load operation time, P power-max is the total power generation of the energy storage system.

12. The energy management method of a grid-type energy storage system according to any one of claims 7 to 10, characterized in that: The following steps are also included: The SOC of the energy storage system that has not triggered the SOC deviation warning is restricted to run not lower than its discharge boundary value and not higher than its charge boundary value.

13. An energy management system for a grid-type energy storage system, comprising a processor, characterized in that: The processor executes a computer program to implement the steps of the energy management method for a grid-type energy storage system as described in any one of claims 1 to 12.

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