A low-frequency load reduction method for multi-layer deep inertia control of electrochemical energy storage

Abstract

The present invention discloses a low-frequency load shedding method of electrochemical energy storage multi-layer deep inertia control, taking into account the influence of electrochemical energy storage on the implementation effect of low-frequency load shedding, thereby obtaining an improved low-frequency load shedding scheme, solving the grid equivalent inertia considering the energy storage depth-synchronous machine inertia response, calculating the actual power shortage according to the frequency change rate at the disturbance moment, and balancing part of the power shortage by using energy storage virtual droop control and grid load regulation effect, and then removing the remaining shortage in batches by an adaptive low-frequency load shedding strategy, which can more accurately reflect the new frequency response characteristics of the new power system, significantly reduce the load removal amount, and improve the power supply reliability.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical energy storage frequency control, and in particular to a low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control. Background Art

[0002] When a system unit fails or the load suddenly increases, a power shortage occurs and the system frequency decreases. Especially when a large disturbance occurs in the system, the frequency regulation function alone cannot suppress the continuous decrease in frequency. In severe cases, it may cause system collapse and large-scale power outages. Low-frequency load shedding is an important means to maintain stable operation of the power system, especially in the face of severe power shortages or other emergencies. It can quickly reduce the load of the power system and achieve the purpose of maintaining the safety of the power grid frequency.

[0003] In recent years, electrochemical energy storage technology has made significant progress in the planning of new energy sites. Energy storage with fast response speed and flexible control has received widespread attention and is very suitable for assisting grid frequency regulation. With the application of electrochemical energy storage technology in frequency regulation control, it has received high attention from both inside and outside the industry.

[0004] Data shows that the traditional low-frequency load-reduction scheme does not take into account the characteristics and impact of electrochemical energy storage. With the access of high-penetration new energy to the power grid, the frequency characteristics of the power grid have become more complex, and the adaptability of the original low-frequency load-reduction scheme remains to be discussed. Therefore, the research on the adjustment of low-frequency load-reduction schemes considering electrochemical energy storage has become an urgent problem that needs to be solved.

[0005] Chinese patent document CN115800291A discloses an "electrochemical energy storage converter voltage regulation system and control method". The electrochemical energy storage converter voltage regulation system includes a measurement module, a battery cabinet SOC equivalent calculation module, an energy storage reactive power calculation module, a voltage regulation mode judgment module and a power distribution module, etc. The control method includes: after voltage fluctuation occurs, when the reactive power compensation demand of the power system is less than the current maximum reactive power of the energy storage, an equal margin allocation strategy based on the maximum reactive power is adopted; when the reactive power compensation demand of the power system is greater than the current maximum reactive power of the energy storage, a load reduction and voltage regulation strategy considering the equivalent SOC is adopted; the load reduction and voltage regulation strategy considering the equivalent SOC is: calculating the equivalent SOC value of each battery cabinet and determining the PCS load reduction priority, adjusting the active power and reactive power instructions of each PCS controller based on the energy storage load reduction method, and maximizing the reactive power of the energy storage system. The above technical scheme is difficult to accurately reflect the frequency response characteristics of the power system. Summary of the invention

[0006] The present invention mainly solves the technical problem that the original technical solution is difficult to accurately reflect the frequency response characteristics of the power system, and provides a low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control, solves the equivalent inertia of the power grid considering the energy storage depth-synchronous machine inertia response, calculates the actual power shortage according to the frequency change rate at the moment of disturbance, and uses energy storage virtual droop control and power grid load regulation effect to balance part of the power shortage, and then uses an adaptive low-frequency load reduction strategy to cut off the remaining shortage in batches, which can more accurately reflect the new frequency response characteristics of the new power system, significantly reduce the load cutting amount, and improve the power supply reliability.

[0007] The above technical problems of the present invention are mainly solved by the following technical solutions: The present invention comprises the following steps: S1 applies a virtual inertia control strategy to the energy storage system, and balances part of the power shortage by utilizing the virtual droop control of the energy storage and the load regulation effect of the power grid;

[0008] S2 calculates the active power increment of the primary frequency regulation of the energy storage system;

[0009] S3 calculates the active power deficit of the power system and makes a load reduction plan based on the initial active power deficit;

[0010] S4 determines the priority of load shedding through site selection and capacity determination indicators;

[0011] S5 dynamically optimizes the load reduction in rounds according to the load reduction plan.

[0012] Preferably, the step S1 of applying the virtual inertia control strategy includes considering different energy storage depths and using H ∑ Characterize the equivalent inertial response of the power system with virtual inertial control.

[0013] Preferably, the load reduction plan in step S3 specifically includes that the basic round is divided into four rounds during the load reduction process, and four rounds of action thresholds that decrease evenly are set respectively; according to the actual power grid load reduction method, the original load reduction amount of each round is set to 30%, 25%, 25%, and 20% of the power shortage respectively; in addition, a special round is set, whose action return frequency is greater than the action threshold of the first round of load reduction, and the action delay is set.

[0014] Preferably, in the step S1, according to the definition of the inertia time constant, the virtual inertia expression of energy storage can be obtained as follows:

[0015]

[0016] Among them, S BESS is the rated capacity of energy storage, T1 and T2 are filter time constants, K df is the differential inertia controller gain, u N is the rated voltage of the battery, ωN is the grid frequency differential signal, u d is the d-axis reference current.

[0017] As a preferred option, when an energy storage system contains p energy storage units with the same parameters, which are equivalent to one unit, the virtual inertia time constant H of the aggregated energy storage system is eqE (t) is:

[0018]

[0019] Among them, E Ei (i=1, 2, . . . n) represents the power provided by the i-th energy storage unit.

[0020] As a preference, the power plants in the system are divided into three categories: conventional units, wind farms, and energy storage systems with virtual inertia control, and the number of stations is a, b, and c respectively; then the equivalent inertia time constant H of step 1 is ∑ The expression is:

[0021]

[0022] In the formula, E wfi , E CONj Respectively represent the kinetic energy of wind turbines and traditional turbines, S CONj , S wfi , S EK The rated capacity of traditional units, wind turbines and energy storage;

[0023] If the wind turbine does not participate in the frequency regulation of the power system, the kinetic energy provided by the wind turbine is zero, that is, Then the system equivalent inertia time constant is:

[0024]

[0025] As the penetration rate of new energy increases, the frequency response capability of the system gradually decreases, so variables representing wind power penetration rate and energy storage depth need to be introduced into the system frequency response model. Assuming that wind power and energy storage replace thermal power units in the same proportion, the penetration rate of wind power in the power grid is α, and the depth of energy storage is β, then the equivalent inertia time constant of the system is

[0026]

[0027] Preferably, the step S2 uses a weighted equivalent aggregation method to obtain the active increment of the primary frequency modulation of the energy storage system according to the primary frequency modulation transfer function model of the energy storage system, and the primary frequency modulation transfer function model is used to solve the power increment ΔP provided by the primary frequency modulation response of the energy storage system. mE (s):

[0028]

[0029] Where, T B Represents the battery energy storage time constant; K E Represents the droop control coefficient of energy storage.

[0030] Preferably, the expression of the active power shortage of the power system in step S3 is:

[0031]

[0032] In the formula, H ∑ '(t) is the system equivalent inertia time constant, and dΔf / dt is the system frequency change rate at the disturbance time t1.

[0033] Preferably, the step S4 determines the removal order according to the importance of the load, and the comprehensive index of the importance of the load is:

[0034]

[0035] In the formula, α i is the load frequency characteristic weight of the ith node, β i is the importance weight of load node i, K L is the load frequency adjustment coefficient.

[0036] Preferably, in the process of executing the load reduction plan, the step S5 uses the virtual inertia response of the energy storage to update the calculated value of the power shortage in real time:

[0037]

[0038] Among them, H Σi '(t) is the time-varying equivalent inertia time constant, Δf i is the frequency change rate before and after the i-th round of load shedding, ΔP mE,i- , ΔP mT,i- are respectively the energy storage before the i-th round of load shedding and the primary frequency regulation active increment of the synchronous unit, ΔP d,i-1 is the power deficit before correction.

[0039] The beneficial effects of the present invention are as follows: the equivalent inertia of the power grid considering the energy storage depth-synchronous machine inertia response is solved, the actual power shortage is calculated according to the frequency change rate at the disturbance moment, and part of the power shortage is balanced by using the energy storage virtual droop control and the power grid load regulation effect, and the remaining shortage is removed in batches by the adaptive low-frequency load reduction strategy, which can more accurately reflect the new frequency response characteristics of the new power system, significantly reduce the load removal amount, and improve the power supply reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of the present invention.

[0041] Figure 2 It is a system principle diagram of an embodiment 1 of the present invention.

[0042] Figure 3 It is a comparison diagram of the dynamic changes of the system frequency during the load reduction process of an embodiment 1 of the present invention.

[0043] Figure 4 It is a comparison diagram of the dynamic changes of the system frequency during the load reduction process of an embodiment 2 of the present invention.

[0044] Figure 5 This is a system principle diagram of embodiment 3 of the present invention.

[0045] Figure 6 It is a comparison diagram of the dynamic changes of the system frequency during the load reduction process of Example 3 of the present invention. DETAILED DESCRIPTION

[0046] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the technical solutions of the present application are further described in detail below through embodiments and in combination with the accompanying drawings. It should be understood that the specific implementation method described here is only an optimal embodiment of the present application, which is only used to explain the present application and does not limit the protection scope of the present application. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] Data shows that the traditional low-frequency load-reduction scheme does not take into account the characteristics and impact of electrochemical energy storage. With the access of high-penetration new energy to the power grid, the frequency characteristics of the power grid have become more complex, and the adaptability of the original low-frequency load-reduction scheme remains to be discussed. Therefore, the research on the adjustment of low-frequency load-reduction schemes considering electrochemical energy storage has become an urgent problem that needs to be solved.

[0048] In view of the above-mentioned defects of the prior art of low-frequency load shedding schemes, the present invention provides a low-frequency load shedding scheme that takes into account electrochemical energy storage multi-layer deep inertia control-frequency modulation, which can more accurately calculate the power shortage of the new power system and update the shortage value to more accurately operate each round of low-frequency load shedding, and the frequency recovery dynamic process is closer to the actual situation.

[0049] Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the operations (or steps) as sequential processes, many of the operations (or steps) therein can be implemented in parallel, concurrently, or simultaneously. In addition, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but can also have additional steps not included in the drawings; the process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0050] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0051] Embodiment: A low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control in this embodiment, such as Figure 1 As shown, the following steps are included:

[0052] Step 1: Apply a virtual inertia control strategy to the energy storage system, considering different energy storage depths and using H ∑ Characterize the equivalent inertial response of the power system with virtual inertial control;

[0053] According to the definition of inertia time constant, the virtual inertia expression of energy storage can be obtained as:

[0054]

[0055] Among them, S BESS is the rated capacity of energy storage, T1 and T2 are filter time constants, K df is the differential inertia controller gain, u N is the rated voltage of the battery, ω N is the grid frequency differential signal, u d is the d-axis reference current.

[0056] When an energy storage system contains p energy storage units with the same parameters, they can be equivalent to a unit. Then the virtual inertia time constant HeqE(t) of the aggregated energy storage system is:

[0057]

[0058] Where: E Ei (i=1, 2, . . . n) represents the power provided by the i-th energy storage unit.

[0059] The power plants in the system are divided into three categories: conventional units, wind farms, and energy storage systems with virtual inertia control, and the number of stations is a, b, and c respectively; then the equivalent inertia time constant H of step 1 is ∑ The expression is:

[0060]

[0061] In the formula, Ewfi and ECONj represent the kinetic energy of wind turbines and traditional turbines respectively, and SCONj, Swfi, and SEK are the rated capacities of traditional turbines, wind turbines, and energy storage. Since wind turbines do not participate in the frequency regulation of the power system, the kinetic energy provided by wind turbines is zero, that is, Then the system equivalent inertia time constant is:

[0062]

[0063] As the penetration rate of new energy increases, the frequency response capability of the system gradually decreases, so variables representing wind power penetration rate and energy storage depth need to be introduced into the system frequency response model. Assuming that wind power and energy storage replace thermal power units in the same proportion, the penetration rate of wind power in the power grid is α, and the depth of energy storage is β, then the equivalent inertia time constant of the system is

[0064]

[0065] Step 2: Calculate the actual active power deficit of the power system. The expression of the active power deficit of the power system is:

[0066]

[0067] In the formula, H ∑ '(t) is the system equivalent inertia time constant, and dΔf / dt is the system frequency change rate at the disturbance time t1.

[0068] Step 3: According to the primary frequency modulation transfer function model of the energy storage system, the weighted equivalent aggregation method is used to obtain the active power increment of the primary frequency modulation of the energy storage system. The primary frequency modulation transfer function model is used to solve the power increment ΔPmE(s) provided by the primary frequency modulation response of the energy storage system:

[0069]

[0070] Where TB represents the battery energy storage time constant; KE represents the droop control coefficient of energy storage.

[0071] Step 4: Make a load reduction plan based on the initial active power shortage of the power system. The load reduction plan is as follows: the basic round is divided into 4 rounds during the load reduction process, and its action threshold is set to: 49.2Hz, 49.0Hz, 48.8Hz, 48.6Hz. According to the actual grid load reduction method, the original load reduction of each round is set to 30%, 25%, 25%, and 20% of the power shortage in turn; in addition, a special round is set, and its action return frequency is set to 49.6Hz, and the action delay is 15s.

[0072] Step 5: Determine the priority of load shedding through site selection and capacity determination indicators. The order of shedding is determined according to the importance of the load. According to the Technical Regulations on Automatic Low-Frequency Load Shedding in Power Systems, the comprehensive index of load importance is:

[0073]

[0074] In the formula, α i is the load frequency characteristic weight of the ith node, β i is the importance weight of load node i, K Lis the load frequency adjustment coefficient.

[0075] Step 6: Based on the accurate equivalent inertia time constant of the power system and the active power increment of the primary frequency regulation, dynamically optimize the load reduction round by round. During the execution of the load reduction plan, the calculated value of the power shortage is updated in real time using the virtual inertia response / primary frequency regulation control of the energy storage:

[0076]

[0077] In the above formula, HΣi'(t) is the time-varying equivalent inertia time constant, Δf i is the frequency change rate before and after the i-th round of load shedding, ΔP mE,i- , ΔP mT,i- are respectively the energy storage before the i-th round of load shedding and the primary frequency regulation active increment of the synchronous unit, ΔP d,i-1 is the power deficit before correction.

[0078] Implementation 1:

[0079] The effectiveness of the proposed strategy is verified using a calculation example system built in Matlab / simulink. Figure 2 As shown, in the example system, there are 6 synchronous generator sets G1-G6, 4 wind farms W1-W4 and two energy storage systems E1-E2. Among them, the energy storage systems E1 and E2 are connected in parallel with the wind farms W1 and W4 to the bus 30 and bus 32 respectively. In this example, the energy storage devices can respond to the virtual inertia response process and primary frequency regulation, and the wind turbines do not have the virtual inertia control capability. When the system reaches steady-state operation, the frequency accident of the power shortage of the simulation system is simulated by cutting off the 35-node generator (876MW). The detailed parameters of the example system are shown in Table 1.

[0080] Simulation project: The virtual inertia response of energy storage can effectively improve the frequency change rate of the system when the disturbance occurs, that is, suppress the rate of frequency drop, and further affect the calculation of the system power shortage. Therefore, the following scenario is set to verify the impact of the virtual inertia control of the energy storage system on the load reduction effect.

[0081] At 100s (the system is already stable), the system fault is simulated by cutting off the generators of 35 nodes, and the load shedding results of the following two schemes are compared and analyzed after low-frequency load shedding:

[0082] 1) If the energy storage system in the example adopts virtual inertia control.

[0083] 2) If the energy storage system in the example does not use virtual inertia control.

[0084] The dynamic changes of system frequency in the above two schemes during load shedding are compared as follows: Figure 3The total load reduction and active power shortage are shown in Table 2. Figure 3 It can be seen that after the system has a frequency disturbance, for Scheme 1 with energy storage virtual inertia control applied, it takes 3.65s for the frequency to reach the lowest point, and the frequency steady-state deviation is 49.7781Hz; while for Scheme 2 without energy storage virtual inertia control applied, it takes 3.12s for the frequency to reach the lowest point, and the frequency steady-state deviation is 49.6751Hz. It can be seen that Scheme 1 reaches the lowest frequency point later than Scheme 2, indicating that the energy storage virtual inertia control strategy reduces the system frequency change rate and has a significant improvement on the inertia response of the system.

[0085] Table 1 Parameters of example system I

[0086]

[0087]

[0088] Table 2 Comparison of the impact of energy storage virtual inertia control on low-frequency load reduction results

[0089] Simulation Solution Steady state frequency / Hz Total load reduction / MW Power shortage / WM 1 49.6751 498.36 783 2 49.7781 438.02 689

[0090] It can be seen from the data in Table 2 that after the energy storage system applies virtual inertia control, the calculated power shortage is reduced by 84MW compared with the system without virtual inertia control, and the total load reduction is reduced by 60.34MW. There is a large deviation between the two schemes, which means that when the energy storage system adopts virtual inertia control, it will reduce the system power shortage to a certain extent, which will affect the low-frequency load reduction results of the system. Therefore, it is particularly important to study the low-frequency load reduction scheme that considers the participation of electrochemical energy storage in frequency regulation.

[0091] Implementation Example 2:

[0092] Based on the Matlab / simulink system model established in Example 1, at 100s (the system is already stable), the system fault is simulated by removing 35 node generators, and the load shedding results of the following two schemes are compared and analyzed after low-frequency load shedding:

[0093] 1) If the influence of virtual inertia control of energy storage system is considered during load shedding: Calculate the system's H according to equations (5) and (6) respectively: ∑ '(t), power shortage ΔPd, and load reduction is carried out according to the load reduction process of this scheme.

[0094] 2) If the influence of virtual inertia control of energy storage system is not considered during load shedding: Calculate the system H according to equations (5) and (6): ∑ '(t), power shortage ΔPd, note that H ∑ '(t) does not consider the virtual inertia of the energy storage system, that is, H in formula (5)eqei (t) is 0, so the system's H ∑ '(t) is a constant value, and the load reduction is carried out according to the load reduction process of this scheme.

[0095] Table 3 Comparison of the impact of energy storage virtual inertia on low-frequency load reduction results

[0096] Simulation Solution Steady state frequency / Hz Total load reduction / MW Power shortage / WM 1 49.7781 438.02 689 2 49.6505 484.15 726

[0097] The dynamic changes of system frequency in the above two schemes during load shedding are compared as follows: Figure 4 The total load reduction and active power shortage are shown in Table 3. Figure 4 It can be seen that for Scheme 1, which considers the influence of virtual inertia control of energy storage during load shedding, and Scheme 2, which does not consider the influence of virtual inertia control of energy storage, the time when the frequency reaches the lowest point is about 103.65s, and the frequency change rate of the two schemes is consistent. This is because the energy storage in both schemes adopts virtual inertia control. Combined with Table 3, it can be seen that the power shortage values ​​of Scheme 1 and Scheme 2 are 689MW and 726WM respectively, and the total load reduction of Scheme 1 and Scheme 2 are 438.02WM and 484.15WM respectively. It can be seen that the power shortage and total load reduction of Scheme 1 are lower than those of Scheme 2, and the steady-state frequency in Scheme 1 is 0.1276Hz higher than that of Scheme 2, indicating that the proposed low-frequency load shedding scheme can effectively reduce the load shedding amount and optimize the frequency characteristics under the premise of maintaining frequency stability compared with the traditional low-frequency load shedding scheme. Therefore, it also reflects the advantages of the proposed low-frequency load shedding scheme compared with the traditional low-frequency load shedding scheme.

[0098] Implementation Example 3:

[0099] This example uses Figure 5 In the example system of four machines and two zones built in Matlab / simulink, two zones are connected by two buses. Zone 1 contains a synchronous generator G1, a wind farm and an energy storage system. Zone 2 contains two synchronous generators G2 and G3. Loads L1, C1, L2 and C2 are connected to the interface buses of the two zones respectively. Load L3 is used as a disturbance load. The frequency accident of power shortage of the simulation system is simulated by connecting and removing L3. The detailed parameters of the example system are shown in Table 4.

[0100] Table 4 Parameters of example system II

[0101]

[0102]

[0103] Simulation project: Considering the virtual inertial response of energy storage / primary frequency modulation control, the change curve of system frequency after removing system load under different energy storage depths (0%, 10%, 15%, 20%) is as follows: Figure 6 The specific load reduction is shown in Table 5.

[0104] Table 5 Comparison of low-frequency load reduction results under different energy storage ratios

[0105]

[0106] according to Figure 6 It can be found that: as the proportion of energy storage (0%, 10%, 15%, 20%) increases, the time when the frequency reaches the lowest point is 104.2s, 104.6s, 104.8s, and 104.9s respectively, indicating that as the proportion of energy storage increases, the speed of system frequency decreases. This also verifies that in the power system containing new energy (wind power / energy storage), it is necessary to make full use of the contribution of energy storage to frequency control in order to effectively improve the low-frequency load reduction strategy. And it can be seen from Table 5 that as the proportion of energy storage increases from 0% to 20%, the system power shortage decreases from 783WM to 649WM, and the total load removal amount also decreases from 498.36WM to 402.12WM. At the same time, the system steady-state frequency increases from 49.7885Hz to 49.7923Hz. This shows that as the proportion of energy storage increases, the steady-state frequency of the system also increases, and the load removal amount also decreases accordingly.

[0107] In summary, compared with the traditional low-frequency load reduction scheme, the low-frequency load reduction scheme considering electrochemical energy storage multi-layer deep inertia control-frequency modulation proposed in the present invention can restore the frequency to a higher level with a smaller total load reduction.

[0108] The specific embodiments described herein are merely examples of the spirit of the present invention. The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present application. It should be noted that a technician in the technical field to which the present application belongs may make various modifications or supplements to the described specific embodiments or replace them in a similar manner, but will not deviate from the spirit of the present application or exceed the scope defined in the attached claims. For a person of ordinary skill in the art, multiple variations and improvements may also be made without departing from the concept of the present application. Therefore, the scope of protection of this patent shall be subject to the attached claims.

Claims

1. A low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control, characterized in that: The following steps are involved: S1 applies a virtual inertia control strategy to the energy storage system; considering different energy storage depths and using H ∑ Characterize the equivalent inertial response of the power system with virtual inertial control. According to the definition of inertia time constant, the virtual inertia of energy storage is obtained. When an energy storage system contains p energy storage units with the same parameters, it is equivalent to a unit. Then the virtual inertia time constant H of the aggregated energy storage system is eqE (t) is: Among them, E Ei (i=1,2,...n) represents the power provided by the i-th energy storage unit; S2 calculates the active power increment of the primary frequency regulation of the energy storage system; S3 calculates the active power deficit of the power system and makes a load reduction plan based on the initial active power deficit; S4 determines the priority of load shedding through site selection and capacity determination indicators; S5 dynamically optimizes the load reduction in rounds according to the load reduction plan.

2. A low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1, characterized in that: The step S1 applies a virtual inertia control strategy including considering different energy storage depths and using H ∑ Characterize the equivalent inertial response of the power system with virtual inertial control.

3. The low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1 is characterized in that: The step S1 balances part of the power shortage by using the energy storage virtual droop control and the grid load regulation effect, and then removes the remaining shortage in batches by using the adaptive low-frequency load reduction strategy.

4. The low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1 is characterized in that: The load reduction plan in step S3 specifically includes that the basic round is divided into four rounds during the load reduction process, and four rounds of action thresholds that decrease evenly are set respectively. According to the actual power grid load reduction method, the original load reduction amount of each round is set to 30%, 25%, 25%, and 20% of the power shortage respectively; in addition, a special round is set, whose action return frequency is greater than the action threshold of the first round of load reduction, and the action delay is set.

5. A low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1, 2, 3 or 4, characterized in that: In step S1, according to the definition of inertia time constant, the virtual inertia expression of energy storage can be obtained as follows: Among them, S BESS is the rated capacity of energy storage, T1 and T2 are filter time constants, K df is the differential inertia controller gain, u N is the rated voltage of the battery, ω N is the grid frequency differential signal, u d is the d-axis reference current.

6. A low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1, 2, 3 or 4, characterized in that: The power plants in the system are divided into three categories: conventional units, wind farms, and energy storage systems with virtual inertia control, and the number of stations is a, b, and c respectively; then the equivalent inertia time constant H of step 1 is ∑ The expression is: In the formula, E wfi , E CONj Respectively represent the kinetic energy of wind turbines and traditional turbines, S CONj , S wfi , S EK The rated capacity of traditional units, wind turbines and energy storage; If the wind turbine does not participate in the frequency regulation of the power system, the kinetic energy provided by the wind turbine is zero, that is, Then the system equivalent inertia time constant is: Assuming that wind power and energy storage replace thermal power units in the same proportion, the penetration rate of wind power in the power grid is α, and the depth of energy storage is β, then the equivalent inertia time constant of the system is 7. A low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 6, characterized in that: The step S2 uses a weighted equivalent aggregation method to obtain the active increment of the primary frequency modulation of the energy storage system according to the primary frequency modulation transfer function model of the energy storage system, and the primary frequency modulation transfer function model to solve the power increment ΔP provided by the primary frequency modulation response of the energy storage system. mE (s): Where, T B Represents the battery energy storage time constant; K E Represents the droop control coefficient of energy storage.

8. The low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1 is characterized in that: The expression of the active power shortage of the power system in step S3 is: In the formula, H ∑ '(t) is the system equivalent inertia time constant, and dΔf / dt is the system frequency change rate at the disturbance time t1.

9. The low-frequency load reduction method of electrochemical energy storage multi-layer deep inertia control according to claim 1 is characterized in that: The step S4 determines the removal order according to the importance of the load, and the comprehensive index of the importance of the load is: In the formula, α i is the load frequency characteristic weight of the i-th node, β i is the importance weight of load node i, K Li is the load frequency adjustment coefficient.

10. The low-frequency load reduction method for electrochemical energy storage multi-layer deep inertia control according to claim 1 is characterized in that: In the process of executing the load reduction plan, the step S5 uses the virtual inertia response of the energy storage to update the calculated value of the power shortage in real time: Among them, H Σi '(t) is the time-varying equivalent inertia time constant, Δf i is the frequency change rate before and after the i-th round of load shedding, ΔP mE,i- , ΔP mT,i- are respectively the energy storage before the i-th round of load shedding and the primary frequency regulation active increment of the synchronous unit, ΔP d,i-1 is the power deficit before correction.

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