A Method for a Battery Energy Storage to Participate in the Frequency Regulation Control of a Power System

Abstract

The present invention discloses a method for a battery energy storage to participate in power system frequency modulation control, belonging to the field of power technology. The method includes the following steps: (1) representing different operating states of the energy storage under two consecutive operating periods in the form of 2-bit quaternary coding; (2) dynamically clustering the energy storage according to the 2-bit quaternary coding and performing aggregation calculation of the energy storage frequency modulation coefficient; (3) calculating the energy storage regulation demand considering the constraints of frequency deviation and the lowest limit of frequency dip based on different load fluctuation levels; (4) based on the energy storage clustering information, taking the switching mode with the least impact on the energy storage state change as the target, determining the action order set of the energy storage cluster, and updating the new state of charge of the energy storage; (5) updating the 2-bit quaternary coding of the energy storage, and performing new dynamic clustering of the energy storage according to the updated 2-bit quaternary coding to realize the ability of the energy storage to participate in power system frequency modulation control in continuous periods.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power, and particularly relates to a method for a battery energy storage to participate in power system frequency modulation control. Background Art

[0002] The proportion of clean energy in China is gradually increasing. Among them, clean energy represented by wind energy and solar energy is gradually replacing traditional fossil energy, and China's power system will show the characteristics of gradual penetration of a high proportion of renewable energy. However, the randomness and volatility of clean energy power generation will lead to increased power fluctuations on the power supply side. At the same time, in a low-inertia power system with a high proportion of power electronic devices added, when the power load fluctuates, the rate of change of the power grid frequency and the frequency deviation increase significantly, posing a huge challenge to power system frequency modulation. Therefore, a new frequency modulation method needs to be introduced to solve the frequency modulation problem of traditional frequency modulation units. The battery energy storage system has a fast response speed and high control accuracy, and can effectively participate in the fast frequency modulation of the power system.

[0003] However, at the same time, limited by its capacity limit, cycle life, and operation state control method, the battery energy storage may have situations such as overcharging, over-discharging, and insufficient power when participating in power system frequency modulation. Therefore, a certain control method is needed to control the energy storage. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention proposes a method for a battery energy storage to participate in power system frequency modulation control.

[0005] The object of the present invention can be achieved by the following technical solutions:

[0006] A method for a battery energy storage to participate in power system frequency modulation control includes the following steps:

[0007] Step 1: Represent different operating states of the energy storage in two consecutive operating periods in the form of a 2-bit quaternary code;

[0008] Step 2: Dynamically group the energy storage according to the code; calculate the frequency modulation coefficient of each energy storage and perform an aggregation calculation to obtain the frequency modulation coefficient of the dynamically grouped energy storage;

[0009] Step 3: Obtain the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop, and calculate the energy storage regulation demand considering the frequency deviation limit constraint and the energy storage regulation demand considering the lowest point limit of frequency drop respectively;

[0010] Step 4: Compare the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop with the frequency modulation coefficient of the dynamically grouped energy storage, and take the switching method with the least impact on the energy storage state change as the goal to determine the action order set of the energy storage cluster and update the new state of charge of the energy storage;

[0011] Step 5: Update the 2-bit quaternary code of the energy storage, and perform new dynamic grouping on the energy storage according to the updated 2-bit quaternary code, so as to realize the energy storage participating in the frequency regulation control of the power system in continuous time periods.

[0012] Optionally, in the 2-bit quaternary code, the lower bit represents the current operating state of the energy storage, and the upper bit represents the operating state of the energy storage in the previous time period;

[0013] The 2-bit quaternary code divides the energy storage into four operating states, namely: discharging, floating charge, static, and charging.

[0014] According to the proposed 2-bit quaternary battery energy storage continuous state representation method, the composition of the 2-bit quaternary code for the continuous operation period of the energy storage is as follows:

[0015]

[0016]

[0017] Optionally, the calculation method of the energy storage frequency regulation coefficient for each energy storage is:

[0018]

[0019]

[0020] Among them, K B-Ch is the energy storage frequency regulation coefficient during charging, S is the state of charge of the energy storage, S high is the larger value of the state of charge of the energy storage, S max is the maximum value of the state of charge of the energy storage, n is the curve adaptation coefficient, and its value range is [1, 20]; K B-Disch is K during discharging B , S low is the smaller value of the state of charge of the energy storage, S min is the minimum value of the state of charge of the energy storage.

[0021] Optionally, the calculation method of the energy storage regulation demand considering the frequency deviation limit constraint is:

[0022]

[0023] Among them, Δf| t→∞ is the frequency deviation, ΔP S is the load fluctuation, D is the load active frequency response coefficient, K m is the adjustable frequency regulation capacity coefficient of the system synchronous unit, 1 / R is the governor gain, K B is the energy storage frequency regulation coefficient, R B is the energy storage droop coefficient.

[0024] Optionally, the method for calculating the energy storage regulation demand considering the lowest limit constraint of frequency drop is as follows:

[0025]

[0026] where Δf m (t) is the lowest point of frequency drop, ΔP S is the load fluctuation, T R is the equivalent inertia time constant of the turbine, D is the active power frequency response coefficient of the load, K B is the energy storage frequency modulation coefficient, R B is the energy storage droop coefficient, K m is the adjustable frequency modulation capacity coefficient of the system synchronous unit, 1 / R is the governor gain;

[0027] a, b, a 0 are respectively:

[0028]

[0029] where ξ is the damping ratio, ω n is the natural frequency:

[0030]

[0031] where D is the active power frequency response coefficient of the load, M is the inertia time constant of the generator rotor, T R is the equivalent inertia time constant of the turbine, K m is the adjustable frequency modulation capacity coefficient of the system synchronous unit, 1 / R is the governor gain, K B is the energy storage frequency modulation coefficient, R B is the energy storage droop coefficient, F H is the turbine characteristic coefficient.

[0032] Optionally, the method for obtaining the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest limit of frequency drop includes the following steps:

[0033] (31) Set the frequency deviation limit to 0.2 Hz and the lowest limit of the frequency deviation to 0.5 Hz;

[0034] (32) Calculate the energy storage frequency modulation coefficient K B1 according to the frequency deviation formula;

[0035] (33) Perform curve fitting according to the lowest point calculation formula of frequency drop and calculate the energy storage frequency modulation coefficient K B2 ;

[0036] (34) Based on the two calculations, obtain the energy storage frequency modulation coefficient K B-need = max(KB1 , K B2 );

[0037] Performing curve fitting according to the calculation formula of the lowest point of frequency drop, the obtained fitting formula is:

[0038] K B = 9.0462×10 -6 ×ΔP s 3 - 2.8882×10 -4 ×ΔP s 2 + 0.0239×ΔP s - 0.1022.

[0039] Optionally, step 4 includes the following steps:

[0040] (41) Judging the target state of the current energy storage demand, i.e., discharging or charging;

[0041] (42) Switching the energy storage operation state according to the principle of minimizing the difference between the target state code and the current operation state code;

[0042] (43) Comparing the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop with the energy storage frequency modulation coefficient of dynamic clustering to judge the energy storage switching power and action order;

[0043] (44) According to the load fluctuation and the energy storage action order, evenly distribute the required energy storage energy to each dynamic cluster of actions, and update the state of charge of the energy storage.

[0044] Optionally, the formula for obtaining the required energy storage energy according to the load fluctuation is:

[0045]

[0046] where E e is the required energy storage energy, ΔP s is the load fluctuation, T R is the equivalent inertia time constant of the turbine, T B is the energy storage frequency modulation inertia time constant, K B is the energy storage frequency modulation coefficient, R B is the energy storage droop coefficient, M is the generator rotor inertia time constant, t a is the energy storage operation time, t 0 is the time when the load starts to fluctuate.

[0047] a, b, a 0 are respectively:

[0048]

[0049] where ξ is the damping ratio and ω n is the natural frequency:

[0050]

[0051] where D is the active frequency response coefficient of the load, M is the inertia time constant of the generator rotor, and T R is the equivalent inertia time constant of the turbine, and K m is the adjustable frequency regulation capacity coefficient of the system synchronous units, 1 / R is the governor gain, and K B is the frequency regulation coefficient of the energy storage, and R B is the droop coefficient of the energy storage, and F H is the characteristic coefficient of the turbine.

[0052] Optionally, the new dynamic grouping of the energy storage according to the updated 2-bit quaternary code specifically includes the following steps:

[0053] Update the operating state of the energy storage in the previous time period, and modify the current operating state of the operating energy storage to the target state according to the new energy storage action order. The state of the non-operating energy storage is static or floating charge state, so as to perform new dynamic grouping. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The present invention will be further described below with reference to the accompanying drawings.

[0055] Figure 1 is the flowchart of the method for controlling the frequency regulation of the power system by the battery energy storage participating in the present invention;

[0056] Figure 2 is the initial grouping situation of the battery energy storage system in Embodiment 1 of the present invention;

[0057] Figure 3 is the frequency change situation of the power system after the grouping action of the energy storage system in Embodiment 1 of the present invention;

[0058] Figure 4 is the initial grouping situation of the battery energy storage system in Embodiment 2 of the present invention;

[0059] Figure 5 is the frequency change situation of the power system after the grouping action of the energy storage system in Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0061] Example 1

[0062] This example discloses a method for a battery energy storage to participate in power system frequency modulation control, as Figure 1 , the method includes the following steps:

[0063] Step 1: Represent different operating states of the energy storage in two consecutive operating periods in the form of 2-bit quaternary encoding.

[0064] Among them, first set the basic information of the energy storage, including: energy storage frequency modulation coefficient, energy storage capacity, state of charge of the energy storage, current operating state of the energy storage and operating state of the energy storage in the previous period (2-bit quaternary encoding). For the 2-bit quaternary encoding used, the lower bit represents the current operating state of the energy storage, and the higher bit represents the operating state of the energy storage in the previous period; for the same time period, the 2-bit quaternary encoding divides the energy storage into four operating states, namely: discharging, floating charge, stationary, and charging. The states are mapped using quaternary encoding as: 0 - discharging, 1 - floating charge, 2 - stationary, 3 - charging.

[0065] Step 2: Dynamically group the energy storage according to the 2-bit quaternary encoding and perform aggregation calculation of the energy storage frequency modulation coefficient.

[0066] Among them, each time the energy storage is dynamically grouped according to the 2-bit quaternary encoding, and if the encoding is the same, the grouping is the same; based on the own attributes of each energy storage, its energy storage frequency modulation coefficient K B is obtained. At the same time, the energy storage frequency modulation coefficients of each group are superimposed and aggregated to obtain K B-plus , for comparison with the energy storage regulation demand calculated later.

[0067] Among them, the energy storage frequency modulation coefficient K of each energy storage B The calculation formula is:

[0068]

[0069]

[0070] Among them, K B-Ch is the K during charging B , S is the state of charge of the energy storage, S high is the larger value of the state of charge of the energy storage, S max is the maximum value of the state of charge of the energy storage, n is the curve adaptation coefficient, and its value range is [1, 20];

[0071] K B-Disch is the K during discharging B , S low is the smaller value of the state of charge of the energy storage, S min is the minimum value of the state of charge of the energy storage.

[0072] Step 3: Based on different load fluctuation levels, calculate the energy storage regulation demand considering the constraints of frequency deviation and the limit value of the lowest point of frequency drop.

[0073] Among them, the frequency deviation limit is set to 0.2 Hz, and the limit value of the lowest point of frequency deviation is set to 0.5 Hz; calculate the energy storage frequency modulation coefficient K according to the frequency deviation formula B1 ; perform curve fitting according to the calculation formula of the lowest point of frequency drop, and calculate the energy storage frequency modulation coefficient K B2 ; based on the two calculations, obtain the energy storage frequency modulation coefficient K that simultaneously satisfies the frequency deviation and the limit value of the lowest point of frequency drop B-need = max(K B1 , K B2 ).

[0074] Among them, the formula for calculating the energy storage regulation demand considering the constraint of frequency deviation limit based on different load fluctuation levels is:

[0075]

[0076] Among them, Δf| t→∞ is the frequency deviation, ΔP S is the load fluctuation, D is the load active frequency response coefficient, K m is the adjustable frequency modulation capacity coefficient of the system synchronous unit, 1 / R is the governor gain, K B is the energy storage frequency modulation coefficient, R B is the energy storage droop coefficient.

[0077] Among them, the formula for calculating the energy storage regulation demand considering the constraint of the lowest point limit of frequency drop based on different load fluctuation levels is:

[0078]

[0079] Among them, Δf m (t) is the lowest point of frequency drop, ΔP S is the load fluctuation, T R is the equivalent inertia time constant of the turbine, D is the load active frequency response coefficient, K B is the energy storage frequency modulation coefficient, R B is the energy storage droop coefficient, K m is the adjustable frequency modulation capacity coefficient of the system synchronous unit, 1 / R is the governor gain.

[0080] a, b, a 0 are respectively:

[0081]

[0082] Among them, ξ is the damping ratio, ω nis the natural frequency, and the formula is:

[0083]

[0084] where D is the active frequency response coefficient of the load, M is the inertia time constant of the generator rotor, T R is the equivalent inertia time constant of the turbine, K m is the adjustable frequency regulation capacity coefficient of the system synchronous units, 1 / R is the governor gain, K B is the frequency regulation coefficient of the energy storage, R B is the droop coefficient of the energy storage, F H is the characteristic coefficient of the turbine.

[0085] Among them, the fitting formula for calculating the frequency regulation coefficient of the energy storage according to the lowest point of the frequency drop is:

[0086] K B = 9.0462×10 -6 ×ΔP s 3 - 2.8882×10 -4 ×ΔP s 2 + 0.0239×ΔP s - 0.1022

[0087] Step 4: Based on the energy storage clustering information, aiming at the switching method with the least impact on the energy storage state change, determine the action order set of the energy storage cluster, and update the new state of charge of the energy storage.

[0088] First, judge the target state of the current energy storage demand, that is, discharging or charging; then, according to the principle of minimizing the difference between the target state code and the current operating state code, switch the operating state of the energy storage. That is, the clusters with a code difference of 0 give priority to participating in frequency regulation, and at this time, the energy storage clusters are consistent with the target state. When the required energy storage power is insufficient, then sequentially correct the operating states of the energy storage devices in the clusters with a code difference of 1, a code difference of 2, and a code difference of 3; compare the calculated frequency regulation coefficient K B-need of the energy storage with the frequency regulation coefficient K B-plus of the dynamically clustered energy storage to judge the switching power and action order of the energy storage; according to the load fluctuation and the action order of the energy storage, evenly distribute the required energy storage energy to each group that takes action, and update the state of charge of the energy storage.

[0089] Among them, the formula for obtaining the required energy storage energy according to the load fluctuation is:

[0090]

[0091] where E e is the required energy storage energy, ΔP s is the load fluctuation, T Ris the equivalent inertia time constant of the turbine, T B is the inertia time constant of the energy storage frequency regulation, K B is the energy storage frequency regulation coefficient, R B is the droop coefficient of the energy storage, M is the inertia time constant of the generator rotor, t a is the operation time of the energy storage, t 0 is the time when the load starts to fluctuate.

[0092] Step 5: Update the 2-bit quaternary code of the energy storage, and perform new dynamic grouping on the energy storage according to the updated 2-bit quaternary code to realize the ability of the energy storage to participate in the frequency regulation control of the power system in continuous time periods.

[0093] Update the operation state of the energy storage in the previous time period, and modify the current operation state of the operating energy storage to the target state according to the new action order of the energy storage. The state of the non-operating energy storage is stationary or floating charge state, so as to perform new dynamic grouping.

[0094] In this example, the total system power is 100 kW, the load fluctuation is 10 kW, the load fluctuates at 1 s, and the operating energy storage participates in frequency regulation until 200 s. The relevant parameter settings are as follows:

[0095] D = 1, K m = 0.95, R = 0.05, R B = 0.01, M = 6.7, T R = 8, F H = 0.3, T B = 0.01.

[0096] In the calculation of the relationship between the energy storage frequency regulation coefficient and the state of charge, K B takes 0.05 and n takes 20.

[0097] The total capacity of a single energy storage is set to: 0.5 kWh. The basic information of the remaining energy storage includes: energy storage frequency regulation coefficient, existing capacity of the energy storage, state of charge of the energy storage, current operation state of the energy storage and operation state of the energy storage in the previous time period (2-bit quaternary code), as shown in Table 1.

[0098] In this example, the previous operation state of all energy storage is set to the stationary state, the current operation states of energy storage 1, 2, and 3 are discharging, the current operation states of energy storage 4, 5, and 6 are floating charge, the current operation states of energy storage 7 and 8 are stationary, and the current operation states of energy storage 9 and 10 are charging.

[0099] Table 1 Initial basic information of energy storage in Example 1

[0100]

[0101]

[0102] Dynamically group energy storage according to 2-bit quaternary coding and aggregate the energy storage frequency modulation coefficients. The dynamic grouping is as follows Figure 2 .

[0103] The aggregation of the energy storage frequency modulation coefficients is as follows:

[0104] (1) Discharge energy storage frequency modulation coefficient: K B-plus1 = 0.15;

[0105] (2) Float charge energy storage frequency modulation coefficient: K B-plus2 = 0.15;

[0106] (3) Static energy storage frequency modulation coefficient: K B-plus3 = 0.1;

[0107] (4) Charge energy storage frequency modulation coefficient: K B-plus4 = 0.1.

[0108] Calculate the energy storage regulation demand under different load fluctuations based on the frequency deviation and the limit of the lowest point of frequency drop. Calculate the energy storage frequency modulation coefficient K B1 = 0.3 according to the frequency deviation formula; perform curve fitting according to the formula for calculating the lowest point of frequency drop, and calculate the energy storage frequency modulation coefficient K B2 = 0.1168; take the maximum value K B-need = max(K B1 , K B2 ) = 0.3.

[0109] Based on the energy storage grouping information, with the goal of the switching method that has the least impact on the energy storage state change, since energy storage discharge is required at this time, the energy storage action order should be switched according to the difference, and the order should be discharge, float charge, static, and charge in sequence.

[0110] Since K B-need = K B-plus1 + K B-plus2 , the discharge energy storage should be actuated first, and then the float charge energy storage.

[0111] Determine the energy storage cluster action order set as: Cluster 1 and Cluster 2 act; Cluster 3 and Cluster 4 are static.

[0112] The curve of the system frequency change after the energy storage action is as Figure 3 ;

[0113] Update the energy storage state of charge and the 2-bit quaternary coding, perform new dynamic grouping on the energy storage, and realize the ability of the energy storage to participate in the frequency modulation control of the power system for continuous time periods. The new energy storage information is shown in Table 2:

[0114] Table 2 Energy storage updated information in Example 1

[0115]

[0116]

[0117] Among them, the states of energy storages 1, 2, and 3 at the previous moment were discharging, the states of energy storages 4, 5, and 6 at the previous moment were floating charge, the states of energy storages 7 and 8 at the previous moment were static, and the states of energy storages 9 and 10 at the previous moment were charging. At the current moment, energy storages 1, 2, 3, 4, 5, and 6 participate in discharging, and 7, 8, 9, and 10 are static.

[0118] Embodiment 2

[0119] In this example, the total system power is 100 kW, the load fluctuation is -8 kW, the load fluctuates at 1 s, and the operating energy storages participate in frequency modulation for 200 s. The relevant parameter settings are as follows:

[0120] D = 1, K m = 0.95, R = 0.05, R B = 0.01, M = 6.7, T R = 8, F H = 0.3, T B = 0.01.

[0121] In the calculation of the relationship between the energy storage frequency modulation coefficient and the state of charge, K B takes 0.05 and n takes 20.

[0122] The total capacity of a single energy storage is set to: 0.5 kWh. The basic information of the remaining energy storages includes: energy storage frequency modulation coefficient, energy storage capacity, energy storage state of charge, current operating state of the energy storage, and operating state of the energy storage in the previous time period (2-bit quaternary code), as set in Table 3.

[0123] In this example, the previous operating state of all energy storages is taken as the static state, the current operating states of energy storages 1 and 2 are discharging, the current operating states of energy storages 3, 4, 5, 6, and 7 are floating charge, the current operating state of energy storage 8 is static, and the current operating states of energy storages 9 and 10 are charging.

[0124] Table 3 Initial basic information of energy storage in Embodiment 2

[0125]

[0126] According to the 2-bit quaternary code, the energy storages are dynamically grouped and the energy storage frequency modulation coefficients are aggregated. The dynamic grouping is as Figure 4 .

[0127] Aggregation of energy storage frequency modulation coefficients:

[0128] (1) Discharging energy storage frequency modulation coefficient: K B-plus1 = 0.1;

[0129] (2) Floating charge energy storage frequency modulation coefficient: K B-plus2= 0;

[0130] (3) Static energy storage frequency modulation coefficient: K B-plus3 = 0.05;

[0131] (4) Charging energy storage frequency modulation coefficient: K B-plus4 = 0.1.

[0132] Calculate the energy storage regulation demand under different load fluctuations based on the frequency deviation and the limit value of the lowest point of frequency drop. Calculate the energy storage frequency modulation coefficient K according to the frequency deviation formula B1 = 0.2; Perform curve fitting according to the calculation formula of the lowest point of frequency drop, and calculate the energy storage frequency modulation coefficient K B2 = 0.075; Take the maximum value K B-need = max(K B1 , K B2 ) = 0.2.

[0133] Based on the energy storage grouping information, with the goal of minimizing the impact of energy storage state changes, since energy storage charging is required at this time, the energy storage action order should be switched according to the difference, and the order should be charging, static, and discharging in sequence.

[0134] Since K B-need > K B-plus3 + K B-plus4 , and K B-need < K B-plus1 + K B-plus3 + K B-plus4 . Therefore, the charging energy storage should be actuated first, then the static energy storage, and finally the discharging energy storage.

[0135] Determine the energy storage cluster action order set as: Clusters 1, 3, and 4 act; Cluster 2 is static.

[0136] The system frequency change curve after energy storage action is as Figure 5 ;

[0137] Update the energy storage state of charge and the 2-bit quaternary coding, perform new dynamic grouping of the energy storage, and realize the ability of the energy storage to participate in the frequency modulation control of the power system for continuous time periods. The new energy storage information is shown in Table 4.

[0138] Table 4 Basic Information of Energy Storage in Embodiment 2

[0139]

[0140] Among them, the states of energy storages 1 and 2 at the previous moment were discharging, the states of energy storages 3, 4, 5, 6, and 7 at the previous moment were floating charge, the state of energy storage 7 at the previous moment was static, and the states of energy storages 8, 9, and 10 at the previous moment were charging. At the current moment, energy storages 1, 2, 8, 9, and 10 participate in discharging, and 3, 4, 5, 6, and 7 maintain floating charge.

[0141] In summary, through state encoding, energy storage can participate in the frequency modulation control of the power system more directly and effectively.

[0142] This method is not limited to the above two cases of positive and negative fluctuations of the load, nor is it limited to these two system parameters. The same technical effects can still be achieved under other load fluctuations and system parameters.

[0143] In the description of this specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0144] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the description in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A method for a battery energy storage to participate in power system frequency modulation control, characterized in that, it includes the following steps: Step 1: Represent different operating states of the energy storage in two consecutive operating periods in the form of 2-bit quaternary coding; Step 2: Dynamically group the energy storage according to the coding; calculate the frequency modulation coefficient of each energy storage and perform aggregation calculation to obtain the frequency modulation coefficient of the dynamically grouped energy storage; Step 3: Obtain the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop, and calculate the energy storage regulation demand considering the frequency deviation limit constraint and the energy storage regulation demand considering the lowest point limit of frequency drop respectively; Step 4: Compare the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop with the frequency modulation coefficient of the dynamically grouped energy storage, and take the switching method with the least impact on the energy storage state change as the goal to determine the action order set of the energy storage cluster and update the new state of charge of the energy storage; Step 5: Update the 2-bit quaternary coding of the energy storage, and perform new dynamic grouping on the energy storage according to the updated 2-bit quaternary coding to realize the continuous-time energy storage participating in power system frequency modulation control; The calculation method of the energy storage regulation demand considering the frequency deviation limit constraint is: Among them, Δf| t→∞ is the frequency deviation, ΔP S is the load fluctuation, D is the active power frequency response coefficient of the load, K m is the adjustable frequency modulation capacity coefficient of the system synchronous unit, 1 / R is the governor gain, K B is the energy storage frequency modulation coefficient, R B is the energy storage droop coefficient; The calculation method of the energy storage regulation demand considering the lowest point limit of frequency drop constraint is: Among them, Δf m (t) is the lowest point of frequency drop, ΔP S is the load fluctuation, T R is the equivalent inertia time constant of the turbine, D is the active power frequency response coefficient of the load, K B is the frequency regulation coefficient of the energy storage, R B is the droop coefficient of the energy storage, K m is the adjustable frequency regulation capacity coefficient of the system synchronous units, 1 / R is the governor gain; a, b, a 0 are respectively: where ξ is the damping ratio and ω n is the natural frequency: Among them, D is the load active frequency response coefficient, M is the generator rotor inertia time constant, T R is the equivalent inertia time constant of the turbine, K m is the adjustable frequency regulation capacity coefficient of the system synchronous units, 1 / R is the governor gain, K B is the energy storage frequency regulation coefficient, R B is the energy storage droop coefficient, F H is the turbine characteristic coefficient; The method for obtaining the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop includes the following steps: (31) Set the frequency deviation limit to 0.2Hz and the lowest point limit of frequency deviation to 0.5Hz; (32) Calculate the energy storage frequency modulation coefficient K according to the frequency deviation formula B1 ; (33) Perform curve fitting according to the calculation formula of the lowest point of frequency drop, and calculate the energy storage frequency modulation coefficient K B2 ; (34) Obtain the energy storage frequency modulation coefficient K that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop based on two calculations B-need = max(K B1 , K B2 ); Perform curve fitting according to the lowest point formula of frequency drop, and the obtained fitting formula is: K B = 9.0462×10 -6 ×ΔP s 3 - 2.8882×10 -4 ×ΔP s 2 + 0.0239×ΔP s - 0.1022; Step 4 includes the following steps: (41) Judge the target state of the current energy storage demand, that is, discharge or charge; (42) Switch the operating state of the energy storage according to the principle of minimizing the difference between the target state coding and the current operating state coding; (43) Compare the energy storage frequency modulation coefficient that simultaneously satisfies the frequency deviation and the lowest point limit of frequency drop with the frequency modulation coefficient of the dynamically grouped energy storage to judge the switching power and action order of the energy storage; (44) According to the load fluctuation and the action order of the energy storage, evenly distribute the required energy storage energy to each dynamically grouped action, and update the state of charge of the energy storage.

2. The method for a battery energy storage to participate in power system frequency modulation control according to claim 1, characterized in that, In the 2-bit quaternary coding, the lower bit represents the current operating state of the energy storage, and the higher bit represents the operating state of the energy storage in the previous period; The 2-bit quaternary coding divides the energy storage into four operating states, namely: discharge, floating charge, static and charge.

3. The method for a battery energy storage to participate in power system frequency modulation control according to claim 1, characterized in that, The calculation method of the frequency modulation coefficient of each energy storage is: Among them, K B-Ch is the energy storage frequency modulation coefficient during charging, S is the state of charge of the energy storage, S high is the larger value of the state of charge of the energy storage, S max is the maximum value of the state of charge of the energy storage, n is the curve adaptation coefficient, and its value range is [1, 20]; K B-Disch is K during discharging B , S low is the smaller value of the state of charge of the energy storage, S min is the minimum value of the state of charge of the energy storage.

4. The method for a battery energy storage to participate in power system frequency modulation control according to claim 1, characterized in that, The formula for obtaining the required energy storage energy according to the load fluctuation is: Among them, E e is the energy required for energy storage, ΔP s is the load fluctuation, T R is the equivalent inertia time constant of the turbine, T B is the inertia time constant of the energy storage for frequency regulation, K B is the frequency regulation coefficient of the energy storage, R B is the droop coefficient of the energy storage, M is the inertia time constant of the generator rotor, t a is the operation time of the energy storage, t 0 is the time when the load starts to fluctuate; a, b, a 0 are respectively: where ξ is the damping ratio and ω n is the natural frequency: Among them, D is the load active frequency response coefficient, M is the generator rotor inertia time constant, T R is the equivalent inertia time constant of the turbine, K m is the adjustable frequency regulation capacity coefficient of the system synchronous units, 1 / R is the governor gain, K B is the energy storage frequency regulation coefficient, R B is the energy storage droop coefficient, F H is the turbine characteristic coefficient.

5. The method for a battery energy storage to participate in power system frequency modulation control according to claim 1, characterized in that, The new dynamic grouping of the energy storage according to the updated 2-bit quaternary coding specifically includes the following steps: Update the operating status of the previous time period of the energy storage, and modify the current operating status of the actuating energy storage to the target status according to the new energy storage action order. The status of the non-actuating energy storage is the stationary or floating charge status, so as to perform a new dynamic grouping.

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