Calculation method of frequency regulation parameter requirements of power system based on new energy active reserve

Abstract

The present invention discloses a method for calculating the frequency regulation parameter requirements of an electric power system based on the active reserve of new energy, and relates to the technical field of frequency stability control of electric power systems, including determining the frequency support capabilities of various types of synchronous generators in an electric power system; establishing an electric power system frequency response model according to the nonlinear link of the speed regulator; discretizing the electric power system frequency response model based on the forward difference method; establishing an optimization model based on the active reserve of new energy using a multi-objective function optimization method; calling a solver to solve the model, and obtaining the calculation results of the frequency regulation parameter requirements of an electric power system based on the active reserve of new energy. Therefore, the above method can be used to realize the calculation of the relevant frequency regulation parameters of each wind, photovoltaic and storage unit in the power grid, help the system dispatcher and the new energy station to clarify the frequency safety level of the electric power system in real time and guide the adjustment of each frequency regulation parameter of the new energy, ensure the safety of the operation of the electric power system, and improve the economy of the new energy station.

Description

Technical Field

[0001] The present invention relates to the technical field of power system frequency stability control, and in particular to a method for calculating power system frequency regulation parameter requirements based on new energy active reserve. Background Art

[0002] With the large-scale and high-growth development of new energy, the power supply structure of the power system is changing. Although traditional thermal and hydropower still dominate, new energy units are gradually replacing more and more conventional power sources and occupying a more important position in the power grid. The traditional synchronous generator is directly coupled to the power grid. When the power grid encounters interference, the synchronous generator can automatically release the inertial kinetic energy stored in the rotor to compensate for the power imbalance in the system; at the same time, it can also quickly respond to changes in the system frequency through the speed regulator, effectively preventing the continuous drop in the system frequency. However, compared with traditional synchronous generators, new energy power sources and other grid-connected power electronic equipment show the characteristics of no inertia or low inertia when facing dynamic changes in the power grid, which leads to a decrease in the system inertia level and weakens the system's resistance to various types of disturbances. In addition, in order to maximize the power generation, new energy power sources usually operate in maximum power tracking mode. This traditional control mode does not respond to frequency changes in the power grid and therefore cannot provide active support.

[0003] Therefore, in the event of an expected extreme failure, how to coordinate the control of the rotor kinetic energy, active standby and additional energy storage of renewable energy, while considering the role of energy storage in system frequency regulation to improve the system's comprehensive inertia, has become an important issue facing renewable energy in participating in system frequency regulation. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating the frequency regulation parameter requirements of an electric power system based on new energy active standby, which can provide a large amount of energy in a flexible and fast manner in a short period of time when the electric power system is subjected to low-frequency disturbances, thereby slowing down the rate of decrease of the system frequency.

[0005] To achieve the above object, the present invention provides a method for calculating the frequency regulation parameter requirements of a power system based on new energy active reserve, comprising the following steps:

[0006] S1. Determine the frequency support capability of each type of synchronous generator in the power system, and aggregate each synchronous generator of the same type into an equivalent synchronous machine;

[0007] S2. According to the nonlinear link of the speed regulator, a power system frequency response model of the equivalent synchronous machine is established;

[0008] S3. Discrete power system frequency response model based on forward difference method;

[0009] S4. Establish objective function and constraint conditions based on the active power reserve of new energy;

[0010] S5. Call the solver to solve the model and obtain the power system frequency regulation parameter requirements.

[0011] Preferably, in step S1, the types of synchronous generators include reheat units, non-reheat units, and hydro-turbine units.

[0012] Preferably, in step S2, the established power system frequency response model of the equivalent synchronous machine includes the correction of active power in the primary frequency modulation process, which is specifically as follows:

[0013]

[0014] Where Δf db is the primary frequency modulation dead zone, is the active power limit of the primary frequency modulation of the equivalent synchronous machine, P k is the active power adjustment of the equivalent synchronous unit, K is the speed deviation magnification of the equivalent synchronous unit, and Δf is the system frequency deviation.

[0015] Preferably, in step S3, the discretized power system frequency response model is as follows:

[0016] When a low-frequency disturbance occurs in the system, the power generated by the equivalent synchronous unit in response to a frequency modulation is:

[0017]

[0018] Where P k,n is the additional active power of the equivalent synchronous unit at the nth step of the system, P k,n-1 is the additional active power of the equivalent synchronous unit at the n-1th step of the system, b k,n 、a k,n are the active power adjustment of the dead zone of the equivalent synchronous unit and the speed regulator limit at the nth step of the system, a k,n-1 is the active power adjustment of the speed regulator of the equivalent synchronous unit at the n-1th step of the system, Δf db is the primary frequency modulation dead zone, T RH is the reheater time constant of the equivalent synchronous unit, F HP is the power ratio of the high-pressure cylinder of the equivalent synchronous unit, s is the differential operator, Δn is the differential step size, Δf n is the system frequency deviation at the nth differential step.

[0019] in,

[0020]

[0021] P dis,n=P dis,0 -P i,n -P k,n

[0022] Where H is the inertia time constant of the equivalent synchronous machine, f0 is the rated frequency of the system, S b is the system base capacity, P dis,n-1 is the system power deficit for the n-1th differential step, P dis,n is the power deficit of the system at the nth differential step, P dis,0 is the system active power shortage at the moment of disturbance, P i,n is the active power adjustment of renewable energy at the nth differential step of the system, P k,n It is the active power adjustment amount of the system's nth differential step equivalent synchronous machine in response to primary frequency modulation.

[0023] Preferably, in step S4, the objective function includes a primary objective function and a secondary objective function, which are specifically as follows:

[0024] The main objective function is:

[0025]

[0026] In the formula, ΔP t,n , ΔP p,n , ΔP e,n They respectively represent the additional active power of wind turbines, photovoltaics, and energy storage in the system at the nth differential step. a, b, and c respectively represent the weights of the additional active power of wind turbines, photovoltaics, and energy storage in the main objective function after the disturbance occurs.

[0027] The secondary objective function is:

[0028] minF1′=minA(a t H t +a p H p +a e H e )

[0029] minF2′=minB(b t K t +b p K p +b e K e )

[0030] minF3′=minC(c t P mt +c p P mp +c e P me )

[0031] In the formula, H t , H p , H e are the equivalent inertia time constants of wind turbines, photovoltaics and energy storage, respectively, t , K p , K e are the equivalent regulation coefficients of wind turbines, photovoltaics and energy storage, respectively, mt , P mp , P me A, B, C, and a are the reserved power reserves for wind turbines, photovoltaics, and energy storage. t 、a p 、a e 、b t 、b p 、b e 、c t 、c p 、c e are the weight coefficients of the frequency modulation parameters respectively.

[0032] Preferably, the constraints in step S4 include:

[0033] Based on different renewable energy active power reserves, set constraints on the renewable energy power amplitude in the optimization model:

[0034] ΔP i,n ≤R·P iN

[0035] In the formula, R is the ratio of the preset new energy active reserve to the rated power, ΔP i,n is the active power adjustment of the new energy source at the nth differential step, P iN is the rated active power of the new energy.

[0036] Based on the power system frequency stability guidelines, a stability constraint is established for the system frequency change rate after the disturbance:

[0037]

[0038] Where ROCOF extre The maximum frequency change rate that meets the minimum requirement of system frequency stability, Δf n+1 is the system frequency deviation at the n+1th differential step.

[0039] Based on the power system frequency stability guidelines, a stability constraint is established for the lowest point of the system frequency after the disturbance:

[0040] |Δf n |≤Δf extre

[0041] Where Δf extreThe maximum frequency deviation that is set to meet the minimum requirement of system frequency stability.

[0042] Therefore, the present invention adopts the above-mentioned method for calculating the frequency regulation parameter requirements of the power system based on the active standby of new energy, which can realize the calculation of the frequency regulation parameter requirements of the new energy power system for faults, help system dispatching and new energy stations, clarify the frequency safety level of the power system in real time, guide the adjustment of various frequency regulation parameters of new energy, ensure the safety of power system operation, and improve the economy of new energy stations.

[0043] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flow chart of the method for calculating the frequency regulation parameter requirements of the power system based on the active reserve of new energy;

[0045] Figure 2 A schematic diagram of the improved IEEE 39-node system topology used in the embodiment;

[0046] Figure 3 It is a schematic diagram of the calculation results of the total active power and total energy adjustment of new energy in the embodiment;

[0047] Figure 4 This is a schematic diagram of the calculation results of the active power and energy adjustment amount of the fan in the embodiment;

[0048] Figure 5 It is a schematic diagram of the calculation results of photovoltaic active power and energy adjustment amount in the embodiment;

[0049] Figure 6 It is a schematic diagram of the calculation results of the energy storage active power and energy adjustment amount in the embodiment. DETAILED DESCRIPTION

[0050] The present invention can be explained in more detail by the following examples. The purpose of disclosing the present invention is to protect all changes and improvements within the scope of the present invention. The present invention is not limited to the following examples.

[0051] like Figure 1 As shown, the method for calculating the frequency regulation parameter requirements of the power system based on the active reserve of new energy provided by the present invention comprises the following steps:

[0052] S1. Determine the frequency support capacity of each type of synchronous generator in the power system, and count the main parameters of each synchronous generator in the power grid; aggregate the generators of the same type in the power system into equivalent synchronous machines, and based on the characteristics of different types of generators, obtain the parameters of each type of equivalent synchronous unit according to the existing technology, including inertia time constant, reheater time constant, and high-pressure cylinder power ratio.

[0053] S2. Based on the parameters of each type of equivalent synchronous units, a power system frequency response model is established.

[0054] Among them, the types of synchronous generators include reheat units, non-reheat units, and hydro turbine units. Since the types of synchronous generators in my country are mainly reheat units and non-reheat units, this embodiment takes the reheat thermal power unit as an example to establish the power system frequency response model of the equivalent synchronous machine.

[0055] Firstly, the generators in the reheat unit are aggregated into equivalent synchronous units to obtain the parameters of the equivalent synchronous units. Then, based on the obtained parameters of the equivalent synchronous units, the nonlinear link of the speed governor is considered to establish the power system frequency response model, as follows:

[0056] (1) Based on the swing equation, the frequency dynamic response process after the power grid disturbance is described:

[0057]

[0058] Where f0 is the rated frequency of the system; Δf is the system frequency deviation; H is the inertia time constant of the equivalent synchronous machine; D is the damping coefficient of the equivalent synchronous machine; ΔP m is the power change of the speed regulator, that is, the sum of the power adjustment of the speed regulators of all frequency-regulated units; ΔP e is the change in electromagnetic power, which is generally equivalent to the sudden change in load active power; is the time domain differential operator.

[0059] (2) Based on the SFR model, the frequency response dynamics of the equivalent synchronous machine are characterized, and the power is obtained as ΔP L The governor-prime mover model of the equivalent synchronous machine after the disturbance:

[0060]

[0061] In the formula, ΔP L is the power deficit of the initial disturbance, T RH is the reheater time constant of the equivalent synchronous unit, F HP is the power ratio of the high-pressure cylinder of the equivalent synchronous unit, and s is the differential operator.

[0062] Similarly, for other types of synchronous generators, the governor-prime mover model of the equivalent synchronous machine can be obtained by using the existing technology according to the characteristics of the synchronous generator.

[0063] Considering the nonlinear link of the speed regulator, the correction of active power in the primary frequency regulation process of the equivalent synchronous machine is:

[0064]

[0065] Where Δfdb It is the primary frequency dead zone of the speed regulator, generally ±0.033Hz; is the active power limit of the primary frequency modulation of the equivalent synchronous machine; ΔP k is the active power adjustment of the nonlinear constraint of the equivalent synchronous machine speed regulator; K is the speed deviation magnification factor of the equivalent synchronous unit.

[0066] S3. Discretize the power system frequency response model based on the forward difference method, as follows:

[0067] When a low-frequency disturbance occurs in the system, the power deficit of each differential step in the system is:

[0068] P dis,n =P dis,0 -P i,n -P k,n

[0069] Where P dis,n is the power deficit of the system at the nth differential step, P dis,0 is the active power shortage of the system at the moment of disturbance, P i,n is the active power adjustment of renewable energy at the nth differential step of the system, P k,n It is the active power adjustment amount of the equivalent synchronous machine in response to primary frequency modulation at the nth differential step of the system.

[0070] When a low-frequency disturbance occurs in the system, the frequency deviation of the system is:

[0071]

[0072] Where Δf n is the system frequency deviation at the nth differential step, Δn is the differential step, H is the inertia time constant of the equivalent synchronous machine, S b is the system base capacity, P dis,n-1 is the power deficit of the system at the n-1th differential step.

[0073] When a low-frequency disturbance occurs in the system, the power generated by the equivalent synchronous unit in response to a frequency modulation is:

[0074]

[0075] Where P k,n is the additional active power of the equivalent synchronous unit at the nth step of the system, b k,n 、a k,n are the active power adjustment of the equivalent synchronous unit through the dead zone and speed regulator limit at the nth step of the system, P k,n-1 is the additional active power of the equivalent synchronous unit at the n-1th step of the system, a k,n-1is the active power adjustment of the speed regulator of the equivalent synchronous unit at the n-1th step of the system, Δf db It is the primary frequency modulation dead zone.

[0076] S4. Based on the active reserve of new energy, an optimization model of multi-objective functions is established, as follows:

[0077] In order to minimize the energy demand of new energy frequency regulation resources after the disturbance occurs, the virtual inertia of new energy and the additional active power generated by primary frequency regulation are used as the main objective function:

[0078]

[0079] In the formula, ΔP t,n , ΔP p,n , ΔP e,n They respectively represent the additional active power of wind turbines, photovoltaics, and energy storage in the system at the nth differential step. a, b, and c respectively represent the weights of the additional active power of wind turbines, photovoltaics, and energy storage in the main objective function after the disturbance occurs.

[0080] Based on the main objective function, the weighted sum of frequency modulation related parameters such as inertia time constant and droop coefficient of each new energy (wind turbine, photovoltaic and energy storage) is used as the secondary objective function:

[0081] minF1′=minA(a t H t +a p H p +a e H e )

[0082] minF2′=minB(b t K t +b p K p +b e K e )

[0083] minF3′=minC(c t P mt +c p P mp +c e P me )

[0084] In the formula, H t , H p , H e are the equivalent inertia time constants of wind turbine, photovoltaic and energy storage, respectively, t , K p , K e are the equivalent regulation coefficients of wind turbines, photovoltaics and energy storage, respectively, mt, P mp , P me A, B, C, and a are the reserved power reserves for wind turbines, photovoltaics, and energy storage. t 、a p 、a e 、b t 、b p 、b e 、c t 、c p 、c e are the weight coefficients of the frequency modulation parameters respectively.

[0085] On the basis of the above multi-objective functions, constraints are established based on the system frequency stability requirements, as follows:

[0086] Considering the frequency stability requirements for safe operation of the comprehensive power system and the economic requirements for new energy sites, three different new energy active power reserve levels are set, namely high, medium and low, which are 10%, 8% and 5% of the rated power of new energy respectively. Based on different new energy active power reserves, constraints are set on the new energy power amplitude in the optimization model:

[0087] ΔP i,n ≤R·P iN

[0088] In the formula, R is the ratio of the preset new energy active reserve to the rated power, which is divided into three levels: 10%, 8%, and 5%, ΔP i,n is the active power adjustment of the renewable energy at the nth differential step, P iN is the rated active power of the new energy.

[0089] Based on the power system frequency stability guidelines, a stability constraint is established for the system frequency change rate after the disturbance:

[0090]

[0091] Where ROCOF extre The maximum frequency change rate that meets the minimum requirement of system frequency stability, Δf n+1 is the system frequency deviation at the n+1th differential step.

[0092] Based on the power system frequency stability guidelines, a stability constraint is established for the lowest point of the system frequency after the disturbance:

[0093] |Δf n |≤Δf extre

[0094] Where Δf extre The maximum frequency deviation that is set to meet the minimum requirement of system frequency stability.

[0095] S5. Based on the above objective function and constraints, the solver is called to solve the model, the optimal solution of each variable is obtained and the calculation results of each differential step are output, so as to obtain the frequency regulation parameter requirements of the power system based on the active reserve of new energy and meeting the system frequency stability requirements.

[0096] Among them, the power system frequency regulation parameter requirements mainly include: wind turbine equivalent regulation coefficient K t , Photovoltaic equivalent adjustment coefficient K p , Energy storage equivalent adjustment coefficient K e , fan equivalent inertia time constant H t , Photovoltaic equivalent inertia time constant H p , energy storage equivalent inertia time constant H e , fan reserved power P mt , Photovoltaic reserved power backup P mp , Energy storage reserved power backup P me .

[0097] Verification Example

[0098] like Figure 2 As shown, this embodiment adopts an improved IEEE 39-node system to calculate frequency modulation parameters, which is as follows:

[0099] (1) A load sudden increase of 100MW disturbance is set at the position of bus 17 of the improved IEEE 39-node system, so that the system frequency exceeds the dead zone of the synchronous machine speed regulator's primary frequency regulation action, and the main parameters of each generator in the power grid are counted.

[0100] (2) The synchronous generators in the improved IEEE 39-node system are aggregated into equivalent synchronous machines according to their types, and nonlinear links such as the speed regulator dead zone and amplitude limit are considered to establish a dynamic characteristic model of the power system frequency support under the expected disturbance. In this embodiment, the speed regulator frequency regulation dead zone of the equivalent synchronous machine is set to 0.033 Hz, and the active amplitude limit value is set to 10% of the capacity.

[0101] (3) A differential step size of 0.02 s was used to establish a discretized model of the system frequency response based on the forward difference method, and the discrete expressions of the system power shortage, system frequency deviation, and the additional active power of the equivalent synchronous unit after the disturbance were obtained. The initial system frequency deviation and the initial additional active power of the equivalent synchronous unit were set to 0, and the solver was called to perform multi-objective function optimization calculations.

[0102] (4) The selection range of new energy active power reserve is set to three different reserve levels: high, medium and low, which are 10%, 8% and 5% of the rated power of new energy respectively. Based on different new energy active power reserves, constraints are set on the new energy power amplitude in the optimization model.

[0103] Constraints are established based on the system frequency stability requirements, including new energy active reserve constraints, maximum system frequency change rate constraints, maximum system frequency deviation constraints, etc. Referring to the National Power System Safety and Stability Guidelines, in this embodiment, the new energy active reserve constraint is set to high-end 10% new energy rated power, the maximum system frequency deviation constraint is set to 0.2 Hz, and the maximum frequency change rate constraint is set to 1.0 Hz / s.

[0104] The objective function is established based on the economic requirements of the site and the requirements of system frequency stability, and the objective function weight coefficients are set for the energy adjustment integral, equivalent regulation coefficient, equivalent inertia time constant, and reserved power reserve of wind turbines, photovoltaics, and energy storage. Among them, the energy adjustment integral weight coefficients of wind turbines, photovoltaics, and energy storage are all set to 1.5, and the weight coefficients of the equivalent regulation coefficient, equivalent inertia time constant, and reserved power reserve are set to 1.0, 10.0, and 0.5, respectively.

[0105] (5) Call the solver's solution module to optimize the objective function, calculate the optimal solution of each variable that meets the constraints, and output the calculation results of each differential step; the optimization calculation results can ultimately generate the calculation results of the frequency regulation parameter requirements of the power system based on the active reserve of renewable energy, as shown in Table 1.

[0106] Table 1 Power system frequency regulation parameter requirements

[0107] FM parameters <![CDATA[K t ]]> <![CDATA[K p ]]> <![CDATA[K e ]]> <![CDATA[H t ]]> <![CDATA[H p ]]> <![CDATA[H e ]]> <![CDATA[P mt ]]> <![CDATA[P mp ]]> <![CDATA[P me ]]> Calculation results 10.511 10.102 10.091 5.45 5.41 5.37 2.87 2.87 2.87

[0108] Synchronously, a curve showing the total active power and total energy adjustment of renewable energy changing with time can be generated, such as Figure 3 Similarly, the curves of active power and energy adjustment of wind turbines, photovoltaics, and energy storage changing with time can be generated, as shown in Figure 4 , Figure 5 , Figure 6 shown.

[0109] Therefore, the present invention adopts the above-mentioned method for calculating the frequency regulation parameter requirements of the power system based on the active standby of new energy, which can help system dispatchers and new energy stations to clarify the frequency safety level of the power system in real time, and guide the adjustment of various frequency regulation parameters of new energy, so as to ensure the safety of the power system operation and improve the economy of the new energy stations.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the frequency regulation parameter requirements of a power system based on active reserve of new energy, characterized in that: The following steps are involved: S1. Determine the frequency support capability of each type of synchronous generator in the power system, and aggregate each synchronous generator of the same type into an equivalent synchronous machine; S2. According to the nonlinear link of the speed regulator, the power system frequency response model of the equivalent synchronous machine is established, including the correction of active power in the primary frequency regulation process, as follows: Where Δf db is the primary frequency modulation dead zone, is the active power limit of the primary frequency modulation of the equivalent synchronous machine, P k is the active power adjustment of the equivalent synchronous unit, K is the speed deviation magnification of the equivalent synchronous unit, and Δf is the system frequency deviation; S3. Discrete power system frequency response model based on forward difference method; S4. Establish objective function and constraint conditions based on the active power reserve of new energy; Among them, the objective function includes the main objective function and the secondary objective function, which are as follows: The main objective function is: Where Δn is the differential step size, ΔP t,n , ΔP p,n , ΔP e,n They represent the additional active power of wind turbines, photovoltaic power generation and energy storage in the system at the nth differential step, respectively; a, b, c represent the weights of the additional active power of wind turbines, photovoltaic power generation and energy storage in the main objective function after the disturbance occurs; The secondary objective function is: minF1′=minA(a t H t +a p H p +a e H e ) minF2′=minB(b t K t +b p K p +b e K e ) minF3′=minC(c t P mt +c p P mp +c e P me ) In the formula, H t , H p , H e are the equivalent inertia time constants of wind turbines, photovoltaics and energy storage, respectively, t , K p , K e are the equivalent regulation coefficients of wind turbines, photovoltaics and energy storage, respectively, mt , P mp , P me A, B, C, and a are the reserved power reserves for wind turbines, photovoltaics, and energy storage. t 、a p 、a e 、b t 、b p 、b e 、c t 、c p 、c e are the weight coefficients of the frequency modulation parameters respectively; The constraints include: Based on different renewable energy active power reserves, set constraints on the renewable energy power amplitude in the optimization model: ΔP i,n ≤R·P iN In the formula, R is the ratio of the preset new energy active reserve to the rated power, ΔP i,n is the active power adjustment of the new energy source at the nth differential step, P iN is the rated active power of the new energy; Based on the power system frequency stability guidelines, stability constraints are established for the system frequency change rate after disturbance: Where ROCOF extre The maximum frequency change rate that meets the minimum requirement of system frequency stability, Δf n+1 is the system frequency deviation at the n+1th differential step; Based on the power system frequency stability guidelines, a stability constraint is established for the lowest point of the system frequency after the disturbance: |Δf n |≤Δf extre Where Δf extre The maximum frequency deviation set to meet the minimum requirements of system frequency stability; S5. Call the solver to solve the model and obtain the power system frequency regulation parameter requirements.

2. The method for calculating the frequency regulation parameter requirements of the power system based on the active reserve of new energy according to claim 1 is characterized in that: In step S1, the types of synchronous generators include reheat units, non-reheat units, and hydro turbine units.

3. The method for calculating the frequency regulation parameter requirements of the power system based on the active reserve of new energy according to claim 1 is characterized in that: In step S3, the power system frequency response model is discretized as follows: When a low-frequency disturbance occurs in the system, the power generated by the equivalent synchronous unit in response to a frequency modulation is: Where P k,n is the additional active power of the equivalent synchronous unit at the nth step of the system, P k,n-1 is the additional active power of the equivalent synchronous unit at the n-1th step of the system, b k,n 、a k,n are the active power adjustment of the dead zone of the equivalent synchronous unit and the speed regulator limit at the nth step of the system, a k,n-1 is the active power adjustment of the speed regulator of the equivalent synchronous unit at the n-1th step of the system, Δf db is the primary frequency modulation dead zone, T RH is the reheater time constant of the equivalent synchronous unit, F HP is the power ratio of the high-pressure cylinder of the equivalent synchronous unit, s is the differential operator, Δn is the differential step size, Δf n is the system frequency deviation at the nth differential step; in, P dis,n =P dis,0 -P i,n -P k,n Where H is the inertia time constant of the equivalent synchronous machine, f0 is the rated frequency of the system, S b is the system base capacity, P dis,n-1 is the system power deficit for the n-1th differential step, P dis,n is the power deficit of the system at the nth differential step, P dis,0 is the system active power shortage at the moment of disturbance, P i,n is the active power adjustment of renewable energy at the nth differential step of the system, P k,n It is the active power adjustment amount of the system's nth differential step equivalent synchronous machine in response to primary frequency modulation.

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