Wind power plant subsynchronous oscillation suppression system and method based on energy storage

Abstract

The invention discloses a wind power plant subsynchronous oscillation suppression system based on energy storage. The system comprises an energy storage device, a subsynchronous damping controller and a voltage source converter, the invention discloses a wind power plant subsynchronous oscillation suppression method based on energy storage, and the method comprises the steps: carrying out the filtering processing of a collected voltage signal u of a wind power plant line, obtaining a subsynchronous frequency signal, and obtaining a current signal igref outputted by a subsynchronous damping controller to an energy storage device through the subsynchronous frequency signal; impedance of all wind driven generators and energy storage devices of the wind power plant is obtained, resistance and inductance of all transformers, wind power plant lines and series compensation lines of the wind power plant are calculated, and the transformers comprise box transformers and main transformers; equivalent impedance models of all wind driven generators, transformers, power transmission lines, subsynchronous damping controllers and energy storage devices of the wind power plant are constructed respectively, and an overall impedance model of the wind power plant subsynchronous oscillation suppression system based on energy storage is obtained based on the impedance models. Oscillation suppression is realized through positive damping provided by the converter, and the stability of the wind power plant is improved.

Description

Technical field:

[0001] The present invention belongs to the field of electronic power technology, and in particular relates to a system and method for suppressing sub-synchronous oscillation of a wind farm based on energy storage. Background technology:

[0002] With the continuous change of energy structure, the grid-connected capacity of new energy represented by wind energy and photovoltaics has increased year by year. By the end of 2022, my country's renewable energy installed capacity will exceed 1.2 billion kilowatts, reaching 1.213 billion kilowatts, accounting for 47.3% of the total installed capacity of power generation in the country. Among them, wind power and photovoltaic power generation exceeded 1 trillion kilowatt-hours, reaching 1.19 trillion kilowatt-hours. Wind power generation has become a widely used renewable energy source, and the ability of wind farms to transmit over long distances is improved through series compensation technology. The penetration rate of wind power generation in my country's power system has increased year by year. In order to improve the stability of the power system, measures are usually taken to suppress subsynchronous oscillation. However, as the current mainstream model, the doubly fed wind turbine, its grid connection through the series compensation line will cause electromagnetic interaction between the series compensation line and the doubly fed wind turbine and its converter controller, which will cause subsynchronous oscillation, resulting in a large number of wind turbines damaged. If action is not taken in time, a large number of wind turbines will be disconnected from the network, which will seriously damage the safety and reliability of the wind power generation system. The patent with publication number CN219843438U proposes to adjust the operating parameters of the doubly-fed wind turbine by optimizing the control algorithm. Although this can alleviate subsynchronous oscillations to a certain extent, it lacks effective energy storage and regulation links. When faced with large power fluctuations, it is difficult to solve the energy imbalance problem and the suppression effect is limited. The patent with publication number CN119134339A uses additional damping controllers and other methods to add additional filters to filter out subsynchronous frequency components. This is only from the perspective of signal processing. It cannot effectively regulate the system energy level and cannot buffer the energy impact caused by oscillations. Therefore, there is an urgent need to design a more effective method for suppressing subsynchronous oscillations in wind farms. Summary of the invention:

[0003] Most of the existing technologies do not introduce energy storage devices. When subsynchronous oscillation occurs, it is impossible to quickly and reasonably allocate the energy in the system. During the oscillation, the violent fluctuations in the system energy cannot be balanced and stabilized in time, resulting in continuous impact on the wind turbines, and ultimately causing a large number of wind turbines to be damaged. In view of this, the present invention designs a wind farm subsynchronous oscillation suppression system and method based on energy storage, which has achieved the purpose of suppressing subsynchronous oscillations and improving the stability of wind farms.

[0004] A subsynchronous oscillation suppression system for a wind farm based on energy storage, the subsynchronous oscillation suppression system comprises an energy storage device, a subsynchronous damping controller and a voltage source converter; the energy storage device, the subsynchronous damping controller and the voltage source converter are all installed on the transmission line between the wind farm outlet and the power grid; the energy storage device is close to the wind farm side, the voltage source converter is close to the power grid side, the subsynchronous damping controller is located between the energy storage device and the voltage source converter, and the three are connected in series through the transmission line; wherein the energy storage device comprises a superconducting coil, a cryogenic system, a power control system and a monitoring control system, and the subsynchronous damping controller specifically comprises a filter module, a gain module and a phase shifter module; wherein the filter module comprises a bandpass filter and a bandstop filter.

[0005] Preferably, the low-temperature system of the energy storage device includes: cooling equipment, an insulating container, a temperature sensor and a pressure sensor; the power control system includes an inverter, a power electronic switch, a protection circuit and an inductor coil; the monitoring and control system includes a sensor device, a data acquisition and control unit, a central controller and a communication network.

[0006] Preferably, the energy storage device is a superconducting energy storage device.

[0007] A method for suppressing subsynchronous oscillation of a wind farm based on energy storage, the method specifically comprising:

[0008] The voltage signal u of the wind farm line is collected, and the voltage signal u is filtered through a bandpass filter and a bandstop filter to obtain a sub-synchronous frequency signal, and the sub-synchronous frequency signal is amplified and phase-shifted to obtain a current signal i output by the sub-synchronous damping controller to the energy storage device. gref ; The i gref The electric energy in the power grid is converted and controlled by inputting into a voltage source converter; the impedance of all wind turbines in the wind farm and the energy storage device is obtained. Generally, the number of wind turbines in the wind farm ranges from 1 to 100; the resistance and inductance of all transformers, wind farm lines, and series compensation lines in the wind farm are calculated, and the transformer includes a box transformer and a main transformer; the equivalent impedance models of all wind turbines, transformers, transmission lines, sub-synchronous damping controllers, and energy storage devices in the wind farm are respectively constructed through the resistance and inductance of all wind turbines in the wind farm, the resistance and inductance of transformers, the resistance and inductance of wind farm transmission lines, and the resistance and inductance of sub-synchronous damping controllers and energy storage devices, and the overall impedance model of the wind farm sub-synchronous oscillation suppression system based on energy storage is obtained based on the impedance model.

[0009] Preferably, the method further comprises optimizing the parameters of the subsynchronous damping controller according to the overall impedance model under different working conditions to maximize the worst equivalent resistance under different working conditions.

[0010] Preferably, the equivalent impedance model of the field composed of all wind turbines in the wind farm is:

[0011]

[0012] Where M is the number of wind turbines, R W (s), X W (s) are the resistance and reactance of the wind farm, s is the complex frequency, Z DFIG The equivalent impedance model of a single wind turbine under a certain working condition is:

[0013] Z DFIG =R DFIG (s)+sX DFIG (s)1≤f≤45

[0014]

[0015] Among them, P Q1 is the fitting coefficient (Q1=1,2,3,4,5,6,7,8,9,10,11,12,13,14), R DFIG (s), X DFIG (s) are the resistance and reactance of a single wind turbine, f is the oscillation frequency, s = 2jπf, j is the imaginary unit, π = 3.14;

[0016] The equivalent impedance model of the transmission line is:

[0017] Z NL (s) = R NL +sL NL

[0018] Z CL (s) = R CL +sL NL +1 / (sC)

[0019] Among them, L NL and R NL is the inductance and resistance of the uncompensated transmission line, L CL and R CL To compensate for the inductance and resistance of the transmission line, C is the capacitance of the series compensation line;

[0020] The equivalent impedance model of the energy storage device with multiple additional sub-synchronous damping controllers is: Generally, the number of sub-synchronous damping controllers attached to the energy storage device ranges from 1 to 1000:

[0021]

[0022] Among them, R SS (s), sX SS(s) are the resistance and reactance of the energy storage device, N is the number of subsynchronous damping controllers, Z xT2 (s) is the variable impedance of the energy storage box, Z SDC (s) is the equivalent impedance model of the subsynchronous damping controller:

[0023]

[0024] Among them, H SDC (s) is the transfer function of the subsynchronous damping controller;

[0025]

[0026] Among them, ω P is the associated subsynchronous oscillation angular frequency, ω E is the system angular frequency, ξ E and P are the damping coefficients of the band-stop and band-pass filters, respectively, and K u is the gain of the subsynchronous damping controller, t is the time constant of the subsynchronous damping controller;

[0027] The equivalent impedance model of a single energy storage device with an additional damping controller is:

[0028]

[0029] Among them, Z si (s)(i=1,2,3,4) is the equivalent impedance model of the first, second, third and fourth quadrants of the energy storage device, specifically:

[0030]

[0031] Z si (s) = R si (s)+sX si (s)1≤f≤45

[0032] Among them, P sQ2 is the fitting coefficient (Q2=1,2,3,4,5,6,7,8,9,10,11,12);

[0033] The overall impedance model of the wind farm subsynchronous oscillation suppression system based on energy storage is:

[0034]

[0035] R(s) and X(s) are the resistance and reactance of the system respectively. K1 and K2 are the transformation ratios of the transformer from T1 to T and T2 respectively. T1 and T2 are the box transformers connected to the energy storage device, and T is the main transformer connected to the energy storage device. Their impedance models are:

[0036]

[0037] Among them, R1 and R2 are the box transformer resistors connected to the energy storage device, R3 is the main transformer resistor, and X T1 , X T2 X is the box transformer reactance connected to the energy storage device. T It is the main transformer reactance connected to the energy storage device.

[0038] Preferably, the method for optimizing the parameters of the subsynchronous damping controller is as follows: under different working conditions, the resistance and reactance functions of the wind farm and the energy storage device in the four quadrants with different numbers of wind turbines and different series compensation capacitors are fitted to obtain the resistance and reactance functions of the subsynchronous oscillation suppression system of the wind farm based on energy storage, and the optimized objective function is obtained: R(K u ,t)=min[R1(K u ,t)R1(K u ,t)…R n (K u ,t)], where n is the number of working conditions, K u is a gain with a positive or negative sign, and t is a time constant. The objective function is optimized by the genetic algorithm function of MATLAB to obtain the optimal subsynchronous damping controller parameter K u and t.

[0039] Preferably, the method further comprises simulating the obtained optimal subsynchronous damping controller parameters to verify their effectiveness.

[0040] Preferably, the method further comprises constraining the subsynchronous damping controller before optimizing the parameters, wherein the constraint conditions are:

[0041]

[0042] Preferably, the impedance of all wind turbines and the energy storage device in the wind farm is obtained by an impedance scanning method, and the resistance and inductance of all transformers, wind farm lines, and series compensation lines in the wind farm are calculated.

[0043] The present invention filters the line voltage signal of the wind farm through a bandpass filter and a band-stop filter, and can accurately obtain the subsynchronous frequency signal, and then obtain the current signal igref of the control energy storage device through gain and phase shift, and the current signal is input to the voltage source converter. The voltage source converter transforms and controls the electric energy in the power grid according to the input control signal. In this process, the control strategy of the converter is designed based on the signal provided by the subsynchronous damping controller, so that the converter can present a positive damping characteristic at the subsynchronous frequency. When the system has a subsynchronous oscillation trend, the negative damping will cause the oscillation to continue to intensify, and the positive damping of the converter can generate a force opposite to the oscillation direction, consume the oscillation energy, thereby suppressing the subsynchronous oscillation of the system and enhancing the stability of the entire wind farm and the grid connection system. The output power of the wind farm is volatile, especially when the wind speed is unstable. The energy storage device provided in the present invention can store excess energy when the output power of the wind farm is higher than the grid demand, and release energy when the output power of the wind farm is insufficient. For example, when the wind speed suddenly increases and the output power of the wind farm rises instantly, the energy storage device can absorb part of the energy to prevent a large amount of electric energy from flowing into the power grid and causing fluctuations in parameters such as the power grid frequency and voltage. At the same time, the energy storage device of the present invention uses superconducting coils. Superconducting materials have zero resistance characteristics and can store and release electric energy without energy loss. Compared with traditional energy storage methods, it has higher energy storage efficiency and power density, and can respond to changes in energy demand during subsynchronous oscillation more quickly and effectively. Description of the drawings:

[0044] Attached Figure 1 It is a schematic diagram of the series compensation transmission system of the wind turbine generator set with energy storage access according to the present invention.

[0045] Attached Figure 2 It is a flow chart of the method for suppressing sub-synchronous oscillation of wind farms based on energy storage of the present invention.

[0046] Attached Figure 3 It is a strategy diagram of the wind farm sub-synchronous oscillation suppression method based on energy storage of the present invention. Specific implementation method:

[0047] In order to make the technical solution of the present invention easier to understand, the technical solution of the present invention is now clearly and completely described in combination with embodiments and drawings.

[0048] Embodiment 1:

[0049] A wind farm subsynchronous oscillation suppression system based on energy storage, such as Figure 2As shown, the subsynchronous oscillation suppression system includes an energy storage device, a subsynchronous damping controller and a voltage source converter; wherein the energy storage device is a superconducting energy storage device; the energy storage device, the subsynchronous damping controller and the voltage source converter are all installed on the transmission line between the outlet of the wind farm and the power grid; the energy storage device is close to the wind farm side, the voltage source converter is close to the power grid side, and the subsynchronous damping controller is located between the energy storage device and the voltage source converter, and the three are connected in series through the transmission line; wherein the energy storage device includes a superconducting coil, a cryogenic system, a power control system and a monitoring control system, and the subsynchronous damping controller specifically includes a filter module, a gain module and a phase shifter module; wherein the filter module includes a bandpass filter and a bandstop filter, and the material of the superconducting coil is yttrium barium copper oxide. Specifically, the working mode of the energy storage device is: (1) System startup: a) The cryogenic system is first turned on to cool the superconducting coil to the working temperature. b) The monitoring control system monitors the state of the cryogenic system to ensure that the superconducting coil enters the superconducting state. (2) Energy storage: a) The converter of the power control system converts the grid power into direct current, which flows into the superconducting coil. b) The superconducting coil stores energy through induced current, and the monitoring and control system monitors the current changes and storage status in real time. (3) Energy release: a) According to the grid demand, the power control system converts the direct current in the superconducting coil into alternating current through the converter. b) The monitoring and control system coordinates the energy release process to ensure that the output power is stable and meets the grid demand. (4) Fault emergency: a) If the monitoring and control system detects a quench, overload or cooling fault, the protection circuit is triggered: the bypass resistor absorbs the current to prevent system damage. Stop energy transmission to ensure system safety. The energy storage device uses a superconducting coil. The superconducting material has zero resistance characteristics and can store and release electric energy without energy loss. Compared with traditional energy storage methods, it has higher energy storage efficiency and power density, and can respond to changes in energy demand during subsynchronous oscillation more quickly and effectively. Equipped with a power control system and a monitoring and control system, the charging and discharging power of the energy storage device can be accurately controlled, and the operating status of the device can be monitored in real time to ensure the stable and reliable operation of the energy storage device, providing continuous and stable energy support for suppressing subsynchronous oscillations.

[0050] Embodiment 2:

[0051] like Figure 2 As shown, a method for suppressing sub-synchronous oscillation of a wind farm based on energy storage is specifically as follows:

[0052] Collect the voltage signal u of the wind farm line, such as Figure 3 As shown, the voltage signal u is filtered by a bandpass filter and a bandstop filter to obtain a subsynchronous frequency signal, and the subsynchronous frequency signal is amplified and phase-shifted to obtain a current signal i output by a subsynchronous damping controller to the energy storage device. gref ; The igref Input to the voltage source converter to transform and control the electric energy in the grid;

[0053] The impedance of all wind turbines and the energy storage device in the wind farm is obtained by impedance scanning method, and the resistance and inductance of all transformers, wind farm lines, and series compensation lines in the wind farm are calculated. The transformer includes a box transformer and a main transformer; through the resistance and inductance of all wind turbines in the wind farm, the resistance and inductance of transformers, the resistance and inductance of wind farm transmission lines, and the resistance and inductance of sub-synchronous damping controllers and energy storage devices, equivalent impedance models of all wind turbines, transformers, transmission lines, sub-synchronous damping controllers, and energy storage devices in the wind farm are respectively constructed, and based on the impedance model, the overall impedance model of the wind farm sub-synchronous oscillation suppression system based on energy storage is obtained, specifically:

[0054] The equivalent impedance model of the wind farm composed of all wind turbines is:

[0055]

[0056] Where M is the number of wind turbines, R W (s), X W (s) are the resistance and reactance of the wind farm, and s is the complex frequency Z DFIG The equivalent impedance model of a single wind turbine under a certain working condition is:

[0057] Z DFIG =R DFIG (s)+sX DFIG (s)1≤f≤45

[0058]

[0059] Among them, P Q1 is the fitting coefficient (Q1=1,2,3,4,5,6,7,8,9,10,11,12,13,14), R DFIG (s), X DFIG (s) are the resistance and reactance of a single wind turbine, f is the oscillation frequency, s = 2jπf, j is the imaginary unit, π = 3.14;

[0060] The equivalent impedance model of the transmission line is:

[0061] Z NL (s) = R NL +sL NL

[0062] Z CL (s) = R CL +sL NL +1 / (sC)

[0063] Among them, L NL and R NL is the inductance and resistance of the uncompensated transmission line, L CL and R CL To compensate for the inductance and resistance of the transmission line, C is the capacitance of the series compensation line;

[0064] The equivalent impedance model of the energy storage device of the plurality of additional sub-synchronous damping controllers is:

[0065]

[0066] Among them, R SS (s), sX SS (s) are the resistance and reactance of the energy storage device, N is the number of subsynchronous damping controllers, Z xT2 (s) is the variable impedance of the energy storage box, Z SDC (s) is the equivalent impedance model of the subsynchronous damping controller:

[0067]

[0068] Among them, H SDC (s) is the transfer function of the subsynchronous damping controller;

[0069]

[0070] Among them, ω P is the associated subsynchronous oscillation angular frequency, ω E is the system angular frequency, ξ E and P are the damping coefficients of the band-stop and band-pass filters, respectively, and K u is the gain of the subsynchronous damping controller, t is the time constant of the subsynchronous damping controller;

[0071] The equivalent impedance model of a single energy storage device with an additional damping controller is:

[0072]

[0073] Among them, Z si(s) (i=1,2,3,4) is the equivalent impedance model of the first, second, third and fourth quadrants of the energy storage device, specifically:

[0074]

[0075] Z si (s) = R si (s)+sX si (s)1≤f≤45

[0076] Among them, P sQ2is the fitting coefficient (Q2=1,2,3,4,5,6,7,8,9,10,11,12);

[0077] The overall impedance model of the wind farm subsynchronous oscillation suppression system based on energy storage is:

[0078]

[0079] R(s) and X(s) are the resistance and reactance of the system respectively. K1 and K2 are the transformation ratios of the transformer from T1 to T and T2 respectively. T1 and T2 are the box transformers connected to the energy storage device, and T is the main transformer connected to the energy storage device. Their impedance models are:

[0080]

[0081] Among them, R1 and R2 are the box transformer resistors connected to the energy storage device, R3 is the main transformer resistor, and X T1 , X T2 X is the box transformer reactance connected to the energy storage device. T It is the main transformer reactance connected to the energy storage device.

[0082] According to the overall impedance model under different working conditions, the parameters of the subsynchronous damping controller are optimized to maximize the worst equivalent resistance under different working conditions, specifically:

[0083] A set of subsynchronous damping controller parameters is found through constraints so that it can suppress subsynchronous oscillations of different oscillation frequencies generated by multiple working conditions of the wind turbine, four quadrants of energy storage, and different numbers of wind turbines. The constraints are:

[0084] The steps to optimize the subsynchronous damping controller parameters are as follows:

[0085] (1) Fitting the resistance and reactance functions of the wind farm and energy storage device in the four quadrants under 15 operating conditions with three different numbers of wind turbines and two different series compensation capacitors, with a total of 360 permutations and combinations;

[0086] (2) Obtain the resistance and reactance functions of the overall system under 360 operating conditions;

[0087] (3) According to the resistance curves under 360 working conditions, the optimization objective function is given: R(K u ,t)=min[R1(K u ,t)R1(K u ,t)…R n (K u ,t)], where n is the number of working conditions, K uis a gain with a positive or negative sign, and t is a time constant. The objective function is optimized by the genetic algorithm function of MATLAB to obtain the optimal subsynchronous damping controller parameter K u and t;

[0088] (4) Use the genetic algorithm function provided by MATLAB to optimize the objective function and obtain the optimal result;

[0089] (5) The optimal gain and time constant of the subsynchronous damping controller are simulated to verify its effectiveness.

[0090] Among them, the operating parameters in this embodiment are shown in Table 1:

[0091] Table 1 Operating parameters of 15 wind turbines in the wind farm

[0092] Serial number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 <![CDATA[V k / pu]]> 1 0.96 0.97 0.98 1.03 0.99 1.04 1 1.01 1.05 1.03 0.95 0.98 0.99 1.02 <![CDATA[P k / pu]]> 1 0.95 0.9 0.8 0.7 0.7 0.6 0.6 0.5 0.3 0.2 0.1 0.4 0.3 0.5 <![CDATA[Q k / pu]]> 0 -0.1 0.2 0.3 0.1 0.05 -0.3 -0.05 0.2 -0.1 0 0 -0.15 0.1 0.2

[0093] Among them, V k is the system rated voltage, P k is the reference active power of the wind turbine, Q k is the reference reactive power of the wind turbine. It should be noted that the embodiments described herein are only partial embodiments of the present invention, rather than all implementations of the present invention. The embodiments are only exemplary and their role is only to provide a more intuitive and clear way to understand the content of the present invention, rather than to limit the technical solution described in the present invention. Without departing from the concept of the present invention, all other implementation methods that ordinary technicians in this field can think of without creative work, and other simple replacements and various changes to the technical solution of the present invention, all belong to the protection scope of the present invention.

Claims

1. A wind farm subsynchronous oscillation suppression system based on energy storage, characterized in that: The subsynchronous oscillation suppression system includes an energy storage device, a subsynchronous damping controller and a voltage source converter; the energy storage device, the subsynchronous damping controller and the voltage source converter are all installed on the transmission line between the wind farm outlet and the power grid; the energy storage device is close to the wind farm side, the voltage source converter is close to the power grid side, the subsynchronous damping controller is located between the energy storage device and the voltage source converter, and the three are connected in series through the transmission line; wherein, the energy storage device includes a superconducting coil, a cryogenic system, a power control system and a monitoring control system, and the subsynchronous damping controller specifically includes a filter module, a gain module and a phase shifter module; wherein, the filter module includes a bandpass filter and a bandstop filter.

2. A wind farm subsynchronous oscillation suppression system based on energy storage as claimed in claim 1, characterized in that: The low temperature system of the energy storage device includes: cooling equipment, insulation container, temperature sensor and pressure sensor; the power control system includes converter, power electronic switch, protection circuit and inductor; the monitoring control system includes sensor equipment, data acquisition and control unit, central controller and communication network.

3. A wind farm subsynchronous oscillation suppression system based on energy storage as claimed in claim 2, characterized in that: The energy storage device is a superconducting energy storage device.

4. A method for suppressing subsynchronous oscillation of wind farms based on energy storage, characterized in that: The method specifically comprises: collecting a voltage signal u of a wind farm line, filtering the voltage signal u through a bandpass filter and a bandstop filter to obtain a subsynchronous frequency signal, performing gain and phase shifting on the subsynchronous frequency signal to obtain a current signal i output by a subsynchronous damping controller to an energy storage device. gref ; The i gref The electric energy in the power grid is converted and controlled by inputting into the voltage source converter; the impedance of all wind turbines in the wind farm and the energy storage device is obtained, and the resistance and inductance of all transformers, wind farm lines, and series compensation lines in the wind farm are calculated, and the transformer includes a box transformer and a main transformer; the equivalent impedance models of all wind turbines, transformers, transmission lines, sub-synchronous damping controllers, and energy storage devices in the wind farm are respectively constructed through the resistance and inductance of all wind turbines in the wind farm, the resistance and inductance of transformers, the resistance and inductance of wind farm transmission lines, and the resistance and inductance of sub-synchronous damping controllers and energy storage devices, and the overall impedance model of the wind farm sub-synchronous oscillation suppression system based on energy storage is obtained based on the impedance model.

5. A method for suppressing subsynchronous oscillation of a wind farm based on energy storage as claimed in claim 4, characterized in that: The method also includes optimizing the parameters of the subsynchronous damping controller according to the overall impedance model under different working conditions to maximize the worst equivalent resistance under different working conditions.

6. A method for suppressing subsynchronous oscillation of a wind farm based on energy storage as claimed in claim 4, characterized in that: The equivalent impedance model of the wind farm composed of all wind turbines is: Where M is the number of wind turbines, R W (s), X W (s) are the resistance and reactance of the wind farm, s is the complex frequency, Z DFIG The equivalent impedance model of a single wind turbine under a certain working condition is: Z DFIG =R DFIG (s)+sX DFIG (s)1≤f≤45 Among them, P Q1 is the fitting coefficient (Q1=1,2,3,4,5,6,7,8,9,10,11,12,13,14), R DFIG (s), X DFIG (s) are the resistance and reactance of a single wind turbine generator, f is the oscillation frequency, s = 2jπf, j is the imaginary unit, π = 3.14; The equivalent impedance model of the transmission line is: Z NL (s)=R NL +sL NL Z CL (s)=R CL +sL NL +1 / (sC) Among them, L NL and R NL is the inductance and resistance of the uncompensated transmission line, L CL and R CL To compensate for the inductance and resistance of the transmission line, C is the capacitance of the series compensation line; The equivalent impedance model of the energy storage device of the plurality of additional sub-synchronous damping controllers is: Among them, R SS (s), sX SS (s) are the resistance and reactance of the energy storage device, N is the number of subsynchronous damping controllers, Z xT2 (s) is the variable impedance of the energy storage box, Z SDC (s) is the equivalent impedance model of the subsynchronous damping controller: Among them, H SDC (s) is the transfer function of the subsynchronous damping controller; Among them, ω P is the associated subsynchronous oscillation angular frequency, ω E is the system angular frequency, ξ E and P are the damping coefficients of the band-stop and band-pass filters, respectively, and K u is the gain of the subsynchronous damping controller, t is the time constant of the subsynchronous damping controller; The equivalent impedance model of a single energy storage device with an additional damping controller is: Among them, Z si (s)(i=1,2,3,4) is the equivalent impedance model of the first, second, third and fourth quadrants of the energy storage device, specifically: Z si (s)=R si (s)+sX si (s)1≤f≤45 Among them, P sQ2 is the fitting coefficient (Q2=1,2,3,4,5,6,7,8,9,10,11,12); The overall impedance model of the wind farm subsynchronous oscillation suppression system based on energy storage is: R(s) and X(s) are the resistance and reactance of the system respectively. K1 and K2 are the transformation ratios of the transformer from T1 to T and T2 respectively. T1 and T2 are the box transformers connected to the energy storage device, and T is the main transformer connected to the energy storage device. Their impedance models are: Among them, R1 and R2 are the box transformer resistors connected to the energy storage device, R3 is the main transformer resistor, and X T1 , X T2 X is the box transformer reactance connected to the energy storage device. T It is the main transformer reactance connected to the energy storage device.

7. A method for suppressing subsynchronous oscillation of a wind farm based on energy storage as claimed in claim 5, characterized in that: The method for optimizing the parameters of the subsynchronous damping controller is as follows: under different working conditions, the resistance and reactance functions of the wind farm and the energy storage device in the four quadrants with different numbers of wind turbines and different series compensation capacitors are fitted to obtain the resistance and reactance functions of the subsynchronous oscillation suppression system of the wind farm based on energy storage, and the optimization objective function is obtained: R(K u ,t)=min[R1(K u ,t)R1(K u ,t)…R n (K u ,t)], where n is the number of working conditions, K u is a gain with a positive or negative sign, and t is a time constant. The objective function is optimized by the genetic algorithm function of MATLAB to obtain the optimal subsynchronous damping controller parameter K u and t.

8. A method for suppressing subsynchronous oscillation of a wind farm based on energy storage as claimed in claim 7, characterized in that: The method also includes simulating the obtained optimal subsynchronous damping controller parameters to verify their effectiveness.

9. A method for suppressing subsynchronous oscillation of a wind farm based on energy storage as claimed in claim 7, characterized in that: The method further includes constraining the subsynchronous damping controller before optimizing the parameters, wherein the constraint conditions are:

10. A method for suppressing subsynchronous oscillation of a wind farm based on energy storage as claimed in claim 4, characterized in that: The impedance of all wind turbines and the energy storage device in the wind farm is obtained by an impedance scanning method, and the resistance and inductance of all transformers, wind farm lines, and series compensation lines in the wind farm are calculated.

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