A capacitor and rotor coordinated inertia support stabilization control method for direct-drive wind turbines

Abstract

The present invention discloses a capacitor and rotor coordinated direct-drive wind turbine inertia support stabilization control method, comprising real-time acquisition of direct-drive wind turbine operating data, zero d-axis current control of the machine-side converter, obtaining outer loop control of the machine-side converter, and overspeed load shedding standby of the direct-drive wind turbine; grid-type DC voltage frequency droop control and reactive power error control of the grid-side converter; adding inertia control to the outer loop control, and adding damping stabilization control to the inertia control, obtaining an outer loop control corrected by the damping stabilization control and the inertia control; calculating the difference between the DC voltage and a preset threshold value input to the inertia control, and coordinating the capacitor inertia response and the fan rotor inertia response according to the difference. The present invention can coordinate capacitor electrical energy and fan rotor kinetic energy for inertia support, thereby improving the stability of fan operation.

Description

Technical Field

[0001] The present invention relates to the field of new energy power generation control technology, and in particular to a capacitor and rotor coordinated inertia support stabilization control method for a direct-drive wind turbine. Background Art

[0002] With the widespread integration of distributed renewable energy, wind power penetration is gradually increasing. Direct-drive wind turbines (permanent magnet synchronous generators, PMSGs) have advantages such as not requiring a gearbox and having a wide speed range, and their use in wind farms is increasing year by year. However, because direct-drive wind turbines use back-to-back converters for power transmission, the rotor's kinetic energy is hidden, resulting in a loss of inertial support.

[0003] A PMSG consists of a permanent magnet generator (PMG) and a back-to-back converter. Traditional PMSG generator-side converters employ Maximum Power Point Tracking (MPPT) control to ensure constant tracking of wind turbine output and improve economic efficiency. The grid-side converter uses a phase-locked loop (PLL) to obtain grid frequency and phase information to maintain DC voltage and reactive power stability. However, this control strategy prevents the wind turbine from responding to drops in grid frequency due to inertia, effectively hiding the turbine's inertia.

[0004] To overcome the low inertia issue brought on by the widespread integration of renewable energy, current research is using a DC voltage-frequency droop control strategy to fully utilize the energy stored in DC-side capacitors for inertia support. However, the energy stored in DC-side capacitors is relatively small, and the frequency support effect is not significant. Other research is also using inertia control to feed grid frequency changes back to the generator-side control. When the frequency drops, the generator-side processing is enhanced to utilize rotor kinetic energy. However, even small frequency fluctuations will cause the wind turbine output to respond constantly, and power fluctuations can affect system stability. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a direct-drive wind turbine inertia support stabilization control method with coordinated capacitor and rotor. By coordinating the use of energy stored in the capacitor and rotor for inertia support and performing inertia control according to the grid frequency, the stability of the wind turbine operation can be enhanced.

[0006] The present invention provides a capacitor and rotor coordinated inertia support stabilization control method for a direct-drive wind turbine, the method comprising:

[0007] Acquire operating data of the direct-drive wind turbine in real time, perform zero d-axis current control on the machine-side converter based on the operating data, obtain outer loop control of the machine-side converter, and perform overspeed load shedding standby on the direct-drive wind turbine;

[0008] Perform grid-type DC voltage frequency droop control and reactive power error control on the grid-side converter;

[0009] Adding inertia control to the outer loop control, and adding damping stabilization control to the inertia control, to obtain an outer loop control corrected by the damping stabilization control and the inertia control;

[0010] Calculating a difference between a DC voltage input to the inertia control and a preset threshold value, and coordinating control of a capacitor inertia response and a fan rotor inertia response based on the difference to obtain a final signal expression relationship input to the inertia control;

[0011] The final input signal expression relationship of the inertia control is calculated using the following formula:

[0012]

[0013] Where, is the DC voltage derivative reference value for input inertia control, du dcref is the threshold, is the DC voltage derivative.

[0014] Furthermore, the step of acquiring operating data of the direct-drive wind turbine in real time, applying zero d-axis current control to the machine-side converter according to the operating data to obtain outer loop control of the machine-side converter, and performing overspeed load shedding standby on the direct-drive wind turbine includes:

[0015] Obtain the three-phase current and three-phase voltage output of the direct-drive wind turbine in real time;

[0016] Obtain the wind turbine electrical angular velocity and wind turbine phase of the machine-side converter through an encoder, and perform Park transformation on the three-phase current value to obtain the actual value of the dq axis current of the machine-side converter;

[0017] Using zero d-axis current control on the generator-side converter to track the maximum power of the direct-drive wind turbine to obtain outer loop control of the generator-side converter;

[0018] The direct-drive wind turbine is subjected to overspeed load reduction standby to obtain a given active power value after load reduction that is input into the outer loop control.

[0019] Furthermore, the Parker transform is calculated using the following formula:

[0020]

[0021] Where i sd and i sq are the actual values ​​of the d-axis current and q-axis current of the generator-side converter, ωs is the wind turbine electrical angular velocity, θ s is the fan phase, i sa 、i sb 、i sc is the three-phase current value;

[0022] The outer loop control is calculated using the following formula:

[0023]

[0024] Where, and are the given values ​​of d-axis current and q-axis current of the generator-side converter, respectively, and k psq and k isq is the PI control parameter, P opt is the active power given value of the input outer loop control, P s is the output power of the direct-drive wind turbine calculated by the three-phase current and three-phase voltage values;

[0025] The following formula is used to calculate the active power setpoint after load shedding:

[0026]

[0027] Where, P del is the given value of active power after load reduction, d% is the load reduction coefficient, k opt is the power tracking coefficient, ω r is the direct drive fan speed.

[0028] Furthermore, the step of using grid-type DC voltage frequency droop control and reactive power error control on the grid-side converter includes:

[0029] Using grid-type DC voltage frequency droop control for the phase of the grid-side converter;

[0030] Reactive power error control is used for the amplitude of the grid-side converter.

[0031] Furthermore, the DC voltage frequency droop control is expressed by the following formula:

[0032]

[0033] Where, k is the frequency per unit value obtained by DC voltage frequency droop control, dc is the droop coefficient, u dc is the DC voltage of the input grid-side converter, is the DC voltage reference value, is the base value of the angular velocity at the net side, ω g The angular velocity is obtained for the machine side control, θg Get the phase for machine side control, is the per-unit value of the grid frequency;

[0034] The reactive power error control is expressed by the following formula:

[0035]

[0036] Where u g is the modulation amplitude of the network control voltage, k up and k ui is the PI control parameter, and Q g They are the reference value and actual value of reactive power output by the grid-side converter respectively.

[0037] Furthermore, the step of adding inertia control to the outer loop control and adding damping stabilization control to the inertia control to obtain the outer loop control corrected by the damping stabilization control and the inertia control comprises:

[0038] Low-pass filtering is performed on the DC voltage of the input inertia control, and a coefficient link is added after the derivative is taken to obtain a given value of the active power after the inertia control;

[0039] adding damping stabilization control to the inertia control to obtain a power reference value corrected by the damping stabilization control and the inertia control;

[0040] An outer loop control corrected by the damping stabilization control and the inertia control is obtained according to the power reference value corrected by the damping stabilization control and the inertia control.

[0041] Furthermore, the power reference value corrected by the damping stabilization control and the inertia control is calculated using the following formula:

[0042]

[0043] Where k D is the damping coefficient, P H is the active power given value after inertia control, u dc is the DC voltage for input inertia control, is the DC voltage reference value, P * is the power reference value after correction by damping stability control and inertia control;

[0044] The outer loop control after the damping stabilization control and the inertia control correction is calculated using the following formula:

[0045]

[0046] Furthermore, the step of calculating the difference between the DC voltage and the threshold value based on the DC voltage input to the inertia control and the preset threshold value, and coordinating the control of the capacitor inertia response and the fan rotor inertia response based on the difference includes:

[0047] Derivative the DC voltage input to the inertia control to obtain a DC voltage derivative, and add a dead zone component to the rate of change of the DC voltage;

[0048] determining whether a difference between the DC voltage derivative and a threshold is greater than zero; if so, not adding the inertia control to the outer loop control, maintaining the direct-drive fan in an overspeed load reduction standby state, and using the direct-drive fan capacitor for inertia response;

[0049] If not, the inertia control is added to the outer loop control, and the direct-drive fan capacitor and the direct-drive fan rotor are used for inertia response.

[0050] The present invention provides a method for controlling the inertial support stability of a direct-drive wind turbine using capacitor and rotor coordination. This method coordinates the electrical energy stored in the direct-drive wind turbine's capacitor and the kinetic energy stored in its rotor, enabling both to respond inertially based on the changing frequency of the DC voltage. This overcomes the low inertia issue associated with the widespread integration of new energy sources and improves wind turbine efficiency. Furthermore, the present invention incorporates a novel damping stabilization control mechanism to enhance wind turbine operational stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 1 is a flow chart of a method for controlling the inertia support stability of a direct-drive wind turbine with coordinated capacitance and rotor according to an embodiment of the present invention;

[0052] Figure 2 1 is a schematic diagram of the overall structure corresponding to the capacitor and rotor coordinated direct-drive wind turbine inertia support stabilization control method provided by an embodiment of the present invention;

[0053] Figure 3 yes Figure 1 Schematic diagram of the process of step S10;

[0054] Figure 4 yes Figure 2 Schematic diagram of the corresponding network side structure;

[0055] Figure 5 yes Figure 2 The corresponding machine side structure diagram;

[0056] Figure 6 yes Figure 1 Schematic diagram of the process of step S30;

[0057] Figure 7 yes Figure 1Flow diagram of step S40;

[0058] Figure 8 This is a schematic diagram of the change in the operating point of a direct-drive fan after inertia control is added in the overspeed and load reduction standby state. DETAILED DESCRIPTION

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0060] See also Figure 1 The embodiment of the present invention provides a capacitor and rotor coordinated direct-drive wind turbine inertia support stability control method, including steps S10 to S40:

[0061] Step S10, obtaining the operating data of the direct-drive wind turbine in real time, performing zero d-axis current control on the machine-side converter according to the operating data, obtaining the outer loop control of the machine-side converter, and performing overspeed load reduction standby on the direct-drive wind turbine.

[0062] The following combination Figure 2 , the control process of the embodiment of the present invention is described in detail. The direct-drive wind turbine PMSG is composed of a permanent magnet generator and a back-to-back converter. The traditional PMSG machine-side converter adopts maximum power point tracking MPPT control to ensure real-time tracking of the wind turbine output. The grid-side converter obtains the grid frequency and phase through the phase-locked loop PLL to maintain DC voltage stability and reactive power stability. At this time, the outer loop control of the traditional PMSG machine-side converter can be achieved through the following method: Figure 3 The steps shown result in:

[0063] Step S101, obtaining the three-phase current value and the three-phase voltage value output by the direct-drive wind turbine in real time;

[0064] Step S102, obtaining the wind turbine electrical angular velocity and wind turbine phase of the generator-side converter through an encoder, and performing Park transformation on the three-phase current value to obtain the actual value of the dq axis current of the generator-side converter;

[0065] Step S103, using zero d-axis current control on the generator-side converter to track the maximum power of the direct-drive wind turbine to obtain outer loop control of the generator-side converter;

[0066] Step S104 , performing overspeed load reduction standby on the direct-drive wind turbine to obtain a set active power value after load reduction that is input into the outer loop control.

[0067] After obtaining the three-phase current and three-phase voltage values ​​output by the direct-drive wind turbine in real time, the wind turbine electrical angular velocity ω can be obtained through the encoder for the machine-side converter. s and fan phase θ s , and perform Park transformation on the three-phase current value of the fan:

[0068]

[0069] Where i sd and i sq are the actual values ​​of the d-axis current and q-axis current of the generator-side converter, ω s is the wind turbine electrical angular velocity, θ s is the fan phase, i sa 、i sb 、i sc is the three-phase current value.

[0070] Then, zero d-axis control is used to track the maximum power, so that the expression of the outer loop control can be obtained:

[0071]

[0072] Where, and are the given values ​​of d-axis current and q-axis current of the generator-side converter, respectively, and k psq and k isq is the PI control parameter, P opt is the active power given value of the input outer loop control, P s is the output power of the direct-drive wind turbine calculated by the three-phase current and three-phase voltage values.

[0073] Under normal operating conditions, the active power reference value input to the outer loop is:

[0074]

[0075] Where k opt is the power tracking coefficient, ω r is the direct drive fan speed.

[0076] However, this traditional PMSG control strategy will cause the wind turbine to be unable to respond to the decrease in grid frequency with inertia, which is manifested as the wind turbine's inertia being hidden. In order to overcome this low inertia problem caused by the large-scale access of new energy, we first perform overspeed load reduction on the direct-drive wind turbine. Overspeed load reduction will cause the wind turbine operating point to deviate from the optimal power operating point, but at this time the rotor has greater kinetic energy, and when the wind turbine is inertial support, the wind turbine speed decreases, causing it to generate more power. At this time, the active power set value after load reduction can be obtained as:

[0077]

[0078] Where, P del is the given value of active power after load reduction, d% is the load reduction coefficient, k opt is the power tracking coefficient, ω r is the direct drive fan speed.

[0079] Step S20 , performing grid-type DC voltage frequency droop control and reactive power error control on the grid-side converter.

[0080] See also Figure 4 In the grid-side structure, for the phase control part of the grid-side converter, the present invention adopts a grid-type DC voltage frequency droop control, and its expression is:

[0081]

[0082] Where, k is the frequency per unit value obtained by DC voltage frequency droop control, dc is the droop coefficient, u dc is the DC voltage of the input grid-side converter, is the DC voltage reference value, is the base value of the angular velocity at the net side, ω g The angular velocity is obtained for the machine side control, θ g Get the phase for machine side control, is the per-unit value of the grid frequency.

[0083] For the amplitude control part of the grid-side converter, reactive power error control is adopted, and its expression is:

[0084]

[0085] Where u g is the modulation amplitude of the network control voltage, k up and k ui is the PI control parameter, and Q g They are the reference value and actual value of reactive power output by the grid-side converter respectively.

[0086] Step S30 , adding inertia control to the outer loop control, and adding damping stabilization control to the inertia control, to obtain outer loop control corrected by the damping stabilization control and the inertia control.

[0087] See also Figure 5 and Figure 6 The present invention adds an inertia control link and damping stability control on the machine side. The specific steps are as follows:

[0088] Step S301, low-pass filtering the DC voltage input for inertia control, taking its derivative and adding a coefficient link to obtain a given value of active power after the inertia control;

[0089] Step S302, adding damping stabilization control to the inertia control to obtain a power reference value corrected by the damping stabilization control and the inertia control;

[0090] Step S303 , obtaining an outer loop control after the corrections of the damping stabilization control and the inertia control according to the power reference value after the corrections of the damping stabilization control and the inertia control.

[0091] In order to cooperate with the grid-side control strategy, the present invention adds an inertia control link on the generator side. The DC voltage is first low-pass filtered, then differentiated and passed through the coefficient link. The specific expression is:

[0092]

[0093] Where k H is the equivalent inertia coefficient, P H It is the given value of active power after inertia control.

[0094] At this time, the overall equivalent inertia of the fan H PMSG for:

[0095]

[0096] Where S N is the rated power of the fan, C is the DC capacitor value, u dc0 is the steady-state value of DC voltage.

[0097] According to the above expression, it can be seen that after inertia control, the stored kinetic energy of the fan rotor can also respond to frequency changes, and its inertia is no longer hidden. In the above-mentioned network control strategy, due to the lack of a damping link, it is easy to cause oscillation and instability of the fan. Therefore, the present invention adds a damping stabilization control link on the machine side. At this time, the active power reference value of the outer loop on the machine side is superimposed with a damping signal, and its expression is:

[0098]

[0099] Where k D is the damping coefficient, P H is the active power given value after inertia control, u dc is the DC voltage for input inertia control, is the DC voltage reference value, P * It is the power reference value after correction by damping stability control and inertia control.

[0100] Through the above-mentioned inertia control and damping stability control, the outer loop control is corrected, thereby obtaining the outer loop control after inertia control and damping stability control correction. Its expression relationship is corrected to:

[0101]

[0102] It can be clearly seen that the present invention is to add the fan overspeed load reduction standby, inertia control and damping stability control to the original outer loop control P opt Convert to P del 、P H and P * , thus obtaining the above-mentioned corrected outer loop control expression.

[0103] Step S40, based on the DC voltage input to the inertia control and a preset threshold, calculate the difference between the DC voltage and the threshold, and coordinately control the capacitor inertia response and the fan rotor inertia response based on the difference to obtain a final signal expression relationship input to the inertia control.

[0104] See also Figure 7 In the present invention, the steps of coordinating the capacitor inertia response and the fan rotor inertia response include:

[0105] Step S401, deriving the DC voltage input to the inertia control to obtain a DC voltage derivative, and adding a dead zone component to the rate of change of the DC voltage;

[0106] Step S402, determining whether the difference between the DC voltage derivative and the threshold is greater than zero; if so, not adding the inertia control to the outer loop control, maintaining the direct-drive fan in an overspeed load reduction standby state, and using the direct-drive fan capacitor for inertia response;

[0107] Step S403: If not, then add the inertia control to the outer loop control, and use the direct-drive fan capacitor and the direct-drive fan rotor to perform inertia response.

[0108] Since the grid-side converter adopts DC voltage frequency droop control, the frequency is directly related to the DC voltage, and the change in frequency will be directly reflected in the DC voltage. In order to prevent the wind turbine output from constantly changing due to real-time response to frequency changes, we have added a dead zone link to the input DC voltage change rate to ensure stable operation of the wind turbine.

[0109] Since the DC voltage derivative is proportional to the grid voltage frequency derivative, we set a critical value du for rotor inertia control. dcrefAs the threshold, the input DC voltage is directly derived. When the DC voltage derivative is greater than the threshold, it is considered that the grid frequency is decreasing slowly, and the rotor inertia control is not activated. The fan still maintains the overspeed load reduction standby state. The fan inertia does not participate in the support, and only the electric energy stored in the DC side capacitor is used for inertia response. When the DC voltage derivative is less than the threshold, it is considered that the grid frequency is decreasing quickly, and the inertia control of the fan rotor needs to be activated, and the electric energy stored in the DC side capacitor and the kinetic energy stored in the fan rotor are used for inertia response.

[0110] On the other hand, if the rotor inertia control signal suddenly changes when the DC voltage derivative is less than the threshold, the wind turbine's output power will increase significantly instantaneously. At this time, the grid-side converter output has not yet responded, ultimately causing energy to accumulate on the DC side and increasing the DC voltage. At this point, the DC voltage derivative is positive and greater than the threshold, again causing the rotor inertia input signal to fall into the dead zone. The rotor inertia no longer responds to frequency reductions, affecting overall control effectiveness. Therefore, the DC voltage derivative input for inertia control must be continuous. Therefore, when the DC voltage derivative meets the input conditions, the threshold is subtracted to ensure that the input increases continuously from 0, preventing sudden changes in power output.

[0111] Therefore, after comprehensive processing of the above situations, the final input inertia control signal expression can be obtained:

[0112]

[0113] Where, is the DC voltage derivative reference value for input inertia control, du dcref is the threshold, is the DC voltage derivative.

[0114] See also Figure 8 The figure shows the change in the operating point of the wind turbine after inertia control is added in the overspeed load reduction standby state. Under the overspeed load reduction standby control, when the grid frequency does not change suddenly and no inertia support is performed, the wind turbine operates at position 1 in the figure. When the grid frequency decreases, but the rotor does not need to participate in inertia support, the wind turbine still operates at position 1; when the grid frequency decreases and the rotor needs to participate in inertia support, the wind turbine will generate an additional power of ΔP according to the inertia control and will operate at position 2. If the rotor continues to participate in support and continuously releases kinetic energy, the speed will decrease and eventually stabilize at position 3. Compared with the load-reduced position 1, the output of the wind turbine increases when it is in position 3, and it can maintain stable operation at position 3 with the output balance. If overspeed standby is not adopted, the wind turbine will operate at the traditional maximum power tracking P opt When the fan is running, the increased output will directly slow down the fan, and the fan output will also decrease. If the fan cannot return to the maximum power in time, the fan will continue to slow down until it stops rotating. opt, overspeed load reduction P del It enables the fan to reach a stable point of operation after a sudden change in output. In addition, overspeed reduction increases the fan speed, making it possible to store more kinetic energy for inertia response.

[0115] In summary, an embodiment of the present invention proposes a capacitor and rotor coordinated inertia support stabilization control method for a direct-drive wind turbine. The method obtains the operating data of the direct-drive wind turbine in real time, and uses zero d-axis current control on the machine-side converter according to the operating data to obtain the outer loop control of the machine-side converter, and performs overspeed load reduction standby on the direct-drive wind turbine; uses grid-type DC voltage frequency droop control and reactive power error control on the grid-side converter; adds inertia control to the outer loop control, and adds damping stabilization control to the inertia control to obtain the outer loop control corrected by the damping stabilization control and the inertia control; calculates the difference between the DC voltage and the threshold value based on the DC voltage input to the inertia control and a preset threshold value, and coordinates the capacitor inertia response and the wind turbine rotor inertia response based on the difference to obtain the signal expression relationship finally input to the inertia control. The control method of the present invention effectively coordinates capacitor electrical energy and wind turbine rotor kinetic energy for inertia support. When the grid frequency drop is not severe, only capacitor stored energy is used for inertia response. When the grid frequency drop is severe, inertia control is added, utilizing both capacitor and rotor stored energy for inertia response. As the frequency drop rate increases, the rotor's participation in inertia support increases. The present invention also improves the stability of the DC voltage frequency droop control strategy by introducing a novel damping control on the rotor side. Furthermore, overspeed load shedding control is added to increase the wind turbine's energy available for inertia response.

[0116] Each embodiment in this specification is described in a progressive manner. The same or similar parts of each embodiment can be directly referenced to each other. Each embodiment focuses on the differences from other embodiments. It should be noted that the technical features of the above embodiments can be combined in any way. To keep the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0117] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. A capacitor and rotor coordinated inertia support stabilization control method for a direct-drive wind turbine, characterized in that: include: Acquire operating data of the direct-drive wind turbine in real time, perform zero d-axis current control on the machine-side converter based on the operating data, obtain outer loop control of the machine-side converter, and perform overspeed load shedding standby on the direct-drive wind turbine; Perform grid-type DC voltage frequency droop control and reactive power error control on the grid-side converter; Adding inertia control to the outer loop control, and adding damping stabilization control to the inertia control, to obtain an outer loop control corrected by the damping stabilization control and the inertia control; Calculating a difference between a DC voltage input to the inertia control and a preset threshold value, and coordinating control of a capacitor inertia response and a fan rotor inertia response based on the difference to obtain a final signal expression relationship input to the inertia control; The final input signal expression relationship of the inertia control is calculated using the following formula: Where, is the DC voltage derivative reference value for input inertia control, du dcref is the threshold, is the DC voltage derivative.

2. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 1 is characterized in that: The steps of acquiring the operating data of the direct-drive wind turbine in real time, controlling the machine-side converter using zero d-axis current according to the operating data to obtain the outer loop control of the machine-side converter, and performing overspeed load shedding standby on the direct-drive wind turbine include: Obtain the three-phase current and three-phase voltage output of the direct-drive wind turbine in real time; Obtain the wind turbine electrical angular velocity and wind turbine phase of the machine-side converter through an encoder, and perform Park transformation on the three-phase current value to obtain the actual value of the dq axis current of the machine-side converter; Using zero d-axis current control on the generator-side converter to track the maximum power of the direct-drive wind turbine to obtain outer loop control of the generator-side converter; The direct-drive wind turbine is subjected to overspeed load reduction standby to obtain a given active power value after load reduction that is input into the outer loop control.

3. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 2, characterized in that: The Parker transform is calculated using the following formula: Where i sd and i sq are the actual values ​​of the d-axis current and q-axis current of the generator-side converter, ω s is the electrical angular velocity of the wind turbine, θ s is the fan phase, i sa 、i sb 、i sc is the three-phase current value; The outer loop control is calculated using the following formula: Where, and are the given values ​​of d-axis current and q-axis current of the generator-side converter, respectively, and k psq and k isq is the PI control parameter, P opt is the active power given value of the input outer loop control, P s is the output power of the direct-drive wind turbine calculated by the three-phase current and three-phase voltage values; The following formula is used to calculate the active power setpoint after load shedding: Where, P del is the given value of active power after load reduction, d% is the load reduction coefficient, k opt is the power tracking coefficient, ω r is the direct drive fan speed.

4. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 3 is characterized in that: The steps of using a grid-type DC voltage frequency droop control and reactive power error control on the grid-side converter include: Using grid-type DC voltage frequency droop control for the phase of the grid-side converter; Reactive power error control is used for the amplitude of the grid-side converter.

5. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 4, characterized in that: The DC voltage frequency droop control is expressed by the following formula: Where, k is the frequency per unit value obtained by DC voltage frequency droop control, dc is the droop coefficient, u dc is the DC voltage of the input grid-side converter, is the DC voltage reference value, is the base value of the angular velocity at the net side, ω g The angular velocity is obtained for the machine side control, θ g Get the phase for machine side control, is the per-unit value of the grid frequency; The reactive power error control is expressed by the following formula: Where u g is the modulation amplitude of the network control voltage, k up and k ui is the PI control parameter, and Q g They are the reference value and actual value of reactive power output by the grid-side converter respectively.

6. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 5, characterized in that: The step of adding inertia control to the outer loop control and adding damping stabilization control to the inertia control to obtain the outer loop control corrected by the damping stabilization control and the inertia control comprises: Low-pass filtering is performed on the DC voltage of the input inertia control, and a coefficient link is added after the derivative is taken to obtain a given value of the active power after the inertia control; adding damping stabilization control to the inertia control to obtain a power reference value corrected by the damping stabilization control and the inertia control; An outer loop control corrected by the damping stabilization control and the inertia control is obtained according to the power reference value corrected by the damping stabilization control and the inertia control.

7. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 6, characterized in that: The power reference value corrected by the damping stabilization control and the inertia control is calculated using the following formula: Where k D is the damping coefficient, P H is the active power given value after inertia control, u dc is the DC voltage for input inertia control, is the DC voltage reference value, P * is the power reference value after correction by damping stability control and inertia control; The outer loop control after the damping stabilization control and the inertia control correction is calculated using the following formula:

8. The capacitor and rotor coordinated direct drive wind turbine inertia support stabilization control method according to claim 1, characterized in that: The step of calculating the difference between the DC voltage and the threshold value based on the DC voltage input to the inertia control and the preset threshold value, and coordinating the control of the capacitor inertia response and the fan rotor inertia response based on the difference comprises: Derivative the DC voltage input to the inertia control to obtain a DC voltage derivative, and add a dead zone component to the rate of change of the DC voltage; determining whether a difference between the DC voltage derivative and a threshold is greater than zero; if so, not adding the inertia control to the outer loop control, maintaining the direct-drive fan in an overspeed load reduction standby state, and using the direct-drive fan capacitor for inertia response; If not, the inertia control is added to the outer loop control, and the direct-drive fan capacitor and the direct-drive fan rotor are used for inertia response.

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