An Emergency Power Control Method for Doubly Fed Induction Generator Wind Turbines Based on Fault Transient Energy

Abstract

The present invention provides an emergency power control method for a doubly-fed wind turbine based on fault transient energy; the method includes starting control at the moment of grid fault removal; measuring the rotational speed at the moment of grid fault removal, and calculating a fault transient energy control reference value; calculating the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine during the grid fault; calculating the emergency power control exit moment and implementing control according to the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine and the fault transient energy control reference value. The present invention fully excavates and utilizes the transient energy stored in the doubly-fed wind turbine, can provide stable emergency power support for the power grid, accelerate the speed recovery, relieve the short-time power impact at the moment of fault removal, and enhance the transient frequency support ability of the power system containing doubly-fed wind turbines.

Description

Technical Field

[0001] The present invention relates to the field of power system protection and control, and particularly to an emergency power control method for doubly-fed wind turbines. Background Art

[0002] With the intensification of the energy crisis, the development of new energy has shown an accelerating trend. As the main force of new energy, the installed capacity of wind power has been continuously increasing. While the wind power penetration rate has increased, the proportion of synchronous machine power sources has been continuously decreasing, resulting in a continuous decline in the anti-disturbance ability of the power system. Especially under grid faults, the rapid response of wind power makes the grid transient process more complex, posing higher requirements for the emergency control of the grid. However, the power regulation speed of synchronous machines is relatively slow, and it is difficult to provide effective emergency power support after a fault. Although wind turbines have fast power control capabilities, due to the adoption of maximum power tracking control, wind turbines cannot participate in grid emergency power control by increasing power generation. The lack of emergency power control capabilities has made the stability problem under power system faults increasingly prominent.

[0003] Doubly-fed wind turbines are one of the mainstream models in current wind power generation, with the advantages of high controllability, high wind energy utilization rate, and strong reliability. The scheme of providing support for the power grid by regulating the active power of doubly-fed wind turbines has received attention. Virtual synchronous machine control can simulate the electromechanical characteristics of synchronous generators, enabling the active power of doubly-fed wind turbines to change with the change of the target virtual quantity. There are mainly three types of virtual synchronous machine control: virtual inertia control based on the synchronous machine motion equation, improved MPPT curve control based on multi-stage switching, and inertia support control based on DC voltage. Virtual inertia control is the most widely used VSG control. Researchers have proposed a method for setting the virtual inertia coordination control parameters of wind farms. There is also a study that proposed a new type of non-linear virtual inertia controller based on the target holographic feedback theory and Brunovsky-type completely controllable systems. The target virtual quantity of virtual synchronous machine control is mainly the rate of change of frequency and frequency deviation. Therefore, virtual synchronous machine control is mainly used to solve the frequency modulation problem under small disturbance conditions such as power output fluctuations or load mutations. The applicability of virtual synchronous machine control for doubly-fed wind turbines under grid faults still needs to be further verified.

[0004] Under grid faults, using doubly-fed induction generators (DFIGs) to provide reactive power support for the power grid is a current research hotspot. Researchers have proposed a maximum fault voltage control method for DFIGs considering the impact of source-grid coupling. There are also studies that have proposed a new type of online dynamic coordination control strategy to improve the reactive power capacity of DFIG wind farms. There is relatively little research on using DFIGs to provide active power support for the power grid. Some studies have proposed an emergency control method for wind power clusters based on model predictive control using ultra-short-term wind power prediction. However, the wind speed fluctuation range is not large in a short period, and even if the wind speed is accurately predicted, it is impossible to significantly improve the power output of wind turbines. Some studies have proposed an optimal energy storage allocation strategy to improve the emergency power support ability of DFIG wind farms. However, the cost of energy storage is high, and it is difficult to fully match the installed capacity of wind power. Wind power participating in grid emergency power control still faces the problem of insufficient upward power regulation.

[0005] In order to enable DFIGs to have the ability to increase power, researchers have proposed the idea of power reserve. By accelerating the rotor to make the DFIG operate at a non-maximum power point or by changing the pitch angle to reduce the input mechanical power of the DFIG, the DFIG can increase its active power output when the power grid needs it. The overspeed load shedding control has a fast response time, but the adjustment range is limited. The pitch angle control has the advantage of a wide adjustment range. Therefore, the two often participate in the grid emergency power control together. The power reserve control improves the emergency power control ability of DFIGs. However, overspeed operation sacrifices the operating economy of the wind farm, pitch angle control causes mechanical wear, and the adjustment speed is slow. The engineering practicability of existing methods still needs to be improved.

[0006] During grid faults, the output power of DFIGs decreases or fluctuates, resulting in an imbalance between mechanical power and electromagnetic power. The unbalanced power causes the rotor to accelerate. As the speed increases, transient energy is continuously accumulated in the rotor kinetic energy. However, when the grid fault is removed, the change in electromagnetic power causes the transient energy to dissipate. The transient energy stored during the fault cannot be used to support the power grid. Since the transient energy is consumed as the speed recovers and the speed recovery is slow, the consumption of transient energy after the fault will also cause the power of DFIGs to recover slowly, which is not conducive to the stable operation of the power grid.

[0007] In summary, considering the full utilization of the transient energy of DFIGs under grid faults, fully exploring the emergency power control ability of DFIGs under grid faults, providing stable emergency power support for the power grid, and at the same time accelerating the rapid recovery rate of the speed after grid faults and suppressing the short-term power impact at the moment of fault removal are urgent problems that need to be solved by those skilled in the art. Summary of the Invention

[0008] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides an emergency power control method for doubly-fed wind turbine generators using transient energy, which can solve the problem of insufficient emergency power control ability of doubly-fed wind turbine generators in the existing technologies, make full use of the transient energy stored in the rotor of the doubly-fed wind turbine generator during the power grid fault, control the doubly-fed wind turbine generator after the power grid fault is removed, provide stable emergency power support for the power system, accelerate the speed recovery, relieve the short-time power impact at the moment of fault removal, and improve the emergency power support ability of the doubly-fed wind turbine generator under fault conditions.

[0009] To solve the above technical problems, the technical solution of the present invention is as follows:

[0010] An emergency power control method for doubly-fed wind turbine generators based on fault transient energy, comprising the following steps:

[0011] S101. After a power grid fault occurs, the terminal voltage U of the doubly-fed wind turbine generator is collected in real time pcc . When the terminal voltage returns to the preset range, it is determined that the power grid fault is removed, and the emergency power control is started, and step S102 is executed;

[0012] S102. Measure the speed at the moment when the power grid fault is removed, and calculate the control reference value of the fault transient energy of the doubly-fed wind turbine generator;

[0013] S103. Calculate the maximum fault transient energy accumulated in the rotor of the doubly-fed wind turbine generator during the power grid fault;

[0014] S104. According to the maximum fault transient energy accumulated in the rotor of the doubly-fed wind turbine generator and the control reference value of the fault transient energy, calculate the exit moment of the emergency power control of the doubly-fed wind turbine generator;

[0015] S105. Set the active power control reference value of the doubly-fed wind turbine generator to the control reference value of the fault transient energy, and continue until the exit moment of the emergency power control, and then reset the active power control reference value of the doubly-fed wind turbine generator to the active power control reference value before the power grid fault occurs.

[0016] The present invention provides an emergency power control method for doubly-fed wind turbine generators based on fault transient energy, which makes full use of the transient energy stored in the rotor of the doubly-fed wind turbine generator during the power grid fault, controls the doubly-fed wind turbine generator after the power grid fault, provides stable emergency power support for the power system, accelerates the speed recovery, relieves the short-time power impact at the moment of fault removal, and improves the emergency power support ability of the doubly-fed wind turbine generator under power grid faults. Compared with the existing technologies, the present invention has the following beneficial effects:

[0017] 1. The existing emergency power control technology for doubly-fed wind turbines mainly realizes power reserve control through overspeed load shedding control or pitch angle control. However, overspeed load shedding control reduces the economic efficiency of the wind turbine operation and has a limited adjustment range; pitch angle control has a slow response time and is accompanied by certain mechanical wear, and the dissipation of transient energy after fault removal leads to a slow recovery speed of the rotational speed and active power. The present invention adopts a principle different from the existing technology and utilizes the transient energy stored in the rotor of the doubly-fed wind turbine during the power grid fault. It can not only short-term improve the output power of the doubly-fed wind turbine to provide support for the power system, but also accelerate the rotational speed recovery rate of the doubly-fed wind turbine, effectively alleviating the short-term power impact at the moment of power grid fault removal.

[0018] 2. The existing technology adopts virtual synchronous machine control to enable the doubly-fed wind turbine to participate in the active power regulation of the system. However, due to the change of the target virtual quantity, the active power of the doubly-fed wind turbine changes, making it difficult to provide stable emergency power support after the power system fault. The present invention modifies the power control reference value of the rotor side converter and keeps it constant at the moment of fault removal, actively releasing the transient energy stored in the doubly-fed wind turbine during the fault, and can provide stable power support for the power system for a certain period of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the objectives, technical solutions and advantages of the invention clearer, the present invention will be further described in detail below with reference to the drawings, where:

[0020] Figure 1 is the flow chart of the emergency power control method for the doubly-fed wind turbine using transient energy in the embodiment of the present invention;

[0021] Figure 2 is the flow chart of the emergency power control method for the doubly-fed wind turbine using transient energy in the preferred embodiment of the present invention;

[0022] Figure 3 is the grid connection example diagram of the doubly-fed wind turbine in the embodiment of the present invention;

[0023] Figure 4 is the effect diagram under the embodiment of the present invention, Figure 4 (a) is the power of the doubly-fed wind turbine under the three-phase short-circuit fault, Figure 4 (b) is the rotational speed waveform diagram of the doubly-fed wind turbine under the three-phase short-circuit fault. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] As Figure 1 shown, the present invention discloses an emergency power control method for a doubly-fed wind turbine using fault transient energy, including the following steps:

[0026] S101. After a power grid fault occurs, the terminal voltage U pcc of the doubly-fed wind turbine is collected in real time. When the terminal voltage recovers to the preset range, it is determined that the power grid fault is removed, and the emergency power control is started, and step S102 is executed;

[0027] S102. Measure the rotational speed at the moment when the power grid fault is removed, and calculate the fault transient energy control reference value of the doubly-fed wind turbine;

[0028] S103. Calculate the maximum fault transient energy accumulated in the rotor of the doubly-fed wind turbine during the power grid fault;

[0029] S104. According to the maximum fault transient energy accumulated in the rotor of the doubly-fed wind turbine and the fault transient energy control reference value, calculate the emergency power control exit moment of the doubly-fed wind turbine;

[0030] S105. Set the fault transient energy control reference value as the active power control reference value of the doubly-fed wind turbine and continue until the emergency power control exit moment.

[0031] Specifically, in step S101, the preset range of the terminal voltage is set to 0.95 p.u. to 1.05 p.u. Once it is found that the collected terminal voltage of the doubly-fed wind turbine exceeds the preset range of 0.95 p.u. to 1.05 p.u., that is, 0.95 p.u. ≤ U pcc ≤ 1.05 p.u., it is determined that the power grid fault is removed, and the emergency power control is started, and step S102 is executed.

[0032] It can be understood that the preset range of 0.95 p.u. to 1.05 p.u. is a generally recognized preset range by those skilled in the art. In some extreme cases, the preset range may be appropriately adjusted according to the knowledge of those skilled in the art. The present invention does not make specific limitations on this.

[0033] Specifically, in step S102, the fault transient energy control reference value of the doubly-fed wind turbine is calculated according to the following method:

[0034]

[0035] In the formula, ρ is the air density; R is the radius of the wind turbine; C pmax is the maximum wind energy utilization coefficient; λ opt is the optimal tip speed ratio; ω rf_reval is the rotational speed at the moment when the power grid fault is cleared.

[0036] In specific implementation, in step S103, the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine during the power grid fault is calculated as follows:

[0037]

[0038] In the formula, p is the number of pole pairs of the doubly-fed wind turbine; J is the moment of inertia of the doubly-fed wind turbine; ω rm is the maximum rotational speed after the fault is cleared; ω0 is the rotational speed before the fault occurs.

[0039] In specific implementation, the maximum rotational speed ω rm after the fault is cleared is determined according to the following steps:

[0040] S401. Denote the moment when the power grid fault is cleared as the initial moment t (0) , and the rotational speed at the moment when the power grid fault is cleared is the approximate rotational speed ω (0) at the initial moment t rf(0) . Let k = 1 and start the calculation;

[0041] S402. According to the approximate rotational speed ω (k-1) at the moment t rf(k-1) , calculate the predicted rotational speed at the moment t (k) :

[0042] S403. According to the predicted rotational speed at the moment t (k) : calculate the approximate rotational speed ω (k) at the moment t rf(k) ;

[0043] S404. According to the approximate rotational speed ω (k) at the moment t rf(k) , calculate the predicted rotational speed at the moment t (k+1) :

[0044] S405. According to the predicted rotational speed at the moment t (k+1) : calculate the approximate rotational speed ω (k+1) at the moment t rf(k+1) ;

[0045] S406. If t (k)The approximate rotational speed at a moment is greater than the approximate rotational speeds ω (k-1) and ω (k+1) at the two adjacent moments t rf(k-1) and t rf(k+1) before and after it. Then, let the approximate rotational speed ω (k) at the moment t rf(k) be the maximum rotational speed; otherwise, let k = k + 1, and return to step S404.

[0046] In specific implementation, in step S402, the predicted rotational speed at the k-th moment is determined as follows:

[0047]

[0048] where k = 1, 2…N; N represents the number of moments, and N is a positive integer; is the predicted rotational speed at the k-th moment; ω rf(k-1) is the approximate rotational speed at the (k - 1)-th moment; h is the sampling interval; F[t (k-1) , ω rf(k-1) is the rotational speed-time coupling function, and t (k-1) represents the (k - 1)-th moment.

[0049] In specific implementation, the rotational speed-time coupling function is determined as follows:

[0050]

[0051] where P m0 is the input mechanical power; H is the inertia time constant; k ip is the inner-loop proportional coefficient of the rotor-side PI controller; U s0 is the stator voltage amplitude before the fault; U sf is the stator voltage amplitude after the fault; ω s is the synchronous angular velocity; L s is the stator inductance of the doubly-fed wind turbine generator set; is the reference value of the stator reactive power. τ s = R s / σL s is the stator winding decay time constant; R s is the stator resistance of the doubly-fed wind turbine generator set; L r , L m are the rotor inductance and the excitation inductance of the doubly-fed wind turbine generator set respectively; is the leakage magnetic coefficient; t2 is the grid fault clearing time.

[0052] In specific implementation, the parameter K2 is determined as follows:

[0053]

[0054] In specific implementation, the parameter K3 is determined according to the following method:

[0055]

[0056] In the formula, τ r =R r / σL r is the rotor winding decay time constant, and R r is the rotor resistance of the doubly-fed wind turbine; τ p =k ip / σL r , τ i =k ii / σL r , k ii is the inner-loop integral coefficient of the rotor-side PI controller.

[0057] In specific implementation, the parameter f4(t) is determined according to the following method:

[0058] f4(t)=k ip U s0 cosω s (t - t2)-sinω s (t - t2)

[0059] In specific implementation, the parameter f5(t) is determined according to the following method:

[0060]

[0061] In specific implementation, in step S403, the approximate speed at time k is determined according to the following method:

[0062]

[0063] In specific implementation, in step S404, the output condition is determined according to the following method:

[0064] ω rf(k) >ω rf(k-1) and ω rf(k) >ω rf(k+1)

[0065] In specific implementation, the relevant calculation formulas involved in step S404 and step S405 are the same as those in step S402 and step S403, except that the calculation times are slightly different. Those skilled in the art can complete the relevant calculations of step S404 and step S405 according to step S402 and step S403, and the present invention will not elaborate on this.

[0066] In specific implementation, in step S104, the emergency power control exit time of the doubly-fed wind turbine is calculated according to the following method:

[0067]

[0068] where t2 is the grid fault clearing time; W km is the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine during the grid fault; is the reference value of the fault transient energy control of the doubly-fed wind turbine.

[0069] In a preferred embodiment of the present invention, as Figure 2 shown, the present invention discloses an emergency power control method for a doubly-fed wind turbine using fault transient energy, including the following steps:

[0070] S101. After a grid fault occurs, the terminal voltage U of the doubly-fed wind turbine is collected in real time pcc . When the terminal voltage returns to the preset range, it is determined that the grid fault is cleared, and the emergency power control is started, and step S102 is executed;

[0071] S102. Measure the rotational speed at the grid fault clearing time, and calculate the reference value of the fault transient energy control of the doubly-fed wind turbine;

[0072] S103. Calculate the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine during the grid fault;

[0073] S104. According to the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine and the reference value of the fault transient energy control, calculate the emergency power control exit time of the doubly-fed wind turbine;

[0074] S105. Set the reference value of the fault transient energy control as the reference value of the active power control of the doubly-fed wind turbine, and continue until the emergency power control exit time;

[0075] S106. Reset the reference value of the active power control of the doubly-fed wind turbine to the reference value of the active power control before the grid fault occurs.

[0076] The difference from the above embodiment is that this embodiment also provides the relevant process after the fault recovery, that is, after the emergency power control exit time, the reference value of the active power control before the grid fault occurs is assigned to the reference value of the active power control of the doubly-fed wind turbine, and the doubly-fed wind turbine continues to operate according to the reference value of the active power control before the fault, ensuring the normal operation of the doubly-fed wind turbine.

[0077] To verify the effectiveness of the method of the present invention, as Figure 3Taking the wiring diagram of the example system shown as an example for analysis. The rated capacity of the doubly-fed wind turbine is 1.5 MW, and the rated voltage is 575 V. The doubly-fed wind turbine is connected to the 220 kV AC power grid through a 20 km tie line after stepping up through a transformer. In this invention, a three-phase short-circuit fault occurs on the tie line of the doubly-fed wind turbine as the scenario to verify the speed recovery and power support effect of the doubly-fed wind turbine after the power grid fault is removed. The comparison group is the speed recovery and power recovery effect of the doubly-fed wind turbine without using emergency power control. Observe and analyze the speed recovery and power support effect of the doubly-fed wind turbine after the power grid fault is removed, and record and compare the speed and power waveforms of the doubly-fed wind turbine after the power grid fault is removed.

[0078] Figure 4 (a) and Figure 4 (b) are respectively the power and speed waveform diagrams of the doubly-fed wind turbine under a three-phase short-circuit fault. In the figure, the abscissa is time, and the ordinate is the per-unit value of the effective value of the access point voltage; the red dashed line is the change curve of power and speed when using emergency power control, and the blue solid line is the change curve of power and speed when not using emergency power control. The example shows that when using emergency power control, the active power output of the doubly-fed wind turbine during the emergency power control period is about 0.93 p.u. Compared with not using emergency power control, it effectively alleviates the power impact at the moment of power grid fault removal, and slows down the recovery of active power, providing a relatively stable power support for the system. After the emergency power control is started, the speed decelerates to 1.163 p.u. at a certain acceleration, and then gradually recovers to the initial speed. When not using emergency power control, the rotor slowly decelerates to the initial speed. The emergency power control accelerates the speed recovery and quickly releases the transient energy stored in the rotor, as Figure 4 shown. The method of this invention makes full use of the transient energy stored in the doubly-fed wind turbine during the power grid fault, improving the emergency power support ability of the power system under power grid faults.

[0079] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A double-fed wind turbine emergency power control method based on fault transient energy, characterized in that It includes the following steps: S101. After a power grid fault occurs, the terminal voltage U of the doubly-fed wind turbine is collected in real time pcc . When the terminal voltage returns to the preset range, it is determined that the power grid fault is removed, and the emergency power control is started to execute step S102; S102. Measure the rotational speed at the moment when the power grid fault is cleared, and calculate the fault transient energy control reference value of the doubly-fed wind turbine; S103. Calculate the maximum fault transient energy accumulated in the rotor of the doubly-fed wind turbine during the power grid fault; In step S103, the maximum fault transient energy accumulated in the rotor of the doubly-fed wind turbine during the power grid fault is calculated according to the following method: where p is the number of pole pairs of the doubly-fed wind turbine generator set; J is the moment of inertia of the doubly-fed wind turbine generator set; ω rm is the maximum speed after fault clearing; ω0 is the speed before the fault occurs; S104. Calculate the cut-off time of the emergency power control of the doubly-fed wind turbine according to the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine and the reference value of the fault transient energy control; the maximum speed ω after fault removal rm is determined according to the following steps: S401. Denote the power grid fault clearing time as the initial time \(t\). (0) The rotational speed at the power grid fault clearing time is the approximate rotational speed \(\omega\) at the initial time \(t\). (0) Let \(k = 1\) and start the calculation. rf(0) ​ S402. Calculate the estimated rotational speed at time t according to the approximate rotational speed ω at time t (k-1) at time t rf(k-1) and calculate the estimated rotational speed at time t (k) ​ S403. Calculate the approximate rotational speed ω at time t based on the estimated rotational speed at time t (k) at time t Calculate the approximate rotational speed ω at time t (k) at time t rf(k) ; S404. Calculate the estimated rotational speed at time t according to the approximate rotational speed ω at time t (k) at time t rf(k) and calculate the estimated rotational speed at time t (k+1) at time t S405. Calculate the approximate rotational speed ω at time t based on the estimated rotational speed at time t. (k+1) The estimated rotational speed at time t Calculate t (k+1) The approximate rotational speed ω at time t rf(k+1) ; S406. If the approximate rotational speed at time t (k) is greater than the approximate rotational speeds ω (k-1) and ω (k+1) at the two adjacent times t rf(k-1) and t rf(k+1) , then let the approximate rotational speed ω (k) at time t rf(k) be the maximum rotational speed; otherwise, let k = k + 1 and return to step S404; t (k) The estimated rotational speed at a moment is determined by the following method: where h is the sampling interval; F[t (k-1) , ω rf(k-1) is the rotational speed-time coupling function at time t (k-1) ; S105. Set the active power control reference value of the doubly-fed wind turbine to the fault transient energy control reference value and continue until the exit moment of the emergency power control.

2. The emergency power control method for a doubly-fed wind turbine based on fault transient energy according to claim 1, characterized in that In step S102, the fault transient energy control reference value of the doubly-fed wind turbine is calculated according to the following method: where ρ is the air density; R is the radius of the wind turbine; C pmax is the maximum wind energy utilization coefficient; λ opt is the optimal tip speed ratio; ω rf_reval is the rotor speed at the time of grid fault removal.

3. A method for emergency power control of a doubly-fed wind turbine based on fault transient energy according to claim 1, characterized in that t (k-1) The rotational speed-time coupling function at a moment is determined as follows: Wherein, P m0 is the input mechanical power; H is the inertia time constant; k ip is the proportional coefficient of the inner loop of the rotor side PI controller; U s0 is the stator voltage amplitude before the fault; U sf is the stator voltage amplitude after the fault; ω s is the synchronous angular velocity; L s is the stator inductance of the doubly-fed wind turbine generator set; is the reference value of the stator reactive power; τ s =R s / σL s is the stator winding decay time constant; R s is the stator resistance of the doubly-fed wind turbine generator set; L r , L m are respectively the rotor inductance and the excitation inductance of the doubly-fed wind turbine generator set; is the leakage magnetic coefficient; t2 is the grid fault clearing time; The parameter K2 is determined according to the following method: The parameter K3 is determined according to the following method: where τ r = R r / σL r is the decay time constant of the rotor winding, and R r is the rotor resistance of the doubly-fed wind turbine; τ p = k ip / σL r , τ i = k ii / σL r , and k ii is the inner-loop integral coefficient of the rotor-side PI controller. The parameter f4(t) is determined according to the following method: f4(t) = k ip U s0 cosω s (t - t2) - sinω s (t - t2) The parameter f5(t) is determined according to the following method:

4. A double-fed wind turbine emergency power control method based on fault transient energy according to claim 1, characterized in that, In the said step S403, the approximate rotational speed at the k-th moment is determined according to the following method: where h is the sampling interval; F[t (k-1) , ω rf(k-1) is the rotational speed-time coupling function at time t (k-1) ; is the rotational speed-time coupling function at time t (k) .

5. A dual-fed wind turbine emergency power control method based on fault transient energy according to claim 1, characterized in that In step S104, the exit moment of the emergency power control of the doubly-fed wind turbine is calculated according to the following method: where t2 is the grid fault clearing time; W km is the maximum fault transient energy stored in the rotor of the doubly-fed wind turbine during the grid fault; is the reference value for the fault transient energy control of the doubly-fed wind turbine.

6. A method for emergency power control of a doubly-fed wind turbine based on fault transient energy according to any one of claims 1 to 5, characterized in that After the said step S105, it further includes resetting the active power control reference value of the doubly-fed wind turbine to the active power control reference value before the power grid fault occurs.

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