Method for improving transient stability of wind farm phase modifier based on low penetration power segment recovery

Abstract

The application discloses a wind farm synchronous condenser transient stability improvement method based on low penetration power segment recovery, first, the frequency of the synchronous condenser terminal is measured in real time, the angular acceleration signal is calculated, and the wind farm grid-connected point voltage is measured, and the current stage of the system is judged according to the positive and negative signals; then, the wind turbine restores the active power output at different rates according to different stages of the system. Compared with the control strategy of the low penetration active constant rate ramp recovery of the wind turbine, the method can effectively improve the transient power angle stability of the wind farm synchronous condenser, and has important practical significance for guaranteeing the safe and stable operation of the power system.

Description

Technical Field

[0001] This invention belongs to the field of power systems, specifically the field of stability control of wind turbine grid-connected systems, and specifically relates to a method for improving the transient stability of wind farm synchronous condensers based on low power consumption segmented recovery. Background Technology

[0002] In my country, energy and load are inversely distributed. With the increasing proportion of wind farm output in the power grid, the large-scale, long-distance centralized transmission of wind farms from weak-end areas faces challenges related to voltage security. Synchronous condensers possess excellent instantaneous dynamic reactive power response characteristics and the ability to provide short-circuit capacity support. Deploying synchronous condensers at wind farm sites can improve voltage oscillations and transient overvoltages caused by low short-circuit ratios at the wind farm's sending end, significantly supporting grid strength and promoting wind farm absorption, effectively enhancing the wind farm's transmission limit. However, synchronous condensers installed at wind farm sites are affected by the wind farm and are at risk of accelerated power angle instability after a fault, hindering further improvements in clean energy transmission limits. Therefore, research on improving the transient power angle stability of large-scale wind farm transmission systems and enhancing the wind farm's output limit is of great significance.

[0003] Wind turbine low-voltage ride-through capability refers to the ability of a wind turbine to remain connected to the grid and not disconnect when the voltage at the grid connection point drops. This involves reducing active power output while providing some reactive power support to the grid, thus "riding through" the low-voltage period. After the fault is cleared, the wind turbine's active power typically recovers at a certain ramp rate. However, this traditional active power recovery control strategy does not consider the rotor dynamics of the synchronous condenser, which may adversely affect the power angle stability of the sending-end synchronous condenser, leading to new synchronization stability problems. This patent improves the wind turbine active power control strategy during the fault recovery phase based on the transient speed of the synchronous condenser and the feedback of the wind farm's grid connection voltage, thereby improving the transient power angle stability of the wind farm's synchronous condenser. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a method for improving the transient stability of wind farm synchronous condensers based on low power segmented recovery, and to solve the problem of transient power angle stability of synchronous condensers in large-scale wind farm grid-connected systems.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The method involves measuring or calculating the angular velocity and angular acceleration signals of the synchronous condenser, determining the current stage based on the sign of the frequency signal, and switching the control strategy accordingly. For a wind power grid-connected system containing a distributed synchronous condenser, the method disclosed in this invention includes the following steps:

[0007] ① Obtain the angular velocity ω, angular acceleration a, and grid-connected voltage parameters of the wind farm synchronous condenser;

[0008] ② Send the synchronous angular velocity and angular acceleration signals obtained in step ① into the outer loop of the wind turbine power. Based on the sign of the synchronous angular velocity and angular acceleration signals after the fault is cleared, determine the stage of the rotor swaying process and switch different active power recovery strategies for different stages.

[0009] 1) Phase 1

[0010] a) Criteria for division: Both the angular velocity and angular acceleration of the synchronous adjustment camera are positive;

[0011] b) Control Strategy: The active power of the wind turbine decreases at a rate corresponding to the angular acceleration of the synchronous condenser, and is limited to a specified range. The active power current of the wind turbine drops to a minimum at the maximum allowable unbalanced power of the wind turbine. The rate of change of the active power current of the wind turbine in the first stage is...

[0012]

[0013] In the formula, denoted as the rate of change of the active current of the wind turbine in the first stage; 'a' is the angular acceleration of the synchronous condenser; 'K1' is the adjustment coefficient, and 'K1 > 0'; 'pu' represents the per-unit value of the active current of the wind turbine.

[0014] 2) Phase 2

[0015] a) Criteria for division: The angular velocity of the synchronous adjustment camera is positive, and the angular acceleration is negative;

[0016] b) Control strategy: The active power of the wind turbine recovers according to the synchronous condenser's angular acceleration ramp. The rate of change of the active power current of the wind turbine in the second stage is:

[0017]

[0018] In the formula, The second stage active current change rate is defined as follows: Based on the new energy active current value under command control, a current correction command is added to generate the final second stage active current output command, i.e., I... p2 * =I p2 +u, where, I p2 * This is the second stage active current output command following the additional current correction command, I p2 For the rate of change of active current of the wind turbine in stage 2 Active current value of the fan under control;

[0019]

[0020] In the formula, u is the active current correction command of the wind turbine; ω is the measured value of the relative angular velocity between the synchronous condenser and the receiving end system; v is the per-unit value of the measured value of the grid-connected voltage of the wind turbine; K2, K3, K4 are adjustment coefficients, and K2, K3, K4 > 0;

[0021] 3) Phase 3

[0022] a) Criteria for division: The angular velocity of the synchronous modulator is negative;

[0023] b) Control strategy: The wind turbine's active power is restored immediately;

[0024] ③ Control Exit

[0025] Based on the active power restoration time requirements after wind farm fault clearance, a maximum restoration time is set, which is achieved when the conditions are met.

[0026] ω=0, a=0

[0027] Control will be deactivated if the control time exceeds the wind farm's active power recovery time limit.

[0028] Preferably, the maximum recovery time is set to 2 seconds.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention presents a method for improving the transient stability of synchronous condensers in wind farms based on segmented recovery with low power consumption. It divides the swaying phase of the synchronous condenser rotor dynamically and formulates active power control strategies for each phase. Compared to the traditional constant-rate ramp recovery strategy, this "segmented approach" weakens the negative damping effect of active current recovery during the condenser's acceleration phase and provides positive damping during the deceleration phase, thus facilitating the rapid decay of transient power imbalances to system stability. Real-time measurement of feedback signals during fault transients enables emergency control. Compared to traditional synchronous condenser transient power angle control strategies such as setting according to strategy tables or switching turbines and loads, this invention is more adaptable to different faults and operating scenarios and is less costly. In summary, this invention improves the transient power angle stability of synchronous condensers in wind farms, avoiding problems such as deteriorated power angle stability and frequency deficits caused by slow recovery that may result from traditional constant-rate ramp recovery control. Attached Figure Description

[0031] Figure 1 This is a flowchart of the method of the present invention.

[0032] Figure 2 This is a control structure diagram of the present invention.

[0033] Figure 3 This is a structural diagram of a wind farm with a synchronous condenser for power transmission.

[0034] Figure 4 This is a waveform diagram showing the change of active current in a wind farm over time under the existing constant rate slope recovery strategy and after applying the control strategy of this invention.

[0035] Figure 5 It is a waveform diagram showing the change of the camera's power angle over time under the existing constant rate slope recovery strategy and after applying the control strategy of this invention. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0037] like Figure 1 As shown, this invention is a method for improving the transient stability of a wind farm synchronous condenser based on low-power piecewise recovery, which mainly includes the following steps:

[0038] ① Obtain the angular velocity ω, angular acceleration a, and grid-connected voltage parameters of the wind farm synchronous condenser.

[0039] ②For example Figure 2 As shown, the synchronous condenser angular velocity and angular acceleration signals obtained in step ① are sent to the outer loop of the wind turbine power. Based on the sign of the synchronous condenser angular velocity and angular acceleration signals after the fault is cleared, the stage of the rotor swaying process is determined, and different active power recovery strategies are switched for different stages.

[0040] 1) Phase 1

[0041] a) Criteria for division: Both the angular velocity and angular acceleration of the synchronous modulator are positive.

[0042] b) Control Strategy: The active power of the wind turbine decreases at a rate corresponding to the angular acceleration of the synchronous condenser, and is limited to a specified range. The active power current of the wind turbine is reduced to a minimum of the maximum allowable unbalanced power of the wind turbine. The rate of change of the active power current of the wind turbine in the first stage is...

[0043]

[0044] In the formula, denoted as the rate of change of the active current of the wind turbine in the first stage; 'a' is the angular acceleration of the synchronous condenser; 'K1' is the adjustment coefficient, and 'K1 > 0'; 'pu' represents the per-unit value of the active current of the wind turbine.

[0045] 2) Phase 2

[0046] a) Criteria for division: The angular velocity of the synchronous adjustment camera is positive, and the angular acceleration is negative.

[0047] b) Control strategy: The active power of the wind turbine recovers according to the synchronous condenser's angular acceleration ramp. The rate of change of the active power current of the wind turbine in the second stage is:

[0048]

[0049] In the formula, The rate of change of the active current of the wind turbine in the second stage; based on the active current value of the wind turbine under command control, a current correction command is added to generate the final active current output command for the second stage, i.e., I. p2 * =I p2 +u, where, I p2 * This is the second stage active current output command following the additional current correction command, I p2 For the rate of change of active current of the wind turbine in stage 2 Active current value of the fan under control.

[0050]

[0051] In the formula, u is the active current correction command of the wind turbine; ω is the measured value of the relative angular velocity between the synchronous condenser and the receiving end system; v is the per-unit value of the measured value of the grid-connected voltage of the wind turbine; K2, K3, K4 are adjustment coefficients, and K2, K3, K4 > 0.

[0052] 3) Phase 3

[0053] a) Criteria for division: The angular velocity of the synchronous modulator is negative.

[0054] b) Control strategy: The active power of the wind turbine should be restored as quickly as possible.

[0055] ③ Control Exit

[0056] Based on the active power restoration time requirements after wind farm fault clearance, the maximum restoration time is set to 2 seconds. When the conditions are met...

[0057] ω=0, a=0

[0058] Control will be deactivated if the control time exceeds the wind farm's active power recovery time limit.

[0059] Example:

[0060] The method of this invention is aimed at improving the transient power angle stability of synchronous condensers in wind farms.

[0061] To verify the correctness of the above analysis, a simulation platform was built as follows: Figure 3 The wind farm plus synchronous condenser power transmission system model shown was simulated and verified according to the following parameters:

[0062] The direct-drive wind turbine has an actual output of 500MW; the sending-end synchronous condenser has a capacity of 100MVA; the receiving end is an infinite power grid. Recovery rate commands: Stage 1 is -200% / s, Stage 2 is 200% / s, Stage 3 is 3200% / s; Active power additional control command parameters: K1=150, K2=300, K3=0.5, K4=0.5.

[0063] At 0.5 seconds, a three-phase permanent short circuit occurred on one of the circuits of the double-circuit line. 0.1 seconds later, the protection system tripped and disconnected the faulty line.

[0064] If a constant-rate ramp recovery scheme for the active current of the wind turbine after fault clearance is adopted, simulation analysis is performed for recovery rates of 3200% / s, 500% / s, and 200% / s, and the results are compared with the implementation effect of the design scheme of this invention. Figure 4 and Figure 5 As shown. Figure 4 This is the curve showing the change of active current of the wind turbine over time. Figure 5 The curve showing the change in the power angle of the synchronous condenser at the sending end over time.

[0065] contrast Figure 4 and Figure 5 It can be seen that, compared with the traditional active current constant rate slope recovery control, the method proposed in this invention can effectively improve the transient first swing angle stability of the synchronous condenser at the sending end of the wind farm, and enable the active power of the wind farm to recover quickly after the fault is cleared.

Claims

1. A method for improving transient stability of a phase modifier in a wind farm based on low penetration power segment restoration, characterized in that: By using the frequency signal feedback from the synchronous condenser at the wind farm, the control command for restoring the low-current operation of the wind turbine is adjusted in stages, including: ① Obtain the angular velocity of the wind field synchronous modulator ω angular acceleration and grid-connected voltage parameters; ② Send the synchronous angular velocity and angular acceleration signals obtained in step ① into the outer loop of the wind turbine power. Based on the sign of the synchronous angular velocity and angular acceleration signals after the fault is cleared, determine the stage of the rotor swaying process and switch different active power recovery strategies for different stages. 1) Phase 1 a) Criteria for division: Both the angular velocity and angular acceleration of the synchronous adjustment camera are positive; b) Control Strategy: The active power of the wind turbine decreases at a rate corresponding to the angular acceleration of the synchronous condenser, and is limited to a specified range. The active power current of the wind turbine drops to a minimum at the maximum allowable unbalanced power of the wind turbine. The rate of change of the active power current of the wind turbine in the first stage is... ， In the formula, The rate of change of active current of the wind turbine in the first stage; To synchronize the camera's angular acceleration; It is the adjustment coefficient, and ; Per-unit value representing the active current of the wind turbine; 2) Phase 2 a) Criteria for division: The angular velocity of the synchronous adjustment camera is positive, and the angular acceleration is negative; b) Control strategy: The active power of the wind turbine recovers according to the synchronous condenser's angular acceleration ramp. The rate of change of the active power current of the wind turbine in the second stage is: In the formula, The second stage active current change rate is defined as follows: Based on the new energy active current value under command control, a current correction command is added to generate the final second stage active current output command. ,in, This is the second stage active current output command following the additional current correction command. For the rate of change of active current of the wind turbine in stage 2 Active current value of the fan under control; In the formula, This is a command to correct the active current of the wind turbine. The measured value of the relative angular velocity between the synchronous condenser and the receiving system; This is the per-unit value of the measured grid-connected voltage of the wind turbine; It is the adjustment coefficient, and ; 3) Phase 3 a) Criteria for division: The angular velocity of the synchronous modulator is negative; b) Control strategy: The wind turbine's active power is restored immediately; ③ Control Exit Based on the active power restoration time requirements after wind farm fault clearance, a maximum restoration time is set, which is achieved when the conditions are met. Control will be deactivated if the control time exceeds the wind farm's active power recovery time limit.

2. The method for improving the transient stability of a wind farm synchronous condenser based on low-power piecewise recovery according to claim 1, characterized in that: Set the maximum recovery time to 2 seconds.

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