Transient stability improvement method of wind farm compensator based on lyapunov method

Abstract

The application discloses a method for improving transient stability of a wind farm phase modifier based on a Lyapunov method, which comprises the following steps: first, obtaining the power angle, angular velocity and angular acceleration of a synchronous phase modifier of a new energy sending end system relative to a receiving end system; then, under the condition that the new energy system fault is cleared, generating a wind turbine active current additional control instruction based on the Lyapunov stability theorem according to the obtained power angle, angular velocity and angular acceleration; finally, superimposing the generated wind turbine active current additional control instruction and the control instruction of the original transient control link of the wind turbine to adjust the active output of the new energy. Compared with the traditional strategy of recovering the active current at a constant rate after the low voltage ride through state is ended, the application can more effectively inhibit the power angle instability of the synchronous phase modifier in the new energy station. Meanwhile, the scheme also avoids the problems of weakened inhibition effect and over-regulation caused by the time setting-based control strategy, and has important significance in ensuring the safe and stable operation of the power system.

Description

Technical Field

[0001] This invention belongs to the field of synchronous stability control technology for wind power grid-connected systems, specifically relating to a method for improving the transient stability of wind farm synchronous condensers based on the Lyapunov method. Background Technology

[0002] The large-scale grid connection of wind power has made the operation of new energy power systems more diversified and complex than that of traditional power systems, and its stability mechanism has also changed. Compared with the generation of traditional high-inertia synchronous thermal power units, new energy sources cannot provide the system with rotational inertia and effective dynamic reactive power that match their capacity, resulting in insufficient support for grid voltage and frequency. Synchronous condensers, as synchronous motors without prime movers or mechanical loads, and capable of absorbing or generating reactive power, can effectively improve the system's short-circuit capacity, provide voltage support when the grid is subjected to disturbances, and ensure the safe and stable operation of the power system. To improve the voltage support capability of new energy power plants and ensure that the power system has sufficient voltage stability margin, some studies have proposed deploying synchronous condensers at new energy power plants, and this scheme has also been supported by the State Grid Corporation of China's "Action Plan for Building a New Power System with New Energy as the Main Body".

[0003] However, synchronous condensers, as special synchronous motors without mechanical power input, can sway along with other synchronous generators under unbalanced power driving, posing a risk of power angle instability. In traditional power systems, synchronous condensers have a large stability margin at their steady-state operating point, resulting in a lower risk of power angle instability. However, when synchronous condensers are installed near renewable energy bases, the dynamics of renewable energy during fault crossings and the recovery transients after faults significantly alter the rotor motion dynamics of the condenser, greatly increasing the risk of transient instability. Therefore, researching transient power angle stability control strategies for synchronous condensers at renewable energy power plants is of great significance for ensuring the safe and stable operation of the power system and further improving the renewable energy transmission limit.

[0004] The transient active power output after the wind turbine fault is cleared has a significant impact on the transient power angle stability of the nearby synchronous condenser. For the traditional constant rate slope recovery strategy of active current, different rates have different effects on the power angle stability of the synchronous condenser, and the intermediate boundary is difficult to define. Summary of the Invention

[0005] To overcome the problems existing in the prior art, the present invention aims to provide a method for improving the transient stability of wind farm synchronous condensers based on the Lyapunov method. The present invention designs a wind turbine transient active current supplementary controller based on the Lyapunov second method to adjust the active power output of the wind turbine in real time, thereby avoiding the problem of deterioration of the synchronous condenser's power angle stability caused by improper recovery rate, improving the transient stability of the new energy transmission system, and solving the problem of transient power angle instability of synchronous condensers in new energy power plants.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for improving the transient stability of a wind field synchronous condenser based on the Lyapunov method includes the following steps:

[0008] ① Obtain the power angle, angular velocity, and angular acceleration of the synchronous condenser of the new energy sending system relative to the receiving system;

[0009] ② In the case of clearing the fault in the new energy system, based on the signal obtained in step ①, generate additional control commands for the active current of the wind turbine according to the Lyapunov stability theorem;

[0010] ③ The active current additional control command generated in step ② is superimposed on the control command of the original transient control loop of the wind turbine to adjust the active power output of the new energy source.

[0011] In step ②, based on Lyapunov's stability theorem, the additional active current controller for the wind turbine is determined as follows:

[0012] ΔI p =M1[K1(δ d -δ)-K2ω-a]

[0013] In the formula, ΔI p Add a correction command to the active current of the wind turbine; M1 is the inertia of the synchronous condenser in the new energy sending-end system; δ, δ d ω represents the measured and expected power angle of the synchronous condenser of the new energy sending-end system relative to the receiving-end system, respectively; ω represents the measured angular velocity of the synchronous condenser of the new energy sending-end system relative to the receiving-end system; a represents the angular acceleration of the synchronous condenser of the new energy sending-end system; K1 and K2 are adjustment parameters, with 1 < K1 < 3 and 1 < K2 < 3.

[0014] In step ③, the active power output of the new energy source is adjusted by superimposing the additional control command for the active current of the wind turbine generated in step ② with the control command of the original transient control loop of the wind turbine.

[0015] I p =I p_original +ΔI p

[0016] In the formula, I p_original The control commands for the original transient control loop of the wind turbine are designed to operate on the MPPT curve, with immediate recovery or constant rate ramp recovery; I p This is the final generated active power control command for the wind turbine;

[0017] When satisfied

[0018] (δ d -δ)=0,ω=0,a=0

[0019] That is, control will exit when all three signal errors are 0 or the control time exceeds the time limit for the recovery of active power from new energy sources.

[0020] The required recovery time for the new energy source is 2 seconds. Compared with existing technologies, this invention has the following advantages:

[0021] This invention discloses a method for improving the transient stability of synchronous condensers in wind farms based on the Lyapunov method. By measuring various feedback signals in real time during fault transients and implementing emergency control, this invention, compared to traditional synchronous condenser transient power angle control strategies such as setting according to strategy tables or switching turbines and loads, can more effectively suppress the power angle instability of synchronous condensers in renewable energy power plants. It is more adaptable to different faults and operating scenarios and has lower costs. This method adjusts the active current of renewable energy by measuring the power angle, angular velocity, and angular acceleration of the synchronous condenser in real time, avoiding the weakened suppression effect and over-adjustment problems that may be caused by the constant rate ramp recovery of wind turbine active power, as well as the potential deterioration of the power angle stability of synchronous condensers in renewable energy power plants. This method is of great significance in ensuring the safe and stable operation of the power system. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method of the present invention.

[0023] Figure 2 This is a block diagram of the control structure of the present invention.

[0024] Figure 3 It is a new energy plus synchronous condenser power transmission system topology.

[0025] Figure 4 This is a waveform diagram showing the change of active current of new energy sources over time under the existing constant rate slope recovery strategy and after adopting the control strategy of this invention.

[0026] 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 adopting the control strategy of this invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, this invention is a method for improving the transient stability of a wind field synchronous condenser based on the Lyapunov method, comprising the following steps:

[0029] ① The steps for obtaining the power angle, angular velocity, and angular acceleration of the synchronous condenser of the new energy sending-end system relative to the receiving-end system are as follows: This module... Figure 2 As shown.

[0030] ②For example Figure 2 As shown, when the fault in the new energy system is cleared, based on the signal obtained in step ①, an additional control command for the active current of the wind turbine is generated according to the Lyapunov stability theorem. Figure 2 In this context, s is the Laplace operator; T mea T tran T div and T des These are the time constants for the measurement, transmission, differentiation, and delay components, respectively.

[0031] Based on Lyapunov's stability theorem, the active current supplementary controller for the wind turbine's active current is determined as follows:

[0032] ΔI p =M1[K1(δ d -δ)-K2ω-a]

[0033] In the formula, ΔI p Add a correction command to the active current of the wind turbine. M1 is the inertia of the synchronous condenser in the new energy transmission system; δ, δ d ω represents the measured and expected power angle of the synchronous condenser of the new energy sending-end system relative to the receiving-end system, respectively; ω represents the measured angular velocity of the synchronous condenser of the new energy sending-end system relative to the receiving-end system; a represents the angular acceleration of the synchronous condenser of the new energy sending-end system; K1 and K2 are adjustment parameters, with 1 < K1 < 3 and 1 < K2 < 3.

[0034] ③ For example Figure 2 As shown, the additional control command for the active current of the wind turbine generated in step ② is superimposed with the control command of the original transient control loop of the wind turbine to adjust the active power output of the new energy source.

[0035] I p =I p_original +ΔI p

[0036] In the formula, I p_original The control commands for the original transient control loop of the wind turbine can be designed to operate on the MPPT curve, with immediate recovery or constant rate ramp recovery; I pThis is the final generated active power control command for the wind turbine.

[0037] When satisfied

[0038] (δ d -δ)=0,ω=0,a=0

[0039] That is, control will exit when all three signal errors are 0 or the control time is greater than 2 seconds, which is required for the recovery time limit of the new energy active power.

[0040] Example:

[0041] The method of this invention is aimed at solving the transient power angle stability problem of distributed synchronous condensers in new energy power plants.

[0042] To verify the correctness of the above analysis, a simulation platform was built as follows: Figure 3 The new energy plus synchronous condenser power transmission system model shown was simulated and verified according to the following parameters:

[0043] 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. Measurement time constant: T mea =20ms, T tran =20ms, T div =10ms, T des =10ms; Adjustment parameters: K1=K2=2.

[0044] 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.

[0045] 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.

[0046] 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 stability of the transient first swing angle of the synchronous condenser at the new energy sending end.

Claims

1. A method for improving the transient stability of a wind field synchronous condenser based on the Lyapunov method, characterized in that: Includes the following steps: ① Obtain the power angle, angular velocity, and angular acceleration of the synchronous condenser of the new energy sending system relative to the receiving system; ② In the case of clearing the fault in the new energy system, based on the signal obtained in step ①, generate additional control commands for the active current of the wind turbine according to the Lyapunov stability theorem; ③ The active current additional control command generated in step ② is superimposed on the control command of the original transient control loop of the wind turbine to adjust the active power output of the new energy source; In step ②, based on Lyapunov's stability theorem, the additional active current controller for the wind turbine is determined as follows: In the formula, Add a correction command to the active current of the wind turbine; The inertia of the synchronous condenser in the new energy transmission system; , These are the measured and expected values ​​of the power angle of the synchronous condenser in the new energy sending-end system relative to the receiving-end system; The measured value of the angular velocity of the synchronous condenser of the new energy sending-end system relative to the receiving-end system; For the synchronous condenser angle acceleration of the new energy transmission system; To adjust the parameters, take , ; In step ③, the control commands of the original transient control loop of the wind turbine are designed to operate on the MPPT curve, with immediate recovery or constant rate ramp recovery. In step ③, the active power output of the new energy source is adjusted by superimposing the additional control command for the active current of the wind turbine generated in step ② with the control command of the original transient control loop of the wind turbine. In the formula, The control commands are for the original transient control loop of the wind turbine; This is the final generated active power control command for the wind turbine; When satisfied That is, control will exit when all three signal errors are 0 or the control time exceeds the time limit for the recovery of active power from new energy sources.

2. The method for improving the transient stability of wind field synchronous condensers based on the Lyapunov method as described in claim 1, characterized in that: The required recovery time for the new energy source is 2 seconds.

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