A wind farm transient synchronization stability control method based on phase-modulating mechanism network

Abstract

The present invention discloses a method for controlling the transient synchronous stability of a wind farm based on a phase-modulating mechanism network. First, when the fault of the wind farm grid-connected system is cleared, the phase-locked loop (PLL) output phase of the wind turbine grid-side converter is obtained; then, the difference between the PLL output phase and the phase in steady state is used as a virtual angle to determine the wind turbine active current output control instruction and the wind turbine reactive current output control instruction. Compared with the traditional strategy of using a constant rate ramp to restore active current after the low voltage ride-through state ends, the present invention can more effectively suppress the power angle instability of synchronous phase regulators in new energy stations. At the same time, the present invention also avoids the problems of weakened suppression effect and overmodulation that may be caused by control strategies based on time setting, and is of great significance in ensuring the safe and stable operation of power systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of synchronous stability control of wind power grid-connected systems, and in particular relates to a method for controlling transient synchronous stability of a wind farm based on a phase-modulating mechanism network. Background Art

[0002] A new landscape of centralized grid connection and long-distance transmission of large-scale wind farms is gradually emerging. However, the dynamic reactive power support capacity of centralized renewable energy transmission systems is weak, leading to significant issues with frequency and voltage security and small-disturbance stability, significantly limiting the transmission capacity of wind farms. Synchronous condensers, as a special type of synchronous motor, provide short-circuit capacity, reactive power, and inertia support, offering unique advantages in improving the system's short-circuit ratio and enhancing system voltage and frequency security. Currently, a series of studies have been conducted domestically and internationally on combining synchronous condensers with renewable energy generation, specifically distributed condenser-based grid-connected wind farms. Results have shown that this combination can serve as a new form of grid-supported power source, helping to mitigate transient overvoltages and sub-supersynchronous oscillations in the sending-end system, and suppressing large-scale disconnection of renewable energy sources during transient fault events. In the future, grid-connected wind farms based on distributed condensers are expected to become one of the mainstream construction models for grid-connected wind farms.

[0003] However, despite the numerous advantages of a wind farm network based on phase-shifting mechanisms, synchronous condensers also pose a potential threat to the system's transient power angle stability. As a special type of synchronous motor without a prime mover or mechanical load, synchronous condensers exhibit inertial response characteristics, which dictate that they, along with synchronous generators, bear the unbalanced power during system transients. Generally speaking, synchronous condensers have a large static stability margin and are not susceptible to transient out-of-step. However, when synchronous condensers are installed near a wind farm, output fluctuations during the fault and recovery phases can affect the rotor dynamics of nearby condensers, leading to transient power angle stability issues for the synchronous condensers. Synchronous condenser power angle stability may become another bottleneck limiting the maximum output of renewable energy. Therefore, developing a simple, efficient, and targeted transient synchronous stability control scheme is imperative for the successful construction of a grid-based wind farm based on distributed condensers. Summary of the Invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a wind farm transient synchronous stability control method based on a phase-modulating mechanism network. The present invention adjusts the active output of the wind turbine in real time through the feedback of the PLL measurement phase, thereby avoiding the problem of deterioration of the power angle stability of the wind farm phase regulator due to improper recovery rate, improving the transient stability of the new energy transmission system, and solving the problem of transient power angle instability of the synchronous phase regulator in the new energy station.

[0005] In order to achieve the above object, the technical solution adopted in the present invention is:

[0006] A method for controlling transient synchronous stability of a wind farm based on a phase-adjusting mechanism network comprises the following steps:

[0007] ① After the wind farm grid-connected system fault is cleared, the control starts and obtains the phase of the phase-locked loop (PLL) output of the wind turbine grid-side converter;

[0008] ② Based on the phase of the phase-locked loop (PLL) output obtained in step ①, the difference between the phase and the phase in the steady state is used as the virtual rotation angle to determine the wind turbine active current output control command and the wind turbine reactive current output control command;

[0009] ③ When the control time is greater than the required time limit for the active power recovery of new energy, the control exits, otherwise returns to step ②.

[0010] 2. In step ②, the fan active current output control instruction and the fan reactive current output control instruction are respectively determined as:

[0011] I p =Icos(θ-θ s ), I q = -Isin(θ-θ s )

[0012] Where, I p and I q They are respectively the active current output control command of the fan and the reactive current output control command of the fan; I is the current control command when the fan is in normal operation; θ and θ s They are the phase-locked loop PLL output phase and steady-state phase respectively.

[0013] 3. In step ③, the time limit for recovering the active power of new energy is 2s.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] The present invention provides a method for controlling the transient synchronous stability of a wind farm based on a phase-shifting mechanism network. This method implements emergency control based on measurement feedback. Compared with traditional synchronous machine transient power angle control strategies such as setting according to a strategy table or shedding the machine and load, the present invention can more effectively suppress the power angle instability of synchronous phase-shifting machines in renewable energy stations. It also avoids the problems of weakened suppression effect and over-regulation that may result from time-based control strategies, and is more adaptable to different fault and operating scenarios at a lower cost. Furthermore, the present invention requires less measurement, is simple to implement, and has high reliability, possessing engineering practical value in ensuring the safe and stable operation of power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the method of the present invention.

[0017] Figure 2 It is a control structure block diagram of the present invention.

[0018] Figure 3 It is a wind farm grid-connected system topology based on a phase-adjusting mechanism network.

[0019] Figure 4 This is a waveform diagram of the wind turbine active current changing with time under the existing constant rate ramp recovery strategy and after adopting the control strategy of the present invention.

[0020] Figure 5 It is a waveform diagram of the wind farm phase regulator power angle changing with time under the existing constant rate ramp recovery strategy and after adopting the control strategy of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, the present invention is a method for controlling transient synchronous stability of a wind farm based on a phase-adjusting mechanism network, comprising the following steps:

[0023] ① After the wind farm grid-connected system fault is cleared, the control starts and obtains the phase-locked loop (PLL) output phase of the wind turbine grid-side converter, such as Figure 2 As shown;

[0024] ② When the new energy system fault is cleared, if Figure 2 As shown, according to the phase-locked loop PLL output phase obtained in step ①, the difference between the phase and the steady-state phase is used as the virtual rotation angle to determine the wind turbine active current output control command and the wind turbine reactive current output control command:

[0025] I p =Icos(θ-θ s ), I q = -Isin(θ-θ s )

[0026] Where, I p and I q They are respectively the active current output control command of the fan and the reactive current output control command of the fan; I is the current control command when the fan is in normal operation; θ and θ s They are the phase-locked loop PLL output phase and steady-state phase respectively.

[0027] ③ When the control time is greater than the new energy active power recovery time limit requirement, the control is exited, and the new energy active power recovery time limit is preferably 2s.

[0028] Example:

[0029] The method of the present invention is aimed at the transient power angle stability problem of a wind farm based on a phase adjustment mechanism network.

[0030] In order to verify the correctness of the above analysis, a simulation platform is built as follows Figure 3 The wind farm grid-connected system model based on the phase-adjusting mechanism network shown in the figure was simulated and verified according to the following parameters:

[0031] The actual output of the direct-drive wind turbine is 600MW; the capacity of the synchronous condenser at the sending end is 180MVA; and the receiving end is an infinite power grid.

[0032] At 0.5s Figure 3 When a single-phase ground fault occurs in a single-loop line, the protection will disconnect the faulty phase after 0.1s. The system will not operate in all phases, and the reclosing will be successful after 1s.

[0033] If the conventional solution of constant-rate ramp recovery of wind turbine active current after fault clearing is adopted, simulation analysis is conducted for the cases of immediate recovery and 1 p.u. / s recovery rates, and the effect is compared with the implementation effect of the design solution of the present invention. Figure 4 and Figure 5 shown. Figure 4 is the curve of wind turbine active current changing with time, Figure 5 This is the curve of the power angle of the synchronous phase regulator in the wind farm changing with time.

[0034] contrast Figure 4 and Figure 5 It can be seen that the synchronous condenser becomes unstable during the transient process after the fault is cleared under traditional control, while the method of the present invention effectively controls the power angle instability of the synchronous condenser; compared with the traditional active current constant rate ramp recovery control, the method proposed in the present invention can effectively improve the transient power angle stability of the synchronous condenser in the wind farm based on the phase modulation mechanism network.

Claims

1. A method for controlling transient synchronous stability of a wind farm based on a phase-adjusting mechanism network, characterized by: The following steps are involved: ① After the wind farm grid-connected system fault is cleared, the control starts and obtains the phase-locked loop (PLL) output phase of the wind turbine grid-side converter; ② Based on the phase of the phase-locked loop (PLL) output obtained in step ①, the difference between the phase and the phase in the steady state is used as the virtual rotation angle to determine the wind turbine active current output control command and the wind turbine reactive current output control command; ③When the control time is greater than the required time limit for the active power recovery of new energy, the control is exited, otherwise it returns to step ②; In the step ②, the fan active current output control instruction and the fan reactive current output control instruction are respectively determined as: I p =Icos(θ-θ s ),I q =-Isin(θ-θ s ) Where, I p and I q They are respectively the active current output control command of the fan and the reactive current output control command of the fan; I is the current control command when the fan is in normal operation; θ and θ s They are the phase-locked loop PLL output phase and steady-state phase respectively.

2. The method for controlling transient synchronous stability of a wind farm based on a phase adjustment mechanism network according to claim 1, characterized in that: In step ③, the time limit for recovering the active power of new energy is 2s.

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