A control method for doubly-fed wind turbines in the event of voltage unbalance/harmonic distortion

Abstract

The invention discloses a method for controlling a doubly-fed wind power generator in voltage unbalance / harmonic distortion. Vector control structures of a grid-side converter and a rotor-side converter of the doubly-fed wind power generator are redesigned; electromagnetic torque and stator reactive power auxiliary control rings are added to the rotor-side converter, and consequently electromagnetic torque fluctuation of the doubly-fed wind power generator under the condition of power grid failure can be effectively restrained to guarantee operational safety of an expensive fan gearbox; stator current negative sequence component and harmonic wave component auxiliary control rings are added to the grid-side converter to obtain strictly-symmetrical and sinusoidal total output three-phase current of the doubly-fed wind power generator so as to meet constraints of unit output power quality according to grid connection specifications. Compared with a traditional method, the method for controlling the doubly-fed wind power generator in voltage unbalance / harmonic distortion has the advantages that voltage or current phase sequence separation and negative sequence and harmonic current instruction computation are not needed, and engineering realization is facilitated.

Description

technical field [0001] The invention relates to the operation control technology of doubly-fed wind power generators under non-ideal power grid conditions, and proposes a control method for doubly-fed wind power generators when voltage imbalance / harmonic distortion occurs, in order to reduce the harm of such power grid failures to wind power generators, Improve the steady-state and transient operation performance and non-off-grid operation ability of this type of unit. Background technique [0002] Since most of my country's wind farms are located in remote areas with relatively weak power grids and long power transmission lines, the voltage at the public access points of wind farms may be unbalanced. The single-phase and two-phase ground faults of the power grid, the single-phase power supply conditions of electrified railways, and the uncontrolled rectification method adopted by high-power drag converters used in factories and mines will all cause three-phase unbalance and...

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Problems solved by technology

[0004] (1) The fault conditions of the power grid studied are relatively single, and most of them focus on the voltage unbalanced condition. There is insufficient research on the complex conditions of the power grid containing low-order harmonic components such as the 5th and 7th, and there are few literatures from the voltage From the perspective of mathematical modeling of DFIG under the coexistence of imbalance and harmonic distortion, systematically evaluate the impact of such faults on DFIG units

[0005] (2) When the grid voltage is unbalanced and harmonically distorted, the interaction between the negative sequence and harmonic components in the DFIG stator and rotor currents will not only deteriorate the output current waveform, but also cause fluctuations in electromagnetic torque and bus voltage, directly threatening to the operational safety of gearboxes and DC link electrolytic capacitors

[0006] (3) Under the condition of unbalanced grid voltage, some scholars have proposed that the so-called DFIG wind turbine cooperative control scheme has certain engineering significance, but the calculation of the current reference command of the grid-side and rotor-side converters in the control scheme is heavily dependent on Accurate and fast separation or extraction of the positive sequence and negative sequence components of the grid voltage. At the same time, the calculation of the current command of the grid-side converter requires the power information of the rotor side, which is not conducive to the control decoupling of the two converters, and increases the cost of the scheme. Engineering difficulty

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