Method for suppressing harmonics of power network current of variable-speed constant-frequency doubly-fed wind power generator system

Abstract

The invention relates to a method for suppressing harmonics of power network current of a variable-speed constant-frequency doubly-fed wind power generator system, comprising the following steps of: collecting d q axis components in a synchronous rotating coordinate system oriented by a stator flux linkage; collecting reference values of the d q axis components in the synchronous rotating coordinate system oriented by the stator flux linkage during the steady state of the system,; extracting alternating-current harmonic current components in a power network; obtaining harmonic current reference values of a network-side inverter, which are required adding for suppressing each harmonic current; and summing all harmonic current reference values of the network-side inverter, and adding the result in the current d q axis component reference values of the alternating-current side of the network-side inverter to generate reverse current harmonics to eliminate existed harmonic currents in the power network current. The invention can effectively suppress low-order harmonics which have great damages in the power network current of the doubly-fed wind power generator system, improves the current waveform of the power network, is simple in realization method and convenient for control, and can be widely applicable to harmonic suppression of power network current of the wind power generator systems.

Description

technical field [0001] The invention belongs to the field of wind power generation, in particular to a method for suppressing harmonics of grid current in a variable-speed constant-frequency double-fed wind power generation system. Background technique [0002] In response to the current energy crisis and increasingly serious environmental pollution problems, wind power, as a renewable energy source, has been developing rapidly all over the world. In order to make the wind turbine operate at the best efficiency within a large wind speed range, modern large-scale wind power generation systems all adopt variable speed and constant frequency power generation operation mode, and there are mainly two types of generators used: one is double-fed induction generator ( DFIG), the other is the permanent magnet synchronous generator, because the power converter capacity of the doubly-fed wind power generation system is small (usually 25% to 40%), and the loss is also small, it has beco...

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Problems solved by technology

The structure of the double-fed asynchronous generator is similar to that of the wound induction motor. During the design and manufacture of the motor, due to the influence of nonlinear factors such as the motor winding, air gap and cogging, even if the rotor passes a three-phase balanced sinusoidal current, The stator current of the generator will also contain different levels of harmonic current components generated by the inherent harmonic characteristics of the motor. In addition, usually the wind power system input grid voltage is three-phase balanced, but it also contains a small amount of low-order harmonics. For large As far as the power doubly-fed generator is concerned, even if the low-order harmonic is small, it will generate a large harmonic current component in the stator circuit of the motor

When the power converter is used to control the double-fed generator to enter the normal grid-connected power generation state, such as figure 1 As shown, the grid current is composed of the stator current and the AC side current of the grid-side inverter, so the harmonic current of the stator circuit will flow into the grid, causing harmonic pollution to the grid, especially in the sub-synchronous slip of the wind power generation system. Under normal circumstances, due to the large low-order slip harmonics and the small fundamental active current, the total harmonic distortion of the grid current is large and the waveform is poor. At the same time, when the capacity of the transformer connected to the wind power generation system is small, the Large grid current harmonics will not only increase line and transformer losses, but also cause input grid voltage distortion, further deteriorating the control performance of wind power generation systems

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