Control method for suppressing grid-connected power fluctuations in doubly-fed induction wind power system under grid voltage harmonics

Abstract

The invention discloses a control method of a double-fed induction wind power system for restraining grid-connected power fluctuation under the condition of voltage harmonic of a power grid. The control method of the double-fed induction wind power system for restraining the grid-connected power fluctuation under the condition of the voltage harmonic of the power grid is related to control over a series grid-side converter, control over a parallel grid-side converter and control over a motor-side converter. According to the control method of the double-fed induction wind power system for restraining the grid-connected power fluctuation under the condition of the voltage harmonic of the power grid, PWM driving signals of the series grid-side converter, PWM driving signals of the parallel grid-side converter and PWM driving signals of the motor-side converter are generated through space vector modulation after a series of calculations are carried out. The control objectives that three-phase current of a stator and three-phase current of a rotor of the double-fed wind power generation system are free of distortion, and motor power and electromagnetic torque are free of fluctuation under the condition of the voltage harmonic of the power grid are achieved through the control method, safe and stable operation of an electric generator is ensured, the degree of fluctuation of total output active power and total output reactive power of the double-fed induction wind power system can be greatly reduced, and stability of a power grid connected with a DFIG system under the condition of the voltage harmonic of the power grid is improved.

Description

technical field [0001] The invention relates to a technical improvement of a doubly-fed induction wind power generation system, in particular to a control method for a doubly-fed induction wind power system suppressing grid-connected power fluctuations under grid voltage harmonics, and belongs to the technical field of electric power control. Background technique [0002] For long-distance wind farms connected to weak grids, due to the influence of long AC transmission lines and nonlinear loads, the wind farm bus common connection point (point of common coupling, PCC) at the end of the grid often contains relatively large Severe low-order harmonic voltage (especially the 5th and 7th harmonics), which will have a significant impact on large-scale variable-speed constant-frequency wind turbines that are connected to the grid. For the doubly fed induction generator (DFIG) of the mainstream type of wind power generation, its stator is directly connected to the grid, which will c...

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Problems solved by technology

Among them, the control objective 4 realizes the electromagnetic torque and the output reactive power of the stator without fluctuation at the same time, which relieves the pressure on the transmission shaft system to a certain extent, but the active power output by the stator fluctuates; although the control objective 3 realizes the stator output active power And the reactive power has no sixfold frequency fluctuation at the same time, but the electromagnetic torque has fluctuations. Due to the limitation of the control variables of the rotor-side converter, the proposed control scheme cannot simultaneously realize the stator output active power, reactive power and electromagnetic torque without fluctuation.

It is worth noting that under the above two control objectives, due to the existence of the parallel side converter, the power fed into the grid by the entire system still fluctuates to a large extent, which will have a negative impact on the operation stability of the grid connected to the DFIG system. Negative Effects

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