Improved double-loop DFIG low voltage ride through control strategy under unbalanced voltage

Abstract

The invention provides an improved dual-loop DFIG low voltage ride through control strategy under the unbalanced voltage, aims to prevent a wind turbine off-line phenomenon caused by grid voltage dropand achieve low voltage ride through operation of a doubly-fed induction generator (DFIG). According to a mathematical model and control requirements of a grid-side converter, two types of control targets are designed, a corresponding current command is derived, flexibility of a voltage control link is improved by designing a BP neural network PID controller, the control structure is simplified,a current command value is transformed to a two-phase stationary coordinate system in combination with an improved proportion resonant (PR) controller, and positive and negative sequence simultaneouscontrol of the current part is achieved. An improved dual-loop network side control system is constructed, problems that DC bus voltage fluctuation is too large during low voltage crossing and the ACside current contains negative sequence components are solved, at the end of the paper, the proposed method is verified by simulation, and effectiveness and feasibility of the method are proved by theresult.

Description

technical field [0001] The present invention relates to a control strategy, more specifically, to an improved double-loop DFIG low-voltage ride-through control strategy under unbalanced voltage. Background technique [0002] Since DFIG has the characteristics of direct grid connection on the stator side, the system is more sensitive to grid voltage drop during operation. When the voltage drops, the DFIG unit will produce a serious electromagnetic transient process, causing problems such as unstable currents on the stator and rotor sides, and high bus voltage. Therefore, wind turbines must have low voltage ride through capability. [0003] In order to realize the low-voltage ride-through of the system under unbalanced voltage, most of them adopt the control strategy of dual synchronous rotating coordinate system. Quantities are expressed on the dq axis and then decoupled. This strategy can effectively control the positive and negative sequence currents when the voltage is ...

AI Technical Summary

Problems solved by technology

[0004]The present invention aims at the shortcomings of the traditional control strategy ignoring the negative sequence component of the electromagnetic quantity, complex structure, inflexible controller and slow response, and proposes an unbalanced voltage The improved double-loop DFIG low-voltage ride-through control strategy, through calculating the current command, designing the grid-side control system of the controller of the voltage and current part, improves the control accuracy and rapidity, and the control structure is also simplified.

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