双馈感应风力发电机组的非线性变结构空载并网控制策略

Nonlinear sliding-mode variable structure control for no-load double-fed induction generator cutting-in wind power grids

采用矢量控制结合PI控制来实现双馈感应发电机并网时,电机的各种磁链以及电压电流交叉耦合补偿部分都会降低电网电压跟踪的速度,使动态响应性能不够理想,令超调量增大.本文采用变结构控制与全状态反馈线性化解耦相结合的控制策略,来控制双馈感应发电机组的空载并网过程.在MATLAB仿真模型基础上,从空载并网时发电机定子电压对电网电压的跟踪、并网过渡过程中定转子电流变化情况,和并网后功率调节和最大风能捕获这3个阶段进行了仿真分析.最后将非线性变结构控制器与传统矢量控制外加PI调节控制的仿真结果进行了对比分析.结果表明,采用全状态反馈线性化变结构控制的双馈感应风力发电机组,可以实现发电机的平滑并网,并网效果较好,定子电流对电网冲击小,转子电流实现比较平稳的过渡.并网后,发电机能够有效地进行最大风能捕获,实现变速恒频发电和有功、无功功率的独立调节控制.通过与传统矢量控制的比较分析,可以看出,双馈感应风力发电机组采用状态反馈精确线性化变结构控制器比传统矢量PI控制器对电网电压跟踪速度更快,动态响应更快速、调节时间和超调量更小.

In applying the traditional vector and PI control to a no-load double-fed induction generator when cuttingin the wind power grids, the existing magnetic flux linkages and the compensation between cross-coupling voltages and currents will lower the speed of the generator in tracking the power grid voltage, resulting in a deterioration of dynamic response performances and an increment of the overshoot voltage. To deal with these disadvantages, we propose a nonlinear sliding-mode variable structure control system to improve the no-load cutting-in performance. On a Matlab platform, we investigate by simulation the following three performances in/after the cutting-in processes： the generator stator voltage in tracking the grid voltage in no-load cutting-in; the generator stator/rotor current and voltage variations during the transition period of cutting-in; the power regulation and the maximum power pursuing （MPP） after the cutting-in. Simulation results between the traditional vector and PI control and the proposed control are compared; the conclusions show that the proposed control completely decouples the active power and the reactive power in regulation, realizes a rapid and mild no-load cutting-in, and achieves the MPP control after the cutting-in. The stator current makes only a minor strike to the grid, and the rotor current has a steady transition in the cutting-in period. Consequently, the proposed control method tracks the grid voltage faster and provides a more rapid dynamic response with a smaller overshoot.