基于虚拟磁链的三电平风电网侧变流器研究

Research on Three-level Grid-Side Converter of Wind Generation Based on Virtual Flux

在大功率风力发电应用场合,将虚拟电网磁链作为定向矢量的方法应用于网侧变流器的控制中。建立了三电平网侧变流器的开关函数模型,并在简化三电平SVPWM算法的基础上,提出一种交流侧相电压重构方法。引入三阶级联低通滤波器代替积分环节,以保证所观测的磁链幅值和相位无偏差。针对传统虚拟磁链定向中初始定向角不准确的问题,采用了一种基于预充电回路的新型初始定向角观测方法。同时结合虚拟磁链定向技术,采用定频直接功率控制策略,实现网侧变流器的高动态性能运行。最后在双三电平双馈式风力发电对拖平台上进行了实验研究,实验结果验证了控制策略的正确性及可行性。

In high power wind generation applications, virtual flux orientation is applied in grid-side converter control. Switching function model of three-level grid-side converter is established. One method of AC-side phase voltage reconsitution is proposed based on simplified three-level SVPWM algorithm. In order to steady the phase and amplitude, three-order low pass filter is introduced. In allusion to the issue of inaccurate initial angle in traditional virtual flux, a novel initial angle observation method based on pre-charge circuit is applied. On the base of virtual flux orientation, high dynamic performance of converter is achieved using fixed-frequency direct power control strategy. The experiment study is taken on the platform of dual three-level DFIG system. The results verify the correctness and feasibility of the control strategy.