High-performance complex controller for high-power converters with low pulse ratios

For high-power converters with low pulse ratios (e.g. 80 Hz load frequency with 600Hz carrier frequency for a 27 MVA Variable Frequency Drive), the current control loop design has been a challenge due to the large signal delay and potentially higher-order plant (LCL filter between the converter and machines). The stability issue and cross-coupling effect is a problem in such application. In this paper, a complex current controller with excellent dynamic performance is proposed. The design is done by using the “double-sided frequency modeling” methodology. The stability, decoupling-effect, dynamic response and the robustness of the control loop are analyzed, which provides a design guideline for such applications. The performance of the proposed strategy and the improved state feedback method are compared. And finally simulation results are presented to validate the controller design and analysis.