Robust current control design of a three phase voltage source converter

In this paper, a robust design method for current control is proposed to improve the performance of a three phase voltage source converter (VSC) with an inductor-capacitor-inductor (LCL) filter. The presence of the LCL filter complicates the dynamics of the control system and limits the achievable control bandwidth (and the overall performance), particularly when the uncertainty of the parameters is considered. To solve this problem, the advanced H∞ control theory is employed to design a robust current controller in stationary coordinates. Both control of the fundamental frequency current and suppression of the potential LC resonance are considered. The design procedure and the selection of the weight functions are presented in detail. A conventional proportional-resonant PR controller is also designed for comparison. Analysis showed that the proposed H∞ current controller achieved a good frequency response with explicit robustness. The conclusion was verified on a 5 kW VSC that had a LCL filter.