Stability enhancement and discrete‐time resonant controller synthesis for voltage‐controlled Voltage Source Converters

Abstract

As for the voltage-controlled voltage sources converter (VSC), the inner current loop of dual closed-loop control is equivalent to a virtual impedance, which provides effective damping for the system. However, the time delay caused by computation and transmission becomes increasingly prominent in the low-pulse-ratio cases, which not only limits the achievable bandwidth, but also reduces the stability of the current loop. This paper proposes an enhanced control strategy for current loop by adding the feedback of computation delay into the current controller, to significantly widen the stability region and control bandwidth, and increase the active damping. The parameter design of the current controller is presented based on discrete-time root locus. Subsequently, the voltage controller is directly deduced in the discrete-time domain, which eliminates the poles/zeros deviation caused by discretization. The accurate delay compensation is realized by polezero cancellation, thus avoiding the additional phase compensation for fundamental and harmonic frequencies. Simulation and experimental results validate the effectiveness of the enhanced dual-loop control strategy.