Fast VSC transmission control

Abstract

The aim of the research is to develop a fast controller for voltage source converter (VSC) transmission. The system is highly nonlinear; it has four control inputs and higher order dynamics. The fastest feedback control loop is the inverter DC voltage (Vdci) controller but on its own this cannot achieve satisfactory performance. To improve Vdci performance an additional stabilising feedback loop is developed at the rectifier side. The stabilising loop is a lead-lag second order filter that is designed using the root locus methods. The addition of this controller reduces the overshootings of the Vdci control and it improves the robustness of the overall transmission system. The VSC transmission control under faults is achieved using a dedicated current controller at each converter station. This controller uses special current reference settings to avoid interactions with the small-signal controller. The transition between small-signal and fault control is achieved using minimum elements with the control modulation angle and magnitude inputs. The design is fully tested on nonlinear digital simulator for a range of small-signal and fault conditions, and the responses confirm design goals.