Investigation of Frequency/AC Voltage Control for Inverter Station of VSC-HVDC

In this paper, the frequency and AC voltage control for the inverter station of a VSC-HVDC is investigated when supplying an industrial system that consists of static loads, synchronous and induction motors. The idea of the proposed control strategy is to exploit the rotating masses kinetic energy by slightly decreasing the frequency of the VSC output voltage to ride through the voltage disturbances. The control algorithm is based on a fast inner controller and a slow outer controller, where AC voltage and frequency control are implemented in the outer controller. The studied system is simulated in the electromagnetic transient simulation program PSCAD/EMTDC. Simulation results demonstrate that using the proposed control strategy with suitable reference current limit strategy, AC voltage and frequency can resume their reference values after small disturbances such as motor startings. From the results it can be concluded that the load characteristics and the current limit of the converter have a significant influence on the dynamic performance of the system