Abstract
Voltage source converters (VSCs) have been commonly used due to their flexibility to control voltages and powers independently and bi-directionally. Typically, (e.g. two-level converter), the control system mainly consists of two parts; outer voltage or power flow (real and reactive power) controller and inner current controller. Vector current control based dq decoupling technique enables to control active and reactive power, DC voltage and AC voltage. The d- and q-axis of grid voltages and currents comprise AC and DC components under unbalanced grid conditions. The AC components of the d- and q-axis current have negative impact on the current control loop and converter performance. In this paper, a novel feed-forward current control has been presented and investigated under balanced and unbalanced grid modes for a Modular Multilevel Converter (MMC) system. The Real Time Digital Simulator (RTDS) demonstrates the results of proposed feedforward current control strategy, applied to the Point to Point MMC based High Voltage Direct Current (HVDC) system.