A Control Strategy of a VSC HVDC System for Power System Enhancement

Voltage Source Converter (VSC) based HVDC is the most recent HVDC technology with extruded DC cables in small and medium power transmission. VSC-HVDC converters include Insulated Gate Bipolar Transistors (IGBT´S) and operated with high frequency Pulse Width Modulation (PWM) in order to get high speed control of both active and reactive power . With VSC-HVDC there is an addition degree of freedom. The reactive power can be control separately in each converter by the AC voltage or set manually. The active power flow can be controlled by the DC voltage, the variation of frequency at the AC side or set manually. This means that the active power flow, the reactive power flow, the AC voltage, the DC voltage and the frequency can be controlled when using VSC-HVDC.