HVDC rectifier control coordinated with generator station in radial operation

This paper proposes advanced frequency control strategies for the DC radial system with isolated generators. The DC power order in the DC radial operation is set by an automatic frequency regulator (AFR), which is composed of an integral function and a proportional function. The AFR balances DC transmitted power with mechanical output power of generators to maintain frequency deviation as close as the one in an AC radial link. Also, a universal and autonomous HVDC control strategy is proposed for the secure transfer of the generator operation from an AC-DC parallel to a DC radial. This control can suppress transient frequency within permissible limits, and matches with turbine generator speed controls and turbine over speed protection in a stable manner. A prototype controller is implemented to verify the strategies. The validity and effectiveness are confirmed through a factory test using a DC simulator.