Flexible CSC-HVDC system

The current source converter (CSC)-HVDC system is the key technology for long distance large power transmission. However, the traditional CSC-HVDC has two serious shortcomings: (i) vulnerable to commutation failures; and (ii) not being able to control its reactive power. This study will propose a Flexible CSC topology, which is based on the dc current reinjection conversion concept. The Flexible CSC reduces the converter current waveform to zero during the commutations of valves and, thus, removes the converter dependence on line commutation. The Flexible CSC is also free to control the amplitude and phase of its output ac current. So, it can control freely active power and reactive power. Use this converter to construct a new CSC-HVDC system. This new CSC-HVDC system can operate in four quadrants, so as to control reactive power in wide range. In particular, it can export leading reactive power to the ac grids. This study describes the structure and control of the Flexible CSC and builds an experimental prototype. The simulation and experimental results will be shown to demonstrate the feasibility of the converter topology, the effectiveness of the active reactive power controllability, and the commutation failure elimination method