Operational Mechanism and Characteristic Analysis of Novel Hybrid HVDC system

Conventional HVDC has the advantages of mature state of art and lower cost and the disadvantages of absorbing large reactive power and the danger of commutation fault. Voltage source converter (VSC) based HVDC (VSC-HVDC) has the advantages of flexible operation and control and the disadvantages of high cost. Combining the advantages of the two kinds of transmissions, a novel hybrid HVDC transmission type is analyzed in this paper, which the sending terminal adopts phase control converter (PCC) and the receiving terminal adopts VSC. The hybrid HVDC system can supply to passive network, supply reactive power to AC system and expediently extend to two bi-terminal or multi-terminal systems from conventional HVDC system. The expressions of voltage, current and power in rectifier and inverter sides are deduced. The relationship between the operational variables and control variables is analyzed. The basic regulation characteristics are gotten. The simulation model is founded based on the simulation software PSCAD/EMTDC. Simulation results show that the hybrid HVDC system could be operated steadily when the system active power changes slowly and quickly. It has the application prospect in scope of long distance small load supplying, multi-terminal DC system connection and system black-start etc.