Power surplus mechanism and fault ride through strategies of the hybrid cascaded UHVDC system

Abstract

Hybrid cascaded dc technique has the advantages of long-distance and large capability transmission of the line commutated converter(LCC) based HVDC, and also the advantages of supplying multiple receiving ends, flexible operation and good system supporting ability of the voltage source converter (VSC) based HVDC. It is a good solution for the efficient use of large scale clean energy and the construction of energy internet. Chinese Baihetan-jiangsu UHVDC project is the first hybrid cascaded UHVDC (HS-UHVDC) project in the world. Power Surplus is a serious problem for the HS-UHVDC, which can cause overvoltage of the VSCs, making the system fail to ride-through the ac faults. This paper reveals the power surplus mechanisms of the HS-UHVDC system. Two energy dissipation devices, that is the controllable arrester scheme and the thyristors &blocking diodes are proposed and compared in detail. Then the ac fault ride-through control strategies and the parameter design method of the energy dissipation devices are proposed. It is shown that with the proposed energy dissipation method, the VSC overvoltage can be suppressed and the ac ride-through can be realized, thus solving the power surplus problemofHS-UHVDC effectively.