Network and Isolated Island Operation General Control Strategy of VSC-HVDC System

Abstract

At present, the voltage source converter based high voltage direct current(VSC-HVDC) transmission system lacks the general control strategy under the condition of networking and isolated island operation. According to the characteristics of high voltage power network, this paper introduces the slope control of ac side's frequency-active power and DC side's activity-DC voltage, so as to obtain the general control strategy of VSC-HVDC transmission system's networking and isolated island operation. The frequency command value of converter station can be automatically adjusted according to the operation situation. The control strategy proposed in this paper is universal for the network of converter stations and the operating conditions of isolated islands. It can realize the smooth switching of converter stations in different operating conditions without control switching. Moreover, it can cooperate with the frequency modulation control of power grid, and it is suitable for the interconnection of weak power grids such as remote power grids and offshore wind farms. Electromagnetic transient simulation results show that the general control strategy proposed can effectively control the network and isolated island operating conditions of VSC-HVDC transmission system.