A Frequency Control Method Based on A Coordinated Active and Reactive Power Optimization Adjustment for Weak HVDC Sending-end Power Grid

Abstract

Block fault of large-capacity HVDC (high voltage direct current) transmission line will cause great impact on the weak HVDC sending-end power grid with high proportional renewable energy generation. A large power imbalance resulting from the week HVDC sending-end power block will lead to AC grid frequency increase accordingly. Therefore, active power adjustment is needed to maintain the AC grid power balance. However, it has been found that improper active power adjustment after the HVDC power block will cause steady state overvoltage problem although active power is balanced and grid frequency is satisfied. Based on the analysis of grid frequency and steady state voltage characteristics after the HVDC block fault, a coordinated active and reactive power optimization adjustment method is proposed in this paper. Objective function of active and reactive power coordinated optimization adjustment is to minimize the total power generation cost and grid active power loss such that both grid active power is balanced and voltage constraints are satisfied. Through coordinated optimization adjustment of active and reactive power, both grid frequency and bus voltage are within allowable operation range after the HVDC power block. Case studies carried out on the 3-machine 9-bus system and the actual Qingyu HVDC system validate the effectiveness of the proposed frequency control method.