Study on Coordinated Control of Renewable Energy and Pump-storage Generator connected to MMC-HVDC Grid

Abstract

Two stations (Zhangbei Station and Kangbao Station) of Zhangbei +500 kV four-terminal modular multilevel converter power grid (MMC-HVDC) are used for gathering renewable energy. They are not connected to main grid and operate at islanding mode. The other two stations (Beijing station and Fengning station) are connected to main power grid in North China, as energy consumption center and power balance node of the MMC-HVDC grid. Near Fengning station, pump storage generators are built to provide power support for the system. Due to the complex structure of the system, severe challenges have been posed for the control of MMC converters, renewable energy and pump storage generators. Output of renewable energy is intermittent. Voltage of DC grid is highly sensitive to power unbalance. And power quality requirements of energy consumption center is high. In this paper, coordinated generation control strategy of DC converters, renewable energy and pump storage generators is proposed. A frequency supplementary control is designed for the converter connecting to renewable energy. A Powerfrequency (P-f) droop control is designed for renewable energy generation to coordinate with MMV converters. And a generation control based on power fluctuation on AC transmission line is designed for the pump storage generators. To illustrate the effectiveness of those strategies, a hardware-in-loop simulation is done on real time digital simulation (RTDS) platform. Simulation results show that, under the condition of power fluctuation, the converter and the renewable energy generation cooperate to achieve a selfsuppression of the overall output on MMC-HVDC grid. Furthermore, the pump storage generators can alleviate the power flow fluctuation of AC system caused by DC grid. The coordinated control strategies promotes a flexible connection among the renewable energy, MMC-HVDC grid and the AC power system. As a result, safe and stable operation ability of the whole system is enhanced.