643 / 2019-04-15 10:07:31

Study on Coordinated Control of ±500 kV Flexible DC Power Grid with Renewable Energy and Generation Control

Modular multilevel converters, Optimal control, Power generation control, Wind energy

Two stations (Zhangbei Station and Kangbao Station) of Zhangbei +500 kV four-terminal flexible DC power grid are used for gathering renewable energy. They are connected to large-scale wind farms respectively. 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 flexible DC grid. Near Fengning station, pump storage units 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 converters, wind turbines and pump storage units. Output of wind farm 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, wind farms and pump storage units is analyzed. A strategy of V-F control with frequency supplementary control is designed for the converter connecting to large scale wind farms. A P-f droop supplementary control is designed for the wind farms to coordinate with converters. And a generation control based on power fluctuation of the AC transmission line is designed for the pump storage units. To illustrate the effectiveness of those strategies, a hardware-in-loop simulation is done on RTDS platform. Simulation results show that, under the condition of fluctuating wind, the converter and the wind farms cooperate to achieve a self-suppression of the overall output of wind farms. Furthermore, the pump storage units can alleviate the power flow fluctuation of AC system caused by DC grid. The coordinated control strategies promotes a flexible connection among the wind farms, the flexible DC power grid and the AC power grid. As a result, safe and stable operation ability of the whole system is enhanced.