Coordination Control of Wind Farm Combined with Energy Storage System for Frequency Control

To improve the frequency control of power systems with high penetration of renewable energy resources, this paper proposes a cooperation control method for the wind farm combined with energy storage for inertial support and primary frequency control. The whole station contains a multi-level control architecture based on the mixed hierarchical model predictive control technique that coordinates each unit to respond to frequency fluctuation. In the top layer, a linear model predictive control method is proposed to compute the respective active power reference of the whole energy station. To realize the coordination control of wind turbines, a nonlinear model predictive controller is designed to solve the issue of nonlinear character. The slack variable is introduced to the design of the cost function, which helps allocate the power reference among different turbines according to the maximum available energy and satisfies each unit's power constraint and stability constraint. For the coordination control of energy storage units, the slack variable is introduced to improve the efficiency of balancing states of charge among different units. Finally, simulation results verify the effectiveness of the proposed control structure and method, which decreases the frequency deviation to lower than 60% in the case study.