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Wind farms (WFs) can provide inertial response to power systems through synthetic inertial control. In large scale power systems with high penetration level of wind power, WFs are located in different areas with different wind speed conditions, and it is necessary to coordinate them during inertial control. This paper proposes a hierarchical inertial control (HIC) scheme consisting of a WF level coordination and a wind turbine (WT)/battery energy storage system (BESS) level coordination in active power outputs during inertial control process, in order to improve the system frequency response and reduce the operational cost of each WF. First, the optimal active power references of multiple WFs during inertial control are determined to improve the frequency nadir of the system. Second, the active power references of the WTs/BESS of each WF is optimized to avoid over-deceleration of the WTs' rotor, and minimize the wind energy loss and degradation cost of the BESS. The optimization is achieved by developing a model predictive control (MPC) problem and solving it using the alternating direction method of multipliers (ADMM) to improve the computation efficiency. Simulations on 5 WFs integrated into IEEE 39-bus system were conducted to validate the proposed HIC scheme.

Wind farms (WFs) can provide controlled inertia through synthetic inertial control (SIC) to support system frequency recovery after disturbances. This paper proposes a model predictive control (MPC) based SIC for a WF consisting of wind turbines (WTs) and a battery storage energy system (BESS). In the proposed MPC-SIC, the active power output of the WTs and BESS during the SIC are optimally coordinated in order to avoid over-deceleration of the WTs' rotor, and minimize the loss of extracted wind energy during the SIC and degradation cost of the BESS. The IEEE 39 bus system with a WF consisting of 100 WTs and a BESS is used to validate the performance of the proposed MPC-SIC. Case studies show that, compared with the conventional SIC, the minimum rotor speed among all WTs with MPC-SIC can be improved by 0.08-0.11 p.u., the loss of captured wind energy of WF with MPC-SIC can be reduced by 12%-64% and the degradation cost of the BESS with MPC-SIC can be reduced by 72%-83%. The results proves that with the proposed MPC-SIC, the wind farm can avoid the over-deceleration of the WTs' rotor and reduce the operation cost of the WF by improving the efficiency of wind energy usage and lifetime of the BESS.

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