  Battery energy storage boosts up the response speed of power system frequency
regulation, but must be recharged carefully to minimize the distortion to the
frequency regulation response. This paper proposes a nonlinear feedback
controller to optimize the recharge for storage resources in frequency
regulation. This controller is designed using a data-driven best-hindsight
optimization framework, the resulting nonlinear recharge controller's gain
depends on the storage state of charge as well as its power and energy rating.
The developed controller is compared with two benchmark automatic generation
control designs, one is a proportional-integral-based control from PJM
Interconnection, the other one is based on linear-quadratic regulator.
Simulation results using real area control error data from PJM Interconnection
show the proposed controller achieves smaller deviations in both the area
control error and the storage state of charge compared to the two benchmark
controllers under various storage configurations.
