Zeroth-Order Feedback Optimization for Inverter-Based Volt-VAR Control in Wind Farm

Significant penetration of wind power into power systems gives rise to severe power quality concerns, especially voltage violations. In wind farms, the system model parameters are usually inaccurate or even unknown, which brings great difficulties to the implementation of conventional model-based control methods. Moreover, wind farms are usually partially observable since only a few measurements are available at critical nodes. To provide a practical Volt/Var control (VVC) strategy for such networks, a novel model-free VVC method based on zeroth-order feedback optimization is proposed in this paper, which doesn't rely on any system model parameters. Firstly, the proposed method continuously collects system output measurements and evaluates the objective function value at the current input and at the measured output, thus constructing gradient estimates. Then, the control inputs are updated via an accelerated gradient projection algorithm, where the step length is selected based on Barzilai-Borwein-like rules for constrained optimization to improve the speed of convergence. Numerical tests exhibit a promising performance of the proposed method in voltage control.