Robust Load Frequency Control for Isolated Microgrids Based on Double-loop Compensation

Abstract

Frequency is an important indicator for the operation of microgrids. However, the randomness and uncertainty of renewable energy and load variability may lead to frequency undulation. So, a robust load frequency control (LFC) is proposed for isolated wind-diesel microgrids considering time delay and parameter uncertainty. The control strategy can suppress frequency fluctuation and optimize frequency dynamic response. First, the double compensation loop, including feedforward control and integral sliding mode control (SMC), is devised to provide anti-disturbance compensation for the diesel generator system and ameliorate the frequency stability of independent microgrids. Secondly, a dynamic fuzzy controller, composed of wind speed and load demand, is designed to provide real-time response reference power for doubly fed induction generator systems (DFIGs), which can promote the effective participation of a wind turbine system for frequency regulation. Then, the proportional differential (PD) parameters of a dynamic fuzzy controller and the frequency adjustment compensation of DFIGs can be obtained by using a particle swarm optimization (PSO) algorithm. Thirdly, load demand is an important index of the robust dynamic load frequency control method; the radial basis function (RBF) neural network observer (NNO) based on the LFC model is presented to obtain more accurate load deviations and improve the control precision of LFC. The performance of the proposed LFC method is tested under different operation cases.