Robust frequency control in a wind-diesel autonomous microgrid: A novel two-level control approach

Abstract

Volatile nature in renewable power output, stochastic nature of load and continuous change in system structure are the key factors affecting the stable operation of microgrid (MG), particularly in frequency control. Appropriate control schemes are indispensable to reduce the frequency fluctuations in MG under such scenarios. Concerning to these issues; this paper proposes a novel two-level control mechanism approach to mitigate the frequency fluctuations in the wind-diesel standalone MG. In the first level, from wind turbine generator (WTG) side, a fixed wind power command is replaced by an optimum adaptive wind power command based on the power system operating conditions and wind speed conditions. To perform this task, the fuzzy logic approach (FLA) is employed by considering change in wind velocity and frequency deviation as inputs and change in WTG power as output. In the second level, a robust FLA tuned Proportional Integral (PI) controller is proposed to regulate the output power of the diesel engine generator (DEG) for the further reduction in MG frequency fluctuations. With this proposed two-level approach, the MG frequency fluctuations are within the limits in all possible operating conditions, which include some critical operating scenarios. Moreover, the superiority of proposed approach in dynamic performance enhancement against load and wind power changes is proven by comparing with various powerful controllers in the literature.