Hardy space nonlinear controller design for DC microgrid with constant power loads

Abstract

The increased use of DC microgrid for critical application lead to the necessity of advanced control design for a stable operation of the system. The loads connected to DC microgrid are controlled with power electronic devices and shows the behaviour of constant power load (CPL), which poses a serious challenge to stability as it adds nonlinearity and minimises the effective damping. This paper presents a robust controller design approach based on Hardy Space (H)-infinity control norms to tackle the nonlinearity added by CPL by expanding the region for stability. The design criteria are based on Lyapunov theory of nonlinear systems within the framework of Linear Matrix Inequality (LMI). The necessary and sufficient conditions are obtained in terms of linear matrix inequalities to ensure the transient performance and stability of the system. The LMI equation is solved to maximize the size of the estimated domain of stability. The performance of the proposed controller is verified using simulation in MATLAB/Simulink. The DC microgrid in this paper consists of a solar photovoltaic (PV) unit and a battery as an energy storage system together with loads. The Proposed controller not only ensures the stability of the system but also guarantees the improved transient performance of the closed loop system by expanding the size of the stability region.