Disturbance Observer based Controller Design to Reduce Sensor Count in Standalone PVDG Systems

Standalone photovoltaic distributed generation (PVDG) systems have found their way into many popular off-grid applications like deserts, military and rural development. Generation of power at the consumption site and supplying power in DC make these systems more efficient due to minimization of losses during transmission and conversion. But, these systems suffer from lower inertia and this factor added with uncertainties in power generation and load consumption, greatly affects system stability. Nonlinear control techniques like backstepping although effective, are expensive to implement since they are model-based and demand information from many sophisticated sensors. In this paper, a disturbance observer based on back-stepping control strategy is proposed for grid voltage control and MPPT of an isolated PVDG system with storage consisting of PV array, battery and load. The effects of irradiation and temperature on PV arrays, the variations in loads and battery voltage are modeled in the form of disturbances. Instead of measuring these entities with sensors, the update laws designed in this paper based on Lyapunov stability theory estimate their values which are further utilized for effective control during intermittencies. It can be seen from the MATLAB simulation results that adoption of this technique contributes towards faster and cheaper control of the PVDG system for a greater range of operating conditions.