Sliding mode observer and controller design for solar array current estimation and robust maximum power point tracker in the grid-connected photovoltaic system

Abstract

As people are much concerned with the fossil fuel exhaustion and the environmental problems caused by the conventional power generation, renewable energy sources and among them photovoltaic panels and wind-generators are now widely used. Photovoltaic (PV) sources are used today in many applications such as battery charging, water pumping, home power supply, swimming pool heating systems, satellite power systems etc. They have the advantage of being maintenance and pollution free but their installation cost is high and, in most application, they require a power conditioner (DC/DC converter or DC/AC inverter) for load interface. The output power of PV array is changed by environmental factors, such as illumination and temperature. Since the characteristic curve of a solar cell exhibits a nonlinear voltage-current characteristic, a controller named maximum power point tracker (MPPT) is required to match the solar cell power to the environmental changes. Many algorithms have been developed for tracking maximum power point of a solar cell. Among them, the most commonly used methods are perturb and observe (P&O) algorithm and incremental conductance algorithm. Both algorithms are required to measure the solar array current and voltage to acquire the information on the solar array power and conductance. The additional information such as the measurements of the grid voltage and inductor current are also required for the single-stage grid-connected photovoltaic system to synchronize the phase of the inductor current to the grid voltage. Since the solar array current has a close relation with the solar array voltage and the inductor current, it is possible to estimate the solar array current through state observer. As the state observer requires the exact information on the circuit parameters, such as capacitance and inductance, it is absolutely required to know the exact parameter value However, in the single-stage grid-connected photovoltaic inverter system, the elect...