Dynamic performance of directly coupled photovoltaic water pumping system using DC shunt motor

The dynamic performance of a typical photovoltaic (PV) powered water pumping system is investigated in this work. The system consists of a PV array, a DC shunt motor and a centrifugal pump. The mathematical models of the system under steady-state and dynamic conditions are developed. A computer simulation program is developed to obtain the steady-state performance at any instant in the year and under any atmospheric conditions. The program is also capable of calculating the dynamic performance of the system under any abrupt changes in solar irradiance. The nonlinearity of the magnetization characteristic of the motor due to saturation is taken into consideration. The magnetic characteristic of the shunt motor is measured experimentally. An analytic function representing this characteristic, in the form of a polynomial, was obtained using curve fitting techniques. This analytic function is then used in the models. The study showed that the system attains steady-state conditions quickly after any abrupt change. However, it is important to use dynamic rather than static analysis under fast fluctuating weather conditions.