Matching of a Separately Excited DC Motor to a Photovoltaic Panel using an Analog Maximum Power Point Tracker

Water pumping systems powered by a photovoltaic (PV) source normally use costly permanent magnet dc motors because of difficulties associated with the operation of PV powered shunt, series and separately excited motors. This paper suggests use of a separately excited motor in place of a permanent magnet motor. The proposed scheme uses a single PV source for supplying both armature and field winding. The field winding always receives constant current while the armature current varies depending on the load and the ambient condition, such that the maximum available power is drawn from the PV source. Therefore, the characteristic of a permanent magnet dc motor is achieved using a low cost separately excited dc motor. A simple and cheap analog circuit with single dc-dc converter is used to achieve this characteristic. The proposed scheme is simulated and realized. The scheme works satisfactorily both for centrifugal and constant-torque type loads.