Field and armature control for separately excited DC motors powered by photovoltaic cells

In this paper, the authors have investigated, both by simulation and experimentally, the effect of matching the field and armature windings on the performance of a separately excited DC motor interfaced to two photovoltaic (PV) arrays. Special emphasis has been placed on matching the load line of the field winding which, if directly connected, intersects the I-V characteristics of the array at a voltage close to the open circuit voltage resulting in a very small excitation current and hence poor motor performance. Step-up choppers were used as impedance transformers to match the motor windings to the maximum power lines of the PV arrays. The motor was coupled to a torque meter and the step-up choppers were PWM controlled by a personal computer (PC). The importance of matching the field winding was clearly illustrated whereas matching only the armature winding did not significantly improve the system efficiency