Analysis and Performance of a Chopper Controlled Separately Excited DC Motor

A combination of Fourier analysis of load voltage waveform and Laplace transformation is applied for determining the performance of a separately excited dc motor fed from a chopper controlled supply, under all modes of operation. The analysis takes into account the commutation interval and the results show that contrary to the assumption made in works reported earlier, commutation interval significantly affects the performance. For the case of continuous conduction, independent expressions for current and speed are obtained in terms of applied voltage, load torque, and chopper and machine parameters. However, in the case of discontinuous conduction, Fourier coefficients include speed voltage as an additional quantity and hence the equations for current and speed have to be solved as simultaneous equations. The analysis is used to predict the steady-state and transient response. Computed torque-speed characteristics are compared with the results obtained experimentally.