A new approach for speed control of a d.c. motor fed from ac to dc sepic converter

A complete modelling and numerical simulation of a system comprising a separately excited d.c. motor fed from a single-phase, single-way rectifier are presented in this paper. The strategy of this approach is based on the cascade combination of a diode bridge rectifier and a Sepic (single-ended primary inductance converter) circuit. Both step-up and step-down characteristics of the output voltage can be obtained. The supply current is approximately sinusoidal and its power factor is high. A good performance is achieved with a simple control circuit and only one switch for the converter. Differential equations describing the system behaviour in different modes of operations are presented. Solving these equations enable the predication of the motor performance in both transient and stead-state conditions. The total harmonic distortion of the supply and motor currents are obtained using the numerical simulation of this system. Moreover, the effect of the duty ratio of the converter on the system performance is investigated. The experimental and simulation results confirm the theoretical analysis. The proposed configuration provides a useful rectifier with sinusoidal input current and a satisfactory motor speed regulation.