Battery operated closed loop speed control of DC Separately Excited Motor by Boost-Buck Converter

The Boost-Buck converter, also known as Cuk converter is an alternative power conversion topology which can be used for buck and boost the battery input voltage. Hence a wide range of speed control is possible for a dc separately excited motor using such converter. In this paper, the dynamic modeling of Boost-Buck converter with motor load has been formulated using state-space averaged analysis method. Small-signal model has been derived from the state-space averaged dynamic method for linearization. The input side phenomenon, associated with passive parameters is studied using small-signal analysis to show the right-half-plane (RHP) zero in the control-to-output transfer function. Based on small-signal linearization model, the control law for speed control is derived. Speed is controlled by direct measurement of the speed and input current. The compensators for the speed loop and the current loop are designed based on the frequency responses and root locus technique. The passive parameters such as capacitor and inductors are estimated to limit the capacitor ripple voltage and inductor ripple current. Hysteresis band modulator is used for finding out the switching function of switch. Performance of control method of the compensated Boost-Buck converter is verified by simulation.