A unipolar converter for a switched reluctance motor

A switched-reluctance motor requires a converter circuit to control the unipolar phase current in its phase windings. The authors describe a converter circuit for a four-phase reluctance motor, using only four switches. Unlike previous circuits with one switch per phase, the switches are rated at the motor voltage. Each switch is connected to two of the four phase windings. The switching signals must be carefully derived so that independent control of the phase currents is maintained despite the common connections. Analysis is given to predict the ideal switching algorithm for the converter circuit. This produces the optimum torque at all speeds and currents. Experimental results compare the performance of the proposed converter circuit with that of other circuits with one switch per phase. For a given supply voltage and peak phase current, the novel converter circuit produces superior torque output from the motor. The low number of switches in the converter, together with the performance of the four-phase reluctance motor, makes this an ideal low-cost variable-speed drive.<
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