Robust Torque Control of Switched-Reluctance Motors Without a Shaft-Position Sensor

This paper describes a technique for stabilizing the operation of variable-reluctance stepping-motor drives operating without a shaft-position sensor. In such systems there is a trade-off between the system efficiency and the torque margin (or pull-out torque) which depends on the width of the phase conduction pulse width. The scheme described in the paper permits the motor to run in the steady state with both narrow conduction pulse widths and high efficiency. Under transient or overload conditions the conduction pulse width is increased in response to a change in the dc link current, providing an increase in available torque. Tests on a small motor drive have produced a steady-state torque margin of over 300 percent and of 200 percent under step-change conditions.