Abstract: A current transducer includes a current transformer in which the conductor carrying the current to be monitored constitutes the primary. The transformer secondary is wound on a toroidal core. The transformer is operated below its cut-off frequency such that the output from the secondary is proportional to the differential of the current in the primary. The secondary output is integrated by an integrator to provide a measure of current in the primary and the integrator is initialized at predetermined intervals. A current measuring device for an electric machine, for example a reluctance machine, includes at least one of the current transducers.

Abstract: A switched reluctance machine controller derives an error signal from the difference between a current reference and the phase winding current. The error signal is applied to a pair of hysteresis circuits which define adjacent hysteresis bands above and below the reference current. The magnitude of the hysteresis bands may vary as a function of the current reference. The outputs of the hysteresis circuits are received by control logic which permits current to be applied to the phase winding when the current is below the hysteresis bands, removes current from the phase winding when the current is above the hysteresis bands and allows the phase winding current to freewheel when the current is between the upper and lower hysteresis limits. The power device used for freewheeling alternates between an upper power device and a lower power device.

Abstract: A current limiter for a rectifier circuit includes a fixed resistor 50 and a positive temperature coefficient (PTC) resistor 100 connected in series across a control switch 70. The control switch is connected between a rectifier output and a smoothing capacitor 20. If the switch fails to operate, the PTC resistor heats up, increasing its resistance in the presence of an abnormal current. The increased resistance will limit the current supplied to the rectifier output terminals 40.

Abstract: A power supply circuit is provided for generating a low voltage for powering a control circuit. The power supply circuit is connected to a voltage source having a high voltage relative to the output voltage of the power supply circuit. The power supply circuit includes a power supply capacitor and a charging capacitor connected to the power supply capacitor which charges the power supply capacitor when the power supply circuit is connected to the high voltage source. The power supply also includes an inductor connected to the power supply capacitor which charges the power supply capacitor by resonant action when the power supply circuit is disconnected from the voltage source, so that the power supply capacitor is continuously charged. A pair of diodes are also provided. The first diode is connected between the charging capacitor and the power supply capacitor. The second diode is connected in series with the inductor.

Abstract: A normalization circuit for a phase energization controller receives a rotor position value from a position encoder, and the normalization circuit obtains a normalized rotor position for each phase of a switched reluctance machine. Accordingly, the normalization circuit simplifies the detection of commutation positions for all the machine phases by reducing the commutation position determination to that of a single phase. Also, an initialization circuit for the phase energization controller energizes one or more phases of the switched reluctance motor to set the rotor of the switched reluctance motor to a preferred position to determine an offset value.

Abstract: A switched reluctance machine run as a servo-motor has its torque ripple reduced by shaping the chopping current by which the rotor is rotated relative to the stator. The shaping includes reducing the rate of change of torque with respect to time such that the magnitude of the torque ripple is reduced and therefore more easily rejected by the control function of the machine controller.