Borgwarner Inc.

Daljit Singh

Everett R Geis

Todd L King

James R Gary

Highly reliable and consistent starting is achieved by first initializing the rotor position, namely establishing the rotor in a known starting position. This is accomplished by gating on two pairs of SCRs in sequence and supplying current pulses through the gated SCRs to the stator of the motor to rotate the rotor to a first position and then to a second position, the rotor coming to a complete stop in each of those positions. The rotor aligns itself with the magnetic field created by the stator in each position and any ambiguity in the rotor position is eliminated. Thereafter, the inverter is operated asynchronously in a second mode with predetermined pairs of the inverter SCRs being sequentially gated into conduction at an increasing frequency to current pulse energize the motor to effect step-by-step rotation of the rotor at a faster and faster rate, the motor current being reduced to zero at the termination of each energizing pulse to force commutate the conducting pair of SCRs. After the motor has reached a preset speed, operation in a third mode occurs and the inverter is synchronized with the motor, gating of the SCRs being controlled by the motor voltage in order that the rotor position will be synchronized to the revolving magnetic field created by the stator. During this third operating mode the motor speed continues to increase and the SCRs are forced commutated, as a result of which the rotor follows the stator magnetic field very closely and synchronization will be perfected. When the motor subsequently reaches a given speed sufficiently high to permit motor commutation exclusively, the starting system switches to a fourth and normal running mode wherein the gating of the inverter SCRs continues to be synchronized with the motor and controlled by the motor voltage, but the SCRs will now be commutated only by the motor voltage. Operation in the third mode provides a buffer and ensures a very smooth, reliable, consistent and a relatively short transition from asynchronous, forced-commutation operation to synchronous, motor-commutated operation.

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Elk Grove Village, IL, United States of America

Daljit Singh