Electric motor control
A method and apparatus is disclosed for controlling a system comprising at least one electric motor. The system includes aspects which permit, among other things, electromagnetically disconnecting a failed permanent magnet motor from said system, weight savings in motor control electronics, controllability benefits and other benefits.
1. An electric motor system comprising a motor having a magnetic rotor and a magnetically conductive stator, the stator having at least two windings connected with one another in series, the rotor and stator together defining at least a first magnetic circuit encircling a first portion of a first one of the stator windings, the stator defining at least a second magnetic circuit therein, a second one of the stator windings wrapped around a portion of the stator remote from the first magnetic circuit, the second stator winding and said portion of the stator thereby providing an inductor assembly, the second magnetic circuit passing through said stator portion and encircling a second portion of the first stator winding and a portion of the second stator winding, the second magnetic circuit remote from the first magnetic circuit and remote from the rotor, the motor system having a buck regulation apparatus connected in series between a direct current (DC) electricity source and the second winding, wherein the inductor assembly provides a filter inductor function for the buck regulator.
2. The electric motor system as defined in claim 1 , further comprising a commutation apparatus connected in series between the second and first windings and adapted to commutate DC electricity provided by the second winding into alternating current (AC) electricity to be provided to the first winding.
3. The electric motor system as defined in claim 1 , wherein a plurality of first windings are provided in a three-phase configuration.
4. The electric motor system as defined in claim 1 , wherein second winding is wound in sufficient turns around said stator portion such that electricity passing through the second winding from the direct current source saturates said stator portion.
5. The electric motor system as defined in claim 1 , further comprising a failure detection apparatus communicating with the DC source for interruption of an electricity supply of the DC source to the motor upon detection of a fault in the motor system requiring motor shutdown.
6. The electric motor system as defined in claim 1 , further comprising at least a second motor system as defined in claim 1 , and wherein the at least two motor systems are co-mounted on a common shaft.
7. The electric motor system as defined in claim 6 , wherein the at least two motor systems have a common rotor and stator, and wherein the at least two motor systems are separately controllable, and wherein the windings of the respective motor systems are confined to distinct non-overlapping sectors of the common stator.
8. A method for controlling an electric motor system, the system including at least one motor having a magnetic rotor and a magnetically conductive stator having at least one winding, the rotor and stator together defining at least a first magnetic circuit encircling a first portion of a first one of the stator windings, the stator defining at least a second magnetic circuit therein, the second magnetic circuit encircling a second portion of the first stator winding, the second magnetic circuit remote from the first magnetic circuit and remote from the rotor, the method comprising the steps of:
operating the motor to drive an output shaft thereof, the step of operating including the step of saturating at least a portion of the second magnetic circuit to maintain an impedance of said winding at a first value during operation;
requiring motor shutdown; and then
shutting down the motor, including the step of de-saturating at least said portion of the second magnetic circuit to increase the impedance of the winding to a second value, the second value significantly higher than the first value such that current flow in the winding is effectively limited to a desired value.
9. The method of claim 8 wherein the desired current value is substantially zero, such that drag torque generated by continued rotation of the motor is substantially zero.
10. The method of claim 8 further comprising the step of continuing to drive the output shaft after said step of shutting down the motor.
11. The method of claim 10 wherein the output shaft is driven by at least a second motor connected to the shaft.
12. The method of claim 11 , further comprising the step of adjusting an output torque of the second motor after the step of shutting down, to compensate to the lost torque attributed to said step of shutting down the other motor.
13. The method of claim 8 wherein the step of requiring motor shutdown includes the step of detecting a fault in the motor.
14. The method of claim 8 wherein the step of saturating at least a portion of the second magnetic circuit includes passing a saturating current through a second winding wrapped around a portion of the stator remote from the first magnetic circuit carrying said portion of the second magnetic circuit, and wherein the step of de- saturating at least said portion of the second magnetic circuit includes reducing a current level in said second winding below a saturation current level.