Control strategy of a dual lane fault tolerant permanent magnet motor to reduce drag torque under fault condition

1. A motor drive circuit comprising:

two or more inverters to provide current to a dual lane fault tolerant three-phase permanent magnet motor, each inverter comprising, for each phase of the motor to be driven, a respective switch arm comprising one or more switches;

means for detecting a switch short circuit for any switch within one of the inverters;

means for determining the speed of the motor; and

a controller configured, in the event a switch short circuit is detected within one of the inverters, to:

a): close all switch arms of the inverter containing the switch short circuit when the motor speed exceeds a predetermined threshold, and

b): not to close any of the switch arms not containing the short-circuited switch if the motor speed does not exceed the predetermined threshold.

2. The motor drive circuit of claim 1 , wherein each switch arm comprises two switches connected in series.

3. A method of controlling a motor drive circuit for driving a dual lane fault tolerant permanent magnet motor, the method comprising:

monitoring the motor speed of the dual lane fault tolerant permanent magnet motor;

detecting when a switch short circuit occurs in any switch in any of two inverters connected to the dual lane fault tolerant permanent magnet motor;

comparing the motor speed to a predetermined threshold;

short-circuiting all motor phases of a the dual lane fault tolerant motor connected to the inverter in response to detection of both: i) a switch short circuit in any switch in the inverter, and ii) the motor speed exceeding a predetermined threshold; and

not short-circuiting any motor phases not containing the short-circuited switch if the motor speed does not exceed the predetermined threshold.