Method and system for controlling an inverter for an electric machine

A method for controlling an electric power inverter arranged to supply electric power to a rotary electric machine, the method comprising:

• determining that the rotary electric machine is operating at a stall condition;
• determining a rotational position of the rotary electric machine;
• determining a first zero vector modulation control parameter for the electric power inverter when the rotational position of the rotary electric machine is within a first range of rotational positions of the rotary electric machine, wherein the first range of rotational positions of the rotary electric machine is determined based upon a maximum of a first junction temperature in a diode of the electric power inverter and a second junction temperature in a power switch of the electric power inverter when the electric power inverter is operating the electric machine at the stall condition;
• determining a second zero vector modulation control parameter for the electric power inverter when the rotational position of the rotary electric machine is outside of the first range of rotational positions of the rotary electric machine;
• operating, via a controller, the electric power inverter in a zero vector modulation (ZVM) mode employing the first zero vector modulation control parameter when the rotational position of the rotary electric machine is within the first range of rotational positions of the rotary electric machine;
• and
• operating, via the controller, the electric power inverter in the ZVM mode employing the second zero vector modulation control parameter when the rotational position of the rotary electric machine is outside of the first range of rotational positions of the rotary electric machine.

A system for controlling a rotary electric machine, comprising

• an electric power inverter having a plurality of power switches, wherein the electric power inverter is operatively connected to the rotary electric machine;
• and
• a controller, operatively connected to the plurality of power switches of the electric power inverter and in communication a plurality of sensors that are arranged to monitor the rotary electric machine;
• the controller including an instruction set, the instruction set executable to:
• determine a rotational speed of the rotary electric machine,
• determine the rotary electric machine is operating at a rotational speed that is less than a low speed threshold, wherein the low speed threshold is determined based upon a semiconductor junction temperature in the electric power inverter;
• determine a second parameter for the rotary electric machine, wherein the second parameter corresponds to a rotational position parameter for the rotary electric machine;
• determine a first control parameter for the electric power inverter when the second parameter is within a first range, wherein the first range for the second parameter is determined based upon a maximum of a first semiconductor junction temperature in the plurality of power switches and a second semiconductor junction temperature in the plurality of power switches of the electric power inverter when the electric power inverter is operating the electric machine at the rotational speed that is less than the low speed threshold;
• determine a second control parameter for the electric power inverter when the rotational position of the rotary electric machine is outside of the first range of rotational positions of the rotary electric machine;
• operate the electric power inverter in a zero vector modulation (ZVM) mode employing the first control parameter when the rotational position of the rotary electric machine is within the first range of rotational positions of the rotary electric machine;
• and
• operate the electric power inverter in the ZVM mode employing the second zero vector modulation control parameter when the rotational position of the rotary electric machine is outside of the first range of rotational positions of the rotary electric machine.