Multilevel inverter control

A method for operating a power inverter system for a vehicle, the method comprising:

• determining a commanded torque to be produced by an electric motor of the vehicle;
• comparing the commanded torque to an upper torque threshold for a three-level mode of a multilevel inverter of the vehicle, wherein the multilevel inverter is in electrical communication with the electric motor;
• producing the commanded torque using the electric motor by operating the multilevel inverter in a two-level mode in response to determining that the commanded torque is greater than the upper torque threshold;
• and
• producing the commanded torque using the electric motor by operating the multilevel inverter in the three-level mode in response to determining that the commanded torque is less than the upper torque threshold.

A power inverter system for a vehicle, the power inverter system comprising:

• a traction battery;
• an electric motor, wherein the electric motor is configured to propel the vehicle;
• a multilevel inverter including:
• a direct current (DC) bus in electrical communication with the traction battery;
• a plurality of capacitors forming a neutral point from the DC bus;
• an alternating current (AC) bus in electrical communication with the electric motor;
• a plurality of main semiconductor switches in electrical communication with the DC bus and the AC bus;
• and
• a plurality of auxiliary semiconductor switches in electrical communication with the neutral point and the AC bus, wherein one or more component ratings of the plurality of auxiliary semiconductor switches are chosen to tolerate a current less than or equal to a maximum current required by the electric motor to produce a torque equal to an upper torque threshold;
• a controller in electrical communication with the multilevel inverter, wherein the controller is programmed to:
• determine a commanded torque for the electric motor;
• compare the commanded torque to the upper torque threshold, wherein the upper torque threshold is defined as a maximum torque of the electric motor for which the multilevel inverter is operated in a three-level mode;
• produce the commanded torque using the electric motor by operating the multilevel inverter in a two-level mode in response to determining that the commanded torque is greater than the upper torque threshold;
• and
• produce the commanded torque to the electric motor by operating the multilevel inverter in the three-level mode in response to determining that the commanded torque is less than the upper torque threshold.