System and method for increasing braking performance under multi-phase shorting

A multi-phase shorting system for braking an electric motor, the electric motor including a plurality of motor windings, the multi-phase shorting system comprising:

• a plurality of braking resistors, including at least one braking resistor for each of the plurality of motor windings;
• a plurality of first power switches, including at least one first power switch for each of the plurality of motor windings, with each first power switch being a normally-closed solid state switch connected between a respective motor winding and an electrical ground and in electrical series with the at least one braking resistor, and each first power switch being configured to selectively close to connect the respective motor winding to the electrical ground through the at least one braking resistor;
• a plurality of second power switches, including at least one second power switch for each of the plurality of motor windings, with each second power switch being a normally-closed solid state switch connected between a respective motor winding and the electrical ground, and the plurality of second power switches being configured to selectively close to bypass the plurality of braking resistors and directly connect the plurality of motor windings to the electrical ground and thereby brake the electric motor by diverting power from the plurality of motor windings;
• and
• an electronic controller configured to receive feedback regarding a speed of the electric motor, and based at least in part thereon, to generate and send to the plurality of second power switches a pulse width modulated signal which selectively opens and closes the plurality of second power switches and thereby respectively connects and disconnects the plurality of braking resistors to achieve a particular equivalent average stator resistance for the speed of the electric which results in a power transfer to the plurality of braking resistors and increases a braking torque through a deceleration speed range as the electric motor slows,
• wherein the electronic controller generates and sends the pulse width modulated signal to open the plurality of second power switches for a longer time period when the speed of the electric motor is higher and for a shorter period of time when the speed of the electric motor is lower.

A system comprising:

• an electric motor including a plurality of motor windings;
• a motor controller configured to provide power to and electronically control operation of the electric motor;
• and
• a multi-phase shorting system configured to brake the electric motor, the multi-phase shorting system including—
• a plurality of braking resistors, including at least one braking resistor for each of the plurality of motor windings,
• a plurality of first power switches, including at least one first power switch for each of the plurality of motor windings, with each first power switch being a normally-closed solid state switch connected between a respective motor winding and an electrical ground and in electrical series with the at least one braking resistor, and each first power switch being configured to selectively close to connect the respective motor winding to the electrical ground through the at least one braking resistor,
• a plurality of second power switches, including at least one second power switch for each of the plurality of motor windings, with each second power switch being a normally-closed solid state switch connected between a respective motor winding and the electrical ground, and the plurality of second power switches being configured to selectively close to bypass the plurality of braking resistors and directly connect the plurality of motor windings to the electrical ground and thereby brake the electric motor by diverting power from the plurality of motor windings, and
• an electronic controller configured to receive feedback regarding a speed of the electric motor, and based at least in part thereon, to generate and send to the plurality of second power switches a pulse width modulated signal which selectively opens and closes the plurality of second power switches and thereby respectively connects and disconnects the plurality of braking resistors to achieve a particular equivalent average stator resistance for the speed of the electric which results in a power transfer to the plurality of braking resistors and increases a braking torque through a deceleration speed range as the electric motor slows,
• wherein the electronic controller generates and sends the pulse width modulated signal to open the plurality of second power switches for a longer time period when the speed of the electric motor is higher and for a shorter period of time when the speed of the electric motor is lower.