A device and control method to produce braking torque counter to motor rotation. A converter supplies multiple frequency AC power to the motor. A first frequency is supplied at the normal operating frequency/speed. A second frequency, different from the normal operating frequency, is supplied to produce...http://www.google.ca/patents/US6417644?utm_source=gb-gplus-sharePatent US6417644 - Apparatus and method to generate braking torque in an AC drive
