Torque Modulation Improves the Efficiency of Electric Motors

This paper presents an advanced motor control technique called dynamic motor drive (DMD®), which uses torque modulation to improve system efficiency. Instead of continuous torque output, motor output torque is intermittently controlled between a non-zero torque and zero to minimize total system losses for a given mechanical output. Selection of the torque duty cycle ensures that the average torque during modulation is the same as the requested torque. As a result, during low load operation, system losses are reduced by operating the motor and power electronics intermittently at higher efficiencies than would occur with continuous operation. For operating conditions at which torque modulation cannot provide reduced losses, such as high output torques, continuous operation is used instead. DMD is a cost-effective, software-driven, revolutionary motor control technique applicable to various motor topologies such as synchronous reluctance motors (SynRM), interior permanent magnet synchronous motors (IPM) and electrically excited synchronous motors (EESM).