Operation of Electric Motors with Improved Efficiency

Electric Motors consume 60% of the generated power in the US and according to the latest reports the population of electric motors has crossed the one billion mark. The energy consumed by the huge number of electric motors, and therefore the pollution associated with them have been traditionally deferred to the utility companies. The US Department of Energy (DOE) has acknowledged through the recently announced sponsorship of the industry initiative referred to as the motor challenge that this pollution problem must be considered at the motor level. The preempting of unnecessary power generation by making each motor application more efficient is the guiding principle in the motor challenge program. Specifically, the DOE has estimated that US Industries could save $2 billion by improving the efficiency of electric motors.

Motivated by the above mentioned facts, we at Clemson University's Union Camp Laboratory have used our expertise in nonlinear control of electric motors to design and develop energy efficient controllers for the induction and the brushless dc (BLDC) motors.

Induction Motor

We have designed a nonlinear velocity tracking controller which is based on the full-order model of the induction motor. By utilizing the structure of the velocity tracking controller, we have demonstrated how the magnitude of the desired rotor flux can be adjusted to minimize the power loss in the machine for the setpoint operation. We have illustrated the effect of minimizing the power loss in the machine by conducting experiments on an off-the-shelf standard three-phase induction motor. The results of the experiment are shown below along with the experimental setup used.

Figure 1: Experimental Setup

Figure 2: Curves Showing Variation of Power Loss

In experiments conducted on the bldc motor, we have illustrated how the basic control structure can be modified to minimize the energy consumed by the machine during rotor position/velocity tracking applications. Specifically, we have demonstrated how optimization techniques can be utilized to redesign the desired direct-axis current trajectory. This modification of the control structure reduces the energy consumed by the motor without interfereing with the rotor position tracking performance. Simulation results shown below verify the effectiveness of the method.

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