Brett M. Nee with adviser Patrick L. Chapman
Electric machines are a part of our everyday lives, often taken for granted, and consume sixty percent of our nation’s electricity. Most electric machines are fractional-horsepower, single-phase induction motors, widely used for their reliability, mature manufacturing process, low cost, and nearly speed-independent torque. But the single-phase machine has a significant flaw, low efficiency, which can be improved if single-phase machines are replaced with equally reliable and fundamentally more efficient three-phase (polyphase) electric machines. A power-conversion stage is required. Conventionally, this process is a series string of power electronic converters, each focusing on an individual stage’s function, such as regulating output voltage, current, or speed.
Our research is focused on a system-level design that considers all electrical and mechanical attributes and results in an integrated drive which can increase reliability and energy savings. One example is to use the magnetic steel of the machine as an inductor (Figure 33) in passive or active power-factor correction. Another is to use mechanical characteristics to filter an injected torque ripple in an electric machine to reduce the capacitor current ripple, as shown in Figure 34. Preliminary results show the advantages of an integrated drive design: lower cost with no sacrifice of efficiency.