Induction motor performance testing with an inverter power supply: Part 1

The development of high-power density electrical machines continues to accelerate, driven by military, transportation, and industrial needs to achieve more power in a smaller package. Higher speed electrical machines are a recognized path toward achieving higher power densities. Existing industry testing standards describe well-defined procedures for characterizing both synchronous and induction machines. However, these procedures are applicable primarily to fixed-frequency (usually 60 or 50 Hz) power supplies. As machine speeds increase well beyond the 3600-rpm limitation of 60-Hz machines, a need for performance testing at higher frequencies is emerging. An inverter power supply was used to conduct a complete series of tests on two induction motors (0.5 and 1.0 MW) with speeds up to 5000 rpm. The use of a nonsinusoidal power supply with limited power output capability required the development of measurement techniques and testing strategies quite different than those typically used for 60/50 Hz testing. Instrumentation and techniques for measuring voltage, current, and power on harmonic rich waveforms with accuracies approaching 1% are described. Locked-rotor and breakdown torque. tests typically require large kVA input to the motor, much higher than the rated load requirement. An inverter sized for the rated load requirements of the motor was adapted to perform locked-rotor and breakdown torque tests. Inverter drive protection features, such as anti-hunting and current limit that were built into the inverter had to be factored into the test planning and implementation. Test results are presented in two companion papers. This paper (Part 1) correlates test results with the results of an algorithmic induction motor analysis program. Part 2 presents the test results compared with a Matlab simulation program and also provides a comprehensive discussion of the instrumentation that was essential to achieve testing accuracy. Correlating test results with calculated values confirmed that the testing techniques developed during this testing program are useful for evaluating high-speed, high-power density electrical machinery.