Andrew P. Friedl with adviser P. T. Krein
A modular inverter designed by Professor Krein’s graduate students a few years ago provided the design for two more modular inverters built recently. One is being used to implement induction motor control via direct torque control (DTC), indirect field-oriented control (IFOC), vectorized volts-per-hertz control, and feedback linearization. These controls will be applied to determine which application they best fit: electric and hybrid-electric vehicles, industrial 3-phase motors for lathes and milling, and consumer appliances such as washing machines, air conditioners and compressors. In the same system an encoder with 11-bit resolution was attached to a dynamometer running as a speed feedback device.
As of July 2009, DTC, IFOC, vectorized volts-per-hertz, and feedback linearization have been simulated and are operational in Matlab-Simulink. Also, different switching techniques such as bang-bang (hysteresis), pulse-width modulation (PWM), and space-vector pulse-width modulation (SVPWM) have been applied to vectorized volts per hertz to see which one has superior performance. The average switching frequency was kept the same, in this case 10 kHz, a typical switching frequency in power applications.
Figure 10 presents the torque performance of these three switching techniques overlaid on ideal volts-per-hertz. Figure 11 shows the corresponding speed response. These results indicate that the ideal is truly the best, while SVPWM is next. The performance of PWM with vectorized volts-per-hertz is virtually identical to that of SVPWM. Hysteretic control has a slightly poorer dynamic performance compared to the other two switching techniques. It is important to note that all the switching techniques have similar overall performance. The best switching technique for each motor drive is not yet proved; that is another research goal. Soon, two modular inverters will be running in parallel to debug each motor drive in order to reach this goal.
This research is supported by US Office of Naval Research grant ONN B00014-18-1037.