A virtual instrumentation-based on-line determination of a single/two phase induction motor drive characteristics at coarse start-up

The single/two phase induction motors (S/TPIM) are used in various low-power, low-cost applications. A representative example is the washing machine drum´s main drive. Both manufacturers and designers have augmented their preoccupations and researches to optimize the efficiency of this drive due to the large and increasing number of devices in use and also stimulated by the market requests. At the same time, their efforts have been directed to maintain the drive´s main advantage i. e. its low cost. A simple strategy to optimize the S/TPIM drive´s efficiency is to replace the fixed capacitance of the starting capacitor of the motor with an electronically switched capacitor. In this approach, an accurate dynamic characteristic of the actuator, i.e. electric motor and washing machine´s drum, need to be determined for the implementation of the starting capacitance´s command law. In this paper an estimation method of the drive´s mechanical strain at coarse start-up is presented. The dynamic model of the drive is based on the direct-and quadrature-axis theory; this approach provides accurate estimates of the drive´s response. The on-line measurements of the input voltages and currents are performed with a fast data acquisition board and a virtual instrumentation software environment providing noise-free measurements. The main advantage of this method consists in its simple implementation on the washing machine and to provide torque predictions both in stationary and in dynamic regimes in real operating conditions.