Development of a low cost inverter controlled induction motor drive with emphasis on the effect of power factor correction

In the fractional hp induction motor drive market, there is an absence of low-cost and compact designs. Moreover, given the massive production of appliances which require such drives, there is little need for high-performance microcontroller controlled drives, since the only adjustments to the drive are made at the factory. The developed drive achieves the low cost and compact aims by implementing with analog components the constant Volts per Hertz technique. This simple technique can be used regardless of whether the speed loop is open or closed.

In addition, since there is a growing need for drawing sinusoidal currents from utilities both for an optimal utilization of the utility power plant capacity and to minimize the harmonics injected into it, the developed drive is preceded by a power factor correction circuit, and its effect on the drive’s performance is determined with measurements of the system efficiency and the input power factor. It is found that the decrease in the system efficiency with the PFC circuit is small, and takes place only for speeds lower than 0.72 p.u. for a fan load.