Design and development of a low cost inverter drive for induction motors

The growth in high volume market in variable speed drives is expected due to emerging applications in home appliances, HVAC drives, professional hand tools, automobile accessories, fans, pumps, and process drives. The inverter controlled induction motor drive is a strong competitor for such applications due to the low cost of the motor and to its inherent features such as the simplicity of control requiring no sensors in these low performance applications, brushless as it has no slip rings thus making it truly almost maintenance-free, robust and proven construction and operation. Most of the drive's cost comes from the inverter and its controller. These low performance applications require less than or equal to $35 per hp in the cost of the inverter and its controller. The requirement is that the packaging be the smallest possible compared to the currently available in the market place and should be within 100 cubic inches including the enclosure. This paper addresses issues of design and development of such a low cost inverter and its controller to obtain one hp variable speed induction motor drives. The various issues addressed in detail are: specifications, appropriate control strategy and drive configuration, design of control circuits, their layout in printed circuit boards, layout of power circuit, switching and conduction losses and development of compact cooling arrangement tuning, ease of manufacturability and packaging. Results from a fully packaged one horsepower experimental inverter controlled induction motor drive system are presented.