The generation of well balanced three phase sine waves to control induction motor normally requires complex control circuitry. The introduction of variable speed induction motor into large volume appliances (100 W - 1 kW) requires the design of cost effective solutions. The simplified solution proposed in this paper uses a standard microcontroller including an internal Direct Memory Access (DMA). This solution spares the use of dedicated IC (hardware being replaced by software), and saves over 50% of CPU time to perform any control and supervision tasks. A practical solution to quantize three phase sinewaves, and to create the corresponding DMA table is presented. Motor voltage and motor frequency can be chosen independently. A dead time avoiding cross conduction through the bridge is also created by software. Each of the six digital outputs sets directly the state of the six power MOSFETs (or IGBTs) of the bridge via insulated interface. This interface is described in the second part of the paper. A new fully isolated pulse controlled gate driver is used. No floating auxiliary supply is needed and safety standards are met. Large dV/dt immunity is achieved. Results of practical examples are given.
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