Abstract: A new series of portable electric tools using high frequency three-phase induction motors with built-in power electronic converter. The tools operate from a single phase AC mains and a built-in power electronic circuitry converts the input supply to a three-phase, higher frequency (200-400 Hz) supply, which is used to drive a three-phase induction motor connected to the gearbox. A microprocessor-based controller, with a novel algorithm, generates three-phase, sinusoidal output waveforms and also provides the soft-start feature for the inverter and the motor. The entire electronics is packaged in a novel way within the housing of the tool itself. The output shaft of the motor, either directly or through a gearbox, can be connected to a wide range of tools like Drills, Grinders, Nut Runners, Screw Drivers, Impact Wrenches, Shears, Nibblers, Saws, Sanders, polishers, etc.

Abstract: Three phase sinusoidal waveforms generated from a DC bus voltage using Space Vector PWM method are used to obtain multi-speeds from a 3 Phase AC Induction motor. A novel algorithm generates the switching signals from a micro controller to drive the power devices of the Inverter Bridge, the output of which is applied to the motor. At different speeds, below the rated voltage of the motor, the output voltage V and the frequency f are maintained to keep V/f constant so that the motor torque is kept constant. At above the rated voltage of the motor, only the frequency is increased to obtain constant output from the motor at increased speeds.