A 12-step voltage source inverter control circuit for induction motor drives

In this paper it is shown that the maximum number of steps that an inverter can have is 12. As this is closer to the sinusoidal wave form, its harmonic content is less than the usual 6-step one. A 12-step inverter control circuit is presented for Y-loads. The control circuit is constructed using a timer, a module-24 counter, an EPROM and a number of AND gates. The design is simple and economical. As it utilizes digital electronic components only, the control circuit lends itself for miniaturizing for mass production. The circuit also keeps volt/hertz of the inverter constant which is a necessity for induction motor drives. The number of pulses and the ON time of the timer remains unchanged throughout the operating frequency range making the analysis of the motors simpler. Further more the circuit uses pnp-npn transistor pairs which eliminates the base isolation problem of the inverters.