EPROM-based modulator for synchronized asymmetric regular-sampled SPWM technique

The objective of sinusoidal PWM technique is to synthesize the motor currents as near to a sinusoid as possible economically. Traditionally, PWM control is accomplished using a natural sampling technique. Though its implementation is simple and in real time, it cannot give good performance in the entire operating range. Microprocessor-based PWM generation can offer significant advantages but suffer from computational time limitations. Moreover, it is not economical for general-purpose variable speed drives. A novel technique of PWM signal generation is addressed in this paper. While different requirements of high performance SPWM are fulfilled, the circuit configuration is reduced compared with conventional circuits. A regular sampled, asymmetric, synchronized SPWM with variable gear ratio and third harmonic injection at higher modulation depth, is realized with much reduced hardware. Such reduction in complexity, cost and space are essential to boost the changeover from constant speed to variable speed drive for energy saving in general applications. This was the motivation of work presented. The technique is well suited even for dedicated implementation using a microcontroller.