This document describes inverter circuits used for motor control and other applications, focusing on PWM control. It also describes the differences between two-phase and three-phase modulation techniques as well as circuits for drive power supply and power losses in semiconductor. Theoretically, the rotation speed of a motor can be controlled by varying only the frequency. However, unless both voltage and frequency are controlled, an. Voltage source type inverters are commonly used for all home appliance and industrial power applications. Voltage source type inverters are easier to control. Three common techniques used to control (modulate) the power supplied to a load are pulse-width modulation (PWM), pulse-frequency modulation (PFM),. Converter (Rectifier) The pulse width (duty cycle) is varied to control the output. AC PFM Average output.