Microcomputer Implemented PWM Inverter Using a Unique Pattern of Switching Angles

A method is proposed for implementing a PWM transistor inverter using a microcomputer. The control of the input de voltage to the inverter allows the use of a unique pattern of switching angles and a continuous variation of the output voltage. The periodically measured input de voltage defines completely the switching instants, which are inversely proportional to the measured dc voltage. A 10-bit A/D, converter allows a voltage and consequently a frequency resolution of 0.1 percent. Since the proposed method does not require extensive look-up tables, only about 700 bytes of memory were required for the inverter implementation using a TMS 9900 microprocessor.