Microprocessor based PWM inverter with third harmonic injection

Abstract

The use of a microprocessor system the MC68020, to generate a real PWM scheme to control a three-phase voltage source inverter based on the asymmetric regular sampling technique is described. One of the shortcomings of this scheme, which is the limitation placed on the fundamental voltage that cannot exceed 50% of the input DC voltage at unity depth of modulation, is partially avoided by the injection of a certain amount of third harmonics. A method of smooth variation of the output frequency is also described.<>