Quasi-sliding technique of smooth ratio changing for inverters

A novel technique of quasi-sliding modulation has been applied to the scheme of asymmetrical pulsewidth modulation (PWM) for three-phase voltage source inverter with minimum number of switch commutations. It is based on a direct description of pulse patterns of line-to-line output voltage of inverter in the function of operating frequency of adjustable-voltage adjustable-frequency drive system. To provide smooth continuous shock-less variation of voltage waveform special signals with sliding width are formed step by-step near the center of 60/spl deg/ clock intervals of line voltage. The scheme of modulation presented combines properties of both scalar and vector principles of PWM. It has been given examples of determination on control parameters for inverter with low switching frequency. It has been described also in general form process of gradual transition from PWM to square-voltage at the maximum output frequency of rated control mode.