Asymmetrical scheme of direct digital modulation of output voltage of inverter based on scalar-vector quasi-sliding approach

摘要

The paper describes new method of digital quasi-sliding modulation of line-to-line voltage of 3-phase voltage source inverter, applied to the scheme of asymmetrical pulsewidth modulation (PWM) with minimum number of switch commutations. It is based on 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 Centers of 60° clock intervals of line voltage. It has been presented two main variants of the method proposed: natural modulation and regular modulation. The scheme of modulation presented combines properties of both scalar and vector principles of PWM. It has been given examples of determination of control parameters for inverter with low switching frequency, it has been analysed spectral composition of output voltage of inverter. It has been described also the processes of gradual transition from PWM to square-wave voltage at the maximum output frequency of the rated control mode.