Quasi-sliding strategy of modulation for modified vector PWM for frequency-controlled 3-phase voltage source inverters

The paper presents a quasi-sliding approach to direct synthesis of line-to-line output voltage of 3-phase voltage source inverters for adjustable speed drive application. This strategy of modulation is applied to the scheme of modified voltage space vector control which is characterized by the better performance at the higher range of output frequency. Quasi-sliding modulation provides smooth shock-less ratio changing of pulses of line voltage during the whole control range including overmodulation zone due to continuous step-by-step formation of special sliding signals (pulses and pauses) with variable width, which are changing each other at the boundary frequencies. Positions of pulse patterns are described here mainly by simple algebraic correlations in the function of control frequency of drive system. To avoid undesirable voltage waveforms with double-pulses and double-pauses, additional modulation of signals next to sliding control signals is executed. Special attention is given to analysis of laws of modulation in the zone of the highest output frequencies, where smooth transition from PWM to square-wave voltage is provided