IMPROVED PWM CONTROL FOR GTO INVERTERS WITH PULSE NUMBER MODULATION

This paper proposes pulse number modulation (PNM)-assisted pulse-width modulation (PWM) control to improve the modulation factor of bridge i nverters and to solve voltage uncontrollability in neutral point clamp ed (NPC) inverters, The basic idea is to enlarge the linear region of PWM control via PNM technology. The authors will show the following th rough simulation and experimental results: 1) Conventional bridge inve rters can utilize at most 80% of the nominal inverter capacity because of the limit of the modulation factor, The PWM and PNW combined contr ol is able to improve the modulation factor up to approximately 1.0, 2 ) The PWM and PNM control enables linear voltage control in the NPC in verter even for an extremely small reference, The PNM technology also contributes to a reduction in switching losses.