THREE-LEVEL THREE-PHASE INVERTER APPARATUS

摘要

A three level three-phase inverter apparatus operating on a proposed pulse width modulation method whereby good output voltages are obtained free of the effects of the minimum pulse width constraints of switching devices and whereby the neutral point voltage is controlled. The apparatus has a modulation circuit containing a microprocessor and a voltage vector selection circuit. The microprocessor divides one period into six segments of 60 degrees each. Each segment is divided into four triangular regions each determined by the vertexes of voltage vectors. An output voltage command is given as a vector. Once the segment and region to which a given vector belongs are determined, the voltage vectors corresponding to that region and the order is which to output these vectors are derived from the predetermined vector combinations and their output orders stored beforehand in the voltage vector selection circuit. Each vector output order is arranged so that one voltage vector is replaced by another through a switching operation of any one phase. The time average of these consecutively output voltage vectors in a given carrier period is modulated to coincide with the value of the command vector. This scheme provides good output voltage waveforms while controlling the neutral point voltage.