POWER CIRCUITS FOR OPTIMUM STEPPED-WAVE OUTPUT IN THREE-PHASE SINGLE-WAY STATIC INVERTERS.
NAVAL RESEARCH LAB WASHINGTON D C
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In the three-phase, single-way inverters considered, the stepped-wave approach offers the great advantage of an output waveform that approaches that of a sinusoid. The single-way type inverter is advantageous where the input dc voltage is low, since in this type of inverter the voltage drop in only one switch need be considered. Fourier analysis of a stepped-wave output shows that if the center of each step lies on a sinusoid, the lowest harmonic present is one less than the number of steps in the waveform. Various circuit configurations using single-phase and three-phase cores, which involve interconnection of multiple primary transformer windings, are considered for producing stepped waves with minimum harmonic content. These types of circuit configurations result in poor switch and copper utilization, and have limited power capability. Circuit configurations where interconnection of multiple secondary transformer windings are used result in good copper and switch utilization, and the power capability increases as the number of steps or switches is increased. If in a multiswitch three-phase inverter one half the total number of switches are considered as one input system and the other half as a second input system, voltage regulation may be obtained by varying the phase relation between the two input systems. For three-phase power applications where the input dc voltage is low, inverter-circuit configurations using interconnection of multiple secondary transformer windings appears attractive.
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