The X-connected inverter: a topology with higher fundamental and reduced low-order harmonic voltages

A new inverter topology is presented in the paper, which produces a reduced low-order harmonic voltage waveform because of a natural harmonic cancellation process. Two switches of each limb operate at low switching frequency, whereas the other two switches of the same limb operate at higher switching frequency in conjunction with two additional capacitors. The four switches in each limb are controlled in such a way that the sequence of switching along with the voltage of two additional capacitors cancels out the low-frequency harmonics, thereby creating a pulse-width modulation (PWM) voltage with reduced low-order harmonics at the output with respect to the dc midpoint. By selection of the PWM pattern, the magnitude of fundamental voltage produced at the output can be higher than what would be achieved using sinusoidal PWM from the same dc bus voltage, without bothering about its inherent lower-order harmonics as they would be anyway cancelled. It is thus possible to achieve maximum possible dc bus utilisation theoretically.