Suppression method of increase in motor current at zero output voltage for an electrolytic capacitor-less inverter

To reduce the capacitance of the DC-link capacitor in an AC-DC-AC system, a single-phase to three-phase electrolytic capacitor-less inverter is proposed. The inverter is used to control both the motor and source currents. In particular, it is necessary to sinusoidally control the source current to meet the source current harmonics guideline. The DC-link voltage becomes an absolute value of the source voltage and is almost zero near the zero crossing. As the output voltage is also zero near the zero crossing, the motor current response deteriorates in the method of controlling the source current sinusoidally. The motor current near the zero crossing flows because of the back electromotive force, and the copper loss is significantly large, particularly in the high-speed region. This paper analyzes the motor current response in the zero-output-voltage region and proposes a method to suppress the motor current increase. The proposed method is validated by conducting simulations and experiments.