Source current harmonics and motor copper loss reduction control of electrolytic capacitor-less inverter for IPMSM drive

Abstract

To reduce the cost of an AC–DC–AC system, a single-phase-to-three-phase electrolytic capacitor-less inverter has been proposed. In particular, to satisfy the requirements of a harmonic source current, it is necessary to control the source current under sinusoidal waveform conditions. However, the DC-link voltage becomes an absolute value of the source voltage, and the output voltage is almost zero near the zero-crossing region of the source voltage. In the zero-output-voltage region, the motor current response deteriorates while controlling the sinusoidal source current. When the motor speed is high, the copper loss is always large because the motor current in the zero-output-voltage region depends on the back-electromotive force of the motor. To suppress the copper loss in the zero-output-voltage region, this paper proposes a copper-loss reduction control method that utilizes the initial-condition response of the motor current. The proposed method reduces the motor copper loss while controlling the source current sinusoidally, and improves motor efficiency while satisfying the requirements of a harmonic source current. This paper analyzes the motor current in the zero-output-voltage region and focuses on the initial-condition response of the d-axis current. In addition, an optimal initial value that reduces the copper loss in the zero-output-voltage region is calculated.