Efficiency improvement in motor drive system with single phase diode rectifier and small DC-link capacitor

In this paper, motor drive system fed by single phase diode rectifier without input filter is proposed. The motor drive considered in this paper consists of single phase diode rectifier, three-phase inverter, and small DC-link capacitor. Since DC-link capacitor is small, grid input current of the drive is directly affected by the electrical output power of the inverter. Using this aspect, the control method was proposed which can drive the motor and shape the grid current as a sinusoid simultaneously. However, the drive with this method uses high motor current and has low efficiency because the DC-link voltage periodically falls to zero. To improve the efficiency of the drive, the method that keeps the DC-link voltage higher than a certain limit in order to reduce the flux weakening current is proposed in this paper. With the proposed controller, the harmonic components of the grid current can be suppressed below the limits stated in the regulation IEC61000-3-2. Also, the electrolytic capacitor and PFC circuit of the drive can be removed. The improved performance of the proposed method was verified by the experimental results using the inverter system with a 5μF DC-link capacitor.