Control of three phase inverter for AC motor drive with small DC-link capacitor fed by single phase AC source

If a small DC-link capacitor is used in the DC-link fed by single phase AC source, the DC-link voltage fluctuates severely with twice of the source frequency. To handle this fluctuation, the concept of `average voltage constraint' is proposed in this study. On the basis of the concept, a flux weakening scheme generating d-axis current reference (i
_ds
r*) for Interior Permanent Magnet Synchronous Machine (IPMSM) is devised. And, q-axis current reference (i
_qs
r*) is modified for the unity power factor operation to AC source. The proposed scheme has been applied to inverter driven 1 kW compressor of an air-conditioner. From the experimental results, it has been verified that the compressor operates well at required operating condition regardless of the severe fluctuation of DC-link voltage due to the reduced DC-link capacitor. Also the frequency spectrum of the AC source current reveals that the harmonics of the source current meet IEC 61000-3-2 Class A and that the overall power factor is above 97% without any additional circuit such as an input filter and the power factor correction circuit.