Minimum capacitor size in DC/DC/AC converters by means of novel PWM technique and DC-link structure

As far as either battery or fuel-cell supplies are considered, cascaded DC/DC/AC conversion structures are becoming the breakthrough in traction AC motor drives, due to practical DC source voltage range. Established works provided fundamental knowledge and practice to reduce the size of needed reactive components, which at first appeared a prohibitive drawback. The paper analyses the DC-link current ripple generation of both DC/DC and 3φ-VSI converters. A new PWM strategy of the cascaded converters is reported to provide the minimum RMS current requirement and size of the DC-link capacitor. The proposed PWM strategy can result in even too low capacitance values, in respect of large voltage transient response and safety, so that further DC-link structure is defined to hold overall benefits. Based on a 30 kW prototype all proposals are experimentally tested and successfully validated.