Boost dc-to-dc converters have very good source interface properties. The input inductor makes the source current smooth and hence these converters provide very good EMI performance. On account of this good property, the boost converter is also the preferred converter for off-line UPF rectifiers. One of the issues of concern in these converters is the large size of the storage capacitor on the dc link. The boost converter suffers from the disadvantage of discontinuous current injected to the load. The size of the capacitor is therefore large. Further, the ripple current in the capacitor is as much as the load current; hence the ESR specification of the tank capacitor is quite demanding. This is specially so in the emerging application areas of automotive power conversion, where the input voltage is low (typically 12V) and large voltage boost (4 to 5) are desired. In the UPF rectifier applications, the input voltage varies from zero to maximum value twice in every cycle of the ac input voltage. The duty cycle therefore varies in the full range of zero to one. The inductor current varies from zero to rated current twice in every ac cycle of the input current. On account of these wide operating point variations, the design of the power circuit as well as the closed loop controller is a demanding task. This paper suggests polyphase operation of boost converter to overcome the disadvantages of large size storage capacitor in boost converter and off-line UPF rectifiers and a small signal analysis ofN converters in parallel to an equivalent second order system in such converters, which have not been considered in previous works.
