Boost d.c.-d.c. 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 large. Further, the ripple current in the capacitor is as much as the load current; hence the ESR specification of the tank capacitor is demanding. This paper presents the polyphase boost converter, which overcomes the problem of high ripple current in the tank capacitor, which has not been discussed earlier. Comparison between the specifications of single stage and multistage is thoroughly examined. Digital control is more convenient for such a topology on account of the requirement of synchronization, phase shifted operation and current balancing. The control method is simpler and faster than its original form [10]. It does not depend on the previous duty ratio and it has been tested on four boost converters in parallel. Each is a 35W unit switched at 200 kHz. Experimental results in digital control, synchronization operation and current sharing are presented. The control method is implemented using a TI’s general purpose Digital Signal Processor eZdspF2812. This control scheme is applicable for PFC rectifiers as well.
