Low MOSFET Count Isolated DC-AC Converter

Abstract : This letter proposes a novel soft-switched single-stage-isolated dc-ac converter topology from the industry point of view. The proposed converter requires a lesser number of MOSFETs compared to a widely studied cycloconverter-type (CCT)-isolated dc-ac converter topology. This converter provides lower duty cycle loss, better efficiency, and electromagnetic interference performance compared to a CCT dc-ac converter. Also, it is thermally more stable, thus requires a smaller heat sink. The converter operation is demonstrated in a 1-kW prototype developed with SiC MOSFETs.
 EXISTING SYSTEM :
 • It should be noted here that, although the choice of carrier between triangular waveform and sawtooth waveform does not make much difference in normal three-phase Sine-PWM (SPWM) converters, it makes a significant difference in terms of switching loss for the case of the nine-switch converter. • As can be found in almost all the existing literatures, owing to the XOR operation, the middle switches operate at twice the switching frequency (2fs), because a triangular carrier has been used everywhere.
 DISADVANTAGE :
 ? The previous connection had the disadvantage of not getting the whole Vdc at each of the primary sides. ? One way to avoid the problem can be to choose a gating signal in such a way that the loads do not operate at the same time. ? In that way one of the loads will have the whole input voltage at the primary side and the other will have zero. ? The problem of not having Vdc as primary side voltage like the previous design will still remain. Also depending on the load condition, the voltage level will fluctuate and hence will be difficult to control.
 PROPOSED SYSTEM :
 • In order to avoid the bulky mains transformer and/or to increase power density and efficiency, alternatively, topologies with high-frequency isolation based on a dc–dc system feeding the dc link of a full-bridge dc–ac converter connected directly to the mains are proposed. • However, here, the low losses of the high-frequency isolation transformer have to be seen considering the additional losses of the rectifier stage and, especially, the line-side inverter. • According to the required dc-link voltage level (e.g., 400 V), this power stage, in general, has to be equipped with insulated gate bipolar transistors (IGBTs), which show a nonoptimum efficiency for operating in the partial load area.
 ADVANTAGE :
 Though these converters provide desired performance, they have two major concerns from a product perspective. ? A bulky electrolytic capacitor bank is necessary to integrate the dc-dc stage and dc-ac inverter which reduces the power density. Typically, the standard electrolytic capacitors are rated for 105?C. Thus, a lot of design efforts go into thermal management to achieve a longer product life. ? The control complexity is high. It requires an additional dc voltage sensor to regulate the output of the dc-dc stage.

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