This paper proposes a modified coupled-inductor SEPIC dc-dc converter for high voltage gain (< < 10) applications. It utilizes the same components as the conventional SEPIC converter with an additional diode. The voltage stress on the switch is minimal, which helps the designer to select a low voltage and low RDS-on MOSFET, resulting in a reduction of cost, conduction and turn ON losses of the switch. Compared to equivalent topologies with similar voltage gain expression, the proposed topology uses lower component-count to achieve the same or even higher voltage gain. This helps to design a very compact and lightweight converter with higher power density and reliability. Operating performance, steady-state analysis and mathematical derivations of the proposed dc-dc converter have been demonstrated in the paper. Moreover, extension of the circuit for higher gain (> 10) application is also introduced and discussed. Finally, the main features of the proposed converter have been verified through simulation and experimental results of a 400 W laboratory prototype. The efficiency is almost flat over a wide range of load with the highest measured efficiency of 96.2%, and the full-load efficiency is 95.2% at a voltage gain of 10.
Several single-stage topologies have been introduced since kicking off the three-phase Z-source inverter (ZSI), and among these topologies, the quasi-ZSI (qZSI) is the most common one due to its simple structure and continuous input current. Furthermore, different modulation strategies, utilizing multiple reference signals, have been developed as well. However, prior art modulation methods have some demerits, such as the complexity of generating the gate signals, the increased number of switch commutations with continuous commutation at high current level during the entire fundamental cycle, and the multiple commutations at a time. Hence, this paper proposes two modified space vector (MSV) modulation strategies, aimed at the reduction of the qZSI number of switch commutations at high current level for shorter periods during the fundamental cycle, i.e. reducing the switching loss, simplifying the generation of the gate signals by utilizing only three reference signals, and achieving a single switch commutation at a time. These modulation strategies are analyzed and compared to the conventional ones, where a reduced-scale 1 kVA three-phase qZSI is designed and simulated using these different modulation strategies. Finally, the 1 kVA three-phase qZSI is implemented experimentally to validate the performance of the proposed modulation strategies and verify the reported analysis.
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