New ZVZCS TL DC–DC converter with combined operation modes

Three-level DC–DC converters (TLDCs) have attracted industrial and academic attention because of low main switching voltage ratings, simple clamping structure, and good soft-switching characteristics. This paper proposes a new TLDC with combined operation modes, which can operate in both zero-voltage switching (ZVS) and zero-voltage zero-current switching (ZVZCS) modes. The proposes converter varies soft switching mode with a simple switching combination of S_r1 and S_r2, and follows the best efficiency curves over a wide load range. Compared to conventional ZVS or ZVZCS TLDCs, this solution minimizes the circulating current and increases the overall efficiency. In addition, the current stress of the flying capacitor is also low. And, all these good features are realized by two low VA rating MOSFETs. This paper discusses the circuit, operating principles, and some steady-state characteristics. Finally, experimental data from a 1 kW prototype demonstrates the validity and characteristics of the proposed converter.