A Hybrid Resonant ZVZCS Three-Level Converter Suitable for Photovoltaic Power DC Distribution System

Abstract

A novel hybrid resonant zero-current-switching (ZCS) three-level DC-DC converter based on a dual transformer with two output filter capacitors is proposed in this paper, which is suitable for application in distributed photovoltaic power generation at medium voltage integrated with a DC distribution network. The proposed converter adds an auxiliary circuit to the traditional neutral point clamped (NPC) three-level (TL) circuit, which contains the basic NPC three-level circuit. Pulse width modulation (PWM) is adopted in the auxiliary circuit portion to realize the power and voltage regulation of the whole converter, and enable the main switches to operate with a fixed duty cycle. This has the advantages of simplified control. By reasonable design of the turn's ratio of the main transformer, the main three-level circuit can deliver most of the power and achieve ZCS within the under full load range that significantly reduced the switching losses. Therefore, the turns ratio of the auxiliary transformer can be optimized to reduce the loss of the converter further and improve the conversion efficiency as discussed in detail, while the parameters' design principles are put forward. Finally, a prototype of 300V-1.5kV/1.5 kW is built to verify the performance of the proposed converter. INDEX TERMS Pulse width modulation, zero-voltage-zero-current-switching, photovoltaic. I. INTRODUCTION

High Performance Flexible Structure Three-Level DC-DC Converter: A Candidate DC Interface for Microgrids With Distributed Energy Resources

“…S1 and S3 can obtain zero-voltage turn-on over a wide load range because the output inductance provides enough energy to discharge or charge the output capacitors of the primary switches. For example, the turn-on instant of S3 is in Fig.4 (b), and the ZVS condition of S3 is [18]…”

“…And then, S1 or S3 can turn OFF with ZCS. For instance, the turn-off instant of S3 is in Fig.4(e), and the ZCS condition of S1 is [18]…”

“…Therefore, the proposed converter and the converter in Fig.6 (a) allow customers to achieve high input dc-dc power conversion by using cheap and high-performance two-level power modules without a reduction in reliability. Fig.8 provides a detailed capacitor comparison, and the data of the proposed converter is calculated according to (18) to (21). The proposed converter features a reduced current rating of the primary capacitors.…”

“…Reference [17] reported a high-efficiency TL dcdc converter with reduced circulating current and rectifier voltage stress. Hybrid resonant zero-current-switching (ZCS) TL dc-dc converter in [18] is well suitable for applications in DERs at medium voltage level. In [19], the active cutting-off switches are moving out of the main power transfer loop, which ensures zero-voltage zero-current switching (ZVZCS) over a wide load range and reduced conduction loss.…”

A Control Strategy Based on Intermediate Bus Voltage Information for Wide-Range High-Efficiency Step-Up DC–DC Converters

“…In recent years, renewable energy such as photovoltaic energy has drawn a lot of attention, which is more abundant and cleaner compared to fossil energy [1]- [3]. As an important component of PV power generation systems, DC-DC converters have developed rapidly due to their inherent advantages in control, protection, increased voltage levels and efficiency [4]- [7]. Fig.…”