Abstract
High-performance DC interfaces play a pivotal role in microgrids with distributed energy resources (DERs), which would significantly improve the utilization of DERs and the flexibility of the prosumers. For a candidate DC interface converter, how to maintain the performance over a wide operation range becomes the biggest challenge. This paper proposes a flexible structure soft-switching three-level (TL) dc-dc converter, which adds four high-speed MOSFETs and one low-speed electronic relay to achieve overall optimum performance over a wide range. Under high output or low input voltage conditions, the relay and the extra MOSFETs on the primary side are ON permanently. The proposed converter is a zero-voltage switching (ZVS) converter, which guarantees ZVS for all primary switches even under 0 load currents. Under low output or high input voltage conditions, the relay and the extra MOSFETs in the secondary side are OFF permanently. The proposed converter is a zero-voltage and zero-current switching (ZVZCS) converter, and two added MOSFETs provide ZVZCS operation not only for the main primary switches but also themselves over a wide range. Other advantages of the presented converter include reduced filter size, no primary side circulating currents, and reduced current stress of the clamping capacitor. Besides, the switching loss caused by the added power devices is low because of the full range of soft-switching operation and low on-state resistance of these devices. This paper discusses the circuit configuration, operation principle, soft switching characteristics, technical comparison, and experimental results from a 1-kW prototype prove the rightness of the presented converter.
Highlights
Recently, high-level integration of distributed renewable energy resources (DERs) into the grids becomes an irreversible trend [1]–[4], which is a promising solution to environmental pollution and an alternative to burning fossil fuels for electric power generation [5]
In a microgrid with DERs, high-performance DC interfaces are necessary to improve the utilization of DERs and the flexibility of the prosumers [6]–[10]
Several promising solutions for high voltage dc-dc conversion improve the performance of the DC interface in the applications of DERs [9]
Summary
High-level integration of distributed renewable energy resources (DERs) into the grids becomes an irreversible trend [1]–[4], which is a promising solution to environmental pollution and an alternative to burning fossil fuels for electric power generation [5]. The three-level (TL) dc-dc converter is an attractive choice because of some outstanding merits, e.g., the one-half voltage stress on the primary switches, compact clamping circuits, and soft-switching operation over a wide load range [11]–[14]. Reference [12] proposed a secondary modulation TL dc-dc converter, which merits the compact primary structure, wide soft-switching load range, and the reduced filter’s size. A new full-bridge TL dc-dc converter in [20] adopts a variable circuit structure, which can change the topology structure according to the operation condition This converter can adjust the current stress of the primary circuit over a wide load range, which active stables the junction temperature of the main switches [21].
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