Derivation of operation mode for flying capacitor topology applied to three-level DAB converter

Abstract

This paper discusses a Dual Active Bridge (DAB) DC-DC converter utilizing to three-level flying capacitor topology for a battery conversion system. With applying to a multi-level topology, the voltage stress is reduced in all switches. In addition, the low order harmonic components are reduced due to five-level waveform. In a two-level DAB converter, the efficiency becomes low when the input voltage is not closed to the nominal voltage. In order to improve the efficiency at the input voltage fluctuation, this paper also proposes the operation mode of the three-level DAB converter at the input voltage fluctuation. The output voltage waveform of the inverter is determined by the relationship among the efficiency of the two modes which are so called the full-bridge mode and the half-bridge mode. In this paper, the changing point between the half-bridge and the full-bridge mode is derived using the loss calculation. In the simulation, the ZVS range and the inductor current are compared with the two-level and the three-level inverter. It is confirmed that the ZVS range is extended by 60%. In addition, the fundamental operation of the proposed DAB converter is confirmed by the experimental results.I.

A Review of DC Fast Chargers with BESS for Electric Vehicles: Topology, Battery, Reliability Oriented Control and Cooling Perspectives

“…The last two bi-directional systems are 3-level flying capacitor (FC) [57] and neutral point clamped (NPC) DAB converters [58,59]. For visual clarity, the secondary sides are omitted in Figure 5c,d.…”

Review of Dual-Active-Bridge Converters With Topological Modifications

“…At the same time, the voltage stresses of the switches also become unbalanced, and overvoltage across devices will occur if the imbalance is severe. The DAB/DAB3 converters with NPC bridge cells have been carried out for PV generation systems [90]- [93], the bidirectional fast electric vehicle (EV) chargers [96], the interfaces of grid to microgrid [99], battery interface systems [101], [105], airborne wind turbines [103] and SSTs [104], [109].…”

“…However, when using clamped diodes, it is crucial to turn off the outside switches before the inside switches to avoid losing the voltage clamping ability, such as S1 should be turned off before S 2 . To solve this problem, flying capacitors as the clamped circuit are introduced in [101]. The drive signals of outside and inside switches are complementary, improving the voltage clamping problem caused by the switching sequence.…”

Optimal phase‐shift control of three‐level dual‐active bridge DC–DC converter with minimum reflux power for wide voltage conversion ratio range application

“…Introducing 3L topologies into the traditional 2L‐DAB structure is able to increase the available control degree‐of‐freedom (DOF) to further improve the DAB performance. A 3L neutral point clamped (NPC) full‐bridge (with clamped diodes [13, 14], or with flying capacitors [15]), is used in the high voltage side, and the modulation strategy drives the high voltage bridges to generate a five‐level voltage waveform. In addition to the phase‐shift (PS) angle between the two sides of the transformer, two other control variables are used to enable 3L characteristics and to regulate the system performance.…”