Abstract
The switched-capacitor (SC) converter has become a hot candidate to replace power electronics transformer (PET) in commercial and residential applications, especially in micro-grids. However, its poor regulation blocks it wide application. This paper presents an improved phase-shift control strategy for a resonant bridge modular switched-capacitor (RBMSC) ac-ac converter. On the basis of maintaining existing merits of the reported BMSC-based ac-ac converter, its output voltage can be adjusted continuously with a relatively wide margin, breaking through inherent difficulty in step-less regulation. Meanwhile, the bidirectional operation, including step-down and step-up modes, could be realized conveniently by changing the of range phase-shift angle. In addition, the partial switches are turned on under zero voltage switching (ZVS) and all switches realize ZVS turn-off, resulting in reduction of switching loss. Due to one switch in each bidirectional switch always works under synchronous rectification state instead of diode conduction, conduction loss will be reduced compared with other SC ac-ac converters. Most importantly, the safe-commutation issue in the introduced resonant branch is well solved and the voltage spike across switches is alleviated significantly. Finally, the experimental results are provided to demonstrate the validity of the theoretical principle of the converter.
Highlights
Auto-transformer is most important device to realize power flow between various voltage levels
The power electronics transformer (PET), which utilizes the conventional switched-mode ac-ac converter, becomes an alternate candidate [1]–[4], yet even when a flexible regulation performance could be obtained, it hardly avoids the issues of low power density, restrained efficiency and large copper requirement due to inductor utilization
Known from above modes discussion, capacitors C4 and C5 in series, which acts as a constant voltage source during switching period, will halves to suffer from vH, so the voltages across C4, C5 are maintained to be vH /2.The basic equivalent circuits at different modes and the state-plane diagram of the converter are shown in Fig. 6(a) and Fig. 6(b), respectively
Summary
Auto-transformer is most important device to realize power flow between various voltage levels. The paper comes to introduce a control strategy for resonant bridge modular switched-capacitor (RBMSC) ac-ac converter in low voltage distribution network, where the topology of BMSC has been presented in [21] It inherits the merits of the BMSC-based topology, such as capacitorvoltage self-balancing, low power device cost and output voltage ripple [28]. Known from above modes discussion, capacitors C4 and C5 in series, which acts as a constant voltage source during switching period, will halves to suffer from vH , so the voltages across C4, C5 are maintained to be vH /2.The basic equivalent circuits at different modes and the state-plane diagram of the converter are shown in Fig. 6(a) and Fig. 6(b), respectively. The line voltage with thousands of switching periods could be regulated and the ac-ac conversion with continuous voltage gain is realized
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