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An Improved LLC Resonant Converter with phase-shift controlled dynamic series-parallel reconfiguration-windings for hold-up applications

This paper presents an improved LLC resonant converter with phase-shift controlled dynamic series-parallel reconfiguration windings for applications with hold-up time requirement, such as distributed power systems and server supplies. By adding two diodes to the secondary-side rectifiers, the structure of the secondary-side windings can be reconfigured to provide the regulated output voltage with phase-shift control. When the phase-shift angle achieves 180°, maximum voltage gain can achieve up to twice as normal operation. Since the converter always operates around the resonant frequency in normal state, high efficiency can be achieved. Without considering the voltage gain requirement, soft-switching of normal operation is the only consideration when designing the magnetizing inductance. Therefore, circulating current and conduction losses induced by the magnetizing inductance can be reduced significantly. Operation principles, characteristics and design considerations are discussed in detail. Experimental results are given to verify the effectiveness and advantages of the converter.