BOOST PWMCONTROL SCHEMEFOR A HALF BRIDGE LL RESONANT CONVERTERFORHOLD-UPSTATE OPERATION

Abstract—In this paper, the proposed converter is predicated on a moiety-bridge LLC resonant converter structure and a single auxiliary switch is integrated at the primary side. The converter has two different operational characteristics. It shows the same operational characteristic with the conventional LLC resonant converters during nominal state. However, when ac line lost and the converter enters into the hold-up time state, which requires wide voltage gain changes,the control method of the proposed converter is transmuted to the PWM method utilizing the auxiliary switch. Since the proposed converter compensates wide voltage gain variation with PWM method of the auxiliary switch, the frequency variation range for the LLC resonant converter is highly reduced in the proposed converter. Therefore the transformer in the proposed converter can be designed at the optimal operating point and it results in decremented conduction loss of the magnetizing inductor current. Furthermore, the maximum voltage gain of the proposed converter is facilely incremented by elongating the obligation ratio of the auxiliary switch. It avails to decrement the link capacitance. To verify the efficacy of the proposed circuit, operational principle will be expounded and experimental results will be presented with following designation. 100 kHz of switching frequency, 250–400 V of input voltage range, 250 V of output voltage, and 75 W output potency. Index Terms—Boost PWM control and zero voltage switching(ZVS), hold-up time, LLCresonant converter. In recent years, considerable researches have been performed for ac/dc converters to increment the puissance density and to amend th