| Current-fed dual active bridge(DAB)is a suitable solution for applications requiring bidirectional power flow capability,galvanic isolation,low current ripple and wide voltage range.Compared with the conventional voltage-fed DAB,the current-fed DAB has lower current ripple in the low voltage side(LVS).Since voltage matching control can be realized,the current stress can be reduced and zero-voltage switching(ZVS)can be achieved for all switches in a wide voltage range.However,the current-fed DAB converter still has its disadvantages.The power transfer stage is limited when the LVS bottom switch duty cycle is large,which has bad influence on the conversion efficiency.In addition,the power density of the current-fed DAB is limited because of the use of DC inductors.For current-fed DAB bidirectional DC–DC converter,an optimized duty cycle control is proposed.The LVS bottom switch duty cycle can operate down to 50% to minimize the circulation stage.The conduction loss of switches can be reduced by using lower voltage rating MOSFETs for LVS,and the current ripple is also minimized in the proposed duty cycle range.Meanwhile,a voltage mismatching control with adaptive clamp voltage regulation is proposed to achieve ZVS for all switches throughout full operation range.Besides,magnetic-integrated technique is used for LVS DC inductors.Core loss can be reduced by the reduction of flux linkage ripple in the center leg,and power density can also be improved due to the small inductance value and the use of only one core.In this thesis,the operation principle of the converter with the proposed control is given firstly.The analysis of the optimized duty cycle range,the voltage mismatching control,ZVS conditions,the adaptive clamp voltage and the magnetic-integrated inductors are discussed in detail in the following chapters.The effectiveness of the theoretical analysis is verified by the experimental results of a 1kW laboratory prototype. |
