This study presents a new LLC resonant converter with two transformers in parallel for the electric vehicle battery charger. This topology achieves the zero-voltage switching for main switches in the entire charging profile. In addition, the zero-current switching for output rectifier diodes is extended under charging condition. The proposed charger provides a wide range output voltage for the battery system. Moreover, in order to maintain the high efficiency under charging, the charger adopts a bidirectional switch. At low-output power condition, the charger uses one transformer to transfer the energy. Finally, the design procedure is provided and implemented in a prototype charger with the input DC link 400 V and the output voltage of 36-58 V. Experimental results are presented to demonstrate the system performance. The maximum power is up to 700 W and the peak efficiency is as high as 93.6%.

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LiFePO 4 batteries are suitable for high power applications because of their advantages of large discharge current and high efficiency. Owing to the characteristics of LiFePO 4 batteries, it may cause overcharge/over-discharge and reduce the cycle life of the battery when series-connected batteries are used. This study proposes a charge equaliser based on an interleaved active clamp flyback converter. The interleaved topology reduces the output ripple current. Therefore the rectifier diode conduction loss can be reduced. With a clamp capacitor and leakage inductance, the switches are turned on with zero-voltage switching while the voltage stress of switch is reduced. Furthermore, a constant switching frequency and duty ratio are designed to achieve a simple control for the proposed system. The simulations and experimental results are provided to verify the performance of the proposed charge equaliser.

Two modified rectifications for improving the charge equalisation performance of series-connected battery stack are proposed in this study. Not only high reliability can be achieved because only one power switch is required, but also the control circuit is simple due to no voltage sensors. In addition, high efficiency can be achieved because of zero-voltageswitching. In this study, two modified rectifications are presented to eliminate the voltage differences between the odd and even batteries, which are not removed by the conventional methods, and reduce the number of transformer windings and diodes. Hence, the cost, size and complexity of the system can be reduced. The circuit topology and operation analysis of the proposed equaliser are described in detail. Finally, the simulations and experimental results are provided to demonstrate the performance of the proposed charge equaliser.

This study presents an improved solar system with maximum power point tracking (MPPT). A digital signal processor is used to control the converter with the proposed control; thus, the system can implement MPPT independently for each solar panel whether it is under shading, various irradiation conditions or with faulty solar cells. A modified MPPT method is designed to reduce the power oscillation significantly, thus the power loss is reduced. With the proposed scheme, most of the solar panel available output power is delivered to the load only through a diode, reducing the converter power loss. In addition, the converter only handles part of the solar panel output power. Therefore, the system cost is reduced due to the low-power rating converter. A laboratory prototype is constructed and tested to evaluate the effectiveness of the proposed system. The proposed photovoltaic (PV) system and the PV balancer are compared through simulations and experiments under various shading conditions. The experimental results show that the proposed PV system can produce more output power with high efficiency.