Lithium Battery Charging And Management System Based On Wide Bandgap Device

Battery as a power source of new energy vehicles is an important direction for future development of the car. Currently, the vast majority of car battery using lithium-ion battery, and can use the on-board car charger to charge/discharge the battery. However, the car interior space is narrow, the working condition is poor, and lithium batteries have some problem such as working voltage changes, poor security, and over charge/discharge seriously affect the battery life. This requires car charger with high efficiency, high power density, high reliability, but also to adapt to a wide range of battery voltage characteristic. In addition, in order to detect the battery working state, provide a basis for automotive equipment, it is necessary to research battery management system in-depth.Based on the characteristics of the electric car battery, we proposes an onboard bidirectional electric vehicle charger. Referred charger has the following characteristics: 1) The output voltage can be varied over a wide range; 2) not only to charge the battery, but also can deliver energy back to the grid; 3) the use of digital controls; 4) high energy density; 5) charge and discharge protection. Meanwhile, on the basis of the proposed bidirectional charger, the paper also studied the mating battery management system, the characteristic parameters of battery can be dynamically monitored and be transmitted to the charger in real time. The charger can adjust the proper operating state based on the information.Owing to the bi-directional capability, soft switching capability and high efficiency, the cascade structure of bridgeless PFC and LLC was selected as the topology of the bidirectional charger. In order to improve the efficiency and power density, SiC and GaN devices with wide band gap has been applied. In addition, the paper also proposed a charging policy to decouple the input and output power, thereby reducing the voltage pulsating of DC bus, and the use of film capacitors instead of electrolytic capacitors further improve the performance of the converter.An 1 kW experimental testing platform was built to verify the proposed control strategy of power decoupling. The platform consists of a onboard charger, battery management system and power battery pack. Experimental results show that with the power decoupling strategy the voltage pulsating on DC bus significantly reduced, and can achieve high efficiency in the full range of the lithium battery voltage.