Fast Charging of Lithium-Ion Batteries using Constant Temperature Constant Voltage (CT-CV) Method

Abstract

Lithium- ion batteries have higher energy density, low self-discharge, decent cycle life and are eco-friendly. Because of these characteristics, they have been a widely used as rechargeable battery in portable electronic devices, electric vehicles (EVs), grid energy storage, and renewable energy. Several charging methods have been introduced in literature with changed suggestions on charging time and life cycle. Most of these methods use an open-loop approach while CT-CV is a closed-loop charging method which uses the instantaneous cell voltage and current. Closed loop charging reduces the time that it takes to charge a big capacity battery. When charging a smartphone, this approach keeps the temperature constant while charging quickly. Existing Lithium-ion battery charging methods lack detailed design and control circuits that use constant temperature and constant voltage (CT-CV) in close-loop techniques. Our work addresses this gap by explaining the circuit control and implementation of the CT-CV technique by employing a feed-back proportional integral derivative (PID) controller with rectifier feeding the buck converter. Voltage Mode Control (VMC) and Average Current Mode (ACM) control methods are implemented to maintain the battery voltage, current and temperature at safe limits. In this thesis, MATLAB Simulink is used for simulations. As per simulation results, 23% faster charging is achieved by implementing VMC and almost 50% faster charging is attained by employing ACM technique in the PID controller. Moreover, a power factor of unity is achieved as rectifier current and voltage waveforms are sinusoidal, which increases the efficiency of the Li-ion battery. The results are verified by conducting experiment in which the proposed method is compared with the reference battery and the most commonly used CC-CV method. No technique has been implemented on the reference battery in order to regulate its voltage and current. According to experimental results, the proposed technique charges up to 25% faster than the reference battery and the CC-CV method.