PERFORMANCE IMPROVEMENTS OF LEAD ACID BATTERIES WITH ACTIVE CELL BALANCING METHOD OF SWITCHED-CAPACITOR BOOST CONVERTER (S-CBC)

• Main Author: FRIANSA, KOKO
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/22836
• Institution: Institut Teknologi Bandung

Battery is one of the devices to store energy and have a very important role in today's energy provider systems, such as in smart microgrid applications, and telecommunications devices. Battery usually installed in series to meet voltage requirements for the load and installed in parallel to increase battery capacity. Battery with installed in series have possibility of energy unbalance in each cell due to the different chemical characteristics between cells. Cell energy unbalance in the battery causes one of each cell to be faster to reach upper limit of the cell voltage during charging or to be faster to reach the lower limit of the cell voltage during discharging. If one of the cells reaches the cell voltage limit, then the cell will quickly damaged. In general, the battery can-not stand alone and usually installed Battery Management System (BMS) which has a protection system that will cut-off the battery system if one of the cells reaches the cell voltage limit. Installing a protection system is not enough because the other cell energy not well utilized. To utilize the other cell energy so installed cell balancing. <br /> <br /> In this research, to balance the energy between cells that serves to improve battery performance. The cell balancing using active cell balancing method of Switched-Capacitor Boost Converter (S-CBC) consists of a capacitor and a dc-dc boost converter. The S-CBC cell balancing is working by selecting the highest cell energy then transferred to the lowest cell energy. The dc-dc boost converter takes energy from the capacitor so that the energy of the capacitor is utilized optimally and the energy transferred from cell to capacitor becomes large. The energy transferred to the cell balancing is affected by 5 parameters, i.e. capacitor capacity, switch frequency, duty cycle, series resistance and the upper-lower voltage difference of the capacitor. Capacitor capacity, series resistance and the capacitor upper-lower voltage difference is determined at the beginning, so that the frequency and duty cycle can be changed. The simulation results show the optimal energy value transferred in the S- CBC with a capacitor capacity is 1.1 F, the series resistance is 5 Ohm, and the capacitor upper-lower voltage difference is 5V shows the frequency is 0.5 Hz and the duty cycle is 50%. <br /> <br /> The S-CBC cell balancing was tested in two stages. The first test phase was performed by comparing the performance of the S-CBC cell balancing circuit with a conventional switched capacitor circuit. The results show that the S-CBC cell balancing circuit is 4.6 times faster than the conventional circuit at 0.5 Hz frequency with 81% efficiency. The second test phase was performed to see performance of the lead acid battery system in the process of discharging in lead acid battery 48 V with nominal voltage 12 V in each cell and nominal capacity 7 Ah with discharging current is 1 A. The results show voltage deviation between cells without cell balancing circuit is 0.30 V, whereas using S-CBC cell balancing the voltage deviation between cells is 0.08 V. The capacity and energy of the battery without using a cell balancing show 3.06 Ah and 147 Wh, while using S-CBC the capacity and energy of the battery indicates 3.28 Ah and 156 Wh.