High integrated battery monitoring system with active balancing up to ±10A

Abstract

This master's thesis describes the development, construction, and setup of a flexible and modular, highly integrated battery monitoring system. The electronic unit uses an active balancing process with currents up to ±10A to redistribute and balance the electrical energy within a battery stack. In order to be able to charge and discharge an accumulator cell with this high current, a galvanic isolated DC/DC converter is necessary, which can transfer energy bidirectionally with low losses. The output of this converter is connected to a power multiplexer, which selects a desired accumulator cell of the battery stack in a targeted manner. This enables the cell voltage to be measured and the flow of energy to or from the cell. This allows the DC/DC converter unit to be used jointly by several accumulator cells connected in series, thereby reducing installation space and costs considerably. While the multiplexer has a structure that is as simple as possible to keep the outlay for implementation low, the bidirectional DC/DC converter uses two highly efficient converter stages to implement the potential separation and the voltage adjustment to the accumulator cell. The function and structure of these two converter stages, which are independent of one another, are dealt with in detail in this work, with a mathematical model also describing the interaction of the entire battery management system. Furthermore, all peripheral modules, such as auxiliary power supply, analog measuring unit, communication and digital control unit, of the DC/DC converter module are presented and explained. The performance of the presented concept is proven by measurements on a hardware prototype. Based on the input and output power, the efficiency as well as the power loss of the DC/DC converter, the multiplexer and the entire electronic were determined. The implemented battery management system allows the selected cell to be balanced in a short time with an efficiency of up to 85%. In addition, the cell voltage measurement, which is particularly important for monitoring the battery, was checked and tested. After adjusting the electronic, a voltage measurement with a resolution of ±500µV is possible. This allows the state of charge of each individual cell to be determined with great accuracy.