Robust adaptive control of current in test equipment for lithium ion battery systems
This thesis project have the purpose of investigating possibilities for a current control with respect to cell voltages in the testing procedures of large battery systems. The main goal is to design and implement a control that is not in need of considerable tuning, but still has stability and performance during all different conditions of testing. The dynamics of the battery system is largely dependant on the temperature, but other factors such as age also affect the behaviour, and most importantly the dynamics changes for different battery systems.
Current control in a battery cell is relatively easy and with classic control theory methods one can achieve robustness with regards to stability, and this is largely used as a foundation for evaluating possibilities. To achieve good performance an adaptive control method is selected, where the changing gain of the system is one of the most important properties to determine. More specifically, a parameter based recursive least squares method is applied. Some special consideration is taken within designing the control to work in the digital networked system that constitutes the test rig with battery system, actuator and control.
Generally, the significant properties of the cells in the battery system can be determined by the adaptation, and the performance is good considering the responsiveness of the subsystems surrounding the control. However, there are parts that may still be improved within the control by considering compensation for imperfections in the network and the treatment of data in closed systems.
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