Electronic-network modelling of rechargeable NiCd cells and its application to the design of battery management systems

In the first part of this paper, the development of a simulation model for a sealed rechargeable NiCd cell is described. Based on the concept of this cell type, a mathematical description of the various physical and electrochemical processes occurring inside the cell can be given. Subsequently, these equations are introduced in the form of electronic components into an electronic-circuit simulator. This enables the user to simulate the most important cell characteristics like voltage, temperature and internal gas pressure simultaneously and coherently under a wide variety of charging, discharging and open-circuit conditions. The construction of the model enables the user to investigate the course of each of the various reactions taking place inside the cell. Moreover, the electrical and thermal interaction with the surrounding electronics attached to the cell and with other cells, e.g., in a battery pack, can also be simulated. In the second part of this paper, some examples of simulations of cell characteristics are presented. The results of the simulated phenomena show good qualitative agreement with measured cell characteristics. An understanding of phenomena such as charge efficiency, self-discharge and overdischarge is presented using the model. Simulation of battery behaviour in an electronic system enables a system designer to design the optimal Battery Management System around the battery. In the third part of this paper, an example of applying the model in an electronic system is given, i.e., a shaver. Also, simulations of several cells connected in series forming a battery or battery pack are described.