Sensorless battery cell temperature estimation circuit for enhanced safety in battery systems

Today, battery electric vehicles as well as stationary battery system demand lithium-ion batteries. Lithium titanate battery cells with their excellent charge and discharge rate capabilities in combination with their long lifetime have become an attractive option for these kinds of applications. However, to ensure safe operation of lithium batteries — especially in high power applications — temperature observation is mandatory. So, it is highly important to have a reliable thermal management system with proper temperature estimation. Normally, an external temperature sensor is placed on the surface of the battery case. This method is not very appropriate because only the external battery temperature can be detected, which is delayed by the thermal coupling between sensor and cell, and thermal capacity of the battery cell. This paper describes the development of a circuit that performs sensorless temperature estimation of a lithium-ion battery cell. A functional prototype was developed and comprehensive tests are performed to verify the functionality of this prototype. It is demonstrated that it is possible to determine the internal equivalent temperature of the cell using the measurement results of the developed circuit. Further, the circuit concept can be easily integrated into the monitoring system of high power battery systems. As a result, the developed prototype may enhance the safety of battery systems by proper temperature estimation of lithium-ion batteries used in electric vehicles and stationary energy storage systems.