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

Abstract

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

Non-Zero Intercept Frequency: An Accurate Method to Determine the Integral Temperature of Li-Ion Batteries

“…The values of the corresponding RCelement can then frequently be computed through impedance measurements. Srinivasan et al [27], [28] as well as Schwarz et al [29] related the internal battery temperature to the phase shift between an applied sinusoidal current and the resulting alternating voltage. The internal battery temperature has also been correlated to the real part [14] and imaginary part [30] of the impedance at a predefined frequency.…”

A review on various temperature-indication methods for Li-ion batteries

“…Obviously, the measurement uncertainty is also dependent on the used measurement equipment. Since common electrochemical measurement equipment is not suitable for on-board applications, several authors presented proof-of-concept PCB that can perform these on-board electrochemical measurements [277,281,287,[294][295][296][297][298]. By integrating the PCB functionalities into a small chip [299], batteries inside a battery pack can be monitored for voltage, impedance and temperature by a single device, enabling accurate SoC, SoH, and temperature measurements at individual battery level.…”

Thermal monitoring of LiFePO4 batteries using switching harmonics

“…10.3 kHz, to avoid SOC influence. In [29] they also use the phase shift between voltage and current for temperature estimation, including SOC correction for a more precise estimation. In [31], the intercept frequency, which is the frequency in the Nyquist plot where the imaginary part is zero, was shown to be dependent solely on the cell temperature, not being affected by SOC and aging.…”

“…LIB temperature can be directly measured using temperature sensors [32], as RTD (Resistance Temperature Detector) [29], like a PT100 [5], or thermocouples [26], [33]. While the sensors themselves can be cheap, their installation and the subsequent cabling, signal conditioning and acquisition, add cost and complexity, and can compromise the system reliability as there are more elements susceptible of failure.…”