Improvements to the fuel economy and rate of charge is instrumental in making Electric Vehicles a viable alternative to Internal Combustion Engine Vehicles. Electric Vehicles typically use Lithium‑ion (Li-ion) batteries to power their propulsion system due to their high energy and power density compared to other cell chemistries. However, significant research is required to understand the characteristics of Li-ion batteries in order to increase their performance, and consequently refuelling rates and range.
Established research demonstrates that cell instrumentation may be used to obtain enhanced cell characteristics. Such systems currently require a wired connection from the sensor embedded within the cell to the external data acquisition system. The addition of a wire harness within the battery pack and the increased risk of irreversible damage to the instrumented cell results in a regression of the performance enhancements expected from in-situ cell characterisation. An alternative method of data acquisition is therefore required for data acquisition from instrumented cells.
This project aims to produce a Power Line Communication system for use within an Electric Vehicle Li-ion battery pack. This system will take into consideration the significance of noise, power consumption, communication performance, and the environmental impact of prospective systems.
This study will be exploring Power Line communication approaches for both cell‑to‑cell and cell‑to‑BMS systems. The benefits of in-situ Power Line communication system within an Electric Vehicle energy storage system includes the co-ordination of instrumented cells, allowing for unprecedented improvements in performance through cell reconfiguration and thermal protection.
Power Line communication (PLC) allows simultaneous data and power transfer on the same wiring network. This project will seek to design a communication system that does not require significant changes to current battery pack designs. However, the effects of a system with coexisting Li-ion cells and a PLC system must be investigated.
Shown below are two constellation diagrams of a simulated quadrature amplitude modulated (QAM) signal with a carrier frequency of 1 MHz transmitted through two Li-ion cells in series. The Li-ion cells both attenuate and delay the signal transmitted through the cell. For a QAM signal with only two constellation points (2-QAM), which transmits two bits per symbol, the calculated bit error rate (BER) is theoretically 0. This is because the simulated attenuation, phase shift and noise applied to the signal is not significant enough for errors to occur. In contrast, when using 256-QAM the margin of error is greatly reduced, which increases the significance of the effects the Li-ion cells have on the signal so much that a BER above 98% is obtained.
The proposed in-situ Power Line communication system for Electric Vehicle battery packs within this project will be designed to mitigate the effects of the Li-ion cells on the signal characteristics of the system.