AUS RESEARCH EXTENDS BATTERY-POWERED VEHICLES LIFETIME AND DRIVING DISTANCE

Dr. Habib Ur Rehman

Professor of College of Engineering Department of Electrical Engineering

American University of Sharjah

Fossil fuel consumption which creates environmental pollution is largely attributed to the transportation industry. The Intergovernmental Panel on Climate Change ascribes nearly 14% of greenhouse gas emissions as a direct result of fossil fuel consumption by the transportation industry.

Battery-powered electric vehicles (BEV) have been an attractive alternative with their lower operational and maintenance costs while having no air pollution. However, one of the shortcomings of battery powered BEVs is that these batteries cannot run for very long distances, having a limited drive range because of low energy density compared to traditional Internal Combustion engines. For example, lithium-ion batteries have 200-300 WH/L while gasoline-fueled cars have 8800 Wh/L.

For this reason, UAE’s American University of Sharjah, Professor and Researcher Habibur Rehman and Dr. Shayok Mukhopadhyay along with graduate students have presented a project that can extend the drive range and lifetime of the battery.

The project presents two battery energy management (BEM) strategies that decrease battery energy consumption and state of charge (SOC) decline, thus lowering battery state of health (SOH) degradation.

In addition, they have developed a model-in-loop strategy employed to estimate the battery bank runtime and lifetime.

So, what is being looked into exactly? The runtime represents the time required to go from 100% state of charge (SOC) to 20% SOC. The battery lifetime is directly related to its state of health (SOH). Therefore, it is important to keep track of the battery's SOH because it indicates the maximum releasable battery capacity.

For EV applications, a battery reaches its end-of-life (EOL) when its SOH drops by 20% or becomes less than 80% SOC. A longer runtime will allow vehicles to travel longer distances before requiring recharging, and a longer lifetime will allow the batteries to operate for a longer time before requiring replacement.

By allowing battery management systems to accommodate the effects of temperature and battery health degradation, the usable life of an EV’s battery can be accurately estimated and extended. The work can also be used to predict whether the batteries are overheating, which could help make newer generation EV batteries last longer and reduce the risk of fire.

In addition, the work can also be applied to other robotic systems and has been shown to need much less experimental data compared to other available methods. Prof. Rehman commented that this work could also be used in lithium-ion batteries being used for solar panels.

The research, which was funded by AUS Faculty Research Grants and AUS Undergraduate Research Grants, presents two battery energy management (BEM) techniques for an electric vehicle (EV) traction system which incorporates an indirect fieldoriented (IFO) induction motor (IM) drive system.

In contrast to most of the existing work, the proposed BEM techniques operate without any prior knowledge of driving or road information.

The BEM technique incorporates two cascaded fuzzy logic controllers (CSFLC). In CSFLC, the fuzzy logic controller (FLC) generates the reference current signal for regulating the motor speed, while the second FLC generates a variable gain that limits the current signal variation based on the battery SOC.

The second BEM technique is based on model predictive control (MPC) which generates the current signal for the speed regulation.

The work introduces a new way of tuning the MPC input weight using battery information using fuzzy-tuned model predictive controller (FMPC), where an FLC adjusts the input weight in the MPC objective function such that the battery SOC is considered while generating the command current signal.

Furthermore, this work utilizes a model-in-loop strategy comprising a Chen and Mora (CM) battery model and the experimentally obtained battery bank power consumption to estimate the increase in battery bank runtime and lifetime.

The experimental results validated that the proposed CSFLC and FMPC BEM techniques exhibit a lower reduction in the battery SOC and SOH degradation, thus prolonging the battery bank runtime and lifetime as compared to the conventional FLC and MPC speed regulators.

So exactly how much longer can a battery life increase? Rehman explains, “We developed control techniques for extending the battery drive range without much compromise on the motor drive performance which propels the vehicle. Also, our energy management techniques will operate the battery in a safe temperature mode and thus will not affect the battery's state of health badly. The battery drive range and life are expected to increase by about 5 to 10% using our energy management and control techniques.”

He states, “We have been working on the Li-ion high energy density batteries. These batteries are much smaller in size, and weight as compared to Lead Acid batteries which have been most commonly used in solar systems. However, Li-ion batteries, though expensive, are also being deployed in solar systems. In addition, the Li-ion batteries that are used in EVs can be reused in solar systems when their energy storage capacity goes below 80% at which time; they are no longer feasible for the EV application.”

In conclusion, the research assists in sustainability efforts in two ways according to Rehman, first, it consumes less battery energy for driving the same distance and thus less electric power for charging the battery and secondly, the battery life is extended which will reduce the number of discarded batteries that need to be recycled.