The popularity of electric vehicles (EVs) as an environmentally friendly alternative to conventional gasoline internal combustion engine vehicles has been on the rise. This has led to major research efforts directed at developing efficient EV batteries. However, an important inefficiency of EVs is caused by inaccurate estimation of battery power. This method of assessing the state of charge of EV batteries by measuring the current output of the battery is used to calculate an estimate of the remaining driving range of the vehicle.
Typically, battery currents in EVs can reach hundreds of amps. Yet commercial sensors capable of detecting such currents are unable to measure small variations in milliampere levels of current. This results in an uncertainty of about 10% in the battery charge estimate. This means that the EV’s driving range can be extended by 10%. This in turn will reduce the inefficient use of batteries.
Fortunately, a team of scientists has now come up with a solution. In their research, they report a detection technique based on a diamond quantum sensor that can estimate battery power within 1% accuracy when measuring the high currents typical of EVs. The research team from Tokyo Institute of Technology in Japan was led by Professor Mutsuko Hatano, and their study was published in Scientific Reports.
“We developed diamond sensors that are sensitive to milliamp currents, are compact and can be implemented in automobiles. In addition, we measured a wide range of currents and detected milliamp levels in noisy environments,” said Professor Hatano.
The researchers reportedly developed a prototype sensor using two diamond quantum sensors placed on either side of the car’s bus bar (the electrical connection point between the input and output currents). They then used a technique called “differential detection” to eliminate the common noise detected by the two sensors, leaving only the actual signal intact. This in turn allowed them to detect a small current of 10 mA in the background ambient noise.
Next, the team of scientists used a hybrid analog-digital control of the frequencies generated by the two microwave generators to track the magnetic resonance frequencies of the quantum sensors within a bandwidth of 1 gigahertz. This resulted in a large dynamic range (ratio of maximum current detected to minimum current) of ±1000 A. In addition, a wide operating temperature range of -40 to +85°C was confirmed to cover conventional vehicle applications.
Finally, the research team tested the prototype in Worldwide Harmonized Light Vehicle Test Cycle (WLTC) driving, a standard test for EV energy consumption. The sensor accurately tracked charge/discharge currents from -50A to 130A and additionally demonstrated the accuracy of battery charge estimation to within 1%.
So what are the implications of these findings, said Professor Hatano, “Increasing battery usage efficiency by 10% will result in a 10% reduction in battery weight, which will result in a 3.5% reduction in operating energy and 5% reduction in producing energy for the 20 million new EVs in the 2030 WW. This, in turn, is equivalent to a 0.2% reduction in CO2 emissions in WW transportation in 2030.”
We certainly hope this breakthrough brings us one step closer to a carbon neutral society!” .