Range of the touchstone | diamond quantum sensor electric vehicle driving can be expanded by 10%

The remaining range of an electric car is difficult to predict accurately, and the current state of the art battery current sensors cannot accurately predict charge. Because the battery current of electric cars can reach up to hundreds of amps, while the average current is only about 10 amps, and ordinary sensors do not have tens of milliamps of accuracy when maintaining a dynamic range of hundreds of amps, the charging state must be estimated with a fuzzy estimate of about 10%, which makes battery use inefficient.

Tokyo Institute of Technology researchers have come up with a solution to the inefficiency of electric cars. In research published in Scientific Reports, the team reports a detection technique based on a diamond quantum sensor that can estimate battery power with 1% accuracy when measuring high currents in electric vehicles.

Commercial sensors capable of detecting electric vehicle batteries, which typically run in the hundreds of amperes, cannot measure small changes in current at the milliampere-level, resulting in about 10 percent ambiguity in estimating battery power, meaning an EV's range can be extended by 10 percent with accurate measurements.

For the study, the team built a prototype sensor using two diamond quantum sensors placed on either side of a car's busbar, the electronic connector that allows current to flow in and out. They used a "differential detection" technique, which eliminated the common noise detected by the two sensors and left only the actual signal, allowing them to detect a current as small as 10 milliamps in the background noise.

The team used a hybrid analog-digital control of the frequencies generated by the two microwave generators to track the magnetic resonance frequency of the quantum sensor over a bandwidth of 1 gigahertz. They found that the magnetic resonance frequency can achieve a large dynamic range of ±1000 amps (the ratio of the maximum current detected to the minimum current). In addition, the sensor operates in a temperature range of -40 °C to 85°C, covering the general temperature range of vehicle applications.

Finally, the team put the prototype through a Global Uniform Light Vehicle Test Cycle (WLTC) driving test, a standard test of electric vehicle energy consumption. The sensor accurately tracked charging and discharging currents from -50 amps to 130 amps, with an accuracy of less than 1 percent for battery charge estimates.

(a) Sensor head structure in which the diamond is placed at the fiber tip. The green laser is shone onto the diamond through an optical fiber (green arrow), and the center of the NV glows red. This is detected by optical fiber (red arrow). (b) Configuration diagram of the differential sensor with the sensor head located on the front and back of the bus (current path) and (c) the same photo. 

"Improving battery efficiency by 10 percent is expected to reduce the operating energy consumption of 20 million new electric vehicles in 2030 by 3.5 percent and the production energy consumption by 5 percent," the researchers said. This in turn is equivalent to a 0.2 percent reduction in global transport CO2 emissions by 2030." 

Using diamond quantum sensor made of diamond applied in new energy vehicles, current measurement range of ±1,000 A, accuracy of 10 mA, can effectively reduce the on-board battery capacity of electric vehicles, and improve power consumption by reducing weight, will greatly reduce the CO₂ emissions in the field of transportation, help global energy conservation and emission reduction green development. 

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