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Scientific Reports

High-precision robust monitoring of charge/discharge current over a wide dynamic range for electric vehicle batteries using diamond quantum sensors

Yuji Hatano, Jae-Won Shin, Junya Tanigawa, Yuta Shigenobu, Akimichi Nakazono, T. Sekiguchi, Shinobu Onoda, Takeshi Ohshima, Keigo Arai, Takayuki Iwasaki, Mutsuko Hatano

Published Sep 6, 2022• 78 citations
Publisher

Abstract

Abstract Accurate prediction of the remaining driving range of electric vehicles is difficult because the state-of-the-art sensors for measuring battery current are not accurate enough to estimate the state of charge. This is because the battery current of EVs can reach a maximum of several hundred amperes while the average current is only approximately 10 A, and ordinary sensors do not have an accuracy of several tens of milliamperes while maintaining a dynamic range of several hundred amperes. Therefore, the state of charge has to be estimated with an ambiguity of approximately 10%, which makes the battery usage inefficient. This study resolves this limitation by developing a diamond quantum sensor with an inherently wide dynamic range and high sensitivity for measuring the battery current. The design uses the differential detection of two sensors to eliminate in-vehicle common-mode environmental noise, and a mixed analog–digital control to trace the magnetic resonance microwave frequencies of the quantum sensor without deviation over a wide dynamic range. The prototype battery monitor was fabricated and tested. The battery module current was measured up to 130 A covering WLTC driving pattern, and the accuracy of the current sensor to estimate battery state of charge was analyzed to be 10 mA, which will lead to 0.2% CO2 reduction emitted in the 2030 WW transportation field. Moreover, an operating temperature range of − 40 to + 85 °C and a maximum current dynamic range of ± 1000 A were confirmed.

DOI
10.1038/s41598-022-18106-x

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Abstract Accurate prediction of the remaining driving range of electric vehicles is difficult because the state-of-the-art sensors for measuring battery current are not accurate enough to estimate the state of charge. This is because the battery current of EVs can reach a maximum of several hundred amperes while the average current is only approximately 10 A, and ordinary sensors do not have an accuracy of several tens of milliamperes while maintaining a dynamic range of several hundred amperes. Therefore, the state of charge has to be estimated with an ambiguity of approximately 10%, which makes the battery usage inefficient. This study resolves this limitation by developing a diamond quantum sensor with an inherently wide dynamic range and high sensitivity for measuring the battery current. The design uses the differential detection of two sensors to eliminate in-vehicle common-mode environmental noise, and a mixed analog–digital control to trace the magnetic resonance microwave frequencies of the quantum sensor without deviation over a wide dynamic range. The prototype battery monitor was fabricated and tested. The battery module current was measured up to 130 A covering WLTC driving pattern, and the accuracy of the current sensor to estimate battery state of charge was analyzed to be 10 mA, which will lead to 0.2% CO2 reduction emitted in the 2030 WW transportation field. Moreover, an operating temperature range of − 40 to + 85 °C and a maximum current dynamic range of ± 1000 A were confirmed.
Considering the rising popularity of electric vehicles (EVs), it is essential to enhance the cruising mileage and extend the lifetime of batteries. To accomplish this, accurate monitoring of the charge and discharge current of the battery over a wide temperature range is essential. We developed a compact diamond quantum sensor head with a size of 1 × 1 × 0.5 cm3, consisting of a (111) high-pressure and high-temperature synthesized diamond with nitrogen-vacancy centers, by electron beam irradiation, which was adhered to the top of the multimode fiber and surrounded by the microwave antenna, for EV battery monitoring. We demonstrated that our quantum sensor achieved the current measurement accuracy of 10 mA in the −150 to 150 °C temperature range with a bandwidth of 500 Hz under atmospheric pressure and confirmed that the diamond quantum sensor meets the performance requirements of EV current sensors. Moreover, the temperature dependence of shot noise and external magnetic field noise were investigated, and their relation to the linewidth and contrast of the optically detected magnetic resonance spectrum were analyzed. At high temperatures, the contrast decreased because shortening of the singlet lifetime, which accelerate the initialization. At low temperatures, the contrast was slightly decreased. This is possibly a result of increased losses due to condensation on the microwave antenna.
Taking advantage of the wide dynamic range feature of diamond quantum sensor, a prototype battery monitor for electric vehicles (EVs) with a measurement range of ±1000 A and an accuracy of 10 mA has been developed1 using HPHT-Ib diamond irradiated with 3✕1018 cm-2 electron beam (EB). A battery monitor prototyped with a 150 μm thick 2✕1018 cm-3 nitrogen doped layer grown on a 150 μm thick heteroepitaxial (111) CVD substrate, has also confirmed 10 mA accuracy2,3. In this presentation, we demonstrate that these battery monitors can track the current in actual EV. The current was measured as the resonance frequency difference (RH-RL) on the ODMR spectrum . The current from the battery to the motor was supplied to the busbar. Electronics and optics were within cooler-box size and could be placed on the rear seat of the EV enabling the measurement during driving. The EV was driven in the WLTC (World-wide Light vehicle Test Cycle) mode on a chassis dynamometer and the whole mode could be correctly tracked by both sensors. For more abrupt current changes than in WLTC mode, HPHT-Ib monitor showed better trackability. Improving the trackability of the heteroepitaxial monitor, increasing the NV concentration and enhancing fluorescence intensity should certainly be effective.
Key implementation points for achieving full accuracy in simultaneous temperature and magnetic field measurement and linearity when applying diamond quantum sensors to electric vehicle (EV) battery monitors were investigated. Both the static and busbar current magnetic field are required to be aligned to the NV-axis. If misalignment should exist, the resonance frequency midpoint move in the direction opposite to the temperature change under a large busbar current due to the transverse magnetic field effect. Misalignment could be quantified with an accuracy of ±1° by analysing the resonance frequency midpoint change under a current of ±1,000 A. The transverse magnetic field effects compensation estimated from misalignment, confirmed that the resonance frequency midpoint changed consistently with temperature changes. Furthermore, linearity over a wide dynamic range also improved. Moreover, it will contribute to accurate alignment of the two sensors for differential detection to eliminate external noise as common mode. These are expected to expand the application of diamond sensors for high-precision measurement in a wide dynamic range.
Abstract A platform for heteroepitaxial (111) chemical vapor deposition (CVD) diamond quantum sensors with preferentially aligned nitrogen vacancy (NV) centers on a large substrate is developed, and its operation as an electric vehicle (EV) battery monitor is demonstrated. A self‐standing heteroepitaxial CVD diamond film with a (111) orientation and a thickness of 150 µm is grown on a non‐diamond substrate and subsequently separated from it. The high uniformity and crystallinity of the (111)‐oriented diamond is confirmed. A 150‐µm thick NV‐diamond layer is then deposited on the heteroepitaxial diamond. The T 2 value measured by confocal microscopy is 20 µs, which corresponds to substitutional nitrogen defect concentration of 8 ppm. The nitrogen‐vacancy concentration and T 2 * are estimated to be 0.05 ppm and 0.05 µs by continuous wave optically detected magnetic resonance (CW‐ODMR) spectroscopy in a fiber‐top sensor configuration. In a gradiometer, where two sensors are placed on both sides of the busbar, the noise floor is 17 nT/Hz 0.5 in the frequency range of 10–40 Hz without magnetic shielding. The Allan deviation of the magnetic field noise in the laboratory is below 0.3 µT, which corresponds to a busbar current of 10 mA, in the accumulation time range of 10 ms to 100 s.
Negatively charged nitrogen-vacancy (NV) centers in diamond have been extensively studied as a promising high sensitivity solid-state magnetic field sensor at room temperature. However, their use for current sensing applications is limited due to the challenge of integration and miniaturization of the diamond NV sensor. Here, we demonstrate an integrated NV sensor fabricated with standard microfabrication process. The sensor device incorporated with a toroidal magnetic yoke enables a high-precision wide range direct current sensing with galvanic isolation. The performance of the diamond NV current sensor in an open loop configuration has been investigated. A current measuring range of 0 A ~ 1000 A with an uncertainty of 46 ppm are achieved. Taking advantage of dual spin resonance modulation, temperature drift is suppressed to 10 ppm/K. This configuration opens new possibilities as a robust and scalable platform for current quantum sensing technologies.
Energy conservation and battery life extension are key challenges for the next-generation hybrid electric vehicles. In particular, the temperature and electric currents in a storage battery need to be monitored simultaneously with ∼1 kHz signal bandwidth for optimum battery usage. Here we introduce a centimeter-scale portable quantum sensor head, consisting of a diamond substrate hosting an ensemble of nitrogen-vacancy (NV) color centers with a density of ∼3 × 1017 cm−3. One diamond surface is attached to a multi-mode fiber for simultaneous optical excitation and readout of the NV centers, while the other diamond surface is attached to a coplanar microwave guide for NV spin ground-state mixing. Signal bandwidth of 1 kHz was realized through time-domain multiplexing of the two-tone microwave frequency modulation at 20 kHz. Two microwave frequencies were locked to the two resonance points that were determined from the optically detected magnetic resonance spectrum. From the mean and the difference of the deviation from the two locked frequencies, the temperature and magnetic field were obtained simultaneously and independently, with sensitivities of 3.5 nT/Hz1/2 and 1.3 mK/Hz1/2, respectively. We also showed that our sensor reached a minimum detectable magnetic field of 5 pT by accumulating signals for over 10 000 s.