Development of multi-functional spintronic sensors for monitoring critical parameters of electric vehicles

Abstract

Electric vehicles (EVs) have gained remarkable attentions in recent years due to the merits of good driving performance, high energy efficiency, and friendly environmental impact. Energy storage system, traction system and vehicle charging system are the most critical components in EVs, which should be continuously monitored with respect to the reliability, safety and efficiency. However, in conventional monitoring techniques, multiple kinds of sensors are employed in EVs for individually monitoring critical parameters, such as temperature, rotation speed, current and other critical parameters. This leads to the high complexity of monitoring system and high construction cost for EVs, which are undesired for the rapid market expansion of EVs. This thesis explores and develops a series of novel technologies and applications of multi-functional spintronic sensors for monitoring those critical parameters of EVs, which can overcome the above-mentioned drawbacks of the conventional techniques. As a basic literature review, advanced spintronic sensors including giant magnetoresistive (GMR) sensors and tunneling magnetoresistive (TMR) sensors and their common applications are firstly overviewed in Chapter 2. Following this, a new temperature measurement approach for energy storage system in EVs is proposed in Chapter 3, which uses a GMR sensor as the temperature transducer based on the principle of Johnson noise thermometry (JNT). The GMR-based JNT provides the absolute temperature by measuring the power spectral density of thermal noise across the GMR sensor and its resistance. The temperature measurement performance was experimentally investigated under both changing magnetic field and temperature. Moreover, a practical demonstration for monitoring the surface temperature of a battery pack on the laboratory EV testbed was also presented to show the feasibility of the GMR-based JNT. Consequently, a rotation speed measurement technique for traction system in EVs through the stray magnetic field sensing is presented in Chapter 4. PMSMs are always the promising candidates for traction system in EVs. By sensing the stray magnetic field outside the motor stator yoke with TMR sensors, the rotation speed of a PMSM can be accurately measured. Both FEM simulation and experiments are performed to verify the proposed method. Similarly, Chapter 5 provides the inter-turn short-circuit fault detection technique for PMSMs based on the idea of stray magnetic field sensing. The distribution of stray magnetic field can also provide the health conditions of stator windings in a PMSM. The proposed technique is also validated in experiments under various operating conditions. On the other hand, wireless power transfer (WPT) technique has been used for wireless EV charging nowadays. Chapter 6 presents a multiple-purpose technique to monitor the charging performance of wireless EV charging, and detect the coil misalignment and foreign metal objects during charging process. The magnetic field distribution between the transmission and receiving coils are measured by the TMR sensor matrix, which provides the critical information on the charging performance, coil misalignment position, and the existence of metal objects between coils. Both simulation and experiments are provided to demonstrate the feasibility and novelty of the proposed technique.