Electric and Hybrid Vehicles (Video)

This panel session video contains the following presentations:
1. The Distribution of Relaxation Time for Variable Temperature Cycle Aging of Electric Vehicle Power Battery
Changes in the ambient temperature of batteries in the use of electric vehicles accelerate the aging and attenuation resulting in increased internal resistance and performance degradation. The in situ electrochemical impedance measurement method is an effective tool for detecting electrochemical reactions on multiple time scales inside the battery. In this paper, the relaxation time distribution method is used to investigate the electrochemical impedance of the battery to reveal the aging mechanism during the temperature changes. In order to solve the problem of low frequency resolution of existing impedance spectrum analysis methods, the quantity and actual impedance in electrochemical reaction process are effectively analyzed. Gaussian process regression and regularization are an efficient tool for obtaining the distribution of functions and the minimization parameter. It is proved that through the conversion analysis of the frequency domain impedance data, it is helpful to obtain the true state of the battery more accurately. It lays a theoretical foundation for the further research of battery fault diagnosis, state estimation, life prediction and other methods..

2. Transient Analysis in Dynamic Reconfigurable Battery System
With the fast-paced deployment of battery energy storage systems (BESSs), efficiency and safety issues of BESS, caused by the notorious bucket effect, have become prominent. Therefore, dynamic reconfigurable battery system (DRB) provides a promising approach to overcome the bucket effect by integrating batteries with power electronics switches in a systematic fashion and dynamically changing battery cell topology based on battery status. However, since the battery energy flow is digitized within milliseconds, there is no theoretical study of the transient behavior of DRB. In this paper, we will fill this gap by establishing a hybrid system model with considerations of the dynamic behaviors of battery cell and power electronics switch, and then to study the transient response of the hybrid system at different working frequencies under constant discharging current profiles. Both analytical study and simulation analysis are carried out, which providing design insights for such hybrid system design.

3. Research and Application of Turbo-Generator Rotor Winding Condition Detection Based on Sinusoidal Spiral Pulse Wave
The measurement of DC resistance, AC impedance and distributed voltage of the rotor winding, as well as waveform methods such as differential coil method and repetitive surge oscilloscope method (RSO), are employed in diagnosing the generator rotor winding turn to turn insulation conditions. Such methods still have limitations or even make occasional misdiagnoses in the sensitivity of diagnosing early-stage turn to turn short circuit of the generator rotor, and cannot display the panorama of distributed electromagnetic characteristics of the generator rotor winding of the whole course. What's worse, various non-circuit faults including slight winding deformation, turn to turn insulation displacement, and oil-related winding contamination can be barely identified. This paper presents a rotor winding condition detection method based on the sinusoidal spiral pulse wave technology that fully demonstrates the whole-course distributed electromagnetic characteristics of the rotor winding (i.e. details of each large coil), sensitively reflecting the rotor winding turn to turn short circuit and meanwhile swiftly detecting non-circuit faults such as slight winding deformation, turn to turn insulation displacement and oil-related winding contamination. This method has been repeatedly verified on 600MW, 900MW and 1250MW units, with satisfactory application results achieved. Therefore, it is proved that such technology is effective in detecting generator rotor winding conditions and significant in enhancing the generator-operating reliability, thus deserving a broad promotion and application within the industry.

4. Multi-Objective Optimization of Stator Direct Cooling for Direct-Drive Permanent-Magnet Wind Generators
In order to make full use of the heat dissipation advantage of the evaporative cooling technology under the high heating load for electrical machines, the analysis and multi-physics coupling optimization for a 10MW direct-drive surface-mounted permanent-magnet (PM) wind generator with stator direct cooling method are proposed in this paper. First of all, the interrelation between multi-physics fields in evaporative cooling wind generators (ECWGs) is studied. Then the heat convection performance of hollow conductors under the influence of fluid-thermal coupling is studied based on the small inclination angle self-circulation cooling experiment. Next, the multi-objective optimization model with two different stator inner direct cooling modes is proposed to achieve the lightweight and cost reduction design of ECWGs. The optimization of a 10 MW direct-drive PM wind generator is carried out and the electromagnetic and cooling performance are investigated by FEA module to verify the correctness of results in this paper. Finally, the optimization results with single in-winding cooling and hybrid in-iron and in-winding cooling are compared and analyzed based on the weight, price, cooling and electromagnetic performance to demonstrate the advantages of hybrid cooling method in lightweight design optimization of ECWGs.