Performance of a bidirectional V2G charger under Extreme Temperature Conditions

In recent years, the potential scarcity of conventional energy vectors like fossil fuels and the increasing environmental challenges motivated the widespread study on electric vehicles (EV) seen as a possibility to reduce emissions in the transports sector. With the advent of smart charging technologies, the charging and storage capabilities of EVs could make them valuable assets to electricity networks, helping enhance grid stability and lower electricity prices. The innovation introduced by the new vehicle-to-grid (V2G) systems lies in the possibility of bidirectional energy flow, allowing the storage system to exchange energy from and to the grid. For this new way of looking at these assets to be profitable the performances of the bidirectional chargers need to be extensively studied in all the possible operating conditions. Furthermore, it is not only important to study the technology behind the foreseen exploitation of V2G bidirectional chargers, but also the environment in which they will be inserted in. The great variability in the registered temperatures across Europe (ranging frequently between -30°C and 45°C) poses serious questions on the profitable extensive adoption of these systems; as a matter of fact, studying the market potential of a new technology is closely linked to how it behaves when it is exposed to the external environment. A complete discussion is available on the effects that external conditions can have on batteries and conventional fast chargers. However, the impact on the grid of the performances of V2G chargers without the influence of the battery requires analysis as it will affect both the infrastructure’s dimensioning and design. In this thesis work a V2G bidirectional charger supplied by the Officine Edison Laboratory has been analyzed under three significant temperature regimes (-20°C, 20°C and +40°C) using a thermostatic chamber. The conversion efficiency, current total harmonic distortion, power factor and standby power were registered in these conditions. The obtained results highlighted a strong dependance of the conversion capabilities of the device with the temperature; moreover, no negative effects emerged at low temperatures proving how at these regimes the bottleneck of the performances is represented by the battery pack itself which, during our tests, wasn’t thermally conditioned together with the converter. A second test phase followed to investigate another interesting topic, namely the working temperature range of the unit. Based on the working range given in the data sheet of the WB, an analysis of the unit's ability to work outside this range was carried out. The power derating strategy, the corresponding curves and the logic overview were registered exploring the WB behavior at the extreme temperature of 55°C. Then the operating range at the opposite extreme (-25°C) was analyzed. The final objective of this discussion led to an extensive characterization of the effects of temperatures on the performances of the device. The peculiarity of having thermally conditioned only the bidirectional converter has finally made it possible to physically isolate our results from the effect of the temperature’s effect over battery storage system.