EDLC Lifetime Holistic Estimation for Heavy-Duty Applications

摘要

In the last years, the world is facing the challenge of reducing gas emissions from urban and interurban transport means while maintaining the current mobility opportunities. This emerging global scenario boosted the need of more efficient means of transport. In this context, tramways represent one of the most suitable solutions due to their low energy consumption per passenger [1]. On the contrary, their high upfront infrastructure cost and the unsightly impact of overhead cables are hampering a greater market penetration. An effective approach to tackle aerial cables barrier would be to deploy on-board energy storage systems (OESS) [1]. Given the high specific power and high cycling capacity of the Electric Double Layer Capacitors (EDLC), these devices are one of the most attractive OESS for its implementation in this type of heavy-duty applications [2]. During the last years technology has improved rapidly to a high level of maturity, however few publications updated the impact of voltage, temperature and charge-discharge current on EDLC lifetime. In addition, the existing updated studies are based on short-term experiments at very high voltage and temperatures [3], [4] and their adaptability to more realistic conditions would be arguable. The present work approaches the lifetime estimation of EDLC based on the aforementioned ageing impact factors, and considering the application realistic operation conditions. A system optimisation tool based on lifetime estimation has been developed with the objective of guaranteeing the targeted tramway operation mode, while optimizing the costs of the infrastructure and the OESS. A model for EDLC lifetime estimation is presented, which was developed based on long-term experimental ageing tests, along with validation tests based on a real tramway application profile. It relies on the principle that the lifetime of an EDLC is inversely proportional to the redox reaction rate [5], and considers the impact of voltage (V), temperature (T) and current (I_RMS) in a single model (Eq.(l)). In addition, it deals separately with the influence of calendar and cycling ageing. t (V, T, I_RMS to 20% cap. loss) = M ((Vref-V)/Vref)[-n] x exp(Ea/G x (1+U (Tref-T)/Tref) [-1/ B]) x exp (L x I_RMS/C) (1) where, Ea is the activation energy (eV); B is the Boltzmann constant (B = 8.617e-5 eV/K); T and Tref are the surface temperature of the EDLC and reference temperature (K), respectively; V and Vref are the terminal voltage and nominal voltage of the EDLC (V), respectively; IRMS is the RMS current measured in the EDLC (A); C is the capacitance of the EDLC (F); and G, M, n, U, and L are constant parameters. The power demand profile of the Kaohsiung-Taiwan tramway route (first 100% catenary free operation in the world), developed by CAF, has been used to test the estimation algorithm. The developed lifetime estimation model is suitable for applications of different nature. It can estimate EDLC lifetime operated on different heavy-duty applications, such as the tramway or the hybrid electric bus, as well as the lifetime of EDLC used on less demanding stationary applications, such as an Uninterrupted Power System (UPS).