Optimal sizing of an hybrid series bicycle equiped with supercapacitor
Conception optimale d'un vélo à architecture hybride série et à base de supercondensateur
Résumé
This thesis presents, analyses and solves several scientific problems related to the hybrid series bicycle.
Initially introduced in the car industry, this architecture type features a 100% electrical (chainless) transmission. This allows the decoupling of user effort from the bicycle dynamics.
The transmission is equipped with a generator subsystem that converts the user’s mechanical power into electricity as well as a motor subsystem that converts electricity back to mechanical power in order to propel the bicycle. In addition, this project foresees the implementation of an energy storage system based on supercapacitors, which are more respectful of the environment than batteries. The challenge was to propose a bicycle with this new storage system that provides the same comfort as e-bikes.
Associating supercapacitors with a hybrid series structure for light mobility purposes is an original approach. It raises several scientific problems that are discussed in this work.
Firstly, the use of a supercapacitor as the main energy source was analysed, considering the small embedded energy amount stored compared to batteries. A multicriteria approach was used and aging tests were carried out in order to determine the relative lifespan of batteries and supercapacitors for an energy equivalent usage.
Secondly, the hybrid series architecture was modelled and analysed. Indeed, energy is transferred through several energy conversions, and losses occur at each stage. If energy losses are too significant, the system may not be able to work correctly. Therefore, simulations were undertaken in order to compare the travel capacity of both the normal bicycle and hybrid series bicycle, taking into account the efficiency of both architectural types. Minimum efficiency requirements could be extracted from the results. Finally, a more detailed efficiency computation was undertaken using component databases in order to validate the feasibility of the desired efficiency.
The management of energy within the hybrid series architecture was then examined. The hybrid series architecture decouples input and output effort and therefore offers a degree of freedom to the system. This degree needs to be controlled in order to run the bicycle. A control strategy was established by reproducing optimal control solutions using fuzzy logic tools. Simulation results were found. Practical tests were undertaken on a homemade laboratory test bench. The results pave the way for further testing and energy management strategies.
Finally, the impact of cycling on a hybrid structure was analysed. Two major topics are discussed. The first concerns pedalling effort and the associated user movement, which may be uncomfortable due to very low generator inertia. The second consists in proposing a model and measurements concerning cyclist effort and fatigue on a hybrid bicycle compared to the traditional bicycle. On the basis of these analyses, this thesis provides conclusions on the advantages of decoupling for the cyclist.
Le travail présenté dans ce mémoire porte sur un vélo autonome en énergie, à architecture hybride série (VHS) avec comme système de stockage des supercondensateurs.
Le VHS dispose d’une transmission 100 % électrique qui permet un contrôle découplé entre le mouvement de pédalage et l’avancement du cycle. Il est constitué d’un ensemble générateur qui convertit la puissance mécanique humaine sous forme électrique ainsi que d’un moteur qui assure la traction du vélo. En parallèle, le système de stockage à base de supercondensateurs permet d’envisager un véhicule plus respectueux de l’environnement.
La pertinence de l’utilisation de supercondensateurs en remplacement des batteries a nécessité un comparatif multicritère des deux technologies. Il a été complété par des tests de vieillissement à usage énergétique équivalent.
Les conversions successives de puissance induisent des pertes qui peuvent rendre le vélo inutilisable. Une estimation du rendement minimum à atteindre est présentée. Le réalisme du résultat est appuyé par une modélisation du véhicule.
Le degré de liberté du système (pas de lien entre le pédalage et le mouvement du vélo) doit être contrôlé . La synthétisation d’une stratégie de commande par observation de comportements optimaux a permis d’obtenir des résultats en simulation puis en pratique.
Cette étude a été enrichie par des recherches concernant l’impact du VHS sur le cycliste. La première réflexion a consisté à reproduire un mouvement de pédalage fluide sur une génératrice à faible inertie. La seconde propose une analyse de l’effort d’un utilisateur sur le VHS comparée au vélo traditionnel. Ces deux approches ont permis de conclure sur l’avantage du découplage pour le cycliste.