Design and Modeling of Charg- ing Systems for Electric Buses

Student thesis: Master's Thesis

Abstract

wo different typologies of off-board chargers are designed and compared. These typologies are used for fast DC conduction charging for the bat- teries of heavy electric vehicles. The first typology consists of 200KW six switches based AC to DC converter. The second system is also the 200KW charger based on the modular approach. This modular approach consists of two rectifiers, and every rectifier consist of six switches connected in parallel. This modular approach can also be used for charging high power batteries safely because the power is distributed between two modules in this system. The chargers observe the real initial behavior of battery during charging with constant power and constant voltage control schemes. The control schemes are based on DQ transformation for controlling the battery power and battery voltage. The Grid to Vehicle charging mode is selected to simulate the electric bus battery behavior during charging mode. The batteries are assumed empty with initial SOC of (20%) during charging simulation for seclected three different cases. The inverted pantograph based off board charger is selected. It is used to recharge the bus with in 3 to 6 minutes. The various charging systems and charging strategies are also explained with brief introduction on off board chargers. The batteries behavior and their brands available for fast DC conduction charging are also comprehensively described. Subsequently, various types of buses for fast DC conduction charging are elaborated. A suitably selected bus and its motor specifications are defined for an electric bus model in order to extract the energy required by bus for covering the suitable distance in selected cases. Three cases are used. In the first case, there is only one charger installed at the start of the 17Km route. In the second case, there are two chargers installed at both ends of the 17 Km route. In the third case, an additional charger is installed in the middle of the 17Km route in addition to two chargers installed at both ends. A suitable driving cycle is used with 50 Km/hr average speed to simulate the energy behavior of selected bus in inner cities. The battery sizes of battery operated electric buses are calculated for the three selected cases. The first case needs a large battery and it takes more time to recharge as compared to other batteries utilized in the other cases. The batteries are connected to the 200KW chargers for achieving the charging results as explained above. Finally, an approximate cost is given suitable for both charging typologies.
Date of Award2 Sep 2019
Original languageEnglish

Keywords

  • Chargers
  • electric vehicles

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