Projects:2015s1-73 Improved Electric Micro-Bus Design for Nepal
Project 73, titled Electric Vehicle Design and formerly known as Improved Electric Micro-Bus Design for Nepal, consists of group member Lukas Matthews, Jia Yi Lim, Michael Thompson, and Jinyi Lu.
Throughout 2015, Project 73 memebers have looked at the various elements that combine to make practical and functional electric vehicles. Initially the team focussed on improving the "Safa Tempo", an existing electric powered, three wheeled, ten-seater electric taxi that currently operates in Kathmandu, Nepal. Investigation into the shortcomings of this existing technology and the possible performance increases that could implemented was conducted in the first half of the year. However, due to a lack of funding and the horrific earthquake that struck Nepal on the 25th April 2015, it was decided that implementation of this project was no longer possible. From there the team contacted Dr Nesimi Ertugrul who offered to supply the team with the necessary funding to successfully convert his 2003 Mazda MX5 into an electric vehicle. With the help of Dr Carsten Marksgraf, the team was able to investigate the best possible modification methods and was able to successfully implement an Infineon HybridKit1 - PinFin as well as a Toyota Prius MG2 motor into the Mazda vehicle.
Contents
Background
This project aims to convert an existing internal combustion engine (ICE) vehicle, 1993 Mazda MX-5 into a fully functional electric vehicle. As a part of the on-going project, focus for this year is to implement a 50kW Infineon HybridKIT1 Pin Fin controller into the car. A vehicle controller drives electric motor by converting battery energy into appropriate forms which corresponds to the driver’s command.
The project is highly motivated by the increasing global concern on vehicle greenhouse emission. ICE vehicles source its energy from combustion of fuels, which produces harmful gas such as carbon dioxide, nitrogen oxide and carbon monoxide. As for electric vehicles, chemical batteries are the source of energy and it does not yield any harmful emissions.
Objectives
Functional inverter with Field Orientated Control (FOC)
Phase current monitoring with the use of current sensors
Data logging via CAN Bus
System integration
A vehicle with running wheels, controlled by a throttle
Theory
Overview
Figure illustrates a general overview of an electric vehicle with the main components in the car. Infineon[10] provides useful insights on the overview of an electric vehicle components. Firstly, the charging system is an AC/DC converter module, which allows car owner to charge up the vehicle batteries from household power. A battery management system (BMS) is included in the battery system for an efficient battery operation. BMS is critical to ensure the battery lifetime, which corresponds to driver’s financial burden. An auxiliary power system acts as a range extender by charging up a 12V power supply from the high voltage battery system. This power is then used to run the vehicle auxiliaries. A controller, or sometimes known as inverter, is also connected to the battery system. This controller converts DC input from battery system into AC output in order to drive and control the electric motor. This intelligently controlled inverter is often designed and programmed to minimize switching losses and maximize thermal efficiency, or even enabling regenerative braking, hence controller is one of the key component for an efficient vehicle. With the commands and AC power from the controller, electric motor converts electrical energy into mechanical torque, propelling the electric vehicle. Lastly, in order to integrate and connect all the individual automotive modules in a vehicle, an internal central communication networking system is usually implemented.
Communication System
A vehicle contains various on-board computing electronic devices to support vehicle efficiency, performance, and user experience. In order to have a closed loop system, data exchange between devices is usually required. This is the part where a vehicle communication network is required. For this project, the group focuses on the development and implementation of a Controller Area Network (CAN) bus. CAN bus is a serial bus communications used to support real-time distributed control system in automobiles and industrial control system. CAN bus system uses bit-serial transmission in twisted-pair cabling as illustrated in Figure 4, enabling communication between CAN devices, or sometimes known as network nodes [8]. Every node on the system receives all transmitted messages. Therefore, identifiers are used for nodes to determine if the messages received are of interest. Twisted-pair cabling is a common practice for CAN bus wiring to reduce noise during transmission by connecting one wire to CAN Low and the other to CAN High [8]. Such method allows data to be transmitted via differential voltage (balanced line) signalling [8]. To recover the signal, CAN Low signal will be inverted, and then added to CAN High signal by the CAN transceiver [8]. Such process will cancel and minimize any noises induced during the transmission process [8]. A pair of 120 ohms resistors are often recommended to be connected on each end of the CAN bus to minimize reflections of signal [8]. However, this is unnecessary for short cable length, less than 40m.
Controller
A controller is connected to the battery system. Controller converts DC input from battery system into a controlled AC output in order to drive the electric motor.
Torque of an electric motor has to be controlled during normal driving conditions to maintain vehicle speed. This can be done by controlling the rotor’s mechanical speed and phase currents. 𝑇=3/2 𝑝(𝜑∙𝑖_𝑞+(𝐿_𝑑−𝐿_𝑞)∙𝑖_𝑑∙𝑖_𝑞)
FOC is the process of controlling the stator current vector in the (d,q) reference frame, based on Clarke and Park Transform.
CANBus
Various on-board computing devices are usually installed inside an electric vehicle. CAN bus is a serial bus communication used to support real time vehicle data exchange in a closed loop system. Lauterbach JTAG Debugger was initially used for such purpose but it is highly prone to electromagnetic interference (EMI) issues. NI USB 8473-s CAN bus device is used for this project. Receive function was developed to read values from controller such as voltage, current, position, and temperature. Software used for the development is MATLAB.
Result
Outcomes for this project are:
Controller is installed into the car
FOC is functioning
Field weakening
CAN bus is able to receive and display readings from the controller
Implementation of controller, CAN bus and cooling system hardware into the vehicle.
Future Work
Battery pack upgrade
Battery management system (BMS)
Motor upgrade with regenerative braking
Send function for CAN bus
