31-03-2014, 04:22 PM
Electric Vehicle Drive Simulation with MATLAB/Simulink
Abstract
The paper presents the simulation of a basic electric vehicle motor-drive system that is used to
investigate power flow during both motoring and regeneration. The simulation assumes a DC
permanent magnet motor, an ideal motor controller combined with a proportional-integral
controller, and the electric vehicle battery. The model can be used to evaluate the electric drive’s
energy flow and efficiency for specific speed and torque load conditions. Some of the key
system parameters were specified and others were modeled as ideal. A stable
MATLAB/Simulink model was developed and validated. It was then used to determine the
system performance and energy flow over a given set of motoring and regeneration speed/torque
conditions. The model could be used to augment instruction in energy conversion or vehicle
systems courses.
Introduction
This past year electric vehicles were mass produced for the first time in history, and there is a
need to include more learning experiences that are related to that topic. “The 2010 – 2020 time
period has been described as the upcoming ‘tipping point’ ...the transition from the Internal
Combustion Engine (ICE) as the prime mover of vehicles to electric propulsion systems.” 1
“Education is really the important foundation for where the industry is headed in this field. 2
Currently there are no ABET accredited Automotive Engineering or Technology degree
programs that contain electric vehicle courses3. A literature search for electric vehicle
educational revealed a few single-offering or special topics courses,4-9 The Department of
Energy has awarded funds under the Advanced Electric Drive Vehicle Education Program to
support the development of new courses for graduate, undergraduate, secondary students,
teachers, technicians, emergency responders, and the general public. 10, 11 However, industry is
largely training engineers ‘in-house’, and educational experiences in this technology are needed
now to prepare a well trained and educated workforce to support the development of Smart Grid
and Electric Vehicle applications.
Drive Cycle
To assist in the design process, vehicle driving tests and vehicle driving simulations are
completed to help support the design process to determine if the design is appropriate for the
desired application.
A driving cycle is a set of second-by-second set of vehicle velocity values that the simulated
vehicle is to attain during the simulation. The need of a drive cycle is to reduce the quantity of
expensive on-road tests, and also reduce both the time of test and fatigue of the test engineer.
The drive cycle process brings the road to the dynamometer or to the computer simulation.
Drive cycles are used in vehicle simulations to model the drive system and predict the
performance of the drive system. There are many standard driving cycles used for testing road
vehicles for fuel economy and other purposes. Some driving cycles are developed theoretically,
and others are direct measurements of a representative driving pattern. A driving cycle can
include frequent speed changes or extended periods at constant speed. An example of vehicle
simulator is ADVISOR produced by AVL Engineering16 and other on-line road load and fuel
economy simulations.17
Electric Vehicle Drive Train Operation
In a typical gasoline powered vehicle the gas tank is not a part of the design model. Gasoline is
consumed by the engine, but the engine does not put gasoline back into the gas tank. A
paradigm shift from internal combustion engines to electric vehicles is that in an electric vehicle
the battery is part of the drive train as shown below in Figure 1: Electric Vehicle Drive Train.
The drive train consumes energy from the battery during motoring. The drive train can also add
charge to the battery if the motor is operated as a generator during regeneration. This can occur
during braking or if the vehicle is being powered by an Internal Combustion Engine (ICE). In
the diagram, the battery is frequently constructed of Lithium Ion cells, and supplies 300+ volts
and high current to the power electronics. A battery controller monitors key battery parameters
and controls the battery pack.
DC Motor:
As noted earlier, Battery Electric Vehicles (BEV) and Hybrid Electric Vehicles (HEV)
frequently use special, high efficiency Permanent Magnet Synchronous Motors (PMSM). This
type of motor may be referred to as a brushless DC motor because it runs from DC voltage but
does not have brushes. PMSM motors actually use AC voltage that is supplied by the Motor
Controller. The motor controller inverts the DC voltage to produce an AC voltage at the proper
voltage and frequency. The motor voltage is frequently a 10-20 KHz Pulse Width Modulated
AC voltage where the voltage and frequency are adjusted to provide the proper motor speed and
magnetic field values.
Drive System Model
The Speed and Torque values were written to the MATLAB Workspace, and the values were
then read into the model speed and torque look-up tables. The Clock input to the look-up tables
used the following time base values that were setup in the model parameters table: Tmin = 0,
Tstep = 0.01, Tstop = 100 seconds.
The displayed Scope values were also written to the MATLAB Workspace as Structures with
Time. A MATLAB script was used to pre-load the speed and torque data in the Workspace, Run
the Simulation, obtain the key data from the Scope Structures, and plot the data. The complete
Motor Drive Model is shown below in Figure 7: Motor Drive Model.