School of Information Technologies
Faculty of Engineering & IT
ASSIGNMENT/PROJECT COVERSHEET – INDIVIDUAL ASSESSMENT
Unit of Study: ELEC9206 Electrical energy conversion system
Assignment name: Report on electric motor and generator
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I understand that failure to comply with the the Academic Dishonesty and Plagiarism in Coursework Policy, can lead to severe penalties as outlined under Chapter 8 of the University of Sydney By-Law 1999 (as amended). These penalties may be imposed in cases where any significant portion of my submitted work has been copied without proper acknowledgement from other sources, including published works, the internet, existing programs, the work of other students, or work previously submitted for other awards or assessments.
I realise that I may be asked to identify those portions of the work contributed by me and required to demonstrate my knowledge of the relevant material by answering oral questions or by undertaking supplementary work, either written or in the laboratory, in order to arrive at the final assessment mark.
Student ID: 470490859
Student name: Virag Wasnik
ELECTRICAL ENERGY CONVERSION SYSTEM
SEM 2, 2018
REPORT ON ELECTRIC MOTORS AND GENERATORS USED IN ELETRIC VEHICLES
The University of Sydney
Date of submission: 19/10/2019
Introduction ………………………………………………… 4
History of electric vehicle ……………………………………… 4
Electric vehicle ……………………………………………… 4
Hybrid vehicle ………………………………………………. 6
BLDC Motor ………………………………………………… 7
AC Induction motor ……………………………………………. 9
Generators …………………………………………………… 12
Configuration of power generator ………………………………. 13
Conclusion ………………………………………………………… 14
Reference ……………………………………………………… 15
Bibliography ……………………………………………………… 16
Today due to the tremendous development in technology we can see the electric vehicles in our surrounding. These vehicles have several advantages over the problem of exhaust emission of combustion engine such as they are pollution free does not produce greenhouse gases, does not require fuel etc.
Since 1960 several attempts had been made to design electric vehicle. The scientific researchers and a team of engineers from the various background such as mechatronics, electrical, electronics, mechanical, automotive and software engineers have developed an electric vehicle today. This report will discuss the various applications of electric motors and generators in hybrid vehicles and electric vehicles. Also, we can see a difference between the combustion engine vehicle and the electric vehicle that how the motors and generators play a vital role in such vehicles.
The key concept of designing an electric vehicle is to reduce the toxic emission from combustion engine vehicle and to make fuel-efficient vehicle. In this report first, we will see the past, present and future trends of hybrid vehicles, the working of electric motors, generators and batteries for the successful design of such vehicles and finally its efficiency and cost in practical life.
History of electric vehicle
The electric vehicles use its total power to run the vehicles from the batteries and other electrical resources and do not produce any emission hence they also known as ZEV means zero-emission vehicles. Electric vehicles use an electric motor or traction motor for propulsion. The power system in the electric vehicle consists of rechargeable batteries, electric motors, generators, and controllers.
If we look at the history of an electric vehicle the trend come into existence in the year 1832 to 1839 when Robert Anderson from Scotland made an electric carriage. Then A.L Ryker and William Morrison came into action and made electric wagon and America start giving attention to electric vehicles. But in the year 1912 when the gasoline price drops down the production of electric vehicle decline also the cost of these vehicles were too high around $1750 and the combustion engine vehicle cost for $650 hence, mass production of combustion engine vehicle increases, and electric vehicle completely disappear. Again, in the 1960s the electric vehicle comes into action the reason was the combustion engine vehicle was unhealthy for the environment and creating a huge amount of pollution.
The design of electric motor is very simple it consists of electric motor, dc controller, pack of rechargeable batteries and potentiometer. The battery is connected to the electric motor via a switch. When the switch is ON the amount of electricity is passed through the motor and the gear box of the vehicle and the motor runs which drives the wheels to run the vehicle in an efficient manner. The basic structure of electric vehicle is shown below in two different ways.
Fig.1 Block diagram shows the battery usage
Fig2. Various parts in electric vehicle
The fig.1 shows the battery usage for the operation of electric vehicle and fig.2 shows the various parts use in electric vehicle. The electric vehicle uses AC or DC motor if it is a DC motor then it may use 96 V to 192 V of energy for 20 KW rating. The operational principle of electrical motor is depending upon changes in magnetic flux it allows the shaft to rotate this occur because of electromagnetic induction. The DC motor have certain limitations it cannot be overdrive because DC motor get overheated after a certain operating point and can damage the motor.
Hence, engineers decided to install AC motors in electric vehicle such as BLDC motor, AC induction motor and brushed DC motor. The most commonly used motor is BLDC motor which consist of permanent magnetic rotor which is surrounded by a stator which is wounded. Generally, 3 phase motors are used which runs on 220 V to 240 V and has a 300 V battery pack. AC motors are widely used because they are available in various sizes, power ratings and shapes. The DC motor also have a future it may work as a generator because of regenerating breaking feature which can the recharge the battery.
The batteries provide power to the controller it stores the energy to drive the car the energy is stored in the form of chemical energy and when require it convert it into electrical energy. It ranges in voltage there are three type of batteries are used in electric vehicle such as lithium ion battery is most commonly used, lead acid and nickel metal hybrid batteries.
The controller shown in the above fig.1 and 2 control the amount of current supplied to the motor. The battery power is supplied to the controller to drive the motor. It supplies maximum power when driver press the pedal at full position and it supplies zero current when the driver releases the pedal. In fig. 2 we can see the potentiometer connected to the dc controller its function is to provide an information about the signal to the controller which decide the amount of power required to deliver.
The hybrid vehicle consists of an internal combustion engine (ICE) which uses fuel like diesel or gasoline. The electric motor and ICE provide power to the engine such as accelerating the vehicle. The set of battery and internal combustion engine store the energy. The batteries used in hybrid cars are rechargeable and it recharge automatically when we drive the car. The fig.3 shows the basic structure and various parts of hybrid vehicle. It mainly consists of an internal combustion engine, electric motor, rechargeable battery, generator and a power split device.
Fig.3 Structure of hybrid car
The heart of the hybrid vehicle is internal combustion engine. The internal combustion engine is design with advance technology it increases the efficiency of the vehicle and reduces the emission in environment and it is small in size. The combustion engine is run by the fuel like gasoline or diesel.
The electric motor is another most significant part of the vehicle. Its function is to take energy from the battery when driver need to accelerate the car and when the speed of car slow down it returns the energy to the battery because of this function it works as generator.
The power split device shown in the above figure is connected between the generator and electric motor its function is to provide continuous variable transmission. The operation of hybrid vehicle is very simple when the driver accelerates the pedal the energy is converted by the generator and store it in the battery this stored energy is used to run the electric motor. It is interesting to note that electric motor and internal combustion engine work simultaneously and provide power to power spilt device. The power split device turns the transmission by combining both the power. Similarly, transmission turns the wheels of vehicle and in this way the vehicle drives.
In hybrid vehicles the energy is stored in the battery when braking operation is converted into electricity. When braking operation occur, the electric motor is reversed and instead of using electricity to turn the wheel, the wheel turns the motor and generate electricity. In this way, the speed of vehicle slows down by the wheels which consumes the energy to run the motor. When the vehicle stops the electric motor and the combustion engine shut of automatically, but the battery provide energy to run the air conditioning, lights and display unit of dashboard.
The top selling hybrid vehicle in the market are Toyota Prius, Honda civic hybrid, Ford fusion hybrid and many more.
Electric Motors in EV
The manufacturer of electric vehicle best performance and well thought out drive technology motors. As we discussed that various motors are used in electric vehicle. The commonly used motors are BLDC motor, AC induction motor and brushed DC motor.
BLDC motors also known as “DC machine with solid state communication” was first introduced in the year 1962 by T.G. Wilson and P.G. Trickey which was applicable for some low power application. When the permanent magnets and high-power transistors are invented BLDC motor are used for the high-power applications.
Fig.4 BLDC Motor
In 1970’s for industrial application permanent magnet synchronous motor came into action. Today these motors are used for various application such as aerospace, medical, automotive, instrumentation and automation. There are two significant types of permanent magnet synchronous motors which is based on back EMF. One is having sinusoidal-wave back emf known as permanent magnet synchronous AC motor (PMSM) and another one is based on trapezoidal back emf which is known as permanent magnet brushless DC motor (BLDC) motor. The advantage of BLDC motor is it has a very high starting torque.
It is very significant for designing an electric vehicle to select the type of motor for its drive system. In fig.5 we will see the application of BLDC motor in two pole motor drive system. In BLDC motor the exact position of permanent magnet is an important factor because of electronic commutation it requires complex algorithm for the operation of BLDC motor. The rotor detection is depending on two algorithm one is based on sensor other is without sensor. It is shown in the fig.5 that the hall effect sensor is connected at constant position at 120 electrical degree phase difference on the non-rotating end of the motor to detect the rotor angle.
The permanent magnet rotor position help to generate the hall effect. The controller decodes these signals so that correct voltage level is fed to the three-phase voltage source inverter which drives the BLDC motor. As per the practical experiments the acoustic noise of BLDC motor is higher than the SR motor when the operating speed is high. The main drawback of these motors is it has very complex structure and provide lower efficiency at high operating speed.
Fig.5 BLDC motor with two pole motor drive system.
The internal structure of BLDC motor is shown in the fig.6. For high resolution application optical encoder has been used as position sensor. BLDC motor require less maintenance, the efficiency is high and as the parament magnet provide a high-speed range and high dynamic response hence, it is used for the motor wheels applications.
Fig.6 Internal view of BLDC motor.
AC Induction motor
We have already studied about the induction motors in lectures. The concept of induction motor is applicable in electric vehicle and the efficiency of induction motor will provide the results for the entire operating region. The automotive industry is still doing research on appropriate for the electric vehicle operation to achieve efficiency, cost and reliability. The fig.7 shows the structure of three phase induction motor.
Fig.7 Three phase induction motor
Now, we will see the propulsion and design of induction motor in an electric vehicle. The design of vehicle is depending on various factor such as size of motor, aerodynamics, speed, acceleration, mass of vehicle etc. The pre-sizing of induction motor depends upon three different factors initial acceleration, maximum speed of vehicle and maximum gradeability. Hence, certain parameters are obtained while doing the induction motor pre-sizing which is given below.
Acceleration: 0-50 Km/h.
Vehicle Mass: 1500 kg
Rolling resistance coefficient: 0.015
Aerodynamic drag coefficient: 0.3
Front area: 0.8 m2
Maximum speed: 120 Km/h
Maximum speed of induction motor: 3500 rpm.
As we know that the overall efficiency of induction motor is above 85% to 97%. The losses are distributed into two types friction and windage loss 10% and iron losses are 20%. The fig.8 shows the equivalent circuit of induction motor and it is similar to transformer. In induction motor the stator and rotor resistance is high and the winding used in induction motor is distributed. There is an air gap of its magnetic circuit hence, we use the equivalent circuit due to large excited current.
fig.8 Equivalent circuit of induction motor
Another significant concept in induction motor is slip. It is defined as the difference between the synchronous speed and actual rotor speed to synchronous speed. Therefore, the slip is proportional speed when the speed varies the slip also varies and hence, the torque also changes. Therefore, the torque slip curve shows the variation of torque and slip. The fig.9 shows the torque slip characteristics.
fig.9 Torque slip characteristics.
Therefore, from the above basic knowledge of induction motor, it is clear that to drive a car the starting torque required is very high. It directly affects the speed hence; AC induction motor will be an option to install in EVs. It is the most efficient machine and has an overload capacity and the strength of motor is very high which is necessary for the hazardous condition.
On May 30th, 2016 Steve Baker explained how Tesla is introducing induction motor in their electric car due to robust advantages. He said that small changes were made in the motors such as the brushes are removed because of the smaller life of brushes and cause friction and physically engage the rotating shaft. Permanent magnets the most significant part of the motor is also eliminated which will reduce the weight of the motor and also reduces the breakage and shortage. The fig.10 shows the tesla’s S-model induction motor used in electric cars.
Fig.10 Tesla’s S-model induction motor.
The generator is most widely used in hybrid vehicle which is considered as a source of power. The internal combustion engine and the generator provide power to the vehicle to run efficiently. The fig.11 below shows the Toyota’s hybrid vehicle basic structure which explains how generator is working.
There are two power sources one is combustion engine which provide maximum efficiency and other is motor provide surplus energy. The Power drive system splits the energy of engine in two parts. One part is provided to generator which produce electricity and drives the electric motor. The other part is directly given to the wheels. The distribution of these two energies is controlled by the power unit which gives maximum efficiency.
Fig.11 Toyota Hybrid vehicle
It is interesting to note that propulsion system of hybrid vehicle uses two types one is series hybrid and other is parallel hybrid. In this report the series hybrid is considered because it increases the fuel efficiency and reduces the emission and also its structure is less complex than parallel hybrid system. In series hybrid the engine is linked with the generator first not directly with the transmission because the electricity production is required due to this design series hybrid is easy to build and the transmission system is not necessary. Hence, the series hybrid system is suitable for a heavy-duty vehicle such as tuck, buses etc.
The series hybrid system is a combination of the power generator, batteries, reduction gear, and traction motors. The DC generator is used which supply power to the system and recharge the battery. The power produced by the generator is dynamically changed due to the state of battery charge, the slope of the road, the speed of the vehicle, acceleration. The focus is on fuel efficient vehicle which can be achieved by the combining generator and combustion engine. The fig.12 shows the internal structure of dc generator and the actual generator use in hybrid vehicle.
Fig.12 Generator used in hybrid vehicle
Configuration of power generator
The combination of engine and generator is known as power generator. A damping plate has been coupled between the engine and generator. A CAN bus is used for communication among the three different unit known as Battery control unit (BCU), Generator control unit (GCU) and Engine control unit (ECU). As shown the in fig.13 a power command is fed from BCU to GCU visa CAN bus. The state of sensor is calculated by BCU it is shown in the figure that a throttle request or command is send to ECU and in conventional vehicle this command is considered for accelerator pedal.
Fig.13 configuration of power generator
The generator can operate at its maximum peak power which may cause overheating hence, an overheating protection system such as temperature sensor which detect the generator temperature when the temperature reaches above safety and de-rate maximum output power. Hence, avoid burning of generator.
The advance technology and a competition in the car market are robust. The companies like Tesla, Toyota, Nissan, Kia, Volkswagen etc started to build and launch the hybrid and electric vehicle in the market. There is new development in the batteries that can charge the cars within few hours. According to a recent research in University of Glasgow, Scotland, the energy is stored using Nano molecules and output is provided in the form electricity or hydrogen. This technology will help the user to refuel the car similar to refuelling the car at petrol station.
The long-distance travelling is possible by using electric cars in the year 2017 Chevrolet introduced its electric vehicle Chevi Bolt which can travel 238 miles in one charge which is a tremendous technology in the world of EV. Also, the drastic declination in battery cost reduces the overall cost of EVs. The EV or hybrid cars ranges from $23000 to $250000. Companies like Tesla is at the peak in making EV cars and invest lot of money for advance technologies.
Fig. Actual model of hybrid car with power generator unit
In conclusion, there are numbers of ways and choices available to select the exact motor for the application of EV or hybrid vehicle. The pre-sizing of motor and to install the machine is not an easy task. Various methodology and task are there in front of engineers to select the electric motor to drive a vehicle. The generator and engine unit develop a hybrid vehicle which make a fuel-efficient and environment friendly vehicle. The technologies made in electric motors are generators are significant for the development of future cars.
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