Foresight Scenario Analysis of Motor System of Electric Vehicle

In order to describe the trend of motor system development of electric vehicle and to figure out the factors that would affect the external drives and the internal resources, the thesis uses scenario analysis method to be the basic framework, adding modified Delphi method to clarify time transition into five categories: changeless, changeable, disappeared, uncertain states and newborn. More precisely, the five factors is used to construct “Scenario Analysis of Markov Modified Delphi Method”. The thesis focuses on motor system to do the Foresight analysis, using the transition concept of Markov Chain to clarify the key factors of uncertain states into motor system: brushless DC (BLDC) motor, surface permanent magnet synchronous motor and Switched Reluctance In-Wheel Motor. Moreover, the changeless concept of Markov Chain is used to be background, adding the key factors of changeable and uncertain states to clarify seven kinds of scenario portfolio: basic scenario, scenario assumption I, scenario assumption II, future scenario, breakthrough scenario I, breakthrough scenario II and challenge scenario. It could make the government, industries and related departments realize the development trend of key components about electric vehicle by the scenario descriptions. It can increase their willingness to invest in the related researches to achieve future image, also shape the usable engineering technique and integrated system concepts of electric vehicles in 2020 for public.


Introduction
Under the trends of energy saving and carbon reduction, electric cars have become an inevitable alternative.Although the mainstream of the power system in vehicles is still internal combustion engine which has gone through one hundred years of development, and its energy conversion efficiency continues to be improved, the oil consumption and carbon dioxide emissions are gradually becoming unacceptable.In fact, only 25% of the energy produced by gasoline is transmitted to the tires.On the contrary, electric motors can convert 80% of the kinetic energy, it is much higher compared with the fuel conversion efficiency.Therefore, whether electric cars can truly replace the existing fueled vehicles, issues such as size, light weight, high efficiency and low cost of the motor drive system became critical.Therefore, this research mainly studied the development status of electric car motor system and it used the Markov chain time state transfer views to carry out the scenario analysis of modified Delphi and Markov transition.It speculated the possible motor technology development and potential by 2020.Some key factors were analyzed and an engineering development approach was used to build a combination of future life scenarios.They provide decision making references in the R&D direction for industries, research institutes, and government organizations.

Literature Review
If motors are differentiated by electric current, they can be divided into two broad categories: DC motors and AC motors.AC motors have the characteristics of high efficiency, high output, regenerative braking capacity, etc.In addition to being widely used in industrial products, some are also being used on electric vehicles.If classified according to magnetic fields, there are four kinds of motors: brushed DC motor, AC induction motor, brushless motor, and reluctance motor, etc. (Wen-Hai Liu, Sheng-Lung Lee, 2007).Brushless motor has the highest operating efficiency and power density.However, its cost of unit power is higher; reluctance motor has the lowest cost of unit power, but its cost of drive is apparently higher; AC induction motor has many advantages, but its power density is the lowest among these four motors, and its volume and weight are less than ideal; brushed DC motor is constrained by its maximum speed limit and its relatively poor reliability, it's difficult to be developed for high speed, and as a result, its use in electric cars has gradually been eliminated; induction motor has a better torque output in high speed, it's suitable to be used in wider, fasterspeed suburban areas, and it also has a lower demand for magnetite ore; brushless motor has a better torque output at low speed, and it's suitable to be used in short distance, slow speed urban areas.However, it's difficult to acquire the permanent magnet material (NdFeB magnets); reluctance motor is constrained by factors such as the high controller cost, low conversion efficiency, and so on.Currently, there is not a breakthrough in this technology.In-wheel motors are divided into four major categories, permanent magnet brushless motor, induction motor, switched reluctance motor, and transverse flux motor.Among them, the application of permanent magnet brushless motor is most common, and the transverse flux motor is a very competitive new low speed high torque motor.Currently, the in-wheel motor technology of Mitsubishi Motors is the most mature.It has the direct function of reducing vehicle weight, increasing range, and improving handling (Wen-Hai Liu, Sheng-Lung Lee, 2009).

Methodology
The research flow followed the steps in the modified Delphi method, the key factors of motor system through the consensus from the experts group were used as a basis, finally, the key factors were developed and the Markov modified Delphi method scenario analysis was used to conduct analysis of each step, the development scenarios of motor system of electric cars were then built.

Questionnaire design
The first survey was a structured questionnaire which was designed by researchers according to literature.It asked the participants to choose the significance of each item, and to provide other opinions or views as the reference basis of feedback.However, in the second questionnaire, the collective measure of each item from the first questionnaire was attached as a percentage.There are pros and cons of publishing experts' agreement percentage, i.e., it enables fast convergence, making participants understand the opinions of most experts, and avoiding the same views as the previous survey, and lost the meaning of the second survey.Similarly, after the second questionnaire was received, the data must be sorted and analyzed to provide the collective measurement to participants as a reference, then the participants were asked to complete the third questionnaire, the process continued like this until the consensus has been reached.

The selection of experts
As to the number of experts to be selected, the Delphi method requires the number to be at least 10 persons, but not more than 30 persons.If the number of experts exceeds 30, their contribution to the research will be limited, and if there are too

Sc m
The

Content description of the scenario combination 1. The basic scenario
Little Wang is a design engineer of a certain car manufacturer.In order to identify an electric car motor suitable for use in Taiwan's high temperature environment, little Wang considered the following motors: Permanent magnet brushed DC motors, embedded permanent magnet synchronous motors, switched reluctance motor, synchronous AC reluctance motor and in-wheel permanent magnet brushless motor.First of all, because the brush of a permanent magnet brushed DC motor must be replaced often, it was quickly disqualified by little Wang.Embedded permanent magnet synchronous motors have the risk of magnet becoming demagnetized easily due to high temperature, and it's relatively costly to replace permanent magnets, thus, it is not a suitable motor.The advantage of either switched reluctance motor or synchronous AC reluctance motor is the maintenance is very fast and cheap, but the drive controller is very expensive, if, after the vehicle warranty period, the controllers malfunction, it would be a costly expense by that time, and it does not meet the durability requirement of the people in Taiwan.Later, little Wang decided to adopt a permanent magnet brushless in-wheel motor.Although in-wheel motor is a little more expensive, but its reliability, transmission efficiency and weight are all better than the above-mentioned motors.2. Hypothetical scenario I Little Wang would like to design a vehicle with a high weight bearing capacity to replace the current truck.According to the truck usage characteristics, it must be designed to meet the needs of stop-go deliveries, the long-distance truck usage, and the climbing ability.Therefore, the motor must meet the requirements of having a great torque and long high-speed operation.Finally, little Wang adopted permanent magnet brushless in-wheel motor, other than satisfying these features, due to the design of in-wheel motors, the mechanical shift control device, clutch, transmission, drive shaft, differential, and so on used in traditional vehicles were all omitted.This greatly simplifies the drive system, the whole vehicle, and the chassis structure, and the effective use of space and the transmission efficiency have both been improved.3. Hypothetical scenario II Due to the improvement in semiconductor technology in the future, the costs of controllers for the reluctance motors are significantly reduced.In the future, a large number of cars will start using switched reluctance motors and synchronous AC reluctance motors.Relative to the previous generation of electric cars, the switched reluctance motors has a simple design in construction and inexpensive maintenance, and it does not have the demagnetization issues due to high temperature as found in embedded permanent magnet synchronous motors and permanent magnet brushless in-wheel motors.4. The Future scenario As electric cars become popular, the consumers are gradually getting used to and accepting the performance of electric cars.In response to the requirement of an electric car that has low maintenance and is durable, little Wang, therefore, launched a cheap electric car design, and selected a switched reluctance motor.In addition to having simple maintenance, the motor can operate normally in high temperature which satisfies the vehicle requirement of the general public.5.The challenging scenario Sales of an electric car with in-wheel switched reluctance motor designed by little Wang was discontinued due to poor sales, and the car manufacturer carried out a series of review meeting.In the selection of a motor, the in-wheel switched reluctance motor was already adopted due to its ability to meet the needs of long-distance use and the weight-bearing requirement, but it was not very much accepted by the market.After a series of customer surveys, it was discovered that parts can be stolen from the electric car easily, and the stolen parts were not the motors, but the motor controllers.The electric car with in-wheel switched reluctance motors can be identified easily from its appearance, and the components that have the highest values in the vehicle are the controllers which not only can be stolen easily, but they can also be sold easily.Because the vehicle cannot be used without the controllers, having become famous with the high theft rate, the electric car model resulted in poor sales.As a result, the car manufacturer had to re-design to consider whether to replace the motor with brushless DC motor.

Conclusion
In recent years, various countries raced to develop green energy-related industries, and they're seizing the electric car markets actively.However, the current price of electric vehicles is still too high, the most important factor is the motor which accounts for more than 25% of vehicle cost.Therefore, in order to make electric cars become popular sooner, the investment in the R&D of