According the benefits of permanent magnet technology it is

According to recent statistics
given by United States government agency on global consumption of electricity in
the year 2016 was approximately 22000 TWh (Yearbook.enerdata.net, 2018). The
growth of electricity consumption is rapid, and it is predicted to reach 30116
TWh in the year 2030. Although one of the most important goals for
international energy policy is to prevent climatic change, in layman’s term
reducing global worming effect. Therefore, it is predicted that carbon dioxide
emission will be little as compared to present scenario. To achieve maximum
electricity production to cater ever growing requirement of electricity with
reduced carbon footprint it is necessary for all the countries to adopt
efficient renewable energy sources such as solar and wind, without the help of
renewable natural energy sources to produce electricity it is impossible to
reduce ambitious carbon foot print goal globally (Aleksashkin and Mikkola, 2008).  

Crucial role in energy production
and consumption of energy is played by electromechanical energy conversion
devices mainly generators and motors. Therefore, to cater the international
policies to reduce carbon emission and ever-growing energy requirement it is
necessary to enhance the efficiencies of electromechanical energy conversion
devices such as generators as well as motors. New enhanced area of permanent
magnet technology has emerged which can be effectively utilised for generators
as well as motors. When considering efficient solution for generating and
motoring then permanent magnet technology for electromechanical power
consumption is unavoidable. It is possible to create competitive distributed
energy technology with new conversion apparatus due to sophistication of
available energy conversion technologies with permanent magnets. One of the
obvious example of similar development is direct driven windmill generators, by
utilizing the benefits of permanent magnet technology it is possible to enhance
the efficiency of the generators stated in the for the application (Aleksashkin
and Mikkola, 2008).

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Industrial use of the permanent
magnet is started since the invention of very first permanent magnet at the
beginning of the 20th century. For electric machines such as
rotating as well as linear machines permanent magnet motors are used which is
the well-known application. Such application has both modes motoring as well as
generating. Permanent magnet motors are in use for decades in various
applications due to its low initial cost and simple structural requirements.
The applications of permanent magnet machines have been exploited recently for
more challenging tasks due to improvement of permanent magnet characteristics
and low cost. Therefore, it is found that most modern applications of permanent
magnets are efficient as well cost competitive (Aleksashkin and Mikkola, 2008).

All electromagnetics energy
conversion devices which incorporates permanent magnet technology are described
by the term ‘permanent magnet machine’. A single or multiple permanent magnet
are used for magnetic excitation. Variety of configurations could be found in
the energy converter that employs permanent magnet technology, several examples
are, generator, motor, stepper motor, alternator, actuator, linear motor,
control motor, transducer, brush less DC motor, tachometer and many more. The
stator of the motor is like the stator of the multiphase AC motor. The new
component incorporated in the permanent magnet motor is rotor, the rotor is
complete contrast to that of conventional rotors. In this application, rotor
relies of magnetic excitation unlike excitation by electric current in the
winding of multiphase AC motors. To achieve the higher efficiency for the
desired load characteristics, high efficiency, high power factor as well as
performance, it is necessary to optimise the configuration of the rotor,
mechanical design and electromagnetic rotor and the design of the
electromagnetic stator (Rizk et al, 2000). The direct drive wind turbine
application requires a machine with high power density, high power torque, high
efficiency with low design operating speed. The primary reason to use direct
drive permanent magnet machine is that the machine has an ability to reduce the
cost of converting wind power to mechanical power simply by eliminating the
necessity of step up gear box. The speed increasing gear box is usually
incorporated in wind mill to amplify the small rpm of the wind rotor to higher
rpm to produce electricity. The cost associated for the operation as well as
maintenance of direct drive permanent magnet machine is very low as compared to
gear coupled machines. The role of low speed, high power direct drive electric
machines are extensively limited to special applications such as large
hydroelectric generators therefore they are not commonly used in the industry. Therefore,
low speed and high torque motors need reliable evaluation and experimentation
to analyse their suitability for the wind turbine application as a direct drive
device. Such suitable application could be revolutionary due its high
performance, low cost and simple structural requirements. (Baywaters et al,
2005)

This project work is an effort to
design the permanent magnet machine for the application of wind turbine. The
need and benefits of using permanent magnet machines are briefly described in
earlier paragraphs. The primary motivation for the project work is the needed
initiative to reduce the carbon foot print in the field of electricity
production, which can be achieved by utilising renewable natural resources
considering present scenario. The permanent magnet machines are the possible
solution due to various benefits offered by them with competitive cost.

This progress report contains a
brief introduction of permanent magnet technology, along with their benefits
and technical operation which is followed by the aim and objectives laid down
for the project work. Literature review at this moment is primarily on
permanent magnet machines, their classification and construction. The project
plan illustrates the gnat chart which shows the primary plan laid out for the
project since project selection till project completion. Progress of the work
however shows the similar gnat chart with the actual progress shown on it along
with the comments. Summary and conclusion chapter summarises the progress
report considering the current work progress, difficulties, and future schedule
for completion of the project.

 

 

 

 

1.0   Aims and objectives

Aim of this project work is to
design a permanent magnet motor for application in wind turbine. To achieve
this aim successfully following objectives have been laid down,

–         
To
carry extensive research, online as well as offline on the subject of permanent
magnet motors/generators and wind turbine

–         
To
select a wind turbine to understand the capacity that will help the design

–         
To
study and design different components of the permanent magnet of the motor
based on requirement of wind turbine, this objective need extensive study as it
will have required to design or select the power density/torque, efficiency, operating
speed etc

–         
Finite
element analysis of the design to find the suitability of the design for wind
turbine under various conditions

It is necessary to note that, a
wind turbine is a huge device, therefore actual assembling and testing of the
permanent magnetic machine will be costly at academic level, therefore, the
efforts will be taken to scale down the wind turbine to a level which
assembling of prototype and testing of the permanent magnetic machine will be
cheap in terms of cost.

 

2.0   Literature review

Wind energy is an inexpensive
renewable energy source which has an ability to make significant contribution
to the electricity utility network. However, there are two problems associated
with the construction of wind power generators which has to be addressed, the
first one being the instability of the wind speed and the second one is
rotating speed of the wind turbine which is low due to the large diameter of
the rotor blades. The technologies have been developed to estimate the variable
speed constant frequency to counter the instability of the wind speed. The
later issue was addressed by using conventional solution of gear box to
increase the speed which helps to reduce the size of generators. Although
solution of gear box has several disadvantages as it generates noise and
vibrations, losses in gear drive is high since it is a mechanical device, ned
of constant lubrication and periodic maintenance (Fengxiang, 2005). The cost of
gear box is also high.

Direct driven variable speed
permanent magnet machines are being a subject of attention due to various
advantages offered by them such competitive cost and possibility to eliminate
the gear box from wind turbine structure. Energy capture is increased in such
application by using variable speed. Due to removal of gearbox weight and
losses in wind mill reduces drastically which enhances system efficiency.
Frequency of periodic maintenance is also reduced saving finances of the
organization. Although, large numbers of poles are required to construct a
generator due to low rotational speed; it is necessary for the generator that
it should be efficient naturally with competitive cost. To supply power to the
grid, frequency converter is required due to the variable speed scheme.
According to (Fengxiang et al, 2005) small pole pitch can be achieved by
incorporating large pole numbers with permanent magnets. A simple and effective
generator construction is shown in figure 1 of appendix 1 in the form of disc
type axial flux configuration. The stator in the figure shown is a toroidal
wound accommodating rectangular coils which forms an air gap winding. Permanent
magnets are attached to the rotor disc located on both side of stator.

According to (Spooner et al, 1996), the assembly of the permanent
magnet machine is the crucial problem during its construction. No strong forces
are present at the time of assembly as the assembly of the magnet is carried
out individually and iron parts are already located in the position in the
modern assembly practice of permanent magnet machines.

To reduce the assembly problems
of PM generators the modular construction is proposed by to (Spooner et al,
1996). The paper presented by to (Spooner et al, 1996) says that, for the large
grid connected wind turbines, direct coupled, permanent magnet, synchronous
with radial field and multipole machines can be used. The power rating could be
between 100 kW to 1 MW and pole numbers could be between 100 to 300. Employing
modular constructions help to reduce need of detail design, number of tools and
drawings. The modular assembly practice can be utilised in vast ranges of
machines. The standard ferrite magnet blocks are used in the rotor module,
whereas the stator module is formed by single rectangular coil embedded in
simple E-cores. The assembly of the magnetised parts can be arranged easily
which improves the efficiency of the machine with low reluctance. The multipole
permanent magnet is shown in figure 2 of appendix 1 whereas modular arrangement
of magnet is shown in figure 3 of appendix 1 which help to visualise the
difference.

 

The progress of the work shown
here is divided in to two parts,

1.     
Design
of permanent magnet machine

2.     
Finite
element analysis of the design

During the study of permanent
magnet machine, various important design parameters were studied which is
incorporated in the design of the permanent magnet machine,

Rated
power of the machine- Velocity
of the wind speed and speed ration of driving shaft governs the rated output of
the generator. For this project work, minimum wind speed of 4 km/hour is
considered, the rpm produced by the shaft and output of the generator with
single phase connection will be calculated theoretically and evaluated during
FEA analysis if the design.

Number
of phases and poles- Number
of stator poles decide the number of phases in the machine. The thumb rule is
the number of stator poles are twice than number of phases. It has been found
that during research, torque ripple increases with small numbers of phases
where as cogging torque reduces with large pole numbers. Considering these
constraints, three phase machine is selected. By using electrical engineering
handbook by (Chen, 2004), 24 number of stator poles are selected to reduce the
torque ripples. The rotor pole is selected considering the relation between the
rotor and stator.

Frame
size- Dimension for all
electrical machines are freeze by International Electro-Technical Council known
as IEC, which comply the ISO regulations. The stator and rotor ratio selected
at this moment is 1:16 but it may change during the course of designing
depending upon the need. The structure size is yet to be finalized although
preliminary selection of the ratio fixes the frame structure.

Air
gap- The probability of cogging
torque increases due to use of permanent magnets therefore to reduce the same
and to increase the flux density air gap will be limited to a range of 0.5 to
1.0 mm.

Machine
specification- Although design of
permanent magnet machine is ongoing, and all the parameters are not fixed yet.
Even though tentative specification of permanent magnet rotor is given below
based on selection through engineering handbook and ratio, just a note, below
specification might change depending on the design requirements,

The design of PM machines will be
validated in FEA (Finite Element Analysis) software developed in the
university. The FEA software is a powerful tool which help to analyse the
design and allows necessary changes before actual production and assembly. Various
scenarios can be simulated to check the performance of the PM machine.

In this project work, FEA will be
used to check the designed structure of the machine, excitation of the rotor,
material properties and torque produced due to different rotor position as well
as wind current. The step by step approach will be used to find solution of
continuum problem during FEA analysis; for example, elements are created by
dividing the continuum region by using different shapes of elements. It may be
possible that different shapes of element produce similar solution for the
continuum. It has been found during familiarization of software that it is
quickly possible to express material properties, constraints and excitation
although it is comparatively difficult to express. Other important parameters
will be calculated by using solution of system equation, such as,
electromagnetic problems, Components of magnetic flux density are nodal
unknowns. By using these components torque, induction and several other
electromagnetic parameters will be calculated and compared with the design one.

Following assumptions are made to
determine distribution of magnetic field inside the machine. These assumptions
are primary and may changed during actual simulation of the design,

1.     
Since the
magnetic field outside the status stamping is almost negligible hence the
magnetic vector potential line of outer periphery of the status stamping is
treated as zero

2.     
Hysteresis
effects are neglected as magnetic material is isotropic for stator and rotor
stampings

3.     
Components
of Z- directions are Current density (J) and magnetic vector potential (A)

4.     
Distribution
of magnetic field along the generator’s axial direction inside the generator is
constant

5.     
End
effects are considered to be zero

 

The progress report includes
brief overview of permanent magnet machine with its application in wind
turbine, benefits of the same if used in the wind turbines followed by aim,
objectives and glimpse of literature review which primarily emphasis on construction,
assembly and capacity of permanent magnet. Project management section shows
gnat chart in detail along with its completion status. Progress report on the
other hand shows the completed work so far in design part as well as future
considerations and assumptions for FEA.

Considering the work put together
in progress report, it can be concluded that progress of the report is as per
the schedule and it will be completed according to plan provided in project
management section. Initial design specification for the PM machine is
completed, along with initial CAD drawing for the same. Detail design procedure
is in process and it will be completed by end of week 8. Study of FEA software
by using similar case studies have been carried out. Once the final design of
the PM machine is completed then CAD modelling and FEA simulation will commence
which is around start of week 9. Any alteration required in the design will be
carried out considering the results of FEA. Comparison of initial and final
design along with FEA justification will be provided.