PERMANENT MAGNET SYNCHRONOUS MOTOR FOR CEILING FAN
FIELD OF INVENTION
[0001] The present invention relates to a motor for ceiling fan. More particularly, the
present invention relates to a permanent magnet synchronous motor for a ceiling fan
having high efficiency in a wide speed range, making it suitable for one to one
replacement ofthe present ceiling fans.
BACKGROUND OF THE INVENTION
[0002] Ceiling fans work on the principle of motor, wherein when a current carrying
conductor is placed in the motor that has magnetic field, it experiences force. In general,
an induction motor used in a ceiling fan comprises a stator installed in a central region
with field coils and die cast rotor mounted along radial surface of annular body. When the
stator generates magnetic field and induces secondary magnetic field due to eddy currents
in the rotor, rotational movement is enabled through interaction of the respective
magnetic fields.
[0003] Induction motor based ceiling fans also typically use a capacitor with a
startup winding connected thereto in order to provide phase shift to load to operate the
motor in multiphase. These induction motors are designed with high rotor resistance so
that their speed can be controlled by varying any of voltage or current or frequency,
which is not a solution for household appliances. Speed control by voltage change
technique increases slip and reduces efficiency. Therefore, these induction motors
typically have poor efficiency of around 60% of maximum output at rated speed, and
below 40% at half speed.
[0004] A conventional ceiling fan with an induction motor having 14 pole to 16 pole
has a maximum rotation speed of 400 rpm at 220V 50 Hz single phase AC power.
Rotation speed can be varied by changing the voltage, which is under the control of the
operator. Maximum speed can also be based on constructional features such as stator
stamping, material used for wire wounded on cores or coils, type of rotor, and number of
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blades mounted, which features are not under the control of operator. Typical power
consumption of a conventional ceiling fan is between 30 to 90 W depending upon speed,
efficiency, capacity and usage or life.
[0005] U.S. Patent Application No. 2012/0251334 describes about a controller that
uses a DIP switch to control the fan rotation speed. DIP switch is operatively connected
to motor to alter the rotation speed matching different loads. These types of fan rotation
speed controllers are selected for proper operating rotation speed depending on the load
and required speed. Controllers can be any of thermostatic, linear regulation, or pulse
width modulation controllers used in graphic cards for gaming applications, or can
include a simple diode or resistor that can control the rotation speed of ceiling fan. These
controllers are easily available in the market and are selected depending on factors such
as load type, speed, application and usage.
[0006] When compared to induction motors, Permanent Magnet Synchronous
Motors (PMSM) are more powerful as their size offers high efficiency, torque, less noise,
vibration, longer motor life, and higher reliability. PMSM motors typically operate with
permanent magnets mounted on radial surface of rotor having different shapes and
optimize the air gap magnetic flux in order to design highly efficient PMSMs. Rotor
magnetic flux generated in PMSM motors is inversely proportional to the air gap and
magnitude of axial force is difficult to withstand because of the arrangement of
permanent magnets and therefore in order to maximize the performance of PMSM and
ensure system stability, the motor requires a balanced magnetic flux with suitable torque
and proper power electronics connected to ceiling fan for proper operation.
[0007] However, these motors are expensive due to added cost of the permanent
magnets mounted internally. Few existing PMSM motor applications include floppy
drives, small printers, and graphic card fans utilize single side axial magnetic flux.
However, these applications are limited to motors having a rating of less than 5W as
these motors are made with air core stators, which in turn limit the magnetic flux density
and air gap.
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[0008] There is therefore a need of a fan and a motor therefor that provides high
torque and high efficiency (above 80%) at rated speed, which is significantly higher in
comparison with other induction motors. There is also a need for a fan that delivers much
better efficiency at lower speeds.
[0009] These and· all other extrinsic materials discussed herein are incorporated by
reference in their entirety. Where a defmition or use of a term in an incorporated
reference is inconsistent or contrary to the definition of that term provided herein, the
defmition of that term provided herein applies and the defmition of that term in the
reference does not apply.
[00010] Unless the context dictates the contrary, all ranges set forth herein should be
interpreted as being inclusive of their endpoints, and open-ended ranges should be
interpreted to include commercially practical values. Similarly, all lists of values should
be considered as inclusive of intermediate values unless the context indicates the
contrary.
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OBJECTS OFmE INVENTION
[00011] It an object of the present invention to design a PMSM motor that provides
high torque and higher efficiency in whole speed range.
[00012] It is another object of the present invention to design a PMSM motor that
provides high operational rotational speeds and high efficiency (above 80%) at rated
speed.
[00013] It is another object of the present invention to design a PMSM motor that
provides significantly higher efficiency than comparative induction motors.
[00014] It is another object of the present invention to design a PMSM motor that
provides a PMSM motor design for a fan that delivers much better efficiency at lower
speeds.
[00015] Various objects, features, aspects and advantages of the present invention
will become more apparent from the detailed description of the invention herein below
along with the accompanying drawing figures in which like numerals represent like
components.
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SUMMARY OF THE INVENTION
[00016] An objective of the present invention is to provide an outer rotor and axial
magnetic flux based PMSM motor configured for a ceiling fan with high torque, required
operational rotational speeds, and efficiency above 80% at rated speed, which is
significantly higher in comparison with other induction motors. It also delivers much
better efficiency at lower speeds.
[00017] The present disclosure relates to a fan consisting a top body rotor and a
bottom body rotor that are assembled together. Fan further comprises of magnets that are
distributed along a lateral surface of the rotors and provide axial magnetic flux through a
stator, which significantly improves the performance ofthe fan.
[00018] The present disclosure further relates to a fan that incorporates use of
radially distributed multiple small stator cores mounted on an insulator and requires less
amount of steel and copper wire and also simplifies the mass production process.
[00019] The present invention further relates to use of a PMSM motor to improve the
efficiency and weight ofthe housing with increased performance.
[00020] The present invention further relates to use of variable speed drive
connected to the fan in order to operate efficiently in different rotational speeds.
[00021] The present invention does not involve any change in mechanical fitting for
a user while using the present ceiling fan. Instead, the overall dimensions and weight of
the fan housing is also reduced along with imparting increased performance.
[00022] Additional aspects of the invention will be set forth in part in the description
which follows, and in part will be obvious from the description, or may be learned by
practice of the invention. The aspects of the invention will be realized and attained by
means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following
detailed description are exemplary and explanatory only and are not restrictive of the
invention, as claimed.
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BRIEF DESCRIPTION OF DRAWINGS
[00023] In the Figures, similar components and/or features may have the same
reference label. Further, various components of the same type may be distinguished by
following the reference label with a second label that distinguishes among the similar
components. If only the fIrst reference label is used in the specifIcation, the description is
applicable to anyone of the similar components having the same frrst reference label
irrespective ofthe second reference label.
[00024] Fig. I illustrates two complete but different VIews of a ceiling fan In
accordance with an embodiment ofthe present invention.
[00025] Fig. 2 illustrates a section view and an isometric cut view of the proposed
motor in accordance with an embodiment ofthe present invention.
[00026] Fig. 3 illustrates a top body rotor and a bottom body rotor with magnets in
accordance with an embodiment ofthe present invention.
[00027] Fig. 4 illustrates a stator assembly and a stator core in accordance with an
embodiment ofthe present invention.
[00028] Fig. 5 illustrates an exploded cut view of the motor in accordance with an
embodiment ofthe present invention.
[00029] Fig. 6 illustrates a block diagram and inter-connections of a ceiling fan with
its variable speed drive in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[00030] Embodiments herein and the various features and advantageous details
thereof are explained lDore fully with reference to the non-limiting embodiments that are
illustrated in the accompanying fIgures and detailed in the following description.
Descriptions of well-known components and processing techniques are omitted so as to
not unnecessarily obscure the embodiments herein. The examples used herein are
intended merely to facilitate an understanding of ways in which the embodiments herein
may be practiced and to further enable those of skill in the art to practice the
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embodiments herein. Accordingly, the examples should not be construed as limiting the
scope ofthe embodiments herein.
[00031] The present invention will be apparent from the following detailed
description, which proceeds with reference to the accompanying drawings, wherein the
same references relate to the same elements.
[00032] The present disclosure relates to a ceiling fan comprising a Permanent
magnet Synchronous Motor (PMSM) having two rotors, each rotor having a permanent
magnet installed in lateral surface of annular body and providing axial magnetic flux for
ceiling fan with high torque, high operational rotational speeds, and efficiency above
80% at rated speed, which is significantly higher in comparison with other induction
motors. It also delivers much better efficiency at lower speeds.
[00033] Fig. 1 illustrates a conventional ceiling fan 100 with no change in
mechanical fitting, which is similar to other ceiling fans and includes a motor 101 and
102 installed inside an annular assembly. In an embodiment, fan blades (as shown in Fig.
1) are mounted on annular assembly in order to to circulate air. As electricity runs
through the motor 102, the motor enables turning of the blades of the ceiling fan and
circulate air throughout the room or closet.
[00034] In an embodiment of the present disclosure, an axial magnetic flux based
PMSM motor can be installed inside the annular assembly and a variable speed drive can
be mounted on the top ofthe fan, as would be described in detail with respect to Fig. 2.
[00035] Fig. 2 illustrates a section view 201 and an isometric cut view 202 of
PMSM motor installed inside annular assembly 200. Annular assembly 200 can include a
housing body made of two parts, namely a top body rotor 204 and a bottom body rotor
203, which can be fastened together with screws or other suitable means. According to
one embodiment, each of the top body rotor 204 and bottom body rotor 203 can also be
coupled to a stator shaft 205. Annular assembly 200 can be made of Die cast aluminum
or stainless steel that have advantages such as good corrosion resistance, good
mechanical properties, high thermal and electrical conductivity, and retains strength at
high temperatures.
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[00036) Fig. 3 illustrates internal view of annular assembly 300 showing bottom body
rotor 301 and top body rotor 302. Fig. 3 further illustrates radial distribution of 24
magnets 303 mounted on lateral surface of bottom body rotor 301 and 24 magnets 304 on
the top body rotor 302. It should be appreciated that any number of magnets can be
configured on one or more of the rotors in order to practice the present invention and
meet the desired efficiency, speed or other working parameters. In a preferred
embodiment, the number of permanent magnets can range from 4 to 48. In operation,
when a stator is powered, magnetic fields in the annular gap between the stator and the
rotors make the rotors to rotate. In case radial magnetic flux is desired, PMSM can be
configured to have curved magnets, which are more expensive than flat magnets, using
which the present invention is being disclosed. However, it is to be understood that any
other type of magnet can be used to get a desired property or outcome from the working
ofthe motor.
[00037) Fig. 4 illustrates stator assembly 400 and stator core 401 (shown in detail in
403). In a preferred embodiment, there are 27 stator cores 401 and 27 copper coils 402
used in the stator assembly. In another embodiment, the number of stator cores in a given
stator can range from 6 to 54. Each stator core 403 can be made up of laminations of
silicon steel or ferrite core joined together and can be placed radially an insulator plate. It
should be appreciated any number of desired stator cores 401 can be positioned within
the stator assembly 400. Copper wire can be wound around each stator core 401 to form
a copper coil 402, which requires fewer amounts of turns and simplifies mass production
process. Stator assembly 400 mounted on insulator plate can be fastened to the ceiling
shaft. In another embodiment, instead of copper wire, aluminum wire can also be used
for wounding around each stator core 401.
[00038) Fig. 5 illustrates an exploded cut view of the motor 500 with increased gaps
between different parts for better visibility. According to one embodiment, top annular
body 501 (top body rotor) and bottom annular body 518 (bottom body rotor) are made of
aluminum alloy consisting of 24 magnets 503 to 509 and 520 to 526 distributed radially
on lateral surfaces and are fastened with steel yokes 502 and 519. Stator is assembled on
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the insulator plate 510 with 27 stator cores 511-517. With this arrangement of stator and
rotor, axial magnetic flux path is completed between the top body rotor magnets 503-509
and the bottom body rotor magnets 520-526 through the stator cores 511-517, thereby
creating double magnetic flux in upper and lower sides ofthe stator.
[00039] When controlled alternating current flows in the stator coils (that are wound
around stator cores 511-517), torque is generated on both top rotor 501 assembly and
bottom rotor 518 assemblies, which improves the performance of axial magnetic circuit
based PMSM motor 500 when compared with that of the conventional radial magnetic
circuit based PMSM motor 500. This arrangement allows significant space for winding in
the stator with axial magnetic flux being created on both sides of the stator.
[00040] It would be appreciated that even though the present disclosure illustrates a
motor design based on 24 Pole 27 Slots rotor-stator assembly, all other possible
combinations such from 2 pole to 48 pole rotor with different stator slots can also be used
and configured in such a design.
[00041] According to certain embodiments, PMSM motor may include a variable
speed drive (VSD) that allows the speed of the fan motor to be continuously varied. A
VSD will vary the frequency and· voltage ofthe electricity supplied to the motor such that
the motor may be operated at different speeds. In an implementation, the motor receives
input signals from a VSD controller that is electrically coupled to the motor, wherein
based on the desired or actual speed, the VSD controller motor is operated at different
speeds.
[00042] In an embodiment, variable speed drive (VSD) can be required to run a
PMSM motor, which improves the speed, torque, and energy performance of a PMSM
motor. A VSD is typically based on Digital Signal Controller/Microcontroller, which has
more flexibility in speed control such as speed control from potentiometer, external
frequency input, serial interface with infrared ofRF remote etc.
[00043] Fig. 6 illustrates an exemplary block diagram 600 and inter-connections of
ceiling fan with VSD connected in parallel. In an exemplary working embodiment, the
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control power from 220V 50 HZ AC mains is applied to the Variable Speed Drive
(VSD), which runs the PMSM ceiling fan at different speeds.
[00044] The foregoing illustrated and described embodiments of the invention are
susceptible to various modifications and alternative forms, and it should be understood
that the invention generally, as well as the specific embodiments described herein, are not
limited to the particular forms or embodiments disclosed, but cover all modifications,
equivalents and alternatives falling within the scope of the appended claims. By way of
non- limiting example, it will be appreciated by those skilled in the art that particular
features or characteristics in one embodiment may be combined as suitable with features
or characteristics described in another embodiment.
AOVANTAGES OF THE INVENTION
[00045] The present invention designs a PMSM motor that provides high torque and
high efficiency.
[00046] The present invention designs a PMSM motor that provides high operational
rotational speeds and high efficiency (above 80%) at rated speed.
[00047] The present invention designs a PMSM motor that provides significantly
higher efficiency than comparative induction motors.
[00048] The present invention designs a PMSM motor that provides a PMSM motor
design for a fan that delivers much better efficiency at lower speeds.

We Claim:
1. A permanent magnet synchronous motor comprising a top body rotor having a
fIrst set of permanent magnets, a bottom body rotor having a second set of
permanent magnets, and a stator positioned between said top rotor body and said
bottom rotor body, wherein said stator comprises a plurality of stator cores,
wherein an axial magnetic flux path is created between said top body rotor and
said bottom body rotor through said stator.
2. The motor of claim 1, wherein said motor comprises an annular space, wherein
said stator is placed in said annular space.
3. The motor of claim 1, wherein said fIrst set ofpermanent magnets are distributed
radially along lateral surface of said top body rotor, and wherein said second set of
permanent magnets are distributed along lateral surface of said bottom body rotor
to create said axial magnetic flux path.
4. The motor of claim 1, wherein said plirality of stator cores are distributed radially
on an insulator plate.
5. The motor of claim 1, wherein said axial magnetic flux is created at both sides of
the stator.
6. The motor of claim I, wherein said motor is confIgured for a fan.
7. The motor of claim 6, wherein said fan comprises a variable speed drive controller
operatively coupled with said motor to control speed ofsaid fan.
8. The motor of claim 6, wherein said fan further comprising a plurality of fan
blades.
9. The motor of claim 1, wherein said permanent magnets are flat permanent
magnets.
10. The motor of claim 1, wherein said stator is wound around by means of a stator
coil, wherein when controlled alternating current flows through said stator coil,
torque is generated on both top body rotor and bottom body rotor.
11. The motor of claim 1, wherein said stator coil is copper or aluminium coil.
12. The motor of claim 1, wherein number of stator cores in said stator range from 6
to 54.
13. The motor of claim 1, wherein number of permanent magnets in each of said ftrst
set of permanent magnets and said second set of permanent magnets range from 4
to 48.
14. A fan comprising a permanent magnet synchronous motor (PMSM), wherein said
motor further comprises a top body rotor having a ftrst set of permanent magnets,
a bottom body rotor having a second set of permanent magnets, and a stator
positioned between said top rotor body and said bottom rotor body, wherein said
stator comprises a plurality of stator cores, wherein an axial magnetic flux path is
created from said top body rotor to said bottom body rotor through said stator.