Content uploaded by Mahesh Rao
Author content
All content in this area was uploaded by Mahesh Rao on Jun 22, 2018
Content may be subject to copyright.
1
Energy efficient Ceiling fans using BLDC motors- A
practical implementation.
Dr. Mahesh Rao, Ph.D(USA)
Professor and Head, Dept of CSE
Vidyavardhaka College of Engineering,
Gokulam, Mysore:
Email: maheshrao.cs@vvce.ac.in
Abstract— A brushless DC (BLDC) motor is a synchronous
electric Motor powered by direct-current (DC) electricity and
having an electronic commutation system, rather than a
mechanical commutator and brushes. In BLDC motors,
current to torque and voltage to rpm are linear relationships.
This linearity provides an excellent opportunity to use the
BLDC motor in the conventional ceiling fans. This paper
presents practical implementation of such BLDC motor for
ceiling fan application along with the actual power
measurements in comparison with conventional ceiling fans.
Complete electronics and the associated advantages and
disadvantages of this BLDC ceiling fans are also presented.
Keywords— Brushless DC Motor, Ceiling fans, energy
conservation.
1. Introduction
In the past decade, India has been recording a phenomenal
GDP growth of more than 8% per annum and this growth is
fueling the demand for energy requirements tremendously.
Even though the energy demand is not linearly related to the
GDP growth in India, it does have a bearing on the growth.
The below graph indicates the typical demand of power in
India and its expected demand by 2020 [1].
As the ways to generate energy is limited in India due to
various factors such as the environment and availability of
raw materials (fossil fuels etc), which lend to only
conservation as the best option to curtail the energy needs as
much as possible. In order to understand the various segments
and their energy consumptions etc, we can look at the below
graph and the accompanying table. It is clear that residential
sector is the one where a maximum conservation is possible
while the other sectors are so commercialized that it is not
neither possible nor is there enough incentive to propose and
sustain any major conservation of energy through other
alternate energy efficient appliances in these sectors. So the
focus in this paper has been on the residential sector and more
specifically on the ceiling fans which sells more than 30
million units per year with an installed base of more than 250
million units in India.
Fig 1. India Primary Energy Demand
From the above graph it is clear that the energy consumption
by various segments are as in the table 1.
Sl#
Segments
% of total
1 Heavy Industries 23
2 Transportaion 21
3 Agriculture 18
4 Residential 18
Table 1: Energy Consumption by various segments
Further when the residential consumption was analyzed, it is
found that the total consumption of power by Ceiling fans
amounts to 6% which is more than that of the TV + Fridge
combined.
This paper describes a method of using Brushless DC Motor to
reduce the power consumption of the ceiling fans by more
than 50% with out sacrificing on the performance or any other
features.
2. Historical Background:
This section describes the basics of the various kinds of
motors and their typical advantages and disadvantages along
with the potential market opportunity for the proposed solution
in the ceiling fan power consumption problem
DC Motors (brushed) are there in the market for commercial
use from as early as 1886 and the concept of the BLDC motors
2
and its commercial use was from 1962, however, due to
various limitations, one of them being mainly the electronics,
BLDC motors were confined to few applications only.
Typically we see three kinds of motors in the market place.
While there are various other specific types used in specialized
applications, it is enough for the purpose here to consider
these three and their applications and differences in general.
They are:
Direct current (DC) motor: DC applied to both the
stator and the rotor (via brushes and commutator), or else
a permanent magnet stator.
Synchronous (or stepping) motor (AC): AC in one, DC
in the other (i.e., rotor or stator). If it has a permanent-
magnet rotor, it is much like a BLDC motor.
Induction motor (AC): AC in both stator and rotor
(mentioned for completeness).
A BLDC motor has an external armature called the stator, and
an internal armature (permanent magnet) called the rotor
which is more like an AC motor (permanent magnet type).
The main difference is the controller implementation and the
way in which the AC (switched DC) is fed into them. The AC
supplied is not a pure sinusoidal AC but controlled pulse width
modulated waveform through an electronic control into two of
the legs at a time with full positive and negative waveforms,
leaving the third leg not driven at all times.
Typical BLDC motors are high rpm, low torque motors which
are used in computer applications or DVD/CD drives. They
are quiet and have long life with no serviceability related
issues unlike the typical AC or DC motors along with the
other advantage of high efficiency.
Typical conventional motors (brush DC motors) are limited by
their efficiency and the susceptibility of the commutator
assembly to mechanical wear and consequent need for
servicing, at the cost of potentially less rugged and more
complex and expensive control electronics.
BLDC motors offer several advantages over brushed DC
motors, including higher efficiency and reliability, reduced
noise, longer lifetime (no brush and commutator erosion),
elimination of ionizing sparks from the commutator, more
power, and overall reduction of electromagnetic interference
(EMI). In general, BLDC motors are more efficient at
converting electricity into mechanical power than brushed DC
motors. This improvement is largely due to the absence of
electrical and friction losses due to brushes.
A BLDC motor's main disadvantage is higher cost, which
arises from two issues. First, BLDC motors require complex
electronic speed controllers to run. Second, there are not too
many practical uses which are using the BLDC motors in the
commercial sector, that is the volume based cost reductions.
However, due to the advantages which are listed above, and
with the smart low cost electronics, now a days there are
various applications (electric vehicles, hybrid vehicles, PC
cooling fans, exhaust fans, etc) where BLDC motors are being
used commercially, and a new application which is being
looked at for commercialization is the typical ceiling fan.
A typical BLDC fan motor is shown below:
Fig 2.Typical BLDC motor
3. Why BLDC for ceiling fan ?
Today the typical ceiling fan is based on AC motors which are
power hungry. Along with this the typical AC motor based
fans have the rpm control through the capacitor or resistor
based regulators and is not efficient as there is loss in the
regulator itself to some extent. In addition the RPM control is
by controlling the voltage and the voltage fluctuations of the
mains make it very challenging to have constant RPM based
on the AC mains supply. Further, existing AC motor solution,
results in power factor (PF) degradation with no improvement
for PF and there are other ill effects like harmonics injection to
the AC mains, etc.
The total amount of air flow or displacement is based on the
blade size & rpm and does not change due to any other factor.
The proposed solution is to keep the same air flow or
displacement with less of energy usage along with improving
the PF using the BLDC motor based ceiling fans.
Typical BLDC motor based ceiling fan has much better
efficiency and excellent constant RPM control as it operates
out of fixed DC voltage. The proposed BLDC motor and the
3
control electronics operates out of 24V DC through an SMPS
having input AC which can vary from 90V to 270V. A
comparison between BLDC and conventional ceiling fans is
shown below (42” ceiling fan is considered).
BLDc Vs Conventional fan Power consumption
0
10
20
30
40
50
60
70
80
90
90-100 160-170 210-220 280-290 365-375
1 2 3 4 F
RPM
Power in Watts
BLDC fan
Conventional fan
Fig 3. BLDC Vs Convention Ceiling fan (42”) -Power
consumption comparison.
The power consumption is less than half at full speed and is
about 20% at low speed for the BLDC motor compared to the
conventional motor based ceiling fan, as can be seen from the
graph above. The Power Supply (PS) used is at 85%
efficiency and the electronics consumes less than 0.5W. The
power curves for the BLDC ceiling fan considers the total
power consumed from the wall socket.
The mechanical energy required to rotate at full speed
(typically 360rpm) for a 42” conventional ceiling fan is about
0.65Newton Meter. The equivalent electrical energy, as per
the below equation, would be around 26Watts, considering
about 95% efficiency for mechanical to electrical energy
conversion. The total power consumption of 32 watts as seen
in the above design seems to be with in the design boundaries
for such a motor. Further what can be done to lower that
power consumption is discussed in the improvements section
of this paper.
---------1
4. Architecture discussions
BLDC motors come in single-phase, 2-phase and 3-phase
configurations. Corresponding to its type, the stator has the
same number of windings. Out of these, 3-phase motors are
the most popular and widely used. The focus here is on 3-
phase motors.
In a BLDC motor the windings are on the stator and the rotor
is a permanent magnet. To make the rotor turn, there must be a
rotating electric field. Typically a three-phase BLDC motor
has three stator phases that are excited two at a time to create a
rotating electric field [2]. This method is fairly easy to
implement, but to prevent the permanent magnet rotor from
getting locked with the stator, the excitation on the stator must
be sequenced in a specific manner while knowing the exact
position of the rotor magnets. Position information can be
obtained by either a shaft encoder or, more often, by Hall
effect sensors that detect the rotor magnet position. For a
typical three phase, sensor based BLDC motor there are six
distinct regions or sectors in which two specific windings are
excited at a time [3].
BLDC Motors use the DC voltage as input which is converted
using the Pulse Width Modulation Techniques to control the
excitation of the coils to generate the motion in prescribed
fashion. We have proposed an electronic control for the PWM
generation and the motion detection and control through the
“hall effect” sensors which are embedded inside the BLDC
Motor. There is also a way to use the “back emf” generated
by the excitation on the “third leg” of the motor for calculating
the relative position for the motion control [4]. This
sensorless or back emf method, while it reduces the cost of the
motor, has certain challenges and drawbacks and is not being
considered here for the particular application.
Each commutation sequence has one of the windings
energized to positive power (current enters into the winding),
the second winding is negative (current exits the winding) and
the third is in a non-energized condition. Torque is produced
because of the interaction between the magnetic field
generated by the stator coils and the permanent magnets.
Ideally, the peak torque occurs when these two fields are at
90° to each other and falls off as the fields move together. In
order to keep the motor running, the magnetic field produced
by the windings should shift position, as the rotor moves to
catch up with the stator field as shown in Fig 4 below.
Fig 4. Electrical Diagram of a BLDC Motor.
The three legs of the electrical coils as indicated are excited
through the PWM technique so at any point, two of them are
4
applied with the positive and the negative waveforms of the
PWM output while the third is non energized.
In essence we have two components required for the BLDC
motor control: One is the PWM generation and control
electronics for the BLDC motor and the other is the DC
voltage generation based on the AC mains. Both of these are
addressed here and details are provided. In the proposed
BLDC motor based ceiling fan solution, the DC power is
supplied through an SMPS which converts the AC mains
supply to DC voltage (24V or 48V). The electronics of the
BLDC Motor controller as such has the ability to either take
the 24V DC from battery or from AC Mains and the SMPS
design (AC DC converter module) allows varying AC voltage
to be used as input while keeping the constant DC output, as
desired. Speed control of the motor is achieved through the
remote. Fig 4. below indicates the complete BLDC motor
controller diagram.
Fig 5. BLDC Motor controller – block diagram.
5. Solution overview.
Various building blocks and our solution approach and
technology recommendations are discussed in this section.
There are two main components of the BLDC motor control as
implemented here and they are the SMPS power supply and
the electronic controller card.
a. SMPS power supply
The following are the salient features of the Power supply
specifications to which the solution has been delivered with
the help of Power Integrators .
As can be seen, there is wide range of input voltage
variations which the power supply can handle and the
efficiency is at 85%. Typically input voltage variations of
150V AC to 265V AC are common, but in this design it has
been guaranteed for 100V to 265V AC which makes it truly
Universal in nature. Power factor improvement can be
incorporated into such design so that the overall efficiency and
the losses can be minimized, with the increased cost due to PF
improvement components.
The input voltage requirements from 100 to 265V can be
further reduced to 190 to 265V to reduce the cost along with
some of the other safety features such as the Inrush current
protection for high value, stall protection, etc., can be relaxed
to decrease the overall cost of this solution.
Table 2. SMPS specifications
Sl#
Description Min
Typical Max
Units
1
Input voltage 100
230
265
Volts
2
Frequency 47
50/60 63
Hz
3
No load power 500
mW
4
Inrush Current 50
A
5
Output Voltage 24
Volts
6
Output ripple
-
200
200
mVolts
7
Output power 70
Watts
8
output current 9.5
A
9
Efficiency 75
%
Above specs were implemented as shown in the SMPS below
(fig. 6). This power supply is based on the offline fly back
converter using the TOP261EN (Power Integrators IC). The
circuit is designed to operate from 100 VAC to 265 VAC
input and provides one isolated output of 24V, 3A continuous
and 9.5A peak as per the above requirements.
Fig 6. SMPS Power supply PCBA
Input AC is rectified by a Full wave Bridge Rectifier
through the TOP switch and the transformer along proper
filtering circuit for both AC and EMI filtering. Thus
generated 24V DC with further LC filtering for ripple
reduction is being used for the electronics and motor control.
The SMPS met all the required parameters as indicated in the
table and Power Integrators solution using “top switch” did
provide better than expected results [5]
b. Electronics Controller card:
Motor controller is based on Renesas 16 bit R8C25
microcontroller as shown in the below block diagram Fig 7.
The electronics uses 5VDC derived from the SMPS output.
ADC channels of the R8C25 are used for sensing the signals
out of the Hall effect sensors from the BLDC Motor and the
100
-
260V
AC Line In
BLDC Motor Controller
Remote
Control
For Speed
AC DC
Converter
Module
3 Phase
BLDC
Motor
24V from
Battery
IR Wireless
24V DC 24V DC
Or
5
PWM generator drives the 2 stage MOSFET drives as shown
in Fig 7.
Fig 7. Block Diagram of controller card
Based on the hall effect sensor values, we will know the rotor
position with respect to the magnetic poles. The MOSEFT
bridge is switched based on that position information and this
will start the rotation of the rotor and the switching operation
so as to ensure the smooth rotation. Using the PWM
technique, at zero crossing, a dead band is provided so as to
avoid electrical short.
Firmware for the controller was developed using programming
language C with the Renesas provided proprietary tools and
the overall design was validated with that[6,7]. Following
features were implemented in the firmware such as handling
of the PWM generation and maintaining of the proper dead
band, ensuring that with the proper hall effect sensors
feedback, the current drive to the MOSFETs are maximized to
generate highest torque for the given PWM cycle while
controlling the motor speed through the PWM duty cycle.
Further, the speed control is achieved through the IR or
temperature control sensors along with providing the safety
features such as the over current protection, short circuit
protection, inrush current protection, etc.
Fig 8. BLDC controller PCBA
6. Future enhancements:
Following future enhancements can be envisaged based on
either the cost reductions or the performance improvements
1. Decreasing the cost of the electronics by carefully
reviewing some of the specifications such as the
power supply input and output requirements.
2. Redesigning the BLDC motor construction so as to
improve the overall torque generated by the motor
through the number of poles and permanent magnet
positioning, etc. Present motor is a 12 pole motor,
by increasing to 18 poles the RPM and torque can
be further improved, of course, the cost does
increase.
3. Reduction in the air gap between the stator and the
rotor: Present motor was done as the first proto
type and it would require further few variations to
achieve the most optimal design parameters to meet
the power requirements.
4. Thickness of the copper coil used: This can be
experimented to decrease the resistance and the
losses, and to improve efficiency. This may result in
small additions to the power consumption
improvements.
Acknowledgment
Author wishes to thank Bhaskar Thyagarajan, Country
Manager, of Power Integratos, Suresh D, IDH Manager of
Renesas and colleagues, Ramki, Gurudeva, Vinayraj,
Parameshwar, etc., at his former company Aspire
Communications (subsidiary of calsoft) with out whose help
and support the work would not have been possible. Author
also wishes to thank Mr. Jayant Arora of Alfin Motors for
helping with the BLDC motor performance improvements.
References
[1] Stephane de la Rue du can, Michael Mcneil and Jayan
Sathye, “India energy Outlook: End Use Demand in India
to 2020”., Environmental Energy Technolgies Division,
Ernet Orlando Lawrence Berkely National Laboratory,
Jan 2009.
[2] Advances in sensorless control of brushless DC motors,
Agile systems, Edrive Magzine, April 2005.
[3] Brushless DC Motor fundamentals, AN885, Padmaraja
Yedamale, Microchip, 2003.
[4] Jianwen Shao, “Direct Back EMF detection method for
sensorless BLDC Motor drives”, MSCEE Thesis
submitted to VPI, Blacksburg, Virginia, USA, 2003.
[5] Engineering report, EPR 24V, 3A BLDC Motor PSU
using TOP261EN, Power Integrators, July 2009.
[6] 3-phase BLDC Motor Reference Platform MCRP03,
Renesas Technology, USA.
[7] R8C Hardware User’s manual, Renesas Technology,
USA, April 2011
