2019 2nd International Conference on Intelligent Computing, Instrumentation and Control Technologies (ICICICT)

Design and Performance Analysis of Brushless DC

Motor Using ANSYS Maxwell

Mithunraj M.K Gayathri S Warrier Prasanth Pathiyil

Dept. of Electrical Engineering Dept. of Electrical and Electronics Engineering Robert Bosch Engg and
NIT Calicut FISAT,Angamaly Business Solutions Pvt. Ltd
Kerala,India Kerala,India Coimbatore,India
mithun200696@gmail.com sgayathriwarrier@gmail.com Prasanth.Pathiyil@de.bosch.com

S Kanagalakshmi Archana R
Dept. of Electrical Engineering Dept. of Electrical and Electronics Engineering
NIT Calicut FISAT,Angamaly
Kerala,India Kerala,India
kanagalakshmi@nitc.ac.in archanasreenivasan28@gmail.com

Abstract—Brushless Direct Current (BLDC) motors having the and relieves the problem of retaining the magnets against
advantages of better speed versus torque characteristics, high centrifugal force. There is also possibility to use rectangular
dynamic response, high efficiency, long operating life, noiseless instead of arc shaped magnets. Axial flux motors with ap-
operation, higher speed ranges, are superior to brushed DC
motors and induction motors. This paper describes the method preciable reluctance torque leads to wide range of speed at
of designing BLDC motor with detailed design equations. Motor constant power [6].
geometry is built in RMxprt software tool of ANSYS Maxwell. The viable ways to modify rough design of the motor is
The analytical design is then implemented in Maxwell 2D for possible with the help of simulation tools like MagNet, JMAG,
further analysis. Simulation results accomplishing performance RMxprt etc [7]. Motor performance can be prognosticated
characteristics are included. The designed motor exhibits an
efficiency of 87% and is able to meet the designed value of torque. even before its manufacturing is indeed, a great deal. It is
because multiple design iterations can be done faster at low
Index Terms—BLDC,ANSYS Maxwell, RMxprt, FEA cost and new designs are created by optimizing the original
parameters. Performance analysis under faulty condition can
I. INTRODUCTION also be done. Accurate calculation of motor parameters and
In NEMA standard MG7-1987, a brushless DC motor is characteristics is predicted in terms of field computation and
defined as a type of program controlled self-synchronous result analysis [8].
motor with rotor being a permanent magnet [1]. These motors Various designs configurations are available in literature
have been in commercial use since 1886 but commercially having its own merits and demerits. Single-phase permanent
possible since 1962. Unlike the conventional DC, induction magnet brushless DC motor with higher speed is described in
and synchronous motors, brushless motors are motors without [12]. But it suffers Problems of starting, high torque ripple,
brushes [2]. These motor with simple structure has electronic and low torque/ampere are its drawbacks. A two phase motor
commutation which is either independent or integrated into is discussed in [11] with a copper utilization of 100% and
the motor produces high torque per ampere which does not magnet utilization of 67%. But it is given in [9] that the
vary with operation has attracted the motors to wide usage three phase BLDC motor is at least 15% more efficient than
areas including domestic and industrial applications [3]. The two phase BLDC motor of similar ratings. As the number of
increase in demand pushes the motor to come up with different phases increased, the complexity in the motor controller circuit
designs, in terms of geometry and configurations. One of the in terms of components, their design and cost will increase.
configuration is slotted and slot-less BLDC motor. A slot- A three phase BLDC motor with 61% efficiency with same
less BLDC is the motor that comes without stator core [4]. frame size has been discussed in [9]. This paper is targeted at
Depending upon the position of permanent magnets, motors the design and detailed analysis of an 87% efficient interior
having interior mounted rotor are called axial flux motors and brushless DC motor with a speed of 1504 rpm. Transient
radial flux motors are those with rotor mounted on the stator analysis is performed with ANSYS Maxwell 2D to evaluate
[5]. The motor assembly is simplified by interior construction transient state performance.

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 2019 2nd International Conference on Intelligent Computing, Instrumentation and Control Technologies (ICICICT)

II. DESIGN PROCEDURE D. Losses

In design process generally we have two set of vari- Copper losses for two phases,Pcu
ables,independent or input and dependent or output variables.
ρ LN 2 Nc
Independent variables are usually dimensions, winding turns Pcu = 2I 2 (6)
and material properties and dependent variables are perfor- Kwb Ag
mance figures such as torque, efficiency etc. The dependent Where ρ is density of copper, Nc is number of coil per phase,
variables are fixed, so based on certain assumptions design Kwb is the bare wire fill factor and Ag is the area of air gap.
engineer have to find the independent variables using the Windage and friction losses are given by,
analytic equations available. After designing the motor an-
alytically then designer can verify the performance using 3
Pf = Pout (7)
ANSOFT RMxprt. If the design requirements are meeting then 100
2D Transient analysis can be done in MAXWELL 13. Again Weight of stator tooth Wt ,
design engineer have to verify the performance, if it is not
meeting designer have to change the design accordingly and Wt = ρi At Ns L (8)
verify the performance.
Where ρi is density of iron, At is area of cross section of teeth
III. DESIGN EQUATIONS and Ns is number of slots. Weight of stator yoke Wsy ,

A. Torque equation Wsy = ρi Asy L (9)

Torque developed by the BLDC motor is, Where Asy is area of cross section of stator yoke. Weight of
rotor yoke Wr y
T = 2N Nm Bg LRr o I = kt I (1)
Wr y = ρi Ar y L (10)
Where N is the number of turns in the slot, Nm is the number
Where Ar y is area of cross section of rotor. Total weight of
of poles, Bg is the air gap flux density, L is the active length
iron is,
of motor, Rr o is the rotor outer diameter and I is the current
through the conductor. The factor 2N is because three phase Wtotal = Wr y + Wsy + Wt (11)
inverter is operated in 120 degree conduction mode i.e. 2
phases carry current at any given time. Total iron loss Pir on is give by,

Pir on = Lkg ∗ Wtotal (12)

B. Back EMF equation
Back EMF expression for BLDC motor is, Where Lkg is loss in watts per Kg of stator material. Power
input to the motor is given by,
Eb = 2N Nm Bg LRr o Wm = Ke I (2)
Pin = Pout + Pcu + Pir on + Pf (13)
Where Wm is the angular velocity of rotor. Comparing torque
Efficiency of motor η(%),
and back EMF equation it is clear that torque and back emf
constants are equal i.e, Pout
η(%) = (14)
Pin
ke = kt = 2N Nm Bg LRr o (3)
Using all these equation the motor can be designed analytically
C. Output equation and the design can be verified using ANSYS Maxwell.
Specifications of the BLDC motor is shown in TABLE I
Output of machine can be expressed in terms of main and the designed parameters are shown in TABLE II.
dimensions, specific electric and magnetic loadings and speed.
kVA rating of BLDC motor is given by,
TABLE I
2 S PECIFICATIONS OF MOTOR
Q = Co Rr o LWm (4)
Parameter Value
Where Co is the output co-efficient and it is taken as, Rated power 550W
Rated voltage 220V
Rated speed 1500rpm
Co = 11Bav ackw ∗ 10−3 (5) Rated torque 3.5Nm
Rotor type Inner rotor
Where Bav is the magnetic loading,ac is the electric loading Number of phases 3
and kw is the winding factor

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 2019 2nd International Conference on Intelligent Computing, Instrumentation and Control Technologies (ICICICT)

TABLE II instantaneous torque and current are given in fig 1 and 2. The
M OTOR PARAMETERS average current and torque are acceptable values.
Parameter Value
Stator outer diameter 130mm
Stator inner diameter 75mm
Rotor inner diameter 25mm
Length of rotor 60mm
Length of stator 60mm
Length of air gap .6mm
Type of steel M19-24G
Type of magnet XG196/96

IV. SIMULATION USING ANSYS

Analytically designed motor is simulated in RMxprt. It is a
commercial tool developed by ANSYS which is a template- Fig. 3. Winding currents under transient analysis
based electrical machine design tool that provides fast, ana-
lytical calculations of machine performance and 2D and 3D Winding currents in BLDC motor is not smooth. This is one
geometry creation for detailed finite element calculations in of the main reason behind the torque ripple.
ANSYS Maxwell. In addition to providing classical motor
performance calculations, RMxprt can automatically generate
3D or 2D geometry, including all properties for detailed finite
element analysis.
Fig 1 and 2 shows the efficiency-speed curve and speed-
torque curves of the motor. From the figure it is very clear
that motor efficiency is 87% at rated speed around 1504 rpm.

Fig. 4. Moving torque

Torque ripples can be minimized by selecting proper con-

troller for the BLDC motor. Fig 5 shows the cogging torque,
which is undesirable in a motor. It is due to the interaction
between permanent magnets and the slots. This is another
reason for torque ripple in BLDC motor, so its value should
Fig. 1. Efficiency-Speed curve be minimum as possible.

Fig. 2. Torque-Speed curve

Fig. 5. Cogging toque

A. Transient analysis
The aim of transient analysis is to know the motor per- B. Finite element analysis
formance under transient condition. Motion analysis in 2D Finite element analysis (FEA) is done to determine the
is done using Maxwell with a transient period of .04s. The state of saturation of the material and to check whether the

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 2019 2nd International Conference on Intelligent Computing, Instrumentation and Control Technologies (ICICICT)

permanent magnet is demagnetized by electric loading. Stator [9] R.K.Gupta and Ned Mohan, “A Three-Phase Permanent Magnet Brush-
material will have a magnetic flux density limit. So flux density less DC Motor for Low-Power Low-Speed Fan Applications Optimizing
Cost and Efficiency”, Proc. Industry Applications Conference,42nd IAS
in the stator should not exceed this limit. Fig 6 shows the flux Annual Meeting, New Orleans, LA, 2002,pp. 846- 852.
distribution in the motor. [10] Andre Lelkes and Michael Bufe, “BLDC motor for fan application with
automatically optimized commutation angle”, 35th Annual IEEE Power
Electronics Specialists Conference, 2004, Vol.3, pp. 2277- 2281.
[11] Y. Li , T.A. Walls, J.D. Loyd, and J.L. Skinner,“A novel two- phaseBPM
drive system with high power density and low cost”, IEEE Transaction
On Industry Applications, Vol. 34, No. 5, Sept/Oct 1998,pp.1072- 1080.
[12] Lee Ji Young, Geun Ho Lee, Jung Pyo Hong and Jin Hur,“comparative
study of line start permanent magnet, skeleton type brushless and Snail-
cam type switched reluctance motor for a fan”, Sixth International
Conference on Electrical Machines and Systems, 2003.ICEMS 2003,
Vol. 1, pp.183- 186.

Fig. 6. Flux distribution

Flux in the stator and rotor should be less than the maximum
flux density that material can withstand. Otherwise magnetic
saturation will happen. Limiting flux density of stator and rotor
iron material is 1.39. From the figure it is very clear that flux
density is less than 1.39.

CONCLUSION
BLDC motor designed analytically and verified the design
using ANSYS maxwell. Performed transient and finite element
analysis to analyse the performance of the designed motor.
Finite element analysis shows that flux density in the stator
material is within the limit. Transient analysis is to check the
behaviour of the motor under transient condition. It is also
giving acceptable results.

R EFERENCES
[1] Chang-liang Xia, “Permanent Magnet Brushless DC Motor Drives and
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