design of coreless motor by electronic commutation(ec)

Design of Coreless Motor by

Electronic Commutation(EC) P.Anil Kumar

*1 K.Kartheek

2

Assistant Professor*1,2

Electrical and Electronics Engineering Department*1,2

Matrusri Engineering College*1,2

Saidabad, Hyderabad, Telangana-500059

Abstract— Any electrical machine, design of core plays an important role because it has number of advantages. First of all, the iron core

provides high permeability and low reluctance path for magnetic flux and also a strong, rigid support for the windings which is particularly

important consideration for high torque motors. The core also conducts heat away from the rotor winding. But iron core construction also has

several disadvantages. Core type motors has iron losses but in this type of motors there is no iron losses because of the absence of iron core. The

iron armature has a relatively high inertia which limits motor acceleration. This construction also results in high winding inductance which

limits brush and Commutator action of core and brush contact drop efficiency of motor increases.

In this design hallow shape PVC frame is used to support stator winding and rotor is made up with permanent magnets. A hall sensor detects

the position of pole of the rotor and generates a signal to energize stator winding, torque produced between the stator magnetic flux and

permanent magnet rotor. This motor is used where load require high acceleration, retardation and wide variation of speeds.

Keywords—Electronic Commutation (E.C)

I. INTRODUCTION

The development of moving coil or coreless motors dates back to the middle 1930s. But it wasn't until the early 1960s that they were

produced economically enough to gain wide acceptance.

Major advantages of coreless motors include very low inertia, low mechanical time constant, and high efficiency. Because the core is

ironless, its low mass allows more rapid acceleration and deceleration than any other class of dc motor. Other benefits gained by eliminating the

iron core include the absence of magnetic fields acting on the laminations. This interaction in conventional motors appears as torque ripple or

cogging plus a resisting torque that decreases motor efficiency. The absence of iron eliminates cogging and the coreless motor operates

smoothly, even at low speeds.

Elimination of the iron core dramatically diminishes rotor inductance and resultant arcing. Commutator arcing in conventional motors

is caused primarily by the release of stored energy in the armature inductance upon commutation. Excessive arcing produces electrical noise and

reduces the life of brushes. Coreless motors are classified by rotor shapes as cylindrical or disc. Cylindrical rotors are further divided into those

containing inside fields or outside fields. The disc types have pancake, printed, or three-coil rotors.

The cylindrical outside-field motor has the smallest mechanical time constant. The stator is a cylindrical permanent magnet

surrounded by a mild steel housing. The rotor is a hollow cylindrical coil wound of copper wire and located in the center of the stator. A

mechanical time constant of 1 m/sec is not unusual for this type of motor.

The cylindrical inside-field motor is a similar design, but the permanent-magnet stator is located inside the hollow rotor. The motor

also features a low moment of inertia, but the mechanical time constant is typically higher than the outside-field motor because of smaller stator

magnets. Coreless motor Commutator and brushes are typically small, primarily because they are made of precious metals -- gold, silver,

platinum, or palladium. In addition, a smaller commutator has lower peripheral speed, less wear, and accounts for a smaller motor. Outside-field

motors are usually selected for high acceleration. Because of this, the rotor coils must handle a large load torque and dissipate high heat

produced by peak currents. To handle the torque, manufacturers strengthen the rotor with glass epoxy. Since the rotor does not have an iron core

to act as a heat sink, the housing has ports for forced air cooling.

Recent advances in coreless motor design include the replacement of Alnico with samarium-cobalt stator magnets. Also, the

mechanical time constant is reduced by as much as two times with aluminum rotor wire instead of copper.

A Coreless DC motor differs from conventional, iron rotor DC motors in that they are equipped with an ironless, self-supporting,

skew-wound copper coil. Because of this construction, the rotor is very light yielding a low moment of inertia. The rotor also rotates smoothly

without cogging.

High Technology Letters

Volume 27, Issue 8, 2021

ISSN NO : 1006-6748

http://www.gjstx-e.cn/346

II. DESIGN AND ANALYSIS

Until recently, the stator and rotor assemblies of PM brushless motors have included laminated steel cores. Progress in the technology

of disk rotor machines with axial magnetic flux allows for obtaining better steady state and transient performance. With the availability of high

energy PMs that kind of PMBM topology has revealed a new significant feature the disk type stator and rotor can be designed without

ferromagnetic cores. It leads to the reduction of mass and increase in the efficiency of the machine at the same output power or shaft torque.

The electromagnetic torque developed by that machine is dominated by the current -magnet interaction instead of the current-iron

interaction. Besides this, a coreless does not produce any normal force between the stator and rotor at zero current state and torque pulsations are

practically nonexistent.

There is a limit on the increase of the motor torque that can be achieved by enlarging the motor diameter.

Factors limiting the single disk design are:

1. Axial force taken by bearings,

2. Integrity of mechanical joint between the disk and shaft, and

3.Diskstiffness.

The main features of coreless topology, magnetic field distribution in the air gap, approach to calculations of the performance, cost

analysis and evaluation of this new emerging technology.

i. STATOR: The stator is the stationary part of a rotary system, found in electric generators, electric motors. The main use of a stator is to keep

the field aligned

Fig 1.1 Stator Frame

In the regular DC motor the winding is placed inside the armature, this armature is made up of iron with high permeability and low reluctance.

The main aim is to place the conductor without using iron core. So here we are using the wooden and PVC frame rather than ironcore.

The above Fig 1.1shows the placing of copper winds on the frame and the wooden frame is used to support the PVC frame. This copper coil is

energized by pulsating DC which is supplied through electronic commutation circuit. These acts as electro magnets while running.

To energize the stator, a signal from the Hall sensor which sense the position of the rotor permanent magnets.

ii. ROTOR

The rotor is a moving part. Its rotation is due to interaction between the windings and magnetic fields which produces a torque around the rotor

axis. In this motor rotor is made up of permanent magnets

Fig 1.2 Rotor

The permanent magnets are Nd2Fe14B (Neodymium Iron Boron) normally the range of neodymium permanent magnets is N32-N55. According

to the maximum energy product, which relates to magnetic flux output per unit volume. The Grade which we are using is N52 grade because it

has more flux density and easily available in the market.

Neodymium magnets are very brittle and very strong magnetically. Therefore, it is crucial to handle these magnets



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A. Electronic Commutation Circuit

Fig: 2.1 a. Electronic Commutation Circuit

b. Implementation on PCB

In a normal DC motor, a commutator is a moving part of a rotatory electrical switch that periodically reverses the current direction between

the rotor and external circuit. And it converts unidirectional EMF to alternating EMF. But in this coreless motor a electronic commutation

circuit is used to convert the DC voltage into pulsating DC voltage.

The Electronic commutation is much differs from mechanical commutation. Mechanical commutator is made up of commutator segments

and mica insullation but in electronic commutator power electronic switching devices are used. In mechanical commutator arrangement is

located in the rotor but in electronic commutator arramgement is located in the stator. In mechanical commutator shaft position sensing is

inherant in the arrangement but in electronic commutation requies a saperate rotor position sensor ( Hall Sensor ). In mechanical commutator

sliding contacts are placed between commutator and brushes but in electronic commutator there is no sliding contacts so the wont be any

friction. In mechanical commutation sparking takes place at brush contacts but in electronic commutation there is no sparking problem. In

mechanical commutation requires a regular maintenance but in electronic commutation requires less maintenance. In mechanical commutation

control of the voltage is difficult across the tappings but in electronic commutation controlled by PWM techniques. In electronic commutation,

the reliability can be improved by specially designed devices and protecting circuits.

iii. Working of Electronic Commutation Circuit

A DC supply of 6-12 volts is taken from regulated power supply (RPS) is given to the circuit. Circuit is made of MOSFET, transistor and hall sensor arrangement as shown in the figure above. A square wave output of pulsating dc from circuit with the help of hall sensor is given to the stator winding. Due to the current flowing in the stator winding, a magnetic field is created around the winding. The flux linkage between the stator winding and the permanent magnets (neodymium) makes the magnets to rotate.

Hall sensor plays key role in the rotation of permanent magnet rotor it detects magnetic poles (N and S) and according to position of poles it creates magnetic flux in coil by means of primary and secondary switching devices BJT and MOSFET respectively.

The output signal of Hall Sensor is moved to Q1 and Q2. The Q1 and Q2 activate alternatively and the signal is moved to further MOSFET section. The MOSFET1 is activated by one pulse and MOSFET2 is activated by another pulse. The process goes on alternatively.

These alternative signal moves to Coil1 and Coil2. The two coils are energized and creates magnetic field. For testing purpose to check the output of the commutation circuit push buttons are used in the absence of Hall Sensor.

It is a primary object of this invention to provide an improved power supply. Because of using this electronic commutation losses are minimized and also cost reduces compare to mechanical commutation.

A device for implementing the invention includes a core less dc motor apparatus employing a single rotary element apparatus with permanent magnet apparatus attached, magnetic or other bearing apparatus to support the rotary element during operation, stator winding and linking the flux of the magnets.



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Fig. 2.2 Output Wave Form of Electronic Commutation Circuit

iv.Hall Sensor:

Fig. 2.3 Hall Sensor Circuit on PCB

Hall Effect sensors are solid state magnetic sensor devices used as either magnetic switches or to measure magnetic fields. There are three

basic types I'm concerned with here: The Hall effect switch, the Hall Effect latch, and the ratio metric or analog output sensor.

A Hall Effect switch will turn on in the presence of south magnetic field on its face or north magnetic field on the opposite side. It will turn

off when the magnet is removed.

A Hall Effect latch works like a switch, but will stay on when the magnet is removed. It will turn off if the North Pole is applied to the face

or the power is turned off. Below I have the schematic on how to use a Hall switch to make a single pole on/off switch.

A ratio metric Hall Effect sensor outputs an analog voltage proportional to the magnetic field intensity. The devices I will use on a separate

page are uni-polar and in general with no magnetic field applied the output is one-half the supply voltage. The voltage will increase with the

south magnetic pole on the face or decrease with the north magnetic pole on the face.

III. OPERATION

The core less motor works on the principle of Faradays law of electromagnetic induction. Stator contains two coils with number of

turns of N1 and N2 which are excited from the commutation circuit. Rotor having permanent magnets on the stator there is a Hall Sensor which

is used to sense the polarity of the rotor pole. Depending on the polarity of the polarity of pole the stator winding is excited which gives the

repulsion force there by rotor will rotate. There have been provided core less dc motor useful for a variety of purposes, for example as torque

motors. In general, any motor can be classed as a torque motor but the term is usually applied to a motor which is not continuously rotatable

and, in particular cases, is capable of movement through only a limited angle. Such motors are widely used in servomechanisms.

Such a core less dc motor also has application as an angular position-sensing device of high precision, also useful in servomechanism

systems, and the invention will be specifically described in such an environment.

Core-less dc motor heretofore available have been relatively complex and costly and have not met the sensitivity and accuracy requirements

of many applications.

It is an object of the invention to provide a new and improved core less dc motor which is relatively simple and inexpensive in construction

and has extreme sensitivity and accuracy.



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Fig. 3.1 Output Signal

In figure 3.1,shows the output voltage of commutation circuit. This output voltage is moved to stator coils. ‘B’ and ‘C’ shows the activation

positions of Coil1 and Coil2 respectively.

For a complete cycle, two coils are excited similtaniously which creates the alternating flux in the stator coil. When the Hall Sensor sense

the magnetic field of the rotor position gives the signal to MOSFET’s. the output of MOSFET signal moved to stator coils

Fig. 3.2 Basic model of coreless DC motor

IV. BLOCK DIAGRAM

4.1 Block Diagram



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i. Datasheet:

Parameters Value

Output Power 37 W

Speed 990 rpm

Voltage 24 V

Current 1.32A

No of Stator Coils 2

Commutator Electronic Commutation

Air gap 5mm (Edges)12mm (Phase)

Cooling System Natural

Copper Turns/Coil 128

Copper Gauge 22 mm

When the motor is voltage driven, the following equations contain detailed design parameters that are necessary to take

full advantage of the coreless technology.

An ironless rotor motor can be represented by the following simplified. The voltage induced in the rotor (back EMF) is

proportional to the angular velocity of the rotor:

Vi =keѠ ……(i)

Where:

Ke = Back EMF constant, V/rad/s

Ѡ= angular velocity, rad/s

Motor manufacturers normally specify three constants: back EMF constant, torque constant, and velocity constant. If these three

constants are expressed using the proper units their values are equal. So, substitute the torque constant for the back EMF constant

in the equation.

Vi =keѠ ………(ii)

Where:

k = Torque constant, Nm/A

Therefore, the resulting equation is:

Vo=IR+KѠ …….(iii)

Where R = resistance and I = armature current

As seen from the equation the unique characteristics of the coreless DC motor is that the speed and torque function are linear. The

speed is linearly proportional to the applied voltage and the torque is linearly proportional to the current.

T=k(I-Io)…………(Eq. iv)

Where T= Torque, Nm

Io= no-load current, A

Calculating Mechanical Power, Electrical Power and Efficiency:

The Electrical power applied to the motor equals the mechanical power produced by the motor plus the power dissipated

as heat. At a given input power, more mechanical power becomes available to drive the load as the losses diminish.

Pelect=P mech+Pj……………..(v)

Where

Pelect = VI = electrical power, W

Pmech = TѠ = mechanical power, W

PJ = RI2 = power loss, W

The motor efficiency is defined by the ratio of the mechanical power and the electrical power:

Efficiency(ἠ)=Output/Input (Eq. 5.6)

Where

ἠ= motor efficiency

The Torque-Speed Curves graph is a visual representation of the interdependency of various motor characteristics. It

shows motor efficiency, speed, mechanical power, and armature current as functions of torque. The three speed curves were

plotted at different supply voltages and show linear dependency between the supply voltage and the speed. The following

observations can be made:

• The current is proportional to the motor torque.

• The speed is proportional to the supply voltage.

• The maximum efficiency occurs at high speed.

• The mechanical power reaches its maximum when the load torque is equal to half the stall torque.



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V. RESULT AND CONCLUSION

Fig. 5.1Testing Methodology

The Coreless DC motor was tested for the following performance parameters:

(a) Variation of speed verses variation input voltage

(b) Variation of speed verses variation input current

(c) Variation of torque verses variation in rotor speed

(d) Variation of output power verses efficiency A regulated DC power supply unit with a volt range of 0-30V and current range of 0-10A was used to test with different

ranges of voltage, current and torque.

The rotor speed (rpm) was tested by using a laser speed detector. Torque was calculated mathematically. To compare the performance of coreless DC motor with core type DC motor with the same power rating

i. Results Characteristics of motor on No Load

Voltage Current Speed

24 V 0.73 A 1868 rpm

Table 5.1 Characteristics of motor on No Load

Fig 5.1 Readings of motor on No Load

Voltage Current Speed

24 V 2.01 A 990 rpm

Table 5.2 Characteristics of motor on Load (With FAN)

Fig. 5.2 Readings of motor on Load



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Fig. 5.3 Testing of Motor on Load S.

No

Voltage

(Volts)

Current

(Amps)

Speed

(rpm)

Weight

(Kg)

I/P Power

(Watts)

Torque

(Nm)

O/P Power

(Watts)

Efficiency

(%)

1 24 1.10 1540 0.4 26.4 0.098 15.79 59.8

2 24 1.36 1350 0.7 32.64 0.171 24 73.5

3 24 1.56 1260 1 37.44 0.24 31.65 84.5

Fig. 5.4 Characteristics of Efficiency Vs Output &Speed Vs Voltage

ii. Conclusion

In this Paper the Electronic Commutated coreless DC motor is designed and developed. Instead of iron core PVC frame is

used and Control circuit using Hall Sensor is designed. It has been tested at different loads. Because of this there is no iron losses.

Therefore, efficiency increases.

iii. Applications

1. These are used in computer applications

2. In the medical field like Dialysis peristaltic, X-ray shutter positioning drive etc…

3. Bank and office applications

4. Automatic operated entrance door and window.

iv. Future Scope

Now a day’s world is plagued with global issues like fuel shortage, global warming. No doubt Electric Vehicles are the

solution for fighting against these issues. As convectional vehicles has fuel as energy source and engine as prime mover, Electric

vehicles uses battery as energy source and electric motor as the prime mover to drive. The various options available for driving

electric vehicle are DC motor, induction motor, and Coreless DC motors.

In Electric Vehicle, there should a portable power supply. Hence we can use Battery to power the vehicles and DC is the

default power supply. Advantage of this motor is its constant torque characteristics at various rotor positions.

Hence, a DC motor needs a periodic maintenance to prevent it from permanent damage. There will not be any wear and tear while

operating and hence no maintenance required.

VI. REFERENCES

[1] http://www.koshindenki.com/img/file/CL_TechnologyOvr_R3a_Std.pdf

[2] http://solarbotics.net/starting/200111_dcmotor/200111_dcmotor2.html

[3] http://www.ni.com/white-paper/14925/en/

[4] Hakala, H.: Integration of motor and hoisting machine changes the elevator business. Int. Conf. on Electr. Machines ICEM’00, Vol. 3, 2000, Espoo, Finland, pp. 1242-1245

[5] Gieras, J.F., Wang, R.J., Kamper, M.J.: Axial Flux Permanent Magnet Brushless Machine. Springer-Kluwer, Dordrecht-Boston - London-, 2004.

[6] https://www.quora.com/What-is-a-Coreless-motor

[7] http://www.citizen-micro.com/tec/corelessmotor.html

[8] www.designworldonline.com/ironless-dc-motors-deserve-a-second-look

[9] https://en.wikipedia.org/wiki/DC_motor

[10] https://en.wikipedia.org/wiki/Electric_motor



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design of coreless motor by electronic commutation(ec)

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