COMPARISON OF DIFFERENT CONTROL …...electric motors include air conditioners, refrigerators, vacuum cleaners, washers and dryers. However, consumers now demand better performance,

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International Journal of Electrical Engineering & Technology (IJEET)

Volume 9, Issue 2, March-April 2018, pp. 24–36, Article ID: IJEET_09_02_004

Available online at http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=9&IType=2

ISSN Print: 0976-6545 and ISSN Online: 0976-6553

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© IAEME Publication

COMPARISON OF DIFFERENT CONTROL

STRATEGIES FOR BLDC MOTOR DRIVE

SK.Sharmila, K.Esther Rani, A.Anil kumar and T.Naveen

Student, Department of Electrical & Electronics Engineering

Kallam Haranadhareddy Institute of Technology, Guntur, Andhra Pradesh, India

Prabhakara Sharma Pidatala

Associate Professor, Department of Electrical & Electronics Engineering

Kallam Haranadhareddy Institute of Technology, Guntur, Andhra Pradesh, India

ABSTRACT

Brushless DC (BLDC) motor drive is frequently gaining popularity due to their

high efficiency, good dynamic response and low maintenance. Therefore, it is

necessary to have a low cost, but effective BLDC motor speed/torque regulator. This

paper presents a comparison of different control strategies for Brushless DC (BLDC)

motor which the controllers has been designed by using two types of control strategies

first one addresses the PID (Proportional Integral Derivative) controller based on

pole placement technique and the second one addresses the IMC (Internal Model

Control) controller by closed loop control strategy. The simulation results are carried

out by using MATLAB/SIMULINK successfully for closed loop operation of the three

phases BLDC motor. The performance characteristics i.e. speed and load torque of a

BLDC Motor compared for both with and without PID and IMC controllers. The

results presented validate control strategies in improving the motor performance.

Keywords: Brushless DC motor (BLDCM), Hall sensors, PID controller, IMC

controller

Cite this Article: SK.Sharmila, K.Esther Rani, A.Anil kumar, T.Naveen and

Prabhakara Sharma Pidatala, Comparison of Different Control Strategies for BLDC

Motor Drive, International Journal of Electrical Engineering & Technology, 9(2),

2017, pp. 24–36.

http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=9&IType=2

1. INTRODUCTION

Since 1980’s new archetype concept of permanent magnet brushless dc motors has been built

to eliminate sparking, high maintenance, high cost. BLDC motor rapidly growing to satisfy

the demand of household appliances in the market. Common household appliances which use

electric motors include air conditioners, refrigerators, vacuum cleaners, washers and dryers.

However, consumers now demand better performance, reduced acoustic noise [1] and higher

efficient motor for their appliances. Hence, BLDC have been introduced in order to fulfil

Comparison of Different Control Strategies for BLDC Motor Drive


these requirements. In the event of replacing the function of alternators and brushes, the

BLDC motor requires a six pulse inverter and a hall sensor which detects rotor position for

appropriate alternation of current. BLDC motor generally adopts three hall sensors for

deciding the commutation sequence [2]. Some of the benefits are more desirable in speed

versus torque characteristics, high dynamic response, high efficiency, long operating life,

noiseless operation; higher speed ranges [2]. The BLDC are typically permanent synchronous

motor, they are well driven by dc voltage.

However, there are drawbacks in a BLDC motor because of variable speed, and therefore

various controllers are used to overcome these problems. In this paper, we propose to observe

and compare the performance of BLDC motor by Speed Torque characteristics of the BLDC

motor by using PID controller [5] and IMC controller [7]. PID controller basically used to

obtain stability of a system to reduce steady state error and to get better performance of a

system. IMC controller [7] which states that control can be achieved only if the control

system contain either implicitly or explicit then some representation of the process to be

controlled.

2. CONSTRUCTION AND OPERATING PRINCIPLE

It consists of a dc supply by a rectifier arrangement, a dc link capacitor for energy storage, a

Voltage Source Inverter (VSI) consisting of transistor switches, and finally, the three-phase

output of the inverter is supplied to the motor for position sensing purposes, (Hall position

sensor) which is used along with some sort of microcontroller/microprocessor. Although

snubbers are not shown, it is a practice to include snubbers to protect the transistor switches

from voltage spikes generated by switching (fluctuations). Basically, BLDC motor is built

with a permanent magnet rotor and wire wound stator poles.

Figure 1 Represents a BLDC motor along with rectifier and six pulse inverter.

The electromagnetic torque is given by

= phase to neutral back emf of phase A (in volts)

= phase to neutral back emf of phase B (in volts)

= phase to neutral back emf of phase C (in volts)

=current in phase A (in amps)

=current in phase B (in amps)

=current in phase C (in amps)

=angular velocity of the rotor shaft (in radians/sec)

SK.Sharmila, K.Esther Rani, A.Anil kumar, T.Naveen and Prabhakara Sharma Pidatala


( ) ( )

( )BLDC motors are a kind of permanent magnet synchronous

motor. This indicates the magnetic field produced by the stator and the magnetic field

produced by the rotor twirls or rotates at the same frequency. BLDC motor do not experience

the ―slip‖ which is normally observed in induction motors. The stator magnetic circuit is

usually made from magnetic steel sheets. Stator phase windings are inserted in the slots

(distributed winding). Magnetization of the permanent magnets and their displacement on the

rotor are chosen in such a way that the back-EMF (the voltage induced into the stator winding

due to rotor movement) shape is trapezoidal. This allows a rectangular-shaped 3-phase

voltage system to create a rotational field with low torque ripples.

3. EQUIVALENT CIRCUIT DIAGRAM FOR A BLDC MOTOR

A typical dc motor equivalent circuit is illustrated as shown in the circuit shown below. The

basic components of a dc motor represented as armature resistance R and the armature

inductance L in addition, there is the back emf, e. From the figure, the following equations are

used to describe the relationship of operation.

Using the Kirchhoff’s Voltage Law equation is obtained as:

Figure 2 Typical dc motor equivalent electrical Circuit.

( ) ( )

( ) ( )

Similarly, considering the mechanical properties of the dc motor, from the Newton’s

second law of motion, the mechanical properties relative to the torque of the system

arrangement is

4. POSITION SENSORS OF A BLDC MOTOR (HALL SENSORS)

BLDC motor has three hall sensors which is placed in stator by 120 degrees each and

performs the function of six step commutation. when the rotor passes a sensor, it produces

either a high or a low signal to indicate which rotor pole (N or S) has passed this switching of

the three hall effect sensors (from high to low or low to high) provides rotor position

information every 60 degrees .The purpose of commutation is to energize the stator windings

in a particular sequence, following one winding positive, one negative, and third winding as

powered off. Torque production is possible by having attraction and repulsion between the

stator field and the permanent magnets of a rotor. The maximum torque is possible only when

the two fields of stator and rotor gets oriented at 90 degrees to each other and torque gets

reduced other than 90 degrees. Therefore, in order to keep the motor turning the stator

magnetic field should change position as the rotor field.



5. DESIGN OF PID AND IMC CONTROLLERS

A. PID CONTROLLER

The Proportional-Integral-Derivative (PID) controller is about the most common and useful

tool in control systems engineering. In most of the cases, feedback loops are controlled using

the PID algorithm. The main reason why feedback is very important in systems is to be able

to attain a set-point irrespective of disturbances or any variation in characteristics of any form.

Transfer function of PID controller is represented as:

( ) [ ] ( )

( ) ( )

( )

(

)

( ) (

)

Figure 4 Block diagram representation for closed system of a PID controller:

( )

( )

( ) ( )

( ) ( )

Where ( ) ( ) represents number poles for a closed loop transfer function

Choose controller gain constants (for ex: Kp, KI, and KD) so that poles of the close-loop

system in such a way that which keeps the system to be in stable. If the system is canonical

(first order system or second order system) can employ algebra (precise relationships between

poles and the shape of the step response).



If the system is non-canonical (higher order system) the relationships is not exist. One

idea is to place one or two dominant poles to meet our requirements and place the rest of

poles to be significantly faster, so that we can able to sense and omit the effect of the

dynamics for the other transient response.

Proportional gain constant

Integral gain constant

If a system does not have desired response (peak time too large, time response large, much

oscillation, large overshoot) then it can be modified with control.

(Delay Time): It is the time needed for the response to reach half of its final value the

very first time.

tr (Rise Time): It is the time needed for the response to rise from 10% to 90%.

(Peak Time): It is the time needed for the response to reach the first peak of the

overshoot.

(Maximum percent Overshoot): It is the maximum peak value of the response curve.

ts (Settling Time): It is the time required for the response curve to reach and stay within

2% of the final value. Consider the characteristics parameters – proportional (P), integral (I),

and derivative (D) controls, the system, S is to be controlled using the controller, C; where

controller, C efficiency depends on the P, I and D parameters

A. INTERNAL MODEL CONTROLLER

Basically Internal Model Control (IMC) principle states that ―Control can be achieved if and

only if the control system contains either implicitly or explicitly, some representation of the

process to be controlled‖.

The Internal Model Control (IMC) based approach for PID controller design can be used to

control applications in industries. Hence, controller design that maintains disturbance

rejection rather than set point tracking. The parameters of IMC controller depend on the IMC

filter time constant. Increase in the filter time constant always reduces the overshoot to an

acceptable limit, but however reduces the disturbance rejection, desired noise suppression

capability. This study also proposes the procedure method for selection of filter time constant.

6. IMC STRATEGY

The Internal Model Control (IMC) based approach for PID controller design can be used to

meet the requirements in industries hence by using IMC-PID tuning method a clear trade-off

between closed loop performance and robustness to model inaccuracies is achieved with a

single tuning parameter. The actual usefulness of the IMC lies in the fact that much concern

can be put on controller design rather than control system. Stability provided that the process

model is a perfect representation of a stable process.

An open loop control system is controlled directly, and only by an input signal without the

benefit of feedback. Open loop control systems are not commonly used as closed loop control

systems because of the issue of accuracy and output doesn’t reach set point (input). So

controller ( ) set to put control on the plant ( ) then it is clear from basic linear system

theory that the output Y(s) can be modeled as the product of the linear blocks as follows:



Figure 5 Block diagram representation for open loop system of an IMC controller

( ) ( ) ( ) ( )

Then set point tracking can be achieved by designing a controller such that:

( ) ( )

This control performance characteristic is achieved without feedback results inaccuracy.

These features are:

Hence, set point tracking can be achieved by designing a feedback controller such that:

( ) [ ( ) ( )] ( ) ( )

⌈ ( ) ̃ ( )⌉ ( )Feedback control can be theoretically achieved if

complete characteristic features of the process are known feedback control is only necessary

when the process is inaccurate or incomplete. In real life applications, however, process

models have potential of contradiction with the parent process; hence feedback control

schemes are designed to resist or prevent the effects of this mismatching.

A control scheme that has gained popularity in process control has been formulated and

known as the Internal Model Control (IMC) scheme. This design is a simple build up from the

modification of the open loop model strategy and has general structure as represented by

figure below:

Figure 6 Block diagram representation for Closed loop system of an IMC controller:



Where it have parameters like:

Controller ( )

Process ( )

Internal model ̃( )

Disturbance ( )

For the nominal case ( ) ̃( )

Feedback is only affected by disturbance ( ) such that the system is effectively open

loop and hence no stability problems can arise. This control structure also depicts that if the

process ( ) is stable, which is true for most industrial processes, the closed loop will be

stable for any stable controller ( ) Thus, the controller ( ) can simply be designed as a

feed-forward controller in the IMC scheme.

IMC scheme is therefore given by

This brings about two important advantages of applying IMC control scheme. The closed

loop stability can obtain by choosing a stable IMC controller. The closed loop performances

are related directly to the controller parameter, which makes on-line tuning of the IMC

controller very convenient.

Some important properties of IMC scheme

It provides time delay compensation.

Reference signal tracking and disturbance rejection responses can be shaped by a single

filter.

The controller gives offset free responses at the steady state.

7. SIMULATION & ANALYSIS

The simulation model of Closed Loop Brushless DC motor (BLDCM) Drive based on PID

Controller and IMC Controller has been simulated in MATLAB/Simulink. The simulink

model of BLDCM drive without and with PID controller are shown in figures 7, 8. The figure

9 represents the drive with an IMC controller. The test parameters of the motor taken for

simulation are given below.

Rated Power = 1 kW

Rated Voltage = 500 Vdc

Resistance of the stator (Rs) = 21.2 Ω

Inductance of the stator (Ls) = 0.052 H

Viscous coefficient (D) = 1x 10-4 kg-m s/rad

Moment of Inertia (J) = 1x 10-5 kg-m s2/rad

Back emf constant (KE) = 0.1433 v s/rad

Load Torque (TL) = 20 Nm

Motor Torque constant (KT) = 0.1433 kg-m/A

No of Pole Pairs = 1

Speed of the rotor (N) = 3000 rpm

Rotor Magnetic Flux (φ) = 0.11 Weber



Figure 7 Simulink Model of the Closed Loop BLDCM Drive without Controller

Figure 8 Simulink Model of the Closed Loop BLDCM Drive with PID Controller

Figure 9 Simulink Model of the Closed Loop BLDCM Drive with IMC Controller



Fig.10 Speed Response of the BLDCM Drive without Controller

It is represents the speed response of the BLDCM Drive without controller under no-load

condition. During starting the motor is subjected to transient operation with max speed of

6169 rpm and finally settles at around 2850rpm within 0.026 seconds.

Figure 11 Speed Response of the BLDCM Drive without controller and with external load torque.

Figure.11 represents the speed response of the BLDCM Drive without controller and with

an external load torque of 20Nm applied at 0.5 seconds. The figure clearly indicates the need

of a controller to maintain the desired speed.

Figure 12 Speed Response of the BLDCM Drive with PID controller



The figure.12 represents the speed response with PID Controller. Pole placement method

is employed for PID parameters tuning and are obtained as Kp= 7.233, Ki=1666.774 and Kd

= 0.013.The motor runs at an initial speed of 3560 rpm which is greater than the set 3000 rpm

value and then settles at 3000 rpm within 0.035 seconds.

Figure 13 Speed Response of the BLDCM Drive with PID controller and external load torque.

The figure.13 represents the speed response with PID Controller and with an external load

torque applied at 0.5 seconds. Then the motor speed is reduced to about 2123 rpm and reaches

close to the set 3000 rpm within 0.02 seconds.

Figure 14 Electromagnetic Torque (Te)

The figure.14 shows the electromagnetic torque developed by the BLDCM when the

external load torque of 20 Nm is applied.

Figure 15 Stator Back-emfs and Current waveforms of the BLDCM

The figure.15 represents the stator’s back-emfs and currents of the three phase BLDCM

when the external load torque is applied.



Figure 16 Speed Response with IMC Controller

The figure 5.10 represents the speed response with IMC. The motor initially runs at 6292

rpm which is more than the set 3000 rpm and settles within 1.27msec approximately(2910

rpm) to the set value.

Figure 17 Speed Response with IMC and external load torque.

The figure.17 represents the speed response with IMC and an external load torque (20Nm)

at 0.5 seconds. At this instant the speed of the motor remains approximately (2910 rpm) to the

set value

Figure 18 External Load Torque.



8. CONCLUSION

Comparison of performance characteristics of a BLDC motor drive with two different control

strategies by using Matlab/Simulink software.

By the design of PID controller by the method of pole placement technique the gain

constant parameters are obtained as Kp=7.233, Ki=1666.774, Kd=0.013. The major advantage

obtained is maximum overshoot of the speed response of BLDC motor drive is approximately

equal to zero which results in system to be in stable and has observed stator back emf and

current waveforms of a BLDC motor drive. The stability of a system mainly depends upon

characteristic equation of a closed loop control system of a PID controller by pole placement

technique.

The IMC Controller which is designed based on a PID controller the parameters results as

rise time tr=o.oo127 sec, peak time tp=0.0035 sec, settling time ts=0.0197 sec. Even though

having maximum overshoot of a speed response to be high, the transient parameters gives fast

response as compared to PID controller. Elimination of inaccuracy of a system and time delay

compensation with very greater accuracy is done by an IMC based PID controller.

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AUTHOR’S DETAIL

Sk.Sharmila student of B.Tech Final year in Electrical and Electronics

Engineering department, She is one of the department topper and is

placed in academic outstanding excellence. She has interest areas are

Electrical Machines, Power Systems, Control Systems.

Esther Rani. Karri student of B.Tech Final year Electrical and

Electronics Engineering department, During his graduation program

she had involved various technical presentations on Electrical

Networks, Electrical Machines and Power Electronics.

Anil Kumar.A student of B.Tech Final year Electrical and Electronics

Engineering department. His area of interest includes Control

Systems, Electrical Machines and Power Electronics.

Naveen Tadigiri student of B.Tech Final year Electrical and

Electronics Engineering department, His area of interest includes

Power Electronics, Electrical Measurements and Control Systems.

Prabhakara Sharma.Pidatala obtained his B.Tech. in EEE from

Koneru Lakshmaiah College of Engineering, Green fields, AP, India.

He completed his Master of Technology in High Voltage Engineering

from University College of Engineering, JNTU-Kakinada, AP, India

and pursing Ph.D in Andhra University. He is currently working as

Associative Professor in department of Electrical & Electronics

Engineering in Kallam Haranadhareddy Institute of Technology,

Chowdavaram, Guntur, AP, India, since 2013. His area of interest

includes Electrical Machines, Power Systems, Control Systems, Renewable Energy Sources,

FACTS devices.

Documents

COMPARISON OF DIFFERENT CONTROL …...electric motors include air conditioners, refrigerators, vacuum cleaners, washers and dryers. However, consumers now demand better performance,