Speed control of 3-phase induction motor using volthertz control for automotive application

Speed control of 3-phase induction motor using volt/hertz control for automotive application Sachin Hegde, Sachin Angadi, A.B.Raju Electrical and Electronics Department B.V.B.. Modelling

Speed control of 3-phase induction motor using volt/hertz control for automotive application

Sachin Hegde, Sachin Angadi, A.B.Raju Electrical and Electronics Department B.V.B College of Engineering and Technology, Hubballi, India

Email:sachinparameshwar@gmail.com

Abstract—The induction machine is the work horse of the

industry It has rugged construction and is suitable for many

high power applications It has also been a key aspect in

revolutionizing the locomotive and the automotive industries For

such automotive applications speed control becomes the driving

factor Hence in this we discuss controlling the speed of 3-phase

induction motor using constant volt per hertz profile The motor

is controlled using 3-phase inverter SPWM technique is used to

control the inverter voltage Modelling of the induction motor is

done in stationary reference frame and the system in simulated

using MATLAB (simulink) and hardware implementation is done

for the same using TIs F28069M launch pad under varying speed

and load torque conditions

Index Terms—SPWM (sine pulsewidth modulation), 3-phase

induction motor (IM), 3-phase inverter, F28069M launch pad

I INTRODUCTION

Induction motors were used in the past mainly in

applica-tions requiring constant speed because conventional methods

of IM speed control has either been expensive or inefficient

Variable speed applications have been dominated by DC

drives Availability of thyristors, IGBT, GTO have allowed

the development of variable speed induction motor drives The

presence of commutator and brushes is the main disadvantage

of DC motor, which require frequent maintenance and make

them unsuitable for environments which involve explosive and

dirt On the other hand, induction motors, particularly

squirrel-cage are rugged, cheap, light, small, and more efficient, require

lower maintenance and can operate in dirty and explosive

environments Although speed control of induction motor

drives are generally expensive than DC drives, they are used

in number of applications such as pump, steel mills, cranes,

hoist drives, conveyors, traction etc because of the advantage

of induction motor Dominant of them is the traction system

which is used in auto mobiles and locomotives [1].Induction

motor drives have gained equal importance as BLDC motor

drives in automotive industries Both have their advantages

and disadvantages in this we try to see the better parts of

induction motor drives

In auto mobile applications speed control is the most

im-portant crucial part Hence in this we have discussed efficient

way of controlling induction motor which is discussed in later

sections Following methods are employed for speed control

of induction motors: i Pole changing ii Supply frequency

control iii Stator voltage control iv Rotor resistance control

In this we go for frequency controlled induction motor drive There are again two types of variable frequency drive: a) Scalar control b) Vector control

In this we discuss scalar control of induction motor due

to its simplicity compared to vector controlled methods We

go for Volt/hertz control which is a scalar control method for variable frequency drive

II VOLT/HERTZ CONTROL

Due to the advancement in solid state power devices and microprocessors, speed control of Induction motor controlled

by switched power converter are getting popular Switched power converters offer an easy way to regulate both the frequency and magnitude of the voltage applied to a motor

As a result higher efficiency and performance can be achieved

by these motor drives with less noise The most common principle of this is the constant V/Hz principle which requires that frequency and the magnitude of the voltage applied to the stator of a motor maintain a constant ratio So by this, the magnetic field in the stator is kept almost constant for all operating points Thus, constant torque is maintained Also allows the motor to achieve faster dynamic response

Fig 1: Block diagram of closed loop v/f control of induction motor

ns= 120fs

From eqn (1) we can see that synchronous speed is directly proportional to supply frequency So by changing frequency

of stator terminal voltage we can control the sped of induction motor.Apart from frequency, the applied voltage should also

be varied, to keep constant air gap flux and not let it saturate [2] The air gap induced rmf in ac machine is given by

where kw is the stator winding factor, ϕm is the peak air

gap flux, fs is the supply frequency, and T is the number of

turns per phase in stator Neglecting the stator impedance, the

induced emf is approximately equals the supply phase voltage

Hence,

The flux is written as

ϕm= Vph

where

since Kb is a constant, we get

ϕm∝ Vph

fs

(6) Fig.1 represents the closed loop control of 3-phase induction

motor using SPWM technique The actual speed is sensed and

is compared with reference speed This is given to PI controller

whose output is the slip speed this is given to slip limiter which

limits the slip value to rated slip This slip speed is added with

the actual speed to give the synchronous speed This is given

to V/f controller which gives the frequency and voltage as

output According to which SPWM pulses are generated which

is given to 3-phase inverter switches which gives voltage of

required frequency which is given to stator of induction motor

III MODELING ANDSIMULATION

To simulate the system in matlab (simulink), it is essential

to model the system in terms of their mathematical equations

A 3-phase inverter modeling

In applications such as uninterrupted AC power supplies and

AC motor drives, three-phase inverters are commonly used to

supply three-phase loads [3] Here we take 3-phase AC supply

and give it to 3-phase diode rectifier which gives average

output voltage as:

Vdc= 3Vm(L−L)

Now, the output voltages of three phase inverter are given

by

van=(2vao− vbo− vco)

vbn= (2vbo− vco− vao)

vcn= (2vco− vao− vbo)

Line to line rms voltage at fundamental frequency, due to

1200phase shift between the phase voltages is given by

VLL =

√ 3

√

2∗ ma∗Vdc

Fig 2: 3-phase Rectifier and Inverter combination

This voltage is fed to induction motor which controls the speed Fig.2 represents the circuit of 3-phase uncontrolled diode rectifier cascaded with 3-phase fully controller inverter which gives variable voltage variable frequency which is used

to control induction motor

B Induction motor modeling Considering the applied stator voltage and flux linkages the mathematical modeling of the squirrel cage induction motor

in the stationary reference frame using standard nomenclature

is given as Stator flux,

dψds

dψqs

Rotor flux,

dψdr

dt = vdr− Rridr− ωrψqr (14)

dψqr

dt = vqr− Rriqr− ωrψdr (15) Stator currents,

ψds= Lsids+ Lmidr (16)

ψqs = Lsiqs+ Lmiqr (17) Rotor currents,

ψdr= Lridr+ Lmids (18)

ψqr = Lriqr+ Lmiqs (19) Electrical torque developed by IM,

Te=3

2 ∗P

2 ∗ Lm(idriqs− iqrids) (20) Swing equation representing the speed and torque relation,

Jdωr

C Simulation results

The induction motor parameters specified in the appendix

are considered for the simulation and are carried out in

MATLAB (simulink) simulation tool

Fig 3: Simulation of the System

In Fig.3 the block representation of the induction motor

system controlled by 3-phase inverter is shown Fig.4

repre-sents the speed response for 1400 rpm at constant load torque

of 5 Nm Due to the closed loop control the motor speed

remains at constant speed even after the application of load

Fig.5 represents the electrical torque developed by induction

motor Load torque of 5 Nm is applied on the motor Due to

the closed loop control the motor torque developed will settle

at 5 Nm

Fig 4: Speed response for constant load torque

Fig 5: Motor torque characteristic

IV HARWARE IMPLEMENTATION

In this TI’s F28069M launch pad is used to generate

pulses to control the frequency and voltage magnitude of

the 3-phase inverter output Vissim is a special model based

design software which supports all TI launchpads The model developed in Vissim is directly dumped on the F28069M which is designed specially for power control application The hardware setup is as shown in Fig.6 which consists of

1 Induction motor 2 Rectifier and inverter stack 3 F28069M launch pad 4 Regulated power supply

Fig 6: Hardware system set-up

Fig.7 represents the line to line stator voltage applied to the induction motor at a frequency of 25 Hz constant DC voltage is applied to the inverter using rectifier the inverter gives variable frequency and variable voltage when ma is changed in SPWM

Fig 7: Stator applied voltage waveform

Now the results plotted are real time graphs taken by hardware in loop system with the help of F28069M launch pad In Fig.8, time versus speed is plotted The reference speed

is set to 1350rpm The motor starts picking up the speed and settles at the given command speed The circled area is zoomed and shown in Fig.9 which shows the response of the system for different loaded conditions The loads are applied and then removed to see the dynamic response of the system

Fig 8: Speed versus time actual and reference speed

Fig 9: Various loads applied at different time interval

In Fig.10, the speed command is given through step input

The step input varies from 830 rpm to 1380 rpm which is

shown in per unit form As the step changes the motor shows

dynamic change in the speed and settles at the commanded

speed In Fig.11, the proportional and integral values are

changed so as to get small oscillations between the reference

speeds The system shows very good dynamic response

Fig 10: Speed change from 1380rpm to 830rpm

Fig 11: Step change in speed with oscillations

TABLE I: Speed and voltages obtained at different frequencies

speed (rpm) v f vf

430 68 15 4.53

570 90.8 20 4.54

720 113 25 4.52

880 136 30 4.53

1030 158 35 4.51

1182 181 40 4.52

1330 203 45 4.51

1484 226 50 4.52

Table I represents the actual speed of the motor at vari-ous frequency Also corresponding voltages are shown V/f ratio almost remains constant This represents the dynamic behaviour of control strategy

V CONCLUSION

The speed of induction motor is being successfully con-trolled by a low cost development board from TIs F28069M launch pad This is a promising control theory which is low cost and can be implemented for auto mobiles Due to its low cost and high efficiency induction motor can be a great inclusion in the automotive drives Since in automotive drives varying speed and load conditions are very common and requires dynamic response this system provides the necessary requirement This is highly efficient compared to DC motor drives Also this can handle high load torque and provide good dynamic response Simulation and hardware implementation is carried out successfully

APPENDIX

Induction motor specification as used in simulation

Parameters Value

Voltage (V) 220 Frequency (Hz) 60 Current (A) 5.8 Connection delta Rated torque (N-m) 11.9 Rated speed (rpm) 1710

Induction motor parameters at rated frequency:

R1=0.435Ω; X1=X2=0.754Ω;

R2=0.816Ω; Xm=26.16Ω;

Induction motor specifications as used in hardware imple-mentation Here we have used it in delta connection

Voltage (V) 415/230 Frequency (Hz) 50 Current (A) 1.4/2.7 Connection Star/delta Efficiency (%) 70 Rated speed (rpm) 138

ACKNOWLEDGEMENT

I would like to thank Prof P.G Tewari, Principal, BVBCET, Hubballi I would also express my sincere gratitude to Prof.A.B.Raju, HOD, Mr Sachin Angadi, Asst Prof, Electrical and Electronics Dept for their generous guidance and encour-agement throughout the project

REFERENCES [1] Gopal.K.Dubey, Fundamentals of Electrical Drives, second edition, New Delhi, Narosa Publishers, 2001

[2] R Krishnan, Electric motor drives, modeling, analysis and control, first edition, Pearson education inc, 2001

[3] Ned mohan, Tore M Undland, William P Robbins, Power electronics converters, application and design, third edition, John willy,2003 [4] Vijay Babu Koreboina, Shankar J Magajikondi, A B Raju, Modeling, Simulation and PC Based Implementation of a Closed Loop Speed Control

of VSI Fed Induction Motor Drive, IEEE 2010 (2011.01.28-2) [5] Prof.S.P.Das, Advanced electric drives, video lectures 1-9, NPTEL, IIT Kanpur.

[6] Gopakumar, K., Power Electronics and Electrical Drives, Video Lectures 24-35, Centre for Electronics and Technology, Indian Institute of Science, Bangalore.

[7] Texas instruments, Scalar (V/f) Control of 3-Phase Induction Motors, application report, july 2013.