Speed Control of Asynchronous Motor Using Space Vector Pwm Technique

8/11/2019 Speed Control of Asynchronous Motor Using Space Vector Pwm Technique

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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 6545(Print), ISSN

0976 6553(Online) Volume 3, Issue 3, October December (2012), IAEME

222

SPEED CONTROL OF ASYNCHRONOUS MOTOR USING SPACE

VECTOR PWM TECHNIQUE

VISHAL RATHORE1, Dr. MANISHA DUBEY2

1(ELECTRAL& ELECTRONIC, TRUBA/ RGPV, BHOPAL, INDIA,

[email protected])2(ELECTRICAL, MANIT/ MANIT, T.T.NAGAR BHOPAL (M.P), INDIA,

[email protected])

ABSTRACT

This paper presents the Space Vector Pulse Width Modulation (SVPWM) approaches

to the problem of speed and torque control of induction motor and induction motor parameter

adaptation. Such problems are commonly encountered in electric drives and many

applications such as robotics, electric vehicles, and so on. The specific contributions of the

paper are new Space Vector Pulse Width Modulation technique flux/speed observer is

developed by delicately introducing some auxiliary variables ( as inverter output voltage,current, torque and speed of induction motor) and a design parameter. Combining the Space

Vector Pulse Width Modulation torque controller, it is thoroughly analyzed the convergence

of the flux/speed observer and the asymptotic stability of the close loop system. Then the

robustness of the proposed Space Vector Pulse Width Modulation observer/controller scheme

is effectively demonstrated by considering the effect of the variation of the rotor resistance,

the stator resistance and the load torque. The SVPWM approach for the speed and torque

control of induction motor is compared with PI and PID controller connected in the feed

forward path of the system .The results are compared on the basis of time response

specification like (Rise time (tr), Peak time (tp), Settling time (ts), Maximum overshoot

(%MP) ).

Keywords:Induction Motor,PI Controller, Park transformation, Space Vector Pulse Width

Modulation (SVPWM), Three-Phase Voltage Source Inverters.

1. INTRODUCTION

Induction motors are most popular machine in AC drives because of its rugged and

inexpensive construction. Therefore much attention is given to their control for various

applications as compare to other rotating machine. An induction machine, especially squirrel

NTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING

& TECHNOLOGY (IJEET)

ISSN 0976 6545(Print)

ISSN 0976 6553(Online)

Volume 3, Issue 3, October - December (2012), pp. 222-233

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cage, has many advantages when compared with DC machine in terms of cost, construction

and application. Also it is less sensitive to environment variation as compare to DC machine.

Furthermore, it does not require periodic maintenance like DC motors [1]. However, because

of its highly non-linear and coupled dynamic structure, an induction machine requires more

complex control schemes than DC motors. Traditional open-loop control of the induction

machine with variable frequency may provide a satisfactory solution under limitedconditions. However, when high performance dynamic operation is required, these methods

are unsatisfactory [2]. Therefore, more sophisticated control methods are needed to make the

performance of the induction motor comparable with DC motors. Recent developments in the

area of drive control techniques, fast semiconductor power switches, powerful and cheap

microcontrollers made induction motors alternatives of DC motors in industry. The most

popular induction motor drive control method has been the field oriented control (FOC). The

controllers required for induction motor drives can be divided into two major types:

conventional low cost volts per hertz v/f controller and torque controller [1]-[4].

2. MODELING AND DESIGN OF SPACE VECTOR CONTROLLED INDUCTION

MOTOR DRIVE

Induction motors are the most widely used motors in industrial motion control

systems, as well as in home appliances because of their reliability, robustness and simplicity

of control. Until a few years ago the AC motor could either be plugged directly into the mains

supply or controlled by means of the well-known scalar V/f method. When power is supplied

to an induction motor at the recommended specifications, it runs at its rated speed. In this

method, even simple speed variation is impossible and its system integration is highly

dependent on the motor design (starting torque vs. maximum torque, torque vs. inertia,

number of pole pairs). However many applications need variable speed operation. The scalar

V/f method is able to provide speed variation but does not handle transient condition control

and is valid only during a steady state. This method is most suitable for applications without

position control requirements or the need for high accuracy of speed control and leads toover-currents and over-heating, which necessitate a drive which is then oversized and no

longer cost effective. Examples of these applications include heating, air-conditioning, fans

and blowers [9].

2.1Field Orientated Control (FOC)

The Field Orientated Control (FOC) consists of controlling the stator currents

represented by a vector. This control is based on projections which transform a three phase

time and speed dependent system into a two co-ordinate (d and q co-ordinates) time invariant

system. These projections lead to a structure similar to that of a DC machine control. Field

orientated controlled machines need two constants as input references the torque component

(aligned with the q co-ordinate) and the flux component (aligned with d co-ordinate). As

Field Orientated Control is simply based on projections the control structure handlesinstantaneous electrical quantities. This makes the control accurate in every working

operation (steady state and transient) and independent of the limited bandwidth mathematical

model. The FOC thus solves the classic scheme problems, in the following ways [8]. The

ease of reaching constant reference (torque component and flux component of the stator

current).The ease of applying direct torque control because in the (d,q) reference frame the

expression of the torque is:


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1By maintaining the amplitude of the rotor flux ( ) at a fixed value we have a linearrelationship between torque and torque component isq. We can then control the torque by

controlling the torque component of stator current vector.

2.1.1 Space Vector Definition and ProjectionThe three-phase voltages, currents and fluxes of AC-motors can be analyzed in terms

of complex space vectors. With regard to the currents, the space vector can be defined as

follows. Assuming that ia, ib, icare the instantaneous currents in the stator phases, then the

complex stator current vector is defined by:

is = ia + ib + 2ic 2

And represent the spatial operators.

Fig.1Stator current space vector and its component in (a,b,c).

This current space vector depicts the three phase sinusoidal system. It still needs to be

transformed into a two time invariant co-ordinate system. [8] This transformation can be split

into two steps: (a,b,c)(,) (the Clarke transformation) which outputs a two co-ordinatetime variant system. (,)(d,q) (the Park transformation) which outputs a two co-ordinatetime invariant System. The space vector can be reported in another reference frame with onlytwo orthogonal axis called (,). Assuming that the axis-a and the axis- are in the samedirection we have the following vector diagram. The projection that modifies the three phase

system into the (,) two dimension orthogonal system is presented below: 3

4

We obtain a two co-ordinate system that still depends on time and speed.

Fig.2Stator current space vector and its components in (,)


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2.1.2 The (,)(d,q) Projection.This is the most important transformation in the FOC. In fact, this projection modifies

a two phase orthogonal system (,) in the d-q rotating reference frame. If we consider the daxis aligned with the rotor flux, the next diagram shows, for the current vector, the

relationship from the two reference frame:

Fig.3Stator current space vector and its component in (,

) and in the d, q rotating reference frame.

is the rotor flux position. The flux and torque components of the current vector are

determined by the following equations:

5 6

These components depend on the current vector (,) components and on the rotor fluxposition, if we know the right rotor flux position then, by this projection, the d,q component

becomes a constant. We obtain a two co-ordinate system

with the following

characteristics: two co-ordinate time invariant system with iSd (flux component) and iSq

(torque component) the direct torque control is possible and easy.

2.1.3 The (d,q)( ,) Projection.Here, we introduce from this voltage transformation only the equation that modifies

the voltages in d-q rotating reference frame in a two phase orthogonal system:

7 8

The outputs of this block are the components of the reference vector that we call Vr,Vr isthe

voltage space vector to be applied to the motor phases.

2.2 The Basic Scheme for the FOCTwo motor phase currents are measured. These measurements feed the Clarke

transformation module. The outputs of this projection are designated iSand iS.


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International Journal of Electrical E

0976 6553(Online) Volume 3, Issue

Fi

Fig.6Referenc

Where T4and T6are the times

during which the zero vectors ar

Park transformation) and the spossible to determine the uncert

Under these constraints the loc

vertices are formed by the tip

waveforms are symmetrical with

Fig.7

ngineering and Technology (IJEET), ISSN 0976 65

3, October December (2012), IAEME

227

.5SVPWM, vectors and sectors

vector as a combination of adjacent vectors

uring which the vectors V4,V6 are applied an

e applied. When the reference voltage (output

ample periods are known, the following sysinties T4,T6and T0:

s of the reference vector is the inside of a he

s of the eight vectors. The generated space

respect to the middle of each PWM period.

Pattern of SVPWM in the sector 3

5(Print), ISSN

T0the time

of the inverse

em makes it

9

10

xagon whose

vector PWM


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International Journal of Electrical E

0976 6553(Online) Volume 3, Issue

The following diagram shows

inputs for the SVPWM are the

Fig.8

reference vector components

relevant sector limiting vectors.

3. COORDINATE TRANSFO

Coordinate transformati

their inverse transformation.Clar

three-phase AC system to two-

transformation, as shown in: Q

Conversely, change the 2-phasetransformation, also called

transformation Change the tw

transformation. The program is s

To the Y-connected winding wit

Conversely, change the DC syst

ngineering and Technology (IJEET), ISSN 0976 65

3, October December (2012), IAEME

228

he pattern of SVPWM for each sector In c

Hexagon of SVPWM, pattern [4]

) and the outputs are the times to appl

MATION

n includes Clarke transformation, Park transf

ke transformation and inverse transformation C

hase system is called Clarke transformation, a

=

AC system to 3-phase AC system is called i2/3 transformation. Park transformation

-phase AC system to rotating DC system i

hown in Fig.11:

=

hout the central line, there is:

Fig.11Program of Park

m to AC system is called inverse Park transfor

5(Print), ISSN

nclusion, the

y each of the

ormation and

hange the

lso called 3/2

verse Clarkeand inverse

called Park

15

ation.


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3.1 Speed Controller

Speed controller adopts PI controller. The program is shown in Fig.12. The input of

the PI controller is the difference between the given speed * and the practical speed r.

Saturation control link is to limit the output amplitude.

Fig.12Program of speed controller

3.2 Flux Observer Module

The property of vector control frequency converter system is decided by theestimating precision of rotors flux observer to a great extent. Flux observer module contains

an amplitude calculation of rotors flux sub-module and a flux angle calculation sub-module.

The former is used to calculate torque current component ist, and the latter is used in the

coordinate transformation. The latter is more difficult. So here only discusses the sub-module

of the rotor flux angle [1,4].

is calculated by integrating the sum of the angular speed of practical measurement and the

slip angular frequency.

s dt 16Where is the angular speed that could be measured directly, s is the slip frequency scould

be calculated by,

s LmistTrr

17

Where Tr LrRr

is the leakage flux coefficient. The program of the calculation of rotor flux

angle is shown in Fig.13 Signal measurement module is composed of Machine Measurement

Demux in Simulink library power system block sets.

Fig.13Sub-module of the rotor flux angle


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4. SIMULATION RESULTS

To accelerate the dynamic speed of the simulation module, a first-order delay-link 1/z is

adopted in feedback transmission function. Link up the above modules, the total simulating

module could be got, as shown in Fig.14 The induction motor parameters are as follows:

PN=500W, UN =650V, f=50Hz, RS =4.495, Rr =5.365 , LM =0.149H, Lr =0.162H,LS=0.206H.

4.1 Proportional Integral (PI) Controller

In this speed and theta calculation are done with PI controller. The error signal of

speed fed to PI controller and generates reference torque value. The reference theta value

with PI controller use error signal of current (Iq), speed (wm), and flux (phir). The whole

SVPWM control technique in simulation diagram is denoted by the control block. The

simulation with PI controller is shown in Fig.14.

Fig.14Simulation for PI controller

The output voltage of inverter with PI controller is shown in Fig.15. The output voltage is

mainly control by SVPWM pulses are generated by control block.

Fig.15Inverter output voltage waveform with PI controller

Discrete,

Ts = 2e-006 s.

v+-

Voltage measurement

Vab

z

1

g

A

B

C

+

-

Three-phase Inverter

Step

Scope6

Scope5

Scope4

Scope3

Scope2

Scope1

Manual

Switch

0

MULTIMETER

Load Torque

step

Tm

mA

B

C

Induction

Motor

m

is_abc

wm

Te

Demux

DC

650 Volts

120

Constant

In1

In2

In3

Out1

CONTROL

BLOCK

Inv erter Output Voltage

Stator currents Is_abc

Speed wm

Speed wm

Torque Tm


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The three phase current Iabcof motor are vary with torque value or speed controlled value.

The wave form for Iabc for speed controlled value with PI controller is shown in Fig.16.

Fig.16Currents (Iabc) waveform with PI controller

Fig.17Currents (Ia) waveform with PI controller

The waveform of speed control with PI controller shown in Fig.18. At starting the speed

gradually increased up to peak value (more than reference speed) within 1.1 sec, with PI

Controller. And it takes 4.4 sec, to achieve reference value. The parameters with PI controller

given in table-1.

Fig.18Waveform for speed with PI controller.

0 0.5 1 1.5 2 2.5 3-250

-200

-150

-100

-50

0

50

100

150

200

250

Time (sec)

Iabc(Amps)

Iabc with PI Controller

0 0.5 1 1.5 2 2.5 3-200

-150

-100

-50

0

50

100

150

200

250

Time (sec)

Ia(Amp)

Ia with PI controller


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S.No. Parameters PI

1 Rise time (tr) 1.1 sec

2 Peak time (tp) 1.4 sec

3 Settling time (ts) 4.4 sec

4 Maximum

overshoot

(%MP)

23.05 %

Table.1Comparison of parameters with PI and controller

5. CONCLUSION

The simulating results indicate space vector control system has good static and

dynamic properties. It is a stable control method. The two speed control techniques with PIcontroller and with PID controller were used The SVPWM approach for the speed and torque

control of induction motor is compared with PI and PID controller connected in the feed

forward path of the system .The results are compared on the basis of time response

specification like Rise time (tr), Peak time (tp), Settling time (ts) and Maximum overshoot

(%MP).It is found that the results with SVPWM with PID controller are quite satisfactory as

compared to the PI controller. The results indicate the coincidence of the dynamic simulating

process and the practical mobile process as well. So it verifies the correctness of the

simulating model based on the mathematic model combining with Matlab/Simulink.

REFERENCES

[1]

Wu Tao, Zhao Liang, Simulation of vector control frequency converter of inductionmotor based on matlab/Simulink, 2011 Third International Conference on Measuring

Technology and Mechatronics Automation, 2011 IEEE, pp. 265268.

[2] E. Hendawi, Analysis, simulation and implementation of space vector pulse width

modulation inverter, Proceedings of the 9th WSEAS International Conference on

Applications of Electrical Engineering, 2009 IEEE, pp. 124-131.

[3] Chintan Patel, Fast direct torque control of an open-end induction motor drive using 12-

sided polygonal voltage space vectors, IEEE Transactions On Power Electronics, vol.

27, 2012 IEEE, no. 1, pp. 0885-0889.

[4] R. Arulmozhiyal, Space vector pulse width modulation based speed control of induction

motor using fuzzy PI controller, International Journal of Computer and Electrical

Engineering, vol. 1, no. 1, April 2009, pp. 1793-1798.

[5]

Tao Wu, Yi-Lin , Yu Guo, Chao Xu, Simulation of FOC vector control of inductionmotor based on lab view, 2009 IEEE.

[6]

Dr. Rami A. Mahir, Dr. Ziadm M. Ahmed and Mr. Amjad J. H., Indirect field

orientation control of induction machine with detuning effect Eng. &Tech. vol.26, no.1,

2008,pp. 265-277.

[7] M. Menaa, O. Touhami, R. Ibtiouen, M. Fadel, Speed sensorless vector control of an

induction motor using spiral vector model-ECKF and ANN controller, 2007 IEEE, pp.

1165-1170.


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Speed Control of Asynchronous Motor Using Space Vector Pwm Technique