SIMULATION OF FUZZY LOGIC CONTROLLER BASED … · SIMULATION OF FUZZY LOGIC CONTROLLER BASED ... The conventional principles of DTC and Space vector modulation of matrix converter

International Journal of Computer Engineering and Applications, Volume VII, Issue III, Part I,

September 14

98 O. Hemakesavulu , C. Ganesh and M. Manasa

SIMULATION OF FUZZY LOGIC CONTROLLER BASED

MATRIX CONVERTER DTC-SVM METHOD FOR INDUCTION

MOTOR DRIVE

O. Hemakesavulu 1, C. Ganesh

2 , M. Manasa

3

1,2 Associate Professor, Department of EEE, Annamacharya institute of technology and sciences,

Rajampet, AP, India 3 PG Student, Department of EEE, Annamacharya Institute of Technology & Sciences, Rajampet,

AP, India

ABSTRACT: A Fuzzy space vector modulation direct torque control strategy for induction machine based on Matrix converter is proposed to improve the low speed performance of the direct torque control (DTC) system. The generation of torque reference voltage vector were designed in the Fuzzy logic controller. This novel method provides a precious input power factor control capability. The conventional principles of DTC and Space vector modulation of matrix converter were described. The Performance of the proposed drive system is evaluated through simulation using MATLAB-SIMULINK package to identify the effectiveness of new method. The Simulation results of Induction motor control at both steady state and transient state are shown to improve the low- speed performance and strong adaptability of novel control strategy.

Keywords: Matrix converter, Induction motor, Direct torque control method, SVM, Fuzzy Logic Controller, Low Speed performance

[1] INTRODUCTION

The Direct Torque Control (DTC) method has been proposed in the mid 1980’s, The

Direct Torque Control (DTC) method for AC machines is prevalently utilized in many

variable speed drives, especially in case the torque control is more desired than speed

control. Direct torque control (DTC) is a high-dynamic and high performance control technique

for induction motor drives which has been developed in the last two decades as possible

alternative to DC servo drives [1], [2]. In direct torque controlled adjustable speed drives, the

motor flux and the electromagnetic torque are the reference quantities which are directly

controlled by the applied inverter voltage vector. The main advantages of DTC are: fast torque

and flux responses, no need for speed or position sensors and no requirements for coordinate

transformation. DTC has also some disadvantages: the difficulty to control the torque and the

flux at very low speed, the higher current and torque ripple which imply higher machine losses

and noise, the inherent variable switching frequency and the lack of direct current control.

Simulation Of Fuzzy Logic Controller Based Matrix Converter DTC-SVM Method For Induction

Motor Drive


In the past two decades, due to the need to increase the quality and the efficiency of

power supply and usage the three phase matrix converter has become a major modern energy

converter and has emerged from the previously conventional energy conversion modules as one

of the best substitutions. Matrix converter fed motor drive is superior to pulse width modulation

(PWM) inverter drives because it provides bidirectional power flow, sinusoidal input/output

currents, and adjustable input power factor [3], [4] . Furthermore, matrix converter allows a

compact design due to the lack of dc-link capacitors for energy storage. However, only a few

of practical matrix converters have been applied to vector control system of induction motors

(IM) for the reason: Modulation technique and commutation control are more complicated

than conventional PWM inverter [5].

The switching frequency of voltage source inverter is Non-Fixing. Non-Fixing

switching frequency capability of the inverter not to be used fully [6], [7]. Secondly, there is

sharp increase or decrease of torque because only one voltage vector works in a sampling

period and the options of vector is limited. Fuzzy logic control has manifested its

robustness, and has been extensively researched and used as one of the intelligent control

methods in control field [8], [9] ,[10] . The new SVM-DTC strategy uses fuzzy logic controller

substitute the original PI controller. In this paper, a new Fuzzy DTC control for matrix

converter is proposed which allows under the constraint of unity input power factor, the

generation of the voltage vectors required to implement the DTC of three phase induction

motor. Depending on the induction motor operating point such vectors might be applied and

consequently the electromagnetic torque ripple is reduced.

[2] DIRECT TORQUE CONTROL STRUCTURES

[2.1] MATHEMATICAL MODE OF INDUCTION MACHINE

The basic model of DTC induction motor scheme is shown in Fig. 1. At each sample

time, the two stator currents and isa and isb the DC bus voltage Vdc are sampled.

Using the inverter voltage vector, the α,β components of the stator voltage space vector

in the stationary reference frame are calculated as follows.

Vsαref = Vdc (

)

Vsβref=

√ Vdc ( ) (1)

The α,β components of the stator current space vector are calculated using

Isα = isa

Isβ =

√ (2)

The stator flux is a function of the rotor flux which is provides from the flux

observer

Ψsα = σ Ls Isα +

Ψrα

Ψsβ = σ Ls Isβ +

Ψrβ (3)


September 14


Then the magnitude of Stator flux is calculated by

|Ψs| = √Ψ α Ψ β (4)

The electromagnetic torque is calculated by

Te =

p(Ψ α β Ψ β α ) (5)

Where p is the number of poles

The torque and the flux errors are defined is

ΔΨs = |Ψsref| - |Ψs|

ΔTe = Tref – Te (6)

[2.2] PRINCIPLE OF DIRECT TORQUE CONTROL

The basic principle in conventional DTC for induction motors is to directly select stator

voltage vectors by means of a hysteresis stator flux and torque control. As it is shown in Fig 1.

The inverter switching states are determined by the torque and flux errors according

to the sector determined. In order to maintain the estimated and torque within their

boundaries which a by the two hysteresis bandwidths as shown in figure 2b, at each sampling

period, the torque and are estimated and compared with the corresponding reference values

before passing the hysteresis comparator.

Figure : 1. Block Diagram of DTC

In particular, stator flux is controlled by a two-level hysteresis comparator, whereas the

torque is controlled by a three-level comparator. The position of the stator flux is detected,

and the most suitable space vector among 8 space vectors generated by a VSI is selected from

the switching table given in Table 1.


Motor Drive


Table :1. DTC Switching table

[3] DTC MATRIX CONVERTER STRUCTURES (DTC-MC)

[3.1] WORKING PRINCIPLE OF MATRIX CONVERTER

A MC is an AC-AC converter, with m x n bidirectional switches, which connects an m-

phase voltage source to an n-phase load. The three-phase, 3x3 switches, MC shown in Fig.2 is

the most interesting. It connects a three phase voltage source to a three-phase load. The matrix

converter has a simple topology and a compact design due to the lack of DC-link capacitor for

energy storage.. In the MC vsi, i={A,B,C} are the source voltages, isi, i={A,B,C} are the

source currents, vjN, j={a,b,c} are the load voltages, ij, j={a,b,c} are the load currents, vi,

i={A,B,C} are the MC input voltages ii ,i={A,B,C}are the input currents. A switch, Sij,

i={A,B,C}, j={a,b,c} can connect phase i of the input to phase j of the load.

The mathematical model of Matrix converter can be derived from fig 2 as follows:

[

( ) ( ) ( )

] = [

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

] . [

( ) ( ) ( )

] (7)

[

( ) ( ) ( )

] = [

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

] . [

( ) ( ) ( )

] (8)

Sector

6

Sector

5

Sector

4

Sector

3

Sector 2

Sector 1

(

)

(

)

(

,

)

(

)

(

,

)

(

,

)

Decrease

Flux

Increase

Torque

100

110

010

011

001

101

Decrease

Torque

011

001

101

100

110

010

Increase

Flux

Increase

Torque

110

010

011

001

101

100

Decrease

Torque

001

101

100

110

010

011


September 14


Figure: 2. Block diagram of Matrix converter

[3.2] MATRIX CONVERTER THEORY

The three-phase matrix converter module includes nine bi-directional switches as

shown in Figure 3. There are 27 switching configuration states, which mean 27 possible space

vectors can be used to control IM and can be split respectively into 3 groups as shown in

Table 1; in Group I, two output lines are connected to one of the other input lines; in Group II,

all output lines are connected to a common input line; while in Group III, each output line is

connected to a different input line. The corresponding output line-to-neutral voltage vector

and input line current vector have fixed directions as represented in Figure 2. However, Group

III is not useful. Only 18 non-zero space vectors in Group I (±1, ±2, …, ±9) and 3 zero space

vectors in Group II (0a, 0b, 0c) can be usually employed in the modern control techniques for

the matrix converter (such as the Space Vector Modulation, DTC methods, etc.)

(b)

(a)

Figure : 3. (a) output line to neutral voltage vectors

(b) output currents


Motor Drive


[3.3] DTC PRINCIPLES BY MATRIX CONVERTER

The basic DTC principles using matrix converters can be briefly described as follows:

at each sampling period, the proper switching configuration, which allows the compensation

of instantaneous errors in the stator flux magnitude and torque, is selected under the

constraint of unity input power factor. This last requirement of the input side of the matrix

converter is intrinsically satisfied if the average value of sin (ψi) is maintained close to zero,

where ψi is the displacement angle between the input line voltage and input line current. The

hysteresis comparator directly controls this variable and the average value of sin (ψi) is

obtained by applying a low-pass filter to its instantaneous value. The average value of sin (ψi)

is controlled close to zero because the input power factor is aimed close to unity. As a

facultative example, after calculation at the first time of each sampling period and considering

the stator flux vector lying in sector 1, the input voltage vector lying in sector 2, the output of

the torque hysteresis comparator, the flux hysteresis comparator and the hysteresis comparator

of the average value of sin (ψi) are respectively cT = +1, cϕ = 0 and cψ=+1. As shown in

Figure 4, first with cT =+1, cϕ = 0 and the stator flux in sector 1, the suitable voltage vector

V6-vsi is the VSI output voltage vector by the DTC algorithm in a given switching period

from Table 2.

Group

Vector

A B C

Vs αo

ii βi

I

+1MC a b b 2/3Vab 0

2/√ isa

-1MC b a a -2/3vab 0

-2/√ isa

+2MC b c c 2/3vbc 0

2/√ isa

-2MC c b b -2/3vbc 0 - 2/√ isa

+3MC c a a 2/3vca 0

2/√ isa

-3MC a c c -2/3vca 0 -2/√ isa

+4MC b a b 2/3Vab

2/√ isb

-4MC a b a -2/3vab

- 2/√ isb

+5MC c b c 2/3vbc

2/√ isb

-5MC b c b -2/3vbc

-2/√ isb

+6MC a c a 2/3vca

2/√ isb

-6MC c a c -2/3vca

- 2/√ isb

+7MC b b a 2/3Vab

2/√ isc

-7MC a a b -2/3vab

- 2/√ isc


September 14


Table : 2. Possible switching configurations of MC

Then, with the chosen VSI voltage vector V6-vsi, cψ= +1 and the input voltage vector

in sector 2, the opportune matrix converter voltage vector is finally selected as V-5MC from

Table 3.The schematic of the DTC method using the matrix converter fed induction motor is

represented in Figure 4. The reference values of the torque and the stator flux are compared

with the estimated values and coordinate with the average value of the sin (ψi) hysteresis

comparator. In the lower part of the block diagram, the estimators of the electromagnetic

torque, stator flux and the average value of sin (ψi) are represented. These estimators require

the knowledge of input and output of voltages and currents for the matrix converter.

Table :3. DTC switching table using MC

Sector

of v

1

2

3

4

5

6

cψ

+1

-1

+1

-1

+1

-1

+1

-1

+1

-1

+1

-1

V1-Vsi

-3MC

+1MC

+2MC

-3MC

-1MC

+2MC

+3MC

-1MC

-2MC

+3MC

+1MC

-2MC

V2-Vsi

+9MC

-7MC

-8MC

+9MC

+7MC

-8MC

-9MC

+7MC

+8MC

-9MC

-7MC

+8MC

V3-Vsi

-6MC

+4MC

+5MC

-6MC

-4MC

+5MC

+6MC

-4MC

-5MC

+6MC

+4MC

-5MC

V4-Vsi

+3MC

-1MC

-2MC

+3MC

+1MC

-2MC

-3MC

+1MC

+2MC

-3MC

-1MC

+2MC

V5-Vsi

-9MC

+7MC

+8MC

-9MC

-7MC

+8MC

+9MC

-7MC

-8MC

+9MC

+7MC

-8MC

V6-Vsi

+6MC

-4MC

-5MC

+6MC

+4MC

-5MC

-6MC

+4MC

+5MC

-6MC

-4MC

+5MC

+8MC c c b 2/3vbc

2/√ isc

-8MC b b c -2/3vbc

- 2/√ isc

+9MC a a c 2/3vca

2/√ isc

-9MC c c a -2/3vca

- 2/√ isc

II

0a a a a 0 - 0 -

0b b b b 0 - 0 -

0c c c c 0 - 0 -

III

x a b c x x x x

x a c b x x x x

x b c a x x x x

x b a c x x x x

x c a b x x x x

x c b a x x x x


Motor Drive


However, only the input voltages and the output currents of the matrix converter

module are by sensors, while other quantities such as the input voltages of the induction motor

and the input currents of the matrix converter module are calculated from the previous

switching states, the input voltages and the output currents of the matrix converter module

structure. Fig 4 represents the block diagram of DTC-MC with PI controller. The direct torque

control with space vector modulation technique (DTC-SVM) was proposed in order to

improve the classical DTC. In control structures space vector modulation technique is used.

Basically, the controller calculates the required stator voltage vector and then it is realized by

space vector modulation technique. The output of PI controller can be represented as the

stator voltage components in the stator flux oriented coordinates.

Figure :4. Block diagram of DTC-MC with PI Controlle

[4] DESIGN OF FUZZY LOGIC CONTROLLER

Figure 5 shows the block diagram of proposed direct control strategy. The PI controller

was replaced by Fuzzy logic controller. The torque references are compared to the values

calculated in torque estimator and the corresponding errors are sending to the Direct Torque

Fuzzy Controller of the Matrix converter stage control system.

Figure :5. Block diagram of DTC-MC with Fuzzy logic controller


September 14


The torque Fuzzy logic regulator variables, membership functions and output surface is

represented in figure 6.

(a) Torque error

(b) Change in torque error

(c) Output variable

(d) Control surface of Fuzzy logic controller

Figure :6 . The Fuzzy membership functions and control surface area

The associated fuzzy rule matrices of torque fuzzy logic controllers are given in Table

4. The FLC uses 49 rules and in each variable to compute output and exhibits good

performance.


Motor Drive


Table :3. Fuzzy control rule

The torque fuzzy controller also has two input variables and one output variable. Input

variables: torque error ET and change rate of torque error ΔET. Output variable: reference

voltage vector.

Figure :8 . Matlab/Simulink model of DTC-MC

[5] SIMULATION RESULTS

The DTC-MC with both PI and fuzzy logic controller are simulated and the comparison

between the results is performed. Stator flux linkage comparing curves are shown in Figure 7

and Figure 8.Compared with two groups of flux waveform, the flux track amplitude of DTC-

MC with PI controller model is volatile. At certain parts, there is a clear deviation, flux required

for a longer time to reach steady-state, the DTC-MC with fuzzy logic controller, flux track has

always maintained a very good round, flux is required for a short time to reach steady-stat and

flux amplitude fluctuation is small.

ET↓ ΔET

→

NL NM NS ZZ PS PM PL

NL NL NL NM NM NS NS ZZ

NM NL NM NM NS NS ZZ PS

NS NL NM NS NS ZZ PS PM

ZZ NM NS NS ZZ PS PS PM

PS NM NS ZZ PS PS PM PL

PM NS ZZ PS PS PM PM PL

PL ZZ PS PS PM PM PL PL


September 14


Figure :7. Stator flux circle of DTC-MC with PI controller

Figure :8. Stator flux circle of DTC-MC with fuzzy Controller

From the above results a better response is obtained. However in DTC-MC with fuzzy

controller shown in fig 10 has less torque ripples when compared with DTC –MC with PI

controller (fig 8).

Figure :9. Torque response of DTC-MC with PI Controller

Figure :10. Torque response of DTC-MC with Fuzzy controller


Motor Drive


From the above figures the pick up time is small in DTC-MC with fuzzy compared

with DTC –MC with PI.

(a)

(b)

Figure :11. Simulation results at 1500 rpm

(a) DTC-MC with PI (b) DTC-MC with fuzzy

(a)

(b)

Figure :12. Simulation results of Speed reversal

(a) DTC-MC with PI (b) DTC-MC with fuzzy


September 14


From the above results (fig 12) a good response is obtained for both methods with

speed reversal also. The DTC matrix converter with fuzzy controller has better performance

compared with PI controller.

[6] CONCLUSION

This paper presents a Direct Torque Control with Matrix Converter using fuzzy logic

controller method for induction motor. However the DTC method have combined with the

SVM method on matrix converter. The simulation results proved that transient torque response

is excellent. The DTC Matrix Converter with fuzzy controller has a better performance.

However Controlling of torque and reducing the torque ripples was the main goal, so the DTC

Matrix Converter with fuzzy controller possesses less ripples in compare DTC-MC with PI

controller.


Motor Drive


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Documents

SIMULATION OF FUZZY LOGIC CONTROLLER BASED … · SIMULATION OF FUZZY LOGIC CONTROLLER BASED ... The conventional principles of DTC and Space vector modulation of matrix converter