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A Presentation on

Mitigation of Disadvantages in Direct TorqueControl of Induction Motor by Applying Fuzzy Logic

By

Shailendra Sharma

Department of Electrical Engineering,

Shri G S Institute of Technology & Science,Indore - 452003, MP, INDIA.

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Contents of the Presentation

Introduction

Fuzzy based on-line tuned PI Controller

(FPIC) for DTC Fuzzy based torque ripple minimization in

DTC

Conclusions

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Introduction

Advantages of Direct Torque Control (DTC) over

Vector Control:

Doesnt requires coordinate transformation

Doesnt requires PWM pulse generation

Doesnt requires current regulators

Less dependent on machine parameters Easy for implementation

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Schematic of classical DTC

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Drawbacks of classical DTC

The speed regulators are conventional PI controllers (CPIC),

which requires precise math model of the system and

appropriate value of PI constants to achieve high performance

drive. Therefore, unexpected change in load conditions orenvironmental factors would produce overshoot, oscillation of

the motor speed, oscillation of the torque, long settling time and

causes deterioration of drive performance.

The selected voltage vector is applied for the entire switching

period, and thus allows electromagnetic torque and stator flux

to vary for the whole switching period. This causes high torque

and flux ripples.

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Mitigation of Drawbacks of DTC

Methods of improvements

Fuzzy PI Controller (FPIC) to achieve precision speed

control

Fuzzy Logic Duty Ratio Control (FLDRC) to minimize torque

& flux ripple

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Recently, Tien-Chi Chen. et al (2002) has proposed a speed

control method for induction motor drives based on a two-

layered neural network PI controller. However, the off-line

training of neural network is very difficult and there is difficulty in

real time control and its implementation.

When Fuzzy Logic is used for the on-line tuning of the PI

controller, it receives scaled values of the speed error and

change of speed error. Its output is updating in the PI controllergains based on a set of rules to maintain excellent control

performance even in the presence of parameter variation and

drive non-linearity.

The first part of this work replaces the conventional PI controllerwith FPIC which can adjust the gains of CPIC on-line

fuzzy Logic PI Controller

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Schematic of FPIC based DTC

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CONTROLLED

PROCESS

DEFUZZIFICA

TIONMODULE

FUZZY INFERENCE

MODULE

FUZZIFICATIONMODULE

FUZZY DATA

BASE

FUZZY

CONTROLLER

ACTIONS

CONDITIONS

Fuzzy Inference System

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Membership functions for Inputs

Mfs for speed error Mfs for change of speed error

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Membership functions for Outputs

Mfs for KP Mfs for KI

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Fuzzy Control Rules

KP

and

KI

E

E

NL NM NS ZE PS PM PL

N L M S M S ML

Z L M L Z L MLK

P

P L M L Z L ML

N Z S M L M SZ

Z Z S M L M S ZKI

P Z M L L L MZ

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On line Tuning

k 20 0.8(K 2.5)P P

k 0.0125 0.003(K 2.5)I I

= +

= +

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Results for FPIC

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Results for FPIC

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Torque ripple minimization strategy

Major draw back of Classical DTC is high torque & flux ripples

because none of the inverter switching vector is able to produce

the exact stator voltage.

Methodologies available to reduce torque & flux ripples:

Multi level Inverters,

SVM

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Duty Ratio Control

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Fuzzy Logic based Duty Ratio Control

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Design of Fuzzy Logic Controller

Selection of input variables : Ete, Efy, .

Selection of output variable :

Number of fuzzy controllers : 2

Selection of Membership functions : Triangular Selection of defuzzification : centroid

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Membership Functions

Ete (X, Y, Z) = (0, 0.15, 0.3)

(X, Y, Z) = (0, 0.52, 1.04)

(X, Y, Z) = (0.4, 0.7, 1.0).

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Fuzzy Control Rules

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Torque Response Comparison

Torque response for classical DTC Torque response for FLDRC DTC

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Stator Flux Trajectory Comparison

Stator flux trajectory for classical DTC Stator flux trajectory for FLDRC DTC

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[1] Blaschke F., 1972, The principle of field-orientation as applied to the transvector closed-loopcontrol system for rotating field motors, SIEMENS Rev. Vol. 34, pp 217-220.

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education, Inc., 482, F I E, Pataparganj, Delhi 110092, India.

[3] Casadei D., Giovanni Serra., and Angelo Tani., 2001, The use of matrix converters in direct

torque control of induction motors, IEEE transactions on industrial electronics, Vol 48, No 6, pp1057-1064.

[4] Depenbrock M., 1988, Direct Self Control (DSC) of inverter-fed induction motor, IEEE

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[5] Habetler G H., Deepakraj M. Divan., 1991, Control strategies for direct torque control using

discrete pulse width modulation, IEEE transactions on Industry applications, Vol 27, No 5, 893-901.

[6] Habetler G H., Francesco Profumo., Michele Pastorelli and Leon M Tolbert., 1992, Direct Torque

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No 5, pp 1045-1053.

[7] Kang J K., S-Ki Sul, 1999, New Direct torque control of induction motor for minimum torque ripple

and constant switching frequency, IEEE Transaction on Industry Applications, Vol 35, No 5, pp

1076-1082.

References

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[8] Marino P., M. D'lncecco and N.Visciano., 2001, A comparison of direct torque controlmethodologies for induction motor, IEEE porto power tech conference PPT01, September,

Porto, Portugal.

[9] Noguchi T., M. Yamamoto, S. Kondo and I. Takahashi, 1999, Enlarging switching

frequency in direct torque-controlled inverter by means of dithering, IEEE Tran. on Industry

Application, Vol 35, No 6, pp 1358-1366.[10] Peter Vas., 1998, Sensor less Vector & Direct Torque Control, OXFORD University press,

Inc., New York.

[11] Peter Vas., 1999, Artificial-Intelligence-Based electrical motors and dives: Application of

fuzzy, neural, fuzzy-neural and genetic algorithm based techniques, OXFORD University

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[12] Senthil U., Femandes B. G., 2003, Hybrid space vector pulse modulation based direct

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[14] Tiitinen P., 1996, The next generation motor control method, DTC direct torque control,

Proc. Ind. Conf. power electronics, drives and energy systems for industrial growth, New

Delhi, India, pp 37-43.

References

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Machine Parameters

Motor Parameters used for the Simulation

IM Motor Rating 4 KW

Rated Torque 15 Nm

Pole Pair 2

Stator Resistance 1.55 ohm

Rotor Resistance 1.25 ohm

Stator Leakage Inductance 0.172 Henry

Rotor Leakage Inductance 0.172 Henry

Mutual Inductance 0.166 Henry

Motor Inertia 0.016 Kg-m2

Friction Coefficient 0.0

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Thanks & Quiresare Welcome