Monday, April 6, 2009

Direct Torque Controlled Induction Motor Drive 1


ABSTRACT This study presents a detailed comparison between
viable adaptive intelligent torque control strategies of induction
motor, emphasizing advantages and disadvantages. The scope
of this study is to choose an adaptive intelligent controller for
induction motor drive proposed for high performance applications.
Induction motors are characterized by complex, highly non-linear
and time varying dynamics and inaccessibility of some states and
output for measurements and hence can be considered as a
challenging engineering problem. The advent of torque and flux
control techniques have partially solved induction motor control
problems, because they are sensitive to drive parameter
variations and performance may deteriorate if conventional
controllers are used. Intelligent controllers are considered as
potential candidates for such an application. In this paper, the
performance of the various sensorless intelligent Direct Torque
Control (DTC) techniques of Induction motor such as neural
network, fuzzy and genetic algorithm based torque controllers
are evaluated. Adaptive intelligent techniques are applied to
achieve high performance decoupled flux and torque control.
The theoretical principle, numerical simulation procedures and
the results of these methods are discussed.

Figure 1 Basic configuration of DTC scheme

Figure 3 Schematic of DTC using Neural-Network controller

Figure 9 Schematic of fuzzy logic DTC
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A new developed Direct Torque Control principle is used for torque
and stator flux control. Very fast torque response -- typically less
than 2ms -~ can be obtained. A very accurate stator flux observer is
an essential part of the complete concept. Due to this observer no
speed sensor is needed.
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Improved direct torque control of induction motor with
dither injection

Abstract. In this paper, a three-level inverter-fed induction motor
drive operating under Direct Torque Control (DTC) is presented
.Atriangularwave is used as dither signal of minute amplitude
(for torque hysteresis band and flux hysteresis band respectively)
in the error block. This method minimizes flux and torque ripple in a
three-level inverter fed induction motor drive while the dynamic
performance is not affected. The optimal value of dither frequency
and magnitude is found out under free running condition. The
proposed technique reduces torque ripple by 60% (peak to peak)
compared to the case without dither injection, results in low acoustic
noise and increases the switching frequency of the inverter. A
laboratory prototype of the drive system has been developed and
the simulation and experimental results are reported.

Block diagram of three-level inverter-fed DTC induction motor drive.
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Direct Torque Control of Induction Motor Using
Sophisticated Lookup Tables Based on Neural Networks

Induction motor drive based on direct torque control
(DTC) allows high dynamic performance to be obtained
with very simple hysteresis control scheme. Direct
control of the torque and flux is achieved by proper
selection of inverter voltage space vector through a
lookup table .In this paper apart from six sector look up
table used for classical DTC, a modified look up table,
which also use six sectors but with different zones and a
twelve sector table are presented .This paper also
presents the application of neural networks to control
induction machines with DTC. Neural network is used to
emulate the state selector of the DTC. In this paper
Levenberg-Marquardt algorithm is used to train the
neural network. Finally DTC is simulated with and
without neural networks and results are compared.
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In this paper an application of Direct Torque Control with Space
Vector Modulation (DTC– SVM) controlled induction motor for
tram drive is presented. Thanks to its advantages like: excellent
dynamics, low torque ripples, insensitivity for motor parameters
changes, constant switching and low sampling frequency,
DTC–SVM is used in various applications. In proposed case
DTC–SVM is used for tram traction drive based on PWM Voltage
Sourced Inverter Fed Induction Machine. This method was chosen
after comparison with Field Oriented Control (FOC), Switching
Table Direct Torque Control (ST–DTC) and Direct Self Control
(DSC). DTC–SVM combines advantages and eliminates
drawbacks commonly used methods like FOC and ST–DTC.
There are no hysteresis controllers, what gives possibility to
reduce sampling and also switching frequency. It leads to reduce
switching loses (important in high power applications).

Constant switching frequency is ensured by using Space Vector
Modulation strategy. In DTC–SVM linear PI regulators are used.
Both stator flux and electromagnetic torque are controlled directly.
High dynamics is achieved and also good stationary operation
performance is kept. This advantages allow to implement
DTC–SVM for traction drives. The paper presents parallel structure
of DTC–SVM. Operating ranges, including field weakening
region, are described. Some experimental results of the 75kW
induction motor drive which illustrate its performance are attached.

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