Sensorless Direct Torque Control

A Robust Sensorless Direct Torque Control of Induction
Motor Based on MRAS and Extended Kalman Filter
Abstract
In this paper, the classical Direct Torque Control (DTC) of
Induction Motor (IM) using an open loop pure integration suffers
from the well-known problems of integration especially in the
low speed operation range is detailed. To tackle this problem,
the IM variables and parameters estimation is performed using
a recursive non-linear observer known as EKF. This observer is
used to estimate the stator currents, the rotor flux linkages, the
rotor speed and the stator resistance. The main drawback of
the EKF in this case is that the load dynamics has to be known
which is not usually possible. Therefore, a new method based
on the Model Reference Adaptive System (MRAS) is used to
estimate the rotor speed. The two different nonlinear observers
applied to sensorless DTC of IM, are discussed and compared
to each other. The rotor speed estimation in DTC technique is
affected by parameter variations especially the stator
resistance due to temperature particularly at low speeds.
Therefore, it is necessary to compensate this parameter
variation in sensorless induction motor drives using an online
adaptation of the control algorithm by the estimated stator
resistance. A simulation work leads to the selected results
to support the study findings.


Direct Torque Control bloc diagram of a sensorless IM drives.
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Sensorless Direct Torque Control of an Induction Motor
Using Fuzzy Controller
Abstract:
In this paper direct torque control DTC of an induction motor is
developed. A new technique for DTC based on fuzzy logic
concept is proposed, where fast torque response with low ripple
in the stator flux and torque of induction motor can be achieved. In
comparison with the conventional DTC simulation results clearly
demonstrate a better dynamic and steady state performance with
the fuzzy logic DTC. The two approaches are explained in clear
details , which are designed using SIMULINK under Matlab Ver.6
software package. Also, MATLAB/FUZZY toolbox is used to
implement the fuzzy logic controller. Both systems are simulated
under the same conditions.
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SENSORLESS SPEED ESTIMATION OF INDUCTION MOTOR
IN A DIRECT TORQUE CONTROL SYSTEM
ABSTRACT
Fast and robust torque control in a very wide range of speed is
very needed by various industrial AC drive applications.
Therefore, since 1986 [1], direct torque control (DTC) has been
introduced to satisfy this desire. In order to achieve more
economical control, conventional speed sensor has been
replacing by sensorless speed estimation. The sensorless
schemes are used to improve reliability and decrease
maintenance requirements. In this paper, concerned sensorless
techniques of induction machine controlled by DTC algorithm
are openloop estimators and MRAS schemes [2], [3]. To
demonstrate clearly the advantages and disadvantages between
two kinds of sensorless techniques, obtained simulation results
are compared. By enhancing speed estimation, the pure
integrator is replaced by a low-pass filter to avoid DC drift and
saturation problems [2].

MRAS-based speed estimator scheme
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Sensorless three-phase induction motor direct torque
control using sliding mode control strategy
laboratory set-up for motor speed control teaching
Abstract - A three-phase induction motor direct torque
control laboratory set-up for simulation and
experimental activities is presented in this paper. It
includes both PI controllers and sliding-mode controllers
and uses a sensorless method to estimate rotor speed. The
subject of this set-up is to present to the students a
simulation tool based on Matlab SimPowerSystems
toolbox with the possibility to check simulation results
against a DSP based experimental system. The set-up
provides to the electrical engineering students an
excellent learning tool for non-linear control studies
using as example the variable speed three-phase
induction motor control.

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Control and Automation Home

Direct Torque Control of Induction Motor with FUZZY

Genetic Algorithm Optimized PI and Fuzzy Sliding Mode
Speed Control for DTC Drives
Abstract— This paper presents a detailed comparison between
a conventional PI controller and a variable structure controller
based on a fuzzy sliding mode strategy used for speed control
in direct torque control induction motor drive. Genetic algorithms
are used to tune the PI controller gains to ensure optimal
performance. The performance of the two controllers are
investigated and compared for different dynamic operating
conditions such as of reference speed and for load torque step
changes at nominal parameters and in the presence of parameter
variation and imprecision. Results show that the PI controller has
better performance for nominal operating conditions while the
fuzzy sliding mode is more robust against parameter variation
and uncertainty, and is less sensitive to external load torque
disturbances with a fast dynamic response.

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DIRECT TORQUE CONTROL OF INDUCTION MOTOR
WITH FUZZY MINIMIZATION TORQUE RIPPLE
Direct torque control (DTC) is receiving wide atten-
tion in the recent literature [1, 2]. DTC minimizes the use
of machine parameters [3, 4]. This type of control is es-
sentially a sliding mode stator flux-oriented control. The
DTC uses the hysteresis band to directly control the flux
and torque of the machine. When the stator flux falls out-
side the hysteresis band, the inverter switching stator is
changed so that the flux takes an optimal path toward
the desired value [3, 4].
The name direct torque control is derived from the
fact that on the basis of the errors between the reference
and the estimated values of torque and flux it is possible
to directly control the inverter states in order to reduce
the torque and flux errors within the prefixed band limits
[5, 6].

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IMPROVED DTC OF INDUCTION MOTOR WITH FUZZY

RESISTANCE ESTIMATOR
Abstract- The aim of the work is to study the
feasibility of stator resistance estimator in DTC
scheme. Fuzzy logic is used to estimate the stator
resistance. DTC with fuzzy estimator is characterized
by fast torque and flux response in very-low speed
operation.

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DIRECT TORQUE NEURO FUZZY SPEED CONTROL
OF AN INDUCTION MACHINE DRIVE BASED
ON A NEW VARIABLE GAIN PI CONTROLLER
This paper presents an original variable gain PI (VGPI)
controller for speed control of a simplified direct torque neuro
fuzzy controlled (DTNFC) induction motor drive. First, a
simplified direct torque neuro fuzzy control (DTNFC) for a voltage
source PWM inverter fed induction motor drive is presented.
This control scheme uses the stator flux amplitude and the
electromagnetic torque errors through a four rules adaptive NF
inference system (ANFIS) to generate a voltage space vector
(reference voltage). This voltage is used by a space vector
modulator to generate the inverter switching states. Then a VGPI
controller is designed in order to be used as the speed controller
in the simplified DTNFC induction motor drive. Simulation
of the simplified DTNFC induction motor drive using VGPI for
speed control shows promising results. The motor reaches
the reference speed rapidly and without overshoot, load
disturbances are rapidly rejected and the detuning problem
caused by the stator resistance variation is fairly well dealt with.

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Control and Automation Home

Direct Torque Controlled Motor Drive

Direct Torque Controlled Induction Motor Drive

Direct Torque Controlled Induction Motor Drive 1

Direct Torque Controlled Induction Motor Drive 2

Direct Torque Control of Induction Motor with FUZZY

Direct Torque Control of the Asynchronous Motor

Direct Torque Control of the Asynchronous Motor

Other

Sensorless Direct Torque Control

Direct Torque Controlled Induction Motor Drive 2

DIRECT TORQUE CONTROL FOR INDUCTION MOTOR
USING INTELLIGENT TECHNIQUES
ABSTRACT
In this paper, we propose two approach intelligent techniques
of improvement of Direct Torque Control (DTC) of Induction
motor such as fuzzy logic (FL) and artificial neural network (ANN),
applied in switching select voltage vector .The comparison with
conventional direct torque control (DTC), show that the use of
the DTC_FL and DTC_ANN, reduced the torque, stator flux,
and current ripples. The validity of the proposed methods is
confirmed by the simulative results.

Basic direct torque control scheme based ANN

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New Direct Torque Control Scheme of Induction Motor

for Electric Vehicles
Abstract
In this paper, new scheme of direct torque
control of induction motor for electric vehicles is
proposed and the results of an investigation into
suitable torque control schemes are also presented.
The electric vehicle drive consists of rewound
induction motors and a three-level IGBT inverter.
The schemes investigated are Field Oriented Control,
Direct Torque Control (DTC), and DTC using Space
Vector Modulation. The results of Matlab-Simulink
simulations and a comparison between the control
schemes are presented. It is found that the DTC using
Space Vector Modulation scheme is best for this
application.

Circuit Diagram of Space Vector Modulation

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EXPERIMENTAL APPROACH OF DIRECT TORQUE

CONTROL METHOD USING MATRIX CONVERTER

FED INDUCTION MOTOR
ABSTRACT
This paper presents a study on direct torque control method
(DTC) using matrix converter fed induction motor. The
advantages of matrix converters are combined with the advantages
of the DTC technique: under the constraint of unity input power
factor, the required voltage vectors are generated to implement
the conventional DTC method of induction motor. However, since
the first idea about DTC method using MC fed induction motor was
suggested by [1], the current researches just focus on some
simulation results and a little un-explicit experimental result is carried
out. This paper describes the operation of induction motor under the
DTC method in steady-state and transient conditions by the
experimental results, the discussion about the trend of DTC method
using MC is also carried out. Furthermore, the entire system of
matrix converter configuration using 7.5kW IGBT modules
(FR35R12KE3V1) is explained in detail.

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DIRECT TORQUE CONTROL STRATEGY OF
INDUCTION MOTORS
Direct Torque Control of inverter-fed Induction Machine allows
high dynamic performance by means of very simple
control schemes. In this paper various direct torque control
methodologies as conventional DTC (C_DTC), modified DTC
(M_DTC) and twelve sectors (12_DTC) have been analysed
and compared in order to evaluate the influence of the motor
operating condition on steady state performances. A particula
r emphasis on stator flux trajectory, torque ripple and stator
current distortion has been made. Simulation results show the
effectiveness of the proposed methods.

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Direct Torque Control of Induction Motors
D.C. motors have been used widely during the last
century in applications where variable-speed
operation was needed, because its flux and torque can
be controlled easily by means of changing the field
and the armature currents respectively. Furthermore,
operation in the four quadrants of the torque-speed
plane including temporary standstill was achieved.
However, DC motors have basically two drawbacks,
which are the existence of commutators and brushes.
These two disadvantages implied not only periodic
maintenance but also difficulty to work in dirty and
explosive environments; difficulty that sometimes
used to become in impossibility.
On the other hand, induction motors

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Control and Automation Home

Direct Torque Controlled Induction Motor Drive 1

HIGH – PERFORMANCE ADAPTIVE INTELLIGENT DIRECT
TORQUE CONTROL SCHEMES FOR INDUCTION MOTOR DRIVES

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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DIRECT TORQUE CONTROLLED INDUCTION MOTOR DRIVE
UTILIZED IN AN ELECTRICAL VEHICLE
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
Abstract
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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DIRECT TORQUE CONTROLLED PWM
INVERTER FED INDUCTION MOTOR DRIVE FOR
CITY TRANSPORTATION
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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Control and Automation Home

Types of Induction Motor Drive Controllers

There are many different ways to drive an induction
motor. The main differences between them are the
motor’s performance and the viability and cost in its
real implementation.

1.1- Voltage/Frequency:
Despite the fact that V/F is the simplest controller, it
is the most widespread, reaching approximately 90%
of the industrial applications. It is known as a scalar
control and acts imposing a constant relation between
voltage and frequency. The structure is very simple
and it is normally used without speed feedback.
However, this controller doesn’t achieve a good
accuracy in both speed and torque responses mainly
due to the fact that the stator flux and the torque are
not directly controlled. Even though, as long as the
parameters are identified, the accuracy in the speed
can be 2% (except in a very low speed) and the
dynamic response can be approximately around 50ms
.

1.2- Vector Controllers:
In these types of controllers, there are control loops
for controlling both the torque and the flux . The
most spread controllers are the ones that use vector
transform such as either Park or Ku. Its accuracy can
reach values such as 0.5% regarding the speed and
2% regarding the torque, even in stand still.
The main disadvantages are the huge computational
capability required and the compulsory good
identification of the motor parameters.

1.3- Field Acceleration Method:
This method is based on maintaining the amplitude
and the phase of the stator current constants, avoiding
electromagnetic transients. Therefore the equations
used can be simplified saving the vector
transformation in the controllers.
It is achieved some computational reduction,
overcoming the main problem in the vector
controllers and then becoming an important
alternative for the vector controllers.

source
http://www.jcee.upc.es/JCEE2001/PDFs%202000/
8arias.pdf