IMPROVING DIRECT TORQUE CONTROL USING MATRIX CONVERTERS

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IMPROVING DIRECT TORQUE CONTROL USING MATRIX
CONVERTERS

•  
• Technical University of Catalonia. Electronics
  Engineering Department. Colom 1, Terrassa 08222,
  Catalonia, Spain

 University of Malta.Department of Electrical
Power and Control Engineering. Msida
MSD 06, Malta
  Research Student Carlos Ortega García
  Home Supervisor Dr. Antoni Arias Pujol
  Malta Supervisor Dr. Cedric Caruana
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Index

• Introduction
• Matrix Converters.
• Direct Torque Control.
• Classical
• Using Matrix Converters.
• Sensorless Control of a DTC drive using hf
  injection
• Conclusions.

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Introduction

• Matrix Converters (MC)
• Advanced circuit topology capable of generating
  AC-AC.
• Load voltage with arbitrary amplitude and
  frequency, and sinusoidal input/output waveforms.
  
• Power Factor Correction (PFC).
• No inductive or capacitive elements
• are required, thus allowing a very
• compact design.
• A very good alternative to Voltage Source
  Inverters (VSI).

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Introduction

• Direct Torque Control (DTC).
• Simple and robust signal processing scheme.
• No coordinate transformation and no PWM
  generation are needed.
• Quick and precise torque response.
• The torque and flux modulus values and sector of
  the flux are needed.
• High torque ripple.

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Introduction

• High Frequency Signal Injection.
• Non Model-Based method.
• Avoids problems at low and zero speed due to the
  lack of back-EMF.
• No dependence of machine parameters.
• Saliency required.

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Introduction

• Main objectives
• Improve the Direct Torque Control, regarding
  torque ripple, using small vectors of Matrix
  Converters.
• Analysis of different High Frequency signal
  Injection methods for sensorless Direct Torque
  Control.

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State of the Art
Matrix Converters

• A switch, Sij, iA,B,C, ja,b,c can connect
  phase i of the input to phase j of the load.
• Switches states characterized by

A mathematical model of the MC can be derived

• Voltage equations

• Current equations

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State of the Art
Matrix Converters

• Since any output phase can be connected to any
  input phase, there are 27 possible switching
  configurations.
• Applying Clarks transformation to all switching
  states, it can be found that MC can generate
• 18 active vectors, 6 rotating vectors, and 3
  zero vectors.

Output line-to-neutral voltage vectors
Input line current vectors
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Direct Torque Control

• Stator flux ys and torque Te references are
  compared with the corresponding estimated values.
• Both stator flux and torque errors, Ey and ETe,
  are processed by means of hysteresis band
  comparators.

• A proper VSI voltage vector is selected.
• The flux vector reference and the hysteresis band
  tracks a circular trajectory, thus, the actual
  flux follows its reference within the hysteresis
  band in a zigzag path.

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Direct Torque Control using Matrix Converters
Classical DTC using Matrix Converters

• Matrix converter generates a higher number of
  output voltage vectors with respect to a VSI.
• Another variable, ltsin fgt, is introduced to
  control the input power factor.
• Keeping this variable close to zero, unity power
  factor operation is possible.

• A new hysteresis comparator is introduced which
  controls this variable.

Direct Torque Control for Induction Motors Using
Matrix Converters (CPE-05)
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Direct Torque Control using Matrix Converters
The use of small vectors of Matrix Converters

• A new torque hysteresis comparator will provide
  four different levels instead of three to
  distinguish between small and large positive and
  negative torque errors.

• Large vectors will be used when large torque
  error is detected.
• When torque error is small, the small voltage
  vector will be applied.
• Zero vectors will be applied if small torque
  error is detected and back EMF imposes a
  variation in torque towards its reference value.

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Direct Torque Control using Matrix Converters
The use of small vectors of Matrix Converters
Torque ripple performance. Comparison between the
classical use of MC in DTC and the proposed
method.
wref100 rated speed and TL100 rated torque.
Classical DTC using MC
Proposed method
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Direct Torque Control using Matrix Converters
The use of small vectors of Matrix Converters
Torque ripple performance. Comparison between the
classical use of MC in DTC and the proposed
method.

• The use of zero and large vectors in the
  classical method leads into an over/undershoot,
  more pronounced as the speed increases.
• Small vectors are more effective keeping the
  torque within the its reference bands.

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Sensorless Control
Saliency

• Asymmetry in the machine.
• Magnetizing inductance variation.
• Asymmetry in the rotor ? Rotor Position.

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Sensorless Control
a-b frame rotating injection.

• Straightforward in vector controlled drives.
• The carrier can be superimposed to the voltage
  reference.

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Sensorless Control
a-b injection in a DTC drive.

• Flux and Torque processed errors, Hys and HTe,
  converted directly to switching signals.
• No voltage command gt Difficult to inject.
• Injection directly modifying the vector pattern
  imposed by the DTC switching table.

• High bandwidth of hysteresis controllers.
• Difficult to inject outside of this bandwidth.
• Decoupling of fundamental and hf currents is
  necessary

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Sensorless Control
a-b injection in a DTC drive.
Comparison between real and estimated position
Steady state at 375 rpm
Speed reversal.
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Conclusions

• Advantages of Matrix Converters over the
  traditional VSI has been combined with the
  advantages of the DTC scheme.
• The use of small vectors of the MC has been
  investigated.
• High frequency injection in a DTC drive has been
  presented.

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• Thank you.