Reiko Raute

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Sensorless Control of Induction Machines by Using
PWM Harmonics for Rotor Bar Slotting Detection

• Reiko Raute

Dr. Mark Sumner Dr. Cedric Caruana Prof. Greg
Asher Dr. Cyril Spiteri Staines Dr. Joseph
Cilia
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Outline of Presentation

• 1. PWM Carrier Harmonic Analysis
• 2. Equivalent Impedance Measurement with PWM
  Harmonics
• 3. Rotor Bar Modulation
• 4. Saturation Modulation
• 5. Rotor Position Reconstruction
• 6. Results
• 7. Conclusions

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• 1. PWM Carrier HarmonicAnalysis

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1. PWM Carrier HarmonicAnalysis

• PWM strategy
• Fundamental voltage vector
• PWM2 HF voltage vector

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1. PWM Carrier HarmonicAnalysis

• Machine run at rated torque with 30 rpm in vector
  control
• Machine parameters
• Power 5.5 kW
• Pole pairs 2
• Rotor bars 32
• Rated id 7.6 A
• Rated iq 12.5 A
• Voltage 415V (D)
• fPWM 1.818 kHz
• fADC 30 kHz
• All signals filtered
• through a 4th order
• anti aliasing filter
• fc10 kHz

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1. PWM Carrier HarmonicAnalysis

• Spectrum of machine voltage over time

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• 2. Equivalent Impedance Measurement with PWM
  Harmonics

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2. Eq. Impedance Measurement with PWM Harmonics

• Demodulation and impedance vector zPWM2
  calculation

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• 3. Rotor Bar Modulation

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3. Rotor Bar Modulation

• Rotor bar modulation with rotating PWM2 HF vector

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• 4. Saturation Modulation

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4. Saturation Modulation

• Machine operated at steady state with 30 rpm and
  rated load

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4. Saturation Modulation

• Machine operated at steady state with 30 rpm and
  rated load

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• Rotor PositionReconstruction

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5. Rotor PositionReconstruction

• Reconstruction of rotor position from zPWM2
  modulation

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5. Rotor PositionReconstruction

• PLL1 block diagram

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5. Rotor PositionReconstruction

• PLL2 block diagram

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• 6. Results

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6. Results

• Sensorless torque control (0100) at -52 rpm

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6. Results

• Sensorless torque control (100) at ?300 rpm

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6. Results

• Sensorless speed control between ?60 rpm

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6. Results

• Sensorless position control between ?1 mechanical
  revolution

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• 7. Conclusions

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7. Conclusions

• A principle of detecting rotor position
  information from machine saliency has been
  suggested that uses only the PWM carrier
  harmonics.
• It was found that the 2nd PWM harmonic shows the
  strongest signal which forms a pulsating HF
  vector rotating with the fundamental frequency.
• The PWM2 voltage and current harmonic vectors are
  used to calculate an equivalent impedance vector
  zPWM2 which shows clear rotor bar modulation and
  also saturation effects.
• The saturation effect is decoupled by using a
  simple look up table. The rotor bar modulation is
  tracked by a PLL system that gives a mechanical
  speed and position estimate as output. This is
  used for sensorless control.
• Fully sensorless operation in torque, speed and
  position control have been achieved with a
  standard of-the-shelf 5.5 kW induction machine.
• The drive dynamic is limited due to non-linear
  behavior of the saturation effect in the real
  part of zPWM2 during torque transients. The use
  of the weighted PLL input has improved the
  performance and additional techniques, e.g. a
  mechanical observer may allow a further
  improvement of the drive dynamics.