Sensorless Control for Symmetric Cage Induction Motor at Zero Frequency: building an experimental ri

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Sensorless Controlfor Symmetric Cage Induction
Motorat Zero Frequencybuilding an experimental
rigAfter 11 months of the 12-month Marie Curie
EST fellowship atPEMC groupSchool of Electrical
Electronic Engineeringsupervisors Dr. M.
Sumner, prof. G. AsherMatteo Tomasini PhD
student at the Electric Drives LaboratoryDept.
of Electrical EngineeringUniversity of Padova -
Italy
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Outline

• Introduction
• Building the rig
• Control platform Host interface
• Control platform Inverter interface
• Measurements board
• di/dt sensor
• Minimum pulse width PWM
• Real Time Dead Time Compensation
• Conclusions

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Introduction

• For most kind of controls, rotor speed is
  necessary to control induction motors
• Position sensors are available on the market, but
  they involve
• More hardware complexity
• Higher cost
• Increased size of the motor
• Sensor cable
• Possibility of noise issues
• Less reliability / more maintenance
• Incompatibility with hostile environment

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Introduction

• To avoid these issues, many sensorless solutions
  have been proposed

Fundamental Model based
Anisotropies based

• Asymmetries (intentional or not)
• Rotor slots (better on unskewed
• open/semiopen slots)
• Magnetic saturation

They fail to work at zero stator frequency

• Hi-freq. signal injection
• Hi-freq. excitation by PWM switching

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Introduction
Rotor position estimation exploiting rotor slots
anisotropy and Hi-freq excitation by PWM
switching
Rotor slot position
Rotor position
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Control platform Host interface
TMS320C6713 DSK 32-bit floating point 225MHz DSP
Analog I/O Digital I/O PWM generation Dead time
compensation
HPI Interface board Host program (C, Matlab, )
FPGA board
RTDX (Real Time Data Exchange) CCS (Code
Composer Studio) Host program (C, Matlab,
Excel, )
FORGET IT!!! Incompatible with noisy environments
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Host interface for TMS320C6713 DSK
HPI Interface board
40 Kbyte/s ( 1float _at_ 10kHz)
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Host Interface for TMS320C6713 DSK
Virtual oscilloscope
Try it!
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Control platform Inverter interface
Protections Galvanic insulation
Measurement board
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Measurement board
From the inverter
Phase A
Phase B
Phase C
di/dt sensors
To the motor
DC bus voltage measurement
di/dt signals conditioning - voltage clamping
- low pass filtering
current measurements
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Home-made di/dt sensor
Sensitivity 10.1mVs/A
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Time response of the Home-made di/dt sensor
Home-made di/dt sensor
Current
shelf Rogowski coil di/dt sensor
Sinusoidal current 10Arms, 700Hz
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Time response of the Home-made di/dt sensor with
Low-pass filter
gt20ms
Load induction motor (V/f control _at_ 25Hz)
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Minimum pulse width PWM
time shifting of PWM signals
Standard symmetric PWM
Same VTA
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Example of di/dt measurement during null vector
Note improved Low-pass filtering on phase A.
Noise lt 0.5 of full scale
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Real Time Dead Time CompensationVoltage error
Note 100ns ? 0.3V
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Real Time Dead Time Compensation
Big current
Small current
Negative current
Positive current
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Conclusions

• Fully satisfied of the whole system
• Good quality of the di/dt signals (unless spikes)
• Good performance of the Real Time Dead Time
  Compensation
• Weakness quite long settling time for current
  derivative
• Next step
• Extract the rotor position from di/dt signals

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Thank you for your attention!
Matteo Tomasini PhD student at the Electric
Drives LaboratoryDept. of Electrical
EngineeringUniversity of Padova - Italy