1. Sensorless Control for Symmetric Cage Induction Motor at Zero Frequency: building an experimental rig After 11 months of the 12-month Marie Curie EST fellowship at PEMC group School of Electrical & Electronic Engineering supervisors: Dr. M. Sumner, prof. G. Asher Matteo Tomasini PhD student at the Electric Drives Laboratory Dept. of Electrical Engineering University of Padova - Italy

2. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 2 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

3. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 3 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

4. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 4 Introduction To avoid these issues, many sensorless solutions have been proposed Fundamental Model based They fail to work at zero stator frequency Anisotropies based Asymmetries (intentional or not) Rotor slots (better on unskewed open/semiopen slots) Magnetic saturation Hi-freq. signal injection Hi-freq. excitation by PWM switching

5. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 5 eaea ebeb ecec lσalσa lσblσb lσclσc iaia icic ibib uaua ubub ucuc Rotor slot positionRotor position Rotor position estimation exploiting rotor slots anisotropy and Hi-freq excitation by PWM switching: Introduction

6. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 6 Control platform – Host interface RTDX (Real Time Data Exchange) + CCS (Code Composer Studio) + Host program (C, Matlab, Excel, …) FORGET IT!!! Incompatible with noisy environments HPI Interface board + Host program (C, Matlab, …) FPGA board Analog I/O Digital I/O PWM generation Dead time compensation TMS320C6713 DSK 32-bit floating point 225MHz DSP

7. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 7 Host interface for TMS320C6713 DSK HPI Interface board 40 Kbyte/s ( 1float @ 10kHz)

8. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 8 Host Interface for TMS320C6713 DSK graphical interface of my host program Virtual oscilloscope Try it!

9. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 9 Control platform – Inverter interface Protections + Galvanic insulation Measurement board

10. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 10 Measurement board From the inverter To the motor Phase A Phase B Phase C di/dt sensors di/dt signals conditioning: - voltage clamping; - low pass filtering; current measurements DC bus voltage measurement

11. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 11 Home-made di/dt sensor Sensitivity: 10.1 Vs/A

12. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 12 Time response of the Home-made di/dt sensor Current Home-made di/dt sensor shelf Rogowski coil di/dt sensor Sinusoidal current: 10Arms, 700Hz

13. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 13 Time response of the Home-made di/dt sensor with Low-pass filter >20 s Load: induction motor (V/f control @ 25Hz)

14. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 14 Minimum pulse width PWM time shifting of PWM signals V1V1 V2V2 V3V3 V4V4 V5V5 V6V6 V 0,7 Same VTA Standard symmetric PWM V0V0 V1V1 V2V2 V7V7 V2V2 V1V1 V0V0 t(V 1 )<t min t min a b c V0V0 V1V1 V2V2 V7V7 V2V2 V3V3 V0V0 t(V 1 )=t min Red arrows state di/dt sampling a b c

15. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 15 Example of di/dt measurement during null vector Note: improved Low-pass filtering on phase A. Noise < 0.5% of full scale

16. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 16 Real Time Dead Time Compensation Voltage error Note: 100ns 0.3V

17. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 17 Real Time Dead Time Compensation Big currentSmall current Positive current Negative current

18. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 18 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

19. 30 Ago - 1 Sep 2006EPE-PEMC 2006 - Portorož, Slovenia 19 Thank you for your attention! Matteo Tomasini PhD student at the Electric Drives Laboratory Dept. of Electrical Engineering University of Padova - Italy