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

Sensorless Controlfor Symmetric Cage Induction Motor

at Zero Frequency:building an experimental rig

After 11 months of the 12-month Marie Curie EST fellowship atPEMC group

School of Electrical & Electronic Engineeringsupervisors: Dr. M. Sumner, prof. G. Asher

Matteo Tomasini PhD student at the Electric Drives Laboratory

Dept. of Electrical EngineeringUniversity of Padova - Italy

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

Outline

Introduction Building the rig

Control platform – Host interfaceControl platform – Inverter interfaceMeasurements board

di/dt sensor

Minimum pulse width PWM Real Time Dead Time Compensation Conclusions


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 complexityHigher cost Increased size of the motorSensor cablePossibility of noise issuesLess reliability / more maintenance Incompatibility with hostile environment


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


2 ( , , )d

fdt i

u l e

1( , , ) rotor position, field angleqf i lea

ebec

lσa

lσblσc

ia

ic ib

ua

ubuc

, ,a b cdi di di

dt dt dt

Rotor slot position Rotor position

Rotor position estimation exploiting rotor slots anisotropy and Hi-freq excitation by PWM switching:

Introduction


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/ODigital I/OPWM generationDead time compensation

TMS320C6713 DSK32-bit floating point 225MHz DSP


Host interface for TMS320C6713 DSK

HPI Interface board

40 Kbyte/s(≈ 1float @ 10kHz)


Host Interface for TMS320C6713 DSK

graphical interface of my host program

Virtual oscilloscope

Try it!


Control platform – Inverter interface

Protections+

Galvanic insulation

Measurement board


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


Home-made di/dt sensor

Sensitivity: 10.1Vs/A


Time response of the Home-made di/dt sensor

Current

Home-made di/dt sensor

shelfRogowski coil

di/dt sensor

Sinusoidal current: 10Arms, 700Hz


Time response of the Home-made di/dt sensor with Low-pass filter

50 100 150 200 250 300-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

time [s]

current (0.2x)di/dt Rogdi/dt my

>20s

Load: induction motor (V/f control @ 25Hz)


Minimum pulse width PWM

time shifting of PWM signals

V1

V2V3

V4

V5 V6

V0,7

Same VTA

Standard symmetric PWM

V0 V1 V2 V7 V2 V1 V0

t(V1)<tmin

tmin

a

b

c

V0 V1 V2 V7 V2 V3 V0

t(V1)=tmin

Red arrows state di/dt sampling

a

b

c


Example of di/dt measurement during null vector

0 20 40 60 80 100 120 140 160 180 200-300

-200

-100

0

100

200

300

time [ms]

A2D

converters

outp

ut (range: 2

048)

di/dt samples during null vector. fe = 5Hz, no load

dia/dt

dib/dtdic/dt

Note: improved Low-pass filtering on phase A. Noise < 0.5% of full scale


Real Time Dead Time CompensationVoltage error

Note: 100ns ↔ 0.3V

-10 -8 -6 -4 -2 0 2 4 6 8 10-15

-10

-5

0

5

10

15

Current [A]

Ua - U

a*

[V]

DeadTime compensation: V/f control (f = 2.5Hz, fSW

= 5kHz, DT = 3.5s, Udc

= 620V)

No DT comp

current sign onlycurrent sign & ampl


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


Thank you for your attention!

Matteo Tomasini

PhD student at the Electric Drives Laboratory

Dept. of Electrical Engineering

University of Padova - Italy

Documents

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