sensorless control for symmetric cage induction motor at zero frequency: building an experimental...
TRANSCRIPT
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
30 Ago - 1 Sep 2006 EPE-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 complexityHigher cost Increased size of the motorSensor cablePossibility of noise issuesLess reliability / more maintenance Incompatibility with hostile environment
30 Ago - 1 Sep 2006 EPE-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
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 5
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
30 Ago - 1 Sep 2006 EPE-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/ODigital I/OPWM generationDead time compensation
TMS320C6713 DSK32-bit floating point 225MHz DSP
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 7
Host interface for TMS320C6713 DSK
HPI Interface board
40 Kbyte/s(≈ 1float @ 10kHz)
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 8
Host Interface for TMS320C6713 DSK
graphical interface of my host program
Virtual oscilloscope
Try it!
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 9
Control platform – Inverter interface
Protections+
Galvanic insulation
Measurement board
30 Ago - 1 Sep 2006 EPE-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
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 11
Home-made di/dt sensor
Sensitivity: 10.1Vs/A
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 12
Time response of the Home-made di/dt sensor
Current
Home-made di/dt sensor
shelfRogowski coil
di/dt sensor
Sinusoidal current: 10Arms, 700Hz
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 13
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)
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 14
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
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 15
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
30 Ago - 1 Sep 2006 EPE-PEMC 2006 - Portorož, Slovenia 16
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
30 Ago - 1 Sep 2006 EPE-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
30 Ago - 1 Sep 2006 EPE-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