10th European Conference on Power Electronics and

Applications

September 2 – 4, 2003 Toulouse, France

A low cost solution for laboratory experiments in

induction motor control Rui Esteves Araújo(1), Américo Vicente Leite(2), Diamantino Silva Freitas(1)

(1) Faculdade de Engenharia da Universidade do PortoRua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal

(2) Instituto Politécnico de Bragança - Escola Superior de Tecnologia e de GestãoCampus de Sta. Apolónia - Apartado 134, 5301-857 Bragança, Portugal

DS1.1 - 485

Abstract In this poster we present a controller suitable for educational activities in electric drives. A prototype has been designed specifically to meet the requirement of low cost and it contains all of the active functions required to implement the open loop control of an induction motor. In this way, the prototype allows the easy assimilation of important concepts and enables the understanding of the enclosed subsystems.

Keywords: Education tools, laboratory experiments,electric drives.

1. Introduction and motivation The teaching Power Electronics and Electric Drives requires a degree of abstraction which challenges even the most talented student. This is probably one of the reasons for a steadily decreasing number of students in Power Electronics and Electric Drives classes all over the world.

Simply following one of the most general principles of live, the majority of students choose the lowest impedance path through their curricula. To make it all fit, in some cases, it is possible to sacrifice: rigor for vigor and specific details for general principles.

Telecommunications and Computer science profit of a strong interest in the students and can distort the real necessities of engineers in industrial sector.

The purpose of this prototype is not centred on achieving a great dynamic performance of the induction motor control, but on highlighting the main concepts of this issue and leading the students to play with the system and practice in laboratory measurements.

An analogue electronic hardware realization uses the know-how of linear and switching electronics already acquired by the students in previous courses as well as to provide skills in electronic design.

2. The hardware prototypeIt consists of three main sub-systems:

Ramp limiter

Logic anddeadtime

U f

Ua

Ref .

Quadrature sinusoidal oscillat or

cos

sin

start, stopreset

fault, measures

Command,measures and

protection

Comparatorsdq

abc

IM

3 ~

Load

R S T

Power m

odule

Briver board

Powerboard

Controllerboard

Opto-isolationboard

The controller board implements an open loop voltage/frequency control that has been chosen because of its simplicity. A voltage controlled quadrature sinusoidal oscillator generates a two-phase system followed by two analogue multipliers for amplitude modulation and speed inversion. These 90 degree sine and cosine signals are converted into an equivalent three-phase reference system which is compared with the carrier to generate the IGBT’s pulses.

The isolation boaris based on the HCPL2611 opto-couplers

The power boardis based on International Rectifier’s IRMDAC3 Design Kit

Fig. 1. Block diagram of the present prototype.

3. Experimental results

Fig. 2. Some results: (a) DC voltages for frequency and amplitude control of the quadrature sinusoids versus DC input voltage

control ; (b) the three-phase reference system of voltages in a speed reversal; (c) the three phase sinusoidal reference and carrier

signals; (d) the two quadrature sinusoids in an speed reversal ; (e) speed reversal ; (f) the inverter output line-to-line voltage.

12k

12V 12V

X1

X2

Y1Y2

Z1

Z2

MPY100

outX1

X2

Y1Y2

Z1

Z2

MPY100

out

22

12k

12V 12V

22

47k 47k

4.7M

220k470

4.7k

2.2k10k

-15V+15V47k47k 20k

4.7k

2.2k10k

-15V+15V47k47k 20k

(10V) sin(t)

(10V) cos(t)

Input DCvoltage forfrequency

control

A

B

A

B

C

D

E

1k

110k

10k

10k

10k 5k

10k

+15V

-15V10k10k 10k

10k

10k

10k

10V 10V

-15V10k10k 10k

10k

10k

10k

1k

1

1k

11

ref., speedreference:

-10V to 10V

frequency control

amplittudecontrol

A

B

CD

E

FG

4. Conclusions The developed hardware prototype allows the easy assimilation of different concepts and enables the understanding of the enclosed subsystems in order to stimulate the student interest in power electronics as well as to provide him (her) with practical electronic design.

Regarding the disinterest of students in front of Power Electronics and Electric Drives, we have explained what is our actual policy in laboratory to attract them into this domain by using the control system to play with work aiming a practical understanding and exercising of the actual concepts.

Fig. 3. Electronic circuit for amplitude modulation including rotor speed inversion.

Fig. 4. Block diagram of the present prototype.