Pontifical Catholic University of the Rio Grande do Sul Brazil Didactic Platform for Study of AC-AC Converters Dos Reis, F. S.; Lima, J. C.; Fuentefria, F. B.

Table of Contents  INTRODUCTION  BLOCK DIAGRAM  OBJECTIVE  COMMAND AND POWER CIRCUIT  SOURCE AND ZERO DETECTOR  CONTROL CIRCUIT  EXPERIMENTAL RESULTS  CONCLUSIONS

INTRODUCTION The didactic platform to study AC-AC converters, is composed by three basic stages: The command and power circuit integrated; Source and main’s zero detector circuit for system synchronism; Control circuit based on a microcontroller.

OBJECTIVE The main objective of this paper is to relate the development of a flexible didactic platform to study the AC-AC converter, looking for to propitiate with this system a better understanding of the operation of AC-AC converters through a practical experience.

BLOCK DIAGRAM Motor Vcc Start Stop Isolation µC Thyristor Zero Detector Time Base RS-232

COMMAND AND POWER CIRCUIT - 1  The command signals are applied in the power stage using optocouplers, isolating it from the control circuit ;  The power stage is contituted by six thyristors antiparallel connected;  This arrangement may be used as a three-phase AC-AC converter or like three single-phase AC-AC converter, which may be independently controlled.

COMMAND AND POWER CIRCUIT - 2 X5 TIC J3 Phase B 1 2 R7 330 R9 330 R2 390 X3 TIC J1 Input D41N Vcc R8 390 X6 TIC X7 TIC R3 330 R6 330 Vcc J4 Phase C 1 2 D21N X8 TIC U3 MOC R Vcc R R R1 330 D1 1N D3 1N J2 Phase A 1 2 U2 MOC R5 390 U1 MOC D61N Vcc D5 1N R4 330 X4 TIC

SOURCE AND ZERO DETECTOR - 1  This stage was elaborated with the utilization of a step down transformer 110/220V to 12V, used in the power supply and in the zero detector circuit;  In each main cycle two pulses are generated, each one in the beginning of each half cycle;  The microcontroller receives these pulses, which are used as time reference for the thyristor command.

SOURCE AND ZERO DETECTOR - 2

CONTROL CIRCUIT - 1  The control is made using the phase angle control;  An 8051 Atmel AT89C52 was used to control the system;  The microcontroller receives the synchronism information by the zero detector and processes it, giving the proper thyristors phase angle and generates the pulses for the thyristors appropriately;

CONTROL CIRCUIT - 2  The ON/OFF control and the Softstart for AC motors were also implemented in this platform;  To implement this circuits, the control needs to temporize the zero detector pulses using interruptions;  A PC may program several positive or negative acceleration curves, obtained through the continuous phase angle variations;

CONTROL CIRCUIT - 3  The platform can operate autonomously or have its program changed directly though a PC using its RS-232 serial interface;  For autonomous operation the plataform incorporates a display and a small keyboard that allows programming the parameters.

CONTROL CIRCUIT - 4

EXPERIMENTAL RESULTS - 1  For a didactic classroom use of the platform a simple load assembly using incandescent light bulbs was made;  The three phase thyristors had been tuned on correctly;

EXPERIMENTAL RESULTS - 2  The voltage and current in the loads can be easily measured with the aid of a multimeter and an oscilloscope ;  Full developed didactic platform.

CONCLUSIONS - 1  This work is inserted in the context of a solid pedagogic proposal for the Power Electronics teaching, based on the theoretical practical experience mainly in the field of the AC converters;  The system now presented is inserted in a wider proposal, started with a didactic kit family, elaborated for the study of rectifiers circuits and inverter circuits;

CONCLUSIONS - 2  After the implementation of these kits an expressive improvement of the learning process was observed, obtaining high approval indexes different from what happened when the discipline was presented in the traditional way;

CONCLUSIONS - 3  We would like to remark the importance of the popularization of this kind of work, that approaches pedagogic aspects and is concerned with the formation of a new methodology of teaching the Power Electronics disciplines;

CONCLUSIONS - 4  The versatility of the platform and great economy obtained in relation to the available educational kits found on the market are additional advantages of the proposed system.