Puestos de trabajo.

Design and Implementation of Single Phase Fully Controlled Bridge Rectifier Using PIC Microcontroller

C.B. Erney Fabian1, P.P. Diego Alejandro2

Pregrade Student, Dept. of Electromechanical Engg, Francisco of  Paula Santander University, Cúcuta, North of Santander, Colombia1

Pregrade Student, Dept. of Electromechanical Engg, Francisco of  Paula Santander University, Cúcuta, North of Santander, Colombia 2

ABSTRACT: In order to advance in the  firing  angle control of  thyristors  in the single phase fully controlled bridge rectifiers through the actual technology this paper presents a method for obtaining  a regulated dc voltage through digital control. This lineal dc voltage is obtained through the control of phase angle of thyristors with a PIC microcontroller of low gamma. The algorithm control is programmed in C language and the results are verified for different types of load.

KEYWORDS: PIC Microcontroller, fully controlled bridge rectifier, Phase Angle, Isolation Circuit, C language.

I.INTRODUCTION

The firing control  of thyristors for single phase fully controlled rectifiers is based mainly in two strategies of control, the first is cosine control and the second is  the already meet ramp type control these strategies are explained in [1].

These forms of firing are implemented through a ample circuitry which occupy large space in electronics targets besides possess a high cost. In order to contribute in the improvement of firing control of thyristors. This paper presents  a strategy of digital control to control  the firing phase angle of  thyristors in single phase fully controlled bridge rectifiers implemented through a PIC microcontroller.

II. PROPOSED DIGITAL CONTROL

Digital control proposed and implemented in this research work consist  in the activation adequate of thyristors in single phase fully controlled rectifiers  through an algorithm based in the logic necessary to achieve a correct performance of converter. Figure 1 shows the block diagram of control circuit. Microcontroller is used to control one to one the phase angles of thyristors, to read an external interruption from zero crossing detector circuit and too is used to read a analog  signal proportioned for  a potentiometer which will be read for the microcontroller and according to this reading it will be obtained a phase angle determined.

                                                                                                                 Converter[pic 2][pic 3][pic 4]

           AC                         Load[pic 5][pic 6][pic 7][pic 8][pic 9][pic 10][pic 11][pic 12]

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Fig. 1 Basic diagram of firing control circuit

III. SOFTWARE AND HARDWARE

A. Microcontroller

Microcontroller PIC12f675 is used to implement the development of control algorithm. An analogous input and a digital input in addition to the two digital outputs  for the control pulses are used in the microcontroller.The microcontroller performs its operation using  5v of supply.

B. Software

Control algorithm is developed in  embedded C language. The compilation of executable software code is achieved using a test version of  the CCS compiler.

IV. METHODOLOGY

A. Control Voltage 0-5 V

The control voltage of  firing angle  of  thyristors  will be from 0 to 5v, a voltage of zero for 0° and a voltage   of  five for 180°, this voltage  voltage will be provided through the  reading  of  an existent voltage in a potentiometer fed to 5 volts.

B. Zero Crossing Detector Circuit

Zero crossing detector circuit is designed to obtain the digital signal which will indicate to microcontroller the existance of  an extern interruption. Zero crossing detector circuit used is shown in Fig.2

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Fig. 2  Zero crossing detector circuit

C. PIC Microcontroller

PIC Microcontroller   uses  a  analog port  for reading  a  analog signal   of  a potentiometer  with a magnitude between 0 to 5 volts. Control circuit is shown in Fig.3. This analog value read for the channel 0 is converted a digital magnitude which is used as input for the INT pin which permits  to read external interruptions. When a change of  high to low in this pin is detected, it execute of immediate  a subroutine which is used to control the phase angle of  the  thyristors used in this converter. Figure 4 shows the flowchart of control digital implented in the microcontroller.

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        Fig. 3  Control circuit

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                                      No[pic 32]

        If

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End

Fig. 3  Flowchart  of digital control

E. Production of  Control Pulses

The production of control pulses of thyristors is gobernated for the algorithm  of control.//The duration of each  control pulse in a high logic state is same to10us and its position is varied in a axis t from 0 to 8.33ms.This instant determined will depend  of  the  analog reading of voltage existent in the potentiometer that will be realized each time exists  a external interruption in the microcontroller, for this reading it uses the ADC (analog  to digital converter) of 16 bits of microcontroller. This analog reading  is converted in a digital measure through convertor   which is after multiplied by a factor of adjust to obtain the instant of time determined to activate any thyristor.  

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