19-07-2012, 12:09 PM
Microcontroller-Based Single-Phase Automatic Voltage Regulator
Microcontroller-Based_Single-Phase_Automatic_Voltage_Regulator.pdf (Size: 779.08 KB / Downloads: 249)
INTRODUCTION
The automatic voltage regulator or A VR, as the name
implies, is a device intended to regulate voltage
automatically: that is to take a varying voltage level and turn
it into a constant voltage level [4]. Automatic voltage
regulators are widely used in electrical power field to obtain
the stability and good regulation of the electric system. In
typical A VRs, switching is done by electromagnetic relays,
or servomotor, or electronic device, which automatically
selected taps in the transformer to get the required voltage to
boost (add) or buck (subtract) the input voltage. Relay tapchangers
have the problems such as power lost momentarily
during relay change over, unstable output and relay contact
damages. Servo motor types gave the disadvantages that they
have low life of the contact points of the relays [5]. Solidstate
electronic device used A VRs can overcome most of the
above problems as they do not use any moving part and the
output voltage can vary from cycle to cycle [1][3].
HARDW ARE IMPLEMENTATION AND OPERATION OF
THE SYSTEM COMPONENTS
The general operation of the components goes like this:
line voltage is stepped up to 400V using an autotransformer.
Zero crossing detection circuit provides a pulse to the PIC
whenever the line voltage reaches OV. After getting the zero
cross pulse, the PIC determines the delay to send a gatetrigger
pulse for the triac in accordance with the output of the
regulator terminal voltage. Triac, here, is used to control the
phase of the line voltage. The regulator terminal voltage is
always sensed and fed back to the PIC via a measuring unit.
SOFTWARE IMPLEMENTATION FOR THE CONTROL
UNIT
The firmware program for the microcontroller is
compiled with the PIC C Compiler Tool suite version 8.02
from HI-TECH Software. The source code is written in the
MPLAB IDE version 6.60 from Microchip Corporation. The
flow of the program, Fig. 5, goes like this: After initializing
the registers, the PIC waits till the zero crossing of ac cycle
reached in order to synchronize the timing of the program to
the ac mains.
As soon as the PIC accepts a zero cross pulse from the
zero cross detection circuit, it checks the status of the two
inputs, RAO and RA1 (pin 17 and 18). These two pins are
configured as over and under voltage indicators for regulator
terminal voltage. The PIC accepts the two output status of
the measuring unit, which senses the regulator terminal
voltage and feeds back it to the PIC.
CONCLUSION AND FUTURE WORK
This paper has covered the design and implementation of
microcontroller-based A VR. It is just an attempt to introduce
such an A VR of having different design and operation in
comparing currently available A VRs. As this design is
concerned with high voltage, care has been taken in choosing
suitable triac to withstand this high voltage. The uniqueness
of our design is that no moving part is present and as a result,
no maintenance is required. Moreover, lack of mechanical
devices enables our A VR not to be encountered with
disadvantages such as wear and tear of relay contact points,
fatigue of the transfonner taps, etc., which, but, can be found
in some typical A VRs.