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How to make a Automatic Power Factor Controller using micro

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How to make a Automatic Power Factor Controller using micro

by Ashika Wed Oct 02, 2013 4:37 am

The thirst for new sources of energy is unquenchable, but we seldom realize that we are wasting a part of the electrical energy every day due to the laggingpower factor in the inductive loads we use. Hence there is an urgent need to avoid this wastage of energy.

Before getting into the details of Power factor correction, lets just brush our knowledge about the term power factor. In simple words power factor basicallystates how far the energy provided has been utilized. The maximum value of power factor is unity. So closer the value of P.F to unity, better is the utility ofenergy or lesser is the wastage. In electrical terms Power factor is basically defined as the ratio of the active power to reactive power or it is the phase differencebetween voltage and current. Active power performs useful work while React ive power does no useful work but is used for developing the magnetic field

required by the device.

Most of the devices we use have power factor less than unity. Hence there is a requirement to bring this power factor close to unity. Here we are presenting aprototype for automatic power factor correction using PIC Microcontroller.

Circuit Diagram

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Working

Comparator Section

The 230 V, 50 Hz is step downed using voltage transformer and current transformer is used to extract the waveforms of current. The output of the voltagetransformer is proportional to the voltage across the load and output of current transformer is proportional to the current through the load. These waveforms arefed to Voltage Comparators constructed using LM358 op-amp. Since it is a zero crossing detector, its output changes during zero crossing of the current andvoltage waveforms. These outputs are fed to the PIC which does the further power factor calculations.

Microcontroller Section

PIC 16F877A microcontroller is the heart of this Automatic Power Factor Controller, it find, displays and controls the Power Factor.. To correct power factor,first we need to find the current power factor. It can be find by taking tangent of ratio of time between zero crossing of current and voltage waveforms and twosuccessive zero crossing of voltage waveform. Then it displays the calculated power factor in the 162 LCD Display and switches ON the capacitors if required.

Correction Section

When load is connected the power factor is calculated by the PIC microcontroller. If the calculated power factor is less than 0.9 then the relay switches on thecapacitor. The relays are switched using ULN2003 which is basically a driver IC. ULN2003 consists of seven DARLINGTON PAIRS.

The current lead in capacitor compensates the corresponding current lag which is usually present in loads. Hence the phase difference between the current andvoltage will be reduced.

Power Factor Correcting capacitor connected parallel to load through relay, if the relay is energized by microcontroller it will connect the capacitor parallelwith load, if relay deenergized it will remove the capacitor from the load. When the resistive load is on the power factor will be near to unity so themicrocontroller doesnt energize the relay coil. When the inductive load is on the power factor decrease now the microcontroller energize the relay coil in orderto compensate the excessive reactive power. Hence according to the load the power factor is corrected.

MikroC Program

Code: Select all//LCD Module Connectionssbit LCD_RS at RB4_bit;sbit LCD_EN at RB5_bit;sbit LCD_D4 at RB0_bit;sbit LCD_D5 at RB1_bit;sbit LCD_D6 at RB2_bit;sbit LCD_D7 at RB3_bit;sbit LCD_RS_Direction at TRISB4_bit;sbit LCD_EN_Direction at TRISB5_bit;sbit LCD_D4_Direction at TRISB0_bit;sbit LCD_D5_Direction at TRISB1_bit;sbit LCD_D6_Direction at TRISB2_bit;sbit LCD_D7_Direction at TRISB3_bit;

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//End LCD Module Connectionsint powerFactor(){ int a=0,b=0,t=0,x=0; float tm,pf; TMR1L=0; TMR1H=0; do{

if(PORTA.F0 == 1) T1CON.F0 = 1; else if(PORTA.F0 == 0 && T1CON.F0 == 1){

T1CON.F0 = 0;break;

} }while(1); a = (TMR1L | (TMR1H

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Article courtesy of electrosome.com

Ashika

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