Design of Control Circuit Using PIC Microcontroller for Automatic Power Factor Correction

: The power quality of AC systems has been a key issue in recent years because to the ever-increasing quantity of electronics equipment, power electronic equipment, and high voltage power systems. The majority of industrial installations in countries have substantial inductive electrical loads, resulting in a lagging power factor that has serious effects for energy users. As a result, reactive power compensation must be performed in the proper manner. Hence, we worked on this project and created Automatic Power Factor Correction (APFC) system using the PIC18f4520 microcontroller. APFC device measures the power factor, line voltage, and line current. The power factor is calculated using the system's voltage and current, and if it falls below a specified value defined by the utility provider, the device immediately activates capacitor banks to compensate for the reactive power. The phase angle and corresponding power factor are calibrated at that time. The mother board calculates the required compensation and activates the appropriate capacitor banks. This strategy can be used to increase the system's stability and efficiency in both industries and homes.


I. INTRODUCTION
In electrical systems, the power factor is crucial because it dictates how efficiently electrical power is utilized by the load.P.F is a quantity that doesn't have any units attached to it.A resistive load with a power factor of 1 is the most efficient, but if the power factor is lagging, the efficacy of electrical power is reduced, resulting in bigger losses and higher expenditures for customers.[1] Inductive load consumption is high in industries, necessitating reactive power for current magnetization.This reactive power isn't used in any way.As a result, more electricity is required to run a machine beyond its maximum capacity.This results in a low trailing power factor, which can cause voltage fluctuations, power outages, operational losses, increased electricity bills, and utility penalties.[2][3] APFC panels also help to overcome this problem by keeping the power factor near to unity.The ratio of the real power absorbed by the load to the apparent power flowing in the circuit is the power factor of an ac power system.[4] PF= Active Power Apparent Power The amount of actual power used in a circuit is known as active power (P).The measurement units are watts.
Reactive power is the amount of energy consumed in an ac circuit due to inductive and capacitive fields.Reactive power is measured using the VAR unit.The outcome of combining active and reactive power is apparent power.The units of measurement are volts-amps.[5] [VA] It has greater strength than both active and reactive power.
By raising the power factor of a connected load, power factor correction increases the efficiency of the distribution system to which it is connected.[6-7]Linear loads with poor power factor can be improved with the help of a passive network of capacitors or inductors.Non-linear loads, such as rectifiers, induce a distortion in the current pulled from the system.There are three methods for increasing power factor: 1. Bank of Capacitors 2. Synchronous Condensers 3. Advancers in Phases To rectify the power factor, this system employs capacitor banks.One technique to improve power factor is to reduce the phase angle between voltage and current.A capacitor or bank of capacitors connected in parallel with the load provides this reactive power.[8] Less reactive power flows across the line as a result of their role as a reactive power source.Capacitor banks are used to reduce the phase difference between voltage and current.

III. COMPONENTS 3.1 Potential Transformer
A potential transformer (P.T.) is used in this project.It is a type of instrument transformer used to protect and measure electricity systems.A potential transformer is used to step down the incoming higher level primary voltage and secondary voltage to lower primary and secondary voltage.It is connected in parallel with the circuit.440 V ac voltage is fed to the transformer and it will reduce voltage upto 5V.

Current Transformer
A current transformer is a device that changes the quantity of alternating current in a circuit by reducing or multiplying it.It generates a secondary current that is proportional to the primary current.The current transformer measures the high current drawn from the supply.It is connected in series with the circuit.5A CT is used for the system.The reason of using CT in the project is Op-amp needs current less than 50mA.

Relay
A relay is a switch that is activated or deactivated by electricity.The relay's input terminals can be set to accept a single or several control signals.The switch can have an infinite number of contacts, as well as any combination of contact types, such as make, break, and combination contacts.12V relay is used in the system.The main function of relay in this system is switch on and switch off of capacitor banks according to the improvement in power factor.

PIC18F4520
The main part of this project is PIC18f4520 microcontroller.By using algorithm microcontroller does function for the system.The PIC18F4520 is a 40-pin, fully-static 8-bit microcontroller with 36 I/O pins.It's low-cost, low-power, fast, and completely static.With a programming range of 4 to 131 milliseconds, it has Power-on-Reset (POR) and Extended Watchdog Timer (WDT) circuits.It is ideal for low-power applications because of its Power Management features.There are three power management options to choose from.
1. Running Mode 2. 2.Sleep mode 3. Inactive mode 4.7 Operational Amplifier An operational amplifier is a DC-coupled high-gain electronic voltage amplifier having a differential input and, in most cases, a single-ended output.Operational amplifiers were first used in analogue computers to perform mathematical operations in linear, nonlinear, and frequency-dependent circuits.The main function of an Op-amp is to amplify the differential between two inputs and result output.It has two terminals v+ and v-.when the input at v+ is more than v-then output is positive signal and when the input at v-is more then output is negative signal.

Zener Diode
A zener diode is a type of diode that allows current to flow backwards once a certain reverse voltage, known as the Zener voltage, is reached.In small circuits, zener diodes are widely used as voltage references and shunt regulators.

Voltage Regulator
Voltage regulators generate and maintain a consistent output voltage regardless of load or supply input fluctuations.Voltage regulators keep power supply voltages within a safe range for other electrical components.The regulators used in this project are 7805,7812,7912.

Capacitors
In this project the capacitors are used for filtering purpose and to reduce harmonics.Capacitor bank is used to provide the reactive power to the inductive load and increase the voltage according to system strength.It is connected through contactors and relays.Capacitors used in system are 2200µf,220µf,1000µf.

Push Button Or Keys
This system uses keys to set the value of power factor .The four keys are as follows: SET, UP, DOWN, ENTER.Controller is protected by password .Password is set by using these keys.Fig. 2. CT and PT connection and current measurement Fig. 3 VI.WORKING The developed system consist of voltage sensing unit, current sensing unit, data collection and calculation unit, and display the output.Two phases of the supply are connected to PT, which provides voltage, and one phase is connected to CT, which provides current.440 AC voltage is fed to PT and this voltage is step down to 5V which is given to diode.Diode is used as a rectifire which converts ac voltage into pulsating DC.Voltage regulators maintains the DC voltage which is fed to the microcontroller.CT measures the high current and then it converts high current into low current.Because Op-amp requires low current.The PIC microcontroller receives the PT and CT data.These values are sensed by the PIC controller, which is coupled to the relays.PIC microcontroller uses algorithm for the calculation of power factor .It compares the measured pf with the set value which is already set by user using keys.When the system's P.F drops below the set point, the relay activates, sending a signal to the contactor, which activates the capacitor banks.When capacitor banks are turned on, lagging is eliminated, and by increasing capacitance, P.F improves, and the system becomes more stable and efficient.When the connected load is purely resistive then the PF is nearly equal to unity.To improve the PF relay driver will ON the capacitor banks and their respective LED will get ON.9.2 PF at Inductive Load
Figure 4: Working Model