MICROCONTROLLER BASED POWER FACTOR MEASUREMENT AND CORRECTION : MICROCONTROLLER BASED POWER FACTOR MEASUREMENT AND CORRECTION Prepared By
Rahul L. Tiwari
ELETRONICS DEPARTMENT BASIC FORMULAE : BASIC FORMULAE POWER POWER FACTOR : POWER FACTOR DEFINITION:
Power factor (P.F) is the ratio between actual power to the apparent power.
Actual power/Apparent power.
For a purely resistive load the power factor is unity. Active and reactive power are designated by P &Q respectively. The average power in a circuit is called active power and the power that supplies the stored energy in reactive elements is called reactive power. POWER FACTOR DEFINITION : POWER FACTOR DEFINITION Inductive loads cause the current to lag behind the voltage. The wave forms of voltage and current are then "out of phase" with each other. The more out of phase they become then the lower the Power Factor. Power Factor is usually expressed as Cos Phi. (Ø) Slide 5: Consider a canal boat being pulled by a horse.
If the horse could walk on water then the angle (Phi) Ø would be zero and COSINE Ø=1. Meaning all the horse power is being used to pull the load. However the relative position of the horse influences the power. As the horse gets closer to the barge, angle Ø1 increases and power is wasted, but, as the horse is positioned further away, then angle Ø2 gets closer to zero and less power is wasted. Slide 6: Active Power:
Also known as “real power” or simply “power.” Active power is the rate of producing, transferring, or using electrical energy. It is measured in watts and often expressed in kilowatts (KW) or megawatts (MW). The terms “active” or “real” power are used in place of the term “power” alone to differentiate it from “reactive power. Apparent Power:
The product of the voltage (in volts) and the current
(in amperes). It comprises both active and reactive power .
It is measured in “volt-amperes” and often expressed in
“ kilovolt-amperes” (KVA) or “megavolt-amperes” (MVA). POWER FACTOR : POWER FACTOR kVA = (KW)2 + (KVAR)2 1. When the current & the voltage waveforms are in phase as shown then corresponding power waveform of an electric network is as shown . : 1. When the current & the voltage waveforms are in phase as shown then corresponding power waveform of an electric network is as shown . 2. When the current & the voltage waveforms are out of phase then corresponding power waveform of an electric network is as shown in green : 2. When the current & the voltage waveforms are out of phase then corresponding power waveform of an electric network is as shown in green EFFECT OF INDUCTIVE LOAD : EFFECT OF INDUCTIVE LOAD CAUSES OF LOW POWER FACTOR : CAUSES OF LOW POWER FACTOR A poor power factor can be the result of either a significant phase difference between the voltage and current at the load terminals or it can be due to a high harmonic content or distorted/discontinuous current waveform. Poor load current phase angle is generally the result of Poor load current phase angle is generally the result of an inductive load such as an induction motor power transformer, lighting ballasts, welder or induction furnace, Induction generators Wind mill generators and high intensity discharge lightings.
A distorted current waveform can be the result of a rectifier variable speed drive, switched mode power supply, discharge lighting or other electronic load DISADVANTAGES OF LOW POWER FACTOR : DISADVANTAGES OF LOW POWER FACTOR Increases heating losses in the transformers and distribution equipments.
Reduce plant life.
Unstabilise voltage levels.
Increase power losses.
Upgrade costly equipments.
Decrease energy efficiency.
Increase electricity costs by paying power factor surcharges. POWER FACTOR CORRECTION : POWER FACTOR CORRECTION Most loads on an electrical distribution system fall into one of three categories; resistive, inductive or capacitive. In most plant, the most common is likely to be inductive. Typical examples of this include transformers, fluorescent lighting and AC induction motors. Most inductive loads use a conductive coil winding to produce an electromagnetic field, allowing the motor to function. Slide 14: All inductive loads require two kinds of power to operate:
Active power (KW) - to produce the motive force
Reactive power (KVAR) - to energize the magnetic field
The operating power from the distribution system is composed of both active (working) and reactive (non-working) elements. The active power does useful work in driving the motor whereas the reactive power only provides the magnetic field. POWER FACTOR CORRECTION : POWER FACTOR CORRECTION The amount of Power Capacitor KVAR required to correct
A system to a desired Power Factor level is the difference between the amount of KVAR in the uncorrected system and the amount of desired KVAR in the corrected system. The most efficient location for power factor capacitors is at the load. Capacitors work from the point of installation back to the generating source. Individual motor correction is not always practical, sometimes it is more practical to connect larger capacitors on the distribution bus or install an automatic system at the incoming service along with fixed capacitors at the load. CORRECTION : CORRECTION POWER FACTOR CORRECTION : POWER FACTOR CORRECTION POWER FACTOR CORRECTION : POWER FACTOR CORRECTION POWER FACTOR CORRECTION : POWER FACTOR CORRECTION KVAR CORRECTION : KVAR CORRECTION Capacitive Power Factor correction (PFC) is applied to electric circuits as a means of minimising the inductive component of the current and thereby reducing the losses in the supply. The introduction of Power Factor Correction capacitors is a widely recognised method of reducing an electrical load, thus minimising wasted energy and hence improving the efficiency of a plant and reducing the electricity bill. It is not usually necessary to reach unity, i.e. Power Factor 1, since most supply companies are happy with a PF of 0.95 to 0.98.By installing suitably sized switched capacitors into the circuit, the Power Factor is improved and the value becomes nearer to 1 thus minimising wasted energy and improving the efficiency of a plant or power factor can be increased by synchronous motor POWER CAPACITORSPower Factor correction on site with Pole Cap : POWER CAPACITORSPower Factor correction on site with Pole Cap ADVANTAGES OF POWER FACTOR CORRECTION : ADVANTAGES OF POWER FACTOR CORRECTION Eliminate Power Factor Penalties
Increase System Capacity
Reduce Line Losses in distribution systems
Improve voltage stability
Increase equipment life
Save on utility cost
Enhance equipment operation by improving voltage
Improve energy efficiency
Reduction in size of transformers, cables and switchgear in new installations.
Delay costly upgrades.
Less total plant KVA for the same KW working power.
Improved voltage regulation due to reduced line voltage drop. PROJECT TITLE : PROJECT TITLE MICROCONTROLLER BASED
CORRECTION Slide 24: FUNCTIONAL BLOCK DIAGRAM SHORT DESCRIPTION OF EACH BLOCKS OF SYSTEM : SHORT DESCRIPTION OF EACH BLOCKS OF SYSTEM Voltage Waveform Generator
This unit will generate voltage waveform from the A.C. Power Supply. The A.C. input coming from the mains line is step down to 6 V using a transformer. In C.R.O. the output of this unit will show sine wave at 50Hz; which is voltage waveform required for further processing.
Current Waveform Generator
The job of this unit is to produce current waveform using the mains line. This can be achieved by using a Current Controlled Voltage Oscillator. The output of this unit will be sine waveform at 50Hz. Slide 26: Zero Cross Detector
The function of this unit is to detect the Zero voltage level of both the waveforms and to toggle its output between the high and low logic level. Thus when it detects Zero voltage at its input; it toggles it’s output either high or low depending upon the previous condition which gives us square wave for further processing.
This unit will take input from both the ZCD units and will produce a Pulse in the output which is exactly equal to the phase difference in the voltage & current waveforms.
This unit will invert the ex-or output using NOT gate so as microcontroller can get negative going edge trigger. MICROCONTROLLER : MICROCONTROLLER The Microcontroller
It is the heart of the entire system, used for measurement of power factor & controlling it. The microcontroller performs the following steps.
To measure the pulse width of the ex-or output.
To calculate the phase difference ø.
To calculate the Cosine of ø i.e. Power Factor.
To display it on the LCD.
To switch on the capacitors parallel with the inductive load from the capacitor bank.
To continuously monitor the phase difference by performing above step repeatedly till the phase shift is zero. Slide 28: Relay Driver & Relay Array
This is the actual part of the system where all the appliances will be connected with the help of relay. As microcontroller gives command they switch ON/OFF the particular device, i.e. a particular capacitor is either selected from a capacitor bank & applied parallel to the inductive load or it is switched of if not required.
Visual Display Unit
This unit will show the various conditions of the system with the help of LED’s,
i.e. the status of the system.
The Power Supply
This unit will supply the various voltage requirements of each unit. This power supply must be strictly designed to avoid any drifts & should be distributed according to the voltage requirements of each block. Slide 29: Features of 89C51
Following are the features of 89C51 microcontroller as per the datasheet given by Atmel.
Compatible with MCS-51™ Products.
4K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000Write/Erase Cycles.
Fully Static Operation: 0 Hz to 24 MHz.
Three-level Program Memory Lock.
128 x 8-bit Internal RAM.
32 Programmable I/O Lines.
Two 16-bit Timer/Counters.
Six Interrupt Sources.
Programmable Serial Channel.
Low-power Idle and Power-down Modes PIN DIAGRAM OF 89C51 : PIN DIAGRAM OF 89C51 ARCHITECTURE OF 89C51 : ARCHITECTURE OF 89C51 POWER SUPPLY CIRCUIT : POWER SUPPLY CIRCUIT PULSE GENERATOR CIRCUIT : PULSE GENERATOR CIRCUIT RELAY DRIVER CIRCUIT : RELAY DRIVER CIRCUIT NEED OF THE ABOVE PROJECT : NEED OF THE ABOVE PROJECT The main aim of our project is to maximize the Power Factor so as its value is nearly equal to one. This is achieved by
Drawing voltage waveform from the input power supply,
Drawing current waveform from the input power supply,
Measuring the Phase difference,
Calculating Cosine of phase difference,
Switching required capacitor parallel with the load,
Recalculating the power factor,
Repeating the above steps continuously till we get maximum value of power factor i.e. minimum phase difference. USEFULLNESS OF PROJECT : USEFULLNESS OF PROJECT our project is useful in improving the power factor due to which the electrical system’s branch capacity will increase. Uncorrected power factor will cause power losses in the distribution system. One may experience voltage drops as power losses increase. Excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment.
Also at the same time the utility bill will be smaller. Low power factor requires an increase in the electric utility’s generation and transmission capacity to handle the reactive power component caused by inductive loads. Utilities usually charge a penalty fee to customers with power factors less than 0.95. We can avoid this additional fee by increasing the power factor APPLICATION OF THE PROJECT : APPLICATION OF THE PROJECT Used in hospitals and clinics
Used in different laboratories
Used in the input circuit of power converter circuits
Used for phase margin measurement of electronic ballasts. MICROCONTROLLER BASED POWER FACTOR MEASUREMENT AND CORRECTION : MICROCONTROLLER BASED POWER FACTOR MEASUREMENT AND CORRECTION THANK YOU