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Assessment Cover Sheet Complete and attach this cover sheet to your assessment before submitting Assessment Title: Active Power Factor Correction Project Programme Title: Bachelor of Engineering and Technology Course No: ENB6008 Course Title: Power Electronics Student Name: Mustafa Isa Al-Ansari Student ID: 201000754 Tutor: John leek Due Date: 10/1/2015 Supervisor: John leek By submitting this assessment for marking, either electronically or as hard copy, I confirm the following: This assignment is my own work Any information used has been properly referenced. I understand that a copy of my work may be used for moderation. I have kept a copy of this assignment Do not write below this line. For Polytechnic use only. Assessor: Grade/Mark: Comments: Date of Marking: Abstract This document aims to identify a problem in AC to DC converter using bridge rectifier with smoothing capacitor which gives bad power factor. Then come up with circuitry that solve/correct the power factor, known as active power factor correction. firs off all, results will be obtained from AC to DC converter using smoothing capacitor to confirm this method gives poor power factor. This is followed by, identify, build and test new solution to this problem which is active power factor correction that is used to modify the power factor, and make it unity or 0.99, also a brief discussion will be provided on the operation of the circuit. Finally a comparison between the smoothing capacitor result, and active power factor correction results will be made to confirm importance of having unity/ .99 power factor Objectives identify common method that is used to convert AC to DC that gives bad power factor taking experimental results to confirm that power factor is poor Taking simulation results to see whether the theory matches the simulation or not indentifying the problems of having poor power factor providing a solution/circuit to that problem, and decribe the concept of active power factor correction discussing the operation of the circuit, and how it will correct the power factor identifying the components that will be used based on the calculations taking results to confirm that the circuit is having unity power factor, plot some graph such as efficiency , and voltage regulation providing a brief discussion on the results obtained compare the results before , and after correcting the power factor Contents Abstract ......................................................................................................................................................... 2 Objectives ..................................................................................................................................................... 2 Part A............................................................................................................................................................. 4 Introduction .............................................................................................................................................. 4 Results and experimental methodology ................................................................................................... 5 Simulation section ( Part A) ........................................................................................................................ 13 Conclusion ................................................................................................................................................... 14 Part B........................................................................................................................................................... 15 Introduction: ............................................................................................................................................... 15 Calculation of components ......................................................................................................................... 16 Calculate the limiting resistor for pin 8................................................................................................... 17 Inductors calculation............................................................................................................................... 17 The operation of the circuit .................................................................................................................... 17 Results ......................................................................................................................................................... 18 Input parameters .................................................................................................................................... 18 Output parameters. ................................................................................................................................ 19 Conclusion ................................................................................................................................................... 23 References .................................................................................................................................................. 25 Table of figures Figure 1 Input Voltage and Current vs. Time for Bridge Rectifier Circuit ..................................................... 4 Figure 2 Full wave bridge rectifier with resistive load ................................................................................. 5 Figure 3 full wave bridge rectifier with smoothing capacitor ....................................................................... 9 Figure 4the capacitor is only charge in short period of time ...................................................................... 10 Figure 5 output of the smoothing capacitor ............................................................................................... 11 Figure 6 AC to DC converter ( rectifier uning smoothing capacitor)........................................................... 13 Figure 7 simulation result of the rectifier circuit at 10 ohms ..................................................................... 13 Figure 8 Active power factoe correction .................................................................................................... 15 Figure 9 Active power factor correction based on discontinuous mode.................................................... 18 Figure 10 voltage regulation graph ............................................................................................................. 19 Figure 11 efficiency plot.............................................................................................................................. 20 Figure 12 the voltage ,and the current of the bridge are in phase ............................................................. 21 Figure 13 output of the circuit PFC ............................................................................................................. 22 Figure 14 the switching frequency graph ................................................................................................... 23 Table of tables Table 1 input parameters.............................................................................................................................. 6 Table 2 output parameters ........................................................................................................................... 8 Table 3 input parameter using full wave bridge rectifier with smoothing capacitor ................................. 10 Table 4 output parameters ......................................................................................................................... 11 Table 5 THD at different load ...................................................................................................................... 12 Table 6: Measured and calculated Power Factor. ...................................................................................... 12 Table 7 input parameter of the APFC ......................................................................................................... 18 Table 8 output parameter of the APFC ....................................................................................................... 19 Part A Introduction Power factor is defined as the ration of the real to the apparent power or the cos the angle between these two factors. Power factor is presented in numeric form, and has range between 0-1. This range is used to described represents the offset in time, or the delay, between voltage and the current. 1/ unity power factor means that the current is completely in phase with the voltage. the disadanteges of having low power factor are : Higher current results in a greater voltage drop on the line The higher current can push equipment closer to their rated capacities. Cables are rated based on their current carrying capacity. In addition, poor power factor can be occurred in system where no linear load are used within the circuit. the non linear loads can draw non sinusoidal current on the load which means harmonic distortion will be produced, and because of that it effect circuit nearby such as radio or telephone ( RFI). Also non sinusoidal wave form can draw high current which may saturate the substation transformer core. In AC to DC converter, a smoothing capacitor is added to convert the full-wave rippled output of the rectifier into a smooth DC output voltage. This method is considered as waste of energy because the current that is drawn on the load is not completely in the phase with the voltage supply therefore, power factor is poor. In this case having poor power factor is not because of the current being not in phase with voltage, but because the capacitor is charged only when the output approaches (near) the peak for a short period of time near the peak of the voltage waveform. In other word the current is being drawn on the load is not sinusoidal waveform as shown below: Figure 1 Input Voltage and Current vs. Time for Bridge Rectifier Circuit The following section will prove this, and will discuss the problem in further: Results and experimental methodology A transformer was connected to the main to step down the voltage from 240 V rms to 24 v rms. then a bridge rectifier was used with A 10 ohm resistor, and 25 ohms (10+15 in series). The following diagram illustrates the connection between the components. This was done because the power factor value needs to be confirmed for using purely resistive loads and to confirm that the power factor is 1 before adding additional components to the circuit which is a smoothing capacitor that is added after the bridge in order to smooth the output of the bridge. Figure 2 Full wave bridge rectifier with resistive load This was followed by measuring the following parameters Input Voltage in volts input current in amps real power in watts apparent power in VA power factor The above parameters were found using wattmeter, and table below represents the values of these parameters at 10 ohms, and 25 ohms. Table 1 input parameters Load resistor Input voltage Ac secondary 10ohms 23.9 V 10ohms+15ohms 24.7V In series Input current Ac secondary (Amps) 2.3 A 1A Input power (real) Input VA P.F 54.5 Watt 24.4 Watt 54VA 24 VA 1 1 In pure resistive loads, all the power that enters the circuit is consumed by the load and this means that the reactive power is the same as the real power. Thus the reactive(VAR) power is zero, so the waveform of the current is in phase with the voltage supply which makes the power factor to be unity(as the power factor is defined as the ratio of the active power to the apparent power). However, the table above shows a slight difference between the apparent power, and the real power, and this is due to the circuit being not purely resistive, as the wiring in the circuit has a small value of inductance which causes very small difference between the two values (watts and VA). The above figure shows that current is in phase with the voltage which means that power factor is unity, and the THD (total harmonic distortion) is close to zero. After that, the following parameters were measured peak input voltage using scope average DC voltage was measured using DMM by sitting it to VDC( to measure only the DC component) output voltage AC was measured using SCOPE in LabView launcher Output power can be found either by placing the wattmeter after the bridge or by using the formula of power (VRMS2 /Rload). note VRMS should be the experimental, the one on scope Vrms value: = √(2) = = √(2) 32 at 10 ohms =22.6 volt √(2) output power: = = 222 =51 10 2 watt Table 2 output parameters Load resistor Peak input voltage (volts) 10ohms 32 10ohms+15ohms 34 In series Average DC voltage 21 22 Output voltage AC ripple 10v 10v Output power 51 w 21 w The table above show sthat the output power has been reduced; this is because of the power dissipation in the diode.The peak input voltage reduces because the load resistor draws more current as the resistance is increased and due to this, the voltage decreases as the current increases and this shows that it agrees with the theory. This was followed by placing a 10,000uf capacitor in parallel with the load to form an AC to DC converter(and to smooth the output voltage of the bridge). The following figure illustrates the AC to DC converter. Figure 3 full wave bridge rectifier with smoothing capacitor Before the bridge, a wattmeter was placed to measure the following the parameters : Input Voltage in volts input current in amps real power in watts reactive power in VA power factor Load resistor Input voltage Ac secondary 10ohms 23.3 10ohms+15ohms 24.8V In series Input current Ac secondary (Amps) 4.37 A 2.29 A Input power (real) Input VA P.F 79.1 Watt 40.5 Watt 102VA 56.66 VA 0.76 0.7 The table above shows that the input power is not equal to the input VA and this results in a low power factor as shown in the table. The reason for the changing in input voltage is because the resistance draws more current when it is reduced and this is clear from the table as the table shows that the current drawn by the 10 ohm resistor is more than the 10+15 series resistor . Also it shows that that power factor is less than unity, this is because current is non-sunosudial waveform, while the voltage is a pure sine wave. Also, the figure below shows that the capacitor is only changed when the voltage of input supply approaches to the peak, then the diode change in its state in to reverse bias mode , hence the capacitor is not changed after the peak. Figure 4the capacitor is only charge in short period of time The following parameters were measured in this part of the project: peak input voltage using scope average DC voltage was measured using DMM by sitting it to VDC( to measure only the DC component) output voltage AC was measured using SCOPE in LabView launcher output power can be found either by placing the wattmeter after the bridge or by using the formula of power (VRMS2 /Rload). note VRMS should be the experimental, the one on scope Table 3 input parameter using full wave bridge rectifier with smoothing capacitor Load resistor Peak input voltage (volts) 10ohms 29 10ohms+15ohms 31 In series Average DC voltage 27 30 Output voltage AC ripple 2.1 1.3 Output power 48.4 w 21 w ripple voltage formula ∆ = 2∗∗ Table 4 output parameters Load resistor Peak input voltage (volts) 10ohms 2.9 10ohms+15ohms 1.24 In series Figure 5 output of the smoothing capacitor Ripple voltage Pk-pk Ripple voltage pk-pk RMS ripple voltage 2.25 1.2 2.1 1.3 0.7V 0.33v The current peak values: 10 ohm: 10.3 A 25 ohm: 4.5 A The frequency of the ripple current : 100Hz. this was followed by measuring THD ( total harmonic distortion), and then measure the power factor using the following equation = = Table 5 THD at different load Load resistor THD % 10ohms 48 10ohms+15ohms 95 In series Table 6: Measured and calculated Power Factor. Load resistor Measured PF 10 ohm 25 ohm 0.77 0.71 Calculated PF 0.77 0.72 1 √1 + 2 Simulation section ( Part A) This part aims to simulate the AC to DC circuit to compare it with the practical results Figure 6 AC to DC converter ( rectifier uning smoothing capacitor) Figure 7 simulation result of the rectifier circuit at 10 ohms the simulation, and practical results shows the same behavious whena smoothing capacitor is used to smooth the output of the bridge, which it produces a current pulses that is only happen when the voltage of the input voltage reaches near the peak of the waveform. so the I supply is draw non sinusoidal waveform Conclusion When the circuit consisted of only the resistive load (it was a purely resistive circuit), the current was in phase with the voltage thus the power factor was unity which means that the load consumes the whole input power and makes full use of it(the table above proves that VA is the same as input power). When the smoothing capacitor is added in parallel with the resistive load(AC to DC converter), the load does not consume the whole power because the capacitor is charged only when the output approaches (near) the peak for a short period of time near the peak of the voltage waveform. For the rest of the supply cycle, the diodes are reverse biased, and no current flows from the supply. The current waveform consists of short pulses near the voltage peak as shown in the following figure. So using a smoothing capacitor to smooth the output of the bridge is a bad way to convert from AC to DC because the supply current will not be the exact replica of the voltage supply because the capacitor is only charged for a very short period of time, and this peak current will be very high which will saturate the core of the substation transformer , disturb the functioning of all the other components (it could even cause them to fail), and harmonics distortion ( radio frequency interference) which affects the circuits nearby such as radio and mobile phone .Due to the aforementioned problems, a technique called active power factor correction will be discussed in the next part of the document that reduces the emissions of harmonic currents into the AC supply , and improve the power factor of equipments. Part B Introduction: This section will include a solution for part A problem which is using smoothing capacitor to smooth the output of the bridge rectifier results a bad power factor ( between 0.6-0.7). The way the power factor was corrected is by using boost converter topology (as it is shown in figure 8), and it is known as Active power factor correction. The figure below illustrate an active power factor correction. There are two modes used to accomplish active power factor correction: 1. Continuous Conduction Mode (CCM). 2. Discontinuous Conduction Mode(DCM). Figure 8 Active power factoe correction CCM DCM Continuous mode typically suits SMPS power levels greater than 300W. This is where the boost converter’s MOSFET does not switch on when the boost inductor is at zero current, instead the current in the energy transfer inductor never reaches zero during the switching cycle With this in mind, the voltage swing is less than in discontinuous Less voltage swing also reduces EMI and allows for a smaller input filter to be used. Since the MOSFET is not being turned on when the boost inductor’s current is at zero, a very fast reverse recovery diode is required to keep losses to a minimum. In this mode ( discontinuous) the MOSFET turns on when the current reaches zero, and turn off when the current reaches the envelop of the output of the bridge. this mode is used for Switch mode power supplies that have maximum output level of 300 watt or less The active power factor correction circuit was based on the discontinuous conduction mode. Both use boost converter topology but uses different power factor controller as they usea different IC chip. The chip that was used is TDA 4862. Calculation of components Multin (Pin3) 1 + 2 = ( ) 2 where: V out = is the maximum peak voltage of the bridge rectifier 35 V with no load Vin= the input voltage MULTIN. the voltage must not exceeds 4V, so 2 V was decided to be the input voltage of chip R1, and R2 will form a voltage divider netwerk R2 was assumed (10k) So R1 = 1 + 10 35 = 2 ( ) 10 17.5 = ( 1 + 10 ) 10 175 = 1 + 10 165 = 1 1 ≅ 170 There is no a resistor with value of 170 K. As a result, 160 K was used in series with 10 K resistor Pin1 Vsense 1 + 2 = ( ) 2 where: V out = is the desired output voltage it should more than peak voltage of the bridge's output Vin= is the value of the input voltage in pin1 it should be 2.5 because from inside it is connected to a comparator, and V ref is 2.5, so to switch error amplifier on both Vref , and Vsense pin should have the same value which is 2.5 V R1, and R2 will form a voltage divider network R2 was assumed (10k) So R1 = 40 = 2.5 ( 1 + 10 ) 10 1 + 10 16 = ( ) 10 16000 = 1 + 10 150 = 1 Calculate the limiting resistor for pin 8 a capacitor was placed to limit the current to the voltage supply pin (8) maximum current at pin 8 must be 70mA or lower( it was assumed to be 10 mA ) zener diode voltage :16V pin 8 was supplied by the output of the circuit which is 40V. 8 = − 8 = 40 − 16 10 ∗ 10−3 = . Inductors calculation The operation of the circuit Figure 9 Active power factor correction based on discontinuous mode Results After building the circuit on a bread board, then it was tested to make sure that the circuit is actually boosting even at the maximum power which 50 watt. Input parameters The table below will include the input values such as voltage, current,power, and power factor.The values were measured using a watt meter. Table 7 input parameter of the APFC AC Voltage secondary (volts) 25.5 24.6 AC Current secondary (amps) 0.738 0.92 Input power (watt) Input VA Power factor Load(ohms) 18.1 22.7 18.1 22.6 1 1 100 79 24.3 24.3 24 23.9 23.5 1.1 1.1 1.54 1.8 2.6 26.7 27.7 36 42.8 59 26.8 27.8 37.2 43.3 60 1 1 0.99 0.98 0.98 69 66 50 44 30 Output parameters. Table 8 output parameter of the APFC Load current (Amps) 0.39 0.48 0.56 0.6 0.8 0.9 1.3 Ripple voltage (VpVp) 2.8 3.4 4 4.2 5.1 6.5 7.6 Figure 10 voltage regulation graph Ripple RMS voltage Output voltage (V) Output power Load(ohms) 1 1.2 1.4 1.5 1.8 2.3 2.7 40.6 40.4 40.5 40.3 40.3 40.2 39.6 16 20 23.2 24.3 32 37.5 50.7 100 79 69 66 50 44 30 This graph shows the output voltage versus output power it shows that the voltage drops at the maximum load by 1V, and this is due to the number of the primary winding, few windings must be removed to regulate the voltage, and make steady voltage. Figure 11 efficiency plot Figure 12 the voltage ,and the current of the bridge are in phase Figure 13 output of the circuit PFC Figure 14 the switching frequency graph since the input voltage is in phase with the current supply then this mean that all the current is occurred in the first component, the circuit above shows components after the 16Khz which is the switching frequency. these complements may produce RFI. So usually in this circuit , as RFI circuit is added to minimize the effect of RFI. Conclusion to conclude, a problem in AC to DC converter was identify in this document which is when a smoothing capacitor is added in parallel with the resistive load(AC to DC converter), the load does not consume the whole power because the capacitor is charged only when the output approaches (near) the peak for a short period of time near the peak of the voltage waveform. For the rest of the supply cycle, the diodes are reverse biased, and no current flows from the supply. The current waveform consists of short pulses near the voltage peak. this non sinusoidal waveform disturb the functioning of all the other components (it could even cause them to fail), and harmonics distortion ( radio frequency interference) which affects the circuits nearby such as radio and mobile phone . Also, if this technique is commonly used then this will saturate the substation transformer because it produces high peak of current. Then this problem was solved by using active power factor correction based on discontinuous mode that uses boost converter to make the current in phase with voltage. References https://www.fairchildsemi.com/application-notes/AN/AN-42047.pdf http://m.eet.com/media/1149503/24650-46463.pdf http://www.infineon.com/dgdl/AN_TDA4862G.pdf?folderId=db3a304412b407950112b41804e124ae&fi leId=db3a304412b407950112b418052524af http://www.ospmag.com/files/pdf/whitepaper/Power-Factor-and-Input.pdf