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Assessment Cover SheetComplete and attach this cover sheet to your assessment before submitting1381125-638175operation and investigation of domestic light dimmerAssessment TitleBachelor of Engineering TechnologyProgramme Title: ENB6009Course No.:Power ElectronicsCourse Title:Student Name:Mustafa Isa Al-Ansari201000754Student ID:Mr. John leek Tutor:Date submitted: 2/10/2014Due Date:2/10/2014By submitting this assessment for marking, either electronically or as hard copy, I confirm the following:This assignment is our own workAny 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 assignmentAbstract the aim of this assignment is investigate the operation of the light dimmer circuit. This assignment will include theoretical calculations, experimental results, and simulation result. In the experimental result three output parameters will be plotted against alpha which is the firing angle, and a brief description on the method that is used to operate the dimmer will be provided. There will be a compression between theoretical and experimental results. moreover, This assignment will consist of simulation results which are RFI components , the frequency response of the RFI components , and brief description on the reason why the circuit is fitted in the light dimmer circuit. Finally, the attenuation of the RFI components will be discussed if the circuit is expected in EN55015 standard which is the RFI specification in Europe.Objectivesthe objectives of this project are :to investigate the operation of a domestic light dimmerto connect the light dimmer circuit to mains power , and to the light holderto measure the output power, current , and power factor , experimentally, and plot them with respect to phase angel.to measure the total harmonics distortion using DSA, to see whether it fits in the RFI aspect. to draw the dimmer circuit on Altium designer with correct values.to compare the theoretical and experimental result of the output power with respect to the phase angel.to simulate the RFI components (LC filter) , and determine the frequency response using Altium.Contents TOC \o "1-3" \h \z \u Abstract PAGEREF _Toc400056646 \h 2Objectives PAGEREF _Toc400056647 \h 2Technical discussion PAGEREF _Toc400056650 \h 6Finding the RMS value of chopped sine wave PAGEREF _Toc400056651 \h 6converting the alpha into angle in degree PAGEREF _Toc400056652 \h 7Finding the cutoff frequency of the low pass filter (LC). PAGEREF _Toc400056653 \h 8Find the R load of a second order low pass filter PAGEREF _Toc400056654 \h 9Minimum and maximum Time constant PAGEREF _Toc400056655 \h 10simulation results PAGEREF _Toc400056656 \h 12Introduction PAGEREF _Toc400056657 \h 12RFI components PAGEREF _Toc400056658 \h 12Discussion and conclusion on the simulation result PAGEREF _Toc400056659 \h 15Experimental results PAGEREF _Toc400056660 \h 16Introduction PAGEREF _Toc400056661 \h 16Discussion on the output parameter with respect to alpha PAGEREF _Toc400056662 \h 19Harmonic distortion of the dimmer PAGEREF _Toc400056663 \h 21Discussion on the harmonics distortion PAGEREF _Toc400056664 \h 22Operation of light dimmer circuit PAGEREF _Toc400056665 \h 23The circuit's operation PAGEREF _Toc400056666 \h 24Comparing the time constant with off time delay of the chopped sine wave PAGEREF _Toc400056667 \h 24Experimental section conclusion PAGEREF _Toc400056668 \h 25Conclusion section PAGEREF _Toc400056669 \h 26Comparative analysis and discussions PAGEREF _Toc400056670 \h 26References PAGEREF _Toc400056671 \h 27 Table of figure TOC \h \z \c "Figure" Figure 1 The parameters that control the RC time constant PAGEREF _Toc400051397 \h 9Figure 2 second order low pass filter it known as RFI components PAGEREF _Toc400051398 \h 12Figure 3 cutoff frequency which is 256 KHz PAGEREF _Toc400051399 \h 13Figure 4 current agaist alpha PAGEREF _Toc400051400 \h 17Figure 5 power V Alpha PAGEREF _Toc400051401 \h 17Figure 6 power factor agaisnt alpha PAGEREF _Toc400051402 \h 18Figure 7 The theoretical and expermental power verses alpha in degree PAGEREF _Toc400051403 \h 20Figure 8 Light dimmer circuit with RFI components PAGEREF _Toc400051404 \h 22 Table of tables TOC \h \z \c "Table" Table 1 output parameters ( experimental values) PAGEREF _Toc400056623 \h 16Table 2 maximum harmonics PAGEREF _Toc400056624 \h 21Table 3 comparing the time constant with off time delay PAGEREF _Toc400056625 \h 23Technical discussion Finding the RMS value of chopped sine waveThe calculations below are related to the RMS value of chopped sine wave. In the light dimmer the Ac waves are chopped by the triac. In this calculation, half cycle will be used to determine the area under the curve after chopping the sine, and the time will be between α ( the phase angle/ firing angle) to π. Then, the area under the curve will multiplied by 1 divided by the time of half cycle of the real sine wave before chopping it out a which is zero to π. RMS value=1(b-a)abf2 tdtRMS value=1(π-0)απVp2*sin2 (t)dtsin2 t=1-cos?(2t)2RMS value=Vp2(π)απ1-cos?(2t)2dtRMS value=Vp2παπ1-cos?(2t)dtRMS value=Vp2πt-sin?(2t)2 RMS value=Vp2*2πt-sin?(2t)πα RMS value=Vp2*π*π-sin2*π-α-sin2α RMS value=Vp2*π*π-0-α-sin2α RMS value=Vp2*π*π-α-sin2α RMS value=Vp2*1-απ+sin2απ The importance of this equation is that it is going to be used to find out the power which is proportional to Vrms squared. note- the value of alpha must be in radian ( not degree).converting the alpha into angle in degreethe phase angle was not calculated directly, but it was converted from seconds to degrees. This was done by measuring the off time of the chopped sine wave by using the scope cursors and the off time is changes depending on the value of the variable resistor. the following equation was used to convert the delta time ( off time ) into angle in degree which is the phase angle.phase angledegree=offTime*36020msphase angledegree=offTime*18010msOff timedegree6.3ms113.46ms1085.6ms100.84.9ms88.24.2ms75.63.48 ms62.642.2ms39.600Finding the cutoff frequency of the low pass filter (LC).The light dimmer circuit produces harmonics distortion ( radio frequency interference) which affects the circuits nearby such as radio and mobile phone. So low pass filter consists of inductor , and Capacitor is used to minimize the harmonics distortion. The value of L=36.4 uH c= 10 nF were measured using Multi meter on Elvis board. the cutoff frequency is determined by the following equation.Cutoff frequency=12πLC Cutoff frequency=12π36.4uH*10nf Cutoff frequency=263.8 KHzFind the R load of a second order low pass filterThe Rload of the filter can be calculated using the equation of the quality factor of an RLC circuit where R parallel with C and L is in series with C. the value of Q was chosen so it give a normal frequency response so the cutoff frequency can be determined at - 3DBQ=RloadCL0.707=Rload10n36.4uH0.707=Rload10n36.4uH0.70710n36.4uH=RloadRload=42.65 ohmsMinimum and maximum Time constantCalculating the maximum and minimum time constant from the value of the Capacitor and the variable resistor:basically the value maximum value of the variable resistor is 470 Kohms, and minimum value is 0 ohms. The value of the capacitor is fixed which is 100 nF. the RC time constant is determined as the following formula time constant= R*C .Figure 1 The parameters that control the RC time constantWhen the time constant is describe as minimum time constant, this mean that the potentiometer has a very small value, and can be determined as few hundred of ohms. so this value will be assumed as 100 ohms when the time constant is minimum the components in the circuit above can be describe as the followingR2=100R1=3.3K ohmsR3=660K ohmsC2=100nF1Rt=1R2+R1+1R31Rt=13300+100+1660000RT=3.4 kohms=Rminimumminimum time constantTime constant minumum=Rminimum*C2Time constant minumum=Rminimum*C2Time constant minumum=3400*100*10^-9Time constant minumum=340 uswhen the time constant is maximum the components in the circuit above can be describe as the followingR2 maximum=470 KohmsR1=3.3K ohmsR3=660KohmsC2=100nF1Rt=1R2+R1+1R31Rt=1470000+3300+1660000RT=275.64kohms=R maximummaximum time constantTime constant maximum=Rmaximum*C2Time constant maximum=275.64*100*10^-9Time constant maximum=27.6mssimulation resultsIntroductionthe aims of this sections are to draw the RFI components(second order low pass filter) on Altium designer , and simulate the circuit to observe the cutoff frequency of the filter. This section is also required to see whether the attenuation of the RFI components can fit in the curve of the RFI spec EN55015 or not. This section will include a schematic circuit of the light dimmer with brief explanation on how it works. Finally the simulation result of the RFI components ( frequency response) will be represented . RFI componentsthe main aim of light dimmer circuit is to control the brightness of the light by chopping up the current that is drawn on the load. Therefore, a harmonic distortion(RFI) will be produced because the wave is not sine wave anymore. So The light dimmer circuit produces radio frequency interference. this type of frequency affects some electric circuits nearby such as radio and mobile phones. As a result, low pass filter is used in the dimmer to attenuate the harmonic distortion that is produced by the dimmer. The filter consists of an inductor and a capacitor. the figures below represents the schematic circuit of the low pass filter, and the bode plot of the amplitude (db) against the frequency to observe the cutoff frequency of the filter.Figure 2 second order low pass filter it known as RFI components18859541910Note that R2 was calculated in the technical discussion. the following steps are repeated.Q=RloadCL0.707=Rload10n36.4uH0.707=Rload10n36.4uH0.70710n36.4uH=RloadRload=42.65 ohmsFigure 3 cutoff frequency which is 256 KHz-727075408940Discussion and conclusion on the simulation result The circuit of RFI components was simulated using Altium designer, the circuit is shown in figure 2, and the simulation is represented in figure 3. In figure 3, the cutoff frequency is 265 KHz which is very close to the theoretical cutoff frequency (263 KHZ). this means that the simulation , and the theoretical cutoff frequency match each other. The cutoff frequency above is 265 KHz when means the noise that are produces by the bulb will be attenuated when the frequency reaches the 256KHz. Finally, the objective of this section was to indentify the RFI components which are presented in figure 2, simulate the RFI circuit to determine the cutoff frequency. The value of the cutoff frequency was very similar to the theoretical cutoff frequency, which means that the theoretical calculation matches the simulation result. Experimental results IntroductionThe aims of this section are to include the experiment methods on testing a light dimmer, and record the output parameters such as current, power , power factor, and plot them against the phase angle. this section will also include a compression graph between the theoretical and experimental output power against alpha( phase angle). also, a table will be created to record the maximum harmonic distortion that are produced by the light bulb.A light dimmer circuit, bulb, bulb holder and amp plug were given to the students by the tutor in order to wire them up and construct a light dimmer. The light dimmer circuit was connected in series with the amp mains plug and the holder of the bulb. After that, the circuit was checked by the tutor, and the wirings in the holder were covered with an isolation materiel to prevent injuries. Then the amp plug was connected to the main socket , and the bulb was operated which the student could control the brightness of the light by varying the knob of the light dimmer circuit. This was followed by connecting the variac to the connection box, and it was connected to the wattmeter to measure the power, current, supply voltage , and power factor. finally the main power was switched on , the variac was set so it produces 240 volt. A current prob was connected to the connection between the wattmeter ( current) and the connection box, and the other end was connected to the Elvis Board scope channel. to see how the shape of the current wave is look like when it is drawn on the load After checking all the wirings, and making sure that the supply voltage (output of the VARIAC) is 240 volt, then the scope (from LabView launcher) was opened to observe the currents behavior. the shape of the current( current drawn on the load) looked like chopped sine waves. the size of the chopped sine wave is controlled by the knob of the circuit which is a potentiometer resistor, and its function is to change the phase angle. This is accomplish by the time it takes to change up the capacitor , and it is known as RC time constant. By changing the phase angle then the power and the current that are delivered to the bulb changes. The table below includes the relationship between the power, current , and power factor with respect to alpha( phase angle). Moreover, the total harmonics distortion was recorded using DSA in LabView launcher. the reason why these parameters are recorded is because the current, power , power factor have a relationship with the phase angle.Voltage supply = 240 VTable 1 output parameters ( experimental values)Phase anglePower(watt)Current(amp)Power FactorTHD (%)113.436.30.310.4892.6108410.330.5382100.8530.360.637188.2650.380.716175.6800.410.814962.4930.430.893739.61060.450.972001100.4613the table above demonstrate that the current, power, phase angel changes with respect to alpha. These changes are represented in the figures below.19050-170180Figure 4 current agaist alphaFigure 5 power V Alpha-5353050198120Figure 6 power factor agaisnt alphaDiscussion on the output parameter with respect to alphaThe output power and alpha have relationship and it can be explained in the figure5. the power decreases when alpha increases. this happen because alpha affects the brightness by chopping the AC sine waves by an RC time constant which is the time it take to charge a capacitor through a resistor. In this case R is a potentiometer, therefore alpha is changing and causing the power to change. and this mean that alpha controls the power that is consuming by the light bulb. another explanation, when alpha increasing this mean that the off time delay will increase causing the size (size of the wave) of the rms voltage to reduce, and it is known that the power is proportional to RMS voltage square , so power is decreasing because the RMS voltage is decreasing and vice versa. Another graph is represented which is figure 4. this graph shows the relationship between current and alpha. when a current sine wave is chopped the current decreases depending on how much the waves is chopped. figure 4 prove the argument, when alpha is decreasing the current increasing. exactly at zero degrees. the current is not chopped any more. so the power factor can be described as unity. figure 6 shows that at 0 degrees the power factor is 1 which is unity because the current is exact replica of the voltage supply , and they are in phase. The light bulb is basically a resistive load, and it is known that a resistive load have unity power factor. However, the table1 above shows something completely different. The power factor changes with respect to alpha. the reason why the power factor does not stay unity is because the current that is drawn on the load is chopped out which causing the power factor to change. Figure 6 shows that the more the wave is chopped out the lower the power factor is observed which means when alpha is increased the power factor decrease and vice versa.The output power was compared to the theoretical power. the theoretical power was calculated using the formula of Vrms which is :RMS value=Vp2*1-απ+sin2απ the relationship between power and Vrms is that p is proportional to Vrms square. the following formula was used and alpha was converted to radian, and then the answer of the divided by a number to make the two lines appears to each other in order to compare them. this number was considered as the resistance of the light. because vrms square will be a huge number comparing the experimental power. after doing the calculations in Matlab, the graph was looked like the following:Figure 7 The theoretical and expermental power verses alpha in degreeThe figure above represents the theoretical and experimental power against alpha. It is shown that both graph matches each other . However, there is a little bit of a gap because of the schematic error which is because of the bulb which is a changeable resistive load. it change its resistance with respect to temperature. the theoretical power was divided by the resistance at only one state which is when the light is in full brightness the resistance was 500 ohms this value was assumed as the resistance of the light.Harmonic distortion of the dimmerduring the practical part the amplitude of the maximum harmonics were recorded. this was done by reducing the output power to half exactly at 55 watt, the maximum harmonics were appeared in labview DSA. Table 2 maximum harmonicsFrequencyHarmonics orderDB/Vrms50first-32.5150third-35250fifth-43350seventh-45450ninth-47.5550Eleventh -49650thirteenth-51750fifteenth-52.5Discussion on the harmonics distortionThe table above represents the maximum harmonics the bulb is producing. the amplitude reduces as the number of odd harmonics increases, that happening because the harmonics get attenuated by the RFI components as the number of odd harmonics increases ,the graph will look like a decay. table one demonstrate the argument. it can be seen that as the number frequency get multiplied by the number of harmonics the amplitude of the harmonics gets smaller and smaller.Operation of light dimmer circuitThe Light dimmer circuit was drawn using Altium designer software. The circuit was given to the student, and the student measured the values according the circuit. Figure 8 Light dimmer circuit with RFI componentsThe circuit's operationGenerally, a light dimmer circuit is used to control the power this consumed by the light bulb by allowing a portion of an AC signal to pass through the load which is a light bulb. the circuit above is one type of dimmer circuits. The operation of this circuit can be explained as during the positive cycle the capacitor charge through a resistor, and it will charge up until the diac start conducting at 32 volt which is the breakdown voltage of the DIAC, this will cause the capacitor to discharge thought the gate of the TRIAC. one the TRIAC is triggered the current will pass through the bulb and will cause the circuit to be a close circuit. During the negative cycle the same process happen. the capacitor charge in reverse polarity, and the DIAC is bidirectional component , so it will conduct at negative voltage. When the capacitor reaches the breakdown voltage of the DIAC, then the DIAC will start conducting and will let the capacitor to discharge , and triggering the gate of the TRIAC. After that, the current passes through the light bulb , and will close the circuit. The brightness of the light is controlled by changing the phase angle. this happens by an RC time constant which is controlled by potentiometer R2. this value is added to R1 because they are in series and then added in parallel with r3 then the value is multiplied by C2. the value of this equation is called the time constant. In this case, the time constant will be defined as be how fast the capacitor reaches the break down voltage of the DIAC. Moreover, a second order low pass filter is added to the circuit to reduce the RFI ( radio wave interference). R4 is placed in the circuit to limit the current through the paring the time constant with off time delay of the chopped sine waveThe minimum and maximum time constant were calculated in the technical discussion section. The delta time which is the off time delay was observed on LabView scope. the table below include the differences between the theoretical value and the experimental values.Table 3 comparing the time constant with off time delayTime constant ( theory)Off time ( expermental)Minimum value 340 us0Maximum value27 ms6.3 msAs it is shown in the table above there is differences between the experimental and theoretical values. the time constant by itself does not give the correct value of the phase angle. there are some issues such as the tolerance of the resistors and capacitor can affect the value of delta time ( off time).Experimental section conclusionThe objectives of this section were to plot the output parameters(current power and power factor) against alpha, and discuss the relationship between each parameter with respect to alpha, compare the output power with the theoretical power, and discussing the differences. also the section discussed the relationship between the amplitude of harmonics when the number of odd harmonics increase. As they get reduced by the RFI components. finally the time constant was not the correct value that gives the exact phase angle. Conclusion sectionIn conclusion, the operation of the light dimmer circuit were discussed, the RFI components were defined, and simulated, the effect of harmonics distortion were indentified , and the method of reducing the harmonic distortion was provided which by adding second order low pass filter. furthermore, the output parameters were recorded using Labview DSA, scope , and using Wattmeter. the parameter such as current , power, power factor were plotted against alpha to see the relationship, as it was parative analysis and discussionsFirst of all, the experimental power was compared with the theoretical power, there was a little gap between the two lines, but they were so close. the differences between the two graphs happened because the resistance of the bulb change at certain amount of temperature. which effects the power because power is V square divided by R which is the resistance o the bulb. Also, the devices that were used are not so accurate. The cutoff frequency was calculated theoretically(263KHz) and observed in Altium(265KHz). The two value match each other, the differences that is occurred because the device that measure the rfi components is not so accurate, add to that the tolerances of the components. Furthermore, the minimum time constant was compared with the minimum off time of the copped sine waves, as well as the maximum time constant was compared with the maximum off time delay, they minimum time can agree with each other because 340 us is very close to zero, but the maximum time has big error the time constant is 27ms , and the off time delay is only 6.3ms. so they do not agree with each other, to conclude the time constant by itself does not give the correct the phase angle according to the calculations.References ................
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