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Due Date:2/10/2014 Date submitted: 2/10/2014

Programme Title:

Course No.:

Tutor:

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Course Title:

Student ID: 201000754

Student Name: Mustafa Isa Al-Ansari

Mustafa Isa Al-Ansari 201000754

Assessment Title

Mr. John leek

By submitting this assessment for marking, either electronically or as hard copy, I confirm the following:

This assignment is our 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

Power Electronics

Bachelor of Engineering Technology

ENB6009

operation and investigation of domestic light dimmer


Abstract 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 dimmer to connect the light dimmer circuit to mains power , and to the light holder to 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.


ContentsAbstract.......................................................................................................................................................2

Objectives....................................................................................................................................................2

Technical discussion....................................................................................................................................6

Finding the RMS value of chopped sine wave.........................................................................................6

converting the alpha into angle in degree.............................................................................................7

Finding the cutoff frequency of the low pass filter (LC)...........................................................................8

Find the R load of a second order low pass filter.....................................................................................9

Minimum and maximum Time constant................................................................................................10

simulation results......................................................................................................................................12

Introduction...........................................................................................................................................12

RFI components.....................................................................................................................................12

Discussion and conclusion on the simulation result..............................................................................15

Experimental results..................................................................................................................................16

Introduction...........................................................................................................................................16

Discussion on the output parameter with respect to alpha..................................................................19

Harmonic distortion of the dimmer.......................................................................................................21

Discussion on the harmonics distortion.................................................................................................22

Operation of light dimmer circuit..........................................................................................................23

The circuit's operation...........................................................................................................................24

Comparing the time constant with off time delay of the chopped sine wave.......................................24

Experimental section conclusion...........................................................................................................25

Conclusion section.....................................................................................................................................26

Comparative analysis and discussions...................................................................................................26

References.................................................................................................................................................27

Table of figureFigure 1 The parameters that control the RC time constant.......................................................................9Figure 2 second order low pass filter it known as RFI components...........................................................12Figure 3 cutoff frequency which is 256 KHz...............................................................................................13Figure 4 current agaist alpha.....................................................................................................................17Figure 5 power V Alpha.............................................................................................................................17


Figure 6 power factor agaisnt alpha..........................................................................................................18Figure 7 The theoretical and expermental power verses alpha in degree.................................................20Figure 8 Light dimmer circuit with RFI components..................................................................................22

Table of tablesTable 1 output parameters ( experimental values)...................................................................................16Table 2 maximum harmonics....................................................................................................................21Table 3 comparing the time constant with off time delay.........................................................................23


Technical discussion

Finding the RMS value of chopped sine wave

The 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)∫a

b

f 2 ( t )dt

RMS value=√ 1(π−0)∫α

π

Vp2∗sin2(t)dt

sin2 (t )=1−cos (2 t)2

RMS value=√Vp2(π)∫απ 1−cos (2 t)

2dt

RMS value= Vp√2 π √∫

α

π

1−cos (2 t)dt

RMS value= Vp√2 π √[ t−sin (2 t)2 ]

RMS value= Vp√2∗√2π √[ t−sin (2t )] πα


RMS value= Vp2∗√ π

∗√ [ (π−sin (2∗π ) )−(α−sin (2α ) ) ]


∗√ [ (π−0 )−(α−sin (2α ) ) ]


∗√ [π−(α−sin (2α ) ) ]

RMS value=Vp2 ∗√[1−απ +(sin (2α ) )

π ]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.

phaseangle (degree )=offTime∗36020ms

phaseangle (degree )=offTime∗18010ms

Off time degree6.3ms 113.46ms 1085.6ms 100.84.9ms 88.24.2ms 75.63.48 ms 62.642.2ms 39.60 0


Finding 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= 12π √LC

Cutoff frequency= 12π √36.4uH∗10nf

Cutoff frequency=263.8KHz


Find the R load of a second order low pass filter

The 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 - 3DB

Q=Rload √CL0.707=Rload √ 10n

36.4uH

0.707=Rload √ 10n36.4uH

0.707

√ 10n36.4uH

=Rload

Rload=42.65 ohms


Minimum 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 constant

When 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

following

R2=100

R1=3.3K ohms

R3=660K ohms

C2=100nF


1Rt

= 1R2+R1

+ 1R3

1Rt

= 13300+100

+ 1660000

RT=3.4kohms=Rminimum

minimum time constant

Timeconstant (minumum )=R (minimum )∗¿C2

Timeconstant (minumum )=R (minimum )∗C 2

Timeconstant (minumum )=3400∗100∗10−9

Timeconstant (minumum )=340us

when the time constant is maximum the components in the circuit above can be describe as the

following

R2maximum=470Kohms

R1=3.3K ohms

R3=660Kohms

C2=100nF

1Rt

= 1R2+R1

+ 1R3

1Rt

= 1470000+3300

+ 1660000

RT=275.64 kohms=R maximum

maximum time constant

Timeconstant (maximum )=R (maximum )∗¿C2

Timeconstant (maximum )=275.64∗100∗10−9


Timeconstant (maximum )=27.6ms

simulation results

Introduction

the 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 components

the 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.


Note that R2 was calculated in the technical discussion. the following steps are repeated.

Q=Rload √CL0.707=Rload √ 10n

36.4uH

0.707=Rload √ 10n36.4uH

0.707

√ 10n36.4uH

=Rload

Rload=42.65 ohms

Figure 2 second order low pass filter it known as RFI components


Figure 3 cutoff frequency which is 256 KHz


Discussion 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 V

Table 1 output parameters ( experimental values)

Phase angle Power(watt) Current(amp) Power Factor THD (%)

113.4 36.3 0.31 0.48 92.6

108 41 0.33 0.53 82

100.8 53 0.36 0.63 71

88.2 65 0.38 0.71 61

75.6 80 0.41 0.81 49

62.4 93 0.43 0.89 37

39.6 106 0.45 0.97 20

0 110 0.46 1 3

the table above demonstrate that the current, power, phase angel changes with respect to alpha. These changes are represented in the figures below.


Figure 4 current agaist alpha

Figure 5 power V Alpha


Figure 6 power factor agaisnt alpha

Discussion 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 +(sin (2α ) )

π ]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 degree

The 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 harmonics

Discussion on the harmonics distortion

The 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.

Frequency Harmonics order DB/Vrms

50 first -32.5

150 third -35

250 fifth -43

350 seventh -45

450 ninth -47.5

550 Eleventh -49

650 thirteenth -51

750 fifteenth -52.5


Operation of light dimmer circuit

The 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 components


The circuit's operation

Generally, 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 TRIAC.

Comparing the time constant with off time delay of the chopped sine wave

The 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 delay

Time constant ( theory) Off time ( expermental)Minimum value 340 us 0Maximum value 27 ms 6.3 ms


As 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 explained.

Comparative 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

http://www.electronics-tutorials.ws/filter/second-order-filters.html

http://www.lvcem.com/sf/studies/pwrelectronics/TRIAC%20Circuit%20analysis.pdf

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