ELEX_4420_-_Lab_04_-_Single-Phase_FW_Rectifiers
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Lab 4: Single-Phase Full-Wave
Rectifiers
Marcel Moreno
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
Lab 4: Single-Phase Full-Wave
Rectifiers
Objective
To study the behavior of various single-phase rectifier circuits and illustrate some key principles.
Equipment
Three-Phase Rectifier (External Rectifier) (used as single-phase rectifier in this lab)
Capacitors: DC-Link Capacitor (
850
μF
¿
and EMI Filter Bank capacitors
Three-Phase Load Bank (used as DC load)
Power Analyzer: For all the parts we use the power analyzer for measurements.
DMM (x2): One used as current sensor, one as a voltage sensor.
Pre-Lab (2 marks):
A Simulink file is provided (FW_rectifier_LCfilter.slx).
You need to change the transformer winding ratio so that the transformer’s secondary
voltage is 20 V rms.
Add your initials on the input lines of the scope.
RLC values need to be changed according to the following table and for each case, run the
simulation and fill out the table. You will need to remove the L and/or C from the circuit for
some cases.
For each case, capture the scope results. Scale the axes limits as shown below and copy the
plots into your pre-lab report. V
dc
V
rms
THD
v
I
dc
I
rms
THD
i
R = 83 Ω No Filter
16.65
18.77
52.03
0.201
0.226
52.03
R = 62.5 Ω
No Filter
16.59
18.72
52.24
0.265
0.299
52.24
R = 62.5 Ω
C = 40 μ
F
17.84
19.13
38.76
0.285
0379
87.26
R = 62.5 Ω
C = 120 μ
F
20.65
21.09
20.68
0.330
0.560
137.0
R = 62.5 Ω
C = 40 μ
F
L = 1.5 mH
17.98
19.34
39.58
0.288
0.406
99.61
R = 62.5 Ω
18.19
19.75
42.28
0.291
0.424
106
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
C = 40 μ
F
L = 4.5 mH
R = 83 Ω
No Filter
P. Taheri
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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
R = 62.5 Ω
No Filter
R = 62.5 Ω
C = 40 μ
F
R = 62.5 Ω
C = 120 μ
F
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
R = 62.5 Ω
C = 40 μ
F
L = 1.5 mH
R = 62.5 Ω
C = 40 μ
F
P. Taheri
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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
Part A – Single-Phase Full-Wave (Full-Bridge) Rectifier (4 marks)
The purpose of this section is to verify full-wave (full-bridge) rectifier operation. Connect your
circuit in full-bridge configuration as shown in the circuit diagram below (again, the greyed-out
portions of the circuit are unused). 1.
Connect Phase A and N to the autotransformer. Turn the power ON and adjust the knob until
you get 20 V rms
output voltage. You can check the voltage with DMM or power analyzer.
Once the voltage is set, turn the power off.
2.
Set up your power analyzer and connect the power cables for the converter and load bank
and turn them on.
3.
Build the above circuit. Note that we use one DMM as an ammeter, which measures the
output current of the H-bridge. We measure the same current with the power analyzer, but
since the CT clamps cannot measure DC current, we use DMM to get more information.
4.
We measure the output voltage using both power analyzer and DMM. Change the electrical
hookup setting to L1 N (single-phase) and connect L1 and N output ports of the power
analyzer across the resistive load. 5.
Connect the second DMM as a voltage sensor across the load.
6.
We use only one of the three resistors. 7.
Before turning the circuit on, measure the load resistance for these two cases:
Switches #1-3 ON
Switches #1-4 ON
R (
Ω
)
82.7
62
8.
Ask the lab instructor to check your circuit. Turn the load bank’s switches off. Turn ON
the isolation switch to energize your circuit. As with the half-wave circuit, you should now see
the DC-side voltage measurement for your rectifier.
9.
(1.5 marks) For two different resistive loads (light load: switches #1-3 or 83
Ω
, heavy load:
#1-4 or 62
Ω
)
a.
Capture the output voltage (resistor voltage) and current. You need to capture a
picture using the power analyzer and read the data once you are done.
Note
that time and date setting of the power analyzer might be wrong, so please take a note
of the time stamps for each picture.
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
b.
Fill out the following table. Once done (make sure you capture pictures of the power
analyzer for both loading conditions). Once done, power down your circuit.
R ~ 83
Ω
R ~ 62
Ω
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
No
Filter
Power Analyzer
DMM (Voltage)
DMM (Current)
V
rms
V
dc
I
ac,rms
V
ac,rms
V
dc
I
ac,rms
I
dc
R ~ 83
Ω
19.9
0.2
0.22
8.67
16.31
0.11
0.198
R ~ 62
Ω
19.8
0.2
0.30
8.60
16.17
0.14
0.262
Notice that I
dc
measured by DMM is the same as downward shift of the current
waveform displayed by the power analyzer. Power analyzer current clamps cannot
measure DC current and shows i(t)-I
dc
.
Analysis Questions for part A (2.5 marks):
1.
Compare the DC and RMS voltages from power analyzer with theoretical values:
V
o, DC
=
2
V
pk
π
,V
o, RMS
=
V
pk
√
2
For R ~ 83
Ω
V
o, DC
=
2
(
19.9
∗
√
2
)
π
=
17.9
,V
o, RMS
=
(
19.9
∗
√
2
)
√
2
=
19.9
For R ~ 62
Ω
V
o, DC
=
2
(
19.8
∗
√
2
)
π
=
17.8
,V
o, RMS
=
(
19.8
∗
√
2
)
√
2
=
19.8
The Theoretical and power analyzer Dc and Rms voltage are close. 2.
Do the V
dc
and I
ac,rms
measurements from DMM and power analyzer match? Calculate V
rms
based on your DMM readings (
V
o, RMS
=
√
V
o, AC , RMS
2
+
V
o, DC
2
) and see if it matches with the power
analyzer measurement. Based on voltage and current readings, verify Ohm’s law. Is I
dc
=
V
dc
R
?
Is I
ac, rms
=
V
ac,rms
R
? Is I
rms
=
V
rms
R
?
V
o, RMS
=
√
8.67
2
+
16.31
2
=
18.47
No, the V
dc
and I
ac,rms
measurements from DMM and power analyzer don’t match. But the
calculated Vrms is close to the measured Vrms from the power analyzer.
I
dc
=
16.31
83
=
0.196
I
ac, rms
=
19.9
83
=
0.23
I
rms
=
8.67
83
0.104
Ohm’s law prove that my measured value is correct.
3.
Based on the captured picture from the power analyzer, find voltage and current ripples (
Δ v
o
and Δi
) for both loading conditions.
Based on the captured picture from the power analyzer the voltage ripple is 0.2 and current ripple is 0.22 when the resistor is 83
Ω
and 0.2 voltage ripple and 0.30 current ripple when the resistor is 62 Ω
.
4.
Find the output’s peak voltage. If you set the AC voltage on the transformer’s secondary to 20
V rms, peak voltage should be around 20
√
2
. But there is some voltage drop on the diodes.
Calculate the voltage drop across each diode. Is this voltage drop constant or does it change?
Vdiodes
=
Vout – Vin
=
20
√
2
−
20
V
=
8.28
V
Vdiode
=
8.28
4
=
2.07
V
The voltage drop is constant.
P. Taheri
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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
5.
Determine the THD of the voltage (
√
V
rms
2
−
V
dc
2
V
dc
)
and current (
√
I
rms
2
−
I
dc
2
I
dc
)
at each loading
condition. Why is the THD values shown on the power analyzer so different from what we
calculate? What THD value does the power analyzer calculate?
For R = 82
Ω
THDv
=
√
19.9
2
−
0.2
2
0.2
=
99.5%
THDi
=
√
0.11
2
−
0.198
2
0.198
=83%
For R = 62
Ω
THDv
=
√
19.8
2
−
0.2
2
0.2
=
99%
THDi
=
√
0.14
2
−
0.262
2
0.262
=84.5%
The power analyzer only gives the AC part of the THD. That is why it is different from the
calculated.
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
Part B – Single-Phase Full-Wave Rectifier with Capacitive Filter (3 marks)
1.
Make sure the power is OFF. In this part, we use two different capacitors as a filter across
the load. C
dc, low
=
40
μF
and C
dc, high
120
μF
. The first capacitance is made by putting the 10 and
30 μ
F capacitors in the filter box in parallel. The second capacitance is the six capacitors
(three 10 μ
F and three 30 μ
F) put in parallel.
2.
Connect the 24 V ports of the VSC box and the filter box. Then, turn S
1a
and S
2a
switch ON by
energizing their contactors. Measure the capacitance using DMM. It should be around 40
μ
F. C
= 40.2
μ
F
3.
Put the capacitor in parallel with the load.
4.
Ask the lab instructor to double check your circuit. Then, turn the power on.
5.
(0.5 mark) Fill out the table. Capture a picture in your power analyzer. You will download the
pictures later to answer the analysis questions. P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
40
μ
F
Filter Power Analyzer
DMM (Voltage)
DMM (Current)
V
rms
V
dc
I
ac,rms
V
ac,rms
V
dc
I
ac,rms
I
dc
R = 62
Ω
19.8
0.1
0.38
6.61
17.9
0.25
0.289
6.
Turn the power off.
7.
By making all three capacitor sets parallel
(connecting the ends of the capacitor sets as shown
in the picture) and turning all S1* and S2* (six
switches in total) switches on, we can increase the
capacitance to 120 uF (3*(30+10) uF). Measure the
exact capacitance using the DMM. C = 121
μ
F
8.
Ask the lab instructor to double check your circuit. Then, turn the power on.
P. Taheri
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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
9.
(0.5 mark) Fill out the table. Capture a picture in your power analyzer. ~120
μ
F
Filter Power Analyzer
DMM (Voltage)
DMM (Current)
V
rms
V
dc
I
ac,rms
V
ac,rms
V
dc
I
ac,rms
I
dc
R = 62
Ω
20.1
0.1
0.56
3.95
21.24
0.44
0.344
Analysis Questions for part B (2 marks):
1.
Based on downloaded information from the power analyzer. Find the following information for
both capacitor filters:
Voltage ripple (
Δ v
o
)
Current ripple (
Δi
o
)
The discharge time of the capacitors in one full cycle of input (T = 1/60 = 17 ms). You are
measuring 2xt
d
as the capacitor gets charged and discharged twice in one full cycle of the
input (once in the positive half and once in the negative half). You can figure that by
measuring the time span where current is equal to 0. Remember that power analyzer has
a negative offset due to its inability to measure DC currents, so 0 current is displayed at -
I
dc
.
2.
Determine the THD of the voltage and current waveforms. Is THD
v
=
THD
i
? THDv
=
√
3.95
2
−
21.24
2
21.24
=
98%
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
THDi
=
√
0.44
2
−
0.344
2
0.344
= 67%
No, the current THD is worse than the voltage.
3.
Explain the impact of adding a capacitive filter on Δ v
o
, V
dc
, THD
v
, THD
i
, and harmonic values.
Adding capacitive filter will smoothen the curve and will have less ripple because of this the THD will be better.
4.
Are the results similar to the Simulink simulation results? Yes
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
Part C – Single-Phase Full-Wave Rectifier with LC Filter (3 marks)
1.
Make sure the power is OFF. In this part, we use the 40 μ
F capacitor, but we add an inductor in our filter to see the impact of it on output voltage and current. We use two different inductors: 1.5 mH and 4.5 mH.
2.
First, we put a 1.5 mH inductor in series with current sensor as shown in the figure. We use the
40 μ
F capacitor. Make sure the S
1a
and S
2a
switches are closed. We only need one set of the
capacitors in this part (one 10 μ
F + one 30 μ
F). Measure the capacitance to make sure it is
around 40 μ
F. 3.
There are three sets of the inductors in the filter box, but we only use one of them in this case as
shown below:
4.
Ask the lab instructor to double check your circuit. Then, turn the power on.
5.
(0.5 mark) Fill out the table. Capture a picture in your power analyzer: P. Taheri
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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
40
μ
F + 1.5 mH
Filter Power Analyzer
DMM (Voltage)
DMM (Current)
V
rms
V
dc
I
ac,rms
V
ac,rms
V
dc
I
ac,rms
I
dc
R = 62
Ω
20.1
0.1
0.4
6.9
18.39
0.269
0.297
6.
Turn the power off.
7.
This time we put three inductors in series to create a 4.5 mH inductor as shown in the picture.
Notice that this time the neutral connection in the filter box comes from N
c
. Therefore, we create
the 40 μ
F on phase C. In this case, only S
1c
and S
2c
switches are closed.
8.
Ask the lab instructor to double check your circuit. Then, turn the power on.
9.
(0.5 mark) Fill out the table. Capture a picture in your power analyzer.
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
40
μ
F + 4.5 mH
Filter Power Analyzer
DMM (Voltage)
DMM (Current)
V
rms
V
dc
I
ac,rms
V
ac,rms
V
dc
I
ac,rms
I
dc
R = 62
Ω
20.1
0.1
0.28
7.16
18.79
0.291
0.304
Analysis Questions for part C (2 marks):
1.
Based on downloaded information from the power analyzer. Find the following information for
both inductor cases filters:
Voltage ripple (
Δ v
o
)
Δ v
o
=
1.4
V
Current ripple (
Δi
o
)
Δi
o
=
0.19
A
2.
Determine the THD of the voltage and current waveforms. Is THD
v
=
THD
i
? Which one of them
improved more after adding the inductor (compared to part B)?
THDv
=
√
7.16
2
−
18.79
2
18.79
=
¿
92%
THDi
=
√
0.291
2
−
0.304
2
0.304
=29%
The THD of current is worse than the voltage. Adding inductor improves the THD of the
current.
3.
Were the inductors big enough to cause any improvement in the voltage and current
waveforms (in terms of THD and ripples)? No, it is not enough to improve the THD and ripples
of the voltage and current waveform. Based on the waveform we have the voltage is
somewhat close to being sinusoidal but the current is distorted.
P. Taheri
BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications
4.
For the case of 4.5 mH, over one full cycle of the input signal (~17 ms), for how many
milliseconds were all the diodes off (current is zero)? Compared with part B, did adding the
inductors make any difference in this disconnect time? The total time where all diodes are off is 10ms. Compared to part B it is shorter which results in
having a better waveform as it will provide a better DC output because the inductor is higher.
Part D – Downloading the Data
Here are the steps we used to successfully use the AEMC software within AppsAnywhere to
detect the analyzer:
1.
Do NOT
connect the analyzer to the computer before starting the software.
2.
Start AppsAnywhere and then launch the AEMC PowerPad III software.
3.
Do NOT select yes when asked to upgrade
the software to the latest version.
4.
Once the software has started, wait for 5 minutes so the software can initialize.
5.
Now connect the analyzer to the USB port of the computer. The ports on the computer
itself are much more reliable than the ports on the display.
6.
Within the software select Connect Instrument
. The number of the model of the
analyzer should be visible as an option, i.e., 8336
. If you don’t see the analyzer model
number, restart the computer, and try the steps again from the beginning.
7.
Proceed with your data upload.
If you happen to connect the analyzer to the computer before you start the software, you will have to restart the computer, and then start over.
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