Transcript Complex Power in AC Circuit Analysis

Complex Power in AC Circuit
Analysis
Experiment 27
Changes to Circuit
Analysis Section
• Step 6:
– Use MatLAB to plot a graph of the instantaneous
power, p(t), for each value of R2.
Tables 1-4 and Step 16 of
Measurements
• Change 820 0.1F to 820 10mH C
– You must calculate the value of the capacitor that
is required to balance the inductive portion of the
impedance of the resistor and inductor in series.
Measurements
• To measure the instantaneous power, you will measure the
voltage dropped across the components and the current
flowing through them, as measured by the voltage dropped
across the shunt resistor. These measurements can be
multiplied together to obtain the instantaneous power.
The latest version of the oscilloscope
software program has a CH1*CH2
option. However, it is difficult to read
data off of the plot.
Export Data to MatLAB
Select File/Save DSO Data from upper toolbar.
Data Format
The number of data points in the
first column (N) are equivalent to a
period of time (50s in this case).
To change the data listed under N
to time, you must multiply each
value by the fraction 50s/125.
Data Format
0V is equal to the value of 167 for the
data displayed under CH1 and to the
value of 87 for the data displayed under
CH2.
This offset must be removed before
converting the data listed under CH1 and
CH2 can be converted to voltage.
Data Format
The conversion factor needed to change the
data listed under CH1 and CH2 into voltage.
To change the data to voltage after you
have substract off the offset for ground, you
must multiply each value by the fraction
1V/32 for CH1 and 0.1V/32 for CH2 in this
example.
To convert the voltage across the shunt
resistor to current, divide by the value of the
shunt resistor.
Only then can you can multiple the data
listed in CH1 by the data listed in CH2 to
calculate the power.
Importing Data File to MatLAB
• You may do the preprocessing of the data saved
from the oscilloscope in either Excel or in
MatLAB. However, the graphs to be included in
Step 5 of the report template must be
generated using MatLAB.
– There is an Import Wizard in MatLAB.
• For instructions, see:
http://www.mathworks.com/help/techdoc/import_export/br5wz4t.html#f5-91134
http://www.mathworks.com/help/techdoc/import_export/f5-35378.html
These instructions are also available in the MatLAB program in the
Help function
Measurements
• The m-file referred to in the lab manual
(complexpower.m) has been modified.
– Use complexpower_changed.m is posted under
Resources/Technical Support: MatLAB
Conclusions
• You should comment on the accuracy of your
analysis and measurements due to:
– Deviations from nominal values of your
components including the parasitic resistance of
the inductor
– The effect of the shunt resistor
– Digitizing errors associated with the data
outputted by the oscilloscope