Complex Power in AC Circuit Analysis

1
Complex Power in AC Circuit Analysis

• Experiment 27

2
Changes to Circuit
3
Analysis Section

• Step 6
• Use MatLAB to plot a graph of the instantaneous
  power, p(t), for each value of R2.

4
Tables 1-4 and Step 16 of Measurements

• Change to
• 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.

5
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 CH1CH2 option. However, it is
difficult to read data off of the plot.
6
Export Data to MatLAB
Select File/Save DSO Data from upper toolbar.
7
Data Format
The number of data points in the first column (N)
are equivalent to a period of time (50ms in this
case). To change the data listed under N to
time, you must multiply each value by the
fraction 50ms/125.
8
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.
9
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.
10
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_expor
  t/br5wz4t.htmlf5-91134
• http//www.mathworks.com/help/techdoc/import_expor
  t/f5-35378.html
• These instructions are also available in the
  MatLAB program in the Help function

11
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

12
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