1. Lab 3: Simulation of Ex. 6-11
Prepared by Eli Walker
PSID: 1004978
For ECE 5197
Dr. Jung-Uk Lim
2. ii
Index
PSpice Simulation… 1-7
Introduction… 1-2
Methods… 3-4
Results… 4-6
Discussion and Conclusion… 7
PSim Simulation… 7-14
Introduction… 7-10
Methods… 10-12
Results… 12-14
Discussion and Conclusion… 14
3. 1
PSpice Simulation
Introduction
For this project we were asked to simulate Ex. 6-11 from the textbook in both PSpice and PSim;
we will begin by discussing the PSPice simulation here. The circuit we will be constructing and
simulating in PSpice, shown in Figure 1 below, is a model of a buck converter using an ideal
diode and voltage controlled switch.
Figure 1: Buck converter circuit model using an ideal diode and voltage controlled switch, including parameters for each
element. We will construct and simulate this circuit in PSpice.
A buck converter is a DC to DC converter that produces an output voltage that is lower than the
input voltage. The switch in our circuit is used to model a switching transistor and the pulse
voltage source is used to control the switch. The inductor and diode work together to convert
the input voltage to a lower output voltage while the capacitor is used as a filter to produce a
near linear result. The resistor labeled Resr, esr stands for equivalent series resistance, in series
with the capacitor is used to model a real capacitor, which has some internal series resistance.
This produces a slight ripple in the output voltage. As part of the design considerations for this
problem, we are asked to keep the output ripple voltage, denoted ΔV, below 24 millivolts. To
determine the output voltage of any buck converter circuit, we use the following equation:
4. 2
𝛥𝑉 =
𝑉0(1−𝐷)
8𝐿𝐶𝑓2
(eq. 1)
where V0 is the input voltage, D is the duty cycle of the circuit, L is the inductance, C is the
capacitance, and f is the frequency. Evaluating eq. 1 using the parameters given in Figure 1, we
find an output ripple voltage of about 22 millivolts. After we construct this circuit and simulate
it in PSpice, we will use the probe feature to determine the maximum and minimum values of
the output voltage once the system reaches steady-state. We will then take the difference
between these two values to determine the output ripple voltage, ΔV, which will be compared
to the value we obtained using eq. 1. We will also use the probe to plot the inductor current
and output voltage in both the transient and steady states of the circuit.
Constructing the circuit for this example was similar to the previous labs. All of the needed
components are found in the “PSpice component” subsection of the “Place” tab. Figure 2 shows
our circuit after constructing in PSpice.
Figure 2: Our circuit after constructing in PSpice. We will simulate this circuit in order to obtain the desired plots and data points.
This circuit will be simulated using PSpice for 1 millisecond. The inductor current and output
voltage will then be plotted using the Probe feature, in both the transient and steady states.
These plots will be used to determine the output ripple voltage and the maximum and
minimum inductor current values, which are desired to be 4.8 and 3.2 amperes respectively.
These results are produced and discussed thoroughly in the succeeding sections.
5. 3
Methods
The steps taken to simulate our circuit using PSpice are the same as in previous labs. Clicking
the “New Simulation Profile” option from the toolbar allows us to select both the start and stop
times for data collection. For this example, we wish to gather data from 0 to 1 millisecond. This
will allows us to capture the transient and steady states of the system. In order to view the
steady-state of the circuit, we will simply adjust the interval of the x-axis on the plot. One
important difference in this example is that we wish to use an ideal diode model in our design.
In order to accomplish this, we must change the parameters of the PSpice diode model, namely
the emission coefficient, or n. To do this, we select the diode in our circuit, right-click on it, and
select “Edit PSpice Model” as shown in Figure 3.
Figure 3: Illustrating how to change the parameters of the diode.
This will bring up a text editor box. Simply replace everything in this box with “.model Dbreak D
n=0.001” as demonstrated in Figure 4.
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Figure 4: Text editor of the diode parameters. Replace the default text in this box with the circled text from the figure.
Once this is done, click save and close the window. The circuit is now complete and the
simulation parameters have been set. We will now run the PSpice simulation on our circuit. The
results obtained will be produced and discussed in full in the following two sections.
Results
Our circuit after running the PSpice simulation is shown in Figure 5.
Figure 5: Our circuit after running the PSpice simulation.
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Performing the simulation according to the previously discussed parameters allowed us to
obtain the required data. First, Figure 6 shows the transient response of both the inductor
current and the output voltage.
Figure 6: Transient response of the inductor current and output voltage.
As can easily be seen from Figure 6, there is a very large spike at the beginning of the plot
before going back to close to 0. The current then spikes slightly and oscillates for the rest of the
time interval. The output voltage appears to be exactly linear after a slight delay at the start of
the plot. This would be expected from the output of a DC to DC converter. However, as we will
see when examining the steady-state, the output voltage is not entirely linear as there is a slight
ripple. It is also important to note that the last part of the plot from 0.980 milliseconds to 1
millisecond represents the steady-state of the system. This is shown clearer in the following
two figures.
Let us first inspect the steady-state response of the current through the inductor. This plot is
shown in Figure 7 below.
8. 6
Figure 7: Steady-State response of the current through the inductor.
As can be seen from Figure 7, the current through the inductor oscillates from a maximum of
4.7721 amperes to a minimum of 3.2438 amperes for the entirety of the steady-state. In the
Discussion section we will compare these values to the desired quantities of the example.
We will now look at the steady-state output voltage illustrated in Figure 8.
Figure 8: Steady-state response of the output voltage.
Here we can clearly see that the output voltage has a slight oscillation from 1.1911 volts to
1.2130 volts. We will use these values to calculate the output voltage ripple and compare the
result to the solution of eq. 1. This can be found in the following section.
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Discussion and Conclusion
There are several important thing to take away from the figures presented in the preceding
section. First, comparing Figures 7 and 8 show that the inductor current and output voltage are
exactly in phase, their maximums and minimums occur at exactly the same time. This is logical
as the charging and discharging of the inductor provides the current to the filter capacitor,
which in turn produces a near-linear DC output voltage. Secondly, as a parameter of the
problem we desired to produce a maximum inductor current of 4.8 amperes and a minimum of
3.2 amperes. Comparing this to the values we obtained from Figure 7, 4.7721 and 3.2438
amperes, and we can conclude that this parameter has been successfully met. Finally, we will
take the difference of the maximum and minimum values of the output voltage in order to
determine the output ripple voltage, ΔV. This will then be compared to the result of eq. 1. With
a maximum voltage of 1.2130 volts and a minimum of 1.1911 volts, the output voltage ripple is
found to be 22 millivolts, which is identical to the result of eq. 1 and well within the 24 millivolt
limit. It is also pertinent to point at that output voltage is lower than the 3.3 volt input. This
proves that our buck converter model is indeed operating correctly.
We have now completed three separate simulations using the PSpice software. Each of these
simulations increased in complexity culminating in this model of a buck converter. We are now
fully comfortable with the PSpice environment and should have no issues constructing and
simulating even the most complex of circuits.
PSim Simulation
Introduction
This part of the lab is considered with constructing and simulating the same circuit shown in
Figure 1 using a different software library. This time, we will use PSim. PSim, short for Power
Simulation, can perform the same tasks as PSpice such as constructing and simulating circuits
10. 8
and measuring any desired quantities. As the name implies, PSim is mostly used for simulating
power electronics and electric drives. This makes it far more desirable for our purposes. We will
construct and simulate our circuit using the same parameters as previously discussed, and the
obtained data will then be compared to the results obtained from the PSpice simulation.
Constructing the circuit in PSim is similar to the process used to construct it in PSpice. We begin
by selecting the “New Project” option from the “File” menu as shown in Figure 9.
Figure 9: Selecting the "New Project" option from the "File" menu.
After naming the project and selecting a location to save the project, a new work page will
automatically open. We are now ready to construct the circuit. To do this, we simply select the
“Elements” option from the toolbar as illustrated in Figure 10. All of the elements we need for
this circuit can be found in this menu.
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Figure 10: Illustrating how to select a DC voltage source from the "Elements" menu. All of our other required elements can be
found from this menu.
Specifically, Figure 10 illustrates how to select a DC voltage source from the “Elements” menu.
It should be noted that every other element we require for the circuit can be found from this
menu. Once an element has been selected, we use a right click to rotate the element and a left
click to place it. Double clicking on an element will open a dialogue box that will enable us to
edit the parameters of the element. As was previously noted, we will use the same parameters
as the PSpice simulation. After placing all of the required circuit elements, we are ready to
connect each of these using wires. This is done by first selecting the “Wire” option, the pen
icon, from the toolbar. This is shown in Figure 11.
Figure 11: Highlighting the "Wire" option from the toolbar.
12. 10
After connecting all of the elements using wires, our circuit is fully constructed in the PSim
environment, as is shown in Figure 12. It is important to note that PSim lacks the Probe feature
found in PSpice. Therefore, in order to measure the desired values, the inductor current and
the output voltage, we are required to place a current probe in series with our inductor and a
voltage probe in parallel with our load resistor. These probes are circled in Figure 12.
Figure 12: Our fully constructed circuit in PSim. The circled elements are the current probe and voltage probe respectively.
The circuit will now be simulated and the current through the inductor and the output voltage
will be plotted in both the transient and steady-state. These results will be compared to the
plots obtained in PSpice. This data is produced and discussed in detail in the following sections
Methods
In order to simulate our circuit in PSim, we must first set the simulation controller, or clock,
which is identical to setting the simulation profile in PSpice. To do this, we simply select the
“Simulate” option from the toolbar and from there select “Simulation Control”, which is
detailed in Figure 13.
13. 11
Figure 13: Detailing the steps taken to place the simulation controller.
After performing these steps, we can place the simulation controller anywhere in the
workspace. A dialogue box will automatically open allowing us to adjust the simulation
parameters. As in the PSpice simulation, we will choose to collect data from 0 to 1 millisecond.
The circuit is now ready to be simulated. This is simply done by selecting the “Run Simulation”
option from the toolbar, which is shown in Figure 14.
Figure 14: Selecting the "Run Simulation" option from the toolbar.
After successfully completing the simulation, PSim will automatically open a window allowing
the user to select which values to plot. This is shown in Figure 15 below.
14. 12
Figure 15: Illustrating how to select which values to plot.
For our purposes, we will select both of the listed options. We then select “Add” and then “Ok”.
The plots obtained will be produced and discussed in the following sections.
Results
After simulating the circuit we obtain the data we are interested in. As for the PSpice simulation
we will start by producing the plot of the transient inductor current and output voltage.
15. 13
Figure 16: Transient response of the inductor current and output voltage after simulating the circuit in PSim.
We next turn our attention to the steady-state response of the inductor current, shown in
Figure 17. As with the PSpice simulation, in order to view the steady-state of the system, we
will simply change the interval of the x-axis.
Figure 17: Steady-State response of the inductor current.
Again, this plot will be compared to Figure 7 in the following section.
Finally, we will look at the plot of the steady-state output voltage as obtained by the PSim
software simulation. This plot is shown in Figure 18.
16. 14
Figure 18: Steady-State response of the output voltage.
Once again, this will be compared to Figure 8 in the final section of this report.
Discussion and Conclusion
As was stated in the preceding section, we will compare each plot obtained from the PSim
simulation to their corresponding plots from the PSpice simulation. Accordingly, the plot shown
in Figure 16 is identical to that contained in Figure 6. We can this conclude that the transient
portion of the circuit has been correctly simulated in both platforms. Examining Figures 17 and
7 side by side show that the steady-state inductor current in both simulators are identical. In
the same vein, comparing Figures 18 and 8 show that the plot of the output voltage is exactly
the same for both simulations. We can thus conclude that the steady-state response of our
circuit was successfully simulated in both PSpice and PSim.
Constructing and simulating this fairly complex circuit first in PSpice and then in PSim allows us
to familiarize ourselves with the PSim software package. We are now prepared to construct and
simulate any circuit in the PSim environment, which is designed specifically for power circuits
and electric drives.
