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TEACHING AND DEMONSTRATION OF POWER ELECTRONIC
CIRCUIT ANALYSIS
O.W. Andersen
Norwegian Institute of Technology, Trondheim, Norway
Abstract. A demo version of simulation program PECAN (Power Electronic Circuit
Analysis) can be downloaded from Internet address http://www.elkraft.unit.no/~andersen/
and used freely for educational and other purposes. A student can enter component values
simply by answering questions, while a circuit is displayed on the screen. He doesn’t have
to learn how to make up cryptic input files.
Keywords. Teaching, education, demonstration, analysis, power electronic circuits.
INTRODUCTION
SAMPLE CALCULATION
An early version of PECAN was written in 1977 for
mainframe computers, and it has since been improved
and adapted for use on personal computers. The demo
version is limited to 2500 time steps and 40 variables
(node potentials and branch currents). This is considered
to be sufficient for most educational and demonstration
purposes, but the full version can handle 30000 time
steps and 500 variables. It requires a 386/486 with math
coprocessor or Pentium computer, with at least 4 Mb
RAM.
46 input files are included in the demo. Most of them
are for different power electronic circuits, but there are
also some for related problems, such as regulation loops
and electrical machine transients.
When a circuit is examined by a student, he enters a
command (under MS-DOS), such as:
EXAMINE DIORECT2
where DIORECT2 is a three phase diode rectifier with
current source load. A circuit diagram with explanations
appears on the screen, as shown in Fig. 1. The circuit
diagram is marked with node numbers, branch numbers
and component numbers, with prefixes N, B and C.
Fig. 1. Three phase diode rectifier with current source load.
To proceed, the student simply strikes ENTER. After a
few seconds, the calculations are completed. Curves are
displayed in different colors for voltages between nodes
and/or across components, and for branch currents, as
shown in figures 2 and 3. Then, in this case, a Fourier
analysis is performed automatically for a line current,
and a harmonic spectrum is displayed, as shown in Fig.
4.
Voltage between nodes 2 and 3
Voltage between nodes 5 and 6
For the same problem, a student can also change the
component values in a very simple manner and see what
it does to the voltages and currents, with the command:
EXERCISE DIORECT2
In this case, he can change applied voltages, frequency,
inductances and load current. The circuit is displayed on
the screen, and the text above it (Fig. 1) is replaced by
two lines, such as:
Strike ENTER to keep old value 1
Inductances, mH?
The cursor appears after the question mark, and the
student can either keep the old value or change it.
It is suggested to the student what he might do and what
to look for. It can be observed, for example, that triple
harmonic line currents are always absent in this circuit.
It can also be observed how the commutation interval is
affected by the load current and the series inductances.
Fig. 2. Voltages.
Current in branch 7
Current in branch 8
Current in branch 9
Fig. 3. Currents.
Fig. 4. Harmonic spectrum.
STUDENT EXERCISE
LIST OF EXERCISES
A total of 26 exercises of the type just described are
included in the demo. They are:
Basic rectifier with inductive load.
Basic rectifier. Load with internal dc voltage.
Basic circuit with current commutation.
Single phase diode bridge rectifier with voltage source
load.
Three phase diode rectifier with current source load.
Three phase diode rectifier with voltage source load.
Basic thyristor converter, rectifier mode.
Single phase thyristor controlled inductor.
Single phase thyristor bridge rectifier with current
source load.
Three winding transformer with triac controlled inductors.
Step down converter, continuous current mode.
Step down converter, discontinuous current mode.
Step up converter, continuous current mode.
Step up converter, discontinuous current mode.
Buck boost converter, step down, continuous conduction
mode.
Buck boost converter, step up, continuous conduction
mode.
Buck boost converter, step down, discontinuous conduction mode.
Buck boost converter, step up, discontinuous conduction
mode.
Pulse width modulation.
Small 0.75 kW dc motor startup.
Large 75 kW dc motor startup.
Armature short circuit of differentially compounded dc
generator.
Three stage impulse generator wavefront.
Three stage impulse generator wavetail.
Dc motor position control without current control loop.
Dc motor speed control with internal current control
loop.
also possible to use shareware PRINTGL, which can be
downloaded from
http://ourworld.compuserve.com/homepages/ravitz/
With this, plotting can be done from an HP-GL file on
practically any printer and plotter on the market.
OTHER INPUT FILES
Another 20 input files are included for demonstration
purposes only. They are:
Single phase voltage doubler rectifier.
Three phase diode rectifier with dc filter.
Basic thyristor converter, inverter mode.
Three phase thyristor bridge rectifier with current source
load.
Cuk converter.
Flyback converter.
Single phase full bridge square wave mode inverter.
Single phase full bridge inverter, voltage cancellation
switching.
Three phase square wave mode inverter with voltage
source load.
Three phase square wave mode inverter with resistive
load.
Three phase square wave mode inverter with inductive
load.
PWM with bipolar voltage switching.
PWM with unipolar voltage switching.
Single phase full bridge PWM inverter at open circuit.
Single phase full bridge PWM inverter with voltage
source load.
Three phase PWM inverter with voltage source load.
Programmed harmonic elimination of fifth and seventh
harmonics.
Basic resonant converter operating below resonant frequency.
Basic resonant converter operating above resonant frequency.
Transient temperatures on cables.
In addition to output plotted on the screen and on paper,
a numerical output file is created. It includes, if requested, calculated values at each time step, rms values, average values, etc. The file can be studied on the screen and
printed.
A Fourier analysis results in another numerical output
file, containing values of harmonics, crest factors, form
factors and harmonic distortion.
METHOD OF SOLUTION
A linear equation is set up for each node and each
branch at each point in time, starting from t=0. The
lengths of the time steps vary between limits specified in
the input.
For a node, the sum of the currents into the node is set
equal to zero. The equation is used to find one of the
currents. For a branch, the equation may involve old and
new currents (for previous and present points in time)
and old and new node potentials at each end. The equation is used to find one of the new potentials or the new
current.
An inductor has a voltage across it equal to the inductance times the difference between new and old currents,
divided by the length of the time step. Mutual inductances may contribute to the voltage.
This way, the number of linear equations equals the
number of unknown node potentials and branch currents, and can be solved at each point in time by Gaussian elimination.
PLOTTING AND PRINTING
A simple command will result in the creation of an HPGL graphics language file containing plotted output or a
harmonic spectrum. This can be incorporated into a
Microsoft Word, WordPerfect or other word processor
document and subsequently plotted on a printer. It is
REFERENCE
O.W. Andersen, Time Domain Circuit Analysis, IEEE
Computer Applications in Power, pp. 34-38, April 1992.