Power Electronics Laboratory Using PSpice
Muhanunad H. Rashid, and Samir A. Al-Biyat
Department of Electrical Engineering
King Fahd University of Petroleum & Minerals
Dhahran 31261
Fax: 966 - 3 - 860 3535
Abstract:
This paper summarizes the usefulness of the circuit
simulator PSpice in understanding the operation of
power electronic circuit and the control function. It
illustrates through examples the simulation of power
electronic laboratory by using by PSpice.
Introduction
Power electronics is an application oriented and
interdisciplinary course. It uses power semiconductor
devices to perform switching action in order to achieve a
desired conversion strategy. The switching slices the
voltage and current waveforms into various intervals,
whose beginning and end depend on the boundary
conditions, which are fixed by the circuit parameters
and/or control characteristics. The understanding of the
operation of a power electronics circuit requires a clear
knowledge of the transient behavior of current and
voltage waveforms for each and every circuit element at
every instant of time. These features make power
electronics a difficult course for students to understand.
A laboratory helps in understanding power electronics
and its control interfacing circuits. The development of
power electronics laboratory is relatively expensive
compared to other courses in EE curriculum, and as a
result power electronics laboratory facilities are available
in few limited universities.
However, the power
electronics are playing a key role in industrial power
control applications. Many universities are recognizing
the importance of power electronics and offer it as a
lecture course without any laboratory supports.
The student version of PSpice, which is available free
to students, is ideal for class-room use and for
assignments requiring computer-aided simulation and
analysis. Probe is like a theoretical oscilloscope and it
can be used as a laboratory bench to view the waveforms
of currents, voltages, power, power factor, etc. The
capability of Probe along with other features to represent
data in Table, Value, Function, Polynomial, Laplace,
Param, Step makes PSpice versatile simulation tool for
power electronic power courses. Students can design
power versatile electronics circuits, use the PSpice
simulator to verify the design, and make necessary
design modifications.
Single-Phase PWM Inverter
This is the first example to simulate the operation of a
single-phase PWM inverter. It involves the techniques
for generating control signals, the use of a DC pulse
source to generate a triangular or square wave, and
behavioral modeling in PSpice using VALUE and
TABLE descriptions. A half-bridge inverter is shown in
Fig. 1 which was drawn in PSpice using schematic
editor. The inverter drives an RL-load of R = 10 W and
L = 2.5 mH at an output frequency of fo = 1 kHz, and
period To = 1 ms.
For PWM control, the number of pulses per halfcycle is assumed 10. That is, the switching frequency fs
= 10 kHz and switching period Ts = 100 ms. The
carrier voltage vc of triangular wave is represented by a
DC pulse wave of 50% duty chyle, 10 V (peak), ton =
50 ms, toff = 50 ms, and Ts = 100 ms. Assuming a
modulation index of M = 0.7, the reference wave is
represented as a sine wave of 0.7V (peak), and fo = 1
kHz.
The sine wave generator is followed by an ABS value
function whose is then compared with the carrier signal
to give the error signal which is then multiplied by a
limiter with a gain of 10 k.. The output of the limiter is
then multiplied by a DC pulse vg1 of 50% duty cycle, 10
V (peak), ton = 0.5 ms, toff = 0.5 ms, and Ts = 1 ms to
generate the gating signals for transistor Q1. The DC
pulse vg2 is the inversion of vg1, and generate the gating
signals for transistor Q2. It has a delay of tdelay = 0.5 ms,
50% duty cycle, 10 V (peak), ton = 0.5 ms, toff = 0.5 ms,
and Ts = 1 ms. The functional block 'VALUE' is a
voltage controlled voltage source and provides the
isolation from the ground similar to a pulse transformer.
The SPICE plots of Vg1, Vg2, Vref and Vc are
shown in Fig. 2. The instantaneous load current and its
rms value are shown in Fig. 3 which gives a peak load
current of 0.685 A and an rms value of 332 mA.
Figure 1, Single-phase half-bridge PWM inverter
Figure 2, Gating signals
Thyristor Characteristics
This is the second example in simulating the
characteristics of thyristor which is a commonly used
device in introducing the concept of power electronics to
students. It involves derivation of the approximate
model parameters of the thysristor from the
manufacturer's data and simulation of environment. The
thyristor of International Rectifier, type IR18CF is used
Figure 3 PSpice plots of the instantaneous and rms load currents
Figure 4 Thyristor test circuit
as a test device as shown in Fig. 4. The model
parameters are derived from the manufacturers data and
the thyristor is modeled as voltage/current controlled
switch [1].
A gate voltage of VG = 5.894 V is applied to the gate
and the anode to cathode voltage is swept from 0 to 10 V
in order to capture the turn-on point. This is repeated for
VG = 5.898 and 5.91 V. The turn-on characteristics are
shown in Fig. 5 which shows the sensitivity of VG on the
turning point.
Figure 5 Thyristor turn -on characteristics
Conclusion
PSpice can be used to model and simulated power
electronic circuits together with the gating control signals
to obtain the desired conversion strategy. Schematic
editor
has many interfacing devices and components both
analog and digital. Its graphical post-processor Probe is
like a theoretical oscilloscope which allows plotting
functional variables such as power, power factor,
Fourier spectrum. Also, it can be used to find the rms,
average, and peak voltage and current ratings of devices
and components.
Advanced feature such as PARAM allows find the
effects of parameter variations on the performance of the
power conversions and the WORST CASE analysis
allows finding the worst-case due to tolerance in devices
and components values.
The students can observe the effects of changes in
design parameters without actually building the circuit.
This enhances their understanding of the circuit
operation and the control function. In the absence of a
dedicated power electronics laboratory, the laboratory
assignments could be only problems, which are to be
simulated and verified by PSpice. Examples of
laboratory experiments on power electronic are given by
Rashid [2].
PSpice can be used for design verifications of power
electronics circuits. Also for performance evaluation in
terms of parameters such as power factor, and total
harmonic factor.
References
1. Rashid, M.H, Power Electronics Laboratory Using
Pspice.
The IEEE Press, 1996, To be
published.
2. Rashid. M. H., SPICE For Power Electronics and
Electric Power. Prentice - Hall, 1993, Chapter
14 - Applications.
3 Rashid, M.H, SPICE For Circuits and Electronics
Using PSpice . Prentice - Hall, 2nd Edition,
1995.
4. Rashid, M.H., Power Electronics - Circuits, Devices
and Applications Power. Prentice - Hall, 2nd
Edition, 1993.