This paper aims to develop and implement an educational kit for a Sinusoidal Pulse Width Modulation (SPWM) inverter pulse generator circuit, which can be used to educate Electronics Engineering undergraduate students the structure and behavior of a SPWM’s inverter pulse generator. The developed electronic circuit is simulated and implemented using low cost and reliable electronic parts. The concept is to offer under/postgraduate students the opportunity to deeply understand how a SPWM pulse generator works, by virtually and practically experimenting with the pulse generator itself creating the necessary models in the popular platform of MULTISIM (Simulation Tool of National Instruments) and designing/constructing the respective PCB circuits in the also popular platform of ULTIBOARD (Circuit Design Tool of National Instruments). This work is also useful for engineers who deal with operation and maintenance (O&M) of inverters, because it provides a deeper knowledge and understanding of all operational characteristics of every stage of the SPWM electronic pulse generator of an inverter

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Energy Procedia 00 (2018) 000–000
www.elsevier.com/locate/procedia
1876-6102 © 2018 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)
Selection and peer-review under responsibility of the scientific committee of Technologies and Materials for Renewable Energy, Environment
and Sustainability, TMREES18.
Technologies and Materials for Renewable Energy, Environment and Sustainability, TMREES18,
19–21 September 2018, Athens, Greece
Simulation and Implementation of a SPWM Inverter Pulse
Generator Circuit for Educational Purposes
E.A. Samiotis, D.T. Trigonidis, G.A. Vokas*
, P. Papageorgas, A.G. Anastasiadis
Department of Electrical and Electronics Engineering, University of West Attica, P. Ralli & Thivon 250, 12244, Aegaleo, Greece
Abstract
This paper aims to develop and implement an educational kit for a Sinusoidal Pulse Width Modulation (SPWM) inverter pulse
generator circuit, which can be used to educate Electronics Engineering undergraduate students the structure and behavior of a
SPWM’s inverter pulse generator. The developed electronic circuit is simulated and implemented using low cost and reliable
electronic parts. The concept is to offer under/postgraduate students the opportunity to deeply understand how a SPWM pulse
generator works, by virtually and practically experimenting with the pulse generator itself creating the necessary models in the
popular platform of MULTISIM (Simulation Tool of National Instruments) and designing/constructing the respective PCB circuits
in the also popular platform of ULTIBOARD (Circuit Design Tool of National Instruments). This work is also useful for engineers
who deal with operation and maintenance (O&M) of inverters, because it provides a deeper knowledge and understanding of all
operational characteristics of every stage of the SPWM electronic pulse generator of an inverter.
© 2018 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)
Selection and peer-review under responsibility of the scientific committee of Technologies and Materials for Renewable Energy,
Environment and Sustainability, TMREES18.
Keywords: Sinusoidal Pulse Width Modulation; Inverter; Simulation; Pulse Generator; Educational Kit
1. Introduction
As known, inverters are devices that convert a DC source to a variable frequency/RMS value AC source.
Nowadays, due to the excessive growth of renewable energy resources the use of inverters finds a lot of applications
in everyday lives; from a typical UPSs, that everyone might have in their homes, to whole Photovoltaic or Wind Parks
that produce MWh of energy. Other application examples of inverters are in Control Systems of AC Motors, in all
kind of Renewable Energy Systems, in Networks of Electric Energy Transfer Lines, in Production and Storage of

2. 2 Author name / Energy Procedia 00 (2018) 000–000
Electric Energy Systems, in Reduction of Harmonics Active Filters for Improvement of Electric Power Quality, in
Industrial Applications, as a major part of Static VAR compensators (SVCs) [1, 2, 3, 4, 5, 9, 12].
Many inverter topologies with various pulse generating techniques for all applications have been developed
focusing in higher efficiency, less harmonic content, interoperability and higher reliability [6, 7]. However, although
many different (mainly digital) pulse generating kits exist, they are rather insufficient and inadequate for educational
purposes of under/postgraduate students or O&M engineers as the step-by step formulation of the pulse generation
procedure is not always clearly depicted [11]. Therefore, the construction of a kit based in analogue comparators (Op-
Amp IC’s) and logic gates, whose “modus operandi” is way more understandable was attempted.
Initially in this paper, in Paragraph 2, the SPWM inverter basic principles along with the circuit schematics, the
considerations made and the simulation measurements using MULTISIM through the oscilloscope tool during the
simulation process are presented. In Paragraph 3 the used parts are listed and the PCBs made using Multisim/Ultiboard
are developed. After implementation, measurements at the PCB test points were taken and presented along with their
respective pictures-graphs obtained by a real oscilloscope. Furthermore, practical issues encountered during the
realisation process are presented and their respective solutions and improvements in the prototype practical electronic
circuit are provided. Results discussion and Conclusions are made clear in the last Paragraphs 4 and 5.
2. SPWM Inverter basic principles, considerations and simulation
The need of using SPWM except from PWM was created when inductive or resistive loads or even a combination
of them such as electric motors had to be driven and supplied by DC sources with clear, high quality and highly
efficient AC power supplies. Limitations on the harmonic content of voltage output were set by many standards like
EN50160. Using an H-Bridge topology inverter and by switching on and off the switches Q1, Q4 and Q2, Q3, the
exchange of a DC source (VIN) to an AC Voltage applied on the R-L-C load is achieved. Though, unlike the PWM,
the on/off procedure occurs faster and way more times over a period producing pulses with a constantly changing
width. This procedure provides the effect of a smoother RMS value change, thus creating a waveform closer to a real
AC one, in order to avoid the danger of causing damage to an R-L load like a motor. Controllable semiconductor
devices (Thyristors, GTOs, IGBTs, & MosFETs) are used in such DC/AC inverter circuits as shown in Figure 1.
Thereby, the only way for interaction with these circuits is by controlling the activation or deactivation of these
semiconductor devices. This can be achieved by low power circuits called Pulse Generators [2, 3, 4].
Fig. 1. An H-Bridge PWM Inverter Circuit demonstrated with parallel pair
of Diode – Semiconductor Device (MosFETs)
Fig. 2. AC Output of a SPWM H-Bridge Inverter (where
V is the voltage and B is the current on the load)
A SPWM Inverter is a device, as already mentioned, that converts a DC Voltage source to a desired frequency
or/and variable RMS AC Voltage, keeping the output harmonic content very low according to the Administrator and
devices standard [10]. A SPWM inverter can be used to supply with energy mostly ohmic and inductive loads or
devices, while for only ohmic loads or devices a simple Pulse Width Modulation (PWM) Inverter can be used [3, 8].
The theoretical conversion of a DC Voltage to an AC Voltage by an H-Bridge SPWM Power Inverter is shown at
Figure 3, where it is obvious that the harmonic content of the output current is significantly and controllably reduced
in comparison to the one of a simple PWM inverter [2, 3, 4, 5, 6, 7].

3. Author name / Energy Procedia 00 (2018) 000–000 3
The proposed and implemented pulse generator is non-line-communicating, which means that it has a built-in
generator in order to generate the Sinus the cosine and triangle wave it uses for comparison. Consequently, the working
frequency of the Inverter is locked at almost 50Hz for the sinus, to imitate the frequency of the electric power network,
and its variable between 100Hz and 2kHz for the triangle wave. The entire philosophy of this pulse generator for the
SPWM inverter is based into two comparisons; a) triangle vs sinus and b) triangle vs cosine. Such inverters are also
used in autonomous P-V applications, where no electric grid is close to be connected with. The designed circuit used
both for simulation and the PCBs for the generator and the SPWM are shown in Figures 3 & 4.
Fig. 3. Generator Circuit designed in Multisim
Fig. 4. SPWM Circuit designed in Multisim

4. 4 Author name / Energy Procedia 00 (2018) 000–000
Using Multisim for the simulation procedure, it was found that a classical op-amp like LM412 (Low Offset, Low
Drift Dual JFET Input op-amp), which has a typical speed of 2μs according to its datasheet was not a good solution
for being used as a comparator due to is low speed compared to the comparator IC. On the contrary, LM360 (High
Speed Differential Comparator) has an astonishing typical speed of 20ns, almost 100 times faster than LM412 [11].
The comparison between the operation of LM412 and LM360 is shown in Figure 5, where the non-square pulse using
LM412 (green) is replaced by the almost perfect square pulse via LM360 (blue).
Fig. 5. LM’s360 better output than LM412
Following the SPWM methodology as described in [2, 3, 4] the triangle waveform (orange) with the sinusoidal
waveform (red) is compared as shown in Figure 6. From this comparison a series of pulses is obtained, Switch1 is
blue and Switch 2 is cyan that both of them are already driven through a not logic gate in order to obtain a better series
of pulses, as explained in Figure 5. Furthermore, the same triangle waveform (orange) is compared with the cosine
waveform (pink). From this comparison a series of pulses occurs, Switch 3 is black and Switch 4 is grey. Again, those
pulses are driven through a not logic gate for the same reason as described above. The final output is consisted of the
pulse’s series for each switch (SW1- blue, SW2-cyan, SW3-black, and SW4-grey).
Fig. 6. Waveform comparisons and output pulses for controllable switches SW1, SW2, SW3, SW4
3. SPWM Implementation
3.1 Assumptions and Parts Used
In order to make a cheaper but not less reliable circuit Op-Amps without input and feedback resistors can be used,
instead of comparator chips. The components used for the logic functions are one op-amp of TI’s LF412 IC’s and a
NOT gate chip (74LS04). For the power supply several parts and regulators were used. Firstly, a 2x18 V/3A
transformer is used to reduce the AC voltage from the Electric Power Network. A full bridge rectifier (PB1010) is
used to rectify the voltage, while some capacitors are also used for filtering (Electrolytic of Various Values at 35V).
Finally, in order, to supply the logic gates and the op amp a LM7805 and a LM7905 voltage regulators are used.

5. Author name / Energy Procedia 00 (2018) 000–000 5
3.2. Design of the PCB of the SPWM Pulse Generator Circuit
Using NI’s Multisim and Ultiboard, the circuits and the printed board circuits were designed as presented already
in Figures 3 & 4. The PCBs were finally carved with a CNC Router at Electrical & Electronics Eng. Dep. of UWA.
The PCB designs are shown in Figures 7 & 8 and the final boards after assembling and soldering in Figures 9a & 9b.
Fig. 7. Pulse Generator PCB by Ultiboard Fig. 8. SPWM Generator Circuit designed in Ultiboard
(a) (b)
Fig. 9 (a & b). The PCBs after the assembling and soldering
3.3. Graphs from oscilloscope at the test points
After assembling and soldering the PCB certain tests were made to ensure that the circuit works properly, providing
the expected results, similar to the simulated ones. The measuring instrument used was a GWInstek GDS-1102A-U
dual channel/100 MHz oscilloscope. In the 1st
comparator, a sinus wave locked near 50Hz is compared to a triangle
wave variable for 100Hz to 2kHz as shown in Figure 10. In Figure 11 the output of the Opamp is used as comparator.
Blue is the output of the not gate when supplied by the yellow pulse (comparator output).
Fig. 10. Sinus and Triangle Comparison
Fig. 11. Output error of the comparator and the output of a not gate

6. 6 Author name / Energy Procedia 00 (2018) 000–000
Due to the error mentioned before this output is supplied into a not logic gate and the output results/pulses that are
going to feed the S1 (yellow)and S2 (blue) mosfet H-bridge of the inverter shown in Figure 12. In the 2nd
comparator
an inverted sinus also locked at near 50Hz is also compared to same triangle wave. Again, due to the afore-mentioned
error the output of the second comparator is also fed into a not logic gate and the output results/pulses for feeding the
S3 (yellow) and S4 (blue) mosfet H-bridge of the inverter are shown in Figure 13.
Fig. 12. Output Pulses of the SPWM Generator for S1, S2
Fig. 13. Output Pulses of the SPWM Generator for S3, S4
4. Results discussion and proposed improvements
During the design, simulation and implementation process minor or major improvements were made. First to
mention the fact that using comparator chips and buck converters in power supply unit rather than voltage regulators
improved significantly the reliability of the designed circuits. Also, by using the LM360 comparator, the not logic
gate is not needed due to the dual output of the comparator (inverting and non-inverting output). Furthermore, the
internal wave generator of the SPWM is going to be fully variable to the amplitude and the frequency of the triangle
and the sinusoidal wave.
The most important issue of a SPWM inverter is that it can drive efficiently R-L loads such as variable rpm and
power electric motors. It cannot drive capacitive loads because in the positive half-period the capacitor drains power
from the source but in the negative half-period the capacitor returns that drained power to the source. Another problem
is that this generator has a fixed power and frequency output which is not ideal for running high power and variable
frequency motors such as the motors that the electric cars have.
Finally, despite the fact that in the simulation perfect pulses can be seen, into the oscilloscope several spikes due
to noise can be detected. The noise probably occurs due to the fact that the parts that have been used are not of high
grade (space, military, etc.), they are of commercial grade, and they are subside to environment conditions, some
defects of the power supply (PCB rust, humidity temperature etc.) and maybe some defects from production.
5. Conclusions
In this paper an educational kit (simulation & practical electronic circuit) for a Sinusoidal Pulse Width Modulation
type inverter is developed and presented. Initially, the electronic generation pulses circuit was designed in a simulation
software. Then the circuits were designed printed in PCB. After implementation of the pulse generation circuits, a
continuous experimentation took place having as result several minor or major improvements. The operational results
of this SPWM pulse generator were satisfactory, providing pulses exactly as the designed ones during the simulation
procedure through all the test points of the pulse generation circuits.
The use of these circuits is very is useful for educating electrical and electronic engineering undergraduate students
because a deep understanding of all stages of the pulse generation procedure is achieved. The Operation and
Maintenance engineers can have an additional tool for understanding the pulses creation of power electronic part of
the inverters and significantly improve their maintenance skills.

7. Author name / Energy Procedia 00 (2018) 000–000 7
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