Multilevel Inverter with Enhanced THD Value used in Grid Connected

Applications

Y. V. BALARAMA KRISHNA RAO1, VENKATA KOTESWARA RAO N.2,*,

RAJA SATHISH KUMAR3

1Department of Electrical and Electronics Engineering,

Guru Nanak Institutions Technical Campus, Ibrahimpatnam,

Telangana-501506,

INDIA

2Department of Electrical and Electronics Engineering,

Stann's college of engineering and technology, Chirala,

Andhra Pradesh- 523187,

INDIA

3Department of Electrical and Electronics Engineering,

Keshav Memorial Institute of Technology,

Hyderabad,

INDIA

Abstract: - In this work, the relationships among pulse width modulation (PWM), sinusoidal pulse width

modulation (SPWM), and space-vector pulse width modulation (SVPWM) for three-phase inverters will be

analyzed to better comprehend their differences. detailed comparison of the three modulation schemes under

study's Total Harmonic Distortion (THD). High-power applications are increasingly concentrating on converter

technology. This growing importance may be attributed to its improved output waveforms over the 3-



carrier-based sinusoidal pulse width modulation (SPWM). To control and modulate multi-level inverters, many

techniques are employed. These methods are categorized based on how frequently they switch. The ripple

current rating, capacitance value, and voltage balance in the DC bus capacitors are all impacted by the pulse

width modulation techniques. It is crucial to select the modulation method based on the current control

requirements, as this determines the output voltage waveform's harmonic content. SVPWM is gradually

becoming more and more popular in industries because of its improved dc bus utilization and ease of digital

realization. This work examines PWM, Sinusoidal, and SVPWM feeding a load connected to RL. Three

different methodologies' performances are compared as these methods are investigated through simulation with

MATLAB/SIMULINK software.

Key-Words: - Power grid, PWM Techniques, SVPWM, Voltage Source Inverters, Total Harmonic Distortion

(THD), Three-phase inverter, Switching devices, Variable frequency drives.

Received: March 22, 2023. Revised: January 5, 2024. Accepted: February 19, 2024. Published: April 2, 2024.

1 Introduction

A certain amount of the power generated by the

non-renewable plant is inserted by the distributed

generating systems at specific transmission

locations, rather than being used by the loads

entirely. Because all transmission systems operate

on AC, these sources need voltage source inverters

(VSIs) to introduce active and reactive energy into

the system by converting DC to AC. Thus, a

fraction of the power demand is satisfied via

dispersed generation. Power electronic devices like

MOSFETS and IGBTS are included in VSI. The

harmonics issue in the system could be brought on

by often switching these devices to convert DC to

AC power. The SVPWM control-based scheme is

utilized for the inverter, to obtain the reduced

harmonic content output voltage at the distributed

generating systems end. Here, SVPWM for power

converters is recommended to assist lower the

system's harmonics. The input side modulating

signals in this case are added up to a predetermined

voltage, [1], [2]. Afterward, they undergo

WSEAS TRANSACTIONS on POWER SYSTEMS

DOI: 10.37394/232016.2024.19.14

Y. V. Balarama Krishna Rao,

Venkata Koteswara Rao N., Raja Sathish Kumar

E-ISSN: 2224-350X

115

Volume 19, 2024

differentiation using carriers to generate gating

pulses for the inverter.

A higher Inverting voltage level indicates lower

harmonic production which indicates that the

multilevel inters play a vital, especially in high

power applications which will reduce the overall

voltage stress at the load side. The two broad

categories into which the inverters fall are two-level

and multilevel inverters. Reduced harmonic

distortion is one benefit of multilevel inverters over

two-level inverters, [3], [4]. The trapezoidal and

sinusoidal current waveforms are obtained using a

multilevel inverter which is exclusively useful in

electric drive applications, a static VAR

compensator, and an active power filter. AC Drives

with higher performance always require accurate

switching-based configuration of rectifiers and

voltage-source inverters, [5]. On the other hand, the

higher power losses are present in proportion to the

increased switching frequency value. As a result, it

may become less efficient and perhaps cause

damage. Finding the best compatible modulation

technique requires comparing the converter

efficiency under various PWM schemes, [6].

Modulation signals and voltage space vectors were

compared, and examples of both SPWM and

SVPWM implementations are presented along with

related solutions. Three-phase voltage source

inverter (VSI) systems are examples of high-power

applications that typically need lower levels of

harmonic distortion and great efficiency. It is

essential to regulate the voltage source inverters'

output, [7]. Inverter gain can be controlled using a

variety of methods, and the following Figure 1

illustrates the many modulation schemes for multi-

level inverter topologies, [8].

The particular application requirements, such as

the expected result waveform, efficiency, and

control characteristics, determine which PWM

approach is best. Different domains, including

power electronics, motor control, communication

systems, and audio processing, employ distinct

methodologies. The technique known as pulse width

modulation, or PWM, is effective in obtaining the

necessary voltage or current to operate the load.

Because the PWM approach can drive a load with a

maximum output voltage and a lower harmonic

current, it is becoming more and more popular for

AC drives. PWM techniques are used in producing

signals with quality amplitude and frequency which

will help to reduce in THD value of the converters,

[9], [10].

Pulse Width

Modulation

(PWM)

Binary Pulse Width Modulation

(BPWM)

Multiple Pulse Width Modulation

(MPWM)

Pulse Frequency Modulation (PFM)

Pulse Position Modulation (PPM)

Delta Modulation (DM)

Random Pulse Width Modulation

(RPWM)

Carrier-Based Pulse Width

Modulation (CBPWM)

Unipolar Pulse Width Modulation

Bipolar Pulse Width Modulation

Sinusoidal Pulse Width Modulation

(SPWM)

Space Vector PWM (SVPWM)

Fig. 1: Representation of various modulation

techniques

2 About the SVPWM Technique

In the area of variable frequency drives (VFDs), the

SVPWM technique is used in control systems and

power electronics for electric motor applications.

The switching devices like MOSFETs or IGBTs

gating signals are controlled in the way of low

harmonic production using advanced controlling

techniques like SVPWM. The three-phase system

instant current and voltage values are represented as

a space vector in the SVPWM technique. To

produce the final desired output waveform, the

corresponding space vector values of the technique

also change. In the case of the three-phase systems

and electric motor application the SVPWM

WSEAS TRANSACTIONS on POWER SYSTEMS

DOI: 10.37394/232016.2024.19.14

Y. V. Balarama Krishna Rao,

Venkata Koteswara Rao N., Raja Sathish Kumar

E-ISSN: 2224-350X

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Volume 19, 2024

technique is used regularly, [11], [12], to obtain the

controlled output voltage as per the requirement.

From the representation point of view the

SVPWM technique is made with six different

sectors and further, those will replicate the two

different voltage vectors. The three-phase voltage

regulation is always one of the key advantages while

using this technique. The fundamental voltage

component will increase in proportion with the

active vector which is represented in the hexagon

structure of the SVPWM technique on the output

voltage following the zero-voltage vector. The

reference vector in the hexagon always represents

the projected voltage value of the system. The

challenge is to estimate this Obtaining the reference

vector based on the available active voltage vectors,

without changing the balance of the three-phase

system is one of the major challenges, [13].

The SVPWM can provide the required voltage

vector using the switching mechanism. To evaluate

the approximate reference vector, the SVPWM can

find the active vectors' duty cycle with this reduced

harmonic content waveforms are obtained in

coordinating with the controlled switching signal

provided to the power switching devices. Reduction

of harmonic content distortion in the waveform will

lead to improvement in the overall system efficiency

which can be achieved through the SVPWM

technique, [14]. Power electronic-based equipment

like VFDs and UPS are normally equipped with the

SVPWM technique since this apparatus requires

precise three-phase voltage control. Design wise the

SVPWM technique seems more complex on the

other hand which provides more accurate dynamic

performance which leads to a reduction of the

harmonics of the output waveform. In run time

SVPWM technique-based circuit is made based on

advanced digital signal processors (DSPs) and

Microcontrollers, [15], [16].

The six power switches designated S1 through

S6, are responsible for shaping the output. The

switching variables a, a1, b, b1, c, and c1 control

this process. The appropriate lower transistor is

turned off, meaning that the corresponding a1, b1,

and c 1 is 0, when an upper transistor is switched

on, that is, when a, b, or c is 1. Consequently, the

output voltage may be determined by utilizing the

on and off states of the higher transistors S1, S3, and

S5. The voltage space vectors used in the traditional

space vector modulation approach are taken from

the grid's three-phase voltages, [17], [18].

Using a rotating reference vector made up of six

fundamental non-zero vectors arranged in the shape

of a hexagon, the SVPWM procedure is carried out

around the state diagram. The reference angle,

which ranges from 0° to 360°, is compared to the

angle formed by the d-q quantity. The idea is used

to determine the angle at which the reference

voltage vector frames the various reference voltage

sectors. This allows the reference voltage to

function in all sectors at all angles, so covering its

full 360° range of operation, [19], [20].

3 Block Diagram Representation with

Proposed Techniques

Three Phase

Inverter

Input DC

Supply

Measurement

Block

Power

Grid

Load

Representation

PWM/SPWM/

SVPWM

ControlTechnique

Fig. 2: Complete block diagram representation of

with PWM/SPWM/SVPWM with grid-connected

system

A block diagram of the full system with various

modulation strategies to produce the better-

performing one is shown in Figure 2. Here, the

three-phase inverter's input DC voltage is taken

from a non-conventional power-generating system,

such as a solar power generation system. In

addition, if the non-traditional power production

system produces excess power, the three-phase

inverter transforms the DC voltage into a three-

phase AC supply for the utility and feeds the

conventional grid system. A different mechanism is

also developed to supply the supply frequency and

the rectangular wave to the modulation block for the

successful generation of the signals to the inverter.

Controlled switching signals are generated in the

modulation technique block by taking input current

and voltage from the inverter output.

Fig. 3: Reference signal representation to the

modulation technique

WSEAS TRANSACTIONS on POWER SYSTEMS

DOI: 10.37394/232016.2024.19.14

Y. V. Balarama Krishna Rao,

Venkata Koteswara Rao N., Raja Sathish Kumar

E-ISSN: 2224-350X

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Volume 19, 2024

Fig. 4: Frequency waveform representation of the

modulation techniques

Figure 3 and Figure 4 shows the reference

sawtooth waveform and input frequency of the

modulation techniques used in generating the

controlled pulse signals to the three-phase inverter.

4 Simulation Results and Discussions

Simulations are mostly used in power electronic

converter systems to analyze the design

configuration and apply control strategies. The

efficiency of the suggested methods is demonstrated

by several MATLAB/Simulink simulation results

for multilevel inverters with RL loads. Table 1

displays the line voltages and inverter output phase

for the PWM, SPWM, and SVPWM techniques,

along with a comparison of the related THD. For

different switching frequencies, the total harmonic

distortion and output load current was calculated

using the load parameters R=10 ohms, L=6.5 mh,

and an input DC source voltage of 300 v.The

SVPWM-controlled fundamental line current and

output phase current output waveforms are

approximately equal to 25% more than SPWM

output currents and 60% more than PWM output

currents due to higher DC bus utilization in the

SVPWM technique and lower THD compared to

SPWM and PWM approaches. For each of the three

modulation methods, the output voltages derived

from the fundamental line voltage are a root three

multiple of the fundamental phase voltage.

The basic output peak load current in the

SVPWM technique is equal to 25% more than in the

SPWM technique and 60% more than in the PWM

approach, as shown in Table 1 above. The Total

Harmonic Distortion (THD) of the fundamental

output load current is about equal to 25% for

SPWM and 70% for PWM when comparing

SVPWM to SPWM and PWM.

Table 1. Representation of the THD and load

current values corresponding to each switching

frequency

Switchi

frequen

value in

khz

Output

Curren

t with

SVPW

M in

Amps

THD

Value

with

SVPW

M in

Outp

Curre

with

SPW

M in

Amps

THD

Value

with

SPW

M in

Outp

Curre

with

PWM

Amps

Valu

with

M in

40.2

2.17

68.7

40.2

2.0

8.2

52.1

40.2

1.5

6.1

35.2

40.2

1.36

4.2

20.1

40.2

0.96

2.4

15.5

4.1 MATLAB/Simulink Results of the

SVPWM Technique

Fig. 5: FFT Analysis representation of the SVPWM

technique

Fig. 6: Inverter output current waveform

corresponding to the SVPWM technique

Fig. 7: Inverter output voltage waveform

corresponding to the SVPWM technique SVPWM

technique

Figure 5 shows the FFT analysis-related

representation with the SVPWM technique and

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Y. V. Balarama Krishna Rao,

Venkata Koteswara Rao N., Raja Sathish Kumar

E-ISSN: 2224-350X

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given the THD value of 2.17% with starting time at

0.025 sec, fundamental frequency of 50 Hz for 2

cycles. Figure 6 shows the output three-phase

current of the inverter with an average value of 40

Amps. Figure 7 represents the output voltage of the

three-phase inverter with the value of 300 volts.

4.2 MATLAB/Simulink Results of SPWM

Technique

Fig. 8: FFT Analysis representation of the SPWM

technique

Fig. 9: Inverter output current waveform

corresponding to the SPWM technique

Using the SPWM technique and a THD value of

10.00%, Figure 8 illustrates the description of the

FFT analysis for two cycles at a fundamental

frequency of 50 Hz and a starting time of 0.025

seconds. The inverter's output three-phase current,

with an average value of 30 Amps, is displayed in

Figure 9.

4.3 MATLAB/Simulink Results PWM

Technique

Fig. 10: FFT Analysis representation of the PWM

technique

Fig. 11: Inverter output voltage waveform

corresponding to the PWM technique

Fig. 12: Inverter output current waveform

corresponding to the PWM technique

Figure 10 shows the FFT analysis for two cycles

at a fundamental frequency of 50 Hz and a starting

time of 0.025 seconds using the PWM approach

with a THD value of 68.72%. Figure 12 shows the

average three-phase current output of the inverter,

which is 15 Amps. Figure 11 illustrates the three-

phase inverter's 300-volt output voltage.

5 Conclusion

A comparison is made between the three

approaches' performances. When compared to the

SPWM and PWM techniques,

MATLAB/Simulation demonstrates how well the

SVPWM uses the DC bus voltage because its output

is greater than that of the SPWM and PWM when

measured using the fundamental output voltage.

Superior outputs, higher efficiency, and less THD

are achieved by Space Vector Pulse Width

Modulation in comparison to PWM and Sinusoidal

Pulse Width Modulation inverters operating at

different switching frequencies.

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Venkata Koteswara Rao N., Raja Sathish Kumar

E-ISSN: 2224-350X

119

Volume 19, 2024

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The authors equally contributed to the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflicts of interest to declare.

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DOI: 10.37394/232016.2024.19.14

Y. V. Balarama Krishna Rao,

Venkata Koteswara Rao N., Raja Sathish Kumar

E-ISSN: 2224-350X

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