Impact of Sine PWM on Voltage THD in 5-Level Vs 7-Level

Inverters: A Comparative Analysis

Susheela Nunsavath

, Veena Chevula

, Shireesha Bollam

and Venkateswarlu Tadikamalla

Department of Electrical Engineering, Osmania University, Hyderabad, Telangana, India

Keywords: Multilevel Inverter, Total Harmonic Distortion, Modulation Technique.

Abstract: This study focuses on THD and various modulation strategies while analyzing 5-level and 7-level multilevel

inverters for grid systems. As they enable effective DC-to-AC conversion with advantages like lower

switching losses, improved output quality, and compact design, multilevel inverters are essential in renewable

energy applications. These inverters, which are widely used in industrial motor drives, PV systems, and

electric vehicle charging, promote sustainable energy solutions. According to simulation data, the 7-level

inverter provides the best performance with the lowest THD and outperforms the 5-level in terms of THD.

POD is the most successful SPWM approach for reducing THD, according to a comparison analysis. These

results highlight how advanced SPWM techniques and creative inverter designs can enhance grid integration

and power quality.

1 INTRODUCTION

An inverter is a device that converts direct current

(DC) electricity into alternating current (AC)

electricity, enabling the use of DC power sources, like

batteries or solar panels, to power AC appliances. .

This process involves converting a steady DC input

into a switching AC waveform, smoothing it into a

usable sine wave, and adjusting the output voltage as

needed. Inverters are widely used in solar systems,

UPS, electric vehicles, and industrial applications to

provide reliable AC power.

Multilevel Inverters (MLIs) are advanced

inverters designed for high-power and high-voltage

applications (Munawar, Iqbal, et al. , 2024). Unlike

conventional inverters that generate simple two-level

waveforms, MLIs produce a stepped AC output

resembling a sinusoidal waveform. This reduces

harmonic distortion, improves power quality, and

enhances efficiency.

Types of Multilevel Inverters (Singh and

Mohaney, 2024):

https://orcid.org/0000-0002-0142-0870

https://orcid.org/0009-0005-3058-8129

https://orcid.org/0009-0001-4566-7656

https://orcid.org/0009-0002-0364-3733

Diode-Clamped MLI: Uses diodes for voltage

balancing. Ideal for medium-voltage applications but

complex for high levels.

Flying Capacitor MLI: Balances voltage using

capacitors, offering redundancy and flexibility but

requiring complex balancing circuits.

Cascaded H-Bridge MLI: Uses multiple H-bridge

units powered by independent DC sources. It is

modular but needs isolated power sources.

Advantages of MLIs:

Power Quality: Reduced Total Harmonic

Distortion (THD) minimizes external filter

requirements.

Efficiency: Lower switching losses improve

energy efficiency.

Scalability: Easily adaptable to medium and

high-power applications.

Reduced Stress: Lower voltage stress enhances

component reliability.

Applications include renewable energy systems,

industrial drives, electric vehicles, and HVDC

transmission (José, Sheng, et al. , 2002). Despite their

complexity, MLIs offer unmatched efficiency,

550

Nunsavath, S., Chevula, V., Bollam, S. and Tadikamalla, V.

Impact of Sine PWM on Voltage THD in 5 - Level Vs 7 - Level Inverters: A Comparative Analysis.

DOI: 10.5220/0013625000004664

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 3rd International Conference on Futuristic Technology (INCOFT 2025) - Volume 3, pages 550-556

ISBN: 978-989-758-763-4

making them essential for modern high-power

systems.

Challenges include higher costs, control

complexity, and space requirements, but these are

outweighed by their performance benefits (Susheela,

Chandra, et al. , 2024), (Leon, Vazquez, et al. , 2017).

2 MODULATION TECHNIQUE

SPWM is a modulation technique used to control the

output voltage and frequency of inverters (Akshay,

Rakshith, et al. , 2024), (Susheela and Kumar, 2017).

It generates switching signals by comparing a

sinusoidal reference waveform (desired output) with

a high-frequency triangular carrier waveform.

Sinusoidal Pulse Width Modulation (SPWM) is a

widely used technique for generating AC waveforms,

particularly in inverters and motor drive systems. It

modulates the width of pulses based on a sinusoidal

reference waveform to approximate a sinusoidal

output voltage.

There are many advantages of SPWM like

Improved Efficiency, Lower switching losses

compared to other modulation methods, Better

Harmonic Profile (By increasing the carrier

frequency, higher-order harmonics are shifted away

from the fundamental frequency, making filtering

easier) and Scalability (Output voltage and frequency

can be easily controlled by adjusting the reference

waveform).

In pulse-width modulation (PWM) techniques,

different switching methods are used to control the

inverter’s output waveform. PD (Phase Disposition),

POD (Phase Opposition Disposition), and APOD

(Alternate Phase Opposition Disposition) are multi-

carrier PWM techniques, primarily used in multilevel

inverters to manage how the carrier signals are

arranged. In multilevel inverters, several carriers are

needed because multiple levels of voltage are

generated. The arrangement of these carriers

determines the type of modulation technique (Abbas,

Majid, et al. , 2017), (Susheela and Kumar, 2017).

2.1 Phase Disposition

All carrier waves are in phase. Carriers are stacked

vertically as depicted in Figure 1, with each carrier

covering a specific range of the output voltage. The

reference sinusoidal waveform is compared against

all these carriers.

Figure 1: PD PWM Technique

2.2 Phase Opposition Disposition

Carriers are divided into two groups: The carriers

above the reference sinusoidal wave are in phas e

(Susheela and Kumar, 2020). The carriers below the

reference wave are 180° out of phase with those

above it as illustrated in Figure 2.

Figure 2: POD PWM Technique

2.3 Alternate Phase Opposition

Disposition

Each adjacent carrier is 180° out of phase with the

neighbouring carrier (Susheela and Kumar, 2019).

This alternating phase arrangement applies to all

carrier waves as indicated in Figure 3.

Figure 3: APOD PWM Technique

Impact of Sine PWM on Voltage THD in 5 - Level Vs 7 - Level Inverters: A Comparative Analysis

551

3 TOPOLOGY

The Cascaded H-Bridge (CHB) method is a widely

used topology in multilevel inverters due to its

modularity, scalability, and simplicity in

implementation (Ramaprabha, 2022), (Deshmukh,

Chaturvedi, et al. , 2022). It consists of multiple H-

bridge inverter units connected in series, each

producing a separate voltage level. By combining

these voltage levels, a stepped waveform

approximating a sinusoidal output can be generated,

which reduces total harmonic distortion (THD)

without requiring bulky filters (Babaei, 2008).

Figure 4: Inverter Topology

The topology shown in Fig. 4 is same for 5-Level and

7-Level Inverter. For a 5-Level Inverter voltages are

symmetrical such that V1 = 10 V and V2 = 10 V

whose switching table is provided in Table 1. H-

Bridges produce five levels in the output: +20 V, +10

V, 0, -10 V and -20 V.

Table 1: Switching table for 5 – Level Operation.

Mod

Outpu

Switching State

1 +20 V 1 1 0 0 1 1 0 0

2 +10 V 1 1 0 0 1 0 1 0

3 0 V 1 0 1 0 1 0 1 0

4 -10 V 0 0 1 1 1 0 1 0

5 -20 V 0 0 1 1 0 0 1 1

Similarly, for 7-Level Inverter operation mentioned

in Table 2, H-Bridges produce 7 levels: +30 V, +20

V, 10 V, 0, -10 V, -20 V, -30 V for asymmetric

voltages : V1 = 10 V and V2 = 20 V. Symmetrical

setups offer simpler design and control, while

asymmetrical configurations provide more levels

with fewer components, improving harmonic

performance.

Table 2: Switching table for 7 – Level Operation.

Mod

Outpu

Switching State

1 +30 V 1 1 0 0 1 1 0 0

2 +20 V 1 0 1 0 1 1 0 0

3 +10 V 1 1 0 0 1 1 0 0

4 0 V 1 0 1 0 1 0 1 0

5 -10 V 0 0 1 1 0 0 1 1

6 -20 V 1 0 1 0 0 0 1 1

7 -30 V 0 0 1 1 0 0 1 1

4 SIMULATION RESULTS

4.1 5 – Level Inverter

The Inverter is implemented in Matlab Simulink as

illustrated in Figure 5. V1 and V2 are chosen as 10 V.

The output has 5 levels ranging from +20 V to -20 V,

with an RMS value of voltage being 15.2 V.

Figure 5: Simulink Model of 5 – Level Operation

4.1.1 PD PWM

The output shown in Figure 6 is obtained for the 5-

level operation using PD PWM technique with its

respective THD in Figure 7.

INCOFT 2025 - International Conference on Futuristic Technology

552

Figure 6: Output using PD PWM

Figure 7: Voltage THD using PD PWM

4.1.2 POD PWM

Using the POD PWM approach, the result seen in

Figure 8 is produced for the 5-level operation, with

the corresponding THD displayed in Figure 9.

Figure 8: Output using POD PWM.

Figure 9: Voltage THD using POD PWM.

4.1.3 APOD PWM

With the application of APOD PWM, the voltage

waveform obtained is in Figure 10 with its THD in

Figure 11.

Figure 10: Output using APOD PWM.

Figure 11: Voltage THD using APOD PWM.

Impact of Sine PWM on Voltage THD in 5 - Level Vs 7 - Level Inverters: A Comparative Analysis

553

4.2 7 – Level Inverter

Figure 12 shows how the inverter is configured in

Matlab Simulink. V1 and V2 have been set to 10 V

and 20 V respectively. The output contains seven

voltage levels, from +30 V to -30 V, and its RMS

value is 22.4 V.

Figure 12: Simulink model of 7 - Level Operation.

4.2.1 PD PWM

By using the PD PWM technique, the output obtained

is depicted in Figure 13 with the voltage THD in

Figure 14.

Figure 13: Output using PD PWM

Figure 14: Voltage THD using PD PWM.

4.2.2 POD PWM

Using the POD PWM, the result seen in Figure 15 is

produced for the 7-level operation, with the

corresponding voltage THD displayed in Figure 16.

Figure 15: Output using POD PWM.

Figure 16: Voltage THD using POD PWM

4.2.3 APOD PWM

The output shown in Figure 17 is obtained for the 7-

level operation using APOD PWM technique with its

respective voltage THD in Figure 18.

Figure 17: Output using APOD PWM.

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Figure 18: Voltage THD using APOD PWM.

Table 3 shows the comparison of voltage THD

among the PD, POD and APOD modulation

techniques for 5-level and 7-level operation of the

inverter. It is evident from the table that the POD

modulation technique is optimal to use, since it is able

to produce less THD in comparison to other

techniques. It can be observed that increment in the

number of levels is causing the lower value of THD.

Table 3: Comparision of Voltage THD.

Modulation

Technique

Voltage THD (%)

5-level

operation

7-level

operation

PD 27.09 18.23

POD 27.03 18.18

APOD 27.56 18.39

5 CONCLUSION

This study highlights the significance of multilevel

inverters, particularly 5-level and 7-level

configurations, in improving grid integration and

power quality for renewable energy applications by

focusing on Total Harmonic Distortion and various

modulation strategies. The comparative analysis

reveals that the 7-level inverter demonstrates superior

performance with the lowest THD, making it a more

efficient choice over the 5-level counterpart for

achieving optimal power quality. Furthermore, the

investigation of SPWM strategies identifies POD as

the most effective approach for minimizing THD.

These findings emphasize the potential of advanced

SPWM techniques to further enhance the

performance of multilevel inverters in grid systems.

These characteristics make them indispensable in

applications such as industrial motor drives,

photovoltaic systems, and electric vehicle charging

stations. Overall, the study underscores the critical

role of innovative inverter designs and sophisticated

modulation strategies in advancing sustainable

energy solutions. The results provide a strong

foundation for future research aimed at optimizing

multilevel inverters to meet the evolving demands of

modern power systems.

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