Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Num

IJSTE - International Journal of Science Technology & Engineering | Volume 3 | Issue 08 | February 2017 ISSN (online): 2349-784X

Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch Ganesh G. Thakor PG Student Department of Electrical Engineering The Maharaja Sayajirao University of Baroda

Mrs. N. S. Nizami Associate Professor Department of Electrical Engineering The Maharaja Sayajirao University of Baroda

Abstract Analysis of different modulation techniques for reverse voltage nine level inverter is discussed in this paper. Reverse voltage topology requires fewer components compared to existing inverter Topologies and requires fewer carrier signals and gate drives. Therefore, the overall cost and complexity are greatly reduced particularly for higher output voltage levels. Multi carrier Sine Pulse Width Modulation (SPWM) techniques are widely used for different multilevel inverter topologies. The chosen multilevel inverter is simulated for various multicarrier based Pulse Width Modulation (PWM) techniques and selective harmonic elimination method. The multicarrier SPWM techniques include In Phase Disposition (PD) PWM, Alternative Phase Opposition and Disposition (APOD) PWM and Variable Frequency (VF) PWM. It is observed that sinusoidal reference with Alternative Opposition and Disposition (APOD) provides output with relatively low distortion.

Keywords: Multilevel inverter, reduced number of switch, Reverse voltage topology, Selective harmonic elimination, SPWM ________________________________________________________________________________________________________ I.

INTRODUCTION

The multilevel inverters are used in high power and high voltage industry. The main advantages of multilevel inverters are lower Total Harmonic Distortion (THD), less stress on the power switches and higher efficiency. The harmonic content of the output decreases as the number of level increases. There are mainly three types of multilevel inverters named as diode clamped multilevel inverter, flying capacitor multilevel inverter and cascaded multilevel inverter. Each of these topologies has a different mechanism for providing the required voltage levels. But the number of main switches in each topology is equal. The main disadvantage is the increase in number of power switches that normally contributes to the complexity in controlling the power switches. Many methods have been developed to decrease the number of switches.

Among them one is reverse voltage topology. The advantage of using Reverse Voltage Topology is that reduced the number of switches which reduced the complexity in gate drives circuit as well as reduced the number carrier signals in SPWM technique.

In this paper, presented the comparative analysis on MCPWM and SHEPWM method for valuation of harmonic elimination and shown the THD result in Reverse voltage multilevel inverter. Multi-Carrier Pulse Width Modulation (MCPWM) strategies is widely used, because it can be easily implemented to low voltage modules. Normally MCPWM can be categorized as Level Shifted PWM (LS-PWM) and Phase Shifted PWM (PS-PWM) methods. The LS-PWM is characterized into Phase Disposition (PD), Phase Opposition Disposition (POD) and Alternative Phase Opposition Disposition (APOD). Equate the above all methodology, APOD method is the most major process to express harmonics are centered as sidebands around the carrier frequency. Merits of APOD approach in MCPWM have no harmonics occur at the carrier frequency and higher band width the main objective of SHEPWM method is to determine the switching angles to specific lower order harmonics suppressed in the output voltage of the inverter to achieve desired fundamental component with possible minimum THD. II. DESCRIPTION OF REVERSE VOLTAGE MULTILEVEL INVERTER This topology is a hybrid multilevel topology which separates the output voltage into two parts.

1) Level generation part 2) Polarity generation part Level generation part requires high-frequency switches to generate the require levels. The switches in this part should have high-switching-frequency capability. The polarity generation part is responsible for generating the polarity of the output voltage. Within the new strategy, there is not to make use of all the switches in high frequency. This strategy separates output voltage into level generation and polarity generation components. The main concept of this inverter is to use both high frequency switches and low frequency switches and to limit the power devices voltage stress.

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Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch (IJSTE/ Volume 3 / Issue 08 / 030)

Fig. 1: Single phase nine level reverse voltage inverter with reduced number of switches

Fig.1 shows that nine inverter requires eight switches and four DC sources. The left portion of the circuit in Fig.1 generates the required output levels and the right portion of the circuit generates the polarity of the output voltage. The right portion of the circuit is called polarity generation part; it reverses the output of the level generation part when the voltage polarity requires to be changed for negative polarity. This topology requires fewer components in comparison to conventional inverters. Reduced number of switches leads to reduced cost and complexity. This also leads to reduced losses and increased efficiency. Another advantage of the topology is that it just requires half of the conventional carriers for SPWM controller. SPWM for nine-level conventional converters consists of eight carriers, but in this topology, four carriers are sufficient. Table I show the switching sequence for each level. According to the table, there are eight possible switching patterns to control the inverter. It shows the great redundancy of the topology. However, as the dc sources are externally adjustable sources (dc power supplies), there is no need for voltage balancing for this work.

Mode 1 2

Table – 1 Switching Sequence for Each Level 0 V 2V 3V D1,D2,D3,D4 S1,D2,D3,D4 S1,S2,D3,D4 S1,S3,D4 S2,D1,D3,D4 S3,D4,D1 S4,D1

4V S4,S1

III. MODULATION TECHNIQUES Multicarrier Pulse Width Modulation 1) In Phase Disposition (PD) PWM 2) Alternative Phase Opposition and Disposition (APOD) PWM 3) Phase Opposition Disposition with Variable Frequency (VF) PWM Selective Harmonic Elimination PWM In Phase Disposition (PD) PWM In this modulation scheme all the carrier signals are in phase but they are vertically displaced as shown in fig.2. But for each phase of inverter, the carrier signal should be equally displaced in phase as the reference signal is displaced. Here all the four carriers have 3 kHz frequency and are in phase with reference sine wave which has 50 Hz frequency. Fig. 3 and fig. 4 shows phase voltage waveform and FFT analysis of phase voltage respectively.

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Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch (IJSTE/ Volume 3 / Issue 08 / 030)

Fig. 2: In phase Disposition (PD) PWM

Fig. 3: Phase voltage waveform for PD PWM

Fig. 4. FFT analysis for PD PWM

Alternative Phase Opposition and Disposition (APOD) PWM In Alternate Phase Opposition Disposition (APOD) all carriers are in phase opposition with each other as shown in fig. 5

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Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch (IJSTE/ Volume 3 / Issue 08 / 030)

Fig. 5: Alternative phase opposition and disposition (APOD) PWM

Fig. 6: Phase voltage waveform for APOD

Fig. 7: FFT analysis of phase voltage for APOD

Phase Opposition Disposition with Variable Frequency (VF) PWM In this PWM technique, outer carrier having different frequency is being used. The outer band of carriers having less frequency compared to inner band of carriers as shown in fig.-8. Here the upper carrier has frequency of 1 kHz and lower carrier has 3 kHz.

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Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch (IJSTE/ Volume 3 / Issue 08 / 030)

Fig. 8: Phase opposition and disposition with variable frequency

Fig. 9: Phase voltage waveform for VF-APOD

Fig. 10: FFT analysis of phase voltage for VF-APOD

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Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch (IJSTE/ Volume 3 / Issue 08 / 030)

Selective Harmonic Elimination PWM The selective harmonic elimination method at fundamental frequency switching scheme has been implemented for computing the switching angles that eliminate the low order harmonics in 9-level inverter. With modulation index 1 and firing angle 7.5º, 21.6º, 36.8º & 60.2º harmonics 3rd ,5th & 7th becomes almost zero.

Fig. 11: Phase voltage waveform for SHE-PWM Table – 2 3rd, 5th, 7th Harmonics Harmonic order 3rd 5th %Harmonic 0.83% 0.63%

7th 0.07%

Fig. 12: FFT analysis of phase voltage for SHE-PWM

IV. RESULT AND COMPARISON In table 3, different PWM modulation technique is compared.

PWM method PDPWM APODPWM APOD-DF PWM SHE-PWM

THD% 7.94 7.93 10.64 8.69

Table – 3 Fundamental Voltage (Peak) 99.25 99.14 99.14 102.2

Rms value of fundamental voltage 70.18 70.10 70.07 72.24

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Analysis of Different Modulation Techniques for Reverse Voltage Nine Level Inverter with Reduced Number of Switch (IJSTE/ Volume 3 / Issue 08 / 030)

V. CONCLUSION In this paper, a nine level reverse voltage inverter has been presented and analysed by using MATLB/SIMULINK and the results are carried out for different pulse width modulation control strategies like PD, APOD, VF-APOD, AND SHE-PWM. It is found from TABLE 3 that APOD technique provides output with relatively low distortion. SHW-PWM technique provides relatively higher fundamental RMS output voltage and lower switching losses.

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