Five level inverter with SVPWM Control Technique

Author Name(s): Ponnuri Ajay Kumar, Dr. G.Tulasi Ram Das
Author Email: ajay.ponnuri@gmail.com

Abstract

This paper provides the proposed single phase five level inverter with Dc link Switches based on SVPWM technique. This paper focuses on improving harmonic performance of the multilevel inverter and quality of output voltage waveform compared to conventional two-level inverter. It uses two carrier wave and three reference waves which are generated fromSVPWM technique. The whole system is implemented using MATLAB/Simulink. The inverter is connected to R-load,RL-load and performances are analyzed.

Introduction

The Multilevel inverter topologies are the best suited for medium and high voltage applications in the industries. Now a day’s tremendous interest were drawn in the power industry as this inverterexclusively used in increased power rating, reduced THD and reduced EMI. The switching losses are almost negligible because these are switched at low switching frequency compared to conventional multi-level inverters. To endure with associated problems with the two level inverter, multilevel inverters (MLIs) are introduced [1]. The inverter should have the appropriate requirements.

  • Inverter output current should have low total harmonic distortion (THD).
  • To generate a pure sinusoidal output voltage

The output filter, inductor must have suitable value to satisfy the appropriate THDvalue in conventional two level inverter, hence MLIs are introduced for industries and also for grid connected applications [2-4].

The types of multilevel inverters are:-

  • Diode clamped multi level inverter.
  • Cascaded H bridge multi level inverter.
  • Flying capacitor type multi level inverter.

Because of development of power electronic devices like MOSFET,IGBT and SCRs etc…There is a tremendous advance in power electron ic converters this made the multilevel inverters concept practical in industries. The thought of multi-level inverter has become superior advantageous so that several major manufacturers have obtained patents on multi-level power electronic converters. The multilevel inverter will have dominant features in future coming years, particularly in high power applications.

The applications of multi-level inverter are variable speed drives, Power factor control, reactive powercompensation, etc. [5-7]. The Physical structure of Multi level inverters must have the ability to withstanding high input voltages for high power applications. So, A new topology which is capable to scale down the problems faced by the conventional two-level inverter [8].

The advantages of multi-level inverter over the conventional two level inverter is that, the proposed multi-level inverter has less number of switch count. The THD of the proposed multi-level will be less compared to conventional two-level inverter. The most important concept is that the DC-link capacitor voltage must have equally balanced. If it is not balanced equally the output voltage becomes unsymmetrical and it leads to high harmonic content in the load voltage and load current.

The proposed multilevel topology is controlled with carrier based Pulse Width Modulation techniques. So many techniques were proposed in the literature among them the following are the famous CB-PWM.

1) Phase disposition (PD): In this Phase Disposition technique all the carrier waves are in phase with each other

2) Alternative phase opposition disposition (APOD): In which all the carrier waves are phase shifted by 1800 with the adjacent carrier wave.

3) Phase opposition disposition (POD):In this technique, above the zero voltage carrier waves are 180o out of phase with those carrier waves below zero voltage.

4) Space Vector Pulse Width modulation: In this technique it under goes a method, The sector in which it consists of eight states in which two states were in valid. This technique uses volt-sec balance.

Conclusion

The Five level inverter Topology using Space Vector pulse width modulation technique is implemented in MATLAB/Simulink. Uref obtained by using alfa-beta reference frame. The total harmonic distortion is quite low as compared to conventional multi-level inverter. The switches count reduced, besides that the output voltage is nearly pure sinusoidal that means the quality of the wave form is improved.

The result with R and RL load has evaluated. By observation it is seen that the voltage THDof proposed multilevel inverter   with RL-load has little high THD compared to R load i.e., 1.52% & 1.13% respectively.

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