Comparative Analysis of Power Loss using Different Modulation Techniques in Modular Multilevel Converter

Author Name(s): Preeti V. Kapoor, Mohan M. Renge, Sonali Rangari
Author Email: kapoorpv@rknec.edu

Abstract

The application of voltage source inverter in medium and high power application is increasing extremely. Multilevel converters reduces the height of voltage steps at converter output and thus also dv/dt and voltage harmonics. In high power applications high efficiency of converter is the most important aspect. Hence the power loss analysis has to be carry out at early stage of converter design. Power loss evaluation of multilevel converter is much more complicated as compared to two level inverter. This paper provides the software-based solution to calculate the power loss in semiconductor switch. Modular Multilevel Converter (MMC) an emerging topology in multilevel converter is considered for study. It also presents the comparison of power loss analysis with different pulse width modulation technique eliminating the same order of harmonics. The analysis has been carried out in three phase three level MMC driving high power medium voltage three phase induction motor. The converter is controlled by high switching frequency technique i.e. Sinusoidal Pulse Width Modulation (SPWM) and low switching frequency technique i.e. Selective Harmonic Elimination Pulse Width Modulation (SHE-PWM) technique. Comparison in regards with power loss and converter efficiency has been presented. Simulation has been carried out in MATLAB-SIMULINK providing the software-based solution to find the conduction and switching loss in a switch.

Introduction

Multilevel converters are becoming more and more popular solution in medium voltage drives. Many topologies under multilevel converters were presented as in [1-2]. Among the various multilevel converters topologies, MMC is gaining more popularity in the industry and the academics for research mainly due to its modular structure, high scalability to reach different voltage levels, redundant construction, longer maintenance intervals, improved reliability, and higher efficiency. It was first proposed by Lesnicar and Marquardt in 2003. [3] MMC is finding more opportunities in area of variable speed drives since efficiency improvement in this area is required [4,5] and hence it is chosen for study.

Conclusion

Multilevel converters are finding many economic and technical advantages in industries and utility applications. Under various multilevel topologies, Modular Multilevel Converter is emerging as a most popular topology in the field of high-power medium voltage applications. It is critical to evaluate loss in multilevel converter. Among various losses, conduction and switching loss is most dominating. This paper provides simple, efficient and easy implementation of software-based method to evaluate conduction and switching losses of each device. Losses of each device is added to find the total loss and hence converter efficiency is calculated. Comparison of power loss is carried out with both SPWM and SHE-PWM technique applied to three phase three level MMC driving high power medium voltage related induction motor. Comparison is made on the basis of eliminating upto 13th order of harmonics with both the technique. It is observed that percentage loss in inverter with SHEPWM technique is almost reduced by 50 % as compared to SPWM technique. Hence, SHE-PWM modulation technique is the most recommended method for controlling inverter as this technique has lower switching losses and less EMI problems. In addition, it eliminates lower order harmonics and hence minimizes the filter size at inverter output.

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