1.1.15

01 בינואר 2015, 15:00 
Kitot 011 
1.1.15

You are invited to attend a lecture

By

Dr. Alex Ruderman, Associate Professor

Department of Electrical and Electronic Engineering, School of Engineering, Nazarbayev University Kabanbay Batyr Ave 53 Astana, Kazakhstan 010000.

Phone +7-7172-709146

Email alexander.ruderman@nu.edu.kz

 

 

On the subject:

 

Time Domain Analysis of Multilevel Converter Voltage and Current Quality

Today power electronics community is biased towards frequency domain analysis of PWM phenomena. The seminar goal is to show that time domain averaging methods are more adequate for certain integral problems that don't require a specific knowledge of individual harmonics. The power of time domain analysis is demonstrated while elaborating voltage and current quality in multilevel inverters for PWM and staircase (step) modulation. For relatively high frequency PWM, the solution is obtained under the asymptotic assumption – a switching frequency is supposed much higher than a fundamental one. The closed-form asymptotic solution for an arbitrary voltage level count involves only elementary functions and, in fact, presents voltage quality upper bound for nearest level PWM. The asymptotic solution is practically very accurate for relatively high switching-to-fundamental frequency ratios (>25-30). For staircase modulation, voltage and current optimal quality (minimal Total Harmonic Distortion - THD) problems are formulated in time domain as constrained optimization ones. Optimal switching angles that minimize voltage and current THD accounting for all switching harmonics are found using numerical optimization for different inverter level counts and the whole modulation index range 0<M<1. Suggested are simple voltage and current THD ripple-free approximations for arbitrary level counts and modulation indices. While these simple hyperbolic formulas accurately approximate the average trend, local maxima and minima of voltage and current THD may be addressed on separate. The obtained current THD is actually frequency weighted THD that assumes inductance dominated RL-load. For grid-connected applications, normalized current fundamental harmonic is smaller than voltage modulation index and current THD will be larger than frequency weighted voltage one.

 

 

1 January 2014, at 15:00,

Room 011, Kitot Building

 
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