Discontinuous pulse width modulations for two-level three-phase voltage source inverter based on zero-sequence optimization

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Journal ISSN

Volume Title

Sähkötekniikan korkeakoulu | Master's thesis

Date

2019-12-16

Department

Major/Subject

Electrical Power and Energy Engineering

Mcode

ELEC3024

Degree programme

AEE - Master’s Programme in Automation and Electrical Engineering (TS2013)

Language

en

Pages

91 + 11

Series

Abstract

The carrier-based pulse width modulations are used to control the operation of UPS, motor drives, and grid-connected converters. In the UPS and motor drive applications, the connected load can be linearly controlled until 95% of the rated voltage. To operate the load at the rated voltage, the converter operates in nonlinear mode. It makes controller design difficult and cumbersome. In this thesis, the zero-sequence optimization approach has been adopted to improve the DC bus utilization capabilities of discontinuous modulations to linearly control the load to its rated voltage. The optimization problem is devised using the concept of freedom of placement of the zero vectors in the space vector modulation to produce optimized discontinuous modulations. To build the foundations of this document, the operation of a two-level three-phase voltage source inverter and the associated losses are investigated in detail. Furthermore, carrier-based modulations are researched to highlight their important features. All the carrier-based modulation techniques are compared in terms of the linear range of modulation index, efficiency and harmonics at different switching frequencies with the help of 140 kW three-phase voltage source inverter, designed in the MATLAB. The efficiency of the converter decreases when the switching frequency increases, and the load power factor decreases. It is also observed that the THD in the output is high at low switching frequencies, but it decreases exponentially when the load power factor decreases. The results indicate that the discontinuous modulations derived from space vector modulation and zero-sequence optimization have identical behavior.

Description

Supervisor

Kyyrä, Jorma

Thesis advisor

Eskandari, Bahman

Keywords

discontinuous pulse width modulation, zero-sequence optimization, efficiency of converter, three-phase voltage source inverter, space vector modulation, linear modulation range

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