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INVESTIGATION OF THE MATRIX CONVERTER IN A DC SERIES-CONNECTED WIND FARM: Modulation, Control and Efficiency

Holtsmark, Nathalie Marie-Anna
Doctoral thesis
Åpne
Fulltext not available (Låst)
Permanent lenke
http://hdl.handle.net/11250/2379185
Utgivelsesdato
2016
Metadata
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  • Institutt for elkraftteknikk [1596]
Sammendrag
In this thesis a wind energy conversion system for series-connection of DC wind

turbines is considered. The wind park topology offers the advantage of a high

voltage transmission without the need of an offshore platform to support a step-up

transformer and an AC-DC converter. The wind conversion system which is proposed

is composed of a permanent magnet synchronous generator, a three phase

AC-AC converter, a three phase high frequency transformer and a diode bridge rectifier.

Designing the transformer for high frequency operation reduces its volume

and weight, making it possible to place it in the nacelle of the turbine.

Three different converters are considered for the AC-AC conversion: the matrix

converter, the indirect matrix converter and the back-to-back converter. The ACAC

converter feeds the high frequency voltage waveform to the transformer which

brings about a high switching frequency and switching losses. An important effort

is therefore been spent on finding appropriate modulation schemes which can

limit the losses. "High Frequency" modulation schemes suitable for the conversion

system are developed in the thesis.

To make a proof of feasibility by simulation, a simulation model of the conversion

system is build. The model is based on mathematical models of the different

components and includes a detailed model of the converters with the modulation

schemes. A control strategy for the rotor speed is developed and implemented in

the simulation model. The design of a typical 750kW unit is carried out to complete

the simulation model. Simulation results show that the proposed conversion

system and the solutions for the modulation, control and design are valid.

Semiconductor loss calculations are also build into the simulation models to evaluate

the efficiency of the different AC-AC converters. The results of the simulations

show that the developed modulations keep the efficiency at an acceptable level while enabling an increase of the transformer frequency. The matrix converter

and indirect matrix converter have very similar efficiencies. The B2B efficiency is

largely dependent on the desired stator current waveform quality. If a performance

equal to the matrix type of converters are desired, the efficiency of the back-to-back

is lower for all modulations while it is higher if other non-comparative criteria are

used for selecting filter and switching frequency.

An initial experimental verification of the proposed concept is presented in the

thesis. The experimental set-up includes a matrix converter, a high frequency

transformer, a diode bridge rectifier. The matrix converter is connected to a voltage

source instead of a permanent magnet synchronous machine. Designing and building

the matrix converter is part of the thesis and presented here, as well as the

implementation of the modulation with a real-time simulation system.
Utgiver
NTNU
Serie
Doctoral thesis at NTNU;2016:16

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