|dc.contributor.author||Holtsmark, Nathalie Marie-Anna||
|dc.description.abstract||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.||nb_NO
|dc.relation.ispartofseries||Doctoral thesis at NTNU;2016:16||
|dc.title||INVESTIGATION OF THE MATRIX CONVERTER IN A DC SERIES-CONNECTED WIND FARM: Modulation, Control and Efficiency||nb_NO
|dc.subject.nsi||VDP::Technology: 500::Electrotechnical disciplines: 540::Electrical power engineering: 542||nb_NO