Dissertação
Modulação vetorial otimizada para o conversor packed U-cell
Fecha
2020-09-24Autor
Schuetz, Dimas Alã
Institución
Resumen
This master’s dissertation proposes space vector modulation strategies for the Five-Levels Packed
U-Cell converter with optimization on the commutation number and balance of the floating
capacitors by use a cost function. Initially, the converter three-phase topology and their commutation
states are presented, from which the redundant states are highlighted. In sequence, some
concepts of the main modulation strategies for multilevel converters are present and the discontinuous
modulation strategies features are introduced. Based on the discontinuous modulation
features, it is proposed the definition of the reference vector for the space vector modulation
so that, when mapped to the 3D space vector diagram, it remains clamped to one face for
a certain time period. As a result, it is possible to decompose the 3D space vector diagram
in 2D planes, make the search of the reference nearest vectors easier. Furthermore, the space
vector diagram representation in the abc coordinates do not present redundancies in the converter
phase-to-phase voltages space, reducing the algorithm computational effort. In this way,
switching sequence definition ways are proposed in order to minimize the number of phase voltages
transitions between two adjacent vectors, and result in output voltages with half-wave
symmetry. Starting from the Packed U-Cell converter redundancies, the distance about the last
implemented vector is calculated as well as the error between the medium current reference for
balance the capacitor voltages, given by PI controllers, and the prediction current that flows
across these capacitors for each redundant state, remembering the Model Predictive Control technique.
By the proposed cost function, composed by the above mentioned parcels, it is selected
the redundancy that presents the least cost. The proposed modulation strategies performance is
analyzed by simulation and experimental results, considering the connection cases of the Packed
U-Cell converter with a resistive-inductive load. Based on the obtained results, comparative
analyses with previous proposed modulation strategies for this converter are presented, showing
advantages in terms of commutations number and better performance of harmonic distortion
values in the output voltages.