Self-excited induction generator : a study based on nonlinear dynamic methods

An induction generator offers advantages in terms of its low cost, simplicity, robust construction, nature protection against short circuits and ease of maintenance in today’s renewable energy industry. However, the need for an external supply of reactive power (to produce a rotating magnetic flux wave) limits the application of an induction machine as a standalone generator. It is possible for an induction machine to operate as a Self-excited Induction Generator (SEIG) if capacitors are connected to the stator terminals in order to supply the necessary reactive power to achieve generating electrical energy in remote areas. Poor voltage and frequency regulation is the main drawback of a SEIG as the system is highly dynamic under variable load conditions. The regulation of speed and voltage does not result in a satisfactory level although many studies have been focused on this topic in the past. Therefore, the aim of the thesis is to provide a better understanding of the behaviour of a smooth airgap, selfexcited, squirrel cage induction generator as a nonlinear dynamic system when operating under a variety of load conditions, which would hopefully contribute to the development of a better regulated/controlled, viable SEIG system. Allowing for the cross-saturation nonlinear effect, a mathematical Simulink, d -q axis model of the SEIG system utilising currents as state space variables is developed and verified by both the experimental results and numerical analysis. The SEIG computer model is constructed and tested using Matlab/Simulink R2010b throughout the thesis. The self-autonomous system is shown to exhibit a transition from a stable periodic orbit to a quasi-periodic orbit (leading to likely chaotic motion) through a Neimark bifurcation, as a result of small changes in the values of system parameters (such as load resistance, load inductance, rotational speed and self-excitation capacitance). This characteristic dynamic behaviour of the SEIG system is firstly identified in this work and is verified experimentally using a laboratory test rig. The stability of the periodic and quasi-periodic orbits exhibited by the SEIG system when feeding an inductive load ( RL) is numerically analysed and the movement of the eigenvalues of the system’s characteristic matrix when changing a system parameter is presented to verify the qualitative change in system behaviour from a stable period-one orbit to unstable quasi-periodicity. Eigenvalue technique is successfully applied to assess the stability of the period-one and quasi-periodic orbits of the SEIG when feeding variable load conditions.EThOS - Electronic Theses Online ServiceSchool of Electrical and Electronic EngineeringNewcastle UniversityGBUnited Kingdo

Recollements induced by left Frobenius pairs

Let $T$ be a right exact functor from an abelian category $\mathscr{B}$ into another abelian category $\mathscr{A}$. Then there exists an abelian category, named comma category and denoted by $(T\downarrow\mathscr{A})$.In this paper, we construct left Frobenius pairs (resp. strong left Frobenius pairs) over $(T\downarrow\mathscr{A})$ using left Frobenius pairs (resp. strong left Frobenius pairs) over $\mathscr{A}$ and $\mathscr{B}.$ As a consequence, we obtain a recollement of (right) triangulated categories, generalizing the result of Xiong-Zhang-Zhang (J. Algebra 503 (2018) 21-55) about the recollement of additive (resp. triangulated) categories constructed from a triangular matrix algebra. This result is applied to the classes of flat modules and Gorenstein flat modules, the classes of Gorenstein projective modules and Gorenstein projective complexes, the class of Ding projective modules and the class of Gorenstein flat-cotorsion modules.Comment: 24 pages, all comments are welcom

CARNet:Compression Artifact Reduction for Point Cloud Attribute

A learning-based adaptive loop filter is developed for the Geometry-based Point Cloud Compression (G-PCC) standard to reduce attribute compression artifacts. The proposed method first generates multiple Most-Probable Sample Offsets (MPSOs) as potential compression distortion approximations, and then linearly weights them for artifact mitigation. As such, we drive the filtered reconstruction as close to the uncompressed PCA as possible. To this end, we devise a Compression Artifact Reduction Network (CARNet) which consists of two consecutive processing phases: MPSOs derivation and MPSOs combination. The MPSOs derivation uses a two-stream network to model local neighborhood variations from direct spatial embedding and frequency-dependent embedding, where sparse convolutions are utilized to best aggregate information from sparsely and irregularly distributed points. The MPSOs combination is guided by the least square error metric to derive weighting coefficients on the fly to further capture content dynamics of input PCAs. The CARNet is implemented as an in-loop filtering tool of the GPCC, where those linear weighting coefficients are encapsulated into the bitstream with negligible bit rate overhead. Experimental results demonstrate significant improvement over the latest GPCC both subjectively and objectively.Comment: 13pages, 8figure

Effects of Design Parameters on Performance of Brushless Electrically Excited Synchronous Reluctance Generator

Permanent magnet synchronous generators, doubly fed induction generators, and traditional electrically excited synchronous generators are widely used for wind power applications, especially large offshore installations. In order to eliminate brushes and slip rings for improved reliability and maintenance-free operation, as well as to avoid costly permanent magnets, a novel brushless electrically excited synchronous reluctance generator having many outstanding advantages has been proposed in this paper. The fundamental operating principles, finite element analysis design studies and performance optimization aspects have been thoroughly investigated by simulations and experimentally under different loading conditions. The effects of different pole combinations and rotor dimensions on the magnetic coupling capacity of this machine have been specifically addressed and fully verified by off-line testing of the 6/2 pole and 8/4 pole prototypes with magnetic barrier reluctance rotor and a new hybrid cage rotor offering superior performance