Modelling and control of segmented long-stator permanent-magnet linear synchronous motors
Date
2014-03-11
Authors
Lines, Christopher Roger
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Abstract
A novel control strategy for segmented long-stator permanent magnet linear synchronous
motors is presented that is particularly suited to ropeless hoisting. The
stator (primary) is segmented into modular sections that are shorter than the moving
reaction plate (secondary) and a single voltage source inverter per conveyance is
used to power the energised sections. Efficient partial excitation of the stator is
achieved with an intermediate switching layer placed between the stator sections and
the inverter. The common voltage supplied to the sections is controlled with any
standard motor vector control technique. Computer simulation and a purpose-built
laboratory prototype show the strategy to be effective. There is scope for future
research into full sensorless control of the proposed arrangement and a method of
further modulating the supply voltage for those stator sections that are only partially
covered by the reaction plate, particularly when operating at higher speeds.
Stemming from initial efforts to mathematically model the linear motor, a novel
electromagnetic modelling approach was formulated. This hybrid magnetic-equivalentcircuit
(MEC) and finite element method (FEM) approach is suited to efficient
dynamic simulation and is explicated with a worked example. The method yields
accurate results when compared with pure FEM. An MEC formulation is used for
highly-permeable polygonal regions, whereas the magnetic field outside these regions
is solved, by superposition, as the combined effect of boundary conditions that
interface with those MEC regions and any magnetic sources. The required parameter
sets for solving the field outside the regions represented as MECs are purely dependent
on the geometry of the problem space and are thus precomputed. The force acting
on a chosen group of moving components is calculated using an approximation of the
Maxwell Stress Tensor method. Future research could address the present limitation
that the highly-permeable regions are meshed using exclusively-rectangular flux tube
elements.
A dynamic simulation model that caters for the discontinuities of a segmented
stator was ultimately derived using an extended space-vector approach and its
implementation as a generic Simulink R
blockset is detailed. The motor parameters are
determined from static FEM solutions over the range of reaction plate displacement,
assuming no magnetic saturation.