Linear Induction Motors with Modular Winding Primaries and Wound Rotor Secondaries

Abstract

Linear induction motors commonly use double layer windings, which produce good sinusoidal travelling fields, but have relatively bulky end windings and use either half-filled slots or overhanging coil sides at the ends of the machine. Long stator systems are difficult since it is not possible to butt stator modules against each other. Arguably the simplest and most cost effective winding uses modular construction where the coils are planar and do not overlap. Here the end winding is compact and stator sections can be butted together. However modular windings do not produce high quality travelling fields. Two space harmonics of closely the same magnitude are produced that travel in opposite directions, giving induced currents and opposing forces with little net force in plate rotors. The difficulty can be resolved if a wound secondary with a double layer winding is used instead of a plate. Here a substantial induced emf and current is produced only by the field for which the secondary is wound, so that force is produced only in one direction. The use and properties of modular windings for short rotor machines are explored using finite element analysis and the results are validated by practical tests. It is concluded that inexpensive modular windings can be used with wound secondaries to good effect particularly in long stator situations; for example, for electromagnetic launch and urban transport systems.

A five-phase linear induction machine with planar modular winding

“…This winding layout produces more sinusoidal magneto-motive force (MMF) and electromotive force (EMF) distributions, which improves the overall machine performance. On the other hand, it has relatively bulky end windings and uses either half-filled slots or overhanging coil sides at the machine end sides [4,5].…”

“…These advantages comprise short end turns, high torque density, high efficiency, and high slot fill factor, predominantly when segmented stator structure is employed [6]. However, for induction machine, there has been very limited interest in employing modular windings for both linear [4,5] and rotary types [7,8]. This is because the MMF produced by a conventional three-phase modular winding contains two main space harmonics with close magnitude but travel in opposite directions.…”

“…These two components induce rotor currents with different frequencies yielding additional rotor bar losses and with a resultant limited net torque due to the resulting opposite torque components [7]. In [4], the secondary of a LIM is equipped with a double layer winding instead of the conventional plate normally used with LIMs. Hence, the induced emf is produced only by the field on which the secondary is wound.…”

Analysis and modeling of modular curved linear permanent magnet motor

“…Cogging torque is another problem with this winding type. Compared with distributed windings, PM motors with concentrated winding and fractional slots have high-power density, high efficiency, short end-turns, high slot fill factor, low cogging torque, flux weakening capability, and fault tolerance [2].Modular windings have fractional slots and the coils belonging to each phase are concentrated and wound on consecutive teeth [3][4][5][6].…”

Design Optimization, Prototyping, and Performance Evaluation of a Low-Speed Linear Induction Motor With Toroidal Winding

“…In this case, the air-gap flux produces two high harmonics of the same magnitude, often called main components. These components travel in opposite directions and induce eddy currents in the secondary sheet, and hence, two opposing thrusts are created, leading to a poor net thrust [11]. In [11], a long primary LIM with modular winding primary was proposed in which the secondary conducting plate was replaced by a wound rotor secondary.…”