Vehicle propulsion using continuous track linear induction motors on steel plates
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Linear induction motors (LIMs) are zero-carbon emission, non-contacting electrical motors that operate on the same principle as rotary squirrel cage induction motors found prominently in industry today. LIMs are capable of operating over wide speed ranges and are effective for generating linear thrust without requiring gears, pulleys or other components for converting angular motion to linear motion. This thesis explores the concept of a novel robotic vehicle for operation on steel, iron or other surfaces with high magnetic permeability. Two custom designed 4-pole, 3-phase LIM stators, vehicle body, reaction plate tracks, dual variable frequency drive controller board and interface were designed, built and tested. A control strategy utilizing the coupled nature of the attractive normal and linear thrust forces is proposed, focusing on how to achieve peak thrust for given structural and operational parameters, including a phase balancing implementation used to compensate for minor differences in impedances between phases. Simulations and experimental evidence are presented to show the changing ratio of thrust to normal force produced over the slip-frequency operating region of 10-20Hz. With a thrust to normal force ratio selected to suit the operating conditions, the controller outputs a voltage to achieve the requisite flux linkage and Volts-per-Hertz control is used to keep flux linkage constant as the slip-frequency changes during operation. The developed vehicle has a total mass of 28kg and has been experimentally tested to develop a peak thrust force from standstill of 90N for an input power of 1.7kW. Operation of the vehicle on flat surfaces and climbing inclines up to 21° was validated experimentally.