Self-sensing permanent magnet servo motors

Abstract

The use of Permanent Magnet Synchronous Machines (PMSMs) has become widespread across numerous applications and industries. Their high power density, efficiency and accuracy of control make them excellent choices, leading them to become the industrial standard. Two issues concerning PMSMs use in recent years have been associated with the elevated cost of rare earth materials required for the Permanent Magnet (PM) rotor poles and the reliance on a direct rotor position sensor such as an encoder. PMSMs require an accurate rotor position feedback within the control scheme, traditionally provided by an encoder or resolver. These devices are excellent at providing the realtime rotor position accurately but have a negative impact on the machine as a whole. Their use increases the size, weight and cost of the electrical machine, while reducing reliability and often limiting use in extreme environments. This has created motivation for sensorless control of PMSMs, which removes the need for a position sensor. Sensorless control can be categorized into two distinctive aspects. The first is the control scheme and focuses on how position dependent properties can be used to estimate rotor position. The second, which has had less focus, is the machine design. This is focused on the ability of a machine to act as a position sensor with clear position dependent properties. Self-sensing machine design is the common term applied to this field since in essence the machine acts as its own position sensor. This thesis is concerned with self-sensing oriented design. The work presented is focused on PMSMs with inset rotor topologies. A methodology was developed to assess the position tracking capability of a machine and incorporated within a traditional machine design optimization routine. The conceptual design of the machine emphasized a generic geometrical topology, accounting for practical material selections and construction techniques. This ensured the design outcome had widespread implications, as opposed to a novel machine design with limited commercial relevance