Rotor-design and on-line starting-performance analysis of a synchronous-reluctance motor
Purpose ‐ The purpose of this paper is to derive the geometry-based equations for inductances which are used in circuit theory analysis of synchronous reluctance motor (SRM). Transient and steady state performance analyze of SRM by using the 2D time-stepping finite-element method (FEM). Design/methodology/approach ‐ The analytical approach is used to obtain the equations which describe geometry dependent magnetizing inductances of SRM. Transient and steady state performance of the SRM is analyzed by using the 2D time-stepping FEM. The external electric circuit connected with the finite-element model of the SRM geometry allows the study of almost any of the electric and magnetic properties of the machine. Presented SRM model is also connected to the external mechanical loads (friction, rotor inertia and load torque). The use of different materials for the magnetic-pole part of the rotor and for flux barriers was analyzed. The flux barriers in the first SRM rotor were filled with a pure massive electrically conductive ferromagnetic with a proper B-H curve, whereas the rotor magnetic segments were made of non-conductive electric steel described with its B-H curve. The conductive barriers with their end rings form a squirrel cage and allow SRM to start on-line. The flux barriers of the second SRM rotor were made of aluminum but between the second and third flux barrier a massive electrically-conductive ferromagnetic was inserted which during starting-up acted as a part of the squirrel cage. All of the flux barriers of the third SRM rotor were made of electrically-conductive aluminum with iron parts axially laminated. The finite-element SRM models coupled with an electric circuit is also used to evaluate the motor performance at various asynchronous speeds. Findings ‐ Analytical geometry-dependant equations for the
d- and q-axis SRM inductances are derived. On the basis of the proposed 2D time-stepping finite-element analysis, the start-up performance for the SRM rotor design using different materials is established. The torque distribution as a function of time at any of the observed asynchronous speeds is not smooth and uniform. It consists of the stator-to-rotor tooth pulsating torque, and the synchronous and asynchronous component. Research limitations/implications ‐ The main disadvantage of analytical geometry-dependant equations for the d- and q-axis SRM inductances is the linearization of any of the ferromagnetic parts. Practical implications ‐ On the basis of the proposed 2D time-stepping finite-element analysis, the start-up performance, asynchronous run and synchronous torque characteristics for the SRM rotor design using different materials are established. Originality/value ‐ The value of the paper is the closed view about happenings in rotor flux barriers of SRM, mostly regarding the time distribution of induced currents in the rotor flux barriers. On the base of 2D time-stepping FEM, the use of different materials for the magnetic-pole part of the rotor and for flux barriers was analyzed.
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