Parametric instability induced by traveling magnetic load within permanent magnet motors

Abstract

Magnetic load can cause excessive noise and vibration or even parametric instability, damaging permanent magnet (PM) motors on a permanent basis. This work investigates the parametric vibration of a ring stator with an aim to identify mechanical–magnetic coupling parametric vibration. An analytical model is developed by using energy method, where the stator is treated as a thin smooth ring having radial and tangential deflections and subjected to traveling magnetic load. The modeling leads to a partial differential equation with time-variant coefficients depending on pole/slot combination, excitation order, permanence order, and wave number. Principal instability boundaries are identified by multi-scale method as simple closed-form expressions. The expressions govern the relationships between mechanical–magnetic parameters and instability’s occurrence or suppression. Results show that there exist unstable regions that cannot be detectable directly by traditional treatment widely employed when using the multi-scale method, and thus, an alternative avenue is presented. Analytical results are well compared against the numerical ones from the Floque’t theory. The analytical results can find application in parameter’s selection at preliminary design stage of the PM motors to keep stable running.