A new rotor design for flux weakening capability improvement in spoke-type interior permanent magnet synchronous machines

In many applications, electric machines are designed for operation over a wide speed range and require important flux weakening capabilities at high speeds. This paper presents and innovative rotor mechanical design that endows an interior permanent magnet (IPM) machine with an intrinsic capability of reducing its own rotor flux at high speeds. Unlike most state-of-the-art flux-weakening techniques, the design does not involve any additional current source nor demagnetization currents to be injected into stator circuits. It relies on a purely mechanical device that establishes a partial magnetic short circuit between rotor permanent magnets. The device is able to self-activate by centrifugal force when the speed exceeds a given threshold that can be fixed by design. The paper presents criteria for dimensioning the new IPM rotor and a mathematical model to predict its performance. The proposed solution is implemented into a motor prototype whose manufacturing and testing are discussed for experimental validation.