An indirect test method for the characterization of variable reluctance motors

The determination of the characteristics of the variable reluctance motors (both in static and dynamic conditions) represents a quite critical point, due to the heavy nonlinearity of the motor magnetic paths, to the high distortion of the supply voltage from the converter, and to the high level of saturation of the magnetic paths in normal working conditions. This creates a great difficulty in the accurate measurement of the motor magnetic characteristics (saturation curves or flux linkage versus current curves) and consequently in the determination of the mechanical characteristics (static torque versus current and static torque versus rotor position) which are directly related to the saturation curves. The paper proposes an original digital method that, starting from the measurement of the flux linkage in the motor magnetic paths, determines the saturation curves, evaluates the coenergy versus current curves and then the motor torque characteristics in static conditions. It is then shown how the availability of a fast and accurate method for the measurement of the flux linkage allows the determination of the electromagnetic torque in dynamic conditions, too