Quadrature-axis Inductances Research Articles

DC Standstill Torque Used to Measire Lq of Reluctance and Synchronous Machines

An experimental method for measuring the quadrature axis inductance (Lq) of polyphase synchronous machines is developed. It is based on a measurement of developed torque with the rotor at standstill and with the stator winding supplied with dc currents. While applicable to all synchronous machines, it is developed and explained for reluctance motors primarily. Special techniques are used to minimize measurement errors due to hysteresis and due to air gap permeance harmonics. Detailed results are presented for one reluctance motor which has a highly variable Lq, and correlation with other methods is found to be quite good. The effects of saturation are observed, and Lq is found to depend on quadrature axis current in the tested motor, with direct axis current having a slight effect on Lq at larger currents.

Torque Calculations of Polyphase Reluctance Machines

A rigorous solution for the flux-density distribution on the armature surface of a reluctance motor is given by dividing the composite airgap space into two regions and solving Laplace's equation separately in them to get the potential distribution. The fundamental flux density is calculated and, hence, the direct- and quadrature-axis synchronous inductances for a polyphase reluctance machine. It is found possible to calculate the maximum torque in terms of the machine dimensions. Since the solutions are obtained for both rectangular-developed and radial diagrams, the error involved in neglecting the curvature can be determined. A numerical example is also given. The variation of reluctance power with polearc/pole-pitch ratio is calculated and found to be in close agreement with results obtained by previous authors.