Method for evaluating the starting characteristics of solid salient-pole synchronous motors

Abstract

A brief description is given of existing methods of calculation of the asynchronous starting performance of solid salient-pole synchronous motors. These methods evaluate an equivalent impedance to represent the eddy-current loss in the solid-iron pole. This impedance is a variable, dependant on the rotor slip frequency and flux. The power factor of this equivalent impedance is a fixed quantity. The lumped-circuit parameter is then used in an equivalent circuit to calculate the asynchronous values. The harmonic torque and current associated with the Gorges effect need to be examined as these can affect the shape of the characteristics close to half speed and can cause a synchronous motor to run in the region of half speed with a heavy current pulsation. A new computational direct-search method is then described and used to evaluatethe average asynchronous values of torque and current for a solid salient-pole synchronous motor. The method allows for the provision of the distributed entry of flux into the saturable solid pole, pole-tip saturation and the evaluation of space-harmonic flux values. The need to make assumptions about eddy current distribution is eliminated by taking a path of integration on the pole surface. The method is completely general and any relative stator and rotor position can be analysed. Comparisons between the results from this new method, existing methods and test results show that the new method gives consistently accurate answers.