MATHEMATHICAL MODELING OF A SYNCHRONOUS GENERATOR WITH COMBINED EXCITATION

Abstract

The generators of classical design ‒ with a cylindrical stator and rotor ‒ are of interest. This is predetermined by that a given structure is the most common, simple, and technological. The result of the development of such electric machines is a possibility to build a combined series of induction motors and magnetoelectric synchronous machines. In these machines, replacing a short-circuited rotor by a rotor with permanent magnets and controlled working magnetic flux turns the induction machine into a magnetoelectric synchronous one. All existing generators with permanent magnets have a major drawback: there is almost no possibility to control output voltage and, in some cases, power. This is especially true for autonomous power systems. Known methods of output voltage control lead to higher cost, compromised reliability, deterioration of mass-size indicators. This paper reports the construction of a three-dimensional field mathematical model of a magnetoelectric synchronous generator with permanent magnets. The model has been implemented using a finite element method in the software package COMSOL Multiphysics. We show the distribution of the electromagnetic field in the active volume of the generator under control and without it. The impact of a control current in the magnetized winding on the external characteristics of the generator at a different coefficient of load power has been calculated. Applying the devised model has enabled the synthesis of a current control law in the magnetizing winding at a change in the load over a wide range. The results obtained demonstrate that it is possible to control output voltage of the generator with permanent magnets by using an additional magnetizing winding. The winding acts as an electromagnetic bridge for the main magnetic flux, which is created by permanent magnets. Our analysis of results has shown that it is possible to regulate the output voltage of the generator with constant magnets within –35 %, +15 %.