# Magnetic field of a dc motor with excitation from permanent magnets

2023;
: pp. 31 - 37
Authors:
1
Lviv Polytechnic National University

Currently, DC motors with excitation from permanent magnets ( PM DC) are widely used in vehicles, household appliances, portable power tools due to their simple design and low cost. Therefore, the task of creating mathematical models for their calculation, which can be used for design, is urgent. The purpose of the article is to clarify the mathematical model of the magnetic state of the PM DC and experimental verification of the correspondence of the experimental results to the calculation results. The theory of magnetic and electric circuits is used to describe the magnetic state of the PM DC. A refined branched replacement circuit of the PM DC magnetic circuit with concentrated parameters is proposed. In this scheme, permanent magnetic resistances correspond to non-magnetic sections of the magnetic circuit. Sections of the magnetic conductor made of ferromagnetic materials correspond to nonlinear magnetic resistances, which are represented by the dependence F[Ф] of the decay of the magnetizing force on the magnetic resistance on the magnetic flux. The toothed area of the armature, placed under the magnets, is divided into m identical sectors by radial planes perpendicular to the plane of the armature sheets. The substitute scheme of the magnetic circuit is described by a system of nonlinear equations compiled for one pole division of the motor using the method of loop currents. This system contains three equations for the stator loops and (m – 1) equations for the armature loops. The results of the calculation of the magnetic flux and inductions in different sections of the magnetic conductor of the PM DC are presented. The adequacy of the calculation of the magnetic circuit of the PM DC is checked in relation to the magnet flux. The experimental sample of PM DC consists of a stator and an unwound armature. In the diametrical grooves of the armature, filled with dielectric, a measuring coil is wound, the turns of which are located near the air gap. The terminals of the measuring coil are connected to the fluxmeter. The deflection of the fluxmeter needle during the rotation of the armature from the position of the coil, which corresponds to the geometric neutral, to its position, which coincides with the axis of the poles, was recorded. The calculated and experimental values of the magnetic flux coincide with an accuracy of 0.86%, which confirms the adequacy of the proposed mathematical model of the magnetic state of the PM DC. The proposed replacement scheme of the magnetic circuit and the system of equations describing it can be the basis for creating mathematical models for calculating the static characteristics and transient modes of the PM DC.

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