Analytical calculation of magnetic field in active zone of synchronous machines with permanent magnets

Аuthors

Zhuravlev S. V.^1*, Zechikhin B. S.¹, Kuz'michev R. V.²

1. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
2. Experimental Design Bureau "Sukhoi", 23B, Polikarpov str., p/b 604, Moscow, 125284, Russia

*e-mail: zhuravlev_sv@rambler.ru

Abstract

Synchronous machines with rare earth permanent magnets are widely used in aviation and rocket technology as motors for the electric actuators and generators of electrical power systems. These machines are promising for use as the main aircraft generators with a high level of electrification in the DC power supply system of increased voltage 270 V. They are characterized by a large variety of designs, most important of which are versions with radial or tangential magnetized permanent magnet and nonmagnetic or bimetallic holder. Constantly increasing demands to the mass-energy performance of aviation synchronous machines with rare earth permanent magnets, to improve the quality of their designs, the development time and cost reduction are met by continuous improvement of design methods and design techniques based on the calculation and analysis of electromagnetic fields in their active zones.

Rational combination for electromagnetic fields in active zones analysis is traditional methods based on the models with lumped parameters together with circuit theory and computer technologies of numerical finite elements analysis based on the models with distributed parameters and field theory. Traditional methods and created on their basis by way of setting relatively simple and easily observed mathematical interrelations between input geometry and windings parameters with output energy parameters new design methodologies allow quickly and solve the problem of initial active zone geometry of an electric machine and parameters of its windings selection with an accuracy sufficient for engineering analysis. We used numerical methods for electromagnetic fields verified analysis and optimization, where parameters obtained with traditional methods are set as the starting point.

Traditional methods of synchronous machines design and machines with rare earth permanent magnets in particular are based on a number of assumptions and system of calculation coefficients linking the parameters of a real distributed active zone model with lumped parameters of electrical and magnetic circuits. For example, excitation field of synchronous machines is commonly characterized by a system of calculation coefficients κ_f, κ_ф, α_{δ и} κ_Β, determined based on the analysis of excitation winding two-dimensional magnetostatic field or permanent magnets in the smooth working gap brought form the armature side with non-saturated armature and inductor magnetic cores.Saturation consideration is carried out, as a rule, by separate introduction of various correction factors.

An effective method for determining the calculation coefficients of synchronous machines is the method of harmonic analysis of magnetic fields in active zones of electromechanical converters. The article presents new analytical solutions obtained for the magnetic field in the active zone of synchronous machines with rare earth permanent magnets by harmonic analysis. The problem of calculating the magnetic field generated by the permanent magnets of sector form with a constant direction and magnitude of magnetization, located between he two cylindrical ferromagnetic areas with infinite permeability was solved in polar coordinates system. The resulting solution allows determine the excitation magnetic fields and calculate coefficients of synchronous machines with permanent magnets of sector type, as well as prismatic and circular forms with their allocation on the rotor and fastening them with nonmagnetic holder, as well as reversed structure. Also, the problem of the magnetic fields calculation of excitation and armature reaction of synchronous machine with permanent magnets and a bimetallic holder with alternating magnetic and nonmagnetic areas was solved. The solutions presented in the article were checked by comparing the calculation results with the results of numerical finite element analysis. The results mismatch herewith does not exceed 1%.

Keywords:

analytical solution of the magnetic field problem, method of harmonic analysis of active zones, calculation coefficients of synchronous machines with rare earth permanent magnets, nonmagnetic holder, bimetallic holder

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