Bogomir Zidarič, Mykhaylo Zagirnyak, Konrad Lenasi and Damijan Miljavec
To analyze the Jiles and Atherton hysteresis model used for hysteresis losses estimation in soft magnetic composite (SMC) material.
Abstract
Purpose
To analyze the Jiles and Atherton hysteresis model used for hysteresis losses estimation in soft magnetic composite (SMC) material.
Design/methodology/approach
The Jiles and Atherton hysteresis model parameters are optimized with genetic algorithms (GAs) according to measured symmetric hysteresis loop of soft magnetic composite material. To overcome the uncertainty, finding the best‐optimized parameters in a wide predefined searching area is done with the proposed new approach. These parameters are then used to calculate the hysteresis losses for the modeled hysteresis. The asymmetric hysteresis loops are also investigated.
Findings
The classical GAs are good optimization methods when a pre‐defined possible set of solutions is known. If no assumption on solutions is present and a wide searching area range for parameter estimation is selected then the use of the new approach with nested GAs gives good results for symmetric hysteresis loops and further for the estimation of hysteresis losses.
Research limitations/implications
The use of the Jiles and Atherton hysteresis model for asymmetric hysteresis must be explored further. Only one set of optimized Jiles and Atherton hysteresis model parameters used for estimation of hysteresis losses gives good results for only symmetric hysteresis loops. These parameters have limitations for asymmetric hysteresis loops.
Practical implications
Nested GAs are a useful method for optimization when a wide searching area is used.
Originality/value
The originality of the paper is in the establishment of nested GAs and their application in Jiles and Atherton hysteresis model parameters optimization. Also, original is the use of the Jiles and Atherton hysteresis model for hysteresis loop description of soft‐magnetic composite material.
Details
Keywords
Damijan Miljavec and Bogomir Zidarič
This study aims to calculate eddy current losses in permanent magnets of BLDC machine in the generator mode of operation with no‐load.
Abstract
Purpose
This study aims to calculate eddy current losses in permanent magnets of BLDC machine in the generator mode of operation with no‐load.
Design/methodology/approach
Stator slot openings and special design of the stator poles cause changes in the magnetic flux density changes in permanent magnets. The stator windings are not connected to an outer source and no currents flow in them. The induced eddy currents in permanent magnets are dependent solely on the stator geometry. Analytical approach to calculate the eddy current density distribution in permanent magnets is based on known distribution of magnetic flux density in the air‐gap of BLDC. The magnetic flux density distribution is obtained from magneto‐static finite element model of BLDC. For verification of analytical approach the eddy current density distribution in permanent magnets is also calculated by magneto‐transient finite element model of BLDC.
Findings
The eddy current losses in PM obtained with the FEM indicate additional heating of the BLDC machine at high rotational speeds even when it operates at no load. When some special stator designs (the side of the air gap) are needed, the losses in PMs and their heating increase.
Research limitations/implications
To get more precise results, the proposed analytical method for eddy current losses calculation in PM should be further analyzed. More geometric parameters of the BLDC design should be introduced to analytical formulations, especially those which affect variations in reluctance.
Practical implications
When some special stator designs (the side of the air gap) are needed, the losses in PMs should be observed. This is particularly recommended at higher rotation velocities. Any kind of magnetic flux density change induces eddy currents and together with them also power losses. These losses give rise to additional heating of PM. With this, the temperature‐dependent working characteristic of PM (second quadrant of the B‐H curve) moves toward the coordinate origin point. The overall machine performance is reduced. The presented work gives the view about happenings in permanent magnets regarding induced eddy current losses. It is a useful tool for fast estimation and reduction of eddy current losses in PM due to stator geometry.
Originality/value
The value of the paper is the closed view about happenings in permanent magnets regarding induced eddy currents and the calculation of eddy current losses in rotor permanent magnets of BLDC due to stator design. The originality is in the analytical approach to calculate the eddy current losses based only on known magneto‐static flux density distribution in air‐gap of BLDC.
Details
Keywords
Damijan Miljavec, Mykhaylo Zagirnyak and Bogomir Zidarič
The purpose of this paper is to derive the geometry‐based equations for inductances which are used in circuit theory analysis of synchronous reluctance motor (SRM). Transient and…
Abstract
Purpose
The purpose of this paper is to derive the geometry‐based equations for inductances which are used in circuit theory analysis of synchronous reluctance motor (SRM). Transient and steady state performance analyze of SRM by using the 2D time‐stepping finite‐element method (FEM).
Design/methodology/approach
The analytical approach is used to obtain the equations which describe geometry dependent magnetizing inductances of SRM. Transient and steady state performance of the SRM is analyzed by using the 2D time‐stepping FEM. The external electric circuit connected with the finite‐element model of the SRM geometry allows the study of almost any of the electric and magnetic properties of the machine. Presented SRM model is also connected to the external mechanical loads (friction, rotor inertia and load torque). The use of different materials for the magnetic‐pole part of the rotor and for flux barriers was analyzed. The flux barriers in the first SRM rotor were filled with a pure massive electrically conductive ferromagnetic with a proper B‐H curve, whereas the rotor magnetic segments were made of non‐conductive electric steel described with its B‐H curve. The conductive barriers with their end rings form a squirrel cage and allow SRM to start on‐line. The flux barriers of the second SRM rotor were made of aluminum but between the second and third flux barrier a massive electrically‐conductive ferromagnetic was inserted which during starting‐up acted as a part of the squirrel cage. All of the flux barriers of the third SRM rotor were made of electrically‐conductive aluminum with iron parts axially laminated. The finite‐element SRM models coupled with an electric circuit is also used to evaluate the motor performance at various asynchronous speeds.
Findings
Analytical geometry‐dependant equations for the d‐ and q‐axis SRM inductances are derived. On the basis of the proposed 2D time‐stepping finite‐element analysis, the start‐up performance for the SRM rotor design using different materials is established. The torque distribution as a function of time at any of the observed asynchronous speeds is not smooth and uniform. It consists of the stator‐to‐rotor tooth pulsating torque, and the synchronous and asynchronous component.
Research limitations/implications
The main disadvantage of analytical geometry‐dependant equations for the d‐ and q‐axis SRM inductances is the linearization of any of the ferromagnetic parts.
Practical implications
On the basis of the proposed 2D time‐stepping finite‐element analysis, the start‐up performance, asynchronous run and synchronous torque characteristics for the SRM rotor design using different materials are established.
Originality/value
The value of the paper is the closed view about happenings in rotor flux barriers of SRM, mostly regarding the time distribution of induced currents in the rotor flux barriers. On the base of 2D time‐stepping FEM, the use of different materials for the magnetic‐pole part of the rotor and for flux barriers was analyzed.