A Simple Analytical Approach towards Core Loss Estimation of Brushless DC Machines with Trapezoidal Back-EMF

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Name of the Speaker: Mr. Gourab Ghosh (EE13S004)
Name of the Guide: Dr. Lakshmi Narasamma,
Co-Guide: Dr. Krishna Vasudevan
Date/Time: 15th November (Tuesday), 10:00 AM

The flux density variation pattern (FDVP) in various sections of a trapezoidal back-EMF, brushless DC (BLDC) machine stator core is non-sinusoidal. In fact, it is trapezoidal in nature. Due to this reason, core loss estimation becomes a challenging step in the process of designing these machines. Standard finite element analysis (FEA) based machine design tools only take material data sheet values as input and use standard frequency domain (FD) models to estimate loss. The underlying problem in this process is that the loss data provided in material data sheets are for pure sinusoidal FDVP. Available methods that address this problem are computationally intensive and consume a fairly long time. This work proposes a simple theoretical core loss estimation method for these machines. An FD loss expression for trapezoidal FDVP, has been derived from more general time domain models, in this work. The FDVPs in various sections of a BLDC machine stator have been studied and found to be related to the machine design parameters. These relationships have been verified by 2D time stepped FEA. Based on these relationships and the derived FD model, core loss expression for no-load has been proposed.

Various designs have been studied to understand the effects of loading on the FDVP and core loss. Then suitable modifications to loss expressions have been proposed to incorporate these loading effects. Modified core loss expressions have been verified by comparing their loss estimates with numerically calculated losses from time stepped FEA generated FDVPs.

Experimental studies have been conducted on a toroidal M45 steel core sample to verify the FD loss calculation model that has been used to derive the loss expressions. The final core loss expressions have been validated by experimentally measuring core losses of a 5 kW, 10000 rpm BLDC motor.