An Improved Empirical Formulation for Magnetic Core Losses Estimation Under Nonsinusoidal Induction

Calculation of core loss is essential in the design of magnetic components especially in high frequency applications. Existing empirical approaches still present some limitations such as the inaccuracy and the difficulty to apply under nonsinusoidal waveforms. In particular, these methods fail to predict core loss with low duty cycle and when there is a significant change in the frequency. In addition to that, the use of different solutions of Steinmetz parameters for different frequency range can present some discontinuity problems at the boundary of each frequency interval. The main contribution of this study is to develop a new empirical method to estimate magnetic core losses under nonsinusoidal induction. The developed method is enough accurate and user-friendly to apply by designers. The effects of the frequency and the duty cycle are considered. The developed model is verified and compared with the improved generalized Steinmetz equation and measurement data from literature with 3F3 and N67 ferrite materials.

I. Introduction

Switching mode power supplies (SMPS) need to have high efficiency, reduced size and weight in order to comply with standard requirements. Inductive components are widely used in SMPS. They are the bulkiest components in the converter structure and they occupy 30–50% of the total volume. Magnetic core loss calculation is a vital step in the design process of transformers. Achieving an optimized design of magnetic components is based on a good estimation of the core losses [1]–[3]. Several methods have been developed to calculate core loss. They are categorized into three main approaches in the literature: loss separation approach, hysteresis approach, and empirical approach [4]–[6]. In the first approach, magnetic losses are the sum of three types: the eddy current loss, the hysteresis loss, and the excess eddy-current loss. It is widely used in the design of electric machines. Preisach and Jiles Atherton models are hysteresis-based models of magnetic materials. These models are based on macroscopic energy calculation. The main issue of these models is that they only include the static hysteresis losses; however, the dynamic losses are not. Besides, they are difficult to apply since the mathematical model needs several parameters to determine [7]. Designers of power converters base their studies on empirical methods to calculate core loss. These empirical methods are based on Steinmetz equation (SE). This last technique is relatively practical and straightforward to use.