Determination of the roll-off value in the air-gapped inductor of a DC-DC boost converter circuit with FEA parametric simulations

BALKAN JOURNAL OF ELECTRICAL & COMPUTER ENGINEERING, 135 Vol. 8, No. 2, April 2020 Determination of the roll-off value in the airgapped inductor of a DC-DC boost converter circuit with FEA parametric simulations P. ARIKAN, S. BALCI and F. BATTAL  Abstract—The electromagnetic behavior of the inductors used as passive circuit elements directly affects the electrical and mechanical performance of the power electronics circuits. In general, when using inductor core structures with/without airgap length in the classical design process, the dynamic effects of the inductance value are not considered in the design stage. However, the inductance value may change during the operation of the circuit due to electrical and magnetic parameters of the inductor, and this change is called roll-off value of the inductance. In this study, the roll-off value has been determined graphically and numerically based on mechanical parameters (such as air-gap length) and electrical parameters (such as winding turns and DC current amplitude) for an air-gapped ferrite E core designed with finite element analysis (FEA) software. Thus, not only the inductance value has been calculated in the design stage but also the roll-off value during the operation of the circuit has been reported with the parametric simulation studies. Index Terms—FEA parametric simulations, gapped-core, inductor parameters, roll-off value. I. INTRODUCTION N OWADAYS, advanced power electronics application area is growing with the tendency to use renewable energy sources and they are frequently used in daily life with current applications such as electric vehicles [1]. In this context, with the advances in semiconductor technology, both power electronics circuit topologies are developing, and PINAR ARIKAN, is with Department of Engineering Sciences, Karamanoğlu Mehmetbey University, Karaman, Turkey, (e-mail: ). https://orcid.org/0000-0002-7974-9289 SELAMİ BALCI, is with Department of Electrical and Electronics Engineering, Karamanoğlu Mehmetbey University, Karaman, Turkey, (email: ). https://orcid.org/0000-0002-3922-4824 FUNDA BATTAL, is with Department of Electronics and Automation Nevşehir HacıBektaş Veli Univesity, Nevsehir, Turkey, (e-mail: ). https://orcid.org/0000-0002-7233-2843 Manuscript received December 23, 2019; accepted Mar 3, 2020. DOI: 10.17694/bajece.664044 Copyright © BAJECE innovations are provided in magnetic circuit elements in these topologies [2]. The design concept of the magnetic circuit elements has been revised in order to provide smaller size and less power losses [3] with the development of the soft magnetic materials. Especially in the modern design approach, the most suitable design can be reached shortly before the prototype production with the development of software that enables electromagnetic modeling by finite element method, and the revolution in solver performance in computer hardware. The inductors used in DC-DC power converter circuits are known as DC inductors and are exposed to the high frequency ripple on the DC current. The flux density in the inductor core appears to be triangular ripple wave depending on the peak value of the current, and the inductance value is dynamically similar to this ripple wave [4-6]. In the design of the airgapped inductor, the analysis of bad effects such as the fringing flux effects during the determination of the air-gap length can be expressed mathematically in classical design approach. However, for the effects of the air-gap parts on the dynamic inductance and roll-off values of the inductor, electromagnetic modeling facilitates the design process [7]. The software used for electromagnetic modeling with finite element analysis (FEA) is often used to determine the electromagnetic, thermal and cooling performance of the inductor before prototype production. In context, Dang et al. [8] present the electromagnetic modeling, FEA simulation and design stage of a high-power inductor for battery charge system in order to reduce the core volume for electric vehicle. For the thermal coupled FEA, Du et al. [9] present in order to determine an inductor on both its electromagnetic and thermal behavior. Munguia et al. [10] explain how designers can take advantage of the useful features of electromagnetic FEA software to quickly model nonlinear behavior inductors and determine their performance. In addition, software developed in recent years, such as Ansys-Electronics, enables the analysis of both electromagnetic components and power electronics circuits together for the inductor design in power electronics circuits. In this study, roll-off value of the ferrite core inductor has been determined with the parametric FEA software based on mechanical and electrical parameters for air-gapped E core designed for a DC-DC boost converter circuit. The graphs of the incremental inductance changes based on parametric DC current have been obtained with Ansys-Electronics Desktop ISSN: 2147-284X http://dergipark.gov.tr/bajece BALKAN JOURNAL OF ELECTRICAL & COMPUTER ENGINEERING, 2019R3, and roll-off values of the designed inductor have been determined. In addition, flux distributions in the inductor core have been visualized and saturation effect has been examined. Thus, not only the inductance value calculated during the design phase, but also the dynamic inductance value during the operation of the circuit has been reported with the simulation studies. II. THEORETICAL ANALYSIS OF THE INDUCTANCE VALUE IN INDUCTORS WITH AIR-GAPPED CORE 136 Vol. 8, No. 2, April 2020 As the ferrite N87 ferrite core material [15] can be seen in the B-H curve given in Fig. 2, the saturation is delayed by the air gaps in the core in large current (NIsat2) inductor designs to provide a soft saturation flux characteristic. However, although saturation can be delayed by air gaps, sharp saturation occurs only after a certain current value in materials such as ferrite, amorphous, nanocrystalline and Si-Fe. In powder materials such as Kool Mµ, MPP and XFlux, there is no need to determine the air gap length in the core structures and a soft saturation occurs with the distributed air gap feature [16-17]. In order to obtain the desired inductance value in air gap inductor design, Eq.(1) can be written according to the initial permeability value for effective permeability (µeff) [11-12]. eff  f i , H c , Bsat  (1) The magnetic field intensity (Hc) and saturation flux density (Bsat) values and initial permeability (µi) values of the core material are very important, and this information can be reached from the core material datasheet. The basic parameters and the magnetic equivalent circuit for a given airgapped core are given in Fig. 1. Here, the magnetomotor force NI as flux and the reluctances in the path of flux are core and air gap resistance elements as ℜc and ℜ g, respectively [13]. Fig.2. B-H curve for ferrite core material, and soft saturation effect with airgapped core str (...truncated)