Mehrdad Biglarbegian, Neel Shah, Iman Mazhari, Johan Enslin and Babak Parkhideh. Electrical and Computer Engineering Department. Energy Production ...
Design and Evaluation of High Current PCB Embedded Inductor for High Frequency Inverters Mehrdad Biglarbegian, Neel Shah, Iman Mazhari, Johan Enslin and Babak Parkhideh Electrical and Computer Engineering Department Energy Production and Infrastructure Center (EPIC) University of North Carolina at Charlotte Charlotte, USA emails: {mbiglarb, nshah49, imazhari, jenslin,bparkhideh}@uncc.edu
Abstract— This paper describes the design and evaluation of high current toroidal Printed Circuit Board (PCB) embedded inductor applicable for high frequency DC/AC converters (lower than 10MHz). The equivalent circuit model of the inductor is presented and the filtering effectiveness is verified by testing three different geometries with its own characteristics and function through a GaN converter. Besides, the temperature rise analysis is provided for all the prototypes by using finite element methods, and the obtained results are also verified by experiments. The reason behind asymmetric trend of temperature rise for the toroidal PCB embedded inductor is also discussed through both simulation and experiment, and the capability of using a heat sink to lower the temperature increment for different geometries is explained. Keywords— air-core PCB embedded inductor; temperature rise analysis; high frequency; GaN
I.
INTRODUCTION
The demand for ever-increasing switching frequency using wide band gap devices, higher power density, keep driving the development of passive integration technologies in the modern power electronics. With increasing the frequency to the MHz range, magnetic core loss increases drastically [1]. So, air core PCB embedded inductors become a viable solution, as the sizes are shrinking, and the core losses are avoided [2], [3]. It will also lead to a cost reduction, as smaller passive components are less expensive. In general, the advantages of passive components integration will be size reduction, better thermal conduction, high parameter repeatability, high reliability, and cost reduction [3], [4]. Among several structures for the design of PCB embedded inductors described in the previous literature [3], [5], toroidal inductors are chosen in this paper due to their internal encapsulation of the magnetic field avoiding EMI problems. Also, compared to other common structures for a PCB embedded inductor, toroid has some drawbacks addressed in this paper such as relatively lower quality factor and inductance per area, less flexibility, and high resistance caused by thin petals, and the poor fill factor of the vias used in both inner and outer edges [3], [6]. Previous researches have been conducted combining RF circuits and power electronics to design switch mode power supplies (SMPSs) operable at very high switching frequencies
978-1-4673-9550-2/16/$31.00 ©2016 IEEE
(VHF) in the range of (30-300MHz), but this range of frequency is more suitable for resonant DC/DC converters [7]. Contrarily, this paper conducts a comprehensive analysis, and design investigations for three different high efficient toroidal PCB embedded inductors suitable for smoothing the AC current of high frequency hard switched inverters. Moreover, temperature Rise analysis including asymmetric distribution, proximity and skin effect, total harmonic distortion (THD), and thermal resistance are investigated and formulation for the built designs are presented. In section II, the equivalent circuit model of a toroidal PCB embedded inductor is expressed and its temperature rise profile is formulated. Section III shows all the three implemented designs, and their main characteristics such as filtering capability in THD reduction, AC resistance, and temperature profile variations. In section IV, temperature rise analysis including asymmetric distribution, proximity and skin effect, and effective factors are discussed and how it can be affected by using a heat sink will be explained. II.
TEMPERATURE RISE FORMULATION FOR THE PCB EMBEEDEDD INDUCTOR
A. Equivalent Circuit Model of Toroidal PCB Embedded Inductor For the full bridge inverters, it has been assumed that current and voltage ripples set to be 1%. Designing an inductor with the above specifications, not only limit the ripple amplitude, it also helps to effectively filter our high frequency harmonics [3]. Following equation shows the resonant frequency of parallel LC circuit: f cutoff =
1 2π Lmin Cmin
=
1 4π
2
(Vin − Vout ) Dmax × ΔIDmax ΔI × f sw
(1)
f sw ΔV
Typically, in order to be far enough from the high frequency harmonics and decrease the output noise at 10MHz switching frequency, the cutoff frequency is set to be lower than 1/10th of shows the maximum duty the switching frequency. In (1), cycle , is the switching frequency of the inverter and
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is the cutoff frequency of the AC filter, respectively. Therefore, the inductance can be calculated in (2) after simplifying (1): (2) (V − V ) D 2 L = in out 2 max ΔV × f sw × C By choosing a low ceramic capacitor (
