FACULTY OF ELECTRICAL ENGINEERING

Eng. Nicoleta Adina RĂCĂŞAN

PhD THESIS ABSTRACT

CONTRIBUTIONS TO THE IMPROVEMENT OF THE CONDUCTED ELECTROMAGNETIC INTERFERENCE

FILTERS PERFORMANCES

PhD Evaluation Commission:

PRESIDENT: Prof.dr.eng. Radu CIUPA – Dean, Faculty of Electrical Engineering,

Technical University of Cluj-Napoca

SUPERVISOR: Prof.dr.eng. Călin MUNTEANU – Faculty of Electrical Engineering, Technical University of Cluj-Napoca

MEMBERS: Prof.dr.eng. Daniel IOAN – Faculty of Electrical Engineering, „Politehnica” University of Bucharest

Prof.dr.eng. Mihai IORDACHE – Faculty of Electrical Engineering, „Politehnica” University of Bucharest

Prof.dr.eng. Vasile ŢOPA – Faculty of Electrical Engineering, Technical University of Cluj-Napoca

The PhD Thesis public defense takes place Friday 1st of October 2010 at 1000 on “Aula Domşa”, str. C. Daicoviciu 15, Technical University of Cluj-Napoca

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Chapter 1, entitled Introduction to EMI Filters, shows the most important elements resulted

from the specialty literature analysis regarding the general topic of the research realized in the PhD

thesis. So, we start from fundamental principles about electromagnetic compatibility pointing out on

the aspects regarding the susceptibility and immunity problems of the perturbations in the electric-

power-supply network. It is outlined the actual standards and limits of electromagnetic emissions

imposed at international level. There are detailed the test methods of the perturbations induced in

the electric-power-supply network, and the fundamental characteristic elements of this signals

respectively. In the second part of the chapter it is presented the actual stage of the research in the

electromagnetic interference filters’ domain, generic named EMI filters. Are presented the

characteristic elements of the filters realized in the classical technology, by discrete components,

outlining the advantages and disadvantages of this technical solution. In the last part of the chapter

it is presented the functional limits of the electronic passive elements that compose the classical

EMI filters emphasizing the mechanism of parasitic effects that appear in these devices.

Concluding, taking account of the actual demands of limiting the perturbation emissions induced in

the electric-power-supply network, the improvement of the EMI filters performances by

introduction of a new implementation technology able to throw away the technological and

performances barriers impose by the used devices in the classical filters represent a research topic

very actual and important on the international plan.

Chapter 2, entitled EMI Filters and the magnetic planar technology, outlines the

fundamental principles that are the base of the magnetic planar technology, being in the same time

succinct overhung the actual study of the research in this domain. Are emphasized the advantages of

the magnetic planar technology with respect to the conventional classic technologies in the

implemenration of some integrate magnetic devices that compose the power electronic converters.

This technology of planar integration can be implemented also in the case of EMI filters, standing

out the fundamental major differences between the functional demands of this HF integrate passive

devices and those of the EMI filters. In the last part of the chapter is underlined the fact that the

behavior key element of the EMI filters – that is a low-pass filter – can be directly implemented

using a LC structure that is magnetic planar integrated. So, the detail study of the behavior of this

fundamental cell in report with the frequency represent a first important step in the light of

understanding the EMI filters behavior in HF planar magnetic technology, and for the improvement

of theirs performances, the next chapter of the thesis being dedicate to this study. This chapter ends

with the presentation of the fundamental principle used to realize an integrate EMI filter with

magnetic planar technology by interconnecting the LC integrate cells, accentuating the

implementation mode of the CM and DM filter components.

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Chapter 3, entitled Electromagnetic modeling of a LC planar integrate cell, proposes a

modern modeling method in frequency domain of a LC integrate cell. Is stand out the fact that for a

correct functional modeling is adequate the multi-conductor transmission line method generalized

with losses. For a simple structure with two symmetrical conductors, the solution can be convenient

obtained by decompose in even and odd modes. The equivalent circuits with different charge

conditions can be represented by two independent transmission lines series or parallel connected.

For other connections and configurations, the characteristics can be easy determinate using the A

and Z matrixes. The create models stand out the fundamental properties of a LC integrate cell

regarding the behavior of these cells in frequency domain. Therewith, the create numerical models

help to understand the dependence of the frequency characteristics with constitutive

electromagnetic parameters, helping in this way the functional optimization of these structures in

report with the application in which these are used. Last but not least, the create models open the

research topic by modeling with equivalent circuits in the case of planar integrate structures with

very complex geometries. The author contribution in this chapter is the systematization of the

specialty literature in the planar integrated structures modeling domain and the realization of the

response frequency characteristics by analytical and numerical modeling with Mathematica and

PSpice of all the study structures.

Chapter 4, entitled Integrate EMI filters performances improvement by increasing the

losses in the conductors, outlines the author contributions to the integrate EMI filters performances

improvement by increasing the losses in conductors at HF. In this light, for increase the winding

losses at high frequency, is proposed the conductors nickel-plate method. The test of this method

was initially done using a simple model, composed of only two cooper conductors, and then the

technique was extend to more complex structures. This study was realized for common mode

excitation (CM), and for differential mode excitation (DM), each proposed configuration being

tested for a frequency range with values between 100 kHz and 10 MHz, conduction emission

analysis domain.

For the two copper conductors model were analyzed seven types of configurations: pure

cooper conductors, cooper conductors global nickel-plate, cooper conductors partial nickel-plate,

conductors plate with nickel only on above surfaces, and below respectively, conductors plate on

the external surfaces, and cooper conductors plate only on the internal surfaces. Doing this study

result that the bigger losses are obtained for the case of the cooper conductors plate with nickel only

on internal surfaces, for both common and differential mode excitation. For example, at the

frequency of 10 MHz, the losses on the length unit are 2 Ω/m in the case of pure copper conductors

and for the case of the conductors plate with nickel on the external surfaces are 57 Ω/m, and in the

case of the conductors plate with nickel only on the internal surfaces the losses increase, being

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109 Ω/m, that means approximate 50 times bigger that those from the case of pure copper

conductors.

Fig. 4.1. HF losses for two conductor configurations

Starting from this simple model, the conductors plate-nickel technique was extend for a

complex structure, the reference structure that is proposed by the author for the considerate

analyses, named in the chapter Original_structure.

Fig. 4.2. The Original_structure

If in the previous case ware studied all the possible combinations of nickel-plate conductors,

for this structure were analyzed only the models that could be realized practically. So, for the

Original_structure are proposed two alternatives: the solution of plate with nickels only the external

surface of each conductor and the solution of plate with nickel both external and lateral surfaces of

each conductor. For each proposed method were analyzed four cases depending on the supply mode

of the LC integrate structure and of auxiliary winding. Doing this analysis we can conclude that the

most efficient method to increase the HF losses in the case of the Original_structure is the solution

to plate the external and lateral surfaces of each conductor with nickel. This conclusion can be

extend and use also for structures with more complex geometries. Also, we observed that the supply

mode of conductors does not influence significant neither the losses on each conductor nor the total

losses on each structure. In conclusion, observing the losses values, for example at the frequency of

10 MHz, the losses per unit length in the case of pure copper conductors are 0.68 Ω/m, while for the

case in which the external and lateral surfaces are plate with nickel the losses increase, being

approximate 14 Ω/m, that suggest a big potential for the propose technology.

Also, in this chapter are presented some of most suggestive representations of current

densities distributions obtain by numerical modeling both in pure copper conductors and in those

plated with nickel, in CM and DM supply sequences.

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Fig. 4.3. Current density distributions for the Original_structure study configurations proposed

Is interesting to observe that at high frequency, in the case of pure copper conductors, the

current flow on the lateral sides of the conductors, while in the conductors plate with nickel the

bigger current densities are observed only in the areas plated with nickel, for both supply sequences,

that lead at the idea that in HF in this case the losses are not influenced by the supply sequences.

Chapter 5, entitled Integrate EMI filters performances improvement by reducing the

structural parasitic capacitance, shows the author contributions at the EMI filters performances

improvement, that are realized with planar magnetic technology, by reducing the structural parasitic

capacitance. Are presented the principles of structural capacitance reduction of the respective

system, taking account of the problem complexity, are proposed two method of approach the study:

using the energetic method and applying the partial capacitance. Starting with the basic models, we

want to efficient the proposed techniques by 2D and 3D numerical modeling. The conclusion is

unique for all the tested types of the models, that the using of the staggered winding represents the

best compromise between the mechanical stability of the system and the minimal value of the

structural capacitance, the medium factor of reduction being 8. In this light, in the second part of the

chapter, the author outlines the optimal study of the winding staggered such as to obtain the minim

structural capacitance. For this was developed an original optimal design software package.

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Fig. 5.1. The 3D model for the analysis of the structural capacitance

Fig. 5.2. The way the 3D staggered winding is realized, 2 solutions

x

0

xmin xmax

(a) problem formulation (b) objective function variation in the search space

Objective function

1.24E+00

1.34E+00

1.44E+00

1.54E+00

1.64E+00

1.74E+00

0 1 2 3 4 5 6 7 8

no of i t e r a t i on

Fmin = 1.24054 Foptim = 1.24055 reduction to 73% εr

= 8 E-4 [%]

(c) the optimal solution and several start points in the optimal design. Routes to the optimal solution

Fig. 5.3. Testing the convergence of the optimal design algorithm developed

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After it was tested on applications that consist of one and two design variables, it passes at

study of more complex geometries, with until 8 design variables. The obtained results relieving the

optimal arrangement of the conductors, the mode in which the distance between the winding spirals

influence the optimal solution and his oneness, being a very useful tool in the established of the

optimal geometrical configuration of the EMI filter layers structure for the minimization of his

parasitic capacitance. In the last part of this chapter is show an original graphic interface that allows

the easy utility of the developed optimal design algorithm and that helps to directly follow up the

steps with which get to the optimal solution in the optimization process and allow the quick

visualization of the simulation results.

Chapter 6, entitled Integrate EMI filters performances improvement by simultaneously

application of the proposed techniques and experimental validation, shows the authors’

contributions in the direction of simultaneously application of EMI filters performances

improvement proposed techniques on the proposed and developed EMI filters in the anterior

chapters and the validation by experimental measurements of the proposed solutions. As in the

anterior chapters, the study is gradually realized, starting from the proposed techniques

simultaneous effects analysis for a LC structure type ‚nucleus’ of an EMI filter, that is composed of

3 windings. The follow of this realized study both in 2D and 3D cases, is the fact that this structure

realize superior performances in report with the original by simultaneous application of the two

techniques and the fact that the winding stagger does not affect the HF losses by nickel-plate of the

copper conductors, we pass at the study of the structures type EMI filter. We start also in this case

from a simple 2D structure; the good obtain results motivating the pass to the study of the 3D real

structure of the EMI filter.

(a) the original structure (b) the optimized staggered winding

Fig. 6.1. The 2D EMI Filter

Given being the limited 3D numerical modeling possibilities of the cumulative global effects

of the proposed techniques on the transfer characteristics of the filter, his performances are

separately studied. So, for the electrical component, the conclusion being that the structural parasitic

capacitance is decrease until 47% of initial value. For the magnetic component, the response in

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frequency is compared between the original structure without stagger winding and without nickel-

plate, with the final structure that consist of optimal stagger winding and nickel-plate of the

conductors. We determinate that the impedance on the in terminals increase with 32%, the results

being obtained by numerical 3D modeling.

(a) the compact view and the equivalent circuit (b) exploded view of the two structures analyzed

Fig. 6.2. The 3D EMI filter implemented

(a) the filter metallic structures, interconnected (b) structure 1

(c) structure 2 (d) structure 3

Fig. 6.3. The 3D EMI filter – details for interconnections

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Fig. 6.4. The computed transfer function

In conclusion, we can say that the EMI filter parameter improvement techniques proposed and

systematically analyzed in this thesis and which has the purposed the reduction of structural

capacitance and the HF losses increased prove the efficiency by numerical modeling.

For the final validation of the research activity done in this doctorate thesis, in the last part of

the chapter are presented the experimental measurements results. Because of the technological

possibilities limitation, the experimental measurements are realized in the case of some filters type

FTJ (LPF) made in planar magnetic technology. Are compared the frequency responses and the

filter attenuations made in original mode, without stagger between the windings, with filter that

contain the optimal stagger between these. The superior attenuation on the frequency range of the

conduction emissions in the electrical-power network of the BD filter 150 kHz – 30 MHz in report

with SO filter represent the experimental validation of the solution correctitude by the suppression

of the propose structural capacitance and applied in the case of EMI filters. Not the last, has to be

remarked the good attenuation of the planar integrated LC structure – both in SO mode as in the BD

mode – realized in FTJ connection type, in this way we can conclude that the planar integrate

structures are an attractive solution for the passive EMI filter realization.

(a) exploded view (b) experimental measurements set-up

Fig. 6.5. The low pass filter in planar magnetic technology

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Date: 18.AUG.2010 09:27:31 (a) the original structure (SO) (b) the staggered winding structure (BD)

Fig. 6.6. Experimental results of the transfer function for the low pass filter realized in planar magnetic technology

The authors’ contribution in this chapter consists in the design, implementation, 2D and 3D

numerical modeling, and results assumption and interpretation in the case of all the presented

electromagnetic devices. Also, the author design and practically made the LC integrate structures

presented in this chapter and take part to the experimental measurements of their attenuation in FTJ

type configuration and at the dates assumption and results interpretation. The final conclusion of the

chapter is that by the presented and obtained results, we can say that the doctorate thesis purpose

was reach, the propose techniques for the EMI filters performances improvement are full efficient.