Evaluation of the Magnetic Fields and Mutual Inductance between Circular Coils Arbitrarily Positioned in Space

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1 valuation of the Magnetic Fields and Mutual Inductance between Circular Coils Arbitrarily Positioned in Space Ao Anele, Y Hamam, L Chassagne, J Linares, Y Alayli, Karim Djouani To cite this version: Ao Anele, Y Hamam, L Chassagne, J Linares, Y Alayli, et al.. valuation of the Magnetic Fields and Mutual Inductance between Circular Coils Arbitrarily Positioned in Space. Journal of Physics: Conference Series, IOP Publishing, 215, 633, pp <1.188/ /633/1/1212>. <hal > HAL Id: hal Submitted on 13 Oct 215 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 valuation of the Magnetic Fields and Mutual Inductance between Circular Coils Arbitrarily Positioned in Space AO Anele 1,2, Y Hamam 1, L Chassagne 2, J Linares 3, Y Alayli 2, K Djouani 1 1 Dept. of lectrical ngineering, Tshwane University of Technology, Pretoria, South Africa 2 LISV Laboratory, Université de Versailles Saint-Quentin-en-Yvelines, Versailles, France 3 GMaC Laboratory, Université de Versailles Saint-Quentin-en-Yvelines, Versailles, France -mail: aneleamos@gmail.com Abstract. This paper presents the evaluation of the magnetic fields and mutual inductance between circular coils arbitrarily positioned in space. Firstly, based on an advanced and relevant model available in the literature, MATLAB code is implemented to evaluate the mutual inductance between circular coils arbitrarily positioned with respect to each other. The computed results are compared with the numerical results previously published in the literature and a detailed clarification regarding the huge computational errors made are presented. In the second part, a complex and relevant model available in the literature for evaluating the magnetic fields due to a circular coil is presented. Based on the useful information, the model for computing the magnetic fields between two circular coils is formulated. The computed results are validated with experimental measurements. The comparison of the results shows that the developed model and the experimental measurements conducted are accurate and effective. 1. Introduction Air-cored coils are widely used in various electromagnetic applications. They are preferred to the iron-cored type due to their design objectives of controllability and capability of a high power transfer [1]. Nonetheless, the measure of the magnetic fields and mutual inductance between them are of importance to electrical engineers and physicists because within certain limits of coil separation and misalignment, a minimal amount of power is guaranteed [2 5]. Several contributions have been made in the literature concerning the computation of the magnetic fields and mutual inductance between air-cored coils. In this view, mathematical modelling based on the application of Maxwell s formula, Neumann s formula, Biot-Savart law, Lorentz and magnetic vector potential have been presented in [2 9]. In the first part of this paper, MATLAB coding is implemented to compute the mutual inductance between two circular coils arbitrarily positioned with respect to each other. This computation is achieved based on the advanced and relevant model given in [4]. The computed results are presented graphically and numerically and then, compared with the ones presented in [4, 5]. Also, based on a more efficient and relevant model given in [7], the formula for computing the magnetic fields between two air-cored circular coils with and without misalignment is presented. Lastly, experimental measurements are used to validate the computed results. Content from this work may be used under the terms of the Creative Commons Attribution 3. licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1

3 2. Mutual Inductance Model According to [4], the formula for calculating the mutual inductance between inclined circular filaments placed in any position (most general case see Fig. 1a) as a function of the: primary and secondary coils radii, R P and R S, parameters a, b and c defining the centre of the secondary coil and coordinates (x C, y C, z C ) defining the centre of the secondary coil is given by M = µ R S π 2π [p 1 cosϕ + p 2 sinϕ + p 3 ]Ψ(k) dϕ (1) k α = R S R P, β = x C R P, γ = y C RP, δ = z C RP, l = a 2 + c 2, L = a 2 + b 2 + c 2, p 1 = ± γc l, p 2 = βl2 +γab ll, p 3 = αc L, p 4 = βab γl2 +δbc ll, p 5 = βc δa l, k = 4V A +2V, Ψ(k) = (1 k2 2 )K(k) (k), A = 1 + α 2 + β 2 + γ 2 + δ 2 + 2α(p 4 cosϕ + p 5 sinϕ), V 2 = α2 [(1 b 2 c 2 l 2 L 2 )cos 2 ϕ+ c2 l 2 sin 2 ϕ+ abc and (k) = π 2 l 2 L sin2ϕ]+β2 +γ 2 2α βab γl2 ll 1 k 2 sin 2 θdθ. V 3 cosϕ 2αβc l sinϕ, K(k) = π k 2 sin 2 θ dθ µ is the magnetic permeability of free space, k is a variable, parametr Ψ(k) is function of k, α, β, γ, l, L, p 1, p 2, p 3, p 4, p 5, A and V are dimensionless parameters, ϕ is the angle of integration at any point of the secondary coil, K(k) and (k) are the complete elleptic integral of the first and second kinds respectively. Figure 1. (a) Filamentary circular coils with arbitrary misalignment. Also, the geometric configurations and common notation used in the examples studied in [4] correspond to the following cases: (b) lateral misalignment only (θ =, ψ =, axes y z and y z are coplanar), (c) lateral and angular misalignment (ψ =, axes y z and y z are coplanar) and (d) arbitrary lateral and angular misalignment (no coplanar axes anymore). The geometric configurations considered in the examples studied in [4] are shown in Figs. 1b to 1d. In order to have easier link with Grover s formula, the geometric configurations are 2

4 restated in terms of a common notation namely: h = z C, d = x 2 C + y2 C, ρ = h 2 + d 2, cosφ = h ρ and in all cases, the primary coil is located in plane XOY, with its centre at the origin O(,, ). The horizontal and vertical distances between the centres of the coils are d and h respectively and ρ is the lateral misalignment. The first part of this paper is to compute the mutual inductance between filamentary circular coils arbitrarily positioned with respect to each other. In this view, example 12 was studied in [4] and for such case, the following common notations are applied to q. (1): The centre of the secondary coil must be taken at point C(x C =, y C = d, z C = h). d = x 2 sinθ, h = x 1 x 2 sinθ and ρ = h 2 + d 2. It is vital to note that x 1 is the vertical distance when axis z intersects with axis z from origin O, x 2 is the distance between the intersection and the centre of the secondary coil and θ is the angular misalignment. The parameters defining the positioning of the secondary coil plane is that of a spherical Cartesian system of coordinates which is given by: a = sinψsinθ, b = cosψsinθ and c = cosθ. ψ is the rotation angle around axis z, which gives the complete positioning of the secondary coil. 3. Presentation and Discussion of Results for Mutual Inductance Computation The results obtained for the mutual inductance between filamentary circular coils with arbitrary lateral ρ and angular θ misalignment are shown in Fig. 2 and Table 1. Based on the parameters given in example 12 (i.e., R P = 16 cm, R S = 1 cm, x 1 = 2 cm and x 2 = 5 cm), MATLAB software is used to achieve the coding and computation of q. (1). Although the authors of [4] studied only for the case with θ = 6 and ρ =.183 m, the authors of this paper also studied for the cases with θ = 3, ρ =.1587 m and θ = 45, ρ =.1684 m. The results obtained in this paper are graphically presented (see Fig. 1) and also numerically tabulated (see Table 1). Figure 2. Results for mutual inductance between circular filaments with arbitrary misalignment 3

5 In the case with θ = 6 and ρ =.183 m, Fig. 2 shows that the value of the mutual inductance increases from nh to nh when the variable rotation angle ψ ranges from to π and decreases from nh to nh when ψ ranges from π to 2π. This outcome is in agreement with the results obtained in [4] and [5] (see Table 1). However, it is vital to note that the authors of [4] obtained very wrong values for the parameters which define the centre of the secondary coil (i.e., a, b and c see Table 1). With such outcome, it is never possible for the authors to obtain the correct mutual inductance values. Nonetheless, the correct values are obtained in this paper (see Table 1) based on the given common notations, which are a = sinψsinθ, b = cosψsinθ and c = cosθ. Table 1. Computed Values in xample 12, with Variable Rotation Angle ψ and θ = 6 ψ (a, b, c) [4] M (nh) [4] M (nh) [5] q. (179) (a, b, c): This paper M (nh): This paper (;.866;.5) (;.866;.5) π/6 (.433;.75;.5) (.433;.75;.5) π/4 (.75;.433;.5) (.6124;.6124;.5) π/3 (.6124;.6124;.5) (.75;.433;.5) π/2 (.866; ;.5) (.866; ;.5) π/3 (.75;.433;.5) (.75;.433;.5) π/4 (.6124;.6124;.5) (.6124;.6124;.5) π/6 (.433;.75;.5) (.433;.75;.5) π (;.866;.5) (;.866;.5) π/6 (.433;.75;.5) (.433;.75;.5) π/4 (.6124;.6124;.5) (.6124;.6124;.5) π/3 (.75;.433;.5) (.75;.433;.5) π/2 (.866; ;.5) (.866; ;.5) π/3 (.75;.433;.5) (.75;.433;.5) π/4 (.6124;.6124;.5) (.6124;.6124;.5) π/6 (.433;.75;.5) (.433;.75;.5) π (;.866;.5) (;.866;.5) Formulation of the Magnetic Fields Model for two Filamentary Circular Coils According to [7], the magnetic fields in an arbitrary point s(x S, y S, z S ) produced by the primary coil of the radius R P carrying the current I P (see Fig. 1a) is given by µ I P z S x S k B x (x S, y S, z S ) = 8π R P (x 2 S + L y2 S )5/4 µ I P z S y S k B y (x S, y S, z S ) = 8π R P (x 2 S + L y2 S )5/4 µ I P k B z (x S, y S, z S ) = 8π R P (x 2 S + S y2 S )3/4 (2) x S = x C + R S u x cosϕ + R S v x sinϕ, y S = y C + R S u y cosϕ + R S v y sinϕ, z S = z C + R S u z cosϕ + R S v z sinϕ, u = [u x, u y, u z ] = [ ab ll, l L, bc ll ], v = [v x, v y, v z ] = [ c l,, a l ], L = 2K(k) 2 k 2 (k), S 1 k 2 = 2 x 2 S + y2 S K(k) 2 x 2 S +y2 S (R P + x 2 S +y2 S )k2 (k), k 1 k 2 4R = P x 2 S +y 2 2 S (R P + x 2 S +y2 S )2 +z 2 S x S, y S and z S are the parametric coordinates of the secondary coil, u is the unit vector lying in the secondary coil plane between points C and D, v is the cross product of the unit vector of the axis z and u, S and L are dimensionless parameters while K(k) and (k) are the complete elliptic integrals of the first and second kinds respectively. 4

6 Thus, for two coils, the total magnetic fields is the sum of the magnetic fields from each of the coils, which is formulated by the authors of this paper as B x = B xp + B xs = [ µ µ r I P N P (z P + l 2 )x P k P 8π R P (x 2 P + y2 P )5/4 L P ] + [ µ µ r I S N S (z S l 2 )x Sk S 8π R S (x 2 S + y2 S )5/4 L S ] B y = B yp + B ys = [ µ µ r I P N P (z P + l 2 )y P k P 8π R P (x 2 P + L P ] + [ µ µ r I S N S (z S l 2 )y Sk S y2 P )5/4 8π R S (x 2 S + L S ] y2 S )5/4 B z = B zp + B zs = µ µ r I P N P k P [ 8π R P (x 2 P + S µ µ r I S N S k S y2 P )3/4 P ] + [ 8π R S (x 2 S + S S] y2 S )3/4 (3) x P = x C + R P u x cosφ + R P v x sinφ, x S = x C + R S u x cosϕ + R S v x sinϕ, y P = y C + R P u y cosφ + R P v y sinφ, y S = y C + R S u y cosϕ + R S v y sinϕ, z P = z C + R P u z cosφ + R P v z sinφ, z S = z C +R S u z cosϕ+r S v z sinϕ, L P = 2K P (k P ) 2 k2 P 1 kp 2 P (k P ), L S = 2K S (k S ) 2 k2 S 1 ks 2 S (k S ), S P = 2 x 2 P + y2 P K P (k P ) 2 x 2 P +y2 P (R P + x 2 P +y2 P )k2 P 1 kp 2 P (k P ), S S = 2 x 2 S + y2 S K S(k S ) 2 x 2 S +y2 S (R S+ x 2 S +y2 S )k2 S 1 ks 2 S (k S ), kp 2 = 4R P x 2 P +y 2 P (R P + x 2 P +y2 P )2 +z 2 P, k 2 S = 4R S x 2 S +y 2 S (R S + x 2 S +y2 S )2 +z 2 S 5. Computed and xperimentally Validated Results for Magnetic Fields The results obtained for the computation and experimental validation of magnetic fields between two filamentary circular coils without misalignment (i.e., θ = and ρ = ) is shown in Fig. 3. Figures 3a 3c are obtained by applying the following to q. (3): In the case without misalignment, the parameters determinig the positioning of the secondary coil plane are defined as a =, b = and c = 1. The centre points for the two coils become (x C =, y C =, z C = h). h is the varying distance along the symmetry axis of the coils (see Fig. 3d). The parameters used for the computation and experimental measurements are: µ r = 1, µ = 4π 1 7 H m, R P = R S =.65 cm, N P = N S = 95, I P = I S = 1 A. The magnetic field results are obtained when the separation l between the two circular coils are l =.1 m (see Fig. 3a), l =.35 m (see Fig. 3b) and l =.65 m (see Fig. 3c). The measurement of the magnetic fields is conducted on the symmetry axis of the two coils by using Teslameter (see Fig. 3d. For each l, Teslameter is operated to measure the magnetic fields from the mid-point between the two coils to the point outside the coil (i.e., z C = h, which ranges from.9 m to.9 m). Figure 3a shows that uniform magnetic fields is obtained when the separation l between the two circular coils is almost zero (i.e., z P + l 2 and z S l 2 l =.1 m). Figures 3b and 3c show that as l increases, the values of the magnetic fields reduces and a different waveform is obtained. Furthermore, Figs. 3a 3c show that the values and waveforms for B x and B y along the z axis are symmetrical which is always true whenever the magnetic fields is computed on the symmetry axis of two circular coils. The magnetic fields model formulated in q. (3) can be used for the cases with and without misalignment. However, the case without misalignment is considered in this section. The comparison of the results shows that the developed model and experimental measurements conducted are accurate and effective. 5

7 Figure 3. Magnetic fields results and experimental set up. 6. Conclusion The evaluation of the magnetic fields and mutual inductance between circular coils arbitrarily positioned in space is presented in this paper. In the first part of the paper, MATLAB coding is implemented to compute the mutual inductance between two circular coils arbitrarily positioned with respect to each other. This computation is achieved based on the advanced and relevant model given in [4]. The computed results are presented graphically and numerically and then, compared with the ones presented in [4, 5]. Also, the formula for computing the magnetic fields between two air-cored filamentary circular coils with and without misalignment is presented and validation of the results shows that the developed model (see q. 3) and the experimental measurements conducted are accurate and effective. Reference [1] CS Wang, OH Stielau and GA Covic 2, PowerCon, [2] AO Anele, Y Hamam, Y Alayli and K Djouani 214, JMMC, Vol. 1, No. 1, [3] AO Anele, Y Hamam, Y Alayli and K Djouani 214, JMMC, Vol. 1, No. 1, 31-5 [4] S Babic, F Sirois, C Akyel and C Girardi 21, I Trans. Magn., Vol. 46, No. 9, [5] FW Grover 1944, Proc. IR, [6] JT Conway 27, I Trans. Magn., Vol. 43, No. 3, [7] S Babic, and C Akyel 212, PIR B, Vol. 38, [8] JC Maxwell 1954, A Treatise on lectricity and Magnetism [9] AO Anele, Y Hamam, Y Alayli and K Djouani 213, I AFRICON, 1-5 6