EVS28KINTEX, Korea, May 3-6, 2015
Rotating Transformer for a Wound Rotor Synchronous Motor
Jiyoung Lee1,2, Jongmoo Kim1, and Byoungchul Woo1
1Korea Electrotechnology Research Institute, Changwon, Korea2University of Science & Technology, Korea
Introduction
This paper presents a design of a rotary transformer to be used instead of brushes and slip-rings in 7.5kW-grade wound rotor synchronous motor for a propulsion system of electric vehicles.
The basic components of the rotary transformer are pot cores and adjacent windings, which are classified into two parts- primary and secondary as the principles of general transformers. And high frequency is used to reduce the overall volume.
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Introduction
There are five major design variables, which are (1) source frequency, (2) number of turns in primary winding, (3) inner diameter of winding window, (4) outer diameter of core, and (5) height of core. The design variables are optimized by Response Surface Methodology to efficiently transmit the required power. Factor experiments for the optimum design are performed by 2-dimensional axi-symmetry finite element analysis (FEA). In the analysis model for the FEA, the magnetic field is connected to external circuits. The primary circuit is external power source, and the secondary circuit is linked to field winding in the wound rotor synchronous motor. The designed rotary transformer is fabricated, and the characteristic are shown by both analytically and experimentally.
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Rotary Transformer for Exciter
Rotary Transformer for Exciter in Induction machine
[1] M.Ruviaro, F.Runcos, N.Sadowski, I.M.Borges, “Analysis and test results of a brushless doubly fed Induction machine with rotary transformer,” IEEE Trans. on Industrial Electronics 59(6), 2670-2677, 2012[2] http://www.scielo.br/scielo.php?pid=S2179-10742013000200013&script=sci_arttext#f1
Cutaway of a doubly-fed induction generator with a rotary transformer [1][2]
Laboratory scheme for load tests [2]
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Rotary Transformer for Exciter in Synchronous machine
InductionMachine
Rotor : AC field Rotor : DC field
SynchronousMachine
Rec
tifie
r
3ph-Rotary transformer 1~3ph-Rotary transformer
Rotary Transformer for Exciter
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Rotary transformer Configurations
Axial (left) and Pot core (right) rotating transformers [3][4]
[3] J.P.C.Smeets, L.Encica, E.A.Lomonova, “Comparison of winding topologies in a pot core rotating transformer,” IEEE Xplore, 2010[4] J.Legranger, G.Friedrich, S.Vivier, J.C.Mipo, “Comparison of two optimal rotary transformer deisgnsfor highly constrained applications,” IEEE Xplore, 2007
Winding topologies for the pot core rotating transformer, adjacent (left) and
coaxial (right) [3]
Conceptualconfigurationof objective model
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Design Specifications
Contents Values
Primary voltage 106.1 Vrms Primary circuit :Phase-shift DC-DC converterPrimary frequency 20~50 kHz
Secondary required voltage 66.6 Vrms
Secondary circuit :Full bridge rectifier
Secondary required current 3.0 Arms
Secondary power 200 W
Max rotating speed 10,000rpm
Diameter of axis 34 mm
Diameter of outmost housing 144 mm
Max axial length 78 mm
Air-gap length 1mm or less
Core material Mn-Zn soft ferrite
Cooling Natural cooling
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Analysis Model and Design Variables
Primary core
Secondary core
Primary coilSecondary coil
Axis of Sym
metry
Design variables(1) Cx2 (2) Cx4(3) Ch (=Ch1=Ch2)(4) Np (No. of turns in primary)(5) Freq (Primary frequency)
Axi-symmetric model for magnetic field analysis
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Analysis Model and Design Variables
External circuit
Independent variable 2Objective power:
200~300W
Independent variable 1
Independent variable 3
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Response Surface Methodology
è 43 DOE samples for 5 design variables
(DOE: design of experiment)
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Response Surface Methodology
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Response Surface Methodology
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Design Results
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[Unit: mm]
20.537
39
6.5
6.5
3.2
air-gap = 0.5mm(Fill factor : 60% or less)
Axis of Sym
metry
[Variables]Freq=27.5 kHzNp = 40 turns ( Ns=26 turns)Cx1=17, Cx2=20.5, Cx4=39, Ch=6.5 (mm)
[Characteristics]CD1(current density of primary) =3.3 A/mm2
Crms1(current of primary) =2.8APin(power of primary) =231.7W Pload(power of secondary) =220.9WEff_sys(system efficiency) =95.3% Eff_mag(magnetic circuit efficiency) =98.5%
First RSM results
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Design Results
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21
42.5
10.5
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Axis of Sym
metry
[Unit: mm]
Second RSM resultsCore outer diameter 85mm
Core inner diameter 34mm
Housing inner diameter 32mm
Primary core height 10.5mm
Secondary core height 9mm
Air-gap 0.5mm
Core thickness 4mm
No. of turn in primary 28 turn
No. of turn in secondary 18 turn
Diameter of conductor 1.4 mm
Fill factor 40%
Primary frequency 30kHz
Power of sencondary 226 W
Efficiency 95.2 %
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Magnetic Characteristics
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Fabrications
(Primary & Secondary Ferrite core)
(Core + Coil)
(Rotary transformer + Power converter)
(Primary & Secondary coils)
(Core + Coil + Housing)
(Core + Coil + Housing à Epoxy molding)
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Experiments
Secondary power: 300W_max