EVS28
KINTEX, 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, Korea
2University of Science & Technology, Korea
jylee@keri.re.kr
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.
2
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 2dimensional 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.
3
Rotary Transformer for Exciter
Rotary Transformer
for Exciter in Induction machine
Cutaway of a doubly-fed induction generator with a rotary
transformer [1][2]
Laboratory scheme for load tests [2]
[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
4
Rotary Transformer for Exciter
Rotary Transformer
for Exciter in Synchronous machine
Synchronous
Machine
Rectifier
Induction
Machine
Rotor : AC field
3ph-Rotary transformer
Rotor : DC field
1~3ph-Rotary transformer
5
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 deisgns
for highly constrained applications,” IEEE Xplore,
2007
Winding topologies for the pot core
rotating transformer, adjacent (left) and
coaxial (right) [3]
Conceptual
configuration
of objective
model
6
Design Specifications
Contents
Values
Primary voltage
106.1 Vrms
Primary frequency
20~50 kHz
Secondary required voltage
66.6 Vrms
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
Primary circuit :
Phase-shift DC-DC
converter
Secondary circuit :
Full bridge rectifier
7
Analysis Model and Design Variables
Axi-symmetric model for magnetic field analysis
Axis of Symmetry
Secondary coil
Primary coil
Secondary core
Primary core
Design variables
(1) Cx2 (2) Cx4
(3) Ch (=Ch1=Ch2)
(4) Np (No. of turns in primary)
(5) Freq (Primary frequency)
8
Analysis Model and Design Variables
External circuit
Independent variable 3
Independent variable 2
Objective power:
200~300W
Independent variable 1
9
Response Surface Methodology
è 43 DOE samples
for 5 design variables
(DOE: design of experiment)
10
Response Surface Methodology
11
Response Surface Methodology
12
Design Results
[Unit: mm]
First RSM results
[Variables]
Freq=27.5 kHz
Np = 40 turns ( Ns=26 turns)
Cx1=17, Cx2=20.5, Cx4=39, Ch=6.5 (mm)
39
37
20.5
17
3.2
6.5
6.5
Axis of Symmetry
air-gap = 0.5mm
(Fill factor : 60% or less)
[Characteristics]
CD1(current density of primary) =3.3 A/mm2
Crms1(current of primary) =2.8A
Pin(power of primary) =231.7W
Pload(power of secondary) =220.9W
Eff_sys(system efficiency) =95.3%
Eff_mag(magnetic circuit efficiency) =98.5%
13
Design Results
[Unit: mm]
Second RSM results
42.5
21
17
16
9
Axis of Symmetry
10.5
Core 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 %
14
Magnetic Characteristics
15
Fabrications
(Primary & Secondary
Ferrite core)
(Core + Coil)
(Core + Coil + Housing)
(Primary & Secondary coils)
(Core + Coil + Housing
à Epoxy molding)
(Rotary transformer + Power converter)
16
Experiments
Secondary power
: 300W_max
17