Transcript Study of TFPM machines with toothed rotor applied to

Study of TFPM machines with
toothed rotor applied to direct-drive
generators for wind turbines
Maxime R. Dubois
LEEPCI, Dept. of Electrical Engineering
Université Laval, Québec, Canada
Henk Polinder
Lab. of Electrical Power Processing
Delft University of Technology, Delft, The Netherlands
Overview
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6-
Introduction
Advantages of TFPM machines and review of main
topologies
TFPM machine with toothed rotor
Optimization of TFPM machine with toothed rotor and
conventional PM synchronous machine
Comparison between TFPM machine with toothed rotor and
conventional PM synchronous machine
Conclusion
Introduction
Direct-drive
Geared drive-train
- avoided costs of the gearbox
- no oil change
- lower number of bearings
less greasing
- less moving parts
increased reliability
- less acoustical noise and vibrations
- avoided friction losses of the gearbox
- lower generator mass, size and costs
- power electronics converter rated 30% of
nominal power, with related cost and losses
Introduction
Direct-drive
Geared drive-train
- avoided costs of the gearbox
- no oil change
- lower number of bearings
less greasing
- less moving parts
increased reliability
- less acoustical noise and vibrations
- avoided friction losses of the gearbox
- lower generator mass, size and costs
- power electronics converter rated 30% of
nominal power, with related cost and losses
MOST IMPORTANT
ARGUMENT (for now)
Advantages of Transverse-Flux PM machines
- According to literature: TFPM machines obtain lower cost of active material
- NORPIE 2000: summary of machines designs taken from literature
- However:
Numerous Machines = Numerous Constraints !!
10000
Cost / T orque (ECU/kNm )
C o nve ntio na l P M
TO R U S
TF P M
C o nve ntio na l P M
w ith F C
1000
100
0
1
2
3
M a c h in e O u te r D ia m e te r (m )
4
Review of main TFPM topologies
Surface-Mounted TFPM
vs
Flux-Concentrating TFPM
Stator
Rotor
Stator
-High Current loading in both cases (typical 300 kA/m)
-Strong leakage flux between magnets in surface-mounted TFPM
-Higher magnetic loading and torque/mass in flux-concentrating TFPM
Review of main TFPM topologies
Surface-Mounted TFPM
vs
Preferred for cost reduction
Flux-Concentrating TFPM
Stator
Rotor
Stator
-High Current loading in both cases (typical 300 kA/m)
-Strong leakage flux between magnets in surface-mounted TFPM
-Higher magnetic loading and torque/mass in flux-concentrating TFPM
Review of flux-concentrating TFPM topologies
Problems
Double-sided
Difficult rotor
Stacking
Stator
Rotor
Stator
A lot of
powdered
iron
TFPM machine with toothed rotor
Single-sided
Easy rotor
insertion
Laminated
Stator
TFPM machine with toothed rotor
Stator before winding
Stator completed and 1 rotor
Phase mounted
Optimization of TFPM machine with toothed rotor
& conventional PM synchronous machine
For a thorough comparison,
we optimize both machine
types with the same
constraints:
-- machine outer radius
-- efficiency h at full load
-- rotational speed
Machine rotational speed as a function of the generator outside diameter.
Generator outside
diameter (m)
Wind turbine
power range (kW)
Nominal rotational
speed (rpm)
0.5
1.0
2.0
3.0
10 - 30
30 - 100
100 - 200
400 - 600
130
75
46
34
Optimization of TFPM machine with toothed rotor
& conventional PM synchronous machine
Optimization procedure:
-Optimization program calculates cost/torque of thousands of designs of TFPM
machines with toothed rotor for h = 90% and 95%.
-The program identifies the design having the lowest cost/torque.
- Best design is fed into a 3-D finite element software for validation.
-Torque and efficiency are adjusted accordingly.
-Optimization program calculates thousands of designs of conventional PM
synchronous machines having the same torque value as optimized design of TFPM
machine with toothed rotor
-Identification of the conventional PM synchronous machine with the lowest cost of
active material.
Optimization of TFPM machine with toothed rotor
& conventional PM synchronous machine
Main assumptions of the optimization procedure:
-- copper: 6 Euros/kg // lamination and powdered iron: 6 Euros/kg
//
PM: 40 Euros/kg
-- Manufacturing and magnetically-inactive material are not considered in the cost calculations
-- Number of phases is 3
-- In Convent. PMSM. : slots are deep (hs/bt = 4), q =1 and winding is double layer full-pitched
-- Sinusoidal terminal voltage v(t), no-load voltage e(t) and phase current i(t)
-- Sufficient forced air or liquid cooling is provided
-- PM = Nd-Fe-B with Br = 1.1 T
-- steels have linear B(H) characteristics mrFe = 1000 up to the point of saturation of 1.8 T
-- the air gap thickness g is equal to 1/1000th of the machine outside diameter
-- the slot fill factor is set to 0.6 for diameters larger than 2 m and to 0.4 for diameters below 2 m.
-- the specific eddy current losses in Fe-Si laminations at 50 Hz/1.5 T are set to 1.0 W/kg
-- the specific hysteresis losses in Fe-Si laminations at 50 Hz/1.5 T are set to 4.0 W/kg
Modeling of the TFPM machine with toothed rotor
Conventional PM Synchr. Mach.: flux lines are straight in the air gap
TFPM machine modeling: bending of flux lines cannot be neglected.
We use lumped reluctances and equivalent magnetic circuits
Aligned position
Modeling of the TFPM machine with toothed rotor
Unaligned position
p2
T
2

Fs2max  1
1 

 sin 2
 Fs max  pnl cos 

4  Rap Rup 

 P
  Fe
  m
Fsmax, pnl, Rap, Rup are determined from the equivalent magnetic circuit
Comparison between TFPM machine with toothed
rotor and conventional PM synchronous machine
TFPM w TR
C ost/T orque (Euro/kNm )
10000
Conv PM SM
h   
h   
1000
h   
h   
100
h   
h   
10
0
1
2
D ia m e te r (m )
3
Comparison between TFPM machine with toothed
rotor and conventional PM synchronous machine
TFPM w TR
C ost/T orque (Euro/kNm )
10000
Conv PM SM
h   
h   
1000
h   
h   
100
h   
h   
10
0
1
2
3
D ia m e te r (m )
For DD WEC of 600 kW, active material = 23,000 Euros…..about 4% of WEC cost !
Conclusion
The cost/torque comparison between TFPM machines with toothed
rotor and conventional PM synchronous machines was investigated,
using innovative optimization and modeling tools.
For diameters of 1.0 m and below, lower cost/torque is obtained with
the TFPM machine with toothed rotor.
Diameters larger than 1.0 m favor conventional PM synchronous
machines, when air gap is set to 1/1000th of machine diameter.
Efficiency plays a dominant role in the cost/torque of both machine
topologies.
More attention must be paid to the optimization of the mechanical
design and to manufacturing costs.