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Study of TFPM machines with toothed rotor applied to direct-drive generators for wind turbines...
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Transcript of Study of TFPM machines with toothed rotor applied to direct-drive generators for wind turbines...
Study of TFPM machines with toothed rotor applied to direct-drive
generators for wind turbines
Maxime R. DuboisLEEPCI, Dept. of Electrical Engineering
Université Laval, Québec, Canada
Henk PolinderLab. of Electrical Power Processing
Delft University of Technology, Delft, The Netherlands
Overview
1- Introduction
2- Advantages of TFPM machines and review of main topologies
3- TFPM machine with toothed rotor
4- Optimization of TFPM machine with toothed rotor and conventional PM synchronous machine
5- Comparison between TFPM machine with toothed rotor and conventional PM synchronous machine
6- 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
100
1000
10000
0 1 2 3 4
Machine Outer Diameter (m)
Co
st
/ To
rqu
e (
EC
U/k
Nm
)
Conventional PM
TORUS
TFPM
Conventional PMwith FC
- 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 !!
Review of main TFPM topologies
Stator
Rotor
Stator
Surface-Mounted TFPM vs Flux-Concentrating TFPM
-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
Stator
Rotor
Stator
Surface-Mounted TFPM vs Flux-Concentrating TFPM
-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
Preferred for cost reduction
Review of flux-concentrating TFPM topologies
Stator
Rotor
Stator
Problems
Double-sided
Difficult rotorStacking
A lot of powderediron
Optimization of TFPM machine with toothed rotor & conventional PM synchronous machine
Machine rotational speed as a function of the generator outside diameter.Generator outside diameter (m)
0.5 1.0 2.0 3.0
Wind turbine power range (kW)
10 - 30 30 - 100 100 - 200 400 - 600
Nominal rotational speed (rpm)
130 75 46 34
For a thorough comparison, we optimize both machine types with the same constraints:
-- machine outer radius-- efficiency at full load-- rotational speed
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 = 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
Tp
FF
R R
Ps pn l
s
ap up
F e
m
2 2
2 4
1 12m ax
m axco s sin
Fsmax, pnl, Rap, Rup are determined from the equivalent magnetic circuit
Comparison between TFPM machine with toothed rotor and conventional PM synchronous machine
10
100
1000
10000
0 1 2 3Diameter (m)
Co
st/
To
rqu
e (
Eu
ro/k
Nm
)
TFPM w TR Conv PM SM
Comparison between TFPM machine with toothed rotor and conventional PM synchronous machine
10
100
1000
10000
0 1 2 3Diameter (m)
Co
st/
To
rqu
e (
Eu
ro/k
Nm
)
TFPM w TR Conv PM SM
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 synchronousmachines, when air gap is set to 1/1000th of machine diameter.
Efficiency plays a dominant role in the cost/torque of both machinetopologies.
More attention must be paid to the optimization of the mechanical design and to manufacturing costs.