Permanent Magnet High-Speed Generatorfor FTT Micro Turbine

Jinho Kim, Daniel Kirk and Hector Gutierrez

Mechanical & Aerospace EngineeringFlorida Institute of Technology

Performance Requirements

Parameter Power Rating (KW)

Max. Total Weight (kg)

Length(inch)

Stator O.D.(inch)

Speed (RPM)

Temp. Range(F)

Output Voltage,3-PhaseAC(Volt)

Storage (years)

Required 1.2 0.22 1.25 1.3 80k to136k

- 40 to130

180~400 10

Goal 1.8 0.22 1.25 1.3 65k to136k

- 0 to190

180~400 25

Proposed Design

Stator Rotor

Outer Diameter 1.3 inch (33.02 mm) Outer Diameter 19. 625 mm

Inner Diameter 21.625 mm Inner Diameter 6.9 mm

Length 1.25 inch (31.75 mm) Length 1.25 inch (31.75 mm)

Stacking Factor 0.95 Pole Magnet type NdFe35 or SmCo28

Stator Core Material M19-24G Magnet thickness 1.5 mm

Number of Slots 24 Shaft diameter (non-magnetic) 6.9 mm

Air gap (clearance between stator and rotor) 2 mm (air = 1 mm, sleeve = 1 mm).

Machine type: Permanent magnet synchronous generator Number of Poles: 4 Number of Phases: 3 Nominal Speed: 100,000 RPM

Proposed Electrical Layout

Outer core

Inner core Magnet

Shaft

Physical Layout Winding Pattern

Electromagnetic Performance

Permanent Magnet Material NdFe35 SmCo28

Load Line Voltage (RMS) 301.2 V 305.7 V

Line Current (RMS) 2.89 A 2.94 A

Iron-Core Losses 57.2 W 52.3 W

Armature Copper Losses 32.6 W 29.8 W

Total Losses 89.8 W 82.1 W

Output Power 1457 W 1507 W

Input Power 1547 W 1589 W

Efficiency 94.2 % 94.8 %

Rated Torque 0.148 N.m 0.152 N.m

Net Weight 0.154 Kg 0.156 Kg

Simulation by finite element analysis using MAXWELL-AnsoftFour-pole, three-phase design @ 100,000 RPM

Electromagnetic Performance

Output Phase Voltage for NdFeB35, max = 415 V (for SmCo28, max = 402 V)

Air gap flux density for NdFeB35, max = 0.6 T (for SmCo28, max = 0.52 T)

Mechanical Layout in High-Speed Electrical Machinery (18 to 120 kRPM)

U.S. Patent # 5,144,735 (Stark et al.) U.S. Patent # 5,687,471 (Noguchi et al.)

Mechanical Layout in High-Speed Electrical Machinery (18 to 120 kRPM)

U.S. Patent # : 4,625,135 (Kasabian et al.)

Proposed Mechanical Design Permanent magnets bonded to grooves in rotor core Torsional stress in rotor shaft is modest (~ 2.3 MPa) Critical mechanical requirement given by centrifugal forces Containment sleeve required to protect rotor from large centrifugal forces Sleeve made of pre-stressed high-strength material

Containment Sleeve Materials

Aluminum Stainless steel Composite resin

Mechanical strength Low High Medium

Thermal conductivity High Medium Low

Eddy current losses High Medium No

Mass / Inertia Medium High Low

Proposed Mechanical Layout

turbine shaft

permanent magnets (4)

containment sleeve

rotor core

stator

Analysis of Critical Mechanical StressStructural FE analysis of sleeve using ANSYS

Rotational Speed = 100k RPM

Sleeve Material :

AISI Type 302 Stainless SteelTensile Strength, Ultimate 495 MPaTensile Strength, Yield 160 MPa

Sleeve thickness = 1mm

Magnets assumed not bonded or bolted - supported only by sleeve

Max stress at sleeve = 157 MPa

Actual stress would be much less since magnets are bonded and/or bolted

Thermal Analysis

z

r

450 K

Q = R*i^2

Air 300K 50 m/s~300 m/s

FE conduction + convection analysis using ANSYS

Heat source given by stator coils

2-D axisymmetric model

3 cases of air speed

Sleeve thickness = 1mm

Thermal Conductivity:

Stainless steel : 16.2 W/m-K Permanent magnet : 9 W/m-K Copper : 385 W/m-K Carbon steel : 49.8 W/m-K

Air flow = 50 m/s

Air flow = 100 m/s

Air flow = 300 m/s

Results – Temperature Distributions

Thermal Analysis

Layers: shaft (stainless), inner core (carbon steel), magnet, sleeve (stainless), air gap, copper, outer core (carbon steel).

Conclusions

Proposed design meets all electrical requirements Containment of centrifugal forces achieved by pre- stressed sleeve Critical mechanical stresses verified under worst-case conditions Estimated operating temperature ~ 410K Proposed magnetic material (SmCo5) has max service temperature of 523K Loss of nominal magnetic coercivity at the operating temperature ~ 2%

Future Work

Detailed mechanical component design

Detailed 3-D finite-element verification of

Electromagnetic performance

Structural integrity

Thermal analysis – Heat transfer

Analysis / design of electronic power

converter