Dr. Longya Xu The Ohio State University April, 2010

1. Introduction  Major Wind Power System Configurations  Challenges to Remain in Power Grid  Why PM Direct-Driven WTG Getting Popular 2. Initial Design and Performance Analysis  Specifications and Sizing  Stator and Rotor Design  Performance Evaluation 3. Conclusions

V Rated(V, rms) 690Frequency5~11Hz I Rated(A, rms) 1700Speed10~22 rpm KW Rated 2,000Torque (peak) 850kNm The reason for low speed at:10~22 rpm Tip Speed of Wind Blades: v tip = 115 meters/sec. The reason for low Frequency at:5~11 hz

Consider the electrical and magnetic loadings are relatively constant, we have a traditional sizing equation: where subscript “r” indicates rotor related variables. (1)(1) In (1) the electrical loading refers the current along the air- gap in the unit of Ampere per Meter (A/M). The magnetic loading refers the magnetic flux density passing through air-gap in the unit of Tesla.

where subscript “o” indicates the stator related variables and a coefficient proportion to the current density and magnetic flux density. Here current density is in the unit of Ampere per Square Meter and magnetic flux density in Tesla. (2)(2) is also closely Do/Dr related and at certain value of Do/Dr, is maximized, or minimized.

Combining (1) and (2), we have two new sizing equations, one in terms of stator OD (3)(3) (4)(4) another in terms of rotor OD In sizing an electric machine, the new equations take many variables into consideration: electrical loading, magnetic loading, D o /D r ratio, and slot current density.

Stator OD3820mmPole #60 Stator ID3500mmSlot #288 Stack L1300mmAir-gap6mm Sizing Results

Stator Slot Shape and Dimensions Stator current density at 2 MW 0.77(A/mm 2 )

Inner Rotor Outer Rotor

Estimated Copper Losses P cu = 3I 2 R = 2.7~3 kw Assume equal amount of iron and other losses Effi. = 97% Expected energy efficiency P Fe+other = ~3 kw

(1) Outer Rotor with 360 Stator Slots

In order to keep copper losses the same in comparison, some changes are made as follows: Cross-section of stator slot for conductor: 1400mm 2 (288 slots) vs. 1120mm *288/360 (360 slots) Current (peak) flow in each conductor: 1300A(288 slots) vs. 1040A (360 slots)1300*8/10

Torque Production Winding Flux Linkage (1) Outer Rotor with 360 Stator Slots

(2) Outer Rotor with 288 Stator Slots

Winding Flux Linkage Torque Production (2) Outer Rotor with 288 Stator Slots

(3) Inner Rotor with 360 Stator Slots

Winding Flux Linkage Torque Production (3) Inner Rotor with 360 Stator Slots

(4) Inner Rotor with 288 Stator Slots

Winding Flux Linkage Torque Production (4) Inner Rotor with 288 Stator Slots