1. Overview of different wind generator systems and their comparisons 2-4~2-7
陳昱希

2. Outline
Variable speed direct-drive concept with a full- scale power converter
Variable speed single-stage geared concept with a full-scale power converter
Variable speed multiple-stage geared concept with a full-scale power converter

3. Variable speed direct-drive concept with a full-scale power converter
The full-scale power converter can perform smooth grid connection over the entire speed range. However, it has a higher cost and a higher power loss in the power electronics, since all the generated power has to pass through the power converter Types of direct-drive generators used in the market can be classified into the electrically excited synchronous generator (EESG) and the PMSG.

4. Variable speed direct-drive concept with a full-scale power converter
Direct-drive types V.S. geared-drive
Lower generator rotor speed
Higher torque
Larger size
Simplified drive train
Omitting the gearbox.
Higher overall efficiency
High reliability
The most important difference between geared drive wind
turbines and direct-drive types is the generator rotor
speed. The direct-drive generator rotates at a low
speed, because the generator rotor is directly
connected on the hub of the turbine rotor

5. Electrically excited synchronous generator (EESG)
The amplitude and frequency of the voltage can be fully controlled by the power electronic at the generator side.
The EESG has the opportunities of controlling the flux for a minimized loss in different power ranges, because the excitation current can be
controlled by means of the power converter in the rotor side.

6. PM synchronous generator
The advantages of PM machines over EESG
Higher efficiency
No additional power supply for the magnet field excitation.
Disadvantages
High cost of PM material
Difficulties to handle in manufacture

7. PM synchronous generator
Based on the direction of flux penetration.
Radial-flux PM machines
Axial-flux PM machines
Transversal-flux PM machines

8. Radial-flux PM machines
The PMs of radial-flux machines are radically oriented.
Two types of RFPM machines, the slotted surface mounted PM machine and the slotted flux concentrating PM machine

9. Axial-flux PM machines
The axial-flux PM (AFPM) machine is a machine producing magnetic flux in the axial direction.
The slotless single stator double rotor is a typical structure of slotless AFPM machines.

10. Axial-flux PM machines
AFPM V.S RFPM
Advantages
Simple winding
Short axial length
Higher torque/volume ratio.
Disadvantages
Lower torque/mass ratio ,
Difficulty to maintain air gap in large diameter
Difficulty in production of stator core

11. Transversal-flux PM machines
The path of the magnetic flux is perpendicular to the direction of the rotor rotation.
TFPM machines have some advantages, such as higher force density, considerably low copper losses and simple winding.
TFPM machines have some disadvantages, such as the electromagnetic structure is much more complicated ,
low power factor.

12. Variable speed single-stage geared concept with a full-scale power converter
In this scheme, a variable speed pitch control wind turbine is connected to a single-stage planetary gearbox that increases the speed by a factor of roughly10 and a low-speed permanent-magnet generator.
It has the advantages of a higher speed than the direct-drive concept and a lower mechanical component than the multiple-stage gearbox concept.

13. Variable speed multiple-stage geared concept with a full-scale power converter
A PMSG system with a multiple gearbox is used in order to reduce the generator’s volume and improve the generator efficiency in variable speed wind turbine concepts with a full-scale power converter.

14. PMSG system compared with the DFIG system
Advantages
The generator has a better efficiency.
The generator can be brushless.
Disadvantages
Larger
More expensive converter
The losses in the converter are higher

15. Thanks for your listening