14-08-2012, 04:08 PM
Design of a High Temperature Superconducting Generator for Wind Power Applications
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INTRODUCTION
THE quick development of the wind power industry in the
recent decade initiated many efforts on developing new
and high efficiency large scale generators, such as the “directdriven”
permanent magnet generator and the superconducting
generator. As the power of the generator increased rapidly to
meet the keen need of the expanding wind farm, the weight
and size of the generator increased also rapidly. At 5–6 MW,
the weight and size of the low speed “direct-driven” permanent
magnet synchronous generator, as well as those of the gear box
in the high speed “doubly-fed” asynchronous generator system
became serious drawbacks to the economic benefit of the wind
farm. HTS generator was proposed to overcome the problems
because of its high energy density and consequently advantages
in the weight and size [1]–[4]. To develop such generator, problems
including the electromagnetic structure in the cross section;
field distributions in the excitation coils; field effects on
the current carrying abilities of HTS tapes and over-current tolerance
of the windings were put forward. For future design of
Manuscript received August 02, 2010; accepted October 03, 2010. Date of
publication November 18, 2010; date of current version May 27, 2011. This
work was supported by the National Natural Science Foundation, China, under
Grant 50777063, Grant 50677067, and Grant 50507019.
X. Li, D. Zhang, J. Zhang, Q. Qiu, S. Dai, Z. Zhang, D. Xia, G. Zhang,
L. Lin, and L. Xiao are with the Key Laboratory of Applied Superconductivity,
Chinese Academy of Sciences and also with the Institute of Electrical
Engineering, Chinese Academy of Sciences, Beijing 100190, China (e-mail:
xhli[at]mail.iee.ac.cn; xhli2002[at]gmail.com).
Y. Zhou and L. Han are with the Key Laboratory of Applied Superconductivity,
Chinese Academy of Sciences, Institute of Electrical Engineering, Chinese
Academy of Sciences, Beijing 100190 China and also with the Graduate
School, Chinese Academy of Sciences, Beijing 100039 China.
S. Zhu, H. Bai, B. Bian, S. Li, and W. Gao are with Tianjin Jinneng Wind
Power Co., Ltd., Tianjin 300010, China.
Color versions of one or more of the figures in this paper are available online
Digital Object Identifier 10.1109/TASC.2010.2088352
Fig. 1. The schematic diagram of the 100 kW HTS model generator system.
10 MW wind turbine system, a 100 kW model was designed
here, the electromagnetic parameters of the excitation coils in
the rotor were numerically evaluated and optimized according
to the properties of commercial HTS tape.
GLOBAL DESIGN CONCEPT AND STATOR ANALYSIS
Considering common requirements of the large scale wind
turbines, a 100 kW “direct-driven” synchronous HTS generator
with a hybrid structure was proposed for model demonstration
and feasibility tests of 10 MW HTS generators.
Fig. 1 showed the schematic diagram of the 100 kW model
system, including the wind turbine, the generator, the convertor,
etc. The design parameters of the model listed in Table I were
decided based on the common requirements of the wind farm
and the power grid. Here, the output voltage of the generator
was 690 V in 3 phases, thus the phase current was about 84 A.
The output frequency of the system was 50 Hz as the power grid
standard. However, as the rotation speed of the turbine was only
200 rpm, the rotor would have consisted of 15 pairs of poles to
meet the needs of such frequency according to:
SCALING UP ATTEMPT AND DISCUSSION
Based on the conceptual design shown in Fig. 2, attempts
of scaling up to a 10 MW “direct-driven” HTS generator were
made. According to the electrical parameters, the rated output
voltage of the 10 MW generator was selected to be 3000 V in
3 phases, and the rotation speed was 20 rpm, with the output
frequency of 10 Hz. Thus, according to (1), . Taking the
same cross section dimensions of the excitation coils as that in
the 100 kW model, the circumradius of the rotor column was
about 1528.6 mm and with the pole shoes, the outer diameter
of the rotor was 1594 mm. Took the air gap width as 20 mm,
the inner radius of the stator was 1614 mm. FEM estimated air
gap field at the inner radius of the stator was about 0.98 T at the
excitation current of 80 A. In this case, the maximum field in
the excitation coil was about 0.55 T, thus the generator had to
work at 65 K to ensure enough in the tape.