Abstract
Axis-flux wind generators are widely used in vertical axis wind turbines given their high generator diameter-to-length and power-to-weight ratios, flexible field and winding design, improved cooling, and possibility of modular construction. In this paper, an asymmetric-primary axis-flux hybrid-excitation generator (APAFHG) is proposed to provide a controllable maglev force that compensates for the ripple of axial force fluctuation. First, the operation principle of the proposed generator is introduced. No-load performance influenced by direct current (DC) excitation is obtained by using the 3D finite element method (3D-FEM). Second, the load performances are analyzed under two typical operation statuses, namely, symmetrical pure resistance load and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$i_{d}=0$ </tex-math></inline-formula> control strategy load. An alternating current (AC) excitation method is then comparatively analyzed to increase the output power under the maximum armature current. Third, based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> axes dynamic mathematical model, the quantitative calculations of levitation force and torque characteristics are deprived and then tested and verified by using the finite element analysis results. These results show that the proposed generator can be implemented for the decoupling control operation of power and levitation forces and is suitable for vertical axis wind turbines.
Highlights
Wind turbines are mainly categorized into horizontal and vertical axis wind turbines[1].Vertical axis wind turbines are known for their many advantages, including their independence with respect to wind direction, stable force, easy installation and maintenance, and low starting wind speed[2,3]
This paper proposed asymmetric-primary axis-flux hybridexcitation generator (APAFHG) and analyzed its 3D electromagnetic field and no-load performances
direct current (DC) excitation can be implemented to decouple-control the levitation force, whereas alternating current (AC) excitation can be implemented to change the output power under the same armature current and subsequently expand the power range
Summary
Wind turbines are mainly categorized into horizontal and vertical axis wind turbines[1].Vertical axis wind turbines are known for their many advantages, including their independence with respect to wind direction, stable force, easy installation and maintenance, and low starting wind speed[2,3]. Compared with traditional radial flux rotation generators, axial flux generators have a higher generator diameter-to-length ratio and are suitable for direct coupled wind turbine applications, such as vertical axis and directcoupled wind turbines[7-9]. The direct coupling of the high-power axial flux permanent magnet synchronous generator and wind turbine may introduce problems in starting the wind turbine. To address this problem, an asymmetric-primary axis-flux hybridexcitation generator (APAFHG) is proposed in this paper. An asymmetric-primary axis-flux hybridexcitation generator (APAFHG) is proposed in this paper This proposed generator can generate a levitation force with fixed air gap length and is designed to realize a decoupling control of levitation force and output power by using asymmetric primary and hybrid excitation. The proposed APAFHG is suitable for vertical axis wind turbines
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