A novel continuously variable-speed offshore wind turbine with magnetorheological transmission for optimal power extraction

ABSTRACT

The paper introduces a novel magnetorheological transmission (MT) type offshore wind turbine (OWT), which integrates the MT into the traditional-geared train to construct a controllable power split type continuously variable gear train for the OWT. The design and construction of the MT-OWT are proposed. The continuous regulation of the transmission speed of the drive train is achieved by controlling the current of the MT. Then, a generalized utilization coefficient of wind power is defined to describe the overall efficiency of the OWT. A cooperative control strategy is proposed to track the optimal power points and capture the optimal wind kinetic energy with the best energy transmission efficiency by adjusting the electromagnetic torque and the MT of the OWT. The feasibility of the MT-OWT is verified through simulations. The results indicate that the maximum loads in the proposed MT-OWT can be reduced to be around 70% of the GT-OWT when adequate control is applied. Also, the generalized utilization coefficient of wind power can be well maintained around the rated value of around 0.45 and the generator speed can be well maintained around the rated value of around 1000 rpm (105 rad/s) regardless of the variations of the wind speeds and the turbine rotor speeds when using the proposed MT-OWT as compared with conventional OWT.

KEYWORDS:

• Offshore wind turbine
• geared train
• magnetorheological transmission
• wind energy utilization rate
• optimal power control

Nomenclature

c1,c2	=	The normal numbers related to the gear train
Cp	=	The wind turbine power coefficient
Ft	=	The engaging force between the sun gear and the planetary gear
GCp	=	The generalized utilization coefficient of wind power
$K_{\alpha }$	=	The torque coefficient
$K_w$	=	The speed coefficient
$K_{8a}$	=	The torque transfer coefficient from the turbine rotor to the intermediate shaft
$K_a$	=	The torque coefficient
$K_b$	=	a constant coefficient
$K_I$	=	The current coefficient
$P_1$	=	The split power of the first-level sun gear 6
$P_2$	=	The power of the first-level planetary gear
$P_a$	=	The mechanical power that the turbine rotor extracts from the inflow wind
$P_e$	=	The electrical power and the rated speed of the generator
$T_a$	=	The aerodynamic torque of the turbine rotor
$\rho$	=	The air density
v	=	The inflow wind speed
$w_2$	=	The turbine rotor speed in rad/s
$w_6$	=	The rotational speed of the sun gear 6
$w_7$	=	The rotational speed of the planetary gear 7
$w_{g_{rated}}$	=	The rated speed of the generator
$w_i$	=	The speed of the teeth of each gear mechanism
R	=	The turbine rotor radius
$r_6$	=	The radius of the sun gear
$r_7$	=	The radius of the planet gear
$T_8$	=	The intermediate shaft torque
$Z_i$	=	The number of the teeth of each gear mechanism
$\alpha$	=	a positive constant
$\mathrm{\Delta }w=w_8-w_{11}$	=	The rotation speed difference
$\epsilon$	=	the power splitting ratio
${\eta }_e$	=	The efficiency of the generator and the related power electronics
${\eta }_g$	=	The mechanical transmission efficiency of the fixed-ratio speed increasing gear train
${\eta }_v$	=	The transmission efficiency of the MT
$\lambda$	=	The tip speed ratio

Acknowledgements

The work was supported by the Natural Science Foundation of Guangxi under Grant No. 2019JJB160062. The work was supported by the Guangxi Science and Technology Base and Talent Special Project No. 2019AC20266. The work was supported by Guangdong Basic and Applied Basic Research Foundation (Grant No. 2019A1515110709). The work was supported by “the Fundamental Research Funds for the Central Universities” No. 2042022gf0008.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.