Extremum‐seeking control for energy‐harvesting enhancement of wind turbines with hydromechanical drivetrains

Abstract

Efficiency and reliability enhancement of distributed wind energy systems have been the subject of extensive research effort for the purpose of energy cost reduction and power availability. This work investigates the integration of a hydromechanical power split transmission into the drivetrain of a stall-regulated wind turbine with a fixedspeed generator to enhance the overall system efficiency without compromising its reliability. The proposed drivetrain configuration introduces a variable transmission ratio capability, thus enabling the turbine rotor to cope with varying wind speeds independent of the fixed generator speed. An extremum-seeking control approach is adopted to maximize energy harvesting by controlling a variable geometric volume hydraulic pump without the need for wind speed measurement. Compared with a stall-regulated fixed-speed wind turbine, the performance of the proposed wind turbine configuration is evaluated in simulation environment under different wind speed conditions. The results demonstrate the ability of the proposed wind turbine configuration to significantly improve the system overall efficiency in partial and full-load regions of operation. Consequently, the proposed wind turbine configuration with extremum-seeking control can be considered as an efficient and reliable possible alternative for future distributed and isolated wind energy systems. K E Y W O R D S distributed wind turbines, extremum-seeking control, fatigue loading, hydromechanical drivetrain, power splitting, wind turbine efficiency 1 | INTRODUCTION Wind energy represents one of the major renewable energy resources available for sustainable power generation. The installed wind power capacity and the annual wind power generation have grown rapidly worldwide in the last few decades. 1 However, the future growth in wind energy projects is contingent upon the reduction of its cost. Ultimately, the enhancement of both efficiency and reliability of wind energy systems leads to significant reduction in wind power cost and maintains its availability. This objective motivates the implementation of novel wind energy system configurations and the adoption of advanced control algorithms. Based on their electrical configurations, wind energy systems can be classified as either fixed-speed or variable-speed. 2 Basically, stall-regulated fixed-speed wind energy systems are equipped with squirrel-cage induction generators and operate efficiently in the vicinity of a specific wind speed. As the wind speed varies away from that specified value, the efficiency of these systems drops significantly. Stall-regulated fixed-speed configuration represented a viable choice for small and medium-scale wind turbines (i.e., less than 1 MW) due to its low cost and relatively high reliability, 3 especially in distributed and isolated power systems. However, the relatively low efficiency of stall-regulated fixed-speed wind turbines hinders the growth of their installation.