N. Schinas’s research while affiliated with University of Patras and other places

This paper presents different discrete control strategies for a variable speed pitch-controlled wind turbine (WT) which supplies an autonomous system in cooperation with a small hydro power unit. The WT consists of a synchronous generator (SG) with two three-phase stator windings displaced by 300, so as the torque distortions due to the wind fluctuations to be limited. The SG operates in variable speed mode in order to maximize the power absorbed from the wind and minimize the amount of water consumed by the hydro power unit. The requirements from the control schemes are to deliver the total power from the WT to the isolated load under constant voltage and frequency and adjust suitably the power from the hydro unit at the same time. There are two controllers: the rectifier controller, which drives the WT at such value of mechanical velocity that maximum power from the wind is absorbed and the inverter controller, which passes this amount of power to the load under constant voltage. There are two schemes presented in this paper: the first includes two PID controllers and the second includes a robust controller for the rectifier pulsation and a state-feedback controller for the inverter pulsation.

This paper presents a control strategy for a variable-speed pitch-controlled wind turbine (WT) generation scheme for the supply of an autonomous system with no energy storage units. The synchronous generator includes two three-phase stator windings displaced by 30deg that are connected to the transformer load through two dc links with voltage source inverters (VSI). Following priority rules, the load is divided into steps. Each load step can be supplied by the WT when the wind speed varies between two predefined speed levels. The first goal of the WT control system is to supply the load with constant real power under constant voltage as the wind speed varies between two levels and the second is to operate smoothly interchanging the load steps when the wind speed breaks through a speed level. There are two controllers: the inverter controller that keeps the load voltage constant and the pitch controller acting on the blade's angle. Using simulation techniques, the operation of the WT system and the efficiency of the proposed control strategy are demonstrated for a wide range of wind speeds.

A specific wind turbine (WT) generation scheme is used and a control strategy is studied, not only to increase the efficiency of the WT but also to limit the influence on the alternating current (AC) distribution grid. The system is a variable-speed wind-energy conversion scheme, including a synchronous generator with two three-phase stator windings displaced by 30°, which are connected to the AC distribution grid through DC links with Voltage Source Inverters (VSI). A state feedback controller has been designed, using the pole placement technique, to maximize the wind-energy capture. The controller of the DC link secures a smooth supply of the WT electric power to the distribution AC grid by supporting the output voltage and reducing the harmonic distortion. The operation of the proposed system and the efficiency of the control strategy are demonstrated and tested using simulation techniques.