A method (1000-1004) for operating a wind turbine (10, 11) including a drive train (64) including a generator (42) and a rotor shaft (44) mechanically connected with the generator (42) and having an axis (30) of rotation, and a rotor (18) having rotor blades (22-22c). The rotor (18) is mechanically connected with the rotor shaft (44) and rotatable about the axis (30) of rotation. The method (1000-1004) includes determining (1100) that the generator (42) is not operating in a power generating mode, and operating (1200) the rotor (18) to move around a predefined desired angular orientation (α.sub.des) with respect to the axis (30) of rotation in an alternating fashion.

A hydroelectric power generation system includes a water turbine, a generator connected to the water turbine, and a controller. The water turbine is arranged in a flow path through which a fluid flows. The controller performs a pressure control by controlling the generator to regulate a pressure of the fluid downstream of the water turbine. The pressure control includes a first control regulating the pressure in parallel with a regenerative operation of the generator, and a second control regulating the pressure in parallel with a power running operation of the generator.

A power take-off apparatus for a wave energy converter of point absorber type, includes a cylinder attachable to a floating device, a piston that reciprocates inside the cylinder and has a piston rod attachable to a mooring, at least one penstock with a first end in communication with a second end of the cylinder through a first opening, and a second end having a second opening, and a housing above a cylinder first end. The housing communicates with the penstock through the second opening and with the cylinder through a third opening in the housing such that the cylinder, penstock and the housing form a closed loop for a fluid in the power take-off apparatus. A water turbine is arranged inside the housing so that working fluid entering the housing from the at least one penstock causes rotation of the water turbine to drive an electrical generator connected thereto.

The present invention relates to a flow controller configured to selectively act as a pump or as a flow regulator. The flow controller comprises: an inlet for a fluid; an outlet for the fluid; a pump assembly arranged between the inlet and the outlet and configured to pump the fluid through the flow controller from the inlet to the outlet; a hydro electrical generator assembly arranged between the inlet and the outlet, the hydro electrical generator assembly configured to allow the fluid flow through the flow controller from the inlet to the outlet and to generate electricity by transforming flow energy of the fluid flowing through the flow controller into electricity; and a mode controller configured to selectively set the flow controller in a pumping mode or in an electricity generating mode.

A power take-off apparatus for a wave energy converter of point absorber type, includes a cylinder attachable to a floating device, a piston that reciprocates inside the cylinder and has a piston rod attachable to a mooring, at least one penstock with a first end in communication with a second end of the cylinder through a first opening, and a second end having a second opening, and a housing above a cylinder first end. The housing communicates with the penstock through the second opening and with the cylinder through a third opening in the housing such that the cylinder, penstock and the housing form a closed loop for a fluid in the power take-off apparatus. A water turbine is arranged inside the housing so that working fluid entering the housing from the at least one penstock causes rotation of the water turbine to drive an electrical generator connected thereto.

A hydroelectric power generation system includes a water turbine, a generator connected to the water turbine, and a controller. The water turbine is arranged in a flow path through which a fluid flows. The controller performs a pressure control by controlling the generator to regulate a pressure of the fluid downstream of the water turbine. The pressure control includes a first control regulating the pressure in parallel with a regenerative operation of the generator, and a second control regulating the pressure in parallel with a power running operation of the generator.

A method (1000-1004) for operating a wind turbine (10, 11) including a drive train (64) including a generator (42) and a rotor shaft (44) mechanically connected with the generator (42) and having an axis (30) of rotation, and a rotor (18) having rotor blades (22-22c). The rotor (18) is mechanically connected with the rotor shaft (44) and rotatable about the axis (30) of rotation. The method (1000-1004) includes determining (1100) that the generator (42) is not operating in a power generating mode, and operating (1200) the rotor (18) to move around a predefined desired angular orientation (α.sub.des) with respect to the axis (30) of rotation in an alternating fashion.

In a first aspect, a system for rotating an unbalanced direct drive wind turbine is provided. The system includes an auxiliary converter and a power source coupled to the auxiliary converter, wherein the auxiliary converter is configured to supply a current to the wind turbine generator for generating a torque to rotate the hub. In a further aspect, a method of rotating an unbalanced hub of a direct drive wind turbine is provided. In a yet further aspect, a method of installing a blade in a hub of a direct drive wind turbine is provided.

The present invention relates to a flow controller configured to selectively act as a pump or as a flow regulator. The flow controller comprises: an inlet for a fluid; an outlet for the fluid; a pump assembly arranged between the inlet and the outlet and configured to pump the fluid through the flow controller from the inlet to the outlet; a hydro electrical generator assembly arranged between the inlet and the outlet, the hydro electrical generator assembly configured to allow the fluid flow through the flow controller from the inlet to the outlet and to generate electricity by transforming flow energy of the fluid flowing through the flow controller into electricity; and a mode controller configured to selectively set the flow controller in a pumping mode or in an electricity generating mode.

Underwater vehicles capable of self-propulsion are described. An underwater vehicle includes a cross-flow turbine including two or more foils spaced apart from a main shaft. The foils have a pitch that is adjustable under control of a pitch control mechanism. The underwater vehicle also includes a frame supporting the main shaft. The frame enables rotation of the cross-flow turbine. The underwater vehicle additionally includes a generator-motor set including rotor and stator elements. The rotor element is in rotary communication with the main shaft.