Abstract: A power transmission system may include a plurality of renewable-energy devices such as wind turbines or subsea turbines. The devices are connected together in parallel to a subsea cable that carries an ac transmission voltage. Each device includes a turbine assembly that is rotated by wind or water current flows, and a variable speed ac induction generator. A power converter is connected to the subsea cable and is used to interface the generators to a supply network or power grid. The power transmission system is operated such that an indicated operating speed of one or more of the devices is used to control the power converter (e.g. the PWM strategy that is used to open and close the power semiconductor devices) to achieve desired stator electrical quantities at each generator.

Abstract: In an oscillating water column (OWC) assembly power may be generated based on a power reference that is derived from an estimate of the available mechanical power in the air turbine 2 or a measured pressure drop across the turbine. The power reference is used to derive a power control torque reference within a power controller 14. A speed controller 16 uses a comparison of a measured speed of the generator 8 and a maximum speed limit to derive a speed control torque reference. A selector function 22 selects whichever of the power control and speed control torque references is the maximum at any time instant. The selected torque reference is input to an anti stall torque function 24 where it is selectively modified by applying a speed dependent gain that decreases with decreasing turbine speed, preferably so that the main torque reference is zero for a minimum speed limit.

Abstract: A power transmission system may include a plurality of renewable-energy devices such as wind turbines or subsea turbines. The devices are connected together in parallel to a subsea cable that carries an ac transmission voltage. Each device includes a turbine assembly that is rotated by wind or water current flows, and a variable speed ac induction generator. A power converter is connected to the subsea cable and is used to interface the generators to a supply network or power grid. The power transmission system is operated such that an indicated operating speed of one or more of the devices is used to control the power converter (e.g. the PWM strategy that is used to open and close the power semiconductor devices) to achieve desired stator electrical quantities at each generator.

Abstract: In an oscillating water column (OWC) assembly power may be generated based on a power reference that is derived from an estimate of the available mechanical power in the air turbine 2 or a measured pressure drop across the turbine. The power reference is used to derive a power control torque reference within a power controller 14. A speed controller 16 uses a comparison of a measured speed of the generator 8 and a maximum speed limit to derive a speed control torque reference. A selector function 22 selects whichever of the power control and speed control torque references is the maximum at any time instant. The selected torque reference is input to an anti stall torque function 24 where it is selectively modified by applying a speed dependent gain that decreases with decreasing turbine speed, preferably so that the main torque reference is zero for a minimum speed limit.