Abstract: A wood splitter which includes a supporting surface for receiving a section of wood to be split; the supporting surface having a cutting box on one side and a reciprocating moving head on the other side; the cutting box providing a series of spaced stationary knives through which the wood can be forced, to cut the wood, said stationary knives including a horizontal knife along the uppermost margin of the cutting box; the moving head being arranged to be reciprocable towards the cutting box so as to engage wood placed on the supporting surface and push said wood through the cutting box, and then away from the cutting box to allow a fresh piece of wood to be placed on the supporting surface; a top plate connected to the moving head by a connecting arm and movable between a first position in which the lower edge of the top plate overhangs said horizontal knife and a second position in which the top plate is raised vertically relative to the cutting box and is moved horizontally away from the supporting surface.

Abstract: A method of controlling a combined plant to provide frequency support to a power grid operating at a variable grid frequency, wherein the combined plant includes at least one generator and an energy store, and the combined plant is adapted to supply power to the power grid, the method including the steps of charging the energy store at less than its rated power when frequency support is not needed. When frequency support is needed the combined plant is controlled to increase or decrease the overall power that it supplies to the power grid to provide frequency support. The control of the combined plant can be designed to maximize frequency support revenues.

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: A wind turbine typically includes a generator and a rotating mechanical system having a natural period. The present invention relates to a method of controlling generator torque that minimizes oscillations in the speed of the generator rotor. In the event of a grid fault or transient, or a fault in the power converter, the generator torque is decreased at a substantially constant rate with respect to time. The rate at which the generator torque is decreases is proportional to the nominal rated torque of the generator and inversely proportional to an integer multiple of the natural period of the rotating mechanical system.

Abstract: A method of controlling a combined plant to provide frequency support to a power grid operating at a variable grid frequency, wherein the combined plant includes at least one generator and an energy store, and the combined plant is adapted to supply power to the power grid, the method including the steps of charging the energy store at less than its rated power when frequency support is not needed. When frequency support is needed the combined plant is controlled to increase or decrease the overall power that it supplies to the power grid to provide frequency support. The control of the combined plant can be designed to maximize frequency support revenues.

Abstract: A test case is abstracted into a re-useable script or other declarative form that expresses the intent of a task rather that defining how the test will be performed. Tools translate the declarative test into a series of steps corresponding to code that implements the action indicated in the declarative test. The schema for the tests can be dynamic. New forms of test cases can take advantage of new actions so that the library of actions can be extended. Libraries are interchangeable. Test cases can be generated using a state machine. New test cases can be composed dynamically using a state machine to create new test cases.

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 wind turbine typically includes a generator and a rotating mechanical system having a natural period. The present invention relates to a method of controlling generator torque that minimises oscillations in the speed of the generator rotor. In the event of a grid fault or transient, or a fault in the power converter, the generator torque is decreased at a substantially constant rate with respect to time as shown in graph (c). The rate at which the generator torque is decreases is proportional to the nominal rated torque of the generator and inversely proportional to an integer multiple of the natural period of the rotating mechanical system.

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 test case is abstracted into a re-useable script or other declarative form that expresses the intent of a task rather that defining how the test will be performed. Tools translate the declarative test into a series of steps corresponding to code that implements the action indicated in the declarative test. The schema for the tests can be dynamic. New forms of test cases can take advantage of new actions so that the library of actions can be extended. Libraries are interchangeable. Test cases can be generated using a state machine. New test cases can be composed dynamically using a state machine to create new test cases.