Method and apparatus for extracting energy from a fluctuating energy flow from a renewable energy source

A method of operating an energy extraction device to extract energy from a fluctuating energy flow from a renewable energy source, the device comprising:

• a hydraulic pump driven by a rotating shaft, the rotating shaft driven by a renewable energy source, a hydraulic motor driving a load, at least one low pressure manifold and a high pressure manifold in fluid communication with an outlet of the hydraulic pump, an inlet of the hydraulic motor and an elastically deformable fluid retaining body, the hydraulic pump and hydraulic motor each comprising a plurality of working chambers of cyclically varying volume and a plurality of valves for regulating a volume of working fluid displaced by each said working chamber between each said working chamber and each said manifold, at least one valve associated with each said working chamber being an electronically controlled valve, said electronically controlled valves being operated to select the volume of working fluid displaced by each said working chamber on each cycle of said working chamber and thereby regulate a net rate of displacement of working fluid by each of the hydraulic pump and the hydraulic motor,
• the method comprising:
• selecting the net rate of displacement of working fluid by the hydraulic pump to regulate a torque applied by the hydraulic pump to said rotating shaft,
• selecting the net rate of displacement of working fluid by the hydraulic motor to smooth a rate of power transmission to the load, the elastically deformable fluid retaining body receiving and outputting working fluid from and to the high pressure manifold as required, and
• regulating a pressure in the high pressure manifold to remain within an acceptable pressure range,
• wherein the acceptable pressure range comprises a first range and one or more second ranges, either higher or lower than the first range, and
• the pressure within the high pressure manifold is regulated more strongly when the pressure is within the or each second range than in the first range by virtue of the net rate of displacement of working fluid by the hydraulic motor being varied, to change the pressure in the high pressure manifold, responsive to the same magnitude of pressure change in the high pressure manifold, by a larger amount in the or each second range than in the first range.

A method of operating an energy extraction device to extract energy from a fluctuating energy flow from a renewable energy source, the device comprising:

• a hydraulic pump driven by a rotating shaft, the rotating shaft driven by a renewable energy source, a hydraulic motor driving a load, at least one low pressure manifold and a high pressure manifold in fluid communication with an outlet of the hydraulic pump, an inlet of the hydraulic motor and an elastically deformable fluid retaining body, the hydraulic pump and hydraulic motor each comprising a plurality of working chambers of cyclically varying volume and a plurality of valves for regulating a volume of working fluid displaced by each said working chamber between each said working chamber and each said manifold, at least one valve associated with each said working chamber being an electronically controlled valve, said electronically controlled valves being operated to select the volume of working fluid displaced by each said working chamber on each cycle of said working chamber and thereby regulate a net rate of displacement of working fluid by each of the hydraulic pump and the hydraulic motor,
• the method comprising:
• measuring a pressure in the high pressure manifold, selecting the net rate of displacement of working fluid by the hydraulic pump responsive to said measured pressure to regulate a torque applied to said rotating shaft, the elastically deformable fluid retaining body receiving and outputting working fluid equivalent to the difference between the fluctuating energy flow and the energy flow through the hydraulic motor from and to the high pressure manifold as required, and
• in a first pressure range selecting the net rate of displacement of working fluid by the hydraulic motor responsive to said measured pressure to provide a smoothed energy flow to the load, and
• in at least one second pressure range selecting the net rate of displacement of working fluid by the hydraulic motor responsive to said measured pressure to regulate the pressure towards the first pressure range.