Hybrid Control System And Method

The control system according to claim 1, wherein the top-side hydraulic power unit is operable for providing the steady-state power represented by directional control valve leakage, and the sub-sea hydraulic power unit is operable for providing the transient-state power required to operate process and safety valves of the process control means.

The control system according to claim 1, wherein the sub-sea hydraulic power unit comprises a pump driven by an electric motor powered by alternating current which is stepped down from the higher voltage supplied through the umbilical.

The control system according to claim 1, wherein the pump is operable and controlled in the transient-state operation mode to boost the pressure of hydraulic fluid returning from the process control means into a pressure required for operating the process and safety valves of the process control means.

The control system according to claim 1, further comprising:

• a bridge circuit emergency shut down system having comprising at least two sets of directional control valves connected in series, each set including at least two directional control valves connecting in parallel the supply line and the return line, wherein the directional control valves electrically powered through the umbilical and controlled into a normally closed position.

A method for operating the process control means of an electro-hydraulic process control system in a sub-sea production installation, the method comprising:

• feeding hydraulic power, via an umbilical, from a top-side hydraulic power unit for operating the process control means in a steady-state operation mode of the process control system;
• feeding high voltage electric power, via the umbilical, for operating a sub-sea hydraulic power unit, and
• controlling the sub-sea hydraulic power unit between a stand-by mode and an operative mode for operating the process control means, in a transition operation mode of the process control system.