Abstract:
The invention relates to a control system for a subsea installation based on CAN bus technology. A single cable forms a backbone for transmitting signals and/or power from a central control unit to a number of devices or sensors on the installation. Terminals are attached to the cable at intervals, allowing devices to be plugged in while the system is operable. A termination may also include repeaters or amplifiers for transmitting signals over longer distances.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to the field of subsea control systems. More particularly, the invention relates to a control system for controlling a plurality of devices in a subsea installation, the devices being connected to at least one common bus.  
       BACKGROUND OF THE INVENTION  
       [0002]     A standard subsea installation comprises a mixture of hydraulically and electrically operated devices. The hydraulic devices are normally actuators for the operation of valves on the installation. The actuators may be controlled by electrically operated pilot valves that in its turn control control valves, all housed in a control module located at or near the well, the control valves directing the supply of fluid to each actuator, as dictated by the need for operation. Such a system is therefore called an electro-hydraulic system. In addition, injection valves for supplying chemicals may be needed and such valves are usually electric solenoid operated valves. Other devices are electrical of nature, such as sensors for monitoring various parameters in system, such as pressure and temperature, flow rates and sand and scale detectors. These usually communicate with the control system module via a dedicated cable, each sensor being connected separately to the control module, for receiving and transmitting signals and, in some cases, electric power.  
         [0003]     The standard control module used in today&#39;s systems is housed in a container filled with an inert gas such as Nitrogen and pressurised at 1 bar to protect the electronics of the system. It contains the electronics for receiving signals from the sensor devices and for transmitting signals to a control station at a production vessel (FPSO) or other remote location. All the electrical pilot valves are also housed in the control module. The supply line for hydraulic and chemical fluids are connected to the control module with lines extending therefrom to the hydraulic actuators and the chemical injection points as needed. This system is very inflexible. For example, it must be decided beforehand for example how many control valves will be needed. If more control valves will be needed then the control module must be pulled up and exchanged with a new and larger control module. Such an action requires the well to be shut down, resulting in lost production. Usually the control module is made larger than needed in case the system needs to be extended.  
         [0004]     It has been proposed to use directly electrically operated valves, using electric motors, as this will be simpler and eliminate the need for large and costly hydraulic actuators and the use of pilot valves, since the actuators can be directly controlled.  
         [0005]     An all-electric system will eliminate the need for hydraulic piping that is used in today&#39;s subsea installation, resulting in considerable savings, since not only must the pipes be carefully mounted, but they also need to be extensively tested for leaks and flushed clean. Another advantage with an all-electric system is the possibility of a large degree of modularisation. Electrically powered actuators can be made small and compact and are connected to the control module with a cheap and simple cable.  
         [0006]     In an all-electric system it will be possible to configure it as a local area network (LAN), as is well known in many technical areas. Each device may have its own controller unit with a unique address and the electronics in the control-module having a micro processor, a bus controller, a memory unit and an input signal controller. Examples of such systems are described in WO 9914643 and WO 02054163, and in U.S. Pat. No. 5,941,966. It will enable devices to be removed and/or added to the system without shutting the whole system down. Any new device may easily be registered in the central control module by remotely reprogramming the control module processor.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an object of the invention to provide a subsea control system that is wholly electric in nature and uses addressing technology to control any number of devices.  
         [0008]     It is also an object of the invention to provide a subsea control system that is flexible and that can be extended or added upon indefinitely.  
         [0009]     The control system according to the invention allows devices to be installed as necessary, thereby reducing the need for upfront expenditure. With batteries, sensors and actuators all on the same distribution harness, they can be independently retrieved and separately repairable.  
         [0010]     According to the invention there is provided a control system for controlling a plurality of devices in a subsea installation, said devices being connected to at least one common bus, the control system comprising a command unit; each device comprising a control unit having a unique address and means for communicating with the command unit, and each device being removably connected to the common bus.  
         [0011]     According to an embodiment of the invention, the common bus comprises at least one modular cable unit so that a variety of devices, such as motors, sensors, can be connected anywhere to the common bus.  
         [0012]     The features of the present invention are set forth in the appended claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The invention will now be described with reference to the accompanying drawings where  
         [0014]      FIG. 1  is a drawing of a subsea installation which includes a control system according to the invention.  
         [0015]      FIG. 2  is a schematic drawing of a cable backbone bus for use in a system according to the invention.  
         [0016]      FIGS. 3   a - 3   f  are schematic drawings showing various components of the bus shown in  FIG. 2 .  
         [0017]      FIG. 4  is a schematic drawing of a cable harness bus for use in a system according to the invention.  
         [0018]      FIG. 5  is a schematic drawing illustrating the layout of the electrical cabling of the present invention.  
         [0019]      FIG. 6  is a schematic block diagram illustrating a control module.  
         [0020]      FIG. 7  is a more detailed schematic drawing of the cable harness bus shown in  FIG. 4 .  
         [0021]      FIG. 8  is a drawing of an electro-hydraulic pod module. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 1  shows an installation  1  located on the seabed  2  where the control system according to the invention may find use. In this illustrative embodiment, the installation  1  comprises a Christmas tree or other subsea production equipment  11  mounted on a wellhead  12 , the wellhead being the top part of a well that extends down into the ground below the seabed  2 . A vessel  3 , such as a floating processing unit (FPU), is located on the surface  4  of the water. The Christmas tree includes a number of devices, such as sensors, meters, or actuators  13  for the actuation of valves (not shown). A control module  14  is attached to the Christmas tree, the control module housing electronic equipment for receiving signals from and transmitting signals and power to the actuators  13 . A cable  15  extends from the control module  14  to each device or actuator. Other equipment, such as sensors or meters, may also be connected to the control module. A flowline  5  extends from the installation  1  down to the vessel  3 . A local power generating subsystem  30  may be arranged between the flow outlet of the installation  1  and the inlet of the flowline  5  to supply electrical power to the various components of the system. A power cable  31  connects the power generating subsystem with the control module  14 .  
         [0023]     The installation may further comprise a hydro-acoustic communication unit  16  attached to the Christmas tree and connected to the control module  14  via cable  17 .  
         [0024]     The communication unit  16  may also include an acoustic antenna  18 , arranged for communicating with a corresponding acoustic antenna  20  connected to a telemetry transceiver on the vessel  3 . This arrangement provides a telemetry and control signal link  19  between the vessel and the subsea installation  1 .  
         [0025]     The control module  14  also comprises an intelligent processor that controls the electronics in the system and handles communication signals both within the system and from remote locations.  
         [0026]     The control module  14  receives instructions and power through a cable  32  that is connected to a remote source. In one illustrative embodiment shown in  FIG. 5 , the primary electric power is provided by a battery unit  36 , which may be installed in the control module  14  or in another suitable location proximate to the installation  1 .  
         [0027]     In an illustrative embodiment, each device or actuator  13  may be a self-contained module that can be retrieved to the surface for repair or replacement. Other installations where the invention may find utility include, but are not limited to, manifolds, subsea processing systems, workover control systems, or any remote system where a number of controllable devices are in use.  
         [0028]      FIG. 2  is a schematic drawing showing a first illustrative embodiment of a bus connection for use in the system according to the invention. In this embodiment, the bus comprises a number of parts that may be assembled to form the installation.  
         [0029]      FIGS. 3   a - 3   f  are schematic drawings showing various components of the bus shown in  FIG. 2 .  
         [0030]     As can be seen in  FIGS. 3   a - 3   f , the system comprises a number of parts or bus units that in various configurations may be assembled into a backbone cable structure comprising the bus connection. In the simplest case, only two basic units are necessary to form the backbone, as shown in  FIG. 3   a  . In  FIG. 3   a , the first unit is a cable section  40 . Each cable section  40  includes electrical connectors  44  at each end that can mate with corresponding, complementary connectors  45 . Each cable section  40  comprises at least a power line and a signal line. Each cable section  40  may preferably be chosen from a number of uniform lengths for easier manufacture. As illustrated in  FIG. 3   e , the second basic unit is a three-way distribution hub  50  having three connectors  45 . As also can be seen from  FIG. 2 , the use of such distribution hubs  50  allows a cable to be daisy-chained throughout the installation and allows a branch cable to be connected into the main backbone system.  
         [0031]     Other possible units are a two-way hub  58  with two connectors  45  ( FIG. 3   c ), and a one-way or termination hub  42  having only one connector  45 , which is intended to be used as an end termination of the backbone ( FIG. 3   d ). Another example of a hub that may find use in the invention is three-way hub  54  ( FIG. 3   f ), having a repeater  55  incorporated into the hub such that the bus can be extended to an installation remotely located from the main installation.  
         [0032]     Another possible unit is a multi-outlet cable  70  ( FIG. 3   b ). This comprises a splitter  78  that splits the cable into several branches  79  and allows several devices to be connected into the system with only one connector.  
         [0033]     Referring again to  FIG. 2 , it is shown an illustrative embodiment of a bus connection system according to the invention. The backbone cable bus comprises a plurality of essentially interchangeable cable sections  40   a ,  40   b  . . .  40   g . Disposed between each adjacent pair of cable sections are hubs such as three-way electrical hubs  50   a ,  50   b .  50   c ,  50   d ,  50   e  or two-way extension hub  58 , as explained above with reference to  FIGS. 3   a - 3   f  . Each three-way hub facilitates the connection of a device or module such as a sensor, meter, or actuated device, as described further below These devices are connected into the backbone with the same cable units  40 , shown at  40   h ,  40   i ,  40   j ,  40   k . As shown, if there is no need to connect a module or device at a particular hub, a two-way extension hub such as  58  may be used. A two-way hub  58  may be removed and replaced by another three-way hub  50  at a later time, whenever it is desired to add a new device or module to the bus. Alternatively, instead of a two-way hub, another three-way hub may be used, with a blanking plug in the third connector. The last cable section in the backbone cable bus is connected to a one-way or termination hub  42 .  
         [0034]     It should be noted that the modules or devices may include electronics which enable them to function as terminations. However, it is preferred to terminate the bus in a special termination hub  42  as shown. This allows the cable to be “daisy-chained” throughout the installation and forming the backbone. If at a later date it will be necessary to extend the system the termination can be replaced by a junction box and new cables added as needed.  
         [0035]     The control module  14  may be located anywhere on the system.  
         [0036]      FIG. 2  also shows a pressure/transmitter sensor  62  connected to the backbone via the cable  40   i . Another sensor, for example a flowmeter  64 , is likewise connected to the backbone via cable  40   j.    
         [0037]     It is preferred to locate the male connectors  44  on the cables, but the cables may instead have female instead of male electrical connectors, the junction boxes having the corresponding male connectors  
         [0038]      FIG. 2  also shows an example of a satellite extension. Another installation located at some distance away from the main installation can be connected with an extension cable  56 . The larger step out distance makes it necessary to install a repeater or a modem to allow signals to travel a larger distance. The hub  54   a  is connected to or includes a repeater  55   a  which is further connected to the extension cable  56 . The far end of the cable  56  is connected to another repeater  55   b  connected to or included in the hub  54   b . This arrangement allows signals and power to be transmitted to the hub  54   b  at a considerable distance from the main installation. The hub  54   b  may form the start of a new backbone cable, similar to the one above, and enabling this sub-system to be operated from the control module  14 .  
         [0039]     The power for running the electrical devices may be supplied by one or more batteries housed in the control module. Alternatively, the power may be supplied through an umbilical from a remote location. Instead of being housed in the control module, the batteries may be independently retrievable units connected to the backbone in the same manner as described above.  
         [0040]     Another illustrative embodiment is shown in  FIG. 4 , wherein the bus comprises a harness unit  92  that is similar in nature to the multi-outlet cable  70  described with reference to  FIG. 3   b  above. However, instead of a splitter, the harness unit  92  includes a junction  93  that comprises wiring enabling all branches to be in electrical communication with each other, as will be described in more detail later. Each branch  91   a ,  91   b  . . .  91   n  terminates in an electrical connector  90   a ,  90   b  . . .  90   n , that in turn may be connected to devices. In the embodiment shown in  FIG. 4  there are five branches on one side and one branch on the other side, but there may be any number of branches on both sides. Several harness units  92  may be connected together in a daisy-chain arrangement, enabling the bus to be extended as necessary. The bus distributes both power and control signals.  
         [0041]     Each electrical connector may be connected to a corresponding module or device. The various modules or devices may include, but are not limited to, actuators, ( 13   a ,  13   b ), sensors ( 62 ), meters ( 64 ), control modules ( 14 ), additional junctions, or any other devices which may have utility in a subsea installation.  
         [0042]      FIG. 5  is a schematic block diagram showing an illustrative embodiment of the invention, wherein a number of modules or devices are interconnected by a bus. In this illustrative embodiment, the system comprises a control module  14 , a battery module  36 , and actuator modules  37  and  38 . Each module is connected to CAN-bus driver or control line  33  and power supply lines  34  and  35 .  
         [0043]      FIG. 7  is a schematic block diagram showing one possible wiring layout for the cable harness bus shown in  FIG. 4 , It will be understood by those skilled in the art that in the interest of clarity, a number of details have been omitted from  FIG. 7 . In this illustrative embodiment, the system comprises, a junction  93 , and electrical connectors  90   a ,  90   b  and  90   n  connected to the junction. Each of the electrical connectors is connectable to a device or module of any of the various types described above with respect to  FIG. 2  and  4 . Complementary connectors such as  92  are associated with the modules, and connect to the electrical connectors in a manner well know in the art.  
         [0044]     Each electrical connector is connected to the junction  93  via a plurality of lines, wires or cables, which communicate control signals and or electrical power to the electrical connectors, and thus to the individual modules. In the illustrated embodiment, there are six lines, wires or cables extending from the junction  93  to each electrical connector. For each connector, two lines comprise a control signal supply, two lines comprise a control signal return, one line comprises a power supply, and one line comprises a power return. It should be understood that in other embodiments, any number of control or power lines may utilized without departing from the spirit and scope of the invention.  
         [0045]     Specifically, control supply lines  94   a  and  94   b  extend from junction  93  to connector  90   a . Lines  94   a  and  94   b  are electrically connected to each other at the electrical connector  90   a . Similarly, control return lines  96   a  and  96   b  extend from junction  93  to connector  90   a . Lines  96   a  and  96   b  are also electrically connected to each other at the electrical connector  90   a . Finally, power supply line  110   a  and power return line  110   b  extend from junction  93  to electrical connector  90   a.    
         [0046]     Control supply lines  98   a  and  98   b  extend from junction  93  to connector  90   b . Lines  98   a  and  98   b  are electrically connected to each other at the electrical connector  90   b . Similarly, control return lines  100   a  and  100   b  extend from junction  93  to connector  90   b . Lines  100   a  and  100   b  are also electrically connected to each other at the electrical connector  90   b . Finally, power supply line  112   a  and power return line  112   b  extend from junction  93  to electrical connector  90   b.    
         [0047]     Control supply lines  106   a  and  106   b  extend from junction  93  to connector  90   n . Lines  106   a  and  106   b  are electrically connected to each other at the electrical connector  90   n . Similarly, control return lines  102   a  and  102   b  extend from junction  93  to connector  90   n . Lines  102   a  and  102   b  are also electrically connected to each other at the electrical connector  90   n . Finally, power supply line  114   a  and power return line  114   b  extend from junction  93  to electrical connector  90   n . In this particular embodiment, electrical connector  90   n  is a termination point. The corresponding complimentary connector  95  is not associated with a module. Connector  95  includes a load resistor  118  across the control supply and return lines to balance the system impedance.  
         [0048]     As can be seen in  FIG. 7 , the control signal supply and return lines are each arranged in a respective continuous circuit which passes through each electrical connector. Within the junction  93 , supply line  98   b  and return line  100   a  are connected across load resistor  108 , which also serves to balance the system impedance. Return line  100   a  is connected to return line  100   b  at electrical connector  90   b . Return line  100   b  is connected to return line  96   b  within junction  93 . Return line  96   b  is connected to return line  96   a  at electrical connector  90   a . Return line  96   a  is connected to return line  102   a  within junction  93 . Return line  102   a  is connected to return line  102   b  at electrical connector  90   n . Finally, return line  102   b  terminates within junction  93 .  
         [0049]     Supply line  98   b  is connected to supply line  98   a  at electrical connector  90   b . Supply line  98   a  is connected to supply line  94   b  within junction  93 . Supply line  94   b  is connected to supply line  94   a  at electrical connector  90   a . Supply line  94   a  is connected to supply line  106   a  with junction  93 . Supply line  106   a  is connected to supply line  106   b  at electrical connector  90   n . Finally, supply line  106   b  terminates within junction  93 .  
         [0050]     The continuous routing of the control signal supply and return lines through the electrical connectors ensures that the control signals will not be interrupted or degraded even when one or more modules are removed from the system. In this way the illustrated system is provided with “plug and play” functionality. The configuration also results in short stub lengths in the signal network.  
         [0051]     Power supply lines  110   a ,  112   a , and  114   a  are all connected at a power supply node  116   a  within junction  93 . Similarly, power return lines  110   b ,  112   b , and  114   b  are all connected at a power return node  116   b  within junction  93 . The illustrated routing of the power supply lines provides the shortest possible path for the power current, thus minimizing resistive line losses.  
         [0052]     Referring again to  FIG. 5 , each module  30 ,  36 ,  37 ,  38  includes a communication unit or bus controller that communicates according to the protocol on the control line  33 . This may be a CAN-bus or any other suitable bus communication protocol. In order to enable communication, the communication unit comprises a microprocessor or other data processing arrangement which is operatively controlled by executable code, including bus driver code, which is included in a memory. If a CAN-bus is used, the bus controller would be a CAN-bus controller and the bus driver would be a CAN-bus driver. The memory unit may comprise RAM, Programmable Read Only Memory (PROM), EPROM, EEPROM, or any other suitable type of memory unit. Clearly, other bus types can be employed. In other embodiments the memory unit may be reprogrammable from a remote location to facilitate upgrades and/or extensions of the system.  
         [0053]     When an action is initiated by the bus controller, the controller generates a message which includes a unique identifier or address for a particular module, and broadcasts this message on the bus. Each module scans the bus for any messages containing its particular address. Upon receiving&#39;such a message, a particular module may acknowledge the message, respond with any requested information, and/or perform a function according to the instructions in the message. When the command is successfully completed, a reply message may be issued by the module to report the status of the module or completion of the command. This reply message may then be acknowledged by the controller unit, thus completing the control sequence.  
         [0054]      FIG. 6  is a schematic block diagram further illustrating one possible embodiment of the control module. The control module  14  may comprise a controller  301  and a battery  303 , which may be independently disconnectable during operation. In another embodiment the controller  301  and the battery  303  may be permanently embedded in a single control module  14 . The controller  301  (indicated by dotted line) may be based on known processor bus architecture, and may comprise an internal bus  302  which connects a microprocessor  304  and a memory unit  312 . The memory unit  312  may comprise program code preferably held in a non-volatile memory such as Flash or EPROM, and data preferably held in a volatile memory such as RAM, respectively.  
         [0055]     The bus  302  may be further connected to a CAN bus adapter  308 . The CAN bus adapter may comprise an interface between the internal bus  302  and the CAN bus, providing communication between the processor and the modules. In particular, the CAN bus adapter  306  may comprise input circuits for receiving sensor input, and output circuits for providing appropriate actuator control signals, and input/output circuits for providing two-way communication with a remote station. The bus  302  may be further connected to a timer device (not illustrated).  
         [0056]     In one illustrative embodiment, the control module  14  further comprises a rechargeable battery  303 . The battery provides electrical power for the operation of the internal components of the control module, as well as control signals and power for the valve actuators. The battery also provides electrical power to any sensors and meters present in the installation. The battery  303  may normally be charged by power transferred from the remote station. Alternatively, a local power generator propelled by the flow output from the subsea installation (as indicated by  30  in  FIG. 1 ) may be employed as the primary energy source.  
         [0057]     The control module has a programmable processor and is arranged to receive new software downloaded from the remote control station through the communication cable and the communication adapter  308 . This allows the control module to be dynamic and to be updated to reflect changes, such as for example new sensors and new actuators.  
         [0058]     While the embodiments described above contemplate a system where each module receives only electrical control signals and electrical power, in other embodiments it may be necessary to provide certain components of the system with hydraulic control signals or power. To this end, in an additional embodiment of the invention as shown in  FIG. 8 , one or more of the modules may comprise an electro-hydraulic pod  80 . The pod  80  may include one or more control valves such as  120 . A hydraulic supply line  82  may be connected to one side of the pod, and distributed to one or more hydraulic input lines  124  which are routed to the control valves  120  within the pod  80 . On the other side of the valves, the hydraulic output lines  126  terminate in one or more hydraulic couplings such as  122 . An MQC (Multiple Quick Connectors) plate  128  comprises one or more complementary couplings which engage the hydraulic couplings  122  when the MQC plate is attached to the pod  80 . One or more hydraulic lines  130  extend from the MQC plate  128  to power one or more hydraulically operated devices, such as a valve actuator (not shown).  
         [0059]     In this embodiment the pod  80  comprises six control valves such as  120 , with six corresponding input lines and six corresponding output lines. The six control valves may be used to control six hydraulic actuators or other hydraulically operated devices. It will be well understood by those skilled in the art that any number of control valves may be provided in pod  80 , in order to meet the requirements of a particular installation. Pod  80  is provided with at least one electrical connector  132  for receiving a cable such as cable  40 , in order to connect the pod  80  to the bus.