Abstract:
A method of operating a remotely operated underwater vehicle (ROV) includes launching the ROV from a vessel into water; supplying a direct current (DC) power signal to the ROV from the vessel via an umbilical; and sending a first command signal to the ROV from the vessel via the umbilical while supplying the DC power signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to a direct current (DC) powered remotely operated underwater vehicle (ROV) and umbilical. 
         [0003]    2. Description of the Related Art 
         [0004]    Work class ROVs employ electric motors of up to several hundred horsepower. Power is typically supplied by four hundred eighty volt three phase alternating current (AC) which requires cables of relatively large diameter. The cable adds significant weight and drag to the ROV, often comprising the majority of the load on the vehicle. This results in a reduction in the speed and maneuverability of the vehicle and in some conditions, may impact the ability to predictably control the ROV. The additional drag also decreases the efficiency of the ROV as additional thruster power is required to overcome the drag on the cable. 
       SUMMARY OF THE INVENTION 
       [0005]    Embodiments of the present invention generally relate to a direct current (DC) powered remotely operated underwater vehicle (ROV) and umbilical. In one embodiment, a method of operating an ROV includes launching the ROV from a vessel into water; supplying a DC power signal to the ROV from the vessel via an umbilical; and sending a first command signal to the ROV from the vessel via the umbilical while supplying the DC power signal. 
         [0006]    In another embodiment, an ROV includes a chassis; a float connected to the chassis; a thruster connected to the chassis, the thruster including an electric motor; a manipulator connected to the chassis; a video camera connected to the chassis; a light connected to the chassis; a diplexer connected to the chassis and operable to connect to a two conductor tether and split a composite signal from the tether into a DC power signal and a first command signal; a power converter connected to the chassis and operable to receive the DC power signal from the diplexer and supply a second power signal to the thruster motor; and a programmable logic controller connected to the chassis and operable to receive a first command signal from the diplexer, modulate a video signal from the camera, and transmit the video signal to the diplexer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0008]      FIGS. 1A and 1B  illustrate deployment of an ROV to a subsea production tree, according to one embodiment of the present invention. 
           [0009]      FIG. 2  is an isometric view of the ROV. 
           [0010]      FIG. 3A  is a layered view of the umbilical and tether.  FIG. 3B  is an end view of the umbilical and tether. 
           [0011]      FIG. 4  is a system diagram illustrating power supply and data communication between the ROV and the support vessel. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIGS. 1A and 1B  illustrate deployment of an ROV  100  to a subsea production tree  5 , according to one embodiment of the present invention. 
         [0013]    A subsea wellbore  10  has been drilled from a floor  1   f  of the sea  1  into a hydrocarbon-bearing (i.e., crude oil and/or natural gas) reservoir (not shown). A string of casing (not shown) has been run into the wellbore  10  and set therein with cement (not shown). The casing has been perforated to provide to provide fluid communication between the reservoir and a bore of the casing. A wellhead (not shown) has been mounted on an end of the casing string. A string of production tubing may extend from the wellhead to the formation to transport production fluid from the formation to the seafloor  1   f.  A packer (not shown) may be set between the production tubing and the casing to isolate an annulus formed between the production tubing and the casing from production fluid. 
         [0014]    The Christmas or production tree  5  may be connected to the wellhead, such as by a collet, mandrel, or clamp tree connector. The tree  5  may be vertical or horizontal. If the tree  5  is vertical, it may be installed after the production tubing is hung from the wellhead. If the tree  5  is horizontal, the tree may be installed and then the production tubing may be hung from the tree  5 . The tree  50  may include fittings and valves to control production from the wellbore into a pipeline (not shown) which may lead to a production facility (not shown), such as a production vessel or platform. 
         [0015]    A support vessel  15  may be deployed to a location of the subsea tree  5  to perform an intervention operation. The support vessel  15  may include a dynamic positioning system to maintain position of the vessel  15  on the waterline  1   w  over the tree  5  and a heave compensator to account for vessel heave due to wave action of the sea  1 . The vessel  15  may further include a tower and winches for deploying tools to the tree  5  for performing the intervention operation. 
         [0016]    The ROV  100  may be launched into the sea  1  from the support vessel  15  by a launch and recovery system (LARS)  30  to assist the intervention operation. The LARS  30  may be mounted on a working deck of the support vessel  15 . The ROV  100  may be controlled and supplied with power from a control van  300  carried onboard the support vessel  15 . The control van  300  (see  FIG. 4 ) may include a control console  302 , a programmable logic controller (PLC)  305   v,  a power converter  310   v,  and a diplexer (DIX)  315   v.  The control van  300  may receive a low voltage alternating current (AC) power signal from a generator  301  of the vessel or include its own diesel powered generator. The low voltage may be greater than or equal to one hundred volts, two hundred volts, three hundred volts, or four hundred volts and less than one kilovolt. The power converter  310   v  may include a rectifier for converting the low voltage AC signal received from the generator to a low voltage direct current (DC) power signal for delivery to the DIX  315   v  for transmission to a tether management system (TMS)  50  via an umbilical  200   u.    
         [0017]    Alternatively, the power converter  310   v  may include a transformer (not shown) for stepping the low voltage AC power signal to a medium voltage AC power signal, such as greater than or equal to one kilovolt, and then the power converter may convert the medium voltage AC power signal to a medium voltage DC power signal for transmission over the umbilical. Additionally, the power converter  310   v  may include a transformer for reducing the low voltage AC power signal to an ultra-low voltage AC signal, such as less than or equal to one-hundred twenty volts, and then the power converter may convert the ultra-low voltage AC signal to an ultra-low voltage DC power signal for powering the control console  302  and PLC  305   v  or the control van  300  may include an additional power converter (not shown) for powering the control console and PLC. 
         [0018]    The PLC  305   v  may receive commands from the ROV pilot (not shown) via the control console  302  and include a data modem (not shown) and multiplexer (not shown) for modulating and multiplexing the commands into a data signal for delivery to the DIX  315   v  and transmission to the TMS  50  via the umbilical  200   u.  The DIX  305   v  may combine the DC power signal and the data signal into a composite signal and transmit the composite signal to the TMS  50  via the umbilical  200   u  and to the ROV  100  via tether  200   t  (and umbilical  200   u ). The DIX  305   v  may be in electrical communication with the umbilical  200   u  via an electrical coupling (not shown), such as brushes or slip rings, to allow power and data transmission through the umbilical while the LARS  30  winds and unwinds the umbilical. The control console  302  may include one or more hand-operable controllers, such as joysticks  302   c,  and one or more video monitors  302   v.  The multiplexing scheme may be frequency division and commands to the TMS  50  may have a separate channel than commands for the ROV  100 . Communication among the van  300 , TMS  50 , and ROV  100  may be full duplex. The PLC  305   v  may also receive data signals from the ROV  100 , such as video signals from the cameras  125 , via a tether  200   t,  umbilical  200   u,  and DIX  315   v , demodulate and demultiplex the data signals, and display the data signals on one of the monitors  302   v.  In this manner, the ROV pilot may operate the ROV  100  from the control van  300 . The PLC  305   v  may also include an autopilot (not shown) to assist the ROV pilot in operation of the ROV  100 . The ROV pilot may selectively disengage and engage the autopilot and operate the ROV  100  in tandem with the autopilot. 
         [0019]    The LARS  30  may include a frame, a winch  31 , a boom, a boom hoist, and a hydraulic power unit (HPU)  320   v.  The LARS  30  may be the A-frame type (shown) or the crane type (not shown). For the A-frame type LARS  30 , the boom may be an A-frame pivoted to the frame and the boom hoist may include a pair of piston and cylinder assemblies (PCAs), each PCA pivoted to each beam of the boom and a respective column of the frame. The HPU  320   v  may include a hydraulic fluid reservoir, a hydraulic pump, and one or more control valves for selectively providing fluid communication between the reservoir, the pump, and the PCAs. The hydraulic pump may be driven by an electric motor. The winch may include a drum having the umbilical wrapped therearound and a motor for rotating the drum to wind and unwind the umbilical  200   u.  The winch motor may be electric or hydraulic. A sheave may hang from the A-frame. The umbilical  200   u  may extend through the sheave and an end of the umbilical may be fastened to a cablehead of the TMS  50 . The frame may have a platform for the TMS/ROV  50 ,  100  to rest. Pivoting of the A-frame boom relative to the platform by the PCAs may lift the TMS/ROV  50 ,  100  from the platform, over a rail of the vessel  15 , and to a position over the waterline  1   w.  The winch may then be operated to lower the TMS/ROV  50 ,  100  into the sea  1 . Recovery of the ROV/TMS  50 ,  100  may be performed by reversing the steps. 
         [0020]    The ROV  100  may be launched together with the TMS  50 . A top of the ROV  100  may be fastened to the TMS  50  for a top-hat type TMS. Alternatively, the ROV may be housed in the TMS for a cage type TMS (not shown). The TMS  50  may be connected to the LARS  30  by the umbilical  200   u.  The TMS  50  may include a frame, a cablehead, a winch  51 , a PLC  305   t  (see  FIG. 4 ), a power converter (PC)  310   t,  and a DIX  315   t.  The winch  51  may include a drum having the tether  200   t  wrapped therearound and an electric motor for rotating the drum to wind and unwind the tether  200   t.  The power converter  310   t  may receive the low voltage DC power signal from the umbilical via the DIX  315   t,  include an inverter for converting the DC power signal to an AC power signal, and a transformer for stepping the low voltage AC power signal to an ultra-low voltage AC power signal and a rectifier for converting the ultra-low voltage AC to ultra-low voltage DC power signal for powering the PLC  305   t.  The power converter  310   t  may include one or more single phase active bridge circuits as discussed and illustrated in US Pub. Pat. App. 2010/0206554, which is herein incorporated by reference in its entirety. The circuits may be arranged in series to gradually step the DC voltage from low to ultra-low. The converter  310   t  may include a three-phase inverter for receiving the low voltage DC power signal and outputting a three phase low voltage AC signal for powering the winch motor. The converter  310   t  may include a switch for selectively providing the AC signal to the winch motor and the switch may be in communication with the TMS PLC  305   t  for operation thereof. The converter  310   t  may also be capable of reversing the polarity of the AC power signal to the winch motor and the TMS PLC  305   t  may control the polarity. 
         [0021]    Similar to the control van PLC  305   v,  the TMS PLC  305   t  may include a modem and modulator for receiving command signals from the DIX  315   t.  The TMS PLC  305   v  may then release the ROV  100  and operate the tether winch  51  in response to receipt of the appropriate command signals. The TMS  50  may further include one or more sensors (not shown). The TMS PLC  305   t  may send the sensor data to the van PLC  305   v  along a dedicated channel. Additionally, the TMS  50  may include one or more thrusters (not shown) so that the vessel  15  may be moved away from over the tree  5  while the ROV  100  remains at the tree. Additionally, the TMS  50  may include one or more accessory tools (not shown) for the ROV  100 . Alternatively, the TMS  50  may include an HPU (not shown) and the winch motor may be hydraulic. 
         [0022]    The ROV  100  may be connected to the TMS  50  by the tether  200   t.  The tether  200   t  may be in power and data communication with the umbilical  200   u  so that the ROV  100  and TMS  50  are connected to the umbilical  200   u  in a parallel arrangement. The TMS  50  may include an electrical coupling (not shown) similar to the electrical coupling discussed above providing power and data communication between the tether  200   t  and the umbilical  200   u.    
         [0023]    The ROV/TMS  50 ,  100  may be deployed to a depth proximate to the tree  5 . The ROV  100  may then be released from the TMS  50  and driven to the tree by the ROV pilot. The TMS  50  may unwind an excess of the tether  200   t  to maintain sufficient slack in the tether so that the ROV  100  is isolated from vessel heave. The ROV  100  may transmit video to the pilot for inspection of the tree  50 . The ROV  100  may then interface with the tree  5  to assist in the intervention operation. Alternatively, the ROV  100  may be deployed to assist in a drilling operation, completion operation, or abandonment operation. Alternatively, the ROV  100  may be deployed to conduct a subsea pipeline inspection operation. 
         [0024]      FIG. 2  is an isometric view of the ROV  100 . The ROV  100  may be an unmanned, self-propelled submarine that includes a chassis  105 , a float  110 , a cablehead, a PLC  305   r  (see  FIG. 4 ), a power converter  310   r,  a DIX  315   r,  an HPU  320   r,  and one or more: thrusters  115   f,v,t , lights  120 , video cameras  125 , manipulators  130 , and sensors  325 . Each of the ROV components may be connected to the chassis  105 . The ROV  100  may be classified as a work-class, meaning that the thrusters may be capable of producing at least one hundred, one hundred fifty, or two hundred horsepower. The chassis  105  may be made from a metal or alloy, such as aluminum or stainless steel, and the float  110  may be made from a buoyant material, such as syntactic foam, and be located at a top of the chassis. The float  110  may be configured to provide slightly positive buoyancy or neutral buoyancy at the expected working depth. 
         [0025]    The thrusters may include one or more longitudinal thrusters  115   f,  one or more transverse thrusters  115   t,  and one or more vertical thrusters  115   v.  The horizontal thrusters  115   f,t  may be fixed (shown) or vectored (not shown). The thruster motors may be reversible, thereby affording complete three-dimensional movement of the ROV  100 . Each thruster  115   f,v,t  may include a propeller, a shroud, and an electric motor for driving the propeller. Each thruster motor may directly drive each propellor or include a gearbox. Each thruster may have a dedicated motor or two or more thrusters may be driven by one motor and a gearbox. Alternatively, the thruster motors may be hydraulic and driven by the HPU  320   r.    
         [0026]    The sensors  325  may include one or more of: a depth gage, altimeter (i.e., height-off bottom sonar), scanning sonar, temperature sensor, laser line scanner, gyroscope, Doppler velocity log, and/or magnetometer. The cameras  125  may be monochrome or color, standard definition, enhanced definition, high definition, or low light and may be fixed or have panning and tilting capability. As shown, the ROV  100  may include a pair of front facing cameras  125  for stereo vision. Each camera  125  may include its own channel for multiplexed transmission over the tether  200   t  and umbilical  200   u.  Although only a pair of front facing cameras  125  are shown, the ROV may additionally have one or more rear facing, left and right facing, bottom facing, and/or top facing cameras. The lights  120  may include one or more of Hydrargyrum medium-arc iodide (HMI) lights, high intensity discharge (HID) lights, quartz halogen, high intensity light emitting diode (LED) and/or strobe lights. The intensity of the lights  120  may also be adjustable from the surface to accommodate seafloor conditions (i.e., low beam/high beam). As with the cameras  125 , although only a set of front facing lights  120  are shown, the ROV  100  may additionally have one or more rear facing, left and right facing, bottom facing, and/or top facing lights. The lights  120  may also be fixed or have pan and tilt capability. 
         [0027]    The manipulators  130  may each include an arm and a pair of opposable claws and may each have multi-degree of freedom capability (i.e., shoulder, elbow, and wrist movement). The jaws of each manipulator  130  may also be removable for replacement by other tools, such as a snip or drill, carried by the TMS  50 . Each manipulator  130  may include a shoulder, aft arm, forearm, wrist, and hand, each portion pivoted to one or more of the other portions and PCAs and/or hydraulic motors for articulating the portions. The HPU  320   r  may include a hydraulic fluid reservoir, a hydraulic pump, and one or more control valves for selectively providing fluid communication between the reservoir, the pump, and the PCAs/hydraulic motors. The hydraulic pump may be driven by an electric motor. Alternatively, the manipulators  130  may include electric actuators instead of the PCAs/hydraulic motors, such as lead screws, linear motors, and/or stepper motors, and the HPU  320   r  may be omitted. 
         [0028]      FIG. 3A  is a layered view of the umbilical  200   u  and tether  200   t.    FIG. 3B  is an end view of the umbilical  200   u  and tether  200   t.  Each of the umbilical  200   u  and the tether  200   t  may include an inner core  205 , an inner jacket  210 , a shield  215 , an outer jacket  230 , armor  235 ,  240 , and a cover  245 . Alternatively, the cover  245  may be omitted. 
         [0029]    The inner core  205  may be the first conductor and made from an electrically conductive material, such as aluminum, copper, or alloys thereof. The inner core  205  may be solid or stranded. The inner jacket  210  may electrically isolate the core  205  from the shield  215  and be made from a dielectric material, such as a polymer (i.e., polyethylene). The shield  215  may serve as the second conductor and be made from the electrically conductive material. The shield  215  may be tubular, braided, or a foil covered by a braid. The outer jacket  230  may electrically isolate the shield  215  from the armor  235 ,  240  and be made from a seawater-resistant dielectric material, such as polyethylene or polyurethane. The armor may be made from one or more layers  235 ,  240  of high strength material (i.e., tensile strength greater than or equal to one hundred, one fifty, or two hundred kpsi) to support the deployment weight (weight of the TMS  50  and ROV  100 ) so that the umbilical  200   u  may be used to launch and remove the TMS/ROV into/from the sea. The high strength material may be a metal or alloy and corrosion resistant, such as galvanized steel, aluminum, or a polymer, such as a para-aramid fiber. The armor may include two contra-helically wound layers  235 ,  240  of wire, fiber, or strip. 
         [0030]    Additionally, each of the umbilical  200   u  and the tether  200   t  may include a sheath  225  disposed between the shield  215  and the outer jacket  230 . The sheath  225  may be made from lubricative material, such as polytetrafluoroethylene (PTFE) or lead, and may be tape helically wound around the shield  215 . If lead is used for the sheath  225 , a layer of bedding  220  may insulate the shield  215  from the sheath and be made from the dielectric material. Additionally, a buffer  250  may be disposed between the armor layers  235 ,  240 . The buffer  250  may be tape and may be made from the lubricative material. The cover  245  may be made from an abrasion resistant material, such as a polymer, such as polyisoprene or polyethylene. 
         [0031]    Due to the coaxial arrangement, each of the umbilical  200   u  and the tether  200   t  may have an outer diameter  255  less than or equal to one and one-quarter inches, one inch, or three-quarters of an inch. As discussed above, the each of the umbilical  200   u  and tether  200   t  may be capable of delivering at least seventy-five, one hundred twelve, or one hundred fifty kW (for one-hundred, one hundred fifty, or two hundred horsepower thrusters, respectively). As compared to a three conductor (phase) AC umbilical/tether, a significant reduction in weight and diameter is achieved, thereby improving performance of the ROV  100  and improving the portability of the LARS  30  and TMS  50 . For example, replacing a three conductor AC tether/umbilical with the coaxial umbilical/tether may reduce the diameter from two inches to point six five inches and reduce the weight from one point eight pounds per foot to one-half pound per foot. 
         [0032]    Alternatively, the umbilical  200   u  and/or the tether  200   t  may include additional conductors (not shown) for conducting the data signals separately from the power signal. The additional conductors may be electrically conductive and/or optical fiber. If the additional conductors are electrically conductive, they may additionally carry (along same or different conductors) an ultra-low voltage power signal for powering the tether and/or ROV PLCs  305   t,v  instead of converting the signals from the low voltage power signal. Alternatively, the tether armor may be made from a lower strength material or omitted as the tether  200   t  may not have to support the weight of the ROV  100  and the TMS  50 . The low strength material may be may be a polymer, such as an aliphatic polyamide. 
         [0033]      FIG. 4  is a system diagram illustrating power supply and data communication between the ROV  100  and the support vessel  15 . 
         [0034]    Similar to the tether power converter  310   t,  the ROV power converter  310   r  may receive the low voltage DC power signal from the tether  200   t  via the DIX  315   r , include an inverter for converting the DC power signal to an AC power signal, and a transformer for stepping the low voltage AC power signal to the ultra-low voltage AC power signal, and a rectifier for converting the ultra-low voltage AC to ultra-low voltage DC power signal for powering the PLC  305   r.  The power converter  310   r  may also include the one or more single phase active bride circuits, discussed above. The circuits may be arranged in series to gradually step the DC voltage from low to ultra-low. The converter  310   r  may include a three-phase inverter for receiving the low voltage DC power signal and outputting a three phase low voltage AC signal for powering the thruster motors and the HPU motor. The converter  310   r  may also be capable of reversing the polarity of the AC power signal to the thruster motors and the ROV PLC  305   r  may control the polarity. The converter  310   r  may supply the lights  120  with low voltage or ultra-low voltage AC power signals. 
         [0035]    Similar to the TMS PLC  305   t,  the ROV PLC  305   r  may include a modem and modulator for receiving command signals from the DIX  315   r.  The ROV PLC  305   r  may then operate the thrusters and/or the manipulators in response to receipt of the appropriate command signals. The ROV PLC  305   r  may send the sensor data to the van PLC  305   v  along a dedicated channel. Each sensor  325  may have a dedicated channel or data from two or more of the sensors may be time division multiplexed on a single channel. The ROV PLC  305   r  may relay ultra-low voltage DC power signals to the sensors  325  and the cameras  125 . The ROV PLC  305   r  may also be in data communication with the sensors  325  and the cameras  125 . The ROV PLC  305   r  may receive data from the sensors  325  and the cameras  125 , modulate and multiplex the data, and transmit the data to the control van PLC  305   v  via the DIX  315   r,  the tether  200   t,  the umbilical  200   u,  and the DIX  315   v.  The ROV PLC  305   r  may also be in communication with the HPU control valves for selectively operating the valves to control movement of the manipulators  130 . 
         [0036]    The ROV  100  may further include a motor controller (not shown) for operating the thruster motors and the HPU motor. Each thruster motor and the HPU motor may be an induction motor. The motor controller may be integrated with the power converter  310   r  or each motor may have its own motor controller. The motor controller may be in data communication with the PLC  305   r  for receiving pilot/autopilot commands from the control van  300  and sending diagnostic data to the control van  300  (i.e., RPM and temperature). The motor controller may be capable of simple control (i.e. constant speed). Alternatively, the motor controller may be capable of controlling the speed of the motors, such as by variable frequency drive. In this alternative, the motor controller may receive the low voltage DC power signal and construct quasi-sinusoidal motor power signals (i.e., three phases) for speed controlled operation of the motors. 
         [0037]    Alternatively, the motors may be reluctance motors, such as switched reluctance or synchronous reluctance. The reluctance motors may each include a wound stator and a rotor having a multi-lobed laminate core. The motor controller may output stepped, trapezoidal, or sinusoidal power signals to the reluctance motors and the motor controller may control the speed of the motors by controlling the frequency of the power signal. The motor controller may employ an asymmetric bridge or half-bridge circuit for control of the reluctance motors. 
         [0038]    Alternatively, the motors may be permanent magnet motors, such as brushless DC motors (BLDC). The BLDC motors may each include a wound stator, a permanent magnet rotor, and a rotor position sensor. The permanent magnet rotor may be made of a rare earth magnet or a ceramic magnet. The rotor position sensor may be a Hall-effect sensor, a rotary encoder, or sensorless (i.e., measurement of back EMF in undriven coils by the motor controller). The BLDC motor controller may be in communication with the rotor position sensor and include a bank of transistors or thyristors and a chopper drive for complex control (i.e., variable speed drive and/or soft start capability). Alternatively, the motors may be universal motors. Alternatively, the motors may be brushed permanent magnet motors or any other type of AC or DC motors. 
         [0039]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.