GB2547439A

GB2547439A - Communications system

Info

Publication number: GB2547439A
Application number: GB1602794.8A
Authority: GB
Inventors: Puchianu Silviu
Original assignee: GE Oil and Gas UK Ltd
Current assignee: Baker Hughes Energy Technology UK Ltd
Priority date: 2016-02-17
Filing date: 2016-02-17
Publication date: 2017-08-23
Also published as: GB201602794D0

Abstract

A communication system 10 for transmitting data, having a data signal input 12, an AC power input 11, and a power and data port for connection to a power-carrying line 13, 14 (such as umbilical cable), a half-bridge 18 connected between the AC power input 11 and the power and data port, the half-bridge 18 comprising a plurality of switching elements (such as MOSFET transistors) which control the half-bridge 18, the data signal input 12 (such as digital PWM provided by FPGA 17) controlling the switching elements, such that the system 10 is operable to output an AC power signal with a data signal superimposed thereon via the power and data port, wherein a transformer 15 is provided between the AC power input 11 and the half-bridge 18. A method for transmitting data is also claimed. The invention relates to communication-on-power (COP) systems for use in subsea hydrocarbon well facilities.

Description

Communications System

This invention relates to a communication system, a master control station, a hydrocarbon extraction facility and a method of transmitting data.

Background of the Invention

Communication-on-power (COP) systems are electrical power and data transmission systems where an analogue data waveform is superimposed on a power waveform at one end and, at another other end, power and data filters are used to separate the power waveform from the data waveform.

For long offset power and data transmission systems (for example tens or hundreds of miles), this method allows for transmission of power from topside to subsea and bi-directional transmission of data on the same copper wires.

These systems are widely used in control systems for subsea hydrocarbon well facilities.

Fig. 1 schematically shows a known topside control system 1, i.e. the apparatus which would be located at the surface end of a transmission line, commonly known as an umbilical cable, for receiving AC mains power from an input 2 and receiving / outputting a communications data signal from an input / output 3 and outputting / receiving a composite signal, i.e. a communication-on-power signal (COPS) via port 4 to an underwater, e.g. subsea, location via that umbilical (not shown). The communications data signal received at input 3 would typically be provided by a master control station (MCS - not shown) typically having one or more SCS (subsea control system) computers. The MCS is the topside side of the SCS, and performs power conversion and distribution functions, and communication and control functions.

Looking at the power path first, the AC power signal is received by a powerconditioning front end subsystem 5 which outputs conditioned power. The conditioned power signal is fed to a transformer 6 which raises the voltage of the conditioned power, and then on to a diplexer 7, which includes a communications blocking filter subsystem (not shown). Looking at the data path, the communications data signal is received by an analogue modem 8, then passed to diplexer 7. Diplexer 7 produces a composite signal, output via port 4, known as a communication-on-power signal (COPS). This is output to the topside end of the umbilical (not shown) and transmitted to the subsea system.

It should be noted that the data path is bi-directional, so that data signals can also be sent topside from the subsea location. Such signals are conventionally produced by a subsea electronics module (SEM) connected to the subsea end of the umbilical and housed within a subsea control module (SCM) proximate the seabed. The SEM has various functions, including providing control signals to subsea Xmas trees, and receiving monitoring signals therefrom, as is well known in the art. To perform these functions, the SEM includes computing means. In the following discussion, “TX” will refer to signals sent from topside to subsea, while “RX” will refer to signals sent topside from subsea.

In use, the MCS communicates with the subsea part of the SCS using TX (transmit to subsea) and RX (receive from subsea) digital signals. A similar system (not shown) would conventionally be implemented at the subsea end of the umbilical cable, for receiving the COPS and splitting the power and communications data signals.

As prior art may be mentioned: EP-A1-2645587, US-A1-20150009735, EP-A1-2571160, US-A1-20140293488, “Design Considerations for ‘Dual Band’ Communications on Subsea Umbilicals as a Tool for Field Extensions of Subsea Production Control Systems” (Offshore Mediterranean Conference and Exhibition, 20-22 March, Ravenna, Italy, 2013, J. J. Evans et al.) and “Electrical Power Distribution for Subsea Application” (Offshore Technology Conference, 1-4 May, Houston, Texas, 2000, D. Wanderaas et al.).

The known COPS subsea control system as described above exhibits the following problems in particular: - It is component intensive and large in dimensions and footprint. The market is asking for lower footprint and higher RAM systems; and - It is based on antiquated and outdated analogue technology (such as transformer, analogue filters, etc).

It is an aim of the present invention to overcome these problems. The present invention provides an improved system with low footprint, and uses digital technologies to replace the standard analogue methodology.

This aim is achieved by using a new hybrid (analogue power generation plus digital PWM signal generation) system configuration based on: 1. AC power transmission using a classical transformer between the topside (MCS, ETU etc) and the subsea SCS subsystems (SEMs, PCDMs etc); 2. COPS generated by using PWM switch-mode technology; and 3. Modular, standard, off-the-shelf components.

Advantages of the new configuration include: i) Topside subsystem size reduction

There is a significant hardware reduction for the topside subsystem of the SCS, leading to a reduction in the physical size of the new topside subsystem of approximately 50% compared to current subsystems. The hardware reduction includes: a. No communications block filter and no diplexer (and subsequently also no HVTs (High Voltage Transients)); b. No modem. The functionality of the modem is replaced by a single PWM Control 1C (e.g. a very simple FPGA etc.). ii) SEM size reduction

There is a significant hardware reduction for the subsea subsystem of the SCS, leading to an associated reduction in the physical size of the SEM subsystem. The hardware reduction includes: a. No communications block filter or diplexer, (which also leads to the benefit of no HVTs (High Voltage Transients)). b. No modem. The functionality of the modem is replaced by a single PWM control 1C (e.g. a very simple FPGA etc.). iii) Off-the-shelf standard and modular components. iv) Higher RAM (Reliability Availability Maintainability) due to the potential for a higher level of redundancy (the potential use of more than one paralleled half-bridge “brick”). v) Higher versatility and controllability of power characteristics: voltage, frequency, power duty-cycle, etc. vi) A simplified method for the detection of the RX signal topside and of the TX signal subsea (no diplexer plus the availability of a constant value reference for the signal/data). vii) Lower engineering/manufacturing/testing/installation and commission cost due to the system simplification.

The new configuration affects the whole SCS, as follows: 1. For the topside SCS subsystem (MCS, ETU, etc.):

The new COPS configuration is based on classical transformer topology. 2. For the subsea SCS subsystems (e.g. SEM, PCDM, etc.):

The new SEM front-end (functionally compatible with the new Topside Control System) is based on PWM COPS half-bridge topology.

It should be noted that the solution presented here has been successfully simulated.

In accordance with a first aspect of the present invention there is provided a communication system for transmitting data, comprising: a data signal input, an AC power input, and a power and data port for connection to a power-carrying line, a half-bridge connected between the AC power input and the power and data port, the half-bridge comprising a plurality of switching elements which control the halfbridge, the data signal input controlling the switching elements, such that the system is operable to output an AC power signal with a data signal superimposed thereon via the power and data port, wherein a transformer is provided between the AC power input and the halfbridge.

In accordance with a second aspect of the present invention there is provided a master control station of a hydrocarbon extraction facility comprising a communication system according to the first aspect.

In accordance with a third aspect of the present invention there is provided a hydrocarbon extraction facility comprising a master control station according to the second aspect, and an umbilical cable connected to the power and data port.

In accordance with a fourth aspect of the present invention there is provided a method for transmitting data comprising the steps of: providing an AC power signal via a transformer, providing an input data signal, and using a half-bridge to combine the input data signal and the AC power signal from the transformer to form a composite signal having data superimposed on an AC power waveform.

The invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 schematically shows a known topside control system configuration; and

Fig. 2 schematically shows a topside control system configuration in accordance with an embodiment of the present invention; and

Fig. 3 schematically shows a communications-on-power subsea control system in accordance with an embodiment of the present invention.

Throughout this document, the following abbreviations are used: CBF - Communications (a.k.a. Comms) Blocking Filter COPS - Communication-On-Power System HVT - High Voltage Transient MCS - Master Control Station PWM - Pulse Width Modulation RAM - Reliability Availability Maintainability SEM - Subsea Electronic Module SCM - Subsea Control Module SCS - Subsea Control System FPGA - Field-Programmable Gate Array TCS - Topside Control System

ETU - Electric Test Unit, used in the field to test the functionality of the SCS PCDM - Power Conditioning and Distribution Module, an intermediate subsea module that distributes power and communications signals to/from a number of subsea subsystems 1C - Integrated Circuit MOSFET - Metal-Oxide-Semiconductor Field-Effect Transistor A topside control system configuration in accordance with a first embodiment of the invention is schematically shown in Fig. 2.

As shown, the topside control system (TCS) 10, being located within the MCS, is, similarly to the known arrangement, configured for receiving an AC mains power signal (at AC power input 11), receiving and transmitting a communications data signal (at data input / output 12), and transmitting to / receiving from a power-carrying line, i.e. an umbilical cable, COPS, with two copper wires 13, 14 of the umbilical being shown. The AC mains power signal is passed from input 11 to a transformer 15 having two transformer outputs. The first transformer output connects directly to one of the copper wires 14, while the other connects to a half-bridge (also known as a half-H bridge) 18. The communications data signal meanwhile is received via input / output 12 by a computing means 16, including an FPGA (Field Programmable Gate Array) 17 for PWM control, and then passed to the half-bridge 18. Half-bridge 18 outputs to the other copper wire 13. Half-bridge 18 comprises a plurality of switching elements which are controlled, via FPGA 17, by the input communications data signal. In this way, composite COPS is transmitted to, and through, the umbilical cable.

The topside system 10 may conveniently be housed at or within the MCS.

In use, the MCS communicates with the subsea part of the SCS using TX (transmit to subsea) and RX (receive from subsea) digital signals. The RX signal is collected from the umbilical top end, filtered and conditioned by an RX Discriminator (see Fig. 3), a very simple filtering device which filters out the power waveform, as is well-known in the art. The TX signal meanwhile is conditioned by subsystem 16, 17, which as shown comprises an FPGA 17, but may alternatively comprise a similar device (e.g. single board computer, programmable device, etc). The TX signal is conditioned to become a PWM (pulse width modulated) control signal that is used to open or to close subsea switching devices (IGBTs, MOSFETS, etc), (such as switching devices M6 and M7 shown in Fig. 3.) A complementary subsea control system configuration is also provided, which is generally similar to the topside system 10, though lacking a transformer since no power signal is transmitted to the surface. This system 20 is shown, inter alia, in Fig. 3.

Fig. 3 schematically shows a communications-on-power subsea control system (SCS) in accordance with an embodiment of the present invention, with additional circuit details. Reference numerals have been retained as far as possible. This figure shows a topside system 10 (housed within an MCS), a subsea system 20, a representation of the umbilical cable 30, as well as the front end (topside end) of a SEM 40 (which includes the subsea system 20). The subsea system 20 may conveniently be housed at or within an SEM, and / or SCM (not shown), or separately thereto.

Here it can be seen that the half-bridges 18, 28 comprise as switching elements solid state switches, i.e. MOSFETs M7, M8, M13, M14, controlled by respective FPGAs 17, 27. As shown, the topside system 10 includes an RX discriminator subsystem 41 connected between conductor 13 and computing means 16, while subsea system 20 includes a TX discriminator subsystem 42 connected between conductor 13 and the SEM computing means (not shown). These discriminator subsystems act to filter out the power waveform, similarly to prior art systems. A) Topside control system

As described above, the present topside control system design is based on a single half-bridge module for the formulation of the transmitted (TX) communication signal from topside to subsea. Such half-bridges are available commercially “off the shelf.

An exemplary suitable half-bridge module 18 has: - A low DC power input (for example +/- 30V DC), - Digital control PWM inputs. The digital PWM signals are computed by a single chip FPGA 17 (therefore there is no need for complicated modems). This chip translates the string of data coming from the MCS computer and MCS software into digital PWM switching signals that control the ON/OFF switching of the half-bridge 18. - An analogue TX signal/data output. The half-bridge module output is connected to one of the umbilical copper wire conductors 13.

Functionality:

Under PWM control, provided by FPGA 17, the half-bridge 18 generates the TX signal sent from topside to subsea. This signal is “imprinted” on the COPS power waveform.

The RX signal (data sent from subsea to topside) is “imprinted” on the COPS power waveform by the SEM 40 and is interpreted by a topside RX discriminator subsystem 41. B) Subsea control system

An equivalent system is provided at the subsea end of the umbilical which includes corresponding components.

The half-bridge module 28 used subsea has: - A low DC power input (for example +/- 30V DC), - Digital control PWM inputs. The digital PWM signals are computed by a single chip FPGA 27 (therefore there is no need for complicated modems). This chip translates the string of data coming from the SEM computing means into digital PWM switching signals that act to control the ON/OFF switching of the half-bridge 28. - An analogue RX signal/data output. The half-bridge module output is connected to one of the umbilical copper wire conductors 13.

Functionality:

Under PWM control, the half-bridge 28 generates the RX signal sent from subsea to topside. This signal is “imprinted” on the COPS power waveform.

The TX signal (data sent from topside to subsea) is “imprinted” on the COPS power waveform by the topside system and is interpreted by the SEM RX discriminator subsystem 42.

The above-described embodiments are exemplary only, and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art. For example, while the above embodiments show both surface and underwater locations being provided with communication systems in accordance with the present invention, only one of these locations could include such a system, with the other having, for example, a known communication system.

Claims

1. A communication system for transmitting data, comprising: a data signal input, an AC power input, and a power and data port for connection to a power-carrying line, a half-bridge connected between the AC power input and the power and data port, the half-bridge comprising a plurality of switching elements which control the halfbridge, the data signal input controlling the switching elements, such that the system is operable to output an AC power signal with a data signal superimposed thereon via the power and data port, wherein a transformer is provided between the AC power input and the halfbridge.

2. A communication system according to claim 1, wherein the transformer has first and second transformer outputs, the first transformer output feeding to the halfbridge.

3. A communication system according to claim 2, wherein the power and data port comprises first and second output lines, the first output line being connected to the half-bridge and the second output line being connected to the second transformer output.

4. A communication system according to any of claims 1 to 3, comprising a discriminator system for filtering signals received from the power and data port.

5. A master control station of a hydrocarbon extraction facility comprising a communication system according to any preceding claim.

6. A hydrocarbon extraction facility comprising a master control station according to claim 5, and an umbilical cable connected to the power and data port.

7. A hydrocarbon extraction facility according to claim 6, comprising, at an underwater location, a subsea electronics module, the subsea electronics module including a communication system having: an underwater power and data port for connection to the power-carrying line, an underwater half-bridge connected to the power and data port, the underwater half-bridge including a plurality of switching elements controlled by a data signal.

8. A hydrocarbon extraction facility according to claim 7, wherein the powercarrying line is arranged to supply power to the underwater half-bridge.

9. A hydrocarbon extraction facility according to either of claims 7 and 8, comprising a discriminator system for filtering signals received from the underwater power and data port.

10. A method for transmitting data comprising the steps of: providing an AC power signal via a transformer, providing an input data signal, and using a half-bridge to combine the input data signal and the AC power signal from the transformer to form a composite signal having data superimposed on an AC power waveform.

11. A method according to claim 10, comprising the step of taking first and second outputs from the transformer, and connecting the half-bridge to said first output.

12. A method according to either of claims 10 and 11, wherein the half-bridge comprises switching elements, the method comprising using the input data signal to control the switching elements.

13. A method for transmitting data between a surface location and an underwater location of a hydrocarbon extraction facility, comprising providing a surface communication system at the surface location and an underwater communication system at the underwater location, at least one communication system comprising a half-bridge, and using a method according to any of claims 10 to 12 to transmit data from one location to the other via an umbilical cable.

14. A system substantially as herein described with reference to the accompanying figures 2 and 3.

15. A method substantially as herein described with reference to the accompanying figures 2 and 3.