NO335595B1 - POWER MANAGEMENT IN SEA VESSELS - Google Patents

Abstract

The invention relates to a system and method for improving the efficiency of the power plant in a vessel. The system comprises a motion reference unit measuring means for monitoring vessel movements and prediction means for predicting vessel movements based on said measurements, wherein the system also comprises a dynamic load prediction unit which calculates the dynamic load on the system at least in part based on said predicted movements.

Description

The invention relates to a system and a method for increasing the efficiency of the power plant in a vessel, in particular by reducing load and frequency variations caused by variations in large consumer loads in the power distribution system for sea vessels.

Field of the invention

The present invention relates to a method for reducing load and frequency variations in the high-voltage power distribution system while the vessel is controlled by a dynamic positioning system (DP) or equivalent by adjusting the available power or torque for the DP-controlled thrusters in such a way that the conditions for to maintain position is not undermined. The present invention provides a way of combining load control and position/velocity control that has never been done before.

Background for the invention

A dynamic positioning system controls longitudinal, lateral and rotational movement of a vessel, rig, barge or equivalent. A vessel steered by a DP steering system or equivalent must always seek to fulfill an instructed speed and position about the axes being steered. The DP system controls the vessel movements using thrusters, propellers and rudders. For the sake of simplicity, and without loss of generality, we will use the term thruster for any means of propulsion in the remainder of the description of the invention. The most common power system today is diesel-electric, which means that the thrusters are driven by an electric drive motor and that the power is supplied from power generators such as diesel generators, fuel cells, gas turbines, engines that run on two fuels, etc. The power is obtained from a power plant with many consumers, where the thrusters normally dominates. The power is normally supplied to the power plant by diesel generators. Normally, a large number of diesel generators are required to be connected to the power plant to maintain a stable frequency when the consumer load varies, for example from compensation for hoists, hoists, winches and cranes. Frequency variations can be fatal for the power system, and can lead to power outages, failure of subsystems, synchronization problems for generators to be connected to the power supply network and increased fuel consumption. For many years, the offshore industry has wanted to reduce the number of online generators without the risk of frequency variations and potential power outages, but no tangible solution has been produced for this problem. There are several benefits to reducing the number of online generators, such as reduced Nox emissions, reduced soot, reduced fuel consumption and reduced engine maintenance.

In the doctoral dissertation by Damir Radan "Integrated Control of Marine Electrical Power Systems", Department of Marine Technology, Norwegian University of Science and Technology, 28, January 2008, several aspects of regulation of power systems are discussed, and among them the reduction of load and frequency variations in a power distribution system.

A system to handle this is proposed in Norwegian patent application no. 20120344, which concerns a method for reducing frequency and/or voltage variations in the power supply using predicted future load changes used to adjust the speed/power control system on a motor generator set (MGS - Motor Generator Set ) or a turbojet support for the engine or an automatic voltage regulator (AVR - Automatic Voltage Regulator) on the generator. Several predictive load systems are mentioned in the application, including DP thruster output, setting change or start/stop requests to large consumers and cyclical load predictions based on pattern recognition. The solution discussed in application NO20120344 has the disadvantage that it is based primarily on events that have occurred, which has a limited value in a somewhat chaotic environment.

The present application is also related to NO20120507 which describes a system for dynamic load prediction by integrating total predicted load changes on large consumers or other sudden reconfiguration together with the speed/power/voltage control system combined with methods for predicting load variations.

Other solutions for optimizing demand supply are described in US2013/184901, and systems for handling wave compensation and long-term usage patterns in power plants are described in US8265811 and in US2013/116830, respectively. None of these, however, take into account the effect of external forces that affect power consumption. This is achieved with a system as set forth in the appended patent claims.

More specifically, the invention includes the use of a motion reference unit (MRU - Motion Reference Unit; or a vertical reference unit - VRU) which provides roll, pitch and heave positions and speeds (RPH - roll, pitch, heave) to predict dynamic load from wave movements on the ship's effect system. The DP systems mainly concern movements in the longitudinal, lateral and yaw directions (SSY - surge, sway, yaw) and use corresponding sensor inputs. Consequently, RPH-based load prediction subsystems will not produce unwanted closed loops or chain reactions together with the DP system. The load predictions are calculated from direct RPH measurements for motion prediction in combination with control loop states from all RPH-based subsystems at large consumers. The RPH-based load predictions can be used in the predicted load allocation (Predicted Load Allocation) in the DLP application in the same way as the other mentioned load predictors. The load prediction can be performed using two different methods. Short-term that indicates the momentary need due to wave movements or equivalent where the path of the vessel movements is predicted and is thereby able to calculate the momentary need for compensation. This can, for example, be based on known models of the vessel and extrapolation based on the measured movements or simulations.

Long-term movements can be based on measurements over longer periods of time which give, for example, the frequencies and amplitudes of the RPH movements, which may require changes in the load allocation in the power plant. The statistical methods may be of any suitable type.

The present invention will be described in more detail below with reference to the attached drawings which illustrate the invention by means of examples.

Fig. 1 schematically illustrates the vessel with associated equipment.

Fig. 2 illustrates the system function.

Reference is made to Figure 1, where the RPH measurements from a vertical reference unit such as MRU 1 can be used to provide surge load predictions to the power system based on RPH-based high-consumption subsystems including:

- hydraulic cranes 2

- drill heave compensation / riser tensioner 3

helicopter deck stabilization 4

electric winch / dynamic anchoring system 5

yaw stabilization systems such as rudder yaw stabilization 6 and active fins 7

- propeller ventilation predictions 8

All of these will have a power consumption that depends on the vessel movements and can be predicted based on empirical or calculated information. General cyclic load variations from wave motions can be calculated using MRU-RHP measurements directly instead of pattern recognition based on output from high consumption subsystems. This also includes statistical information such as

such as mean movement amplitudes and frequencies.

In Figure 2, the motion reference unit 10 provides an RPH signal to the various high-consuming subsystems for dynamic control purposes, and to the dynamic load prediction (DLP) system 19 for motion prediction. Motion prediction combined with output from high-consuming subsystems 11-16 is used to estimate the power needed in the dynamic load prediction (DLP) system 19, which in turn supplies the dynamic load control (DLC - Dynamic Load Control) system with information to control the the available generators 21. A load distribution system is also used to control how the predicted load and available power are allocated in the system.

The various power consumers that compensate for the movements will be regulated according to their specific needs, based on known information about the characteristics during work. The exemplified units 11-16 above can thus be control systems as described below.

Hydraulic cranes 11

Active heave compensation (AHC) is a technique used on lifting equipment such as hydraulic cranes to reduce the impact of waves during offshore work. AHC comprises a control system that actively attempts to compensate for any movement at a specific point by applying power to gain accuracy. The active heave compensation is typically used to keep the hydraulic crane's load at a fixed position in relation to the seabed, and to avoid the vessel movement being transferred to the load. The AHC control is connected to a motion reference unit (MRU) which feeds the system with accurate real-time information about the movement of the crane end. The crane operator will spool out and reel in on the winch to compensate for the crane end movement.

Marine riser systems 14

A marine riser tensioner is a device used on an offshore drilling vessel that provides an almost constant force directed upwards on the drill pipe regardless of the floating drilling vessel's movements. The marine riser is connected to the wellhead on the seabed and the tensioner must therefore handle the relative movements between the riser and the rig. If there were no tensioners and the rig was moved down, the riser would bend; if the rig is raised, large forces would be transferred to the riser and it would be stretched and damaged. The riser control is connected to a motion reference unit (MRU) which feeds the system with accurate real-time information about the riser movement. The riser guide will take in and release riser to compensate for the heave motion of the drilling rig.

Active helideck stabilization 13

Helicopter access at the right time is critical for many support vessels offshore, and delays represent a significant cost driver. Therefore, increasing the weather window available for safe landing and takeoff will directly affect the operational efficiency of such vessels. Active helideck stabilization systems address some of the critical safety concerns of landing a helicopter on a moving offshore helideck. The stabilization systems are used to regulate the deck motion to compensate for a wave-induced pitching, pitching and heaving motion of a vessel, to ensure a smooth helicopter landing in wave motion. The stabilization system for the helideck is connected to a motion reference unit (MRU) which feeds the system with accurate real-time information about helideck movement. The helideck controller will regulate the position of hydraulic cylinders connected to the helideck to compensate for the wave-induced vessel movement.

Electric winch systems 12

In an electric winch system, the wave motion is compensated by automatically driving the winch in the opposite direction at the same speed. The hook of the winch will therefore retain its position in relation to the seabed or any fixed point outside the vessel. AHC winches are used in ROV systems and for lifting equipment that must work near or at the seabed. Other winch applications are active mooring systems to anchor the vessel to the seabed and towed seismic cable arrangements where active compensation can include tension regulation with the aim of keeping the tension in the cable at a certain level when working in waves. The winch regulation is connected to a motion reference unit (MRU) which feeds the system with accurate real-time information about the vessel movement where the winch is located. Winch load and speed are regulated automatically to compensate for vessel movement during deployment, positioning or towing of cargo.

Rudder ring stabilization 6.15

The main function of the rudder is to correct the course of a ship, but the rudder can also, depending on the type of ship, be used to produce or correct yaw motion. Rudder roll ring stabilization consists of using rudder-induced roll motion to reduce the roll motion induced by waves. Reduced wobble movement is important for many reasons; lateral accelerations that occur due to yaw interrupt tasks performed by the crew and increase the time it takes to complete a mission, yaw accelerations can cause damage to carried cargo, yaw motion increases hull drag, and large yaw angles limit the crew's ability to handle equipment on board and/or to put out and take in equipment. The rudder ring stabilization system receives measurements of the ship's movement from a motion reference unit (MRU) and uses these measurements in an automatic control system that provides appropriate rudder commands.

Active finds 7.15

Active fin stabilizers are normally used to reduce the roll a vessel is exposed to while underway, or later while at rest. The fins extend from the vessel's hull below the waterline and change the angle of attack depending on the vessel's angle of foot and yaw rate. They work in the same way as the stabilizers on an airplane. Cruise ships and yachts often use this type of stabilizer system. A motion reference unit (MRU) provides motion data to the active fin controller which calculates the appropriate fin angle reference for the fin actuator.

Propeller ventilation management 16

Propeller ventilation is when the ship's propeller draws air from above the water surface into the blade. Venting, especially when the propeller comes out of the water, can damage the engine by allowing it to exceed its maximum speed or cause ship generator tripping. Roll, pitch and heave measurements from a motion reference unit (MRU) can be used in conjunction with a suitable vessel model to predict that propeller venting is about to occur, and take appropriate action in the engine/generator dynamic load controls in advance of venting/non-venting - the transition.

The present invention can use the system according to NO20120507 in potentially relatively high-frequency wave pattern loads. The MRU can therefore be used to predict the dynamic loads in each of the examples to be included. A number of examples are discussed in the following and as illustrated in Figure 2.

- MRU RPH measurements are used in the high-consuming subsystems as input data for automatic regulation. Typically, both RPH positions and speeds are used in, for example, PID controllers that run on control computers for each subsystem. Some vessels will have one MRU per large consumer placed at the measurement point of interest, while other vessels

has a reduced number of MRUs so motion data must be weight arm compensated for some

or all subsystem locations before deploying.

MRU RPH measurements are used to calculate short-term predicted motion and long-term statistical motion data such as significant wave amplitude and frequency. Short-term predicted movement is an online real-time process with scope within milliseconds or seconds suitable for dynamic regulation of large consumers in the wave movement area. The statistical long-term movement data can extend over minutes, hours or even days, and represent useful information for manual or automatic

planning the load distribution.

Predicted movement together with output from the high-consuming subsystems' controllers is used for short-term load prediction by the dynamic load predictor. Predicted motion is transformed into predicted power requirements for each high-consuming subsystem before being combined with the controller's output. The output from various controllers can include both controller states and logic information such as activator effect, control deviation, change of regulation setting and start/stop commands given by other subsystems or a human operator. The predicted motion can also be used to predict exceptional conditions that are normally difficult to handle with simple controllers. One such example is the propeller ventilation management, which will otherwise contribute to the dynamic load predictor in a similar way to the various system controllers. Output data from the dynamic load predictor is predicted power consumption which supplies control signals to the dynamic load controllers as described in patent no.

NO20120507.

Statistical data such as significant wave amplitude and frequency generally describe long-term vessel dynamics, which means that they only rarely change due to changes in weather or working conditions. Based on the vessel dynamics and knowledge of DP and HC needs, the load allocation can determine an optimal distribution of thrusters and other large consumers among the different engine generator loads. Each engine should preferably run at a constant high output for maximum efficiency and minimal exhaust emissions. Therefore, some engines can be switched off completely for periods, so that planned repairs and maintenance can be carried out as easily as possible. The resulting configuration of thrusters, bulk consumers and generators is fed to the dynamic load controller but also to the DP system for use in its thruster allocation algorithm. The load allocation includes an allocation of generator power and distribution to produce an adequate dynamic response to handle the predicted

the load requirements. Load allocation is typically performed automatically, but can be overridden manually

by a human operator.

- The dynamic load controller receives input on power requirements from all systems on board a vessel, where the dynamic positioning system normally has the highest priority. The needs are distributed in accordance with the configuration provided by the load distributor. Output data from the dynamic load controller are settings for the motor generator quantities as described in patent no. NO20120344.

To summarize, the invention therefore relates to a system and a method for improving the efficiency of the power plant in a vessel. The system comprises a movement reference unit 1 measuring means for monitoring the vessel movements and prediction means 17, 18 for predicting the vessel movements based on the aforementioned measurements. The predictions can be based on known models for vessel movements in regulated situations. The vessel movements can be monitored in relation to a selected reference, movement or predetermined position and orientation.

The system also comprises a dynamic load prediction unit 19 which calculates the dynamic load on the system at least partially based on the aforementioned predicted movements.

The sensors in the movement reference unit 1 are preferably adapted to measure roll, pitch and heave (RPH) positions and speeds, and the prediction means include short-term prediction means 17 which are adapted to calculate a short-term prediction of the movements such as wave movements or other impacts from the environment.

Short-term movement prediction can include means 16 for predicting propeller ventilation, fo based on the movements to calculate the load change due to a propeller ventilation, e.g. by reducing the power of a propeller that is about to move over the water surface.

The dynamic load prediction unit can also be connected to at least one load consumer 11-15 on the vessel, each of which is adapted to produce a signal indicating a predicted load consumption based on its planned work. Each consumer can also be connected to the movement reference unit 1 to take into account the vessel movements when the power consumption is predicted. The dynamic load prediction unit 19 is connected to the dynamic load control unit 20 which controls the vessel's engine generator quantity 21 based on the predicted load. The prediction means can also include long-term prediction means 18 adapted to collect information about the vessel's movements and calculate a long-term prediction of the movements based on a statistical analysis of said data. This may include a load allocation unit 23 to calculate the load allocation based on the calculated long-term movements and to generate a signal to the load management system 20 indicating the preferred distribution of load over the generators in the power plant.

The dynamic load control unit can also be connected to a dynamic propulsion (DP) system 22 and be able to communicate with the DP system to adjust the power consumption in each thruster to adjust the vessel's position and the consumer load regulation is adapted to assign an available power to each thruster in the system in accordance with the required position or within an allowed window relative to an optimal position.

The DP control system may therefore, if the power required to adjust the position of at least one thruster exceeds the available power, request an increase in the power made available to the thruster from the consumer load control.

Claims (1)

1. System for improving the efficiency of the power plant in a vessel, wherein the system comprises: a movement reference unit measuring means for monitoring the vessel movements and prediction means for predicting the vessel movements based on said measurements, where the system also comprises a dynamic load prediction unit which calculates the dynamic load on the power plant in the system based at least in part on said predicted motions. 2. System according to claim 1, where the sensors are adapted to measure roll, pitch and heave (RPH) positions and speeds, and the prediction means comprise short-term prediction means which are adapted to calculate a short-term prediction of the movements. 3. System according to claim 2, comprising means for predicting propeller ventilation, to calculate, based on the movements, the load change due to a propeller ventilation. 4. System according to claim 2, where the dynamic load prediction unit is also connected to at least one load consumer on the vessel, each of which is adapted to produce a signal indicating a predicted load consumption, where the dynamic load prediction unit is connected to the dynamic load management unit. 5. System according to claim 4, where the at least one load consumer is connected to the movement reference unit and thus receives a signal related to the movement and where the load consumer is adapted to produce a signal indicating the predicted power consumption as a function of the movements. 6. System according to claim 1, where the prediction means comprise long-term prediction means adapted to collect information about the vessel's movements and calculate a long-term prediction of the movements based on a statistical analysis of said data. 7. System according to claim 6, comprising a load allocation unit to calculate the load allocation based on the calculated long-term movements and to generate a signal to the load management system indicating the preferred distribution of load over the generators in the power plant. 8. System according to claim 1, where the dynamic load control unit is adapted to regulate a quantity of engine generators in the vessel based on the predicted load. 9. System according to claim 8, comprising a DP unit connected to the dynamic load management unit and being adapted to adjust adjust the power consumption in each thruster to adjust the vessel's position and the consumer load regulation is adapted to assign an available power to each thruster in the system. 10. System according to claim 9, wherein the DP control system, if the power required to adjust the position in at least one thruster exceeds the available power, requests an increase in the power made available to the thruster from the consumer load control. 11. Method of improving the efficiency of the power plant in a vessel, comprising the steps of measuring the movements of a vessel relative to a reference, to predict the vessel movements based on the aforementioned measurements, and calculating the dynamic load on the system based at least in part on said predicted movements. 11. Method according to claim 10, where the measured movements are swing, stomp and heave (RPH) positions and speeds, where the movement prediction includes short-term prediction means based on these. 12- Method according to claim 10, where the dynamic load prediction is also based on a signal received from at least one load consumer on the vessel, where each is adapted to produce a signal indicating a predicted power consumption, where the dynamic load prediction unit is connected to the dynamic the load control unit. 13. Method according to claim 10, where the prediction also comprises long-term prediction, comprising the step of calculating a long-term prediction for the movements based on a statistical analysis of the mentioned movement data.