A vessel on the open seas is acted upon by external forces produced by wind, tides and waves. Dynamic positioning (DP) systems are known which enable a vessel that approaches a fixed offshore platform, such as an oil rig, windmill, etc., to avoid collision with the platform. A DP vessel will approach an offshore platform, get close without colliding with the platform, make continuous measuring of its position and the external forces acting on the vessel, and automatically compensate for any charges in position using its thruster(s) and stabilizers to maintain a fixed position or station. Standards for such DP systems include DP-1 providing only dynamic positioning, and DP-2 providing redundancy such that a single failure does not result in the loss of station maintenance. Many offshore platforms only permit vessels with a DP system to approach the platform and often a DP-2 system is required.
A DP vessel servicing an offshore platform will have a power plant and a large electrical system capable of operating all shipboard systems. The owners of offshore platforms have disallowed service vessels from using a closed bus tie due to fear of blackout. Specifically, fear that a single-point failure would cause the vessel to lose power, resulting in environmental or human tragedy.
An aspect of at least one of the embodiments described herein is to provide full redundancy of an electrical system of an offshore service vessel while maintaining DP-2 classification.
Another aspect of at least one of the embodiments is to provide a circuit that may be used for storing and transferring energy between galvanically isolated AC bus systems on offshore service vessels while the AC bus tie is open, while maintaining DP-2 classification.
Yet another aspect of at least one of the embodiments is to require lower power storage in a battery than in a system that does not allow transfer of power between isolated buses in a DP-2 system.
A further aspect of at least one of the embodiments is to provide a power distribution system able to be retrofitted into existing vessels, as well as new vessels.
Yet another aspect of at least one of the embodiments is to connect at least one energy storage device such as a battery system to each side of two AC buses, while transferring generator power from one AC bus to another, galvanically isolated AC bus.
A further aspect of at least one of the embodiments is to prevent a zero voltage condition on one bus to propagate to another bus while allowing power to transfer between buses via a galvanic isolator(s).
Yet another further aspect of at least one of the embodiments is to provide a power distribution system that enables a single generator to power all loads of a marine vessel during DP-2 operation.
A further aspect of at least one of the embodiments is to permit running a smaller generator on each isolated bus with the bus tie open and be able to transfer power to the other isolated bus, with or without energy storage, such that a worst case single point failure would only result in half of the ship's AC bus losing power.
Yet another further aspect of at least one of the embodiments is to enable batteries to be sized much smaller than in a system that does not allow transfer of power between the buses through inverters.
A further aspect of at least one of the embodiments is that the batteries, if included, can be used in the spinning reserve calculations for each bus.
Yet another aspect of at least one of the embodiments is to provide significantly enhanced operational capabilities for marine vessels in, e.g., IMO Class DP 2, etc.
These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In this regard, the embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. To further clearly describe features of the embodiments, descriptions of other features that are well known to one of ordinary skill in the art are omitted here.
The articles “a”, “an” and “the” are intended to include both singular and plural forms of the following nouns. Phrases using the term “and/or” include a plurality of combinations of relevant items or any one item among a plurality of relevant items. The term “at least [number]” preceding a list of items denotes any combination of the items in the list that satisfies the expression. In the case of “at least one” the expression includes any one item among a plurality of the listed item(s), as well as multiple items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.
If energy storage is included, many different configurations are possible. In all cases, it is preferred that energy storage is connected onto a common DC link bus and that DC bus is then connected to two or more DC/AC inverters that feed back to the ship's AC bus system. This allows both stored energy, e.g., in batteries, as well as energy from one AC bus to be transferred to the other AC bus while galvanically isolated and with the AC bus tie open.
In the embodiments in
The illustrated embodiments allow for the energy storage on a vessel to be immediately deployed on either AC bus while the AC bus tie is open. Thus energy storage may be utilized for spinning reserve calculations on both bus systems, not just one. This allows vessel operators to save fuel and maintenance costs by running a single generator on one bus or two smaller generators, one on each bus, utilizing the energy storage as spinning reserve.
In the illustrated embodiments, a single generator or two smaller generators can provide power to both isolated bus systems through the inverters. The inverter sizing takes into account both the required power transfer between buses as well as the output and charging capabilities of the energy storage if included.
In the embodiment illustrated in
A normally open bus-tie circuit breaker 21 connects the first and second AC buses 15, 16. First and second galvanic isolators 24, 25 are connected together by (first) DC bus 26 and respectively connected to the first and second AC buses 15, 16 by first and second isolator connection circuit breakers 27, 28. When bus-tie circuit breaker 21 is open, the first and second AC buses 15, 16 are isolated from one another which prevents a failure on one bus from causing a failure on the other bus. When both isolator connection circuit breakers 27, 28 are closed, the first and second AC buses 15, 16 are connected by the first and second galvanic isolators 24, 25 which are bi-directional. As a result, any of the generators G1-G4 can supply power to either of the loads 18, 19 regardless of whether the bus-tie circuit breaker 21 is open or closed, provided both isolator connection circuit breakers 27, 28 are closed.
Each of the DC busses 26,40 shown in
In the embodiment illustrated in
The first and second galvanic isolators 24, 25, when paired with energy storage 30, help maintain the common DC link bus voltage at appropriate levels to maintain the correct AC voltage output. The first and second galvanic isolators 24, 25 also allow the operator to precisely control charging and discharging of energy storage 30.
Each of the first and second galvanic isolators 24, 25 may include a transformer 32 or 33. The system may also include inverters 34, 35 that also provide some galvanic isolation. Each of the inverters 34, 35 may be an insulated-gate bipolar transistor inverter or technology with similar capability that is sized by taking into account both the required power transfer between buses as well as the output and charging capabilities of the battery 30. In the embodiment illustrated in
In the embodiment illustrated in
An alternative way of making the dual galvanically isolated connections to the first and second AC busses 15, 16 is illustrated in
In the embodiments illustrated in
The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the inventive embodiments to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope thereof.
This application claims priority to U.S. Provisional Application No. 63/407,962, filed Sep. 29, 2022, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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63407962 | Sep 2022 | US |