Ship propulsion system

Abstract

The present invention relates to a ship propulsion system and, more particularly, to a ship propulsion system in which two shaft generators are coupled to the same propulsion shaft, and a power transmission path is switched by a control unit such that at least a part of power generated by a main engine is selectively transmitted to at least one of a first shaft generator or a second shaft generator, and thus the shaft generator with high power generation efficiency can be selectively operated, thereby improving propulsion efficiency.

Description

ship propulsion system

[0001] The present invention relates to a ship propulsion system.

[0002] In recent years, the shipping and shipbuilding industries have seen increasing demands for fuel cost reduction, compliance with environmental regulations, and energy resource conservation. Consequently, there is a growing need for technological development to operate ship propulsion systems more efficiently and improve overall energy efficiency.

[0003] Ships operate under a variety of routes, speeds, and load conditions, which can lead to reduced propulsion efficiency or energy waste. These issues not only lead to increased fuel consumption, but also directly impact operating costs and greenhouse gas emissions. Therefore, a method is needed to appropriately control a ship's propulsion system according to operating conditions and efficiently manage the energy flow throughout the entire system.

[0004] An object of the present invention is to provide a ship propulsion system capable of improving the propulsion efficiency of a ship by using a shaft generator coupled to a propulsion shaft and producing electric power by extracting at least a portion of the power generated by the main engine.

[0005] The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned can be clearly understood by a person of ordinary skill in the art from the description below.

[0006] A ship propulsion system according to one aspect of the present invention comprises: a main engine connected to a propulsion unit through a propulsion shaft and generating propulsion power for the ship; a first shaft generator and a second shaft generator, each coupled to the propulsion shaft and generating electric power by extracting at least a portion of the power generated by the main engine; and a control unit switching a power transmission path so that at least a portion of the power generated by the main engine is transmitted to at least one of the first shaft generator and the second shaft generator.

[0007] The above control unit can switch the power transmission path based on the revolutions per minute (rpm) of the main engine.

[0008] The control unit may control at least a portion of the power generated by the main engine to be transferred to the first shaft generator when the rpm value of the main engine is less than the switching threshold value, and may control at least a portion of the power generated by the main engine to be transferred to the second shaft generator when the rpm value of the main engine is greater than the switching threshold value.

[0009] The first shaft generator and the second shaft generator each have different high-efficiency operating sections, which are rpm sections of the main engine capable of operating at high efficiency, and the switching threshold value may be an rpm value included in the high-efficiency operating section of either the first shaft generator or the second shaft generator.

[0010] The control unit switches the power transmission path so that at least a portion of the power generated by the main engine is transmitted to both the first shaft generator and the second shaft generator when the rpm value of the main engine falls within an overlapping section, and the overlapping section may be a section including the switching threshold value.

[0011] The control unit may control, when the rpm value of the main engine is less than the switching threshold value, at least a portion of the power generated by the main engine to be transferred to the first shaft generator, and, when the rpm value of the main engine is greater than or equal to the switching threshold value, at least a portion of the power generated by the main engine to be transferred to both the first shaft generator and the second shaft generator.

[0012] The control unit can adjust the load of the second shaft generator so that the second shaft generator produces rated output when the rpm value of the main engine is greater than or equal to the switching threshold value.

[0013] The control unit can variably control the power output of the first shaft generator in a direction that offsets the output fluctuation of the main engine when a fluctuation in the output of the main engine occurs or is expected as the load of the second shaft generator is adjusted.

[0014] The above control unit can variably control the power output of the first shaft generator in a direction that offsets the torsional vibration when torsional vibration occurs or is expected to occur in the propulsion shaft.

[0015] The control unit can apply a braking force to the rotation of the propulsion shaft by increasing the load of the first shaft generator, and generate electric power from the rotation of the propulsion shaft that rotates while applying the braking force.

[0016] The present invention has the effect of improving the energy efficiency of a ship propulsion system.

[0017] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0018] Figure 1 is a schematic diagram of a ship propulsion system according to a first embodiment of the present invention.

[0019] Figure 2 is a graph showing the output efficiency of the first shaft generator and the second shaft generator shown in Figure 1.

[0020] Figure 3 is a schematic diagram of a ship propulsion system according to a second embodiment of the present invention.

[0021] Figure 4 is a schematic diagram of a ship propulsion system according to a third embodiment of the present invention.

[0022] The objects, specific advantages, and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments, taken in conjunction with the accompanying drawings. In this specification, when reference numerals are assigned to components in each drawing, it should be noted that, where possible, identical components are given the same reference numerals even if they appear in different drawings. Furthermore, in describing the present invention, if a detailed description of a related known technology is deemed to unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

[0023] In addition, the attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

[0024] Additionally, terms including ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by the terms. The terms are used only to distinguish one component from another.

[0025] The present invention encompasses a vessel equipped with the ship propulsion system described below. The term "vessel" encompasses gas carriers, merchant ships transporting various cargoes or people, and offshore plants such as FLNG and FSRU.

[0026] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[0027] FIG. 1 is a conceptual diagram of a ship propulsion system according to a first embodiment of the present invention. For reference, FIG. 1 is a conceptual diagram illustrating at least a portion of the components included in one embodiment.

[0028] Referring to FIG. 1, a ship propulsion system (1) according to a first embodiment of the present invention includes a main engine (10), a first shaft generator (11), a second shaft generator (12), and a control unit (13).

[0029] The main engine (10) is connected to a propulsion device (18) installed at the stern of the ship through a propulsion shaft (17), and the rotational force generated from the main engine (10) is transmitted to the propulsion device (18) through the propulsion shaft (17) to propel the ship. At this time, the propulsion device (18) may be a propeller, and the propeller can rotate through the rotational force from the main engine (10) to form a fluid flow and move the ship forward.

[0030] The main engine (10) is an internal combustion engine that generates power by burning oil fuel (HFO, MDO, etc.) and / or gas fuel (LNG, LPG, etc.), and in the present embodiment, may be a two-stroke propulsion engine such as a ME-GI engine (MAN Electronic-Gas Injection Engine).

[0031] The shaft generator (11, 12) generates electric power by extracting at least a portion of the power generated by the main engine (10). The shaft generator (11, 12) is a type of power take-off device (PTO) in that it extracts and uses a portion of the power supplied from the main engine (10) to the propulsion unit (18). This method of generating power using the shaft generator is effective in saving energy through economical power generation during the operation of the ship.

[0032] The shaft generator (11, 12) may be either an engine mounted shaft generator (EMG) (20) installed at the free end of the main engine (10) or an in-line type shaft generator (20) installed at the propulsion shaft between the main engine (10) and the propulsion unit.

[0033] The two shaft generators (11, 12) of the present embodiment may both be in-line type shaft generators, and considering the engine room space, one may be an engine-mounted shaft generator and the other may be an in-line type shaft generator. In the following description, for the convenience of explanation, it is described as an example that both shaft generators (11, 12) are in-line type shaft generators, but the present invention is not limited thereto.

[0034] Meanwhile, the output efficiency of the shaft generator (11, 12) that generates electric power by using the rotation of the propulsion shaft (17) by the main engine (10) as a power source changes nonlinearly according to the change in the revolutions per minute (rpm) of the main engine (10). In general, the output efficiency of the shaft generator (11, 12) gradually improves as the rpm of the main engine (10) increases, as shown in Fig. 2, but when it exceeds a certain level of rpm, the output efficiency no longer increases but rather decreases.

[0035] This is because, when the rotational speed of the propulsion shaft (17) increases excessively, loss factors that increase in proportion to the speed, such as iron loss, eddy current loss, and bearing friction loss, rapidly increase. The efficiency characteristics of these shaft generators (11, 12) may differ from each other depending on the design specifications of each shaft generator, and therefore, the rpm range of the main engine (10) in which each of the plurality of shaft generators (11, 12) can operate with high efficiency may also differ from each other.

[0036] In this embodiment, two shaft generators (11, 12), a first shaft generator (11) and a second shaft generator (12), are coupled to the propulsion shaft (17). The first shaft generator (11) and the second shaft generator (12) are arranged side by side on the same propulsion shaft (17). The first shaft generator (11) and the second shaft generator are each independent shaft generators, and under the control of a control unit (13) to be described later, either one or both of the first shaft generator (11) and the second shaft generator (12) can extract at least a portion of the power generated by the main engine (10) to generate power.

[0037] The power generated by the first shaft generator (11) and the second shaft generator (12) is converted into stable and standardized power through each power conversion unit (15) and then supplied to the entire ship's electrical system through the distribution panel (16).

[0038] In this embodiment, each power conversion unit (15) may include an AC-DC converter (151), a DC-AC converter (152), and a transformer (153). The AC-DC converter (151) converts variable frequency AC power generated from the first shaft generator (11) and the second shaft generator (12) into DC power. This eliminates voltage and frequency fluctuations due to changes in rotational speed, thereby enabling stable power conversion.

[0039] The DC-AC converter (152) reconverts the DC power converted by the AC-DC converter (151) into AC power with the voltage, frequency, and phase conditions required by the ship system. This enables the supply of power appropriate for the rated AC load and flexible response to various system demands. The transformer (153) converts the AC power generated by the DC-AC converter (152) to the required voltage level. This minimizes power loss and enables stable power transmission.

[0040] Meanwhile, in the present embodiment, the rpm sections of the main engine (10) in which the first shaft generator (11) and the second shaft generator (12) can operate at high efficiency are different from each other and may partially overlap. Referring to FIG. 2, which shows the output efficiency of the first shaft generator (11) and the second shaft generator (12) according to one embodiment of the present invention, the first shaft generator (11) forms a high-efficiency operation section (a) at a lower rpm than that of the main engine (10), and the second shaft generator (12) forms a high-efficiency operation section (b) at a higher rpm than that of the main engine (10).

[0041] For example, the first shaft generator (11) can operate with high efficiency at a low rpm (e.g., 0 to 60 rpm) of the main engine (10) (i.e., section a is 0 to 60 rpm), and the second shaft generator (12) can operate with high efficiency at a high rpm (e.g., 60 to 100 rpm) of the main engine (10) (i.e., section b is 60 to 100 rpm).

[0042] The control unit (13) switches the power transmission path so that at least a portion of the power generated by the main engine (10) is transmitted to at least one of the first shaft generator (11) and the second shaft generator (12). In other words, the control unit (13) determines at least one shaft generator that will receive at least a portion of the power generated by the main engine (10) to produce electric power, and switches the power transmission path so that at least a portion of the power generated by the main engine (10) is transmitted to the determined at least one shaft generator.

[0043] In this embodiment, “switching the power transmission path” means that the control unit (13) changes the power flow so that at least a portion of the power generated by the main engine (10) is transmitted to at least one of the first shaft generator (11) and the second shaft generator (12).

[0044] More specifically, “switching the power transmission path” includes the control unit (13) selecting a shaft generator capable of demonstrating higher power generation efficiency of the main engine (10) and switching the power transmission path through an electrical or mechanical switching means or a power conversion device, etc., so that at least a portion of the power of the main engine (10) is supplied to the shaft generator. The term “switching” is used herein to mean such selective control of power flow.

[0045] In one embodiment of the present invention, the control unit (13) can switch the power transmission path based on the rpm of the main engine (10).

[0046] The control unit (13) monitors the rpm value of the main engine (10), and if the rpm value of the main engine (10) is less than the switching threshold, the control unit (13) can control the power transmission path so that at least a portion of the power generated by the main engine (10) is transmitted to the first shaft generator (11).

[0047] Thereafter, when the rpm value of the main engine (10) becomes higher than the switching threshold, the power transmission path is controlled so that at least a portion of the power generated by the main engine (10) is transmitted to the second shaft generator.

[0048] Conversely, when the rpm of the main engine (10) is gradually reduced to decelerate the ship, the control unit (13) controls the power transmission path so that the second shaft generator (12) receives power from the main engine (10) and when the rpm value of the main engine (10) falls below the switching threshold, the first shaft generator (11) receives power from the main engine (10).

[0049] In this embodiment, the switching threshold may be an rpm value of the main engine (10) included in a high-efficiency operation section of at least one of the first shaft generator (11) and the second shaft generator (12). For example, the switching threshold may be an rpm value of the main engine (10) that is a boundary between the high-efficiency operation section of the first shaft generator (11) and the high-efficiency operation section of the second shaft generator (12). That is, when the main engine (10) operates at an rpm lower than the switching threshold, the first shaft generator (11) operates at a high efficiency, and when it operates at an rpm higher than the switching threshold, the second shaft generator (12) operates at a high efficiency.

[0050] Referring to FIG. 2 again, the switching threshold may be 60 rpm, which is a boundary value between 0 to 60 rpm, which is a high-efficiency operating range of the first shaft generator (11), and 60 to 100 rpm, which is a high-efficiency operating range of the second shaft generator (12).

[0051] Meanwhile, when the control unit (13) changes the shaft generator (11, 12) receiving power from the main engine (10) to one shaft generator (e.g., the second shaft generator (12)) based on the switching threshold value and then immediately stops the operation of the other shaft generator (e.g., the first shaft generator (11)) that was previously operating, a gap in power generation, i.e., power supply, may be interrupted during the shaft generator switching process.

[0052] Therefore, in order to prevent such a gap in power generation from occurring, the control unit (13) can determine an overlapping section (c) including a switching threshold value, and set a power transmission path so that both the first shaft generator (11) and the second shaft generator (12) generate power in the overlapping section (c). In the present embodiment, the overlapping section (c) may be an rpm section with a switching threshold value as an intermediate value.

[0053] Again, referring to FIG. 2, the switching threshold is 60 rpm, and the overlapping section (c) can be set to 59 to 61 rpm including the switching threshold as an intermediate value. At this time, the control unit (13) transmits the power from the main engine (10) to the first shaft generator (11) while the rpm of the main engine (10) increases in the range of 0 to 59 rpm, and transmits the power of the main engine (10) to the second shaft generator (12) when the rpm value of the main engine (10) becomes 59 rpm, thereby generating power using both the first shaft generator (11) and the second shaft generator (12).

[0054] Thereafter, when the rpm value of the main engine (10) reaches 61 rpm, the control unit (13) stops the operation of the first shaft generator (11) and transmits the power of the main engine (10) only to the second shaft generator (12), thereby improving the propulsion efficiency of the ship without causing a power blank period.

[0055] According to this embodiment, the control unit (13) determines a shaft generator that can operate with high efficiency according to the rpm of the main engine (10), and controls a power transmission path to transmit at least a portion of the power generated by the main engine (10) to the corresponding shaft generator (11, 12), thereby improving the power generation propulsion efficiency of the entire system.

[0056]

[0057] In another embodiment of the present invention, the control unit (13) can control the power transmission path so that when the rpm value of the main engine (10) is less than the switching threshold value, at least a portion of the power generated by the main engine (10) is transmitted to the first shaft generator, and when the rpm value of the main engine (10) is greater than the switching threshold value, at least a portion of the power generated by the main engine (10) is transmitted to the first shaft generator (11) and the second shaft generator (12).

[0058] That is, when the main engine (10) operates at an rpm lower than the switching threshold, only the first shaft generator (11) generates power, but when the main engine (10) operates at an rpm higher than the switching threshold, both the first shaft generator (11) and the second shaft generator (12) can generate power.

[0059] At this time, the control unit (13) can adjust the load of the second shaft generator so that the second shaft generator generates a constant amount of power when the main engine (10) operates at an rpm higher than the switching threshold. That is, even if the rpm of the main engine (10) fluctuates, the control unit (13) adjusts the load of the second shaft generator (12) in response to the change in the rpm of the main engine (10), thereby mitigating the change in the output of the second shaft generator (12).

[0060] For example, when the rpm of the main engine (10) decreases, the control unit (13) reduces the load of the second shaft generator (12) to alleviate the output decrease, and when the rpm of the main engine (10) increases, the control unit (13) increases the load of the second shaft generator (12) to prevent over-output, thereby maintaining the output of the second shaft generator (12) constant.

[0061] Meanwhile, when the control unit (13) varies the load of the second shaft generator (12) to keep the output of the second shaft generator (12) constant, the output of the main engine (10) also varies. When a change in the output of the main engine (10) occurs or is expected as the load of the second shaft generator (12) is adjusted, the control unit (13) smooths the output of the main engine (10) by variably controlling the power output of the first shaft generator (11) in a direction that offsets the change in the output of the main engine (10).

[0062] More specifically, when the load of the second shaft generator (12) increases, the overall load felt by the main engine (10) increases, thus increasing the output of the main engine (10). At this time, the control unit (13) can maintain the output of the main engine (10) constant by reducing the load of the first shaft generator (11) and thereby reducing the power output of the first shaft generator (11).

[0063] Conversely, when the load of the second shaft generator (12) is reduced and the overall load felt by the main engine (10) is reduced, the output of the main engine (10) is reduced. At this time, the control unit (13) can increase the load of the first shaft generator (11) to increase the power output of the first shaft generator (11), thereby maintaining the output of the main engine (10) constant. In this way, smoothing the output of the main engine (10) due to variable control of the first shaft generator (11) can improve the fuel efficiency of the main engine (10), which is desirable.

[0064] Meanwhile, even when torsional vibration (TV) occurs or is expected to occur in the propulsion shaft (17), the control unit (13) can damp the vibration of the propulsion shaft (17) by variably controlling the power output of the first shaft generator (11) in a direction that offsets the torsional vibration of the propulsion shaft (17).

[0065] In this embodiment, the control unit (13) can receive information on the change in rotational speed or torque transmitted to the propulsion shaft (17) from a rotation sensor, a torque sensor, or an engine control module, and extract a torsional vibration component existing in a specific frequency band. Thereafter, the vibration of the propulsion shaft (17) can be damped by applying torque of the first shaft generator (11) in real time in a direction opposite in phase while having the same frequency as the extracted vibration frequency.

[0066] In one embodiment of the present invention, the control unit (13) can extract a torsional vibration component, i.e., a torque fluctuation component, corresponding to an intermediate frequency band using a mid-pass filter. More specifically, the control unit (13) can extract a torque fluctuation component corresponding to an intermediate frequency band (e.g., 1 to 3 Hz) using a mid-pass filter and determine this as a torque fluctuation component to be compensated.

[0067] Thereafter, the control unit (13) can control the output of the main engine (10) to be maintained more smoothly by suppressing the increase in torque of the propulsion shaft by increasing the load of the first shaft generator (11) in a section where the torque increases and compensating for the decrease in torque of the propulsion shaft by reducing the load of the first shaft generator (11) in a section where the torque decreases.

[0068] Additionally, when the ship needs to decelerate, the control unit (13) can apply a braking force to the rotation of the propulsion shaft (17) by increasing the load of the first shaft generator (11). More specifically, the control unit (13) can artificially increase the load of the first shaft generator (11) to generate a torque that resists the rotation of the propulsion shaft (17), thereby providing a mechanical braking effect that reduces the rotational speed of the propulsion shaft (17).

[0069] The first shaft generator (11) generates power even while providing a mechanical braking effect, and thus, the power generated by the first shaft generator (11) during the braking of the ship can be supplied to the system load within the ship or stored in a battery, thereby improving the energy efficiency of the ship propulsion system.

[0070]

[0071] In this embodiment, the rated capacities of the two shaft generators (11, 12) may be set differently depending on the operating purpose and system design. For example, in order to utilize the PTH (Power Take-Home) mode, which operates the ship at low speed using the shaft generator as a driving source when the main engine (10) is stopped or in an emergency, it is preferable that the first shaft generator (11) be set to a large capacity so that it can supply sufficient output even under low-speed rotation conditions. On the other hand, the second shaft generator (12) may be set to a small capacity to correspond to general power generation operation.

[0072] On the other hand, in the case where there is no PTH function, the first shaft generator (11) may be set to low capacity to perform initial system startup and gradual increase in output load, and the second shaft generator (12) may be set to high capacity to stably meet the entire power demand in the section where the main engine (10) is operated at a rated speed or higher.

[0073]

[0074] Figure 3 is a conceptual diagram of a ship propulsion system (1) according to a second embodiment of the present invention. Below, the differences between this embodiment and the first embodiment will be primarily described. Any omitted portions will be replaced with the previous description. This also applies to other embodiments below.

[0075] A ship propulsion system (1) according to a second embodiment of the present invention applies a double contra-rotating propeller (CRP) system in which two propellers rotate in opposite directions on the same axis to propel the ship.

[0076] The CRP system, with its two propellers rotating in opposite directions, not only improves propulsion efficiency compared to a single propeller, but also counteracts rotational recoil torque, enhancing the ship's straight-line stability. Furthermore, the counter-rotating rotation realigns fluid flow, reducing noise and vibration and improving fuel efficiency.

[0077] Referring to FIG. 3, the ship propulsion system (1) according to the present embodiment includes a main engine (10), an inner shaft (21), an outer shaft (22), a first shaft generator (11), a second shaft generator (12), a first converter (23), a second converter (24), and a control unit (25).

[0078] The inner shaft (21) is equipped with a rear propeller (211) at the end, and rotates in the forward direction by the main engine (10) to drive the rear propeller (211).

[0079] The outer shaft (22) is formed in a hollow shape into which the inner shaft (21) is inserted, and a forward propeller (221) is provided at the end of the outer shaft (22). The outer shaft (22) rotates in the opposite direction to the inner shaft (21), i.e., in the reverse direction, to drive the forward propeller. At this time, since the inner shaft (21) has a longer length than the outer shaft (22), the end of the inner shaft (21) protrudes outside the outer shaft (22), and a rear propeller (211) is provided at the protruding end of the inner shaft (21).

[0080] In this embodiment, the sizes of the front propeller (221) and the rear propeller (211) can be designed in consideration of their respective propulsion roles, required thrust, and fluid dynamic characteristics, and they can be configured to have the same size or different sizes. In this embodiment, the first shaft generator (11) is coupled to the inner shaft (21) and extracts at least a portion of the power generated by the main engine (10) to generate AC power.

[0081] Meanwhile, in the present embodiment, the second shaft generator (12) is coupled to the outer shaft (22) and receives at least a portion of the AC power generated by the first shaft generator (11) to rotate the outer shaft (22) in the reverse direction. That is, in the present embodiment, the second shaft generator (12) can function as a power take-in (PTI) device that assists the propulsion power of the main engine (10) by rotating the outer shaft (22) when power is supplied from the outside.

[0082] The first converter (23) converts the variable frequency AC power generated by the first shaft generator (11) into DC power. Meanwhile, the first converter (23) can operate as an inverter that converts DC power into AC power and supplies it when power is supplied from the DC link to the shaft generator (11) (e.g., when the shaft generator operates in PTI mode). That is, the first converter (23) is an AC-DC / DC-AC dual-purpose conversion device configured to enable bidirectional power flow, and can flexibly control the power conversion direction according to the driving mode of the propulsion shaft.

[0083] The second converter (24) reconverts at least a portion of the direct current power converted by the first converter (23) into alternating current power with voltage and frequency phase conditions required by the second shaft generator (12) and supplies the reconverted power to the second shaft generator (12), thereby allowing the second shaft generator (12) to rotate the outer shaft (22) using external power to assist propulsion of the ship. According to the present embodiment, when the power generated by the first shaft generator (11) is supplied to the second shaft generator (12) through the first converter (23) and the second converter (24), the power loss is less than about 5%.

[0084] The control unit (25) comprehensively manages the overall operating status of the ship propulsion system in this embodiment and performs control to optimize energy flow and output distribution between each component.

[0085] In this embodiment, the control unit (25) can precisely control the rotation speed and torque of the second shaft generator (12) operating in the motor mode (i.e., PTI mode) by controlling the output voltage and frequency of the second converter (24) to variably control the rotation speed and torque of the second shaft generator (12).

[0086] In one embodiment of the present invention, the control unit (25) calculates an output value required for the second shaft generator (12) to operate in PTI mode based on the rotational speed and torque required by the front propeller (221). Thereafter, the control unit (25) controls the second converter (24) so ​​that the calculated power is supplied to the second shaft generator (12), thereby enabling the second shaft generator (12) to drive the outer shaft (22).

[0087] Meanwhile, in this embodiment, the control unit (25) controls the power flow so that only the power required to drive the second shaft generator (12) among the power generated by the first shaft generator (11) is supplied to the second shaft generator (12) through the second converter (24), and at least a portion of the remaining power is transmitted to the distribution panel (16) connected to the ship's electrical system.

[0088] At this time, the residual power can be converted back into AC power by the third converter (26) and then supplied to the distribution panel (16) by stepping down or stepping up to the required voltage level through the transformer (153). Here, the third converter (26) is a power conversion device for converting direct current power into rated AC power, and can be configured according to the requirements of the distribution system.

[0089] Meanwhile, the third converter (26) performs a rectifier operation to convert AC power into DC power when power from the AC grid is supplied to the DC link. In other words, the third converter (26) is a DC-AC / AC-DC dual-purpose conversion device configured to enable bidirectional power flow, and can flexibly control the power conversion direction depending on the conditions of the grid load or the operating mode.

[0090] In addition, the control unit (25) distributes the total output used for ship propulsion to the front propeller (221) and the rear propeller (211). At this time, the control unit (25) controls the output sharing ratio between the rear propeller (211) connected to the inner shaft (21) and the front propeller (221) connected to the outer shaft (22) by considering the ship's speed, sea conditions, propulsion efficiency, etc.

[0091] More specifically, the control unit (25) can control the power sharing ratio between the rear propeller (211) and the front propeller (221) by adjusting the power output of the first shaft generator (11) and the amount of power applied to the second shaft generator (12) through the second converter (24).

[0092] For example, when the power output by the first shaft generator (11) increases, the rotational force transmitted to the rear propeller (211) through the inner shaft (21) decreases, so the output of the rear propeller (211) decreases, and when the amount of power applied to the second shaft generator (12) increases, the output of the front propeller (221) increases.

[0093] In this way, the control unit (25) can precisely adjust the output sharing ratio between the rear propeller (211) and the front propeller (221) by comprehensively controlling the power extraction and application conditions of each shaft generator (11, 12). In this embodiment, the control unit (25) can control the rear propeller (211) to output 70% of the total output and the front propeller (221) to output 30%.

[0094] Meanwhile, in another embodiment of the present invention, the ship propulsion system (1) may additionally include a gear that converts the forward rotation of the inner shaft (21) into a reverse direction and transmits it to the outer shaft (22), thereby rotating the outer shaft (22) in the reverse direction. In this case, since the outer shaft (22) is rotated by the gear, the second shaft generator (12) coupled to the outer shaft (22) can generate electric power by extracting a portion of the power from the rotation of the outer shaft (22), and at this time, the second shaft generator (12) can function as a power take-off (PTO).

[0095] Of course, even in this case, the second shaft generator (12) can receive power from the first shaft generator (11) or from the outside to rotate the outer shaft (22) together with the gear, and the control unit (25) can adjust the rotation speed and torque transmission conditions of the gear and the second shaft generator (12), thereby allowing the gear and the second shaft generator (12) to smoothly rotate the outer shaft (22) without mutual interference.

[0096]

[0097] Fig. 4 is a conceptual diagram of a ship propulsion system (1) according to a third embodiment of the present invention. Referring to Fig. 4, the ship propulsion system (1) according to the present embodiment includes a main engine (10), an inner shaft (21), an outer shaft (22), a fuel cell (31), a fourth converter (32), a shaft generator (33), and a control unit (34).

[0098] In this embodiment, the main engine (10) rotates the inner shaft (21) in the forward direction to drive the rear propeller (211).

[0099] The fuel cell (31) discharges power under the control of the control unit (34). In the present embodiment, the fuel cell (31) may be a solid oxide fuel cell (SOFC). The direct current power discharged by the fuel cell (31) is converted into a stable DC-link voltage by the DC-DC converter (311) and then supplied to the DC-link.

[0100] The fourth converter (32) is connected to the DC-link and converts at least a portion of the power discharged by the fuel cell (31) and supplied to the DC-link into alternating current and then supplies it to the shaft generator (33).

[0101] In the present embodiment, the shaft generator (33) is coupled to the outer shaft (22) and receives at least a portion of the power discharged by the fuel cell (31) through the fourth converter (32) to rotate the outer shaft (22) in the reverse direction, thereby driving the front propeller (221). That is, the shaft generator (33) of the present embodiment can function as a power induction device (PTI) that assists the propulsion power of the main engine (10) by rotating the outer shaft (22) when power is supplied from the outside.

[0102] In this embodiment, the power discharged by the fuel cell (31) is converted by the DC-DC converter (311) and the fourth converter (32) and then transmitted to the shaft generator (33), thereby enabling the shaft generator (33) to be driven with high efficiency.

[0103] In this embodiment, the control unit (34) comprehensively manages the overall operating status of the ship propulsion system in this embodiment and performs control to optimize energy flow and output distribution between each component.

[0104] In this embodiment, the control unit (34) controls the power flow so that only the power required to drive the shaft generator (33) among the power discharged by the fuel cell (31) is supplied to the shaft generator (33) through the fourth converter (32), and the remaining power is transmitted to the distribution panel (16) connected to the ship's electrical system.

[0105] In one embodiment of the present invention, the control unit (34) calculates an output value required for the shaft generator (33) to operate in PTI mode based on the rotational speed and torque required by the front propeller (221). Thereafter, the control unit (34) controls the fourth converter (32) to supply the calculated power to the shaft generator (33), thereby enabling the shaft generator (33) to drive the outer shaft (22).

[0106] Meanwhile, the control unit (34) controls the power flow so that at least a portion of the remaining power, excluding the power supplied to the shaft generator (33) for driving the shaft generator (33) among the power generated by the fuel cell (31) and supplied to the DC-link, is supplied to the ship's electrical system through the distribution panel (16).

[0107] At this time, the residual power can be converted back into AC power by the fifth converter (35) and then supplied to the distribution panel (16) by stepping down or stepping up to the required voltage level through the transformer (153). Here, the fifth converter (35) is a power conversion device for converting direct current power into rated AC power, and can be configured according to the requirements of the distribution system.

[0108] Meanwhile, since the fuel cell (31) discharges depending on the rate and reaction conditions of the chemical reaction between hydrogen and oxygen, it is difficult to respond quickly to sudden load fluctuations, and reaction delays may occur. Therefore, it is desirable for the fuel cell (31) to output its rated output, as this allows for stable and high-efficiency power supply.

[0109] Accordingly, the control unit (34) controls the fuel cell (31) to produce rated output, supplies some power according to the power demand of the shaft generator (33) for PTI operation, and supplies the remaining power to the system load through the distribution panel, thereby effectively utilizing the power supplied by the fuel cell.

[0110] In addition, the control unit (34) can supply power to the system load by supplying all of the power discharged by the fuel cell (31) to the distribution panel (16) in a section where the double-reversing propeller (CRP) is not used, i.e., when the front propeller (221) is not used or when both the front and rear propellers (211) are not used.

[0111] Meanwhile, the control unit (34) controls the overall propulsion output to be appropriately distributed between the front propeller (221) and the rear propeller (211) by taking into consideration the ship's speed, sea conditions, propulsion efficiency, etc.

[0112] More specifically, the control unit (34) can control the output sharing ratio between the rear propeller (211) and the front propeller (221) by adjusting the output of the main engine (10) and the amount of power applied to the shaft generator (33) through the fourth converter (32).

[0113] In this embodiment, the output of the rear propeller (211) increases as the output of the main engine (10) increases, and the output of the front propeller (221) increases as the size of the power applied to the shaft generator (33) through the fourth converter (32) increases.

[0114] Accordingly, the control unit (34) can precisely adjust the output sharing ratio between the rear propeller (211) and the front propeller (221) by comprehensively controlling the output and authorization conditions of the main engine (10). In this embodiment, the control unit (34) can control the rear propeller (211) to output 60% of the total output and the front propeller (221) to output 40%.

[0115] A ship propulsion system (1) according to another embodiment of the present invention may additionally include a generator engine (not shown). The generator engine is intended to supply power to general system loads such as onboard lighting, cooling, communications, pumps, etc., and may be a general 4-stroke power generation engine such as a DFDG (Dual Fuel Diesel Generator) or a DFGE (Dual Fuel GEnerator). Multiple generator engines may be installed depending on the onboard power demand.

[0116] The generator engine can additionally supply power to the system load and the shaft generator (33) when the fuel cell has difficulty in supplying sufficient power to the system load and the shaft generator (33) due to installation cost and installation volume issues.

[0117] In this case, since the power generation efficiency of the generator engine is lower than the discharge efficiency of the fuel cell (31), the efficiency improvement rate may be lower than when power is supplied to the system load and shaft generator (33) using only the fuel cell (31), but since a lower capacity fuel cell (31) can be used, the initial equipment construction cost of the entire system can be reduced.

[0118] When a generator engine is installed in the ship propulsion system (1), the control unit (34) can control power to be generated by at least one of the fuel cell (31) and the generator engine, taking into account the operating efficiency of the fuel cell (31) and the generator engine.

[0119] In this embodiment, the control unit (34) can control one or both of the fuel cell (31) and the generator engine to operate in parallel by considering at least one of the remaining hydrogen amount of the fuel cell (31), the instantaneous power demand, the fuel cost, and the operating efficiency of each generator engine. For example, the control unit (34) can give priority to discharging by the fuel cell (31) when the remaining hydrogen amount of the fuel cell (31) is equal to or greater than a preset threshold amount, and thereafter, operate the generator engine to cover the shortfall in power.

[0120] Meanwhile, according to the ship propulsion system (1) of the present embodiment, since the shaft generator (33) rotates the outer shaft (22) using power from the fuel cell (31), the rotation of the outer shaft (22) can be performed independently from the operations of the main engine (10) and the inner shaft (21).

[0121] Accordingly, in the case where the rear propeller (211) cannot be driven due to a failure of the main engine (10), the shaft generator (33) can rotate the outer shaft (22) using the power discharged by the fuel cell (31), thereby rotating the front propeller (221) and propelling the ship. At this time, if a controllable pitch propeller (CPP) is used as the front propeller (221), rotational power loss can be minimized by adjusting the blade angle, enabling more effective propulsion.

[0122]

[0123] The present invention encompasses all embodiments resulting from a combination of the above embodiments and known techniques, in addition to the embodiments described above.

[0124] Although the present invention has been described in detail through specific examples, this is intended to specifically explain the present invention, and the present invention is not limited thereto, and it will be apparent that modifications and improvements can be made by those skilled in the art within the technical spirit of the present invention.

[0125] All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims

1. The main engine that is connected to the propulsion system through the propulsion shaft and generates the propulsion power of the ship; A first shaft generator and a second shaft generator, each coupled to the propulsion shaft, for generating electric power by extracting at least a portion of the power generated by the main engine; A ship propulsion system comprising a control unit that switches a power transmission path so that at least a portion of the power generated by the main engine is transmitted to at least one of the first shaft generator and the second shaft generator.

2. In paragraph 1, The above control unit A ship propulsion system that switches the power transmission path based on the revolutions per minute (rpm) of the main engine.

3. In paragraph 1, The above control unit When the rpm value of the main engine is less than the switching threshold, at least a portion of the power generated by the main engine is controlled to be transmitted to the first shaft generator, A ship propulsion system that controls at least a portion of the power generated by the main engine to be transferred to the second shaft generator when the rpm value of the main engine is greater than or equal to the switching threshold value.

4. In paragraph 3, The first shaft generator and the second shaft generator have different high-efficiency operating sections, which are rpm sections of the main engine that can operate at high efficiency. A ship propulsion system, wherein the switching threshold is an rpm value included in a high-efficiency operating section of either the first shaft generator or the second shaft generator.

5. In paragraph 3, The above control unit When the rpm value of the main engine falls within an overlapping range, the power transmission path is switched so that at least a portion of the power generated by the main engine is transmitted to both the first shaft generator and the second shaft generator, A ship propulsion system, wherein the above-mentioned overlapping section is a section including the above-mentioned switching threshold.

6. In paragraph 2, The above control unit When the rpm value of the main engine is less than the switching threshold, at least a portion of the power generated by the main engine is controlled to be transmitted to the first shaft generator, A ship propulsion system that controls at least a portion of the power generated by the main engine to be transmitted to both the first shaft generator and the second shaft generator when the rpm value of the main engine is greater than or equal to the switching threshold value.

7. In paragraph 6, The above control unit A ship propulsion system that adjusts the load of the second shaft generator so that the second shaft generator produces rated output when the rpm value of the main engine is greater than or equal to the switching threshold.

8. In paragraph 7, The above control unit A ship propulsion system that variably controls the power output of the first shaft generator in a direction that offsets the output fluctuation of the main engine when the output fluctuation of the main engine occurs or is expected as the load of the second shaft generator is adjusted.

9. In paragraph 1, The above control unit A ship propulsion system that variably controls the power output of the first shaft generator in a direction that offsets the torsional vibration when torsional vibration occurs or is expected to occur in the propulsion shaft.

10. In paragraph 1, The above control unit A ship propulsion system that applies braking force to the rotation of the propulsion shaft by increasing the load of the first shaft generator, and generates electric power from the rotation of the propulsion shaft that rotates while applying the braking force.

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