JP7520598B2 - Propulsion mechanism for electric propulsion ship and electric propulsion ship - Google Patents

Description

The present invention relates to a propulsion mechanism for an electric propulsion vessel and an electric propulsion vessel equipped with said propulsion mechanism.

An electric propulsion ship is a vessel that obtains propulsion by driving a propeller with an electric motor. Electric motors are easier to accelerate, decelerate, and start and stop than diesel or turbine engines, so they have better maneuverability than vessels propelled by these engines.

Diesel engines that use diffusion combustion of liquid fuels such as heavy oil are widely used as the power source for generators that supply electricity to electric propulsion ships, but in recent years dual fuel (DF) engines that can run on both liquid and gas fuels have been considered as a power source.
This is to reduce the cost of navigation by using the gas generated by vaporizing the liquefied gas cargo of the liquefied gas carrier as gas fuel instead of disposing of it. Another purpose is to reduce the amount of _NOx generated by using gas fuel to run the engine on a heat cycle other than the diesel cycle.

On the other hand, when gas fuel is used, if the combustion method is premixed combustion, the combustion is delayed compared to diffusion combustion in diesel engines, making abnormal combustion such as knocking and misfires more likely to occur. Therefore, it is difficult to run a DF engine with gas fuel, especially when the load fluctuation applied to the electric motor is large, and it has been necessary to run it with liquid fuel.
Therefore, a propulsion engine has been proposed that can be driven by gas fuel regardless of load fluctuations by providing a storage battery in addition to a generator as a power source for the electric motor, and supplying power from the storage battery to the electric motor when the load fluctuation applied to the electric motor becomes large (Patent Document 1).

Special Publication No. 2017-532239

In the configuration of Patent Document 1, a generator generates AC power and a motor is driven by AC, so an inverter device having an AC/DC converter, a DC bus, and a DC/AC converter connects the generator and the motor and adjusts the frequency of the power generated by the generator for motor control. On the other hand, a storage battery is a power source that supplies DC current, so a storage battery is connected to the DC bus of the inverter device, and the power supplied by the storage battery is converted to AC by the DC/AC converter and supplied to the electric motor.
In this structure, the structure of the inverter device becomes complicated, and since the storage battery discharges to the DC bus of the inverter device, it is difficult to control the voltage of the DC bus and it is difficult to stabilize the operation of the inverter device. Therefore, the propulsion mechanism of Patent Document 1 has a problem that the structure is complicated and it is difficult to stabilize the operation.
The present invention has been made in consideration of the above-mentioned problems, and aims to provide a propulsion mechanism for an electric propulsion ship that is powered by a generator that generates electricity using a DF engine that selectively drives diffusion combustion and premixed combustion, and a storage battery, and that has a simpler structure and is capable of stable operation than conventional propulsion mechanisms.

In order to solve the above problems, the propulsion mechanism of an electric propulsion ship of the present invention is a propulsion mechanism for an electric propulsion ship comprising: a generator that generates electricity using a DF engine that is driven by selecting between diffusion combustion of liquid fuel or premixed combustion of gas fuel; a storage battery; an electric motor that drives a propeller when power is supplied from the generator or the storage battery; and a switching control unit that controls selection of connection between the generator, the storage battery, and the electric motor and distribution of power, wherein the electric motor is a DC motor, and the switching control unit is configured to be able to connect and disconnect the storage battery and the electric motor, and when the DF engine is driven by premixed combustion and the electric motor is powered by receiving power from the generator while connected to the generator, the switching control unit is configured to connect the electric motor and the storage battery when a load fluctuation of the electric motor exceeds a predetermined threshold, and the switching control unit is configured to receive a signal indicative of the combustion state of the DF engine from the DF engine .
The electric propulsion ship of the present invention is characterized in that it comprises a propulsion mechanism of the electric propulsion ship described above, a liquefied gas tank for storing liquefied gas, and a supply means for supplying the gas generated by vaporizing or forcibly vaporizing the liquefied gas to the DF engine as the gas fuel.

In this configuration, when the load fluctuation of the DC motor increases while the DF engine is running on gas fuel and exceeds a predetermined threshold, the switching control unit supplies DC current from the storage battery to the DC motor to drive it.
This eliminates the need for a converter to convert DC power to AC power when connecting a DC motor to a storage battery, making it possible to achieve a simpler structure and more stable operation than before.

The present invention provides a propulsion mechanism for an electric propulsion vessel that is powered by a generator that generates electricity using a DF engine that selectively drives diffusion combustion and premixed combustion, and a storage battery, and that has a simpler structure and is capable of stable operation than conventional propulsion mechanisms.

1 is a functional block diagram showing an overview of an electric propulsion ship equipped with an electric propulsion mechanism according to an embodiment of the present invention. 2 is a modification showing a case where the generator in FIG. 1 is an AC generator. FIG. 2 is a diagram showing power supply in the case where an electric motor is driven by a generator that generates power using the driving force of a DF engine in FIG. 1 . FIG. 2 is a diagram showing power supply when an electric motor is driven by a storage battery in FIG. 1 . FIG. 2 is a diagram showing a case in which the electric motor in FIG. 1 is performing regenerative driving. FIG. 4 is a flow chart showing an example of a procedure for sailing a ship using an electric propulsion mechanism according to the present embodiment.

Preferred embodiments of the present invention will now be described in detail with reference to the drawings.
First, the configuration of an electric propulsion ship 1 equipped with a propulsion mechanism 3 according to this embodiment will be described with reference to FIGS. 1 to 5.
Here, the electric propulsion ship 1 is an example of a cargo ship that transports LNG (liquefied natural gas) as cargo, and is equipped with a propulsion mechanism 3 that drives a propeller 17 with an electric motor 11 powered by two sources: a generator 15 that generates electricity using a DF engine 23, and a storage battery 13.
As shown in FIG. 1 , the electric propulsion ship 1 includes a hull 5 , a fuel tank 19 , a liquefied gas tank 21 , and a propulsion mechanism 3 .

The hull 5 is a structural body that forms the hull of the electric propulsion vessel 1, and is configured to enclose the interior of the vessel with the vessel bottom, side walls, and exposed deck. The specific vessel shape, hull structure, and arrangement of watertight bulkheads are designed as appropriate according to the intended use of the electric propulsion vessel 1.

The fuel tank 19 is a tank that stores fuel for the electric propulsion ship 1. The shape, structure, capacity, and installation position of the fuel tank 19 are set appropriately taking into consideration the cruising range required for the electric propulsion ship 1, the displacement and stability of the hull 5, and the cargo load weight.
The fuel stored in the fuel tank 19 is liquid fuel. Liquid fuel here means fuel that is supplied to the DF engine 23 in a liquid state. In the electric propulsion ship 1, petroleum-based liquid fuel such as heavy oil is mainly used as the liquid fuel. Heavy oil C is mainly used in the case of large ships that transport LNG as cargo, but heavy oil A may be used in small ships.

The liquefied gas tank 21 is a tank for storing LNG as liquefied gas. Liquefied gas is a gas that is in a gaseous state at normal temperature and pressure and is liquefied by cooling or compression.
Since liquefied gas is cargo in the electric propulsion ship 1, the shape, structure, capacity and installation position of the liquefied gas tank 21 are appropriately set taking into consideration the displacement and stability of the hull 5, the loaded weight of the liquefied gas, and the temperature and pressure of the liquefied gas when loaded. Although Fig. 1 shows a schematic diagram of a spherical tank independent of the hull 5, such as an independent spherical tank, a structure in which the pressure and weight of the liquefied gas are held by the hull 5, such as a membrane type, may also be used.
Liquefied gas is cargo, but is also used as gas fuel in the electric propulsion ship 1. Gas fuel refers to fuel supplied in a gaseous state to the DF engine 23. The reason why the cargo liquefied gas can be used as gas fuel is that a part of the liquefied gas is vaporized by the intrusion heat due to the temperature difference between the inside of the liquefied gas tank 21 and the outside air during navigation and the temperature rise due to the kinetic energy caused by the movement of the ship, and becomes a gas fuel called BOG (Boil Off Gas). In addition, the liquefied gas may be forcibly vaporized using a vaporizer (not shown) and used as gas fuel.
The liquefied gas tank 21 is provided with a piping for supplying the BOG vaporized from LNG to the DF engine 23 as gas fuel, and a supply means 61 equipped with a pressurizing mechanism for adjusting the pressure of the gas fuel, as necessary.

The propulsion mechanism 3 is a mechanism that propels the electric propulsion vessel 1, and includes a DF engine 23, a generator 15, a storage battery 13, an electric motor 11 which is a DC motor, a reduction gear 7, a propeller 17, and a switching control unit 9.

The DF engine 23 is an internal combustion engine that selectively operates by diffusion combustion of liquid fuel or premixed combustion of gas fuel.
The DF engine 23 is supplied with liquid fuel from the fuel tank 19, and BOG produced by vaporizing the liquefied gas stored inside the liquefied gas tank 21 is supplied as gas fuel.

When the DF engine 23 is driven by diffusion combustion of liquid fuel, the combustion method is compression ignition and the combustion cycle is a diesel cycle.
When the DF engine 23 is driven by liquid fuel, the thermal efficiency is superior to when gas fuel is used because it is a diesel cycle, and since knocking and misfires do not occur, it is also resistant to load fluctuations on the electric motor 11.

When the DF engine 23 is driven by premixed combustion of gas fuel, the gas fuel is mixed with intake air in a pre-chamber of the combustion chamber such as an intake manifold (not shown) before being introduced into the combustion chamber. The combustion method is spark ignition, and the combustion cycle is mainly the Otto cycle.
When the DF engine 23 is driven by gas fuel, it is advantageous in that the BOG can be effectively utilized.

The DF engine 23 can be driven by selectively using diffusion combustion of liquid fuel or premixed combustion of gas fuel, and its structure, shape, dimensions, and installation position are appropriately set so that it can obtain the power necessary to propel the electric propulsion ship 1 and can be mounted on the electric propulsion ship 1. Usually, the size is determined so that it can be mounted in the engine room of the hull 5. Note that with a two-stroke engine, the combustion gas and intake air are mixed during scavenging, making it unsuitable for premixing gas fuel, and therefore the DF engine 23 is preferably a four-stroke engine.
The switching between liquid fuel and gas fuel is, for example, manual, but may also be automatic. Normally, the engine is driven by liquid fuel when starting and stopping, and one of liquid fuel and gas fuel is selected when cruising.

The generator 15 is one of the power sources for the electric motor 11, and generates electricity by transmitting power from the DF engine 23. The generated electricity is supplied to the electric motor 11 and used to propel the electric propulsion ship 1.
The generator 15 has an input shaft to which the power of the DF engine 23 is transmitted, can generate the electric power required to propel the electric propulsion ship 1, and can have an appropriate structure, shape, dimensions, and installation position within the scope of what can be accommodated in the hull 5. The generator 15 is usually disposed in the engine room of the hull 5 adjacent to the DF engine 23.

The generator 15 is preferably a DC generator. By DC generator, we mean a generator that generates DC power.
Since the electric motor 11 of the propulsion mechanism 3 also uses DC, if the generator 15 is a DC generator, the power generated by the generator is supplied to the electric motor 11 as DC.
Therefore, when supplying the electric power generated by the generator 15 to the electric motor 11, a converter for AC/DC conversion is not required, and the structure is simpler than when the generator 15 generates AC power.

The generator 15 may be an AC generator. An AC generator means a generator that generates AC power.
Since the electric motor 11 of the propulsion mechanism 3 is DC, when the generator 15 is an AC generator, the power output section of the generator 15 is connected to a converter 25 as shown in Fig. 2. The converter 25 is a converter that converts AC power into DC power. The AC power generated by the generator 15 is output to the converter 25 and converted into DC power, and is supplied to the electric motor 11.
If the generator 15 is an AC generator, this has the advantage that there is a wider range of options for type and structure than for DC generators, since AC generators are the mainstream for generators on existing ships.
In the following description, unless otherwise specified, the generator 15 will be described as a DC generator.

The storage battery 13 shown in FIG. 1 is one of the power sources for the electric motor 11, and is a battery that can be repeatedly charged and discharged.
The storage battery 13 has a capacitance and number of charge/discharge cycles that can charge and discharge the power required for propulsion of the electric propulsion ship 1, and the basic configuration of the electrodes, electrolyte, etc., as well as the type, dimensions, shape, and installation position of the battery are determined based on the capacity that can be accommodated within the hull 5. A specific example of the type of battery is a lithium ion secondary battery. The power discharged by the storage battery 13 is direct current.

When power is supplied to the electric motor 11 from the generator 15 or the storage battery 13, the electric motor 11 rotates a rotor (not shown) to transmit torque to the propeller 17 to rotate it.
The electric motor 11 can generate the rotational force required to propel the electric propulsion ship 1 using power from the generator 15 or the storage battery 13 and transmit it to the propeller 17, and as long as it can be stored within the hull 5, its structure, shape, dimensions, and installation position can be set as appropriate.

However, the electric motor 11 is a DC motor for the following reasons.
A generator 15 and a storage battery 13 are provided as the power source for the motor that drives the propeller 17 of the electric propulsion ship 1, and an electric propulsion engine that uses the storage battery 13 as a power source when load fluctuations become large while driving the DF engine 23 with gas fuel is well known.
On the other hand, since the power discharged from the storage battery 13 is direct current, when the motor driving the propeller 17 is an AC motor, it is necessary to connect the storage battery 13 and the AC motor via a DC/AC converter and convert the DC power discharged from the storage battery 13 into AC power. In particular, when the generator 15 of the DF engine 23 is an AC generator, an inverter device including an AC/DC converter that adjusts the frequency of the AC power supplied from the generator 15 to the electric motor 11, a DC bus, and a DC/AC converter connects between the generator 15 and the electric motor 11. In this structure, in order to connect the storage battery 13 to the DC/AC converter, it is necessary to connect the storage battery 13 to the DC bus, and since the power flowing through the DC bus is not stable, the operation of the inverter device is likely to become unstable.
In contrast, in the propulsion mechanism 3 according to this embodiment, the electric motor 11 is a DC motor, and there is no need to connect the storage battery 13 and the electric motor 11 via a DC/AC converter, making it possible to simplify the structure.
In addition, since the electric motor 11 is a DC motor, an inverter device is not required whether the generator 15 is DC or AC. Therefore, a stable operation is possible without the unstable structure of connecting the storage battery 13 to the DC bus of the inverter device.

The reducer 7 is a power transmission mechanism equipped with a gear mechanism (not shown) that adjusts the direction and rotation speed of the rotational force generated by the electric motor 11 and transmits it to the propeller 17. The input shaft of the reducer 7 is connected to the output shaft of the electric motor 11 to transmit power from the electric motor 11. The output shaft of the reducer 7 is connected to a boss of the propeller 17 to rotate the propeller 17 in a desired direction and at a desired rotation speed.
The reduction gear 7 can transmit the rotational force required for the navigation of the electric propulsion vessel 1 to the propeller 17, and as long as it can be stored in the hull 5, its structure, shape, dimensions, and installation position can be set appropriately.

The propeller 17 is a thruster that converts the rotational force transmitted from the reduction gear 7 into thrust acting in the direction in which the ship sails, thereby propelling the electric propulsion ship 1. The propeller 17 includes a boss that is connected to the output shaft of the reduction gear 7 to transmit the rotational force, and propeller blades that protrude from the boss in a direction perpendicular to the rotational shaft and convert the rotational force into thrust.
The propeller 17 can generate the propulsive force necessary for the navigation of the electric propulsion vessel 1, and its structure, shape, and dimensions can be appropriately set so long as it does not interfere with other structures such as the hull 5 and the rudder.

The switching control unit 9 is a device that controls the selection of the power line connection and the distribution of power between the generator 15, the storage battery 13, and the electric motor 11, and is connected to these devices by power lines.

Since the switching control unit 9 is a device that selects the connection of DC power and distributes power, it is connected to the storage battery 13 and the electric motor 11 without going through an AC-DC converter such as an inverter device or converter.
Even when the generator 15 is a DC generator, the switching control unit 9 is connected to the generator 15 without going through a converter such as an inverter device or a converter.
When the generator 15 is an AC generator, the switching control unit 9 is connected to the generator 15 via a converter 25 shown in FIG.
As long as the switching control unit 9 can control the selection of the power line connection between the generator 15, the storage battery 13, and the electric motor 11 and the distribution of power, a device combining a known switchboard and its control device may be used.

The switching control unit 9 controls the selection of the connection of the power lines between the generator 15, the storage battery 13, and the electric motor 11 and the distribution of power based on the following conditions.
First, when the DF engine 23 is performing diffusion combustion using liquid fuel and the electric motor 11 is connected to the generator 15 and receives power from the generator 15 to perform power running, the switching control unit 9 maintains the state in which the generator 15 is connected to the electric motor 11. In this state, as shown in Fig. 3, DC power generated by the generator 15 is supplied to the electric motor 11 via the switching control unit 9, and the electric motor 11 is powered. When the electric motor 11 is powered, a rotational force is generated and transmitted to the propeller 17 via the reduction gear 7. The propeller 17 converts the transmitted rotational force into propulsion force to navigate the electric propulsion ship 1.

Whether the DF engine 23 is in diffusion combustion or not may be determined by configuring the DF engine 23 to output a signal indicating the combustion state of the DF engine 23 to the switching control unit 9, and the switching control unit 9 may determine this from the received signal. Alternatively, the switching control unit 9 may be provided with a manual switch for selecting whether the DF engine 23 is in diffusion combustion or premixed combustion, and the switching control unit 9 may determine this by the engineer operating the DF engine 23 operating the switch.

The storage battery 13 is not used as a power source for the electric motor 11 during diffusion combustion using liquid fuel, so the switching control unit 9 does not connect the storage battery 13 to the electric motor 11. This is because diffusion combustion using liquid fuel has a higher ability to follow load fluctuations than premixed combustion using gas fuel, so sufficient power can be supplied to the electric motor 11 without using the storage battery 13 as a power source.

However, if the charging rate of the storage battery 13 falls below a predetermined lower limit charging rate, the switching control unit 9 may supply at least a portion of the electricity generated by the generator 15 to the storage battery 13 to charge the storage battery 13 until it reaches a predetermined upper limit charging rate.
In this way, when the charging rate of the storage battery 13 falls below the lower limit, the generator 15 is used to charge the storage battery 13, thereby preventing the storage battery 13 from running out of power.
The charging rate of the storage battery 13 can be obtained by measuring the discharge voltage and calculating the capacitance by referring to a discharge curve or the like.

When the DF engine 23 is performing premixed combustion using gas fuel and the electric motor 11 is connected to the generator 15 and is powered by receiving power from the generator 15, the switching control unit 9 performs the following control.
First, when the load fluctuation of the electric motor 11 exceeds a predetermined threshold, the switching control unit 9 connects the electric motor 11 to the storage battery 13. The predetermined threshold is a value at which knocking or misfire may occur in the DF engine 23 during premixed combustion.
The load fluctuation here specifically refers to the fluctuation in the load torque of the electric motor 11, and may be calculated from the load rate or the like, or may be actually measured by a torque sensor or the like.

When the electric motor 11 and the storage battery 13 are connected, as shown in Fig. 4, power is supplied from the storage battery 13 to the electric motor 11, and the electric motor 11 is driven. The storage battery 13 has a higher ability to follow load fluctuations than premixed combustion using gas fuel. Therefore, by supplying power from the storage battery 13 to the electric motor 11 when the load fluctuation exceeds a threshold value, even if a load fluctuation occurs that makes it difficult to drive the DF engine 23 stably with premixed combustion, it is not necessary to switch the DF engine 23 to diffusion combustion. Therefore, the conditions of load fluctuation under which the DF engine 23 can be driven with premixed combustion can be broadened.
In addition, since the electric motor 11 is DC, no converter is required to convert DC power to AC power when connecting the electric motor 11 to the storage battery 13. This allows for a simpler structure and more stable operation than in the past.

When the storage battery 13 is connected to the electric motor 11, the switching control unit 9 does not have to connect the generator 15 to the electric motor 11. In this case, the switching control unit 9 may connect the generator 15 to the storage battery 13 without connecting it to the electric motor 11, and charge the storage battery 13 with the generated power. Specifically, the generator 15 supplies the storage battery 13 with power equivalent to the power consumed by the storage battery 13 to drive the electric motor 11, thereby charging the storage battery 13. In this case, it is possible to prevent the storage battery 13 from running out of power while the storage battery 13 is supplying power to the electric motor 11. However, in this structure, the electric motor 11 is driven only by the storage battery 13, so the output of the storage battery 13 needs to be equal to or greater than the maximum output of the generator 15.

When the storage battery 13 is connected to the electric motor 11, the generator 15 may also supply power to the electric motor 11 while maintaining a state in which the generator 15 is connected to the electric motor 11. In this case, the storage battery 13 may supply to the electric motor 11 the amount of power that is insufficient in the amount of power supplied to the electric motor 11 by the generator 15. This configuration is advantageous in that the capacity of the storage battery 13 only needs to be equivalent to the amount of power that is insufficient to be supplied by the generator 15, making it easier to miniaturize the storage battery 13.

When the DF engine 23 is performing premixed combustion using gas fuel, the electric motor 11 is connected to the generator 15 and is powered by receiving power, and the load fluctuation of the electric motor 11 is equal to or less than a threshold, the switching control unit 9 does not connect the electric motor 11 to the storage battery 13, as in the case of diffusion combustion. In this case, the switching control unit 9 maintains the state in which the generator 15 is connected to the electric motor 11.
This is because, when the load fluctuation of the electric motor 11 is equal to or less than a threshold value, the DF engine 23 can operate stably even in the case of premixed combustion. Also, if the storage battery 13 continues to be used as a power source, the battery may run out.
When the electric motor 11 and the generator 15 are connected, electric power is supplied from the generator 15 to the electric motor 11, and the electric motor 11 is driven.

When the charging rate of the storage battery 13 during premixed combustion is equal to or lower than a predetermined lower limit charging rate, the switching control unit 9 may supply at least a portion of the power generated by the generator 15 to the storage battery 13 to charge the storage battery 13 until the charging rate reaches a predetermined upper limit charging rate. The reason for this is to prevent the battery from running out, as in the case of charging the storage battery 13 during diffusion combustion.

When the electric motor 11 is regeneratively driven, specifically when regeneratively generated power is supplied from the electric motor 11 to the switching control unit 9, the switching control unit 9 connects the electric motor 11 to the storage battery 13 and charges the storage battery 13 with the supplied regenerative power as shown in Fig. 5. An example of a case in which the electric motor 11 is regeneratively driven is when the propeller 17 rotates in the reverse direction to when sailing due to the influence of waves or the like. In this case, if there is no device that consumes the regenerative power, the regenerative power will flow into the switching control unit 9, the generator 15, and the storage battery 13 as reverse power, which may cause the breaker to trip or the device to burn out due to heating caused by the increase in power.
One method of consuming regenerative power is to use a resistor to convert it into heat, but by charging the regenerative power into a storage battery 13, a portion of the regenerative power that was previously converted into heat by a resistor can be used as power for navigating the electric propulsion ship 1.
When charging the storage battery 13 with regenerative power, it is preferable not to connect the electric motor 11 to the generator 15. This is because, if connected, there is a possibility that reverse power will flow into the generator 15. Furthermore, when the charging rate of the storage battery 13 is equal to or higher than the upper limit charging rate while the electric motor 11 is in regenerative driving, or when regenerative power that exceeds the discharge capacity of the storage battery 13 is generated, the regenerative power is not charged to the storage battery 13 but is consumed as heat by a resistor (not shown).

When the electric motor 11 is connected to the storage battery 13, the condition for disconnecting the electric motor 11 is when the connection conditions are no longer satisfied. Specifically, when the electric motor 11 is connected to the storage battery 13 while the electric motor 11 is generating regenerative power, the condition for disconnecting the electric motor 11 is when regenerative power generation is no longer performed or when charging is no longer possible.
When the electric motor 11 is connected to the storage battery 13 while the electric motor 11 is in power running, the condition for disconnecting the electric motor 11 is when the DF engine 23 is in diffusion combustion using liquid fuel, or when the load fluctuation of the electric motor 11 becomes equal to or less than a threshold value while the DF engine 23 is in premixed combustion using gas fuel.
The above is a description of the structure of the electric propulsion boat 1 equipped with the propulsion mechanism 3 in this embodiment.

Next, an example of a procedure for sailing the electric propulsion ship 1 equipped with the propulsion mechanism 3 according to this embodiment will be described with reference to Fig. 6. In the following description, an example will be taken of a procedure in which the connection between the electric motor 11 and the generator 15 is maintained even when the electric motor 11 and the storage battery 13 are connected, and the storage battery 13 supplies the electric motor 11 with power that makes up for a shortage in the power supplied by the generator 15 to the electric motor 11.
First, the switching control unit 9 determines whether the electric motor 11 is generating regenerative power based on whether or not reverse power is being supplied from the electric motor 11. If the electric motor 11 is generating regenerative power, the process proceeds to S2. If the electric motor 11 is not generating regenerative power, the process proceeds to S3 (S1 in FIG. 6).
If it is determined in S1 that regenerative power generation is in progress, the switching control unit 9 determines whether the storage battery 13 can be charged with regenerative power, specifically, whether the charging rate of the storage battery 13 is less than the upper limit charging rate and the regenerative power does not exceed the discharge capacity of the storage battery 13 (S2 in FIG. 6). If it is determined that charging is possible, the storage battery 13 is connected to the electric motor 11, the regenerative power is charged to the storage battery 13, and the system returns (S2-2 in FIG. 6). At this time, the switching control unit 9 does not connect the electric motor 11 to the generator 15. If it is determined in S2 that charging is not possible, the storage battery 13 is not connected to the electric motor 11, and a resistor (not shown) is connected to the electric motor 11 to consume the regenerative power as heat energy and the system returns (S2-3 in FIG. 6).

If it is determined in S1 that regenerative power generation is not in progress, the switching control unit 9 connects the electric motor 11 to the generator 15 and drives the electric motor 11 with the power supplied by the generator 15 (S3 in FIG. 6). At this time, if the electric motor 11 and the storage battery 13 were connected because regenerative power generation was in progress until just before, the connection is released. Next, the switching control unit 9 determines whether the DF engine 23 is in gas combustion or not, that is, whether premixed combustion using gas fuel is in progress, and if gas combustion is in progress, the process proceeds to S5, and if gas combustion is not in progress, the process proceeds to S7-2 (S4 in FIG. 6).
If it is determined in S4 that the DF engine 23 is in gas combustion, the switching control unit 9 acquires the load fluctuation of the electric motor 11 (S5 in FIG. 6). Furthermore, the switching control unit 9 determines whether the load fluctuation acquired in S5 exceeds a predetermined threshold value, and if it determines that it exceeds the threshold value, the process proceeds to S7, and if it determines that it does not exceed the threshold value, the process proceeds to S7-2 (S6 in FIG. 6).
If it is determined in S6 that the load fluctuation exceeds the threshold value, the switching control unit 9 connects the storage battery 13 and the electric motor 11, the power supplied by the storage battery 13 compensates for the load fluctuation, drives the electric motor 11, and proceeds to S8 (S7 in Figure 6).

If it is determined in S4 that the DF engine 23 is not gas-burning, or if it is determined in S6 that the load fluctuation does not exceed the threshold, the switching control unit 9 does not connect the storage battery 13 and the electric motor 11, or if they are already connected, it disconnects them and proceeds to S8 (S7-2 in Figure 6).
When S7 or S7-2 is executed, the switching control unit 9 acquires the charging rate of the storage battery 13 (S8 in FIG. 6). If the acquired charging rate is equal to or lower than the lower limit charging rate, the process proceeds to S10, and if the charging rate is not equal to or lower than the lower limit charging rate, the process returns (S9 in FIG. 6).
If it is determined in S9 that the charging rate is equal to or lower than the lower limit charging rate, the switching control unit 9 connects the generator 15 and the storage battery 13, charges the storage battery 13 until the charging rate of the storage battery 13 reaches the upper limit charging rate, and then returns (S10 in Figure 6).
This concludes the description of one example of the procedure for sailing the electric propulsion ship 1 equipped with the propulsion mechanism 3 according to this embodiment.

In this manner, in the propulsion mechanism 3 of this embodiment, when the load fluctuation becomes large while the DF engine 23 is being driven by gas fuel, the switching control unit 9 supplies DC current from the storage battery 13 to the electric motor 11, which is a DC motor, to drive it.
Therefore, a converter for converting DC power to AC power is not required when connecting the storage battery 13 to the electric motor 11, making it possible to achieve a simpler structure and more stable operation than in the past.

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the embodiments. It is natural that a person skilled in the art would come up with various modifications and improvements within the scope of the technical concept of the present invention, and these are also included in the present invention.

1: Electric propulsion vessel 3: Propulsion mechanism 5: Hull 7: Reducer 9: Switching control unit 11: Electric motor 13: Storage battery 15: Generator 17: Propeller 19: Fuel tank 21: Liquefied gas tank 23: DF engine 25: Converter 61: Supply means

Claims (9)

A propulsion mechanism for an electric propulsion ship, comprising: a generator that generates electricity using a DF engine that selectively drives diffusion combustion of liquid fuel or premixed combustion of gas fuel; a storage battery; an electric motor that drives a propeller when power is supplied from the generator or the storage battery; and a switching control unit that selects connections of the generator, the storage battery, and the electric motor and controls distribution of power,
the electric motor is a DC motor,
the switching control unit has a configuration capable of connecting and disconnecting the storage battery and the electric motor, and when the DF engine is driven by premixed combustion and the electric motor is powered by receiving power from the generator while connected to the generator, when a load fluctuation of the electric motor exceeds a predetermined threshold value, the switching control unit has a configuration for connecting the electric motor and the storage battery;
A propulsion mechanism for an electric propulsion vessel, characterized in that the switching control unit is configured to receive a signal indicating a combustion state of the DF engine from the DF engine. 2. The propulsion mechanism for an electric propulsion vessel according to claim 1, wherein the generator is a DC generator. 2. The propulsion mechanism for an electric propulsion vessel according to claim 1 , wherein the generator is an AC generator and is connected to the switching control unit via a converter that converts the generated AC power into DC power. A propulsion mechanism for an electric propulsion ship, comprising: a generator that generates electricity using a DF engine that selectively drives diffusion combustion of liquid fuel or premixed combustion of gas fuel; a storage battery; an electric motor that drives a propeller when power is supplied from the generator or the storage battery; and a switching control unit that selects connections of the generator, the storage battery, and the electric motor and controls distribution of power,
the electric motor is a DC motor,
The switching control unit, when the DF engine is driven by premixed combustion and the electric motor is powered by receiving electric power from the generator in a state where the electric motor is connected to the generator,
When a load fluctuation of the electric motor exceeds a predetermined threshold, the electric motor and the storage battery are connected to each other,
When the electric motor and the storage battery are connected, the switching control unit
A propulsion mechanism for an electric propulsion ship, characterized in that the generator is connected to the storage battery without being connected to the electric motor, and the generator supplies and charges the storage battery with power equivalent to the power consumed by the storage battery to drive the electric motor. When the electric motor and the storage battery are connected, the switching control unit
A propulsion mechanism for an electric propulsion ship as described in any one of claims 1 to 3, wherein the generator is connected to the storage battery without being connected to the electric motor, and the generator supplies and charges the storage battery with power equivalent to the power consumed by the storage battery to drive the electric motor. When the electric motor and the storage battery are connected, the switching control unit maintains a state in which the generator is connected to the electric motor,
4. The propulsion mechanism for an electric propulsion ship according to claim 1, wherein the storage battery supplies to the electric motor an amount of electric power that is insufficient when the electric power supplied to the electric motor by the generator is compensated for by the storage battery. The switching control unit is
A propulsion mechanism for an electric propulsion ship as described in any one of claims 1 to 6, wherein when the charging rate of the storage battery falls below a predetermined lower limit charging rate, at least a portion of the power generated by the generator is supplied to the storage battery to charge the storage battery until the charging rate reaches a predetermined upper limit charging rate. The switching control unit is
A propulsion mechanism for an electric propulsion ship as described in any one of claims 1 to 6, wherein when regeneratively generated electricity is supplied from the electric motor, the electric motor is connected to the storage battery and the supplied electricity is charged to the storage battery. A propulsion mechanism for an electric propulsion ship according to any one of claims 1 to 8 ;
A liquefied gas tank for storing liquefied gas;
An electric propulsion ship comprising a supply means for supplying the gas generated by vaporizing or forcibly vaporizing the liquefied gas to the DF engine as the gas fuel.

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