Shaft generator system

Abstract

To provide a shaft generator system for use with a 2-stroke, uniflow scavenging-type, crosshead internal combustion engine.SOLUTION: The present shaft generator system comprises a shaft generator, a first electric circuit to convert an AC current from a first frequency to a second frequency, and a shaft generator control system constructed to receive a first signal indicating electric power consumption. The shaft generator control system is operatively connected to the shaft generator and is configured to control the power generation amount of the shaft generator based on the first signal. The shaft generator control system is configured to allow the electric power consumption to be different from the power generation amount within a first period of at least two seconds.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a shaft generator system for use with a two-stroke uniflow scavenged crosshead type internal combustion engine, and to a combined propulsion and generator system for propelling a marine vessel. [Background technology]

[0002] Two-stroke internal combustion engines used for ship propulsion have for many years been equipped with shaft generators, which are used to generate electricity for various on-board equipment such as thrusters, pumps, gas reliquefaction plants, reefer containers, and the general hotel load.

[0003] Traditionally, shaft generators are directly coupled to the ship's AC grid, closely coupling the main engine speed and the AC grid frequency. This coupling helps to stabilize both the engine speed and the grid frequency.

[0004] Shaft generators were often connected to the engine through a gearbox, allowing the frequency of the AC grid to be different from the rpm of the engine.

[0005] However, gearboxes can be expensive, and to provide a stable frequency for the AC grid, the available rpm of the engine is limited to a small number of discrete values ​​that depend on the gear ratio of the gearbox.

[0006] To combat the above challenges, shaft generators have been connected to consumers through AC-DC and DC-AC frequency conversion equipment.

[0007] This decouples the main engine speed from the grid frequency, which is a more versatile solution as the shaft generator can operate over a wide range of engine speeds without affecting the grid frequency.

[0008] However, by decoupling the engine speed from the grid frequency, the inherent stabilization of the system is lost.

[0009] As a result, the maximum power output of such shaft generators at a particular engine speed is limited to prevent engine instability.

[0010] Thus, there remains a challenge in providing improved shaft generator systems. Summary of the Invention

[0011] According to a first aspect, the present invention relates to a shaft generator system for use with a two-stroke uniflow scavenged crosshead type internal combustion engine comprising an engine shaft, at least one cylinder, a cylinder cover, a piston, an engine fuel control system, a fuel supply system and a scavenging system, the cylinder having a cylinder wall, the cylinder cover being disposed on an upper portion of the cylinder and having an exhaust valve, the piston being disposed within the cylinder movably along a central axis between bottom dead centre and top dead centre, the scavenging system having a scavenging inlet disposed at a bottom of the cylinder, the fuel supply system being configured to inject fuel into a main combustion chamber defined between the piston and the cylinder cover based on a control signal provided by the engine fuel control system, and the shaft generator system comprising: a shaft generator configured to generate an AC current having a first frequency dependent on the RPM of the shaft; a first electrical circuit for converting the AC current from the first frequency to a second frequency; and a shaft generator control system configured to receive a first signal indicative of power consumption; the shaft generator control system is operatively connected to the shaft generator and configured to control the amount of power generated by the shaft generator based on the first signal; The shaft generator control system is configured to allow power consumption to differ from power generation within a first period of at least two seconds.

[0012] As a result, by introducing deliberate sluggishness into the shaft generator control system, the destabilizing effects resulting from constant power production constraints can be significantly reduced, potentially allowing the shaft generator to produce more power without destabilizing the two-stroke engine to unacceptable levels.

[0013] The internal combustion engine is preferably a large slow speed turbocharged uniflow scavenged two-stroke crosshead type internal combustion engine for propelling a marine vessel or stationary power plant having an output of at least 400 kW per cylinder. The internal combustion engine may include a turbocharger driven by exhaust gases generated by the internal combustion engine and configured to compress the scavenged air.

[0014] The internal combustion engine preferably includes a plurality of cylinders, for example, 4 to 14 cylinders. The internal combustion engine may further include a cylinder cover, an exhaust valve, a piston, a fuel valve, and a scavenging inlet for each of the plurality of cylinders.

[0015] The internal combustion engine may be any type of two-stroke uniflow scavenged crosshead type internal combustion engine, such as a single fuel engine or a dual fuel engine. The fuel supply system may be configured to inject liquid fuel and / or fuel gas into the cylinder. The liquid fuel may be any type of liquid fuel, such as heavy fuel oil or marine diesel oil. The fuel gas may be any type of fuel gas, such as liquefied natural gas (LNG), methane, ammonia, ethane, and liquefied petroleum gas (LPG). The engine may have a diesel cycle mode and / or an Otto cycle mode. As an example, if the engine is a dual fuel engine, the engine may have an Otto cycle mode when running on fuel gas and a diesel cycle mode when running on an alternative fuel, such as heavy fuel oil or marine diesel oil.

[0016] The shaft generator control system may comprise a processing unit. The processing unit may be any processing unit, such as a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller unit (MCU), a field programmable gate array (FPGA), or any combination thereof. The processing unit may comprise one or more physical processors and / or may be a combination of multiple individual processing units. The first period may have a length of at least 5 seconds or 10 seconds, i.e. the shaft generator control system may be configured to allow the power consumption to differ from the power generation within a period of at least 5 seconds or at least 10 seconds.

[0017] The first signal may be a signal measured using a sensor. The sensor may be located in the first electric circuit or in an AC grid connected to the first electric circuit. The sensor may be configured to measure a voltage of the first electric circuit or the AC grid. The sensor may be an indication that power generation is too low if the voltage starts to drop and correspondingly, an indication that power generation is too high if the voltage starts to rise.

[0018] The shaft generator control system may be configured to vary the amount of electrical power being generated by varying the torque of the generator. As an example, the shaft generator control system may be configured to control the generator to gradually increase the torque of the generator when the need for electrical power increases and to gradually decrease the torque of the generator when the need for electrical power decreases.

[0019] In some embodiments, the shaft generator system is configured to allow a difference between power consumption and power generation to be at least 10% of a rated shaft generator power within a first period of time.

[0020] The rated shaft generator power is the maximum power that the shaft generator can generate.

[0021] In some embodiments, the first electric circuit comprises an AC-DC rectifier, a DC grid, and a DC-AC converter, the AC-DC rectifier configured to receive an AC current at a first frequency from the shaft generator, convert the received AC current to a DC current, and provide the converted DC current to the DC grid, and the DC-AC converter configured to receive the converted DC current from the DC grid, convert the converted DC current to an AC current having a second frequency, and provide the AC current having the second frequency to the AC grid.

[0022] In some embodiments, the shaft generator system comprises an additional power source configured to deliver electrical energy when power consumption exceeds power generation of the shaft generator.

[0023] As a result, by providing an additional power source, sufficient power can be delivered to meet the on-board equipment needs even when power production from the shaft generator falls short of power consumption.

[0024] The additional power source may be an electrical energy storage device, such as a chemical battery, a supercapacitor, or a flywheel energy storage system, configured to receive and deliver electrical energy. Alternatively / additionally, the additional power source may be a generating set comprising an internal combustion engine and a generator. The internal combustion engine is preferably a medium or high speed four-stroke engine allowing for rapid control of the amount of power generated. The generating set may further be connected to a flywheel, which also allows the generating set to absorb excess power generated by the shaft generator.

[0025] In some embodiments, the additional power source is also configured to receive electrical energy when the power generation of the shaft generator exceeds the power consumption.

[0026] The additional power source may be directly controlled by the shaft generator control system. Alternatively, the additional power source may comprise a dedicated control system configured to control the additional power source, e.g., to control the additional power source to either receive electrical energy or to deliver electrical energy. The dedicated control system may be communicatively coupled to the shaft generator control system and configured to receive control signals from the shaft generator control system, e.g., the shaft generator control system may send a control signal to the dedicated control system signaling the dedicated control system to control the additional power source to either receive electrical energy or to deliver electrical energy.

[0027] Alternatively / additionally, the dedicated control system may be configured to independently estimate a difference between the power generation and power consumption of the shaft generator and to control the additional power source to either receive electrical energy or deliver electrical energy. The dedicated control system may estimate the difference by receiving a signal corresponding to the first signal.

[0028] In some embodiments, the additional power source is capable of delivering and / or receiving power with an effect of at least 100 kW, at least 250 kW, or at least 500 kW.

[0029] In some embodiments, the additional power source is capable of delivering at least 0.25 kWh, 0.5 kWh, or 1 kWh without receiving power from the shaft generator.

[0030] In some embodiments, the additional power source is capable of receiving at least 0.25 kWh, 0.5 kWh, or 1 kWh without delivering power to the shaft generator system.

[0031] In some embodiments, the additional power source is capable of delivering at least 0.25 kWh, 0.5 kWh, or 1 kWh, with a minimum output of at least 100 kW, at least 250 kW, or at least 500 kW, without receiving power from the shaft generator.

[0032] In some embodiments, the shaft generator control system is configured to receive a signal indicative of a status of the additional power source and to control the shaft generator based on the signal, for example the shaft generator control system may be configured to receive a second signal indicative of a status of the additional power source and to control the shaft generator based on the second signal.

[0033] As a result, it can be ensured that the additional power source is not depleted and is always available.

[0034] The second signal may indicate the ability of the additional power source to supply power to the system. Additionally / alternatively, the second signal may indicate the ability of the additional power source to absorb power from the system. As an example, if the additional power source is an electric energy storage device, the second signal may indicate an energy level of the electric energy storage device, e.g., if the electric energy storage device is a chemical battery, the energy level may be estimated by measuring the voltage of the battery using a voltage sensor. The shaft generator control system may be configured to periodically estimate the energy level of the electric energy storage device and control the power generation of the shaft generator based on the periodic estimate. As an example, if the energy level of the electric energy storage device falls below a desired target, the shaft generator control system may be configured to control the shaft generator to generate more power than is being consumed, thereby restoring the energy level of the electric energy storage device to the desired level. Correspondingly, if the energy level of the electric energy storage device is above a desired target, the shaft generator control system may be configured to control the shaft generator to generate less power than is being used, thereby using the excess electric energy of the electric energy storage device.

[0035] As another example, if the additional power source is a generating set, the second signal may be indicative of the power output of an engine of the generating set. If the engine of the generating set is operating near rated power (maximum power), the shaft generator control system may control the shaft generator to increase the amount of power being generated. If the generating set includes a flywheel, the second signal may be indicative of the speed of the flywheel. If the speed of the flywheel is near its maximum speed, the shaft generator control system may control the shaft generator to generate less electrical energy than is being consumed, thereby allowing the kinetic energy of the flywheel to be converted into electrical energy and the speed of the flywheel to be reduced.

[0036] In some embodiments, the additional source of electrical energy is connected to the DC grid and configured to receive electrical energy and / or deliver electrical energy to the DC grid.

[0037] As a result, electrical energy is easier to receive and deliver to the system since it does not need to be in phase with the AC grid frequency.

[0038] In some embodiments, the DC-AC converter is configured to modify the second frequency when an amount of power being consumed is higher and / or lower than an amount of power being generated by the shaft generator.

[0039] The DC-AC converter may be configured to decrease the second frequency when an amount of power being consumed is higher than an amount of power being generated by the shaft generator and correspondingly, the DC-AC converter may be configured to increase the second frequency when an amount of power being consumed is lower than an amount of power being generated by the shaft generator.

[0040] In some embodiments, the shaft generator control system is operably connectable to an engine fuel control system of a two-stroke uniflow scavenged crosshead type internal combustion engine and configured to receive information from and / or send information to the engine fuel control system.

[0041] In some embodiments, the shaft generator control system is configured to provide information regarding power demand to the engine fuel control system.

[0042] As a result, the engine fuel control system may be able to react faster to changes in power consumption, thereby keeping the engine speed more stable.

[0043] In some embodiments, the shaft generator control system is configured to send a control signal to the engine fuel control system in response to detecting a change in power consumption, the control signal instructing the engine fuel control system to modify the amount of fuel delivered to the cylinders before the engine fuel control system detects a difference between the nominal engine speed and the actual engine speed.

[0044] As an example, if the shaft generator control system detects an increase in power consumption, the shaft generator control system may send a control signal to the engine fuel control system instructing the engine fuel control system to increase the amount of fuel delivered to the cylinders before detecting a decrease in actual engine speed. Correspondingly, if the shaft generator control system detects a decrease in power consumption, the shaft generator control system may send a control signal to the engine fuel control system instructing the engine fuel control system to decrease the amount of fuel delivered to the cylinders before detecting an increase in actual engine speed.

[0045] In some embodiments, the shaft generator control system is configured to receive information regarding the engine speed, and the shaft generator control system is further configured to control the amount of power generated by the shaft generator based on the received information regarding the engine speed.

[0046] In some embodiments, information about the engine speed enables the shaft generator control system to determine a difference between a nominal engine speed and an actual engine speed, and the shaft generator control system is configured to control the shaft generator to reduce power generation when the actual engine speed is below the nominal engine speed and to increase power generation when the actual engine speed is above the nominal engine speed.

[0047] As a result, the shaft generator system may be used to directly stabilize the speed of a two-stroke engine.

[0048] The nominal engine speed is the desired engine speed selected by the engine operator. If an increase in power generation results in more electrical power being produced than is being used, the excess electrical power may be transferred to additional electrical power sources, as described above, and / or transferred to one or more dumb resistors for conversion to heat. Correspondingly, if a decrease in power generation results in less electrical power being produced than is being used, the additional electrical power sources may be used to deliver the additional electrical energy.

[0049] According to a second aspect, the present invention relates to a combined propulsion and generator system for propelling a ship and generating electrical energy, comprising a shaft generator system as disclosed in relation to the first aspect and a two-stroke uniflow scavenging crosshead type internal combustion engine, the two-stroke uniflow scavenging crosshead type internal combustion engine comprising an engine shaft, at least one cylinder, a cylinder cover, a piston, an engine fuel control system, a fuel supply system and a scavenging system, the cylinder having a cylinder wall, the cylinder cover being arranged on an upper part of the cylinder and having an exhaust valve, the piston being arranged in the cylinder so as to be movable along a central axis between a bottom dead center and a top dead center, the scavenging system having a scavenging inlet arranged at a bottom of the cylinder, the fuel supply system being configured to inject fuel into a main combustion chamber defined between the piston and the cylinder cover based on a control signal provided by the engine fuel control system, and the shaft generator is connected to the shaft of the two-stroke uniflow scavenging crosshead type internal combustion engine.

[0050] In some embodiments, the shaft generator control system is operably connectable to an engine fuel control system of the two-stroke uniflow scavenged crosshead type internal combustion engine and configured to receive information from or send information to the engine fuel control system, the shaft generator control system configured to provide information regarding power demand to the engine fuel control system, and the engine fuel control system further configured to control the amount of fuel injected into the main combustion chamber based on the information regarding the power demand.

[0051] As a result, the engine fuel control system can adapt to changes in power demand more quickly, allowing for more stable control of engine speed.

[0052] Different aspects of the present invention may be realized in different ways, including as a shaft generator system and a combined propulsion-generator system, each providing one or more of the benefits and advantages described in relation to at least one of the above aspects, and each having one or more preferred embodiments corresponding to the preferred embodiments described in relation to at least one of the aspects disclosed above and / or in the dependent claims. Furthermore, it will be understood that an embodiment described in relation to one of the aspects described herein may be equally applied to the other aspects.

[0053] The above and / or additional objects, features, and advantages of the present invention will become more apparent from the following illustrative and non-limiting detailed description of embodiments of the present invention, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0054] [Figure 1] 1 illustrates, in schematic form, a two-stroke engine and a generator system for generating electrical energy according to an embodiment of the present invention; [Diagram 2] A schematic diagram of a combined propulsion and generator system for propelling a ship and generating electrical energy is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] In the following description, reference is made to the accompanying drawings which show, by way of example, how the invention may be put into practice.

[0056] FIG. 1 shows, in a schematic manner, a two-stroke engine 100 and a generator system 190 for generating electrical energy according to an embodiment of the present invention. The engine 100 is a two-stroke uniflow scavenging crosshead type internal combustion engine 100. The engine 100 comprises a scavenging system 111, an exhaust gas receiver 108, a fuel supply system, an engine shaft 151 and a turbocharger 109. The engine comprises a number of cylinders 101 (only a single cylinder is shown in the cross-sectional view). Each cylinder 101 comprises a cylinder wall 115 and a scavenging inlet 102 arranged at the bottom of the cylinder 101. The engine further comprises, for each cylinder, a cylinder cover 112 and a piston 103. The cylinder cover 112 is arranged at the top of the cylinder 101 and comprises an exhaust valve 104. The piston 103 is arranged in the cylinder so as to be movable along a central axis 113 between a bottom dead center and a top dead center. The fuel supply system may optionally comprise one or more fuel gas valves 105 (shown only diagrammatically) configured to inject fuel gas into the cylinder 101 during the compression stroke, which allows the fuel gas to mix with the scavenging air and compress the mixture of scavenging air and fuel gas before ignition. The fuel gas valves 105 may be at least partially arranged in the cylinder wall between the cylinder cover 112 and the scavenging air inlet 102. The engine may further optionally comprise an external ignition unit 114, such as a pilot injector configured to inject autoignition pilot fuel. The pilot injector may be configured to inject autoignition pilot fuel into the combustion chamber, into a set of pre-combustion chambers or directly into a pre-combustion chamber arranged in the cylinder cover 112. The set of pre-combustion chambers may comprise an inner pre-combustion chamber and an outer pre-combustion chamber, the outer pre-combustion chamber opening to the main combustion chamber 150 through a first opening and fluidly connected to the inner pre-combustion chamber, where the inner pre-combustion chamber is provided with a pilot injector. The scavenge air inlet 102 is fluidly connected to the scavenge air system. The piston 103 is shown in its lowest position (bottom dead center). The piston 103 has a piston rod connected to a crankshaft (not shown).The fuel gas valve 105 is configured to inject fuel gas into the cylinder during the compression stroke, which allows the fuel gas to mix with the scavenging air and compress the mixture of scavenging air and fuel gas before ignition. The scavenging system 111 comprises a scavenging air receiver 110 and an air cooler 106. Instead of or in addition to the fuel gas valve 105, the fuel supply system may optionally comprise one or more fuel injectors 116 arranged in the cylinder cover 112, configured to inject fuel, for example, either high pressure gas or auto-igniting liquid fuel, at the end of the compression stroke under high pressure. If the fuel supply system only comprises one or more fuel injectors 116 configured to inject auto-igniting liquid fuel, the external ignition unit 114 is not required. The engine 100 may be a dual-fuel engine having an Otto cycle mode when running on fuel gas and a Diesel cycle mode when running on an alternative fuel, for example, heavy fuel oil or marine diesel oil. However, the engine 100 may be single fuel with only a Diesel cycle mode. The engine 100 further includes an engine fuel control system 160. The fuel supply system is configured to inject fuel into a main combustion chamber defined between the piston 103 and the cylinder cover 112 based on a control signal provided by the engine fuel control system 160, thereby controlling the speed and generated power of the engine 100. The engine fuel control system 160 may receive a nominal engine speed 161. The nominal engine speed is typically set by an engine operator. The engine fuel control system 160 may receive a sensor signal indicative of the actual engine speed, for example from a sensor measuring the speed of the engine shaft 151. The engine fuel control system 160 may be configured to control the fuel supply system to increase the amount of fuel injected into the combustion chamber when the actual engine speed is below the nominal engine speed 161, and to decrease the amount of fuel injected into the main combustion chamber when the actual engine speed is above the nominal engine speed 161.The shaft generator system 190 comprises a shaft generator 170 configured to generate an AC current having a first frequency dependent on the revolutions per minute (RPM) of the shaft 151, a first electric circuit 172 for converting the AC current from the first frequency to a second frequency, and a shaft generator control system 171 configured to receive a first signal 182 indicative of power consumption. The shaft generator control system 171 is operatively connected to the shaft generator 170 and configured to control the power generation of the shaft generator 170 based on the first signal 182. The first electric circuit 172 is configured to provide power to an AC grid 173 where the power is made available to on-board equipment, such as thrusters, pumps, gas reliquefaction plants, reefer containers, and general hotel loads. The shaft generator control system 171 is configured to allow the power consumption to differ from the power generation within a period of at least 2 seconds. As a result, by introducing an intentional sluggishness into the shaft generator control system, the destabilizing effects resulting from changes in power consumption can be significantly reduced. This may allow the shaft generator to generate more power without destabilizing the two-stroke engine to unacceptable levels. The first signal 182 is illustrated as originating from the first electrical circuit 172, for example from a sensor disposed in connection with the first electrical circuit 172. However, the first signal 182 may originate from other parts of the system, for example from the AC grid 173.

[0057] FIG. 2 shows a schematic diagram of a combined propulsion and generator system 199 for propelling a vessel and generating electrical energy. The system 199 comprises a shaft generator system 190 and a two-stroke uniflow scavenged crosshead type internal combustion engine 100. The engine 100 comprises an engine shaft, at least one cylinder, a cylinder cover, a piston, an engine fuel control system 160, a fuel supply system, and a scavenging system, the cylinder having a cylinder wall, the cylinder cover being disposed at the top of the cylinder and having an exhaust valve, the piston being disposed within the cylinder movably along a central axis between bottom dead center and top dead center, and the scavenging system having a scavenging inlet disposed at the bottom of the cylinder. The fuel supply system is configured to inject fuel into a main combustion chamber defined between the piston and the cylinder cover based on a control signal provided by the engine fuel control system 160. The shaft generator system 190 comprises a shaft generator 170 configured to generate an AC current having a first frequency dependent on the RPM of the shaft, a first electric circuit 172 for converting the AC current from the first frequency to a second frequency, and a shaft generator control system 171 configured to receive a first signal 182 indicative of power consumption. The shaft generator 170 is connected to an engine shaft 151. The engine shaft is further connected to a propeller (not shown). The engine shaft may be connected to the propeller via a clutch (not shown). The shaft generator control system 171 is operatively connected to the shaft generator 170 and configured to control the power generation of the shaft generator 170 based on the first signal 182, for example by providing a control signal 185 to the shaft generator 170. The shaft generator control system 171 is configured to allow the power consumption to differ from the power generation within a period of at least 2 seconds. The first electric circuit 172 comprises an AC-DC rectifier 174, a DC grid 175, and a DC-AC converter 176. The AC-DC rectifier 174 is configured to receive AC current at the first frequency from the shaft generator 170 , convert the received AC current to a DC current, and provide the converted DC current to a DC grid 175 .The DC-AC converter 176 is configured to receive the converted DC current from the DC grid 175, convert the DC current into an AC current having a second frequency, and provide the AC current having the second frequency to the AC grid 173, where the AC current is made available to the AC consumers 178. The first signal may be recorded by a sensor 180 that senses the power consumption. As an example, the sensor 180 may be a voltage sensor that measures the voltage of the DC grid 175, and if the voltage starts to drop, it may be an indication that the power generation is too low, and correspondingly, if the voltage starts to rise, it may be an indication that the power generation is too high. The shaft generator system 190 comprises an additional power source 177 configured to deliver energy when the power consumption exceeds the power generation of the shaft generator 170. The additional power source 177 is connected to the DC grid 175. The additional power source 177 may be an electrical energy storage device, such as a chemical battery, a supercapacitor, or a flywheel energy storage system, configured to receive and deliver electrical energy. Alternatively / additionally, the additional power source 177 may be a generating set with an additional internal combustion engine and generator. The additional internal combustion engine is preferably a medium or high speed four-stroke engine allowing for rapid control of the amount of generated power. The generating set may further be connected to a flywheel which also allows the generating set to absorb excess power generated by the shaft generator 170, i.e. the generator of the generating set may also act as an electric motor to accelerate the flywheel. The additional power source 177 may be configured to receive electric energy when the amount of power generated exceeds the amount of power consumed. The shaft generator control system 171 is configured to receive a second signal 183 indicative of a status of the additional power source 177 and to control the shaft generator based on the second signal 183. The second signal 183 may be indicative of the ability of the additional power source 177 to supply power to the system. Additionally / alternatively, the second signal 183 may be indicative of the ability of the additional power source 177 to absorb power from the system.As an example, if the additional power source 177 is an electrical energy storage device, the second signal 183 may indicate an energy level of the electrical energy storage device, e.g., if the electrical energy storage device is a chemical battery, the energy level may be estimated by measuring the voltage of the battery using the voltage sensor 181. The shaft generator control system 171 may be configured to control the shaft generator 170 based on the second signal 183, such that the additional power source 177 is capable of delivering a predetermined amount of power at any time, e.g., at least 0.25 kWh, 0.5 kWh, or 1 kWh, without receiving power from the shaft generator 170. Additionally / alternatively, the shaft generator control system 171 may be configured to control the shaft generator 170 based on the second signal 183, such that the additional power source 177 is capable of receiving a predetermined amount of power at any time, e.g., at least 0.25 kWh, 0.5 kWh, or 1 kWh, without delivering power to the DC grid 175. The shaft generator control system 171 is operatively connected to the engine fuel control system 160 and configured to receive information from and / or send information to the engine fuel control system 160. As a result, the engine fuel control system can react faster to changes in power consumption, thereby keeping the engine speed more stable. The shaft generator control system may be configured to provide information about power demand to the engine fuel control system 160. The shaft generator control system 171 may be configured to receive information about the engine speed. The shaft generator control system 171 may be configured to control the amount of power generation of the shaft generator 170 based on the received information about the engine speed. The information about the engine speed may enable the shaft generator control system 171 to determine the difference between the nominal engine speed and the actual engine speed. The shaft generator control system may be configured to control the shaft generator 170 to reduce the amount of power generation when the actual engine speed is below the nominal engine speed and to increase the amount of power generation when the actual engine speed is above the nominal engine speed.As a result, the shaft generator system may be used to directly stabilize the speed of a two-stroke engine.

[0058] Although several embodiments have been described and illustrated in detail, the present invention is not limited thereto and may be embodied in other ways within the scope of the subject matter defined in the following claims, and in particular, it is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.

[0059] In a device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims or are described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

[0060] It must be emphasized that the term "comprises / comprising", when used in this specification, is taken to specify the presence of stated features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. A shaft generator system for use with a two-stroke uniflow scavenging crosshead internal combustion engine comprising an engine shaft, at least one cylinder, a cylinder cover, a piston, an engine fuel control system, a fuel supply system, and a scavenging system, wherein the cylinder has a cylinder wall, the cylinder cover is located on top of the cylinder and has an exhaust valve, the piston is located within the cylinder so as to be movable along a central axis between bottom dead center and top dead center, the scavenging system has a scavenging inlet located at the bottom of the cylinder, and the fuel supply system is configured to inject fuel into a main combustion chamber defined between the piston and the cylinder cover based on a control signal provided by the engine fuel control system, wherein the shaft generator system is A shaft generator configured to generate an AC current having a first frequency dependent on the RPM of the engine shaft; a first electrical circuit for converting the AC current from the first frequency to a second frequency; and a shaft generator control system configured to receive a first signal indicating power consumption. Equipped with, The shaft generator control system is operably connected to the shaft generator and is configured to control the amount of power generated by the shaft generator based on the first signal. A shaft generator system wherein the shaft generator control system is configured to enable the power consumption to differ from the power generation amount within a first period of at least two seconds.

2. The shaft generator system according to claim 1, wherein the first electrical circuit comprises an AC-DC rectifier, a DC grid, and a DC-AC converter, the AC-DC rectifier is configured to receive an AC current of a first frequency from the shaft generator, convert the received AC current into a DC current, and supply the converted DC current to the DC grid, and the DC-AC converter is configured to receive the converted DC current from the DC grid, convert the converted DC current into an AC current having a second frequency, and supply the AC current having the second frequency to the AC grid.

3. The shaft generator system according to claim 1 or 2, further comprising an additional power source configured to deliver electrical energy when the power consumption exceeds the amount of power generated by the shaft generator.

4. The shaft generator system according to claim 3, wherein the additional power source is capable of delivering at least 0.25 kWh, 0.5 kWh, or 1 kWh without receiving power from the shaft generator.

5. The shaft generator system according to claim 4, as dependent on claim 3, wherein the additional power source is connected to the DC grid and configured to receive and / or deliver electrical energy to the DC grid.

6. The shaft generator control system according to claim 1 or 2, wherein the shaft generator control system is operably connectable to the engine fuel control system of the two-stroke uniflow scavenging crosshead type internal combustion engine, and is configured to receive information from and / or send information to the engine fuel control system.

7. The shaft generator system according to claim 6, wherein the shaft generator control system is configured to provide the engine fuel control system with information regarding power demand.

8. The shaft generator control system according to claim 6, wherein the shaft generator control system is configured to receive information relating to engine speed, and the shaft generator control system is further configured to control the amount of power generated by the shaft generator based on the received information relating to engine speed.

9. The shaft generator system according to claim 8, wherein the information relating to the engine speed enables the shaft generator control system to determine the difference between the nominal engine speed and the actual engine speed, and the shaft generator control system is configured to control the shaft generator such that it reduces the amount of power generated when the actual engine speed is less than the nominal engine speed, and increases the amount of power generated when the actual engine speed is greater than the nominal engine speed.

10. A propulsion-generator composite system for propelling a ship and generating electrical energy, comprising a shaft generator system according to claim 1 or 2 and a two-stroke uniflow scavenging crosshead internal combustion engine, wherein the two-stroke uniflow scavenging crosshead internal combustion engine comprises an engine shaft, at least one cylinder, a cylinder cover, a piston, an engine fuel control system, a fuel supply system, and a scavenging system, the cylinder having a cylinder wall, the cylinder cover positioned over the cylinder and having an exhaust valve, the piston positioned within the cylinder so as to be movable along a central axis between bottom dead center and top dead center, the scavenging system having a scavenging inlet positioned at the bottom of the cylinder, the fuel supply system configured to inject fuel into a main combustion chamber defined between the piston and the cylinder cover based on a control signal provided by the engine fuel control system, and the shaft generator connected to the engine shaft of the two-stroke uniflow scavenging crosshead internal combustion engine.

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