Power generator and method for operating a power generator

Abstract

Power generator (10) for feeding energy, in particular obtained from a gaseous fuel, into an electrical power supply network (12), comprising: a generator (14) for generating electrical energy that can be fed into the power supply network (12); an internal combustion engine (16) driving the generator (14), which has a plurality of cylinders (18) to which a fuel-air mixture having a predetermined air ratio (λ) is supplied to achieve a predetermined power (P) of the internal combustion engine (16), and a means (20) which is designed to temporarily change the air-fuel ratio (λ) in at least one of the cylinders (18) in such a way as to prevent ignition of the fuel-air mixture in the cylinder (18); characterized by the fact that the means (20) comprises: at least one compressed air nozzle (22) for the direct or indirect supply of air or an inert gas into the at least one cylinder (18) and at least one valve (24) for regulating the amount of air or inert gas to be introduced, such that ignition of the fuel-air mixture in the cylinder (18) is prevented.

Description

[0001] The invention relates to a power generator for feeding energy, in particular obtained from a gaseous fuel, into an electrical power supply network and a method for operating such a power generator.

[0002] To feed energy into an electrical power grid, it is known to operate an internal combustion engine that drives a generator. The internal combustion engine converts the chemical energy of a fuel, particularly a gas such as biogas, wood gas, mine gas, natural gas, or propane, into kinetic energy, which drives the generator. The generator then converts this kinetic energy into electrical energy, which is fed into the power grid.

[0003] To be allowed to feed energy into a power grid, specific connection guidelines must be followed. Certification authorizing the feeding of energy into the grid is only granted if the technical requirements of these guidelines are demonstrated. Since the 2008 BDEW Medium Voltage Guideline and the VDE AR-N 4120 (TAB High Voltage) and with the entry into force of the VDE AR-N 4110 (TAB Medium Voltage), dynamic grid support has been enshrined in the technical connection guidelines.

[0004] Dynamic grid support, as understood by experts, refers to the behavior of the generating unit that must be demonstrated in the event of faults in the power supply network. A grid fault, also known as a fault ride-through (FRT) event, is defined by experts as a significant deviation of the grid voltage at the point of connection from the nominal voltage at that point. Depending on the type of grid fault, it is then referred to as a low voltage ride-through (LVRT), under voltage ride-through (UVRT), or high voltage ride-through (HVRT), or over voltage ride-through (OVRT). Voltage dips of up to 1500 ms and voltage outages of up to 150 ms can occur.

[0005] During a power grid fault, the load on the generator drops. However, the internal combustion engine continues to generate a constant amount of kinetic energy, which is fed back to the generator. As the resistance torque on the generator drive shaft decreases, the shaft's rotational speed increases accordingly. Such an increase in rotational speed can lead to serious damage to the generator set.

[0006] It is therefore desirable to control the internal combustion engine in such a way that, for example, a low-voltage reverse torque (LVRT) operation can be traversed without a significant increase in the crankshaft speed. It is known to reduce the power output of the internal combustion engine during the LVRT operation. However, a recurring challenge in development is to simultaneously reduce the power output of the internal combustion engine as directly as possible in line with the load reduction, and to increase the power output of the internal combustion engine back to normal operating conditions as directly as possible in line with the return of the load.

[0007] Various methods for preventing ignition in the sense of igniting the fuel-air mixture or for achieving only incomplete combustion in at least one cylinder of an internal combustion engine, in particular a generator, are known from the prior art.

[0008] EP 1 022 450 A2 discloses an internal combustion engine that drives a generator to produce electrical energy. The engine's power output is reduced when the applied load decreases. This is achieved, in particular, by restricting the fuel supply to at least one combustion chamber of a cylinder. However, the cylinder's combustion chamber is filled via a turbocharger, which is intended to prevent ignition within the combustion chamber.

[0009] EP 2 526 279 A1 discloses a stationary power plant characterized by the fact that, to reduce power output, the fuel supply to at least one combustion chamber of the internal combustion engine is at least partially stopped. The gaseous fuel is metered via a gas metering valve. Thus, if the gas metering valve is completely closed, ignition can be prevented.

[0010] DE 10 2017 206 616 A1 discloses a method for operating the combustion chamber of an internal combustion engine of a motor vehicle. The known method is characterized by the fact that compressed air is supplied to the mixture in the combustion chamber during a load change. The supply of air serves to reduce the proportion of recirculated exhaust gas in the mixture during exhaust gas recirculation in order to prevent misfires and thus ensure stable combustion.

[0011] EP 2 876 275 B1 discloses a reciprocating internal combustion engine comprising an electromagnetic valve which, in an open position, couples the combustion chamber of the reciprocating internal combustion engine to a compressed air reservoir. The known auxiliary air injection serves to reduce pollutant emissions when using an exhaust gas turbocharger and to ensure efficient operation of the reciprocating internal combustion engine.

[0012] The invention is based on the objective of proposing a power generator and a method for feeding energy into a power supply network, which immediately reduce the power of the internal combustion engine to enable the vehicle to pass through a network fault.

[0013] This problem is solved by a power generator according to claim 1 and a method according to claim 11. Preferred embodiments of the invention are the subject of claims 2 to 10 and 12 to 14.

[0014] The power unit according to the invention comprises a generator for producing electrical energy that can be fed into the power grid and an internal combustion engine driving the generator, which has a plurality of cylinders. A fuel-air mixture with a predetermined air-fuel ratio is supplied to the cylinders to achieve a predetermined power output from the internal combustion engine. For example, biogas, a combustible gas produced by the fermentation of biomass such as vegetable oil or biogas, is suitable as a gaseous fuel for driving the internal combustion engine.

[0015] Furthermore, the device includes a means configured to temporarily alter the air-fuel ratio in at least one of the cylinders to abruptly reduce the power output of the internal combustion engine, preventing ignition of the fuel-air mixture in that cylinder. The means comprises at least one compressed air nozzle for directly or indirectly supplying air or an inert gas to the at least one cylinder and at least one valve for regulating the amount of air or inert gas supplied.

[0016] Suppressing ignition, or achieving incomplete combustion, is accomplished by actively injecting air or an inert gas, such as nitrogen. This shifts the air-fuel ratio of the mixture in the cylinder so far into the lean range that the mixture is either no longer ignitable or only incomplete combustion occurs, resulting in a significant and immediate reduction in power output.

[0017] Furthermore, the injected air or inert gas can create overpressure in the cylinder and the adjacent fuel-air mixture supply medium, particularly an intake manifold. This prevents the fuel-air mixture in the supply medium from flowing back into the cylinder. This backflow is known to occur in connection with the resonance effect, which can typically lead to better cylinder filling, for which the length of the intake manifold is selected accordingly.

[0018] Furthermore, the device according to the invention enables a particularly gentle reduction in power output for the internal combustion engine during the short period of a power supply failure. This is because a sufficient quantity of injected air remains available to the cylinder, preventing the formation of a vacuum during the intake stroke. Moreover, the injected air is advantageously available as exhaust gas to downstream components, such as a turbocharger turbine, which continues to be driven by the injected air.

[0019] In an advantageous embodiment, the internal combustion engine has six cylinders. Furthermore, the internal combustion engine can be designed as a marine engine. Such a designed internal combustion engine is characterized in particular by a long service life.

[0020] In an advantageous embodiment, the generator is a synchronous reluctance generator. Such a generator can be connected to the power grid much more easily. It is also conceivable to use a synchronous generator as a generator. The requirements for dynamic grid support are less complex than with asynchronous generators. However, synchronous generators typically need to be synchronized with the power grid before they can feed energy into it. They can also become desynchronized under certain circumstances. This occurs, for example, when passing through a grid fault. The generated energy is synchronized with the power grid when, in particular, the phase angle of the generator is identical to the phase angle of the electrical power grid.

[0021] These difficulties cannot arise with a synchronous reluctance generator. It synchronizes itself and cannot desynchronize due to excitation from the network.

[0022] An energy supply network is a network for the transmission and distribution of electrical energy to one or more consumers. Such a network can include overhead lines and underground cables, as well as associated facilities such as switching stations and transformer substations. The energy supply network can also include electrically interconnected power grids, which are also referred to as a grid interconnection network. Furthermore, it is also conceivable that the energy supply network operates in a so-called islanded mode, which is supplied with electricity, for example, by a biomass-fired combined heat and power plant or a cogeneration unit.

[0023] In an advantageous embodiment, the compressed air nozzle for directly supplying air or inert gas into the cylinder is arranged on the cylinder itself. The compressed air nozzle can, for example, be located in the cylinder head next to a supply opening for the fuel-air mixture. This results in a short transmission path and allows for the targeted creation of overpressure in the respective cylinder. Ignition can thus be prevented particularly effectively and quickly.

[0024] Furthermore, the generator set has an intake manifold designed to supply the fuel-air mixture to the cylinder. In an alternative embodiment of the generator set, the compressed air nozzle for the indirect supply of air or inert gas to the cylinder is arranged on the intake manifold. In an advantageous embodiment of this, the compressed air nozzle is located in a section of the intake manifold near the cylinder. Due to the lower prevailing pressures compared to the pressures during a power stroke and the lower temperatures in the intake manifold, a more economical and simpler placement of the compressed air nozzle can be achieved.

[0025] In a further advantageous embodiment, the valve is designed as a solenoid valve. Such a valve is characterized by particularly fast response times, so that the time between the detected network fault and the opening of the compressed air nozzle valve is short. These solenoid valves can be directly controlled, pilot-operated, positively controlled, and / or pressure-controlled.

[0026] In a known manner, the internal combustion engine can have several cylinders. In an advantageous embodiment, each cylinder is assigned a valve. By assigning a valve to each cylinder, air or inert gas can be supplied to each cylinder individually.

[0027] In a further advantageous design, the valves can be controlled individually. Accordingly, ignition in each cylinder can be prevented independently, allowing the power output of the internal combustion engine to be reduced in stages.

[0028] Advantageously, the device comprises a compressed air reservoir suitable for storing compressed air for immediate injection. The compressed air reservoir can have a volume between 10 and 100 liters and a pressure of up to approximately 20 bar. Ideally, the compressed air reservoir can be spherical, ensuring uniform pressure distribution across the reservoir walls. However, the compressed air reservoir can also have other shapes, such as a cylinder. The cylindrical shape allows for lighter and more space-efficient storage. Furthermore, the compressed air reservoir can be made of a soft material, like a balloon or bellows, or a rigid material, such as metal or plastic. In another advantageous embodiment, the compressed air reservoir also includes a pressure regulator.The pressure limiter is specifically designed to measure the pressure in the compressed air reservoir or, in the form of a pressure relief valve, to release excess pressure.

[0029] Advantageously, the compressed air reservoir is connected to the compressed air nozzle via a fluid-conducting connection. If the internal combustion engine has multiple cylinders, a large number of compressed air nozzles connected to a single compressed air reservoir can be present. Advantageously, several compressed air nozzles can also be assigned to a single cylinder. Consequently, only one compressed air reservoir, or at least fewer, is required. In a further advantageous embodiment, it is also conceivable that two or more compressed air nozzles are each connected to a compressed air reservoir. This would allow for the use of compressed air reservoirs with a smaller volume. Preferably, the compressed air nozzles of the cylinders with longer time intervals between individual ignitions are connected to the compressed air reservoir. This ensures, for example, a balanced fill level in the compressed air reservoir during operation of the internal combustion engine.

[0030] In an advantageous embodiment, the compressed air tank has a constant volume. A constant volume is particularly advantageous for compressed air tanks made of a solid material, such as metal.

[0031] Advantageously, the compressed air tank is connected to a compressor via a fluid-conducting connection, which is designed to fill the compressed air tank with air or inert gas. Consequently, multiple uses are possible. In a further advantageous embodiment, the compressor is connected to a pressure regulator, which switches off the compressor when a preset upper pressure limit is reached. If the pressure reaches a lower limit due to air withdrawal, the compressor refills the compressed air tank.

[0032] The aforementioned statements and advantages also apply to the claimed method.

[0033] The following section provides a more detailed explanation of exemplary embodiments of the power generator according to the invention, with reference to the accompanying drawings. These drawings show: Fig. 1 a power generator for feeding energy into a power supply network and Fig. 2 an alternative design of the power generator according to Fig. 1.

[0034] Fig. Figure 1 shows a power generator 10 for feeding energy into an electrical power supply network 12. The power generator comprises an internal combustion engine 16 and a generator 14. The generator 14 is driven by the internal combustion engine 16 via a shaft.

[0035] The described internal combustion engine 16 has six cylinders 18, wherein in Fig. Figure 1 shows only one cylinder 18. The cylinder 18 comprises a cylinder head, which closes off a combustion chamber of the internal combustion engine 16 at the top. The term "top" here refers to the perspective of the oscillating piston 18b.

[0036] The cylinder head 18a contains an intake manifold 19, which may include a throttle valve, and an exhaust manifold. The intake manifold 19 is limited to the combustion chamber by an intake valve. The exhaust manifold is limited to the combustion chamber by an exhaust valve.

[0037] The cylinder head 18a additionally features a compressed air nozzle 22 with a valve 24. The compressed air nozzle 22 is designed to introduce compressed air into the combustion chamber of the cylinder 18. The valve 24 is designed to regulate the intake of compressed air. The compressed air nozzle 22 is connected to a compressed air reservoir 26. The compressed air reservoir 26 serves to provide a supply of compressed air. The compressed air reservoir 26 is in turn connected to a compressor 28. The compressor 28 serves to fill the compressed air reservoir 26 with air or inert gas so that the compressed air reservoir 26 is filled with a sufficient quantity of air at a pressure above 1 bar.

[0038] During normal operation of the power unit 10, a fuel-air mixture is supplied to the combustion chamber of cylinder 18 via the intake manifold 19 to operate the internal combustion engine 16. The power output P of the internal combustion engine 16 is determined by the quantity of fuel-air mixture supplied, which can be regulated, for example, by a throttle valve. The power output P directly influences the rotational speed of the shaft that drives the generator 14 to produce electricity.

[0039] The in Fig. The generator 14 shown in Figure 1 is a synchronous reluctance generator. As long as the generator 14 feeds a current synchronized with the power supply network 12 into the power supply network 12, a load is applied to the generator 14. The load generates a resistive torque, which in turn is transmitted to the shaft. The internal combustion engine 16 must therefore generate sufficient power P so that the shaft rotates at a specific speed.

[0040] The generator 14 is considered to be synchronized with the electrical power supply network 12 when a voltage U G , a phase position φ G , a phase sequence and a frequency f G of generator 14 identical to a voltage U N , a phase position φ N , a phase sequence and a frequency f N of the electrical power supply network 12 are.

[0041] As soon as a network fault occurs in the power supply network 12, the load drops. Consequently, the resistance torque also drops and the rotational speed of the shaft increases, provided the power P is not reduced.

[0042] As soon as a network fault is detected, the inventive method for reducing the power P of the internal combustion engine 16 is applied.

[0043] For this purpose, valve 24 opens the compressed air nozzle 24 shortly before and during the intake stroke, allowing air or inert gas to flow into the combustion chamber of cylinder 18. This creates overpressure in the combustion chamber of cylinder 18. Consequently, no or insufficient ignitable fuel-air mixture enters the combustion chamber of cylinder 18, and ignition in subsequent strokes is prevented. As a result, cylinder 18 does not generate any significant power P that can be transmitted to the shaft, but it still allows the shaft, in particular the camshaft, to rotate, since the piston can continue to move up and down.

[0044] Fig. Figure 2 shows an alternative design of the power unit 10 according to Fig. 1. Identical or functionally equivalent components may have the same reference numerals.

[0045] The power generator 10 according to Fig. Figure 2 shows a power generator 10 comparable to the embodiment shown in Figure 2. Fig. 1, which, however, has an alternative arrangement of the compressed air nozzle 22. Here, the compressed air nozzle 22 is arranged on the intake tract 19 and is designed to inject air or inert gas into this area shortly before and during the intake stroke. The injection of air or inert gas creates an overpressure in the area of ​​the intake tract 19, originating from the compressed air nozzle 22. The overpressure generated by the air or inert gas prevents the supply of a fuel-air mixture to the cylinder 18. Consequently, as in the previously described embodiment, the power output P is also immediately reduced.

[0046] The power generator 10 according to the invention is characterized by the particularly fast and effective reduction of the power P of the internal combustion engine 16 during a power grid fault. Furthermore, the power of the internal combustion engine 16 can be restarted just as quickly and effectively. In addition, the method according to the invention is particularly gentle on the internal combustion engine 16 and enables a particularly long service life. Reference symbol list 10 generators 12 Energy supply network 14 Generator 16 Internal combustion engine 18 cylinders 18a Cylinder head 19 Intake tract 20 means 22 Compressed air nozzle 24 valve 26 compressed air tanks 28 Compressor λ air ratio P Performance

Claims

[1] Power generator (10) for feeding energy obtained in particular from a gaseous fuel into an electrical power supply network (12), comprising: a generator (14) for generating electrical energy that can be fed into the power supply network (12); an internal combustion engine (16) driving the generator (14) and having a plurality of cylinders (18) to which a fuel-air mixture having a predetermined air ratio (λ) is supplied to achieve a predetermined power (P) of the internal combustion engine (16), and a means (20) designed to temporarily change the air ratio (λ) for abruptly reducing the power (P) of the internal combustion engine (16) in at least one of the cylinders (18) in such a way that ignition of the fuel-air mixture in the cylinder (18) is prevented; characterized by that the agent (20) comprises: at least one compressed air nozzle (22) for directly or indirectly supplying air or an inert gas into the at least one cylinder (18) and at least one valve (24) for regulating the amount of air or inert gas to be introduced in such a way that ignition of the fuel-air mixture in the cylinder (18) is prevented. [2] Power generator (10) according to claim 1 characterized by that the compressed air nozzle (22) is arranged on the cylinder (18) for directly supplying air or inert gas into the cylinder (18). [3] Power generator (10) according to claim 1 characterized by an intake tract designed to supply the fuel-air mixture to the cylinder, wherein the compressed air nozzle (22) for indirectly supplying air or inert gas into the cylinder (18) is arranged on the intake tract. [4] Power generator (10) according to one of claims 1 to 3 characterized by that the valve (24) is designed as a solenoid valve. [5] Power generator (10) according to one of claims 1 to 4 characterized by that each cylinder (18) is assigned a valve (24). [6] Power generator (10) according to claim 5 characterized by that the valves (24) can be controlled individually. [7] Power generator (10) according to one of claims 1 to 6 characterized by that the means (20) comprises a compressed air tank (26) which is suitable for holding a reservoir of compressed air for immediate injection. [8] Power generator (10) according to claim 7 characterized by that the compressed air tank (26) is fluidly connected to the compressed air nozzle (22). [9] Power generator (10) according to claim 7 or 8 characterized by that the compressed air tank (26) has a volume that is constant. [10] Power generator (10) according to one of claims 7 to 9 characterized bythat the compressed air tank (26) is fluidly connected to a compressor (28) which is designed to fill the compressed air tank (26) with air or inert gas. [11] Method for operating a power generator (10) according to one of claims 1 to 10, characterized by the following procedural steps: a) supplying the fuel-air mixture into the cylinder (18) to achieve a predetermined power (P) of the internal combustion engine (16); b) driving the generator (14) by means of the power (P) to generate electrical energy which is fed into the power supply network (12); c) blowing in air or an inert gas by means of the compressed air nozzle (22) to prevent the ignition of the fuel-air mixture into the at least one cylinder (18), so that the power (P) of the internal combustion engine (16) is abruptly reduced in a low voltage ride-through (LVRT) case. [12] Method according to claim 11 characterized by that the compressed air tank (26) is filled with air or the inert gas by the compressor (28) before the valve (24) opens to blow in the air or the inert gas. [13] Method according to claim 11 or 12 characterized by that by means of the injected air or inert gas an overpressure is generated in the intake tract (19) and / or in the cylinder (18) before the supply of the fuel-air mixture. [14] Method according to one of claims 11 to 13 characterized by that all cylinders (18) are controlled individually.

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