GENERATION UNIT WITH SAFE GRID COUPLING OF AN ASYNCHRONOUS MACHINE

Description

TECHNICAL FIELD

[0001] The present invention relates to measures for simple, safe and gentle grid coupling of a generation unit with an asynchronous machine driven by an energy converter operating according to a thermodynamic cycle process, and to a generation plant consisting of one or more of these generation units. TERMS AND DEFINITIONS

[0002] A generating unit (JU) is understood to be a machine that converts non-electrical energy into electrical energy.

[0003] A generating plant (EGP) is defined as a plant containing one or more generating units (JUs) and all electrical equipment necessary for its operation. This electrical equipment may include, for example, transformers or programmable logic controllers (PLCs) for regulating the active and reactive power output of the individual JU(s) or the EGP as a whole.

[0004] Direct grid coupling refers to a connection in which an asynchronous machine is connected to a power grid without an intermediate converter.

[0005] A direct connection is understood to be an electrical connection in which two electrical systems or electrical components are connected without intermediate power electronics or switching devices. BACKGROUND OF THE INVENTION

[0006] Well-known thermodynamic or fluid-dynamic processes, especially thermodynamic cycles, serve to convert thermal or kinematic energy into electrical energy. In a thermodynamic cycle, such as a Rankine cycle, a working fluid, usually water or, in the case of the Organic Rankine Cycle, other working fluids such as refrigerants, hydrocarbons, or silicone oils, is alternately evaporated by the addition of heat at high pressure and, after expansion, during which mechanical power is released, condensed by the removal of heat at low pressure. The resulting mechanical power is converted by an electric motor and fed into a power grid.

[0007] To maintain grid stability, variable excitation synchronous machines or asynchronous machines with frequency converters are preferably used as electrical machines. An asynchronous machine driven by the Organic Rankine Cycle with a frequency converter is known, for example, from EP 3940913 A1. However, these systems are relatively expensive and hardly competitive on the market, especially at comparatively low feed-in power levels. Furthermore, they are relatively maintenance-intensive and, in the case of the asynchronous machine with a frequency converter, subject to losses due to the power electronics.

[0008] Other systems are known from DE102018209054 A1 and from DE3705310 A1.

[0009] A well-known solution to counteract these disadvantages is to utilize the robustness of the power grid and couple the asynchronous machine directly to the grid, i.e., without a frequency converter. However, this approach presents a significant problem for thermodynamic or fluid-dynamic processes, especially for thermodynamic cycles of the type mentioned above, since the residual energy contained in the process and its input, which continues to flow briefly after an emergency shutdown, can only be dissipated slowly.

[0010] In the event of an emergency shutdown of the generating unit, the braking effect exerted on the rotor of the asynchronous machine by the field generated in the stator by the grid disappears, and the rotor, driven by the residual energy in the thermodynamic cycle, can accelerate dangerously – potentially to a high degree, even damaging the asynchronous machine and the coupled expansion machine. Similarly, when the generating unit is directly connected to the power grid, high inrush currents can occur, causing an unacceptable drop in grid voltage. Furthermore, even when operating as a generator, an asynchronous machine consumes inductive reactive power, which, depending on the grid characteristics, can alter the voltage or at least increase the current without any benefit.

[0011] The invention is based on the objective of providing a production unit that overcomes the aforementioned disadvantages. SUMMARY

[0012] According to a first aspect of the invention, a generating unit, EZE, is provided comprising an asynchronous machine with a connecting branch for direct grid coupling to a power grid, an energy converter which operates according to a thermodynamic or fluid-dynamic process, in particular a thermodynamic cycle process and thus drives the asynchronous machine to generate electricity, and an excitation component, wherein the excitation component is formed from capacitors which are connected to the asynchronous machine.

[0013] The capacitance of the capacitors can form a resonant circuit with the inductance of the asynchronous machine. Through resonance, this circuit allows a sufficiently high voltage to be excited from the very small voltage induced in the stator by the rotor remanence. This voltage can contribute to the magnetization of the asynchronous machine and prevent high inrush currents during synchronous connection to the power grid. Furthermore, it prevents the rotor from spinning up during an uncontrolled shutdown, such as an emergency shutdown of the EZE (Electricity Control Unit) or the asynchronous machine, because it can dissipate power in a braking resistor, thus acting as a brake.

[0014] The capacitors can be connected directly to the asynchronous machine, i.e., without intermediate power electronics or switching devices.

[0015] Alternatively, the capacitors can be connected to the asynchronous machine via a switching device.

[0016] The power grid can be a public three-phase power grid on land, preferably a low or medium voltage grid, or a ship power grid.

[0017] The thermodynamic cycle can be a Rankine Cycle, preferably an Organic Rankine Cycle.

[0018] The energy converter can be a Rankine cycle machine, preferably an organic Rankine cycle machine, with an expansion machine. The expansion machine can be mechanically coupled to a shaft of the asynchronous machine. Heat, in particular waste heat, can be supplied to the Rankine cycle machine to drive the expansion machine.

[0019] The asynchronous machine can be integrated into the expansion machine. The asynchronous machine can be a three-phase asynchronous machine with a squirrel-cage or short-circuit rotor.

[0020] The expansion engine and the asynchronous engine can be housed in a sealable, i.e., semi-hermetic, enclosure with one or more steam connections, in particular a steam inlet for live steam and a steam outlet for exhaust steam, and the electrical connection. The asynchronous engine can have a rated output between 50 and 5000 kW, preferably between 100 and 2000 kW, and particularly between 150 and 1000 kW.

[0021] The capacitors can be connected in a star or delta configuration.

[0022] The EZE can also include braking resistors, which can be connected to the asynchronous machine via a braking resistor switching device. The braking resistors can be connected in a star or delta configuration.

[0023] In the event of a shutdown, for example an emergency shutdown, of the EZE from the grid, the braking resistors can convert the residual energy supplied by the thermodynamic or fluid-dynamic process into heat energy.

[0024] The braking resistor switching device can have working contacts to connect the braking resistors to the asynchronous machine or to disconnect the braking resistors from the asynchronous machine.

[0025] The working contacts can be normally closed working contacts for actively switching on the braking resistors.

[0026] Alternatively, the working contacts can be normally open contacts for actively switching off the braking resistors. This ensures that in the event of a control system failure or a failure of the control voltage supply, the working contacts are closed to safely brake the rotor of the asynchronous machine.

[0027] Alternatively, the braking resistor switching device can have normally closed working contacts and an inverting element in its control system and thus be actively switched off in order to safely brake the rotor of the asynchronous machine in the event of a control system failure.

[0028] Furthermore, the EZE can include a control unit for controlling the braking resistor switching device. The control unit can be configured to connect the braking resistors to the asynchronous machine once or several times based on a measured EZE voltage, preferably at a time when the measured EZE voltage exceeds a limit value, when the EZE is disconnected from the power grid, particularly during an emergency shutdown of the EZE.

[0029] Furthermore, the EZE can include a mains switching device such as a contactor, a circuit breaker or a load break switch for connecting or disconnecting the EZE from the mains and a control unit for controlling the mains switching device.

[0030] The control unit can be configured to synchronize the frequency of the asynchronous machine with the frequency of the power grid. For synchronization, the control unit can regulate the speed of the asynchronous machine to the grid speed using the feed pump as an actuator.

[0031] The control unit can further be configured to synchronously connect the asynchronous machine to the power grid, preferably by calculating a differential voltage based on a measured grid voltage and a measured EZE voltage, and then switching on the grid switching device based on this differential voltage, taking into account the switching-on time of the switching device and other significant delay times, for example, of coupling relays, below a threshold value of the differential voltage, preferably at a voltage level between 0 V and 150 V, particularly less than 100 V. The threshold value can be the zero crossing of the differential voltage.

[0032] In particular, the control unit can be configured to record the differential voltage over a time interval to synchronize the switching, in order to form a differential voltage curve, in particular a sinusoidal differential voltage curve, and to convert the differential voltage curve, preferably with a regression model over the voltage maxima, in particular an envelope demodulator, into an envelope.The control unit can determine one or more properties of the envelope, such as the current gradient of the envelope, and, based on this one or more properties and information about the power switching device, in particular the pull-in time for closing its working contacts, and other significant delay times, for example of coupling relays, determine a command time to transmit a switch-on command to the power switching device at which the differential voltage after the pull-in time has elapsed is below the limit value, and can send the switch-on command to the power switching device at the determined command time.

[0033] The energy converter can comprise an expansion machine and an evaporator, which can evaporate a working fluid using the supplied heat and feed it into the expansion machine for conversion into mechanical power. Furthermore, the energy converter can include a feed pump, the speed of which can be controlled and which can be configured to draw the working fluid from the expansion machine, preferably from an intermediate condenser for condensation, and return it to the evaporator. The control unit can be configured to regulate or control the speed of the feed pump, thereby adjusting the pressure ratio of live steam to the pressure in the condenser, so that the speed of the expansion machine is synchronized with the mains frequency or speed.

[0034] The EZE can further comprise a second energy converter, preferably an internal combustion engine. The second energy converter can generate the waste heat that is supplied to the first energy converter, in particular the Rankine Cycle machine or the Organic Rankine Cycle machine, for power generation.

[0035] The second energy converter can be operated with petroleum or petroleum derivatives, preferably methane or heavy oil, or with gases such as natural gas, landfill gas, sewage gas, mine gas, biogas or hydrogen gas.

[0036] The second energy converter can also include and drive an electric generator.

[0037] According to a second aspect of the invention, a generation plant (EGA) is provided, comprising at least one generation unit (EZE) according to the first aspect of the invention, and connected to a power grid for electricity generation. The power grid can be a public onshore power grid or a ship power grid.

[0038] The EZA can also include a second EZE, which can be connected to the power grid in parallel with the first EZE.

[0039] Furthermore, the EZA (Electricity Supply Unit) can include a transformer with low-voltage and high-voltage sides for direct connection to a grid connection point. The first EZE (Electricity Supply Unit) and the second EZE can be connected in parallel with the low-voltage side of the transformer. The interposed transformer allows any voltage differences between the grid and the EZEs to be equalized and / or the EZA network to be isolated (protective separation) from the upstream grid. LIST OF ABBREVIATIONS

[0040] EZE generation unit EZA generation plant RCRankine Cycle (as a thermodynamic cycle) ORCOrganic Rankine Cycle FIGURES

[0041] Preferred embodiments of the invention are explained in more detail below with reference to the drawings. They show: Figure 1 a schematic setup of an EZE with an ORC machine as an energy converter according to a first embodiment of the invention; Figure 2 an exemplary voltage curve of a differential voltage between the power grid and the asynchronous machine with an indicator that specifies a preferred time for switching on the EZE. Figure 3 a schematic control loop for synchronizing the frequency of the asynchronous machine with the mains frequency for the safe switching on of the EZE. Figure 4 a schematic setup of an EZE with an ORC machine for utilizing the waste heat of an internal combustion engine, according to a second embodiment of the invention; and Figure 5 a schematic structure of a power generation plant with a feed-in to a network with a higher voltage level, encompassing a large number of power generation plants. DESCRIPTION

[0042] Figure 1 shows a schematic setup of an EZE 1 according to a first embodiment of the invention, in which the energy converter is an ORC machine 2. I. EZE with an ORC machine

[0043] The ORC machine 2 is supplied with heat power 3, which it converts into mechanical power and transmits via a shaft 4 to the rotor of an asynchronous machine 5. The heat power 3 can be supplied by a heat source, such as one in Fig. 4The combustion engine 37 shown is supplied to the ORC machine 2 via a heat transfer medium, such as gas, steam, thermal oil, or water. There, a working fluid is evaporated using the heat input 3 via a heat exchanger 6 (evaporator). The resulting live steam is then directed to an expansion machine 7. In the expansion machine 7, the live steam is expanded, delivering mechanical power that drives the asynchronous machine 5 coupled to the expansion machine 7. The steam is then condensed by heat extraction via a condenser 8. A feed pump 9, operated at variable speed (controlled or regulated), pumps the liquid working fluid back to the evaporator 6, where it is evaporated again. The cycle is now closed. The heat extracted by the condenser 8 can be used as usable heat for subsequent processes.Furthermore, the ORC machine 2 includes a controllable bypass valve 10 to control, and in particular reduce, the pressure differential across the expansion machine 7. The bypass valve 10 is controlled via a control unit 20. Alternatively or additionally, the bypass valve 10 can be switched manually.

[0044] The asynchronous machine 5 is directly coupled to a power grid 11 via a connecting branch, i.e., without an intermediate frequency converter, and feeds the heat power 3, converted into electrical power, into the power grid 11, preferably a public three-phase grid or a ship's power grid. The connecting branch can consist of power lines, switches, contactors, relays, plug and / or soldered connections.

[0045] An excitation component 12, consisting of a capacitor bank with at least one capacitor 13 for each phase, is connected in parallel to the asynchronous machine 5 and the power grid 11. In the illustrated embodiment, the capacitors 13 are connected in a delta configuration. In other embodiments, the capacitors 13 can be connected in a star configuration. The capacitors 13 themselves can, in turn, consist of series, parallel, or mixed connections of individual capacitors. Likewise, the excitation component 12 with the capacitors 13 can also be connected in series between the asynchronous machine 5 and the power grid 11. The excitation component 12 generates a voltage at the asynchronous machine 5, which is not yet connected to the grid, thus magnetizing it and reducing the inrush currents. This is achieved through a voltage-synchronized grid connection (see Chapter II).With grid connection (EZE 1) and a small difference between generator voltage and grid voltage, the inrush currents can be reduced by at least 80%, preferably 50%, compared to connecting a corresponding generating unit without excitation component 12. Furthermore, in grid-connected operation of the EZE 1, the excitation component 12 compensates for the inductive reactive power consumption of the asynchronous machine, thereby reducing the apparent current of the EZE 1 and placing less strain on the power grid.

[0046] Braking resistors 14 are also connected in parallel to the asynchronous machine 5 and the power grid 11 via a braking resistor switching device 15. In the illustrated embodiment, the braking resistors 14 are connected in a star configuration. In other embodiments, the braking resistors 14 can be connected in a delta configuration. The braking resistor switching device 15 has normally open contacts 16, which in the illustrated embodiment are configured as normally closed contacts for actively switching on the braking resistors 14. Alternatively, the normally open contacts 16 can be normally closed contacts for actively switching off the braking resistors. This ensures that in the event of a control system failure or a failure of the control voltage supply, the normally open contacts 16 are closed to reliably brake the rotor of the asynchronous machine 5.

[0047] Furthermore, the EZE 1 has a network switching device 17, preferably a contactor, a circuit breaker or a load break switch, for connecting and disconnecting the EZE 1 from the power grid 11. The network switching device 17 is connected in series between the asynchronous machine 5 and the power grid 11.

[0048] Furthermore, the EZE 1 comprises two voltage measuring devices 18, 19 for measuring the EZE voltage and the mains voltage, preferably for calculating the differential voltage between the EZE 1 and the mains power supply 11. The voltage measuring device 18 for measuring the EZE voltage is arranged between the asynchronous machine 5 and the mains switching device 17. The voltage measuring device 19 for measuring the mains voltage is arranged between the mains switching device 17 and the mains power supply 11. Likewise, the differential voltage across the mains switching device 17 can be measured directly with only one voltage measuring device.

[0049] Furthermore, the EZE 1 has a locally or remotely arranged control unit 20, which is connected directly or via further elements such as coupling relays, coupling contactors or optocouplers to the braking resistor switching device 15 and the mains switching device 17, in particular to their control contacts, in order to close or open the respective working contacts.

[0050] The control unit 20 can be a VPS (Programmable Logic Controller), a PLC (Programmable Logic Controller), a microcontroller, or a classic electronic circuit with analog and digital components. In a VPS, its function is represented by "wiring and selection of signal and switching devices," in a PLC and a microcontroller by software, and in electronic circuits by the selection of components and their routing.

[0051] Additionally, protective functions can also run on the controller. These functions can also be implemented on the controller already present in the system for controlling the ORC.

[0052] Furthermore, the control unit 20 is connected to the feed pump 9 and the bypass valve 10 to control the pressure differential across the expansion machine 7. II. EZE Grid Connection

[0053] Before the EZE 1 is connected to the power grid 11, the voltage of the EZE 1 is adjusted to the power grid 11, i.e. synchronized, in order to prevent high switching currents.

[0054] Within a thermodynamic process such as the ORC, the speed of the expansion machine 7 cannot be controlled with the same precision as, for example, in an internal combustion engine, and is subject to relatively large speed fluctuations, particularly in smaller systems below 5000 kW rated power, where a steam regulator is preferably omitted. Furthermore, the voltage amplitude of the asynchronous machine 5 cannot be adjusted when excited with non-switchable capacitor banks. This amplitude is frequency-dependent due to the resonance effect.

[0055] Figure 2 shows an exemplary voltage curve of a differential voltage (as an absolute value) between the power grid 11 and the asynchronous machine 5 at approximately 5 Hz frequency difference between the EZE voltage and the grid voltage.

[0056] To ensure smooth connection of the EZE 1 to the power grid despite the aforementioned challenges, the control unit 20 is designed to control the speed of the feed pump 9 and / or the opening of the bypass valve 10, thus synchronizing the speed of the expansion machine with the grid frequency or grid speed. For example, if the feed pump 9 rotates faster, more live steam pressure is built up, resulting in a higher pressure ratio across the expansion machine 7, causing it to rotate faster. In one embodiment, the EZE 1 also includes a steam control valve on the high-pressure side of the expansion machine 7.

[0057] Figure 3Figure 22 shows a schematic control loop for synchronizing the speed of the expansion machine 7, and thus the asynchronous machine 5, with the speed or frequency of the power grid 11. Such control can be performed by the control unit 20. Here, a frequency 23 of the asynchronous machine 5 is determined based on the measured EZE voltage using the voltage meter 18. Based on the control deviation 24, relative to the frequency 25 of the power grid 11, which is determined based on the measured grid voltage using the voltage meter 19 or is preset, the speed 27 of the feed pump 9 is set using a controller 26. This, in turn, sets the pressure ratio 28 (live steam pressure / condensing pressure) and thus the speed or frequency of the expansion machine 7 or the asynchronous machine 5.

[0058] After the frequency of EZE 1, as in Figure 3shown, to which the power grid 11 has been adjusted, a suitable time, which at best corresponds to a natural zero crossing 29 of the differential voltage 21, is determined for the connection.

[0059] For this purpose, the control unit 20 determines the differential voltage 21 based on the measured mains voltage and the measured EZE voltage. Based on the differential voltage 21, the control unit 20 switches on the mains switching device 17 when the differential voltage 21 is below a limit value 35, preferably at a voltage value between 0 V and 150 V, particularly at less than 100 V.

[0060] In a preferred embodiment for controlling the connection (voltage-synchronized mains connection), the control unit 20 is configured to connect the EZE 1 predictively, i.e., taking into account the available pull-in time 30 until the normally open contacts of the mains switching device 17 close. For this purpose, the control unit 20 records the differential voltage 21 over a predefined time interval 31 to generate a differential voltage waveform, in particular a sinusoidal differential voltage waveform. The differential voltage waveform is then converted into an envelope 33 using a regression model over the voltage maxima 32, in particular an envelope demodulator.One or more properties of the envelope 33, such as a current gradient, are determined, and based on one or more properties and information about the mains switching device 17 and other relevant elements in the control circuit, i.e. the pull-in time 30 until the working contacts close, a command time 34 to 34' for transmitting a switch-on command to the mains switching device 17 is determined, at which the differential voltage 21 after the pull-in time 30 has elapsed is below the limit value 35.

[0061] This results in a significantly larger time window for activation.

[0062] The activation algorithm cyclically checks the following: whether the current frequency is within a permitted tolerance around the mains frequency, whether the current frequency is outside a dead band around the mains frequency, whether the current frequency is increasing, and whether a value of the envelope 33 after the pull-in time 30 of the mains switching device 17 and other relevant elements in the control circuit is below a maximum permitted limit 35.

[0063] If all conditions are met, the output of the control unit 20 is activated to switch on the mains switching device 17. After the pull-in time 30 has elapsed, its working contacts are closed and the asynchronous machine 5 is connected to the mains power supply 11. III. EZE grid disconnection

[0064] Furthermore, the control unit 20 is configured to connect the braking resistors 14 to the asynchronous machine 5 once or several times based on the measured EZE voltage when the EZE 1 is disconnected from the power grid 11, particularly during an emergency shutdown of the EZE 1. For this purpose, the control unit 20 compares the measured EZE voltage with a limit value and switches the braking resistors 14 on when the measured EZE voltage exceeds a limit value, or off when the measured EZE voltage falls below a limit value. In other embodiments, a two-position controller can be used.

[0065] When electrical energy is fed into a power grid, the rotating asynchronous machine 5 is slowed down by the power grid 11. The rotor of the asynchronous machine 5 is driven by the mechanical power from the upstream process, e.g., the enthalpy of the working fluid mass flow of the ORC process, via the expansion machine 7. The expansion machine 7 attempts to accelerate the asynchronous machine 5. However, the stator of the asynchronous machine 5 generates a rotating magnetic field that is fixed and dependent on the grid frequency, which holds the rotor of the asynchronous machine 5 in place, taking slip into account. Assuming a lossless system, the mechanical force of the expansion machine 7 opposes the electromagnetic force of the current from the power grid 11.

[0066] When the asynchronous machine 5 is disconnected from the power grid 11, the electromagnetic force ceases. Two load cases can be distinguished: a) The ORC machine 2 is shut down by reducing its input power. At a minimum asynchronous machine power, the grid switchgear is opened. The residual energy from the upstream process is so low that the rotor accelerates only slightly after grid disconnection. A small overvoltage is excited by the capacitor; or b) the asynchronous machine 5 experiences an emergency shutdown or grid failure under full load. The rotor of the asynchronous machine 5 accelerates sharply. The asynchronous machine 5 and the coupled expansion machine 7 or turbine can be mechanically overloaded. A high overvoltage can be excited by the capacitor.

[0067] To counteract this efficiently, braking resistors 14 are used. They close a circuit with the capacitor-excited asynchronous machine 5. The current flowing in the stator of the asynchronous machine 5 generates a magnetic field that flows through the windings or the cage of the rotor of the asynchronous machine 5 and brakes the machine.

[0068] In the case of the asynchronous machine 5, moments can only occur if there is a speed difference, i.e., a slip, between the rotor and the stator, because only then do temporal changes in the magnetic flux take effect, leading to induction.

[0069] The braking resistors 14 are dimensioned so that they can convert the electrical energy into heat energy without damage in the event of an emergency shutdown or a power failure at full load.

[0070] To prevent the braking resistors 14 from being continuously energized when the EZE 1 is connected to the grid, the braking resistor switching device 15 is installed upstream of them. It is only closed when the grid switching device 17 is open. Since the capacitor-excited asynchronous machine 5, which is then disconnected from the grid, represents a source whose voltage drops under load, there is a risk of partial loss of excitation when the braking resistors 14 are switched on, which is accompanied by a partial loss of braking power, according to deltaP_Brems = 3 * deltaU_Erregung ∧ 2 / R_Brems in a three-phase circuit, assuming the phase dimensions.

[0071] Furthermore, some of the residual energy is dissipated from the ORC, causing the rotational speed and frequency to decrease. Due to the resulting deterioration of the resonant circuit's behavior, the excited voltage also decreases. Therefore, a minimum excitation voltage is another condition for switching on the braking resistors. This allows the braking resistors 14 to be switched on and off several times during a braking process. The schematic sequence during the braking process is as follows: a) EZE 1 is disconnected from the power grid 11, voltage is high and rising, b) braking resistors 14 are switched on, c) voltage drops due to resistive load and falling frequency, d) braking resistors are switched off, e) voltage rises due to lack of load and frequency increase (residual energy from the ORC is still available), f) braking resistors are switched on again and g) back to step c).

[0072] To ensure maximum safety, the brake resistor switching device 15 is actively switched off so that it is closed in the event of a control system failure. IV. EZE with an internal combustion engine and an ORC machine for utilizing the waste heat of the internal combustion engine

[0073] Figure 4 Figure 1 shows a schematic diagram of an EZE 36 according to a second embodiment of the invention. The EZE 36 comprises, in addition to the components of the first embodiment according to Figure 2, the following components: Figure 1 furthermore an internal combustion engine 37, whose waste heat is used by an ORC machine 38.

[0074] The ORC machine 38 comprises, in addition to the first heat exchanger 6 (evaporator), a second heat exchanger 39 (preheater). Both heat exchangers 6, 39 are each connected via a heat transfer medium circuit with a pump 40, 41 to an exhaust gas heat exchanger 43, 42 for transferring heat from an exhaust gas stream 44 of the internal combustion engine 37. Furthermore, the ORC machine 38 comprises a third heat exchanger 45 for transferring heat from a coolant of the internal combustion engine 37. Also included is Figure 4 The cooling circuit coupled to the internal combustion engine 37 is shown with an engine radiator 46, from which the heat of the coolant is extracted via the third heat exchanger 45 and a pump 47. The ORC machine 38 further comprises a condenser 8, which is part of a cooling circuit with a radiator 48 (e.g., an air cooler) and a coolant pump 49. Alternatively, the condenser 8 can also extract the heat directly, as in EZE 1 according to Figure 1 depicted, released into the air.

[0075] In one embodiment, the EZE 36 is supplemented by an electric generator 50, which is driven by the internal combustion engine 37 to generate electricity. Its electrical energy can be fed into the power grid via a frequency converter or via direct coupling (not shown). V. EZA

[0076] Figure 5 shows a schematic structure of a generation plant, EZA 51, which comprises a plurality of EZEs 52...54, wherein one or more of the EZEs 53, 54 of the EZE 1 in Figure 1 or the EZE 36 in Figure 4 correspond. As in Figure 5 As shown, the electrical energy provided by the EZEs 52...54 can be fed into the public power grid 58, in particular a medium voltage grid with 20 kV or another voltage level of this range, or into a ship power grid via transformers 55...57 at a grid connection point.

[0077] The EZEs 52...54 can each be connected to the low-voltage side of a respective transformer 55...57. VI. Protection mechanisms

[0078] To ensure that all of the above-mentioned functions of the EZE 1 can be performed reliably at all times, the following checks are carried out: Checking the mains voltage and generator voltage for direction of rotation, checking the mains voltage and generator voltage for symmetry, monitoring for overfrequency to detect faulty controller settings (P, I, D), checking the excitation. Before each start-up: checking the value of the braking resistor 14. During each switching-on: evaluating the potentially age-related pull-in time 30 of the mains switching device 17 and other relevant components in the control circuit and storing it for the next switching operation. If the last switching-on operation and thus the last measured value of the pull-in time 30 is too far in the past: performing a "dry switch" without voltage before starting up the machine to accurately determine the values ​​and test the important switching devices (mains switching device 17, braking resistor switching device 15, main switch, braking resistor measuring contactor), preferably checking for feedback within a specific time. VII. Design of the capacitors

[0079] A conventional asynchronous machine can be operated as a self-excited asynchronous generator. The procedure is described, for example, in the textbook "Electrical Machines", 17th edition, Rolf Fischer, 2017.

[0080] For the design of the capacitors 13, a driven machine shaft is advantageous so that the machine with its number of poles p can be operated at synchronous speed n_sync, according to n_sync = 2 * f * 60 s / 2 * p * 1 min .

[0081] The current flowing in power grid 11 is purely a magnetizing current; it is measured, and the necessary capacitor capacitance is calculated from it. Theoretically, this current could be measured while a hermetically sealed air conditioning compressor was running. However, this is impossible because an air conditioning compressor can only operate with fluid and the lubricant it contains. Even with the compressor and fluid mechanically coupled internally, this constitutes a mechanical load and therefore no longer represents idling. Operating the hermetically sealed air conditioning compressor without fluid and lubricant can destroy the machine. Even operation with the wrong direction of rotation, which is not externally apparent, can unintentionally destroy the machine.

[0082] For these reasons, the following explanations of the design of the capacitors 13 for excitation are subject to the special characteristics of an electrical machine which is housed in the same casing as the thermodynamic expansion machine 7.

[0083] The parameters of the equivalent circuit can usually be obtained from the manufacturer of the electric machine. For no-load operation, i.e., slip s = 0, the magnetic coupling and the rotor circuit are eliminated. Therefore, the no-load current, which corresponds only to the pure magnetizing current I_u, can be easily calculated using... I_u = U / R_s + 2 * Pi * f * L_s calculate and is the voltage, divided by the impedance consisting of the stator resistance Rs and the (frequency-dependent) stator reactance 2*Pi*f*L_s.

[0084] Commercially available three-phase power capacitors are typically internally connected in a delta configuration. The required capacitor size can be determined according to... C = I_u sqrt 3 * 2 * Pi * f * U will be calculated.

[0085] The calculation shown represents the rough design of the excitation capacitance. From this, a starting value for the fine-tuning is determined – this is necessary because the nominal values ​​of commercially available capacitors are only available in a certain granularity – in order to then determine the reliably functioning and procurable capacitance using a heuristic approach. a) Accelerating and maintaining the generator at a specific speed by varying the feed pump speed or by using the generator speed controller, b) Measuring the actual excited voltage and comparing it with the expected target voltage, c1) If deviation is too large: shutdown, correction of the capacitance, then a) c2) If deviation is within the specified tolerance: finished or a) with further speed.

[0086] The result is a capacity which, under real-world conditions – line lengths, line routing, measurement inaccuracies during initial design, etc. – reliably excites a voltage that leads to successful synchronization with networks with the expected parameters of frequency and voltage. VIII. Advantages of the invention

[0087] simple, safe, inexpensive, readily available parts, high efficiency, grid compatible, small footprint and low heat generation

Claims

1. Generating unit, GU (1, 36), comprising: an asynchronous machine (5) with a connecting branch for direct grid connection to a power grid (11); an energy converter (2) that operates according to a thermodynamic or fluiddynamic process, in particular a thermodynamic cycle process, and thus drives said asynchronous machine (5) for generating electricity, and characterized by an excitation component (12), where said excitation component (12) is formed from capacitors (13) that are connected to said asynchronous machine (5).

2. GU (1, 36) according to claim 1, where said energy converter (2) is a Rankine Cycle machine, preferably an Organic Rankine Cycle machine, with an expansion engine (7), where said expansion engine (7) is coupled mechanically to a shaft of said asynchronous machine (5), and where said Rankine Cycle machine is supplied with heat output (3), in particular waste heat, to drive said expansion engine (7).

3. GU (1, 36) according to claim 2, where said asynchronous machine (5) is integrated into said expansion engine (7) and is preferably a three-phase asynchronous machine with a short circuit rotor or squirrel-cage rotor.

4. GU (1, 36) according to claim 3, where said expansion machine (7) and said asynchronous machine (5) are housed in a closable, i.e. semi-hermetic housing with one or more steam connections, in particular a steam inlet for live steam and a steam outlet for waste steam, and an electrical connection.

5. GU (1, 36) according to one of the preceding claims, where said asynchronous machine (5) has a rated power of between 50 and 5000 kW, preferably between 100 and 2000 kW, in particular between 150 and 1000 kW.

6. GU (1, 36) according to one of the preceding claims, where said capacitors (13) are starconnected or delta-connected.

7. GU (1, 36) according to one of the preceding claims, where said GU (1, 36) comprises brake resistances (14) which are connected to said asynchronous machine (5) via a brake resistance switching device (15), preferably as a star connection or a delta connection.

8. GU (1, 36) according to claim 7, where said brake resistance switching device (15) comprises operating contacts (16) for connecting said brake resistances (14) to said asynchronous machine (5) or to disconnect said brake resistances (14) from said asynchronous machine (5), respectively, where said operating contacts (16) are closing operating contacts for actively switching on said brake resistances (14) or opening operating contacts for actively switching off said brake resistances (14) in order to securely brake said rotor of said asynchronous machine (5) in the event of a failure of the control device such as a failure of the control voltage supply.

9. GU (1, 36) according to one of the claims 7 or 8, where said GU (1, 36) comprises a control unit (20) for controlling said brake resistor switching device (15), which is configured to connect said brake resistances (14) once or several times to said asynchronous machine (5) based on a measured GU voltage when said GU (1, 36) is disconnected from said power grid (11), in particular in the event of an emergency shutdown of said GU (1, 36), preferably at a point in time at which the measured GU voltage exceeds a limit value.

10. GU (1, 36) according to one of the preceding claims, where said GU (1, 36) comprises a grid switching device (17), preferably a contactor, a circuit breaker, or a load-break switch, for connecting or disconnecting said GU (1, 36) to / from said power grid (11), and a control unit (20) for controlling said grid switching device (17), where said control unit (20 is configured to connect said asynchronous machine (5) synchronously to said power grid (11), preferably in that said control unit (20) forms a differential voltage (21) based on a measured grid voltage and a measured GU voltage and, based on this, connects said grid switching device (17) below a limit value (35) of said differential voltage (21), preferably at a voltage magnitude between 0 V and 150 V, in particular less than 100 V.

11. GU (1, 36) according to claim 10, where said control unit (20) is configured to record said differential voltage (21) over a time interval (31) for synchronizing the connection in order to form a differential voltage profile, in particular a sinusoidal differential voltage profile, and to convert the differential voltage profile to an envelope (33), preferably using a regression model via the voltage maxima (32), in particular an envelope detector, to determine one or more properties of said envelope (33), such as a present gradient of said envelope (33) and to determine a command point in time (34), based on the one or more properties and information about said grid switching device (17), in particular its pull-in time (30) for closing its operating contacts, for transmitting a switch-on command to said grid switching device (17), at which said differential voltage (21) is below said limit value (35) after said pull-in time (30) has elapsed, and to sends said switch-on command to said grid switching device (17) at said determined command point in time (34).

12. GU (1, 36) according to claim 10 or 11, where said energy converter (2) comprises an expansion machine (7) and a vaporizer (6) capable of vaporizing a work fluid with the heat output (3) supplied and directs it into said expansion machine (7) for conversion to mechanical power, and a feed pump (9), the rotational speed of which can be controlled and which is configured to obtain the work fluid from said expansion machine (7), preferably from a condenser (8) for liquefaction connected therebetween, and to convey it back to said vaporizer (6), where said control unit (20) is configured to regulate or control the rotational speed of said feed pump (9), with which the pressure ratio of live steam is adjusted in relation to the pressure in said condenser (8), so that the rotational speed of said expansion machine (7) is made to match the grid frequency or the grid rotational speed of said power grid (11).

13. GU (1, 36) according to one of the preceding claims, where said GU (1, 36) comprises a second energy converter, preferably an internal combustion engine (37), where said second energy converter generates waste heat which said first energy converter (2) is supplied with for generating electricity.

14. GU (1, 36) according to claim 13, where said GU (1, 36) comprises an electrical generator (50), where said second energy converter is configured to drive said electrical generator (50).

15. Generating system, GS (51) with at least one GU (1, 36) according to the preceding claims, where said GS (51) is connected to a power grid (58), in particular a public power grid on land or a ship electrical system, for generating electricity.