Synchronous-condenser mode operating method of a clutch-less energy conversion system

Abstract

A method and system to operate an energy conversion system are disclosed. The system comprises a gas turbine, an electric machine unit connected to the turbine and the grid, and a gearbox between them. The electric machine unit can function as a generator to drive the gas turbine or convert the turbine's mechanical energy into electricity for the grid. The method involves operating the electric machine unit to deliver active and reactive power to the grid, gradually reducing the gas turbine's output, removing protections to inject power into the grid, and activating synchronous-condenser mode. In this mode, the electric machine unit is dragged by the grid and absorbs active power to provide reactive power on demand, while the combined inertia of the gas turbine, gearbox, and electric machine unit provide grid stability. A control logic unit is also included to execute this method.

Description

Synchronous-condenser mode operating method of a clutch-less energy conversion systemDescriptionTECHNICAL FIELD

[0001] The present disclosure concerns a synchronous-condenser mode operating method of a clutch-less gas turbine energy conversion system.BACKGROUND ART

[0002] The present invention relates in the field of power generation systems, particularly those incorporating 4-pole electrical machines capable of achieving synchronous speeds necessary for grid stability. The balancing of energy sources within the grid is an important issue, with an increasing reliance on renewable energy introducing design problems which are not present with traditional fossil fuel sources, such as natural gas fueled gas turbines.

[0003] Modern electrical grids face significant quality and stability problems primarily due to the integration of renewable energy sources alongside conventional fossil fuel sources. A main issue is the inherent low inertia of renewable energy sources, such as wind and solar power, which leads to frequency deviations during fluctuations in load. This variability, compounded by the unpredictable nature of renewable sources due to environmental factors like wind availability and cloud cover, makes demand and supply balancing exceedingly difficult.

[0004] The grids’ stability is paramount. However, grids with a significant proportion of renewable energy are at risk of blackouts due to instability, especially when facing sharp or sudden changes in load. Moreover, there is a risk of load disconnection under abnormal frequency conditions, which compromises the quality of the electrical supply. Also, the amount of active power vs reactive power shall be maintained within a limited angle (cos (p > 0.85) to avoid malfunction of the electrical motors connected to the grid.

[0005] Existing power generation systems, particularly Gas Turbine Generators (GTGs) utilized as peaker power generators, have traditionally used only the inertia ofthe electric generator itself to stabilize the grid, and not other important contributors to a greater value of total inertia. These systems are either operated with a flame in the combustor for starting and loading or as synchronous condensers with the gas turbine in a stationary state without a flame in the combustor. Neither of these configurations adequately addresses the low inertia and the resulting frequency deviations introduced by renewable energy sources.

[0006] While the prior art includes mechanisms such as self-synchronizing clutches to enable generator synchronization with the grid whilst the rest of gas turbine shafts are not spinning, these systems have not been optimized to overcome the specific problems posed by the high renewable penetration in the power grid.

[0007] The prior art includes the US patent US 11808211B2 and the US patent application US20230332673A1, which provide solutions regarding power transmission in aircraft and train systems, which, although not directly addressing grid stability issues.

[0008] The relevant prior art also includes the patent applications US 2018 / 298777 Al, US 2016 / 036230 Al, and US 2021 / 317781.

[0009] It is therefore desirable to overcome the technical problems inherent in the prior art by leveraging all contributors to total inertia, that is the Low-Pressure Turbine (LPT) rotor, the wheels of the gearbox and the electrical generator.SUMMARY

[0010] In an aspect, the subject matter disclosed herein concerns a method of operating an energy conversion system, which includes a gas turbine for generating mechanical energy and an electric machine unit. The electric machine unit is mechanically connected to both the gas turbine and a power grid, capable of operating as a generator to drive the gas turbine or as an energy converter to convert mechanical energy from the gas turbine into electrical energy for the power grid. The method also comprises a speed adjustment device connected between the gas turbine and the electric machine unit, with the power grid connected to renewable energy generator units.

[0011] A further aspect of the present disclosure is drawn to a method comprising steps of checking the operation of the electric machine unit as a generator, reducing the operation of the gas turbine to a minimum active power, removing protections toallow power injection into the power grid, and activating a synchronous-condenser mode. This mode enables the electric machine unit, assisted by the combined inertia of the gas turbine and the speed adjustment device, to absorb active power and deliver reactive power, thereby contributing to the stability of the power grid.

[0012] Within the present disclosure, an active electrical power is understood as a flow of active power from an electric machine to a grid while the electric machine unit operates as generator, and as a flow of active power from a grid to an electric machine while the electric machine operates in synchronous-condenser mode, in which the electric motor behaves as a motor. In other words, the active power comprises the power produced by the mechanical power of the gas turbine.

[0013] Within the present disclosure, an active power flow inversion is understood as an inversion of power flow of active power when the generator starts behaving as a motor or vice-versa. Particularly, the inversion may comprise a change of flow from the power produced by the turbine towards the distributor, or a change of flow to a power generated by the distributor and absorbed by the electric motor.

[0014] In the context of the present disclosure, the skilled person will understand that a reactive power is a power stored by a clutch-less gas turbine energy conversion system or given back to the system to balance the grid.

[0015] In another aspect, disclosed herein is a method where the step of reducing the operation of the gas turbine includes ramping down to the minimum and adjusting an automatic voltage regulator to manage the reduction in power generated. Additionally, the method includes operating a control system that adjusts the speed of the gas turbine by regulating the fuel input and controlling the generator to maintain specific reactive power levels.

[0016] In another aspect, the subject matter disclosed herein concerns a method including the steps of disabling the automatic voltage regulator and a circuit breaker, and shutting down the fuel valves of the gas turbine to allow an active power flow inversion. The method further comprises checking a switch of the energy conversion system from synchronous-condenser mode to generating mode, and reactivating the gas turbine.

[0017] In another aspect, disclosed herein is an energy conversion system comprising a gas turbine, an electric machine unit, and a speed adjustment device. The system includes a control logic unit configured to execute the method steps disclosed above, with the electric machine unit adapted to operate as both a generator and an energy converter, effectively integrating with renewable energy generator units connected to the power grid.

[0018] Finally, a further aspect of the present disclosure is drawn to an energy conversion system with a double shaft gas turbine including a compressor, a high-pressure turbine, a low-pressure turbine, and a speed adjustment device connected to the low- pressure shaft. This device is adapted to multiply the inertia of the rotor of the low- pressure turbine, facilitating reduced speed suitable for the grid frequency.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 illustrates a schematic of a clutch-less energy conversion system, according to an embodiment of the solution;Fig. 2 illustrates a flowchart showing the switching to the synchronous-condenser mode;Fig. 3 illustrates an electrical machine capability curve where some operating points of the energy conversion system are highlighted; andFig. 4 illustrates a schematic of a clutch-less energy conversion system, according to an embodiment of the solution.DETAILED DESCRIPTION OF EMBODIMENTS

[0020] According to one aspect, the present subject matter is directed to a method and system designed to augment the rotational kinetic energy (generally referred as inertia) made available to an electrical grid, which is particularly beneficial for grids with insufficient inertia or those characterized as "weak." Traditional approaches to strengthening grid inertia have relied on a combination of different elements: a synchronouscondenser which is an electrical machine operating without a turbine driver, primarily to regulate the grid voltage and manage reactive power; a gas turbine driver equipped with a self-synchronizing clutch that allows spinning of the electric generator machine while the rest of the gas turbine is not spinning, typically activated during reactive power demand times to rephase the grid, or during a peak demand to deliver also active power to the grid; and an array of electrical battery energy storage systems, which are called upon to deliver an immediate response to sudden drops in power generation or spikes in energy demand.

[0021] In the present disclosure, these elements are combined into a single, integrated apparatus, to eliminate the need for separate hardware components. The resulting conjoined system comprises a gas turbine driver interconnected through a gearbox to an electric generator. The integrated design not only simplifies the complexity and reduces the spatial footprint required for separate systems but also enhances the operational efficiency of the grid. The synchrony between the electrical grid and the generator is managed to facilitate the instantaneous provision of inertial support and reserve power when needed.

[0022] Referring now to the drawings, Fig. 1 shows a clutch-less gas turbine generator system 1.

[0023] The energy conversion system 1 comprises a gas turbine 2 that generates mechanical energy. The gas turbine 2 is mechanically connected to an electric machine unit 3 that is also connected to the power grid 5. A control logic unit U control the operation of the gas turbine generator system 1.

[0024] Renewable energy generator units are connected to the power grid 5, for contributing additional clean energy, promoting a versatile and resilient energy supply. However, such clean energy generation systems or plants cause an instability to the power grid 5, in terms of active vs reactive power and in terms of frequency fluctuation.

[0025] In one embodiment, the gas turbine 2 is a double-shaft type, comprising an axial-compressor 21, an high-pressure turbine 22, and a low-pressure turbine 23.

[0026] The double shaft gas turbine 2 contributes to improve the grid 5 stability. Thedouble shaft gas turbine 2, through its inertia and operational characteristics, can dampen fluctuations in the power supply and in frequency, as better explained below.

[0027] The high-pressure turbine 22 is connected to the axial compressor 21 through the high-pressure shaft 23. The low-pressure turbine 24 comprises a low-pressure rotor (not shown in the figures) and a low-pressure shaft 25. The low-pressure shaft 25 is coupled to a gear box 4. The gas turbine 2 also comprises a fuel combustor 24.

[0028] The gas turbine 2 also comprises a set of inlet guide vanes 261. The inlet guide vanes 261 in a gas turbine 2 are arranged at the entry of the axial compressor 21 section. The inlet guide vanes 261 comprise an array of adjustable blades that direct and regulate the flow of incoming air into the gas turbine 2 subsequent stages.

[0029] The function of the inlet guide vanes 261 is to control the angle, speed, and flow of the air, entering the compressor or turbine, to regulate the amount of air flow entering the gas turbine 2 as a function of its rotating speed, and prevent issues like compressor 21 stall or surge.

[0030] In adjustable versions, the inlet guide vanes 261 are controlled via an actuator or the like, connected to the control logic unit U, to adapt, though them, the airflow dynamically in response to varying load conditions and operational requirements.

[0031] By modifying the angle of the inlet guide vanes 261, the flow rate and rotor speed can be optimized to maintain downstream conditions of pressure and flow entering the subsequent sections of gas turbine 2 (combustor and turbine sections).

[0032] The inlet guide vanes 261 also facilitate rapid adjustments to meet changing power demands and reducing absorbed power of the compression session (either from the starting system during startup or from the turbine section during operation) while protecting the gas turbine 2 internal components from excess vibration or surge conditions.

[0033] The gas turbine 2 also comprises nozzle guide vanes 262.

[0034] Nozzle guide vanes 262 in a gas turbine 2 are a series of stationary (but with geometrically variable area of hot gas passage) airfoils situated between high-pressure and low-pressure turbines. They comprise adjustable blades designed to direct andregulate the high-velocity gas flow coming from the high-pressure turbine, ensuring it enters into the low-pressure turbine section, thus controlling the optimal split of the expansion power (enthalpy) going to the high-pressure rotor, and the remaining expansion power going to the low-pressure rotor (and consequently to the electric generator through the gearbox connection). The optimal split is governed by control system U and varied in different load demand conditions (more active power demanded make nozzle guide vanes to reduce area of hot gas passage, less active power demanded make nozzle guide vanes to increase area).

[0035] Their function of the nozzle guide vanes 262 is to convert the high-pressure gas flow from the combustor into a high-velocity jet directed toward the turbine rotor, where this kinetic energy is transformed into mechanical energy that drives the rotor blades. By controlling the gas flow direction and angle, the nozzle guide vanes 262 ensure efficient energy transfer to the rotating components, thereby maximizing the power output and efficiency.

[0036] The gas turbine 2 also comprises a starter motor 27. The starter motor 27 provides the necessary starting energy for the high-pressure rotor 21 to start its operating.

[0037] The energy conversion system 1, as mentioned, also comprises a gearbox 4. In general, the energy conversion system 1 comprises a speed adjustment device 4, which in the present embodiment is a gearbox.

[0038] In other embodiments, the speed adjustment device 4 may be a hydraulic coupling or a torque converter.

[0039] The gearbox 4 is linked to the low-pressure shaft 26 and is specifically designed to amplify or increase the inertia of the rotor within the low-pressure turbine 25, or the gas turbine 2 in general, thereby enhancing energy transfer efficiency, as better explained below.

[0040] In some embodiment, the gearbox 4 comprises an epicyclic gearbox. This component offers reduced permanent losses compared to traditional gearbox types with parallel shafts. The epicyclic system minimizes energy waste.

[0041] In some embodiments, the epicyclic system can be configured for a fixed speed ratio, ensuring consistent and predictable mechanical performances. This can beachieved by means of sprockets and / or cogwheels with a fixed speed ratio configured to rotate both clockwise or counterclockwise. In this way, the direction of rotation of the epicyclic system determines the direction of the power generated.

[0042] Advantageously, epicyclic gears provides low losses, e.g. less than 1% mechanical losses in 100% power transmission, and long life of moving parts such as sprockets, bearings, and shafts, because the epicyclic gears are less stressed than to the teeth of “parallel axis” type gears.

[0043] In some examples, the epicyclic gears comprise gear wheels with fixed reduction ratio, set in the factory construction by choosing the diameters and the number of teeth of the gear wheels, wherein said epicyclic gears are capable of operating in bidirectional direction so that a power can flow in both directions.

[0044] Usually, the slow shaft connected to the generator is dragged. In the synchro- nous-condenser mode, a slow shaft becomes capable of dragging the fast shaft, which is connected to the low-pressure turbine, e.g. at 7800 rpm under normal rated speed. In operative conditions, this speed may vary between 50% to 105% thereof.

[0045] When the grid drags the generator, the power flowing in the gearbox changes direction with respect to the usual direction of flow in which the slow shaft connected a generator is dragged. Typical examples of a generator comprise a four-poles generator running at a speed between 1500 rpm and 1800 rpm with a frequency of 50 Hz.

[0046] In synchronous-condenser mode, the speed of the fast shaft preferably varies between 95% and 105% of 7800 rpm. Accordingly, the frequency varies between 95% and 105% of 50Hz.

[0047] In some embodiment, the epicyclic gearbox 4, is able to multiply the rotational kinetic energy (sometimes also called inertia) of the rotor of the low-pressure gas turbine 25 by approximately 27 times in the present invention. The rotational kinetic energy transferred by low-pressure turbine 25 rotor is1QK = -2I = W X R2wherein, K is the rotational kinetic energy to be transferred (save for possible losses) the I is the moment of inertia, W is the weight of the rotor of the low-pressure gas turbine 25, a> is the angular speed of the same rotor of the low-pressure gas turbine 25, while R is the radius of the rotor. It has to be considered that the number R is a derived equivalent radius considering the mass distribution of the rotating rotor, which can have different shapes. After the gearbox 4, the rotational speed is reduced, in the embodiment at issue, is such that the transmission ratio squared is 27. This contributes to the stabilization of the power grid 5, because the contribution to the total kinetic energy of the electrical machine alone becomes almost the double due to the contribution of the gearbox 4 wheels and the low power turbine 25.

[0048] The energy conversion system 1 is intended to optimize energy generation and conversion. The interplay between the gas turbine 2, the electric machine unit 3, and the gearbox 4 ensures the system is adaptable to varying power demands.

[0049] The gas turbine comprises also at least a fuel valve 28. The fuel valves 28 are adapted to adjust the flow of fuel efficiently to the combustor of the gas turbine 2. The fuel valve comprises an actuator that receives real-time control signals from the logic control unit U, adjusting the valve position to match varying load demands. The fuel valves 28 integrate a flow metering system to measure fuel quantities to ensure optimal combustion.

[0050] The electric machine unit 3 can operate in two different ways.

[0051] Specifically, electric machine unit 3 may operate as a synchronous condenser, to provide power to the gas turbine 2 (also known as motoring of the gas turbine). Alternatively, the electric machine unit 3 may operate as an electric generator that converts the mechanical energy received as driving torque from the gas turbine 2 into electrical energy suitable for injection into the grid 5.

[0052] In some embodiments, the electric machine unit is a four-pole electrical machine capable of achieving synchronous speeds up to or greater than 3600 revolutions per minute. The usage of a four-pole electrical machine provides for higher speeds with respect to a two-pole electrical machine, allowing for increased grid stability.

[0053] The gas turbine unit 2 starter motor 27 may comprise a Variable FrequencyDrive (VFD), to control of the crank speed on the high-pressure shaft 26.

[0054] The electric machine unit 3 comprises also an automatic voltage regulator 31. An automatic voltage regulator (AVR) is configured to stabilize voltage output. The automatic voltage regulator 31 comprises a voltage sensing circuit that monitors the generator’s output voltage, comparing it to a predetermined reference voltage. Upon detecting a discrepancy between the sensed and reference voltage levels, the AVR adjusts the excitation current supplied to the generator's field windings through signal amplification circuitry. This adjustment alters the magnetic field strength of the rotor, thereby controlling the output voltage to match the desired level. The AVR operates within a continuous feedback loop to dynamically regulate the generator's voltage output, preventing fluctuations and ensuring a reliable voltage stabilization, even under varying load conditions or fluctuating grid voltages.

[0055] The electric machine unit 3 is also provided with a circuit breaker 32.

[0056] The circuit breaker 32 is designed to interrupt the flow of electrical current to protect the electric machine unit 3 from overloads and short circuits and to electrically connect / disconnect the electrical machine unit 3 to the grid. The circuit breaker 32 comprises, usually, a detection system that monitors current levels in real time. Upon detecting current exceeding the predefined threshold, the device triggers an electromechanical switch that separates the contacts. Often, the circuit breaker 32 further comprises an arc suppression system that minimizes damage to the contacts by quenching electrical arcs as the circuit opens. The resettable mechanism allows for rapid restoration of electrical connectivity.

[0057] In some embodiments, the circuit breaker 32 is an “ANSI 32” relay, a standard device used to protect against reverse power conditions by monitoring for reverse power flow that could cause the gas turbine 2 to be driven as a motor (anti-motoring). The relay’s normal (first) threshold prevents reverse power from damaging the turbine by ensuring that power generation remains within safe operational limits and maintains the integrity of the grid system.

[0058] The gearbox 4 connected between the gas turbine 2 and the electric machine unit 3, serving to reduce rotational speed to the speed of generator suitable for the gridfrequency and simultaneously serving to increase the inertia of the gas turbine 2 referred at speed of electrical machine. This setup allows the mechanical energy generated to be efficiently converted and adapted for use in the power grid 5.

[0059] As mentioned, the energy conversion system 1 comprises also a control logic unit U. The control logic unit U is functionally connected to both the gas turbine 2 and the electric machine unit 3. The control logic unit U is programmed to manage the interactions between components of the energy conversion system 1. Specifically, the control logic unit U is programmed to execute the steps specified in a computer program.

[0060] The control logic unit U can be implemented in several ways.

[0061] In one embodiment, the control logic unit U can be implemented as a programmable microprocessor, which is a compact and highly efficient option. Microprocessors offer high processing speeds and can be customized for specific control tasks.

[0062] In another embodiment, the control logic unit U can be a PLC (Programmable Logic Controller). On the other hand, the PLC is specifically designed for industrial control applications, making it a robust and reliable choice. PLCs are known for their durability and resistance to harsh industrial environments, including vibrations, temperature variations, and electrical noise.

[0063] In some other embodiments, the control logic unit U can be integrated in a computer, thus offering the most flexibility and computational power among the alternatives.

[0064] As mentioned, the energy conversion system 1 aims at optimizing the inertia of the gas turbine 2 components and reducing electrical losses.

[0065] The energy conversion system 1 is designed with an increased inertia of the low-pressure turbine 25 and its associated gearbox 4, to sum up to the inertia of the standard electric generator 3.

[0066] The inlet guide vanes 261 and the nozzle guide vanes 262 may be adjusted by a specific program.

[0067] Fig. 4 shows an embodiment of clutch-less energy conversion system equipped with the inlet guide vanes 261, the nozzle guide vanes 262 and an anti-surge valve ASV. These components may be controlled by means of the synchronous-condenser mode to provide a reactive power. This limits the absorption of an active portion of the power, without affecting the exchange of reactive portion of the power produced.

[0068] The energy conversion system 1 operates as follows.

[0069] With reference to Fig. 2, the operation of the gas turbine generator system 1 is illustrated, where the flowchart of an operating method 100 is shown, which comprises a series of steps and sub-steps.

[0070] In the method 100, the first step involves checking the operation 110 of the electric machine unit 3 as a generator so that the energy conversion system 1 delivers both active and reactive power to the electrical power grid 5.

[0071] In particular, in the following reference is also made to Fig. 3, showing the operating point of the electric machine unit 3. When electric machine unit 3 as a generator, the energy conversion system 1 injects both active and reactive power (operating point A).

[0072] In case the energy conversion system 1 has to pass to the synchronous-condenser mode, following a command from the control logic unit U, the operation continues with the gradual reduction 120 of the gas turbine 2 activity until a minimum active power is reached. During this phase, the automatic voltage regulator 31 is adjusted to follow the reduction of the generated power by ramping down (step 121) the gas turbine 2 operation. Specifically, this reduction is managed by controlling the speed of the gas turbine 2 through fuel input adjustments (sub-step 1211) and regulating (substep 1212) the automatic voltage regulator 31 to maintain stable reactive power.

[0073] Therefore, the method comprises controlling a speed of the gas turbine 2 through the speed adjustment device 4, to maintain specific reactive power levels and / or to allow an active power flow inversion.

[0074] The method 100 then advances to the protection removal 130, where the automatic voltage regulator 31 and the circuit breaker 32 are disabled 131 by the control logic unit U. The fuel valves 28 of the gas turbine 2 are shut down 132 to facilitate theinversion of active power flow.

[0075] Once protections are removed, the synchronous-condenser mode (see step 140) is then activated, allowing the electric machine unit 3 to draw power from the grid 5 while delivering reactive power on demand. The combined inertia of the gas turbine 2, gearbox 4, and electric machine unit 3 contributes to grid 5 stability during this mode.

[0076] The automatic voltage regulator 31 operates in MV AR control mode, while the control logic unit U remains in droop mode. The control logic unit U adjusts the gas turbine 2 to maintain the minimum active power output and nominal, overexcited reactive power.

[0077] As the gas turbine 2 powers down, the automatic voltage regulator 31 tunes the rotor (field) current of the synchronous machine according to the unit capability curve, maintaining stability even at very low power factors.

[0078] The circuit breaker 32 protection (an ANSI 32 in the embodiment) switches to the second threshold, permitting a continuous absorption of up to 500 kW of power. The control logic unit U closes the fuel valves, and consequently interrupt the flame in the combustion zone of the gas turbine, and also initiating the deceleration of the gas turbine 2 low-pressure shaft 26. At this point, the electric machine generator 3 is driven by the power grid 5 and absorbs active power to compensate for its iron and copper losses. The transition from generator to synchronous condenser is then completed, as can be seen considering the point B of Fig. 3, where only reactive power is generated.

[0079] Specifically, the energy conversion system 1 exchanges reactive power with the power grid 5 to meet the grid operator's demand, any time, aimed at improving the power factor (cos<p) and bringing it closer to one (typically 0.85).

[0080] Moreover, the polar inertia I (expressed in kg • m2of the rotating masses (generator rotor, gearbox gears, low power shaft 26) and their angular velocity (rota- tional kinetic energy K (namely, - / fl ) confer stability to the power grid 5 in the presence of disturbances (load changes). In power grids 5 with a strong renewable component (solar panels, wind turbines), which essentially lack inertia, these changes couldresult in frequency variations when loads are added or removed due to the lack of rotational kinetic energy. Once brought to the desired speed, high rotational kinetic energy makes it hard to slow down or speed up, and thus ensuring stability of the grid 5.

[0081] Still referring to point B of Fig. 3, it can be seen that a minimal amount of active power from the grid (<500 kW) is absorbed to cover its electrical dissipation losses and other mechanical losses from the gearbox 4 and ventilation losses of the low power turbine 25. This is why the point is slightly on the negative side of the axis of the abscissa (active power).

[0082] In this mode, the synchronous condenser mode, the electric machine generator 3 accepts MV AR raise / lower commands from the grid operator through the control logic unit U. This configuration enables the delivery of reactive power on demand while the combined inertia of the low-pressure shaft 26, gearbox 4, and the electric machine generator 3, contributes to grid stability.

[0083] Subsequently, the energy conversion system switch is checked (step 150) to ensure the transition from the synchronous-condenser mode to the (normal) generating mode, where the gas turbine 2 resumes mechanical energy generation and the electric machine unit 3 functions as an energy converter.

[0084] In reactivating (step 160) the gas turbine 2, the automatic voltage regulator 31 is adjusted (step 161) to minimize reactive power exchange with the power grid 5, and a synchronizing valve is opened (step 162), to gradually slow down the gas turbine 2 until it stops completely. The gas turbine 2 is then reactivated (step 163) by initiating its startup sequence, bringing it to a Full Speed No Load (FSNL) state where it runs with flamed combustors in self-sustenance (without supplying electrical output power to the grid 5).

[0085] In transitioning an energy conversion system into synchronous-condenser mode, the gas turbine 2's deceleration is executed in a gradual manner. This ensures stability of the system by preventing abrupt changes that could lead to mechanical stress. During the reduction step, the system’s control logic unit U decreases the fuel input, modulating the turbine’s speed.

[0086] After that, the energy conversion system 1, the inlet guide vanes (IGV) and the nozzle guide vanes (NGV) are maintained in a closed position, while the anti-surge valve (ASV) are held open. This arrangement protects the axial compressor of the gas turbine from the risk of surging, and also reduces the absorbed active power from the grid when operating in synchronous condenser mode, without affecting the exchange of reactive power. Keeping the IGV and NGV closed restricts the flow of air and gas through the gas turbine 2, to limit the power consumption from the grid and to maintain the axial compressor in safe conditions.

[0087] Within the present disclosure, the inlet guide vanes IGV are variable geometry vanes which modulates the mass flow of air entering the gas turbine, while the antisurge valve ASV is an ON / OFF valve capable of extracting air at axial compressor discharge, thus avoiding the axial compressor instability, the so-called surge, at low speed.

[0088] Within the present disclosure, the nozzle guide vanes NGV are variable geometry vanes capable of modulating the area of gas passage from high pressure turbine to the low pressure turbine. Closing the nozzle guide vanes NGV decreases the passage area and thus more expansion occurs on low pressure turbine. Accordingly, less expansion on high pressure turbine occurs. Ther nozzle guide vanes NGV regulate the expansion so that the passage area increases at the opening of the nozzle guide vanes NGV.

[0089] After closing the synchronizing valve, the electric machine unit 3 voltage, frequency, and phase angle are matched to those of the grid 5 before reconnecting, and the circuit breaker 32 is reactivated so that the electric machine unit 3 can deliver power once fully synchronized.

[0090] The method 100 involves regular checks of the operation 110 of the electric machine unit 3 to monitor the switch of the energy conversion system 1 from generating mode to synchronous-condenser mode, ensuring seamless transition where the gas turbine 2 is shut down and the electric machine unit 3 maintains generator function.

[0091] Operationally, when the energy conversion system 1 passes from the synchro- nous-condenser mode to the normal operating mode, the control logic unit U initiates the start-up process by engaging the gas turbine 2 starter motor 27. The energy startermotor 27 brings the gas turbine 2 to its crank speed of approximately 20% of its high- pressure rotor nominal speed, where the high-pressure shaft 26 rotates at a rate that ensures proper lubrication and ignition. This gradual acceleration minimizes mechanical stress on the gas turbine 2 components and establishes a stable rotational speed before moving to the next operational phase.

[0092] After reaching crank speed, the gas turbine 2 low-pressure shaft 26 accelerates to full speed no load (FSNL). During this acceleration, the automatic voltage regulator 27 injects field current into the rotor of the gas turbine 2, generating high voltage at the alternator terminals. The frequency and phase of the gas turbine 2 are aligned with the grid 5. Once synchronization is verified, the circuit breaker 32 closes to establish a secure electrical connection, enabling the transmission of electrical power.

[0093] The gas turbine 2 operates in droop mode, regulates the output of the gas turbine 2 to deliver a minimum, preselected level of active power to the power grid 5. Droop mode proportionally reduces the gas turbine 2 output as energy conversion system 1 decreases, providing stability in the power grid 5.ADVANTAGES

[0094] An advantage of the present invention is that the large inertia of the low-pressure turbine (LPT) and gearbox, in addition to the electric generator inertia, provides increased stability without requiring a special generator or clutches.

[0095] Another advantage of the present invention is that the Inlet Guide Vanes (IGV) and Nozzle Guide Vanes (NGV) are controlled according to a specific program to reduce permanent losses, including air ventilation and mechanical losses.

[0096] It is also an advantage of the present invention that the epicyclic gear results in lower permanent losses compared to other gearbox types, such as those with parallel shafts.

[0097] An advantage of the present invention is that an electric motor, using a variable frequency drive (VFD), can control the crank speed of the first shaft to optimize electrical consumption, reducing permanent losses while maintaining a permanently purged duct condition, leading to shorter start times.

[0098] Another advantage of the present invention is that the double-shaft gas turbine architecture (operated in synchronous condenser mode) greatly reduces permanent electrical consumption in comparison to a single-shaft GT without a clutch.

[0099] It is also an advantage of the present invention that the speed-reducing gearbox multiplies the inertia of the LPT rotor by 27 times when reduced to the speed of the generator, contributing to grid stability.

[0100] While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

[0101] Reference has been made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to "one embodiment" or "an embodiment" or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase "in one embodiment" or "in an embodiment" or "in some embodiments" in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0102] When elements of various embodiments are introduced, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0103] The subject matter described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structuralmeans disclosed in this specification and structural equivalents thereof, or in combinations of them. The subject matter described herein can be implemented as one or more computer program products, such as one or more computer programs tangibly embodied in an information carrier (e.g., in a machinereadable storage device), or embodied in a propagated signal, for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). A computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, subprograms, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0104] The processes and logic flows described in this specification, including the method steps of the subject matter described herein, can be performed by one or more programmable processors executing one or more computer programs to perform functions of the subject matter described herein by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus of the subject matter described herein can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0105] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a readonly memory, or a random access memory, or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magnetoopticaldisks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of nonvolatile memory, including by way of example semiconductor memory devices, (e.g., EPROM, EEPROM, and flash memory devices); magnetic disks, (e.g., internal hard disks or removable disks); magnetooptical disks; and optical disks (e.g., CD and DVD disks). The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0106] To provide for interaction with a user, the subject matter described herein can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, (e.g., a mouse or a trackball), by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well. For example, feedback provided to the user can be any form of sensory feedback, (e.g., visual feedback, auditory feedback, or tactile feedback), and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0107] The techniques described herein can be implemented using one or more modules. As used herein, the term “module” refers to computing software, firmware, hardware, and / or various combinations thereof. At a minimum, however, modules are not to be interpreted as software that is not implemented on hardware, firmware, or recorded on a non-transitory processor readable recordable storage medium (i.e., modules are not software per se). Indeed “module” is to be interpreted to always include at least some physical, non-transitory hardware such as a part of a processor or computer. Two different modules can share the same physical hardware (e.g., two different modules can use the same processor and network interface). The modules described herein can be combined, integrated, separated, and / or duplicated to support various applications. Also, a function described herein as being performed at a particular module can be performed at one or more other modules and / or by one or more other devices instead of or in addition to the function performed at the particular module. Further, the modules can be implemented across multiple devices and / or other components local or remote to one another. Additionally, the modules can be moved from one device and added to another device, and / or can be included in both devices.

[0108] The subj ect matter described herein can be implemented in a computing systemthat includes a backend component (e.g., a data server), a middleware component (e.g., an application server), or a frontend component (e.g., a client computer having a graphical user interface or a web browser through which a user can interact with an implementation of the subject matter described herein), or any combination of such backend, middleware, and frontend components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet.

Claims

Synchronous-condenser mode operating method of a clutch-less energy conversion systemCLAIMS1. A method (100) of operating an energy conversion system (1), wherein the energy conversion system (1) comprises: a gas turbine (2), for generating mechanical energy; an electric machine unit (3), mechanically connected to gas turbine (2) and to a power grid (5), wherein the electric machine unit (3) can operate as a generator, to drive the gas turbine (2), or as an energy converter, to convert the mechanical energy received by the gas turbine (2) into electric energy to be injected into the power grid (5); a speed adjustment device (4) connected between the gas turbine (2) and the electric machine unit (3), and capable of rotating with the gas turbine (2) and the electric machine (3); and wherein the power grid (5) is connected to renewable energy generator units; wherein the operating method (100) comprises the following steps: checking the operation (110) of the electric machine unit (3) as a generator, so that the energy conversion system (1) delivers active power and reactive power to the grid (5); reducing (120) the operation of the gas turbine (2) up to a minimum active power; removing (130) the protections, for allowing the electric machine unit (3) to inject power into the power grid (5); activating (140) a synchronous-condenser mode, wherein the electric machine unit (3) is dragged by power grid (5) and absorbs active power, to be capable of delivering reactive power, contributing to the stability of the power grid (5) with the combined inertia of the gas turbine (2), the speed adjustment device (4) and the electric machine unit (3), wherein the speed adjustment device is adapted to increase the inertia of a rotor within the gas turbine (2).

2. The method (100) according to claim 1, wherein the reducing (120) step comprises the following sub-steps: ramping down (121) the operation of the gas turbine (2) to the minimum; and adjusting (122) an automatic voltage regulator (31), to follow the reduction of the power generated by the gas turbine (2).

3. The method (100) according to the preceding claim, wherein the ramping down (121) comprises the following sub-steps: operating (1211) a control system that adjusts the speed of the gas turbine (2) by adjusting the fuel input; and operating (1212) an automatic voltage regulator (31) to control the generator to maintain a specific reactive power.

4. The method (100) according to any one of the preceding claims, wherein the protection removing (130) step comprises the following sub-steps: disabling (131) the automatic voltage regulator (31) and a circuit breaker (32); and shutting down (132) the fuel valves (28) of the gas turbine (2) to allow an active power flow inversion.

5. The method (100) according to any one of the preceding claims, further comprising the following steps: checking the switch (150) of the energy conversion system (1) from the synchronous-condenser mode, to generating mode, wherein the gas turbine (2) generates mechanical energy and the electric machine unit (3) operates as energy converter; and reactivating (160) the gas turbine (2).

6. The method (100) according to the preceding claim, wherein the reactivating step (160) comprises the following sub-steps: adjusting (161) the automatic voltage regulator (31) to have a minimum exchange of reactive power to the power grid (5); opening (162) a synchronizing valve to slow down gradually the gas turbine (2) until it stops; andreactivating (163) the gas turbine (2), wherein the startup sequence of the gas turbine (2) is activated to bring the gas turbine (2) to a Full Speed No Load state, wherein the gas turbine (2) runs without delivering electrical power to the power grid (5), and the synchronizing valve is closed to match the electric machine unit (3) voltage, frequency, and phase angle with those of the power grid (5) before connecting it and the circuit breaker (32) is reactivated, allowing the electric machine unit (3) to start delivering power to the power grid (5) once it is synchronized.

7. The method (100) according to any one of the preceding claims, wherein the gas turbine is a double shaft gas turbine (2), comprising: a compressor (21), high-pressure turbine (22), a high-pressure shaft (23), connecting the compressor (21) and the high-pressure turbine rotor (22), a low-pressure turbine (25), having a low-pressure rotor and a low- pressure shaft (26), connected to the rotor; and wherein the speed adjustment device (4) is connected to the low-pressure shaft (26) and wherein the gearbox (4) is adapted to multiply the inertia of the rotor of the low-pressure turbine (25) and to reduce the speed to the generator speed suitable for the grid frequency.

8. The method (100) according to the preceding claim, wherein the activating (140) a synchronous-condenser mode step comprises: controlling, by means of the synchronous-condenser mode, a set of inlet guide vanes (261) arranged at an entry of the compressor (21), and / or a set of nozzle guide vanes (262) arranged between the high-pressure turbine (22) and low-pressure turbine (25), and / or one or more anti-surge valves (ASV) to provide a reactive power.

9. The method (100) according to any one of the preceding claims, wherein the gas turbine (2) is maintained at crank speed, when the energy conversion system (1) is operating at the synchronous-condenser mode.

10. The method (100) according to any one of the preceding claims, wherein the step of checking the operation (110) of the electric machine unit (3) as a generator comprises the switch of the energy conversion system (1) from the generating mode to synchronous-condenser mode, wherein the gas turbine (2) is shut off and the electric machine unit (3) operates as a generator.

11. The method (100) according to any one of the preceding claims, wherein the speed adjustment device is a gearbox (4), preferably an epicyclic gearbox.

12. The method (100) according to the preceding claim, wherein the gearbox (4) is a bidirectional gearbox having a fixed speed ratio.

13. The method (100) according to any one of the preceding claims, wherein the electric machine unit (3) is a four-pole electrical machine capable of achieving synchronous speeds necessary for grid stability.

14. An energy conversion system (1), comprising: a gas turbine (2), for generating mechanical energy; an electric machine unit (3), mechanically connected to gas turbine (2) and to the power grid (5), wherein the electric machine unit (3) can operate as a generator, to drive the gas turbine (2), or as an energy converter, to convert the mechanical energy received by the gas turbine (2) into electric energy to be injected into the power grid (5); a speed adjustment device (4), connected between the gas turbine (2) and the electric machine unit (3), adapted to multiply the inertia of the gas turbine (2); and a control logic unit (U), operably connected to the gas turbine (2) and to the electric machine unit (3), configured to execute the method according to any one of claims 1-13; wherein the to the power grid (5) is connected the renewable energy generator units.

15. The energy conversion system (1) of the preceding claim, wherein the gas turbine (2) is a double shaft gas turbine (2), comprising: a compressor (21),high-pressure turbine (22), a high-pressure shaft (23), connecting the compressor (21) and the high-pressure turbine rotor (22), a low-pressure turbine (25), having a low-pressure rotor and a low-pressure shaft (26), connected to the rotor; and wherein the speed adjustment device (4) is connected to the low-pressure shaft (26) and wherein the speed adjustment device (4) is adapted to multiply the inertia of the rotor of the low-pressure turbine (25).

16. The energy conversion system (1) of any one of the claims 14-15, wherein the gas turbine (2) comprises an energy starter (27) for starting the compressor (21).

17. The energy conversion system (1) of any one of claims 14-16, wherein the speed adjustment device is a gearbox (4), preferably an epicyclic gearbox.

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