Geothermal power station fcb island operation control method and system

Abstract

The application provides a geothermal power station FCB island operation control method and system, belongs to the technical field of geothermal power station FCB island operation, and the method comprises the following steps: collecting the switch states of the main transformer outlet, the generator outlet and the medium-voltage bus circuit breaker in real time, generating an FCB trigger signal when three conditions are met at the same time, and synchronously sending the FCB trigger signal to a steam discharge circuit, a steam turbine DEH control system and a generator excitation control system through hard wiring; the steam discharge circuit executes front-of-the-machine pressure override control, adjusts the valve opening degree based on the pressure deviation and the change rate; the excitation system executes voltage-frequency cross compensation closed-loop control; the DEH system quickly sheds load to auxiliary power load, switches the primary frequency modulation mode to maintain frequency stability. The application is suitable for the characteristics of the geothermal power station, improves the unit operation stability under the FCB working condition, and guarantees the safe island operation of the unit when the power grid fails.

Description

Technical Field

[0001] This application belongs to the field of FCB islanding operation technology for geothermal power plants, specifically relating to a control method and system for FCB islanding operation of geothermal power plants. Background Technology

[0002] Geothermal power generation, as a stable and controllable baseload renewable energy source, has become an important component of the new power system. Geothermal power plants rely on underground geothermal fluids to drive steam turbines to generate electricity. Their energy supply is not affected by external factors such as weather and day / night cycles, giving them an inherent advantage in ensuring continuous supply during grid failure scenarios.

[0003] As the power grid coverage expands, the risk of grid disconnection caused by extreme natural disasters and line faults continues to exist. Generator units with FCB islanding capability can maintain stable operation of plant power after disconnection from the main power grid, becoming the core power source for black start of the power grid. This is crucial for improving the power system's anti-disturbance capability and fault recovery efficiency.

[0004] Existing FCB control technologies are mostly adapted to thermal power plants and other generator sets with boiler combustion regulation, but they cannot adapt to the core characteristics of geothermal power plants that have no boiler and a continuous supply of geothermal steam. After FCB is triggered, excess steam is prone to unstable pressure in front of the generator due to the inability to quickly and controllably discharge it. At the same time, existing solutions have problems with poor synchronization of FCB signal transmission and insufficient ability to suppress voltage and frequency coupling fluctuations under islanded operation conditions. This can easily lead to alternating voltage and frequency fluctuations, thereby causing the unit to trip and failing to ensure the safe and stable operation of geothermal power plants under FCB conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for controlling the FCB (Fuel Cell Flow Control) islanded operation of a geothermal power plant. Targeting the core characteristics of geothermal power plants—no boiler and continuous geothermal steam supply—this method achieves precise triggering, synchronous control, smooth transition, and stable operation of the unit under FCB conditions. It solves the problems of pressure instability, asynchronous operation, large parameter fluctuations, and unit tripping that easily occur in existing geothermal power plants under FCB conditions.

[0006] In a first aspect, embodiments of this application provide a method for controlling the islanded operation of a geothermal power plant's FCB (Fuel Cell Block) system, the method comprising: S1. Real-time acquisition of switch status signals of main transformer output circuit breaker, generator output circuit breaker and medium voltage bus circuit breaker. When the FCB triggering conditions of main transformer output circuit breaker open, generator output circuit breaker closed and medium voltage bus circuit breaker closed are met simultaneously, an FCB triggering signal is generated. S2. The FCB trigger signal is synchronously sent to the steam discharge circuit, the turbine DEH control system, and the generator excitation control system via a hard-wired circuit; S3. After receiving the FCB trigger signal, the steam discharge circuit executes the override control of the steam pressure in front of the turbine. Based on the opening formula of the pressure deviation and pressure change rate in front of the turbine, it adjusts the valve opening to discharge excess geothermal steam and maintain the stability of the turbine in front pressure. S4. After receiving the FCB trigger signal, the generator excitation control system maintains the automatic adjustment state, performs generator output voltage-frequency cross-compensation control, and performs output voltage closed-loop control after compensating the voltage setpoint based on the frequency deviation to maintain the stability of the generator output voltage under islanding conditions. S5. After receiving the FCB trigger signal, the turbine DEH control system quickly reduces the unit load to the plant power load, switches the load control loop to the following state, and simultaneously switches the main control loop to the primary frequency regulation control mode to maintain the unit frequency stability.

[0007] Furthermore, in step S1, the generated FCB trigger signal is simultaneously uploaded to the unit's DCS system through a redundant communication link for real-time monitoring of FCB operating conditions, recording of action timing, and fault tracing. When a hardwired circuit fails, the communication link is activated for backup.

[0008] Furthermore, in step S3, the specific steps for the overdrive control of the steam pressure before the actuator are as follows: Open all pressure relief valves; If the real-time load of the unit is greater than the preset percentage × rated load when the trigger is activated, the valve opening will be adjusted after a delay of m seconds after the pressure relief valve is fully opened. If the unit's real-time load is less than or equal to the preset percentage × rated load when triggered, the valve opening will be adjusted directly without delay after the pressure relief valve is fully opened.

[0009] Further, in step S3, the formula for the opening degree based on the pressure deviation and pressure change rate before the machine is:

[0010] in, This represents the real-time opening degree of the pressure relief valve, with a value ranging from 0% to 100%. This represents the maximum valve opening, fixed at 100%. This refers to the real-time pressure at the turbine inlet. This is the setpoint for the machine's pre-pressurization. This is the upper limit of the safe pressure before the machine. This represents the real-time rate of change of the pressure before the machine. This represents the maximum allowable rate of change in the pressure before the machine. This is the pressure deviation weighting coefficient. This is the weighting coefficient for the rate of change of pressure.

[0011] Further, in step S4, the formula for the voltage-frequency cross-compensation control is:

[0012] in, To compensate for the generator output voltage setpoint, This is the generator's rated output voltage. This is the frequency-voltage compensation coefficient. The rated frequency of the generator excitation control system. The generator setpoint is the real-time frequency of the unit; the generator excitation control system performs PID closed-loop regulation based on the compensated voltage setpoint.

[0013] Furthermore, in step S5, the specific steps for switching the main control loop to primary frequency modulation control mode are as follows: S51. Calculate the real-time droop coefficient based on the deviation of the plant's power load. The formula for calculating the droop coefficient is as follows:

[0014] in, This is the real-time droop coefficient for primary frequency modulation. As the baseline adjustment coefficient, The load fluctuation correction factor uses a preset value. For real-time plant power load, For rated plant power load, This represents the absolute value of the plant's power load deviation. S52. Substitute the real-time droop coefficient of primary frequency regulation into the primary frequency regulation power correction formula to calculate the turbine inlet valve adjustment command. The power correction formula is as follows:

[0015] in, This is the primary frequency modulation power correction value. This refers to the real-time speed of the steam turbine. The rated speed of the steam turbine. This refers to the rated active power of the generator unit.

[0016] Secondly, embodiments of this application also provide an FCB islanding control system for a geothermal power plant, the system comprising: FCB trigger logic unit, steam emission control unit, generator voltage-frequency cross compensation control unit, turbine frequency regulation control unit; The signal input terminals of the FCB trigger logic unit are connected to the auxiliary contacts of the main transformer output circuit breaker, the generator output circuit breaker, and the medium-voltage bus circuit breaker, respectively. The signal output terminals are connected to the trigger signal input terminals of the steam emission control unit, the turbine frequency regulation control unit, and the generator voltage-frequency cross compensation control unit through hard-wired circuits, respectively. The signal input terminal of the steam emission control unit is connected to the turbine inlet pressure detection device and the unit power transmitter, and the signal output terminal is connected to the unit pressure relief valve, which is used to perform inlet steam pressure override control and valve opening adjustment. The generator voltage-frequency cross compensation control unit is integrated into the generator excitation control system. The signal input terminal of the generator voltage-frequency cross compensation control unit is connected to the generator outlet voltage transformer and the unit frequency detection device, respectively, and the signal output terminal is connected to the generator excitation winding. The turbine frequency regulation control unit is integrated into the turbine DEH control system. The signal input terminal of the turbine frequency regulation control unit is connected to the turbine speed sensor, the unit power transmitter, and the plant power load detection device, respectively, and the signal output terminal is connected to the turbine inlet steam regulating valve.

[0017] Furthermore, the FCB trigger logic unit has a built-in judgment circuit. When three conditions are met simultaneously—the main transformer outlet circuit breaker is open, the generator outlet circuit breaker is closed, and the medium-voltage bus circuit breaker is closed—an FCB trigger signal is output. A single signal fault will not trigger a malfunction.

[0018] Furthermore, the steam emission control unit incorporates a load override control module and an opening degree calculation module; The load-sharing override control module has a preset judgment threshold, which is used to execute the corresponding delay control logic; The opening calculation module has a built-in opening formula, which is used to output real-time adjustment commands for the pressure relief valve.

[0019] Furthermore, the turbine frequency control unit incorporates a droop calculation module and a primary frequency control closed-loop control module; The adjustment calculation module has a built-in formula for calculating the adjustment coefficient. The generator voltage-frequency cross-compensation control unit has a built-in voltage compensation calculation module, which contains the calculation formula for frequency-voltage cross-compensation.

[0020] As can be seen from the above technical solutions, the present invention has the following advantages: By implementing load override control and steam discharge regulation, excess geothermal steam can be quickly and controllably discharged, maintaining stable pressure at the turbine inlet. A hard-wired circuit is used to synchronously transmit FCB trigger signals, eliminating communication delays and signal loss, ensuring synchronized operation of the steam discharge, turbine speed regulation, and generator excitation systems. A dual-link transmission scheme with hard-wired and redundant communication is configured to prevent FCB signal failures and erroneous activations. Voltage-frequency cross-compensation control addresses the alternating fluctuations caused by strong voltage and frequency coupling in islanded operation scenarios. A primary frequency regulation scheme based on plant power load deviation quickly adapts to plant power load fluctuations, shortens frequency stabilization time, and reduces parameter overshoot. A three-state and logic judgment system is employed for the main transformer output circuit breaker, generator output circuit breaker, and medium-voltage bus circuit breaker, triggering only under actual FCB operating conditions: unit disconnected from the main grid, generator operating normally, and plant power bus connected. This avoids false triggering caused by grid fluctuations or single switch signal failures, resulting in high accuracy in operating condition identification. This application effectively improves the grid adaptability and safe operation capability of geothermal power plants. Attached Figure Description

[0021] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the FCB islanding control method for geothermal power plants in this application. Figure 2 This is a schematic diagram of the FCB islanded operation control system for the geothermal power plant in this application. Detailed Implementation

[0023] The various embodiments of the invention will be described more fully in the specific steps of the FCB islanding control method for geothermal power plants, which will be described in detail below. The invention may have various embodiments, and adjustments and changes may be made therein. However, it should be understood that there is no intention to limit the various embodiments of the invention to the specific embodiments disclosed herein, but rather the invention should be understood to cover all adjustments, equivalents, and / or alternatives falling within the spirit and scope of the various embodiments of the invention.

[0024] It should be understood that, when used in this specification, the term "comprising" indicates the presence of the described feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0025] The terms "one embodiment" or "some embodiments" used in this application mean that one or more embodiments of this application include the specific features, structures, or characteristics described in that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this application do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0026] To make the objectives, features, and advantages of this invention more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solutions protected by this invention. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] The core technical terms used in this solution are explained uniformly as follows: FCB (Fast Cut Back) refers to the control process of instantly reducing the generating load to a level that only meets the power needs of the generator unit after it is disconnected from the main power grid, so as to achieve uninterrupted and continuous stable operation. Islanding operation (also known as isolated grid operation) that is associated with FCB operation mode refers to the operating state in which the generator unit is completely disconnected from the external power grid and independently supplies power to the plant's internal auxiliary equipment. It is the core operating mode of the unit after FCB is triggered.

[0028] DEH, or Digital Electro-hydraulic Control System for Steam Turbines, is the core system for controlling steam turbine speed, load, and steam intake. It is also the core actuator for load and frequency control of the unit under FCB (Fuel Circuit Breaker) conditions.

[0029] The turbine inlet pressure refers to the steam pressure before the turbine inlet. It is a core parameter for ensuring the stable operation of the turbine. Large fluctuations in this parameter can directly lead to unit tripping. It is also the control object under the FCB (Future Combustion Block) condition of a geothermal power plant.

[0030] Primary frequency regulation is a fundamental function of steam turbines that automatically adjusts the steam intake according to changes in system frequency (corresponding to unit speed) to quickly maintain the frequency stability of the power grid or islanded grid. It is a control method to maintain the frequency stability of the unit during islanded operation.

[0031] Please see Figure 1 The diagram shows a flowchart of the FCB islanding control method for a geothermal power plant. The method includes: S1. Real-time acquisition of switch status signals of main transformer output circuit breaker, generator output circuit breaker and medium voltage bus circuit breaker. When the FCB triggering conditions of main transformer output circuit breaker open, generator output circuit breaker closed and medium voltage bus circuit breaker closed are met simultaneously, an FCB triggering signal is generated. S2. The FCB trigger signal is synchronously sent to the steam discharge circuit, the turbine DEH control system, and the generator excitation control system via a hard-wired circuit; S3. After receiving the FCB trigger signal, the steam discharge circuit executes the override control of the steam pressure in front of the turbine. Based on the opening formula of the pressure deviation and pressure change rate in front of the turbine, it adjusts the valve opening to discharge excess geothermal steam and maintain the stability of the turbine in front pressure. S4. After receiving the FCB trigger signal, the generator excitation control system maintains the automatic adjustment state, performs generator output voltage-frequency cross-compensation control, and performs output voltage closed-loop control after compensating the voltage setpoint based on the frequency deviation to maintain the stability of the generator output voltage under islanded conditions. S5. After receiving the FCB trigger signal, the turbine DEH control system quickly reduces the unit load to the plant power load, switches the load control loop to the following state, and simultaneously switches the main control loop to the primary frequency regulation control mode to maintain the unit frequency stability.

[0032] As a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process of this embodiment, another FCB islanding operation control method for geothermal power plants is provided. The application scenario of this embodiment is a geothermal power plant with a rated capacity of 30MW. The unit parameters are as follows: the rated speed of the steam turbine is 3000rpm, the rated frequency is 50Hz; the rated outlet voltage of the generator is 10.5kV, the rated power load of the plant is 1.5MW; the rated value of the steam turbine inlet pressure is 4.2MPa, the upper limit of safety is 4.5MPa, and the maximum allowable pressure change rate is 0.1MPa / s; the unit is equipped with 4 pressure relief valves, and the maximum discharge capacity of a single valve corresponds to the steam flow rate of 50% of the rated load.

[0033] The method includes the following steps: S1. Real-time acquisition of switch status signals of main transformer output circuit breaker, generator output circuit breaker and medium voltage bus circuit breaker. When the FCB triggering conditions of main transformer output circuit breaker open, generator output circuit breaker closed and medium voltage bus circuit breaker closed are met simultaneously, an FCB triggering signal is generated. In step S1, the generated FCB trigger signal is simultaneously uploaded to the unit's DCS system through a redundant communication link for real-time monitoring of FCB operating conditions, recording of action timing, and fault tracing. When a hardwired circuit fails, the communication link is activated for backup.

[0034] In some embodiments, the auxiliary contact switch status signals of the main transformer output circuit breaker, generator output circuit breaker, and medium-voltage bus circuit breaker are collected in real time through the DI module of the unit PLC, and the built-in hardware three-way AND judgment circuit continuously performs operating condition judgment: An FCB (Foreign Circuit Breaker) condition is determined and an FCB trigger signal is generated only when all three conditions are met simultaneously: the main transformer output circuit breaker is open (the unit is disconnected from the external power grid), the generator output circuit breaker is closed (the generator is running normally and has not stopped), and the medium-voltage bus circuit breaker is closed (the plant service bus is connected and can supply power to the plant service equipment). The generated FCB trigger signal is simultaneously uploaded to the unit's DCS system via a redundant industrial Ethernet communication link for real-time video monitoring of FCB operation, SOE action timing recording, and post-fault tracing.

[0035] S2. The FCB trigger signal is synchronously sent to the steam discharge circuit, the turbine DEH control system, and the generator excitation control system via a hard-wired circuit; In some embodiments, the generated FCB trigger signal is synchronously sent in the form of a switch signal to the DCS control module of the steam emission control loop, the switch input terminals of the turbine DEH control system, and the switch input terminals of the generator excitation control system via a relay hard-wired circuit. The signal transmission delay is ≤1ms, ensuring that the three major control loops receive the trigger command synchronously without any timing deviation. When the hard-wired circuit fails, the backup trigger logic of the communication link is automatically triggered, and the FCB trigger signal is sent through the redundant communication link between the DCS and the DEH and excitation systems to ensure reliable command transmission.

[0036] S3. After receiving the FCB trigger signal, the steam discharge circuit executes the turbine inlet steam pressure override control, adjusting the valve opening based on the opening formula of turbine inlet pressure deviation and pressure change rate to discharge excess geothermal steam and maintain stable turbine inlet pressure; the specific steps of executing the turbine inlet steam pressure override control in step S3 are as follows: Open all pressure relief valves; If the real-time load of the unit is greater than the preset percentage × rated load when the trigger is activated, the valve opening will be adjusted after a delay of m seconds after the pressure relief valve is fully opened. If the unit's real-time load is less than or equal to the preset percentage × rated load when triggered, the valve opening will be adjusted directly without delay after the pressure relief valve is fully opened.

[0037] In step S3, the opening formula based on the pressure deviation and pressure change rate before the machine is:

[0038] in, This represents the real-time opening degree of the pressure relief valve, with a value ranging from 0% to 100%. This represents the maximum valve opening, fixed at 100%. This refers to the real-time pressure at the turbine inlet. This is the setpoint for the machine's pre-pressurization. This is the upper limit of the safe pressure before the machine. This represents the real-time rate of change of the pressure before the machine. This represents the maximum allowable rate of change in the pressure before the machine. This is the pressure deviation weighting coefficient. This is the weighting coefficient for the rate of change of pressure.

[0039] In some embodiments: Override control: Immediately outputs a full-open command to fully open all 4 pressure relief valves, discharging excess geothermal steam as quickly as possible to avoid overpressure at the machine entrance. Load sharing delay judgment: Real-time load data from the unit's power transmitter is read. In this embodiment, the preset percentage is 50% of the rated load, and the delay m is 5 seconds. If the unit's real-time load is greater than 15MW (50% of rated load) when the FCB is triggered, the pressure relief valve will remain fully open for 5 seconds. After the pressure stabilizes before standby, the system will switch to automatic closed-loop regulation mode. If the unit's real-time load is ≤15MW (50% of rated load) when the FCB is triggered, the pressure relief valve will open fully without delay and directly switch to the automatic closed-loop regulation mode. After switching to automatic mode, the system collects real-time detection data from the pressure transmitter before the machine, calculates the pressure deviation and pressure change rate before the machine, and uses the opening formula to calculate the real-time valve opening command. In this embodiment... k 1 is 0.6. k 2 is taken as 0.4, and the opening formula is:

[0040] For example, when the FCB is triggered, the unit load is 24MW (80% of the rated load). After 5 seconds, the real-time inlet pressure P=4.35MPa and the pressure change rate P=0.03MPa / s. Substituting into the formula, the valve opening S=42%. The steam emission control unit outputs a 42% opening command to the pressure relief valve, continuously adjusting in a closed loop to maintain the inlet pressure stable within the range of 4.2MPa±0.05MPa.

[0041] S4. After receiving the FCB trigger signal, the generator excitation control system maintains automatic adjustment and executes generator output voltage-frequency cross-compensation control. Based on the frequency deviation, it compensates for the voltage setpoint and then executes closed-loop output voltage control to maintain stable generator output voltage under islanding conditions. In step S4, the formula for the voltage-frequency cross-compensation control is:

[0042] in, To compensate for the generator output voltage setpoint, This is the generator's rated output voltage. This is the frequency-voltage compensation coefficient. The rated frequency of the generator excitation control system. The generator setpoint is the real-time frequency of the unit; the generator excitation control system performs PID closed-loop regulation based on the compensated voltage setpoint.

[0043] In some embodiments, voltage data from the generator outlet voltage transformer and frequency data from the unit frequency detection device are collected in real time, and the compensated voltage setpoint is calculated using a cross-compensation formula. In this embodiment... U set =10.5kV, f set =50Hz, k 4 is set to 1.0, and the compensation formula is:

[0044] After the FCB is triggered, the unit's real-time frequency is 50.5Hz. Substituting this into the formula, the compensated voltage setpoint is calculated. U corr =10.395kV, by reducing the voltage setpoint to suppress the voltage rise caused by the increase in frequency, and to avoid alternating fluctuations in voltage and frequency; Based on the compensated voltage setpoint, PID closed-loop regulation is executed to adjust the generator excitation current in real time, maintain the generator output voltage within ±2% of the rated value, and ensure the power supply safety of plant equipment.

[0045] S5. After receiving the FCB trigger signal, the turbine DEH control system quickly reduces the unit load to the plant power load, switches the load control loop to the following state, and simultaneously switches the main control loop to the primary frequency regulation control mode to maintain the unit frequency stability.

[0046] In step S5, the specific steps for switching the main control loop to primary frequency modulation control mode are as follows: S51. Calculate the real-time droop coefficient based on the deviation of the plant's power load. The formula for calculating the droop coefficient is as follows:

[0047] in, This is the real-time droop coefficient for primary frequency modulation. As the baseline adjustment coefficient, The load fluctuation correction factor uses a preset value. For real-time plant power load, For rated plant power load, This represents the absolute value of the plant's power load deviation. S52. Substitute the real-time droop coefficient of primary frequency regulation into the primary frequency regulation power correction formula to calculate the turbine inlet valve adjustment command. The power correction formula is as follows:

[0048] in, This is the primary frequency modulation power correction value. This refers to the real-time speed of the steam turbine. The rated speed of the steam turbine. This refers to the rated active power of the generator unit.

[0049] In some embodiments, the turbine inlet regulating valve is quickly closed by the speed control system to rapidly reduce the active load of the unit from the current load to 1.5MW; The original power grid load command control loop is switched to follow mode and no longer responds to external power grid load commands. At the same time, the turbine main control loop is switched to primary frequency regulation control mode. Real-time acquisition of plant power load data and calculation of real-time droop coefficient; in this embodiment, the baseline droop coefficient is used. δ 0 = 4%, load fluctuation correction factor k 3=0.5, rated plant power load P L0 =1.5MW, the droop coefficient formula is:

[0050] When the real-time plant power load P L When the current droop is 1.2MW, the real-time droop coefficient is calculated by substituting into the formula. δ=3.6%, which improves the frequency modulation response speed by reducing the droop factor and adapts to low load conditions; In this embodiment, the turbine speed sensor collects real-time speed data, and the real-time droop coefficient is substituted into the power correction formula to calculate the turbine inlet valve adjustment command. n set =3000rpm, P rated =30MW, the power correction formula is:

[0051] When the real-time speed n act =3030rpm, real-time droop coefficient δ =3.6%, substituting into the formula, we obtain the power correction value Δ P f = At 8.33MW, the DEH system closes the turbine inlet regulating valve according to this correction value, reducing the unit output and speed, and continuously maintaining the unit frequency within the range of 49.5Hz~50.5Hz through closed-loop regulation.

[0052] After the FCB is triggered, the unit in this embodiment can complete the switching of all control modes within 2 seconds and achieve stable control of the pressure, frequency and voltage before the unit within 5 seconds. There is no risk of overpressure or overspeed tripping. It can maintain islanded operation for a long time and can quickly complete grid connection operation after the grid fault is restored.

[0053] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0054] Please see Figure 2 The diagram shows a schematic of the FCB islanding control system for a geothermal power plant. The system includes: FCB trigger logic unit, steam emission control unit, generator voltage-frequency cross compensation control unit, turbine frequency regulation control unit; The signal input terminals of the FCB trigger logic unit are connected to the auxiliary contacts of the main transformer output circuit breaker, the generator output circuit breaker, and the medium-voltage bus circuit breaker, respectively. The signal output terminals are connected to the trigger signal input terminals of the steam emission control unit, the turbine frequency regulation control unit, and the generator voltage-frequency cross compensation control unit through hard-wired circuits, respectively. In some embodiments, the FCB trigger logic unit is implemented based on the unit's redundant PLC. Its signal input terminals are connected to the auxiliary contacts of the main transformer output circuit breaker, generator output circuit breaker, and medium-voltage bus circuit breaker via hard-wiring to collect the status signals of the three switches. It has a built-in hardware three-way AND judgment circuit, and only outputs the FCB trigger signal when the three signals simultaneously meet the FCB trigger conditions. Its signal output terminals are connected to the trigger signal input terminals of the steam emission control unit, turbine frequency regulation control unit, and generator voltage-frequency cross-compensation control unit via hard-wiring circuit, and communicate with the unit's DCS system through a redundant communication link.

[0055] The signal input terminal of the steam emission control unit is connected to the turbine inlet pressure detection device and the unit power transmitter, and the signal output terminal is connected to the unit pressure relief valve, which is used to perform inlet steam pressure override control and valve opening adjustment. In some embodiments, the steam emission control unit is integrated into the unit's DCS system, with a built-in load override control module and opening calculation module; its signal input terminal is connected to the turbine inlet pressure transmitter and the unit power transmitter respectively to collect pressure and load data in real time; its control output terminal is connected to the electric actuators of four pressure relief valves to output valve opening and closing adjustment commands, and to perform inlet steam pressure override control and closed-loop regulation.

[0056] The generator voltage-frequency cross compensation control unit is integrated into the generator excitation control system. The signal input terminal of the generator voltage-frequency cross compensation control unit is connected to the generator outlet voltage transformer and the unit frequency detection device, respectively, and the signal output terminal is connected to the generator excitation winding. In some embodiments, the generator voltage-frequency cross-compensation control unit is integrated into the generator excitation control system (the ABBUNITROL 6000 excitation system is used in this embodiment), and has a built-in voltage compensation calculation module; its signal input terminal is connected to the generator outlet voltage transformer and the unit frequency detection device respectively to collect voltage and frequency data in real time; its control output terminal is connected to the generator excitation winding to output excitation current adjustment commands and perform voltage-frequency cross-compensation and closed-loop control.

[0057] The turbine frequency regulation control unit is integrated into the turbine DEH control system. The signal input terminal of the turbine frequency regulation control unit is connected to the turbine speed sensor, the unit power transmitter, and the plant power load detection device, respectively, and the signal output terminal is connected to the turbine inlet steam regulating valve.

[0058] In some embodiments, the turbine frequency regulation control unit is integrated into the turbine DEH control system (in this embodiment, a Siemens T3000 DEH system is used), and has a built-in differential calculation module and a primary frequency regulation closed-loop control module. Its signal input terminals are respectively connected to the turbine speed sensor, the unit power transmitter, and the plant power load detection device to collect speed, power, and plant power load data in real time. Its control output terminal is connected to the electro-hydraulic actuator of the turbine inlet regulating valve to output inlet valve regulation commands and execute unit load shedding and primary frequency regulation closed-loop control.

[0059] The FCB trigger logic unit has a built-in judgment circuit. When three conditions are met simultaneously—the main transformer output circuit breaker is open, the generator output circuit breaker is closed, and the medium-voltage bus circuit breaker is closed—it outputs an FCB trigger signal. A single signal fault will not trigger a malfunction.

[0060] The steam emission control unit has a built-in load override control module and an opening degree calculation module. The load-sharing override control module has a preset judgment threshold, which is used to execute the corresponding delay control logic; The opening calculation module has a built-in opening formula, which is used to output real-time adjustment commands for the pressure relief valve.

[0061] The turbine frequency control unit has a built-in differential calculation module and a primary frequency control closed-loop control module. The adjustment calculation module has a built-in formula for calculating the adjustment coefficient. The generator voltage-frequency cross-compensation control unit has a built-in voltage compensation calculation module, which contains the calculation formula for frequency-voltage cross-compensation.

[0062] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the islanded operation of a geothermal power plant's FCB (Fuel Cell Block) system, characterized in that: The method includes the following steps: S1. Real-time acquisition of switch status signals of main transformer output circuit breaker, generator output circuit breaker and medium voltage bus circuit breaker. When the FCB triggering conditions of main transformer output circuit breaker open, generator output circuit breaker closed and medium voltage bus circuit breaker closed are met simultaneously, an FCB triggering signal is generated. S2. The FCB trigger signal is synchronously sent to the steam discharge circuit, the turbine DEH control system, and the generator excitation control system via a hard-wired circuit; S3. After receiving the FCB trigger signal, the steam discharge circuit executes the override control of the steam pressure in front of the turbine. Based on the opening formula of the pressure deviation and pressure change rate in front of the turbine, it adjusts the valve opening to discharge excess geothermal steam and maintain the stability of the turbine in front pressure. S4. After receiving the FCB trigger signal, the generator excitation control system maintains the automatic adjustment state, performs generator output voltage-frequency cross-compensation control, and performs output voltage closed-loop control after compensating the voltage setpoint based on the frequency deviation to maintain the stability of the generator output voltage under islanding conditions. S5. After receiving the FCB trigger signal, the turbine DEH control system quickly reduces the unit load to the plant power load, switches the load control loop to the following state, and simultaneously switches the main control loop to the primary frequency regulation control mode to maintain the unit frequency stability.

2. The geothermal power plant FCB islanding operation control method according to claim 1, characterized in that, In step S1, the generated FCB trigger signal is simultaneously uploaded to the unit's DCS system through a redundant communication link for real-time monitoring of FCB operating conditions, recording of action timing, and fault tracing. When a hardwired circuit fails, the communication link is activated for backup.

3. The FCB islanding control method for geothermal power plants according to claim 1, characterized in that, In step S3, the specific steps for the overdrive control of the steam pressure before the actuator are as follows: Open all pressure relief valves; If the real-time load of the unit is greater than the preset percentage × rated load when the trigger is activated, the valve opening will be adjusted after a delay of m seconds after the pressure relief valve is fully opened. If the unit's real-time load is less than or equal to the preset percentage × rated load when triggered, the valve opening will be adjusted directly without delay after the pressure relief valve is fully opened.

4. The FCB islanding operation control method for a geothermal power plant according to claim 1, characterized in that, In step S3, the opening formula based on the pressure deviation and pressure change rate before the machine is: in, This represents the real-time opening degree of the pressure relief valve, with a value ranging from 0% to 100%. This represents the maximum valve opening, fixed at 100%. This refers to the real-time pressure at the turbine inlet. This is the setpoint for the machine's pre-pressurization. This is the upper limit of the safe pressure before the machine. This represents the real-time rate of change of the pressure before the machine. This represents the maximum allowable rate of change in the pressure before the machine. This is the pressure deviation weighting coefficient. This is the weighting coefficient for the rate of change of pressure.

5. The FCB islanding control method for a geothermal power plant according to claim 1, characterized in that, In step S4, the formula for the voltage-frequency cross-compensation control is: in, To compensate for the generator output voltage setpoint, This is the generator's rated output voltage. This is the frequency-voltage compensation coefficient. The rated frequency of the generator excitation control system. The generator setpoint is the real-time frequency of the unit; the generator excitation control system performs PID closed-loop regulation based on the compensated voltage setpoint.

6. The FCB islanding control method for a geothermal power plant according to claim 1, characterized in that, In step S5, the specific steps for switching the main control loop to primary frequency modulation control mode are as follows: S51. Calculate the real-time droop coefficient based on the deviation of the plant's power load. The formula for calculating the droop coefficient is as follows: in, This is the real-time droop coefficient for primary frequency modulation. As the baseline adjustment coefficient, The load fluctuation correction factor uses a preset value. For real-time plant power load, For rated plant power load, This represents the absolute value of the plant's power load deviation. S52. Substitute the real-time droop coefficient of primary frequency regulation into the primary frequency regulation power correction formula to calculate the turbine inlet valve adjustment command. The power correction formula is as follows: in, This is the primary frequency modulation power correction value. This refers to the real-time speed of the steam turbine. The rated speed of the steam turbine. This refers to the rated active power of the generator unit.

7. A geothermal power plant FCB islanding operation control system, characterized in that, The system is used to implement the method as described in any one of claims 1-6, the system comprising: FCB trigger logic unit, steam emission control unit, generator voltage-frequency cross compensation control unit, turbine frequency regulation control unit; The signal input terminals of the FCB trigger logic unit are connected to the auxiliary contacts of the main transformer output circuit breaker, the generator output circuit breaker, and the medium-voltage bus circuit breaker, respectively. The signal output terminals are connected to the trigger signal input terminals of the steam emission control unit, the turbine frequency regulation control unit, and the generator voltage-frequency cross compensation control unit through hard-wired circuits, respectively. The signal input terminal of the steam emission control unit is connected to the turbine inlet pressure detection device and the unit power transmitter, and the signal output terminal is connected to the unit pressure relief valve, which is used to perform inlet steam pressure override control and valve opening adjustment. The generator voltage-frequency cross compensation control unit is integrated into the generator excitation control system. The signal input terminal of the generator voltage-frequency cross compensation control unit is connected to the generator outlet voltage transformer and the unit frequency detection device, respectively, and the signal output terminal is connected to the generator excitation winding. The turbine frequency regulation control unit is integrated into the turbine DEH control system. The signal input terminal of the turbine frequency regulation control unit is connected to the turbine speed sensor, the unit power transmitter, and the plant power load detection device, respectively, and the signal output terminal is connected to the turbine inlet steam regulating valve.

8. The FCB islanding control system for a geothermal power plant according to claim 7, characterized in that, The FCB trigger logic unit has a built-in judgment circuit. When three conditions are met simultaneously—the main transformer output circuit breaker is open, the generator output circuit breaker is closed, and the medium-voltage bus circuit breaker is closed—it outputs an FCB trigger signal. A single signal fault will not trigger a malfunction.

9. The FCB islanding control system for a geothermal power plant according to claim 7, characterized in that, The steam emission control unit has a built-in load override control module and an opening degree calculation module. The load-sharing override control module has a preset judgment threshold, which is used to execute the corresponding delay control logic; The opening calculation module has a built-in opening formula, which is used to output real-time adjustment commands for the pressure relief valve.

10. The FCB islanding control system for a geothermal power plant according to claim 7, characterized in that, The turbine frequency control unit has a built-in differential calculation module and a primary frequency control closed-loop control module. The adjustment calculation module has a built-in formula for calculating the adjustment coefficient. The generator voltage-frequency cross-compensation control unit has a built-in voltage compensation calculation module, which contains the calculation formula for frequency-voltage cross-compensation.

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