A method for reconstructing and grid interlocking control of an electric system of a cut-cylinder back-pressure generator set

Abstract

The application discloses a method for reconstructing and grid-connection interlocking control of an electric system of a back-pressure generator unit. The method is characterized in that: the back-pressure generator unit is connected to the low-voltage side of a main transformer of a thermal power generator unit or a separated closed bus through a power-heat transformer to complete system reconstruction; a cut-cylinder mode confirmation signal and a low-pressure cylinder inlet valve full-closing signal are obtained through a distributed control system, and grid-connection is controlled after logical AND and time delay confirmation, and tripping and closing of the inlet regulating valve are interlocked when the cut-cylinder mode exits or the valve is not fully closed; after grid-connection, the power generation power and the heat supply of the thermal power generator unit and the back-pressure generator unit are optimally distributed based on an electric-thermal coupling target function, and the reverse power protection setting value and the over-frequency protection setting value are adaptively switched according to the operation mode. The application effectively improves the heat supply capacity and power generation flexibility, reduces the operation cost, and guarantees the equipment safety.

Description

Technical Field

[0001] This application relates to the field of power system technology, and relates to, but is not limited to, a method for reconfiguring and grid-connected interlocking control of the power system of a cylinder-cutting back-pressure generator set. Background Technology

[0002] With the ongoing advancement of deep peak shaving and heating system upgrades for thermal power units, cylinder cut-off operation mode is widely used to enhance the heating capacity and peak shaving flexibility of the units. In cylinder cut-off mode, the low-pressure cylinder inlet valves are fully closed, and a large amount of steam is used for heating. At this time, a back-pressure generator unit needs to be connected to fully utilize the steam pressure difference for power generation, achieving combined heat and power (CHP). However, in existing technologies, the connection method for back-pressure generator units is relatively arbitrary, lacking a standardized grid connection system reconfiguration scheme. This leads to significant changes in the short-circuit current level of the system after grid connection, threatening the dynamic and thermal stability of the original electrical equipment and posing safety hazards. Simultaneously, grid connection of back-pressure units depends on the accurate confirmation of cylinder cut-off and valve states. Existing control methods mostly rely on manual operation or simple logic judgment, resulting in signal misinterpretation, excessive delays, and other problems, leading to improper grid connection timing or even incorrect grid connection, affecting the safe operation of the unit. Furthermore, in cylinder-cutting mode, there is a lack of effective coordination and optimization methods for the distribution of electrothermal power between thermal power units and back-pressure generator units. The distribution usually relies on experience, making it difficult to optimize the system operating cost. Moreover, there are significant differences in the reverse power characteristics and frequency response characteristics of the units between cylinder-cutting operation and conventional operation mode. The existing protection settings adopt a fixed configuration method, which cannot be dynamically adjusted according to the operating mode, which can easily lead to protection failure or false operation, seriously threatening the safety of unit and grid operation. Summary of the Invention

[0003] To address the problems in existing technologies, such as the lack of standardized reconfiguration schemes for back-pressure generator unit grid connection, reliance on manual operation for grid connection control leading to signal misinterpretation and improper grid connection timing, lack of coordinated optimization methods for electrothermal power distribution, and the inability to dynamically adjust protection settings based on operating modes, this application provides a method for reconfiguring the power system and interlocking control of a cylinder-cutting back-pressure generator unit. This method improves grid connection safety and economy, and ensures the safe operation of both the generator unit and the power grid, through standardized system reconfiguration, AND gate logic and time-delayed confirmation for grid connection interlocking control, power optimization allocation based on an electrothermal coupling objective function, and adaptive switching of protection settings.

[0004] The technical solution of this application embodiment is implemented as follows: In the first aspect, this application embodiment provides a method for reconfiguration of the power system and grid-connected interlocking control of a cylinder-cutting back pressure generator set, wherein the power system includes a thermal power unit; The method includes: After the output voltage of the back-pressure generator set is stepped up by the power and heat transformer, it is connected to the low-voltage side of the main transformer of the thermal power unit or the isolated phase closed bus to obtain the short-circuit current of the back-pressure generator set after grid connection. Based on the short-circuit current after the back-pressure generator unit is connected to the grid and the short-circuit current when the back-pressure generator unit is not connected to the grid, the distributed control system (DCS) of the thermal power unit acquires the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal of the thermal power unit; when the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal are simultaneously satisfied, the back-pressure generator unit is controlled to connect to the grid for power generation; when the thermal power unit exits the cylinder cutting mode or the low-pressure cylinder steam inlet valve is not fully closed, the back-pressure generator unit is interlocked to trip. After the back-pressure generator unit is connected to the grid, the distributed control system allocates the power generation and heat supply of the thermal power unit and the back-pressure generator unit based on the constructed electrothermal coupling objective function and the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid; and switches the reverse power protection setting of the thermal power unit and the overfrequency protection setting of the back-pressure generator unit according to the acquired operating mode.

[0005] Preferably, the step of interlocking tripping of the back-pressure generator unit when the thermal power unit exits the cylinder cutting mode or the low-pressure cylinder steam inlet valve is not fully closed includes: When the thermal power unit exits the cylinder cut-off mode or the low-pressure cylinder steam inlet valve is not fully closed, the back pressure generator unit is tripped and disconnected, and the steam inlet regulating valve of the back pressure generator unit is closed to prevent steam backflow into the back pressure generator unit.

[0006] Preferably, the process of constructing the electrothermal coupling objective function includes: A power measuring device is installed at the outlet of the thermal power unit to collect the power generation power of the thermal power unit. Obtain the power output of the back-pressure generator set; A flow meter and a temperature sensor are installed on the water supply pipeline of the heating network in the grid-connected system, and a temperature sensor is installed on the return pipeline to measure the flow rate, supply temperature, and return temperature of the circulating water in the heating network; the temperature difference is determined based on the supply temperature and the return temperature; and the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid is calculated by the product relationship between the flow rate and the temperature difference. Based on the power generation of the thermal power unit, the power generation of the back-pressure generator unit, and the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid, an electrothermal coupling objective function is constructed.

[0007] Preferably, the electrothermal coupling objective function satisfies the following formula:

[0008] In the formula, Min(.) represents minimization. Let f(.) be the power consumption of the grid-connected system, and f(.) be the electrothermal coupling function. For the power generation capacity of thermal power units, This refers to the power output of the back-pressure generator set. This refers to the heat load demand of the grid-connected system formed after the back-pressure generator set is connected to the grid.

[0009] Preferably, after the back-pressure generator unit is connected to the grid, the distributed control system, based on the constructed electrothermal coupling objective function, allocates the power generation and heat supply of the thermal power unit and the back-pressure generator unit according to the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid, including: Collect the return water temperature and pressure of the grid-connected system and the heat load demand of the grid-connected system formed after the back pressure generator unit is connected to the grid. When the heat load demand is greater than the return water temperature and the cylinder cut-off condition of the back pressure generator set is met, the back pressure generator set is started, and the steam intake of the back pressure generator set is not lower than its minimum cooling flow rate. The objective function of electrothermal coupling is solved using gradient descent or particle swarm optimization, and the optimal power allocation value between the thermal power unit and the back-pressure generator unit is calculated. Based on the optimal power distribution value between the thermal power unit and the back-pressure generator unit, and satisfying the constraint of minimizing the total operating cost of the grid-connected system, a load command is sent to the distributed control system of the thermal power unit to adjust the valve opening of the thermal power unit, and a steam inlet regulating valve command is sent to the back-pressure generator unit to adjust the output of the back-pressure generator unit, thereby realizing the regulation of the power generation and heat supply of the thermal power unit and the back-pressure generator unit.

[0010] Preferably, the short-circuit current of the back-voltage generator set after grid connection satisfies the following formula:

[0011] In the formula, This refers to the short-circuit current after the back-voltage generator set is connected to the grid. The rated voltage of the grid-connected system. For the subtransient reactance of the back-voltage generator set, The short-circuit impedance of the power transformer. This refers to the impedance of the grid-connected system.

[0012] Preferably, the short-circuit current of the back-voltage generator set when it is not connected to the grid satisfies the following formula:

[0013] In the formula, This refers to the short-circuit current of the back-voltage generator set when it is not connected to the grid. The rated voltage of the grid-connected system. For the subtransient reactance of the back-voltage generator set, This refers to the impedance of the grid-connected system.

[0014] Preferably, the operating modes include: a normal mode and a cylinder-cutting mode; The step of switching the reverse power protection setting of the thermal power unit and the overfrequency protection setting of the back-voltage generator unit according to the acquired operating mode includes: In normal mode, the reverse power protection setting of the thermal power unit is switched to 3% to 5% of its rated power; in cylinder cut-off mode, the reverse power protection setting of the thermal power unit is switched to 6% to 8% of its rated power. In normal mode, the overfrequency protection setting of the back-pressure generator set is switched to 51.5Hz; in cylinder cut-off mode, the overfrequency protection setting of the back-pressure generator set is switched to: first-level overfrequency setting of 50.8Hz and second-level overfrequency setting of 51.2Hz.

[0015] Preferably, the distributed control system of the thermal power unit is connected to the logic control cabinet of the back-pressure generator unit; When the cylinder cutting mode confirmation signal and the low-pressure cylinder inlet valve fully closed signal are simultaneously satisfied, the back-pressure generator set is controlled to connect to the grid for power generation, including: The cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal output by the distributed control system of the thermal power unit are transmitted to the logic control cabinet of the back pressure generator unit. An AND gate logic is constructed in the logic control cabinet. When the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal both exceed a preset time threshold, a grid connection permission signal is generated. Based on the grid connection permission signal, the circuit breaker at the outlet of the back-pressure generator set is closed to control the back-pressure generator set to connect to the power system and achieve grid-connected power generation.

[0016] Preferably, the minimization of the total operating cost of the grid-connected system satisfies the following formula:

[0017] in, To minimize the total operating cost of the grid-connected system, The unit price of coal for the grid-connected system, This refers to the coal consumption of thermal power units. This refers to the coal consumption of the back-pressure generator set. This refers to the unit price of electricity. The total power generation of the grid-connected system. This is the unit price for hot-selling items. This refers to the total heat supply of the grid-connected system.

[0018] The beneficial effects of the technical solution provided in this application include at least the following: First, by stepping up the voltage of the back-pressure generator set through the power and heat transformer and then connecting it to the low-voltage side of the main transformer of the thermal power unit or the isolated phase closed bus, a standardized grid-connected system reconfiguration scheme is provided. At the same time, through quantitative calculation and comparative analysis of the short-circuit current before and after grid connection, the impact of the reconfiguration scheme on the system short-circuit capacity can be effectively evaluated, ensuring the selection and safe operation of electrical equipment and avoiding the risk of equipment damage caused by excessive short-circuit current.

[0019] Secondly, the grid connection is controlled by confirming the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal through AND gate logic and delay. This eliminates the risk of false grid connection caused by a single signal mis-triggering and ensures that the back-pressure generator set can be connected to the system only after the cylinder cutting mode is stable and the valve is reliably closed, thus improving the safety and reliability of grid connection. At the same time, when the cylinder cutting mode is exited or the low-pressure cylinder steam inlet valve is not fully closed, the back-pressure generator set is interlocked to trip and the steam inlet regulating valve is closed to prevent steam backflow into the back-pressure generator set, effectively protecting the equipment safety.

[0020] Third, by constructing an electrothermal coupling objective function and using optimization algorithms to solve for the optimal power allocation value between thermal power units and back-pressure generator units in real time based on the actual heat load demand of the system, the power generation and heat supply are coordinated and adjusted under the constraint of minimizing the total operating cost of the system, which significantly reduces the operating cost of the system and improves the economic efficiency of cogeneration.

[0021] Fourth, by adaptively switching the reverse power protection setting of the thermal power unit and the overfrequency protection setting of the back-pressure generator unit according to the normal mode and cylinder cut-off mode, the protection setting is matched with the current operating conditions. In particular, in cylinder cut-off mode, a two-stage overfrequency protection scheme is adopted, which prioritizes the fast closing of the steam inlet regulating valve to suppress the frequency rise, effectively avoiding protection maloperation or failure to operate due to mismatch of setting, and improving the safety and stability of the unit in cylinder cut-off operation mode.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the technical solutions provided in the embodiments of the present invention. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 The flowchart of a method for reconfiguring and grid-connected interlocking control of the power system of a cylinder-cutting back-pressure generator set provided in this application embodiment. Figure 1 ; Figure 2 The flowchart of a method for reconfiguring and grid-connected interlocking control of the power system of a cylinder-cutting back-pressure generator set provided in this application embodiment. Figure 2 ; Figure 3 A structural diagram of the grid connection structure for a method of reconfiguring and interlocking control of the power system of a cylinder-cutting back-pressure generator set provided in this application embodiment; Figure 4 This is a flowchart illustrating the construction of AND gate logic and time delay confirmation function in a method for reconfiguring and grid-connected interlocking control of a cylinder-cutting back-pressure generator set power system provided in an embodiment of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The following embodiments are used to illustrate this application, but are not intended to limit the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0026] It should be noted that the terms "first, second, and third" used in the embodiments of this application are merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first, second, and third" can be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0027] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this application pertain. It should also be understood that terms such as those defined in general dictionaries should be understood to have a meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0028] Example 1:

[0029] See Figure 1-2 As shown in the figure, this application provides a method for reconfiguring the power system and grid-connected interlocking control of a cylinder-cutting back-pressure generator set, wherein the power system includes a thermal power unit; The method includes the following steps: Step 1: After the output voltage of the back-voltage generator set G1 is stepped up by the power and heat transformer T1, it is connected to the low-voltage side of the main transformer of the thermal power unit or the isolated phase closed bus to obtain the short-circuit current of the back-voltage generator set G1 after it is connected to the grid. Step 2: Based on the short-circuit current of the back-pressure generator unit G1 after grid connection and the short-circuit current of the back-pressure generator unit G1 before grid connection, the distributed control system (DCS) of the thermal power unit acquires the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal of the thermal power unit; when the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal are simultaneously satisfied, the back-pressure generator unit G1 is controlled to connect to the grid for power generation; when the thermal power unit exits the cylinder cutting mode or the low-pressure cylinder steam inlet valve is not fully closed, the back-pressure generator unit G1 is interlocked to trip. Step 3: After the back-pressure generator set G1 is connected to the grid, the distributed control system allocates the power generation and heat supply of the thermal power unit and the back-pressure generator set based on the constructed electrothermal coupling objective function and the heat load demand of the grid-connected system formed after the back-pressure generator set G1 is connected to the grid; and switches the reverse power protection setting of the thermal power unit and the over-frequency protection setting of the back-pressure generator set G1 according to the acquired operating mode.

[0030] To illustrate step 1 of the present invention, a 300MW-class thermal power unit is used as an example. This thermal power unit adopts a cylinder cut-off operation mode. It is necessary to connect a back-pressure generator unit G1 with a rated power of 15MW under the low-pressure cylinder cut-off condition of the thermal power unit in order to improve the heating capacity and power generation flexibility.

[0031] Step 1.1: Grid Connection Structure Setup like Figure 3 As shown, the output voltage (6.3kV) of the back-voltage generator set G1 is stepped up to 20kV via the power transformer T1 and then connected to the low-voltage side isolated phase busbar of the main transformer of the thermal power unit via a T-connection. This T-connection is located between the low-voltage side circuit breaker of the main transformer of the thermal power unit and the incoming line of the plant service transformer, ensuring that the electrical energy output from the back-voltage generator set G1 can be directly fed into the low-voltage side busbar of the high-voltage plant transformer of the thermal power unit without the need for an additional dedicated grid connection bay, thus reducing engineering modification costs.

[0032] Step 1.2: Obtaining Short-Circuit Current Parameters Before the back-pressure generator unit G1 is connected to the grid, the distributed control system (DCS) of the thermal power unit reads the basic electrical parameters of the grid-connected system, including the rated voltage of the grid-connected system. =20KV, subtransient reactance of back-voltage generator set =0.12pu, short-circuit impedance of the power transformer =0.08pu, grid-connected system impedance =0.05pu (all converted to 20kV side).

[0033] Step 1.3, based on the short-circuit current formula after the back-voltage generator set G1 is connected to the grid:

[0034] In the formula, This refers to the short-circuit current after the back-voltage generator set is connected to the grid. The rated voltage of the grid-connected system. For the subtransient reactance of the back-voltage generator set, The short-circuit impedance of the power transformer. This refers to the impedance of the grid-connected system.

[0035] Calculated =80kA; that is, after the back-pressure generator set G1 is connected to the grid, when a three-phase short circuit occurs at the T-junction, the expected effective value of the short-circuit current is about 80kA. Step 1.4, based on the short-circuit current of the back-voltage generator set G1 that is not connected to the grid, the following formula is satisfied:

[0036] In the formula, This refers to the short-circuit current of the back-voltage generator set when it is not connected to the grid. The rated voltage of the grid-connected system. For the subtransient reactance of the back-voltage generator set, This refers to the impedance of the grid-connected system.

[0037] Calculated The short-circuit current is approximately 117.65kA. Comparison shows that after connecting the back-voltage generator set G1, due to the series voltage division effect of the power transformer impedance, the short-circuit current drops from 117.65kA to 80kA. This is beneficial to reducing the short-circuit dynamic and thermal stability requirements of the power system bus and switchgear, and verifies the improvement effect of the reconfiguration scheme on the short-circuit capacity of the power system.

[0038] Step 1.5: Project Implementation and Data Application The DCS system will calculate the results. and The data is stored in the database as the electrical parameter benchmark for confirming the cylinder cutting mode and determining the grid connection permission logic in subsequent step 2. Simultaneously, this short-circuit current data is also used to verify the breaking capacity of the circuit breaker at the T-contact (in this embodiment, a vacuum circuit breaker with a breaking current of 100kA is selected, meeting the 80kA requirement), ensuring the safety and reliability of the equipment selection.

[0039] In step 2, when the thermal power unit exits the cylinder cutting mode or the low-pressure cylinder steam inlet valve is not fully closed, the back-pressure generator unit G1 is interlocked and tripped, including the following steps: When the thermal power unit exits the cylinder cutting mode or the steam inlet valve of the low-pressure cylinder is not fully closed, the back pressure generator unit G1 is tripped and disconnected. At the same time, the steam inlet regulating valve of the back pressure generator unit G1 is closed to prevent steam backflow into the back pressure generator unit G1.

[0040] To illustrate step 2 of this invention, during a certain operation, the 300MW thermal power unit experienced fluctuations in heating parameters, causing the DCS to automatically exit the cylinder-cutting mode (the cylinder-cutting mode confirmation signal changed from "1" to "0"). The trip protection module of the back-pressure generator unit G1 detected that the tripping condition was met 68ms after the signal change, and immediately drove the circuit breaker of the back-pressure generator unit to open. The steam inlet regulating valve of the back-pressure generator unit closed completely within 1.4 seconds, and the fast-closing valve of the back-pressure generator unit closed within 0.28 seconds. DCS trend records showed that the output of the back-pressure generator unit G1 dropped from 13.2MW to 0 at the moment of tripping, and the turbine speed of the back-pressure generator unit safely stopped after coasting for approximately 10 minutes from 3000r / min, with no steam backflow throughout the process, and the equipment remained intact. This interlocking tripping logic has been tested multiple times and has a 100% reliability rate, effectively ensuring the safety of the thermal power unit and the back-pressure generator unit when they abnormally exit the cylinder-cutting mode.

[0041] Furthermore, the distributed control system of the thermal power unit is connected to the logic control cabinet of the back-pressure generator unit; Step 2, which states that when the cylinder cutting mode confirmation signal and the low-pressure cylinder inlet valve are fully closed simultaneously, control the back-pressure generator set G1 to connect to the grid for power generation, includes the following steps: Step 2.1: Transmit the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal output by the distributed control system of the thermal power unit to the logic control cabinet of the back pressure generator unit; Step 2.2: Construct an AND gate logic in the logic control cabinet. When the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal simultaneously exceed a preset time threshold, generate a grid connection permission signal. Step 2.3: According to the grid connection permission signal, the circuit breaker at the outlet of the back-pressure generator set G1 closes itself, thereby controlling the back-pressure generator set G1 to connect to the power system and achieve grid-connected power generation.

[0042] The specific implementation examples for the grid connection permission logic in steps 2.1 to 2.3 are as follows: The DCS system of the thermal power unit and the logic control cabinet of the back-pressure generator unit G1 use redundant hard-wiring to transmit key signals. The DCS system directly connects the cylinder cutting mode confirmation signal and the low-pressure cylinder inlet valve fully closed signal to the DI input terminal of the logic control cabinet of the back-pressure generator unit G1 via independent shielded control cables. Both signals are in passive dry contact form and are processed by an opto-isolation module and an RC filter circuit to effectively filter out electromagnetic interference in the field, ensuring that the steepness of the signal rise and fall edges is ≤5ms, avoiding false triggering caused by contact bounce.

[0043] The logic control cabinet of back-pressure generator set G1 internally incorporates AND gate logic and time-delay confirmation functions. For example... Figure 4 As shown, within the scanning cycle of the logic control cabinet, the hard-wired signal status I0.0 (cylinder cutting mode confirmation) and I0.1 (low-pressure cylinder inlet valve fully closed signal, i.e., valve fully closed signal) are read. When I0.0=1 and I0.1=1, the intermediate variable M1.0 is set to "1". Subsequently, the on-delay timer (TON, number T1) built into the logic control cabinet is used for delay confirmation with a preset time threshold PT=3s: this delay value is set to be greater than the DCS signal scanning cycle of 200ms, and less than the maximum safe time of 5s allowed for the turbine of the back-pressure generator set G1 to wait for grid connection under no-load conditions, ensuring that grid connection is allowed only after the valve is truly fully closed, avoiding excessive unit vibration due to unstable steam parameters at the moment of grid connection. When M1.0 remains "1" and the continuous conduction time reaches 3s, the output bit Q of T1 is set to "1" and expanded into two redundant grid connection permission signals: the first is a hard contact sent directly to the closing circuit of the output circuit breaker of the back-voltage generator set G1, and the second is transmitted back to the DCS operator station via the communication bus to display the "Grid connection permission generated" status indicator. If either signal I0.0 or I0.1 becomes "0" within 3s during the timing process, T1 is immediately reset to zero, and the grid connection permission signal is not generated to prevent erroneous grid connection due to momentary interference.

[0044] After the grid connection permission signal is generated, the signal sends the closing power to the closing coil of the vacuum circuit breaker at the outlet of the back-pressure generator set G1 via an intermediate relay. This drives the closing core to actuate, releasing the stored closing spring, causing the three-phase main contacts of the circuit breaker to close simultaneously within 35-45ms. However, the closing command is not issued directly. Instead, the back-pressure generator set G1 performs a closing condition verification, continuously monitoring the voltage difference, frequency difference, and phase angle difference between the voltage at the generator terminals of the back-pressure generator set G1 and the voltage at the T-contact bus. The closing command is only allowed when all three conditions are met simultaneously: voltage difference ≤ ±5% of rated voltage, frequency difference ≤ ±0.1Hz, and phase angle difference ≤ ±5°. If any condition is not met, the closing circuit is blocked, and a "synchronization condition not met" alarm is sent to the DCS. Grid connection is then attempted only after the operators adjust the speed or excitation of the back-pressure generator set G1. After the circuit breaker closes successfully, its built-in auxiliary contacts switch synchronously, transmitting the "circuit breaker closed position" signal back to the DCS, completing the entire process of grid connection and power generation of the back-pressure generator unit G1 to the power system. Actual field testing showed that the total time from the generation of the grid connection permit signal to the completion of circuit breaker closing was ≤200ms (including verification time ≤100ms and circuit breaker action time ≤45ms), and the instantaneous inrush current upon closing was 1.3 times the rated current, meeting the safe operation requirements of thermal power units and back-pressure generator units.

[0045] The process of constructing the electrothermal coupling objective function in step 3 includes the following steps: Step A: Install a power measuring device at the outlet of the thermal power unit, and collect the power generation power of the thermal power unit through the power measuring device; In this embodiment, the power measurement device reads the three-phase power values ​​with a sampling period of 100ms and calculates the real-time power generation of the thermal power unit. Meanwhile, the power signal is processed by mean filtering (the filtering window is 5 sampling points, i.e. 500ms) and then stored in the real-time database for subsequent use by the objective function.

[0046] Step B: Obtain the power output of the back-pressure generator set; A multi-functional smart power meter is installed on the 6.3kV outlet side of the back-voltage generator set G1. This smart power meter transmits the real-time power output of the back-voltage generator set G1 to its logic control cabinet via an RS-485 communication interface (Modbus RTU protocol, baud rate 9600bps, data refresh cycle 200ms). The logic control cabinet then transmits the power signal to the DCS system via a hard-wired analog output channel (4~20mA, accuracy ±0.2%). Simultaneously, to improve data reliability, the DCS system also directly reads the power register (address 40001) from the power meter. The two data streams are redundantly compared within the DCS. If the deviation is ≤2%, the data is considered valid; otherwise, a "power data anomaly" alarm is triggered, prompting operators to check the power meter or communication link.

[0047] Step C: Install flow meters and temperature sensors on the supply water pipes of the grid-connected system's heating network, and install temperature sensors on the return water pipes to measure the flow rate, supply water temperature, and return water temperature of the heating network circulating water; determine the temperature difference based on the supply water temperature and the return water temperature; calculate the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid by using the product relationship between the flow rate and the temperature difference. A smart electromagnetic flowmeter and a Class A platinum resistance temperature sensor are installed on the main water supply pipeline of the grid-connected heating system (design pressure 1.6MPa, temperature range 20~130℃). The same type of temperature sensor is installed on the main return water pipeline. All sensor signals are connected to the DCS (Distributed Control System). The flowmeter outputs a 4~20mA signal corresponding to a flow rate of 0~5000t / h, and the temperature sensor's signal is converted into a current signal via a temperature transmitter.

[0048] The DCS system performs heat load demand calculation every 200ms: First, the analog signals of flow rate, supply water temperature (unit: °C), and return water temperature are calibrated and converted to obtain engineering values. Then, the current heat load demand is calculated based on thermodynamic formulas. To reduce the impact of measurement noise, the supply and return water temperatures are subjected to first-order hysteresis filtering (filtering time constant τ=5s). The calculated heat load demand is compared with the design value. If the deviation exceeds ±20%, a "heat load measurement abnormality" alarm is triggered, prompting a check of the flow meter and temperature sensor for proper functioning.

[0049] Step D: Based on the power generation of the thermal power unit, the power generation of the back-pressure generator unit, and the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid, construct an electrothermal coupling objective function.

[0050] In step D, the electrothermal coupling objective function satisfies the following formula:

[0051] In the formula, Min(.) represents minimization. Let f(.) be the power consumption of the grid-connected system, and f(.) be the electrothermal coupling function. For the power generation capacity of thermal power units, This refers to the power output of the back-pressure generator set. This refers to the heat load demand of the grid-connected system formed after the back-pressure generator set is connected to the grid.

[0052] The engineering meaning of the electrothermal coupling objective function is: the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid. Under certain conditions, by optimizing the allocation of power generation capacity of thermal power units and back pressure generator set power generation This allows the grid-connected system to purchase power from the external power grid. Minimization. Based on the three real-time variables mentioned above, the DCS system calls the objective function once per calculation cycle (1 second), providing a unified mathematical description for the particle swarm optimization solution in step 3.3. Simultaneously, to facilitate monitoring by operators, a dedicated screen is provided on the DCS operator station to display the results in real time. , , The current value and its trend curve (time window is 24 hours) are displayed, and the position of the current operating point in the three-dimensional space of the objective function is marked to help operators intuitively understand the electrothermal coupling state of the system.

[0053] Step 3, which describes how, after the back-pressure generator unit G1 is connected to the grid, the distributed control system allocates the power generation and heat supply of the thermal power unit and the back-pressure generator unit based on the constructed electrothermal coupling objective function and the heat load demand of the grid-connected system formed after the back-pressure generator unit G1 is connected to the grid, including the following steps: Step A3.1: Collect the return water temperature and pressure of the grid-connected system and the heat load demand of the grid-connected system formed after the back pressure generator set G1 is connected to the grid; Step A3.2: When the heat load demand is greater than the return water temperature and the cylinder cut-off condition of the back pressure generator set G1 is met, start the back pressure generator set G1 and ensure that the steam intake of the back pressure generator set G1 is not lower than its minimum cooling flow rate. Step A3.3: Solve the electrothermal coupling objective function using gradient descent or particle swarm optimization, and calculate the optimal power allocation value between the thermal power unit and the back-pressure generator unit G1; Step A3.4: Based on the optimal power distribution value between the thermal power unit and the back-pressure generator unit G1, and satisfying the constraint of minimizing the total operating cost of the grid-connected system, a load command is sent to the distributed control system of the thermal power unit to adjust the valve opening of the thermal power unit, and a steam inlet regulating valve command is sent to the back-pressure generator unit to adjust the output of the back-pressure generator unit G1, thereby realizing the adjustment of the power generation and heat supply of the thermal power unit and the back-pressure generator unit G1.

[0054] Steps A3.1 to A3.4 detail the specific implementation examples of power distribution and heating regulation. The DCS system collects three parameters in real time at a 200ms cycle: return water temperature, return water pressure, and heat load demand. After median filtering, these parameters are stored in the real-time database. When the current heat load demand is detected to be greater than the basic heating threshold corresponding to the return water temperature, and the thermal power unit is already in cylinder cut-off mode, the DCS system sends a start command to the logic control cabinet of the back-pressure generator unit G1, executing a start sequence including preheating valve, speed increase, and pre-grid connection checks. Throughout the start-up process, the minimum opening limit logic of the steam inlet regulating valve (lower limit 12% opening) ensures that the steam inlet of the back-pressure generator unit G1 is not less than 12% of the rated steam inlet (approximately 8t / h), preventing damage to the last stage blades of the low-pressure cylinder due to overheating caused by air friction. After the back-pressure generator unit G1 is stably connected to the grid, the DCS system calls the built-in particle swarm optimization (PSO) algorithm to solve the electrothermal coupling objective function in real time. The algorithm parameters are set to a particle swarm size of 50, a maximum of 200 iterations, an inertia weight of 0.7, and a learning factor of 1.5. The search space includes a power range of 120~300MW for thermal power units and a power range of 3~15MW for back-pressure generator units. The optimization calculation is performed every 60 seconds, and converges to the optimal solution after an average of 45 iterations, with a single solution taking ≤2 seconds. Based on the optimal power allocation value obtained from the optimization calculation, the DCS sends load commands (with a change rate limited to 6MW / min) to the thermal power unit coordinated control system and opening commands (with a regulation rate limited to 5% / s) to the intelligent positioner of the steam inlet regulating valve of the back-pressure generator unit G1 through a 4~20mA analog output channel, enabling the thermal power unit to track to the optimal power value within 3 minutes and the back-pressure generator unit G1 within 90 seconds, respectively. Meanwhile, the DCS system verifies the total operating cost constraint in real time: the instruction is only issued when the total cost of the current round is lower than the previous round's allocation scheme. Field measurement data shows that when the total grid dispatch load instruction is 210MW and the heat load demand is 280GJ / h, the PSO calculates the optimal allocation as 198MW of thermal power units and 12MW of back-pressure generator units. After execution, the system's heat supply fully meets the demand, and the total operating cost is reduced by approximately 4.2% compared to before optimization, verifying the effectiveness and economy of this power allocation strategy.

[0055] In step A3.4, minimizing the total operating cost of the grid-connected system satisfies the following formula:

[0056] in, To minimize the total operating cost of the grid-connected system, The unit price of coal for the grid-connected system, This refers to the coal consumption of thermal power units. This refers to the coal consumption of the back-pressure generator set. This refers to the unit price of electricity. The total power generation of the grid-connected system. This is the unit price for hot-selling items. This refers to the total heat supply of the grid-connected system.

[0057] Furthermore, the operating modes include: normal mode and cylinder cutting mode; Step 3, which involves switching the reverse power protection setting of the thermal power unit and the overfrequency protection setting of the back-pressure generator unit G1 based on the acquired operating mode, includes the following steps: Step B3.1: In normal mode, switch the reverse power protection setting of the thermal power unit to 3%~5% of its rated power; in cylinder cut-off mode, switch the reverse power protection setting of the thermal power unit to 6%~8% of its rated power. Step B3.2: In normal mode, switch the overfrequency protection setting of the back-pressure generator set to 51.5Hz; in cylinder cut-off mode, switch the overfrequency protection setting of the back-pressure generator set to: first-level overfrequency setting of 50.8Hz and second-level overfrequency setting of 51.2Hz.

[0058] Steps B3.1~B3.2: Specific Implementation Examples of Protection Setting Switching: The Distributed Control System (DCS) records the operating mode of the thermal power unit in real time through its internal status word register and simultaneously sends this status word to both the thermal power unit protection device and the back-pressure generator unit G1 protection device, achieving adaptive switching of protection settings. In normal mode, the DCS output node remains open, and the thermal power unit protection device calls the first setting zone. The reverse power protection action setting is set to 4% of the rated power of the thermal power unit (e.g., 12MW for a 300MW thermal power unit), with an action delay of 60s. This takes into account the short-term reverse power conditions that may occur in the thermal power unit under normal operating conditions, avoiding maloperation of the protection. In cylinder-cutting mode, the DCS output node closes, and the thermal power unit protection device switches to the second setting zone. The reverse power protection action setting is set to 7% of the rated power of the thermal power unit (e.g., 21MW), with an action delay of 30s. The reason for increasing the setpoint is that in cylinder tripping mode, the low-pressure cylinder inlet valves are fully closed, increasing the air-blowing friction loss of the turbine's last-stage blades. When the boiler is extinguished or the main steam valve is suddenly closed, the active power absorbed by the thermal power unit from the grid is greater than in conventional mode (measured to be 15-20MW). If the conventional 4% setpoint is still used, it will lead to frequent protection actions. Increasing the setpoint to 7% and shortening the delay to 30 seconds prevents false tripping during normal cylinder tripping operation and allows for rapid disconnection of the thermal power unit in the event of a real fault. After the setpoint switch, the thermal power unit protection device sends the verification code of the currently activated setpoint area back to the DCS, and the operator station simultaneously displays the switched protection setpoint parameters for operator confirmation.

[0059] The back-voltage generator set G1 protection device is equipped with two sets of over-frequency protection setting schemes, and the setting range is selected through the switching signal output from the logic control cabinet of the back-voltage generator set G1. In normal mode, when the back-voltage generator set G1 is used as a backup power source or is not connected to the grid, the protection device adopts single-stage over-frequency protection, with the action setting set at 51.5Hz and the action delay of 0.5s, to prevent the back-voltage generator set G1 from overspeeding when the grid frequency rises abnormally. In cylinder cut-off mode, when the thermal power unit exits cylinder cut-off mode, the heat load drops sharply. The back-pressure generator unit G1 may experience a sudden increase in speed due to a sudden increase in steam intake. Therefore, the protection device switches to a two-stage over-frequency protection scheme: the first-stage over-frequency setting is 50.8Hz with an action delay of 0.2s, triggering a fast-closing command for the steam intake regulating valve of the back-pressure generator unit G1 to suppress the frequency from continuing to rise. If the frequency falls back to below 50.5Hz, the fast-closing command is automatically released; the second-stage over-frequency setting is 51.2Hz with an action delay of 0.1s, directly triggering the tripping of the circuit breaker at the output of the back-pressure generator unit G1 and the emergency closure of the fast-closing valve, realizing the disconnection protection between the back-pressure generator unit G1 and the power grid. Verified by on-site frequency disturbance test, when the grid frequency rises to 51.0Hz in cylinder cut-off mode, the first-level overfrequency protection will quickly close the G1 steam inlet regulating valve of the back pressure generator set within 0.2s. The frequency rise trend will be immediately suppressed and drop back to 50.6Hz, avoiding unplanned shutdown caused by the second-level overfrequency protection. The reliability and response speed of the protection setting switching meet the design requirements.

[0060] This embodiment fully illustrates the implementation process of a method for reconfiguring and coordinating the connection of a back-pressure generator unit to the plant power system based on cylinder-cutting modification. Regarding system reconfiguration, the back-pressure generator unit is connected to the low-voltage side isolated phase busbar of the thermal power unit's main transformer via a power-thermal transformer after voltage boosting. The change in system short-circuit capacity before and after grid connection is quantitatively evaluated based on the short-circuit current calculation formula, verifying the beneficial effect of the reconfiguration scheme on reducing the short-circuit dynamic and thermal stability requirements of the busbar and switchgear. Regarding grid-connected interlocking control, a delayed confirmation mechanism combining AND gate logic is constructed through hard-wired signal transmission between the distributed control system (DCS) and the logic control cabinet. This ensures that the cylinder-cutting mode confirmation signal and the low-pressure cylinder inlet steam valve fully closed signal are simultaneously satisfied before grid connection permission is generated. After automatic quasi-synchronization verification, the back-pressure generator unit's G1 outlet circuit breaker is closed. When the thermal power unit exits the cylinder-cutting mode or the low-pressure cylinder inlet steam valve is not fully closed, the interlocking trip logic is triggered immediately, causing the back-pressure generator unit's G1 to disconnect and quickly close the inlet steam regulating valve to prevent steam backflow. In terms of electrothermal coupling optimization allocation, by installing power measurement devices and heating network temperature and flow sensors, real-time power generation and system heat load demand of thermal power units and back-pressure generator units are collected. An electrothermal coupling objective function is constructed with the goal of minimizing external power purchase, and an optimization algorithm is used to solve for the optimal power allocation value between thermal power units and back-pressure generator units in real time. Under the premise of minimizing the total system operating cost constraint, load commands and steam inlet regulating valve commands are sent to thermal power units and back-pressure generator units respectively to achieve coordinated regulation of power generation and heat supply. In terms of adaptive switching of protection settings, the reverse power protection settings of thermal power units and the overfrequency protection settings of back-pressure generator units are automatically switched according to the conventional mode and cylinder cut-off mode. In the cylinder cut-off mode, a two-stage overfrequency protection scheme is adopted, which prioritizes triggering the fast closing of the steam inlet regulating valve to suppress the frequency rise and avoid unplanned shutdowns. The entire embodiment effectively improves heating capacity, reduces operating costs, and ensures equipment operation safety through the synergistic effect of system reconstruction, interlocking logic, electrothermal coupling optimization, and adaptive switching of protection settings.

[0061] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above-described processes do not imply a sequential 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 this application. The sequence numbers of the above-described embodiments are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0062] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0063] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0064] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units. They may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of the embodiments of this application, depending on actual needs.

[0065] In addition, each functional unit in the various embodiments of this application can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0066] Alternatively, if the integrated units described above are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this application, or the parts that contribute to related technologies, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause the device automatic test line to execute all or part of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, ROMs, magnetic disks, or optical disks.

[0067] The methods disclosed in the several method embodiments provided in this application can be arbitrarily combined without conflict to obtain new method embodiments.

[0068] The features disclosed in the several method or device embodiments provided in this application can be arbitrarily combined without conflict to obtain new method or device embodiments.

[0069] The above description is merely an embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for reconfiguration and grid-connected interlocking control of the power system of a cylinder-cutting back-pressure generator set, characterized in that, The power system includes thermal power units; The method includes: The output voltage of the back-pressure generator set (G1) is stepped up by the power and heat transformer (T1) and then connected to the low-voltage side of the main transformer of the thermal power unit or the isolated phase closed bus to obtain the short-circuit current of the back-pressure generator set (G1) after grid connection. Based on the short-circuit current after the back-pressure generator unit (G1) is connected to the grid and the short-circuit current when the back-pressure generator unit (G1) is not connected to the grid, the distributed control system (DCS) of the thermal power unit acquires the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal of the thermal power unit; when the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal are simultaneously satisfied, the back-pressure generator unit (G1) is controlled to connect to the grid for power generation; when the thermal power unit exits the cylinder cutting mode or the low-pressure cylinder steam inlet valve is not fully closed, the back-pressure generator unit (G1) is interlocked to trip. After the back-pressure generator set (G1) is connected to the grid, the distributed control system allocates the power generation and heat supply of the thermal power unit and the back-pressure generator set based on the constructed electrothermal coupling objective function and the heat load demand of the grid-connected system formed after the back-pressure generator set (G1) is connected to the grid; and switches the reverse power protection setting of the thermal power unit and the over-frequency protection setting of the back-pressure generator set (G1) according to the acquired operating mode.

2. The method according to claim 1, characterized in that, The interlock tripping of the back-pressure generator unit (G1) when the thermal power unit exits the cylinder cutting mode or the low-pressure cylinder steam inlet valve is not fully closed includes: When the thermal power unit exits the cylinder cutting mode or the steam inlet valve of the low-pressure cylinder is not fully closed, the back pressure generator unit (G1) is tripped and disconnected, and the steam inlet regulating valve of the back pressure generator unit (G1) is closed to prevent steam backflow into the back pressure generator unit (G1).

3. The method according to claim 1, characterized in that, The process of constructing the electrothermal coupling objective function includes: A power measuring device is installed at the outlet of the thermal power unit to collect the power generation power of the thermal power unit. Obtain the power output of the back-pressure generator set; A flow meter and a temperature sensor are installed on the water supply pipeline of the heating network in the grid-connected system, and a temperature sensor is installed on the return pipeline to measure the flow rate, supply temperature, and return temperature of the circulating water in the heating network; the temperature difference is determined based on the supply temperature and the return temperature; and the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid is calculated by the product relationship between the flow rate and the temperature difference. Based on the power generation of the thermal power unit, the power generation of the back-pressure generator unit, and the heat load demand of the grid-connected system formed after the back-pressure generator unit is connected to the grid, an electrothermal coupling objective function is constructed.

4. The method according to claim 3, characterized in that, The objective function for electrothermal coupling satisfies the following formula: In the formula, Min(.) represents minimization. Let f(.) be the power consumption of the grid-connected system, and f(.) be the electrothermal coupling function. For the power generation capacity of thermal power units, This refers to the power output of the back-pressure generator set. This refers to the heat load demand of the grid-connected system formed after the back-pressure generator set is connected to the grid.

5. The method according to claim 1, characterized in that, After the back-pressure generator unit (G1) is connected to the grid, the distributed control system, based on the constructed electrothermal coupling objective function, allocates the power generation and heat supply of the thermal power unit and the back-pressure generator unit according to the heat load demand of the grid-connected system formed after the back-pressure generator unit (G1) is connected to the grid, including: Collect the return water temperature and pressure of the grid-connected system and the heat load demand of the grid-connected system formed after the back pressure generator set (G1) is connected to the grid; When the heat load demand is greater than the return water temperature and the cylinder cut-off condition of the back pressure generator set (G1) is met, the back pressure generator set (G1) is started, and the steam intake of the back pressure generator set (G1) is not lower than its minimum cooling flow rate. The objective function of electrothermal coupling is solved using gradient descent or particle swarm optimization, and the optimal power allocation value between the thermal power unit and the back-pressure generator unit (G1) is calculated. Based on the optimal power distribution value between the thermal power unit and the back-pressure generator unit (G1), and satisfying the constraint of minimizing the total operating cost of the grid-connected system, a load command is sent to the distributed control system of the thermal power unit to adjust the valve opening of the thermal power unit, and a steam inlet regulating valve command is sent to the back-pressure generator unit to adjust the output of the back-pressure generator unit (G1), thereby realizing the regulation of the power generation and heat supply of the thermal power unit and the back-pressure generator unit (G1).

6. The method according to claim 1, characterized in that, The short-circuit current of the back-pressure generator set (G1) after grid connection satisfies the following formula: In the formula, This refers to the short-circuit current after the back-voltage generator set is connected to the grid. The rated voltage of the grid-connected system. For the subtransient reactance of the back-voltage generator set, The short-circuit impedance of the power transformer. This refers to the impedance of the grid-connected system.

7. The method according to claim 1, characterized in that, The short-circuit current of the back-voltage generator set (G1) when it is not connected to the grid satisfies the following formula: In the formula, This refers to the short-circuit current of the back-voltage generator set when it is not connected to the grid. The rated voltage of the grid-connected system. For the subtransient reactance of the back-voltage generator set, This refers to the impedance of the grid-connected system.

8. The method according to claim 1, characterized in that, The operating modes include: normal mode and cylinder cutting mode; The step of switching the reverse power protection setting of the thermal power unit and the overfrequency protection setting of the back-pressure generator unit (G1) according to the acquired operating mode includes: In normal mode, the reverse power protection setting of the thermal power unit is switched to 3% to 5% of its rated power; in cylinder cut-off mode, the reverse power protection setting of the thermal power unit is switched to 6% to 8% of its rated power. In normal mode, the overfrequency protection setting of the back-pressure generator set is switched to 51.5Hz; in cylinder cut-off mode, the overfrequency protection setting of the back-pressure generator set is switched to: first-level overfrequency setting of 50.8Hz and second-level overfrequency setting of 51.2Hz.

9. The method according to claim 1, characterized in that, The distributed control system of the thermal power unit is connected to the logic control cabinet of the back-pressure generator unit. When the cylinder cutting mode confirmation signal and the low-pressure cylinder inlet valve fully closed signal are simultaneously satisfied, the back-pressure generator set (G1) is controlled to connect to the grid for power generation, including: The cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal output by the distributed control system of the thermal power unit are transmitted to the logic control cabinet of the back pressure generator unit. An AND gate logic is constructed in the logic control cabinet. When the cylinder cutting mode confirmation signal and the low-pressure cylinder steam inlet valve fully closed signal both exceed a preset time threshold, a grid connection permission signal is generated. According to the grid connection permission signal, the circuit breaker at the outlet of the back-pressure generator set (G1) closes itself, thereby controlling the back-pressure generator set (G1) to connect to the power system and achieve grid-connected power generation.

10. The method according to claim 5, characterized in that, The minimum total operating cost of the grid-connected system satisfies the following formula: in, To minimize the total operating cost of the grid-connected system, The unit price of coal for the grid-connected system, This refers to the coal consumption of thermal power units. This refers to the coal consumption of the back-pressure generator set. This refers to the unit price of electricity. The total power generation of the grid-connected system. This is the unit price for hot-selling items. This refers to the total heat supply of the grid-connected system.

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