Nuclear power unit coupling steam supply method and system based on thermal load change

Abstract

The invention discloses a nuclear power unit coupling steam supply method and system based on thermal load changes. The problems that in the prior art, the utilization rate of residual pressure steam of a nuclear power unit is not high, and system corresponding delay and low operation efficiency are caused by heat supply load changes are solved. The method comprises the steps that in the heating season, a valve is controlled to make steam enter a residual pressure steam turbine, the heating heat load of the current period time step is calculated, and the valve opening degree is controlled till the steam flow reaches the heating heat load; the excess pressure steam turbine is connected with a motor through an automatic clutch, and the motor is controlled to drive or generate electricity according to the acting condition of the excess pressure steam turbine; and establishing a motor control optimization model, calculating an optimal control sequence in a period, and controlling motor operation. Heating steam and industrial steam are supplied while exhaust of the high-pressure cylinder of the nuclear power unit is achieved, the motor is driven by the pressure difference of the heating steam to do work on the steam compressor, abundant pressure energy is converted into electric energy through power generation of the motor, and the utilization rate of the heating steam is further increased.

Description

Technical Field

[0001] This invention relates to the field of nuclear power waste heat utilization technology, and in particular to a method and system for coupled steam supply to nuclear power units based on changes in heat load. Background Technology

[0002] Nuclear energy has been successfully applied in power generation due to its low-carbon, clean, safe, and efficient characteristics. From the perspective of comprehensive utilization, nuclear energy also has enormous potential in my country's centralized heating sector. Compared to traditional centralized heating methods such as coal-fired heating, nuclear heating is low-cost, green, low-carbon, and highly effective, effectively alleviating the pressure on traditional coal-fired heating.

[0003] Cogeneration (CHP) schemes for thermal power units are already mature. Compared to thermal power units, nuclear power units have lower steam parameters, with the main steam being saturated steam. Furthermore, nuclear power units generally do not have intermediate-pressure cylinders; the steam extraction port is typically the high-pressure cylinder exhaust port. The humidity of the high-pressure cylinder exhaust steam from a nuclear power unit is approximately 12%. Industrial steam demand requires a certain degree of superheat; excessively high steam humidity cannot meet the requirements for supplying industrial steam. The high-pressure cylinder exhaust pressure of a nuclear power unit is approximately 0.98 MPa, while the required pressure for heating steam is 0.3-0.4 MPa, and the required pressure for industrial steam is 1.2-2.0 MPa. For heating steam, the high-pressure cylinder exhaust pressure is too high, resulting in unutilized pressure energy. For industrial steam, the high-pressure cylinder exhaust pressure is too low. Additionally, because nuclear power plants are located in restricted development zones, the distance for supplying industrial steam from nuclear power plants is generally long, requiring even higher pressure for the steam leaving the plant. Currently, some systems utilize steam compressors to pressurize steam, driven by steam turbines. These turbines use excess steam for power generation, thus achieving excess steam recovery and utilization. However, when the amount of excess steam is large, full recovery and utilization are still impossible, resulting in low efficiency. Furthermore, for heating steam, the heating load fluctuates constantly due to temperature changes during the heating season. The system cannot adjust the heating load in a timely manner according to these temperature changes, leading to low system efficiency. For example, patent application number 202411104203.5, entitled "Comprehensive Utilization System of Waste Heat Steam in Nuclear Power Plants," discloses a steam compressor connected to a turbine drive system to provide driving force for the compressor. The turbine is connected to a first steam supply branch. This patent utilizes waste heat steam to drive the turbine and provide driving force for the steam compressor, achieving resource recovery and utilization. However, it also suffers from the aforementioned problems: when there is a large amount of waste heat steam, full recovery and utilization are impossible, resulting in low efficiency. Summary of the Invention

[0004] The present invention mainly addresses the problems of low utilization rate of residual steam in nuclear power units, system delay caused by changes in heating load, and inefficient operation in the existing technology, and provides a method and system for coupled steam supply to nuclear power units based on changes in heating load.

[0005] The above-mentioned technical problems of the present invention are mainly solved by the following technical solution: a nuclear power unit coupled steam supply method based on heat load variation, the system including a residual pressure steam turbine, a steam compressor connected to a motor, the residual pressure steam turbine being connected to the motor via an automatic clutch, the method including: Get heating status; During the heating season, control the valve to allow steam to enter the residual pressure steam turbine, calculate the heating load corresponding to the ambient temperature at the current cycle time step to reach the required heating flow rate, and control the valve opening until the steam flow rate reaches the heating load. The residual pressure steam turbine and the motor are connected by an automatic clutch, and the motor drive or generator is controlled according to the work done by the residual pressure steam turbine. Predict the turbine power at each time step within the current cycle, establish a motor control optimization model, calculate the optimal control sequence within the cycle, and control the motor operation. During the non-heating season, the connection between the residual pressure steam turbine and the motor is disconnected by an automatic clutch, and the motor drives the steam compressor.

[0006] This invention enables the simultaneous supply of heating steam and industrial steam from the exhaust gas of a nuclear power unit's high-pressure cylinder, meeting steam supply parameter requirements and achieving cascaded energy utilization. It adds a connection between the residual pressure steam turbine and the steam compressor motor, utilizing the pressure difference of the heating steam to drive the motor to perform work on the steam compressor, and converting the excess pressure energy into electrical energy through the motor, further improving the utilization rate of heating steam.

[0007] As a preferred approach, calculating the heating load includes: Get the ambient temperature at the current time step and set the indoor temperature; The temperature difference between indoor temperature and ambient temperature is the temperature difference value. The sum of the product of the temperature difference value and the comprehensive heat transfer coefficient and the minimum heating load is the heating load at the current ambient temperature.

[0008] In this scheme, both the overall heat transfer coefficient and the minimum heating load are related to the current ambient temperature. Obtaining the overall heat transfer coefficient and minimum heating load involves fitting functions for the overall heat transfer coefficient and the minimum heating load under different ambient temperatures based on historical operating data. The overall heat transfer coefficient and minimum heating load at the current ambient temperature are then calculated using these two functions. Finally, the heating load is calculated based on the overall heat transfer coefficient, minimum heating load, ambient temperature, and indoor temperature.

[0009] As a preferred option, controlling the valves to allow steam to enter the residual pressure steam turbine includes: Slowly open the inlet valve of the residual pressure turbine until the turbine speed reaches the rated speed.

[0010] As a preferred option, the required work of the steam compressor is set, and the work of the current residual pressure steam turbine is obtained; Determine whether the work done by the residual pressure steam turbine is greater than the work required by the steam compressor. If so, the motor switches to generator mode to convert the excess work into electrical energy. If not, the motor switches to drive mode to convert electrical energy into work to drive the steam compressor.

[0011] This solution determines whether the motor operates in drive mode or generator mode based on the work done on both sides of the motor. The steam compressor increases the steam pressure to the pressure required by the industrial user. After being heated by the electric heater, the steam is supplied to the industrial user through heating pipes. The amount of steam required by the industrial user remains essentially constant, meaning the amount of work done by the steam compressor also remains essentially constant. During the heating season, the amount of heating steam varies with the ambient temperature. The lower the ambient temperature, the greater the amount of heating steam required; the higher the ambient temperature, the less heating steam required. The amount of heating steam affects the amount of work done by the residual pressure steam turbine. When the work done by the residual pressure steam turbine exceeds the work required by the steam compressor, the motor switches to generator mode, converting the excess work into electrical energy, which is then fed into the power plant's auxiliary power system via a four-quadrant frequency converter. When the work done by the residual pressure steam turbine is not greater than the work required by the steam compressor, the motor switches to drive mode, converting electrical energy into work to drive the steam compressor, thus stabilizing the steam pressure at the compressor outlet.

[0012] As a preferred approach, turbine power prediction acquisition includes: The heating steam flow rate is obtained by dividing the heating load by the difference between the heating steam enthalpy and the heating return water enthalpy. The predicted power of the turbine is obtained by multiplying the turbine flow rate, turbine efficiency, and enthalpy drop of steam at the turbine inlet and outlet, where the heating steam flow rate is equal to the turbine flow rate.

[0013] In this scheme, the heating steam flow rate is obtained based on the ratio of the heating load to the difference between the heating steam enthalpy and the heating return water enthalpy. The residual pressure steam turbine is connected in series with the heat exchanger, and the turbine flow rate is equal to the heating steam flow rate. The predicted turbine power is calculated based on the turbine flow rate, the inlet and outlet parameters of the residual pressure steam turbine, and the turbine efficiency.

[0014] As a preferred approach, a motor control optimization model is established, including: Construct the objective function and constraints; A control value function is constructed based on the difference between the DC bus voltage, the motor speed and the set value, the motor power, and the rate of change of motor torque. Based on the power balance and torque balance relationships, we construct equations relating motor power to DC bus voltage and electromagnetic torque to motor speed. Substituting the relational expression into the control value function yields the objective function.

[0015] When constructing the objective function, the period, time step, control time domain, and weighting coefficients are set. Specifically, the control value function is the sum of the weighted squares of the differences between the DC bus voltage and the setpoint at each time step of the period, the differences between the motor speed and the setpoint, the motor power, and the rate of change of motor torque. The setpoints are the corresponding DC bus voltage setpoint and motor speed setpoint.

[0016] The specific formula for the relationship between motor power and DC bus voltage is as follows: the product of the derivative of DC bus voltage with respect to time and DC bus capacitance is equal to the ratio of motor power plus steam compressor power minus turbine predicted power minus converter power loss to DC bus voltage.

[0017] The specific formula for the relationship between electromagnetic torque and motor speed is that the product of the derivative of motor speed with respect to time and the motor's moment of inertia is equal to the difference between the turbine torque and the torque of the steam compressor, the motor, and the friction torque.

[0018] By substituting the equations relating motor power to DC bus voltage and electromagnetic torque to motor speed into the control value function for DC bus voltage and motor speed, we obtain the value function, i.e., the objective function, concerning motor power, electromagnetic torque, rate of change of motor power, and rate of change of motor torque.

[0019] As a preferred embodiment, the constraints include motor power limits, motor torque limits, DC bus voltage limits, motor speed limits, and motor power change rate limits.

[0020] As a preferred approach, the motor power control sequence and motor torque control sequence in the control time domain are obtained by minimizing the objective function and satisfying all constraints.

[0021] By minimizing the objective function while satisfying all constraints, a set of motor power control sequences and motor torque control sequences in the control time domain can be obtained. Typically, the control time domain is less than the period. These calculated motor power control sequences and motor torque control sequences are used as control commands. The motor power control sequence is sent to the grid-side converter to control its power interaction with the grid, and the motor torque control sequence is sent to the motor-side converter to control the motor's electromagnetic torque.

[0022] A nuclear power unit coupled steam supply system based on heat load variation includes a steam generator and a turbine high-pressure cylinder connected thereto. The first outlet of the turbine high-pressure cylinder is connected to a residual pressure steam turbine. The outlet of the residual pressure steam turbine is connected to a steam-water heat exchanger and then to the steam generator. The second outlet of the turbine high-pressure cylinder is connected to a steam compressor. The outlet of the steam compressor is connected to an industrial steam pipeline through a steam heater. The residual pressure steam turbine is connected to a motor through an automatic clutch. The motor drives the steam compressor. The motor is connected to the power grid through a four-quadrant frequency converter.

[0023] This invention achieves simultaneous supply of heating and industrial steam from nuclear power plant extraction steam through a coupled steam supply system. A steam generator produces saturated steam, and the high-pressure cylinder of the turbine performs work on the incoming saturated steam. The exhaust outlet of the high-pressure cylinder is divided into multiple paths, with the first path leading to a residual pressure steam turbine that drives a steam compressor. The steam utilizes its excess pressure energy in the residual pressure steam turbine, and after depressurization, it exchanges heat with the heating network water through a steam-water heat exchanger. The heating network water is used for urban heating. The residual pressure steam turbine is connected to a motor via an automatic clutch, utilizing the pressure energy in the turbine to drive the motor. The motor is connected to the steam compressor and to the power grid via a four-quadrant frequency converter. The four-quadrant frequency converter supports motor operation in four states: forward motoring, regenerative braking, reverse motoring, and reverse braking (i.e., the operating mechanical characteristic curve covers the four quadrants of the mathematical coordinate axis). The motor selects to generate or consume electricity based on the work done by the residual pressure steam turbine and the steam compressor, achieving bidirectional flow of electrical energy. Simultaneously, the motor can also disconnect from the residual pressure steam turbine via an automatic clutch, allowing it to drive the steam compressor independently. The second outlet of the turbine's high-pressure cylinder enters the steam compressor, increasing the steam pressure to the level required by industrial users. The steam then passes through an electric heater to reach the temperature required by heat users, and is finally connected to external heating pipelines to supply heat to users outside the plant.

[0024] As a preferred embodiment, the third outlet of the high-pressure cylinder of the steam turbine is connected to the low-pressure cylinder of the steam turbine, the low-pressure cylinder of the steam turbine is connected to the condenser, and the condenser is connected to the steam generator after passing through the condensate pump, the low-pressure heater, the deaerator, the feedwater pump, and the high-pressure heater in sequence.

[0025] The high-pressure cylinder of the steam turbine also includes a third outlet, which enters the low-pressure cylinder of the steam turbine to continue doing work. The steam coming out of the low-pressure cylinder of the steam turbine passes through the condenser, condensate pump, low-pressure heater, deaerator, feedwater pump, and high-pressure heater before returning to the steam generator.

[0026] Therefore, the advantages of the present invention are: 1. By increasing the work done by the residual pressure steam turbine, the steam pressure is reduced, and the residual steam pressure is utilized to simultaneously supply heating steam. By adding a steam compressor, driven by the residual pressure steam turbine, the residual steam pressure is utilized, and industrial steam is supplied at the same time.

[0027] 2. A detachable motor is installed between the residual pressure steam turbine and the steam compressor. The motor compares the work done on both sides to control the motor drive or generate electricity. The pressure difference of the heating steam is used to drive the motor to do work for the steam compressor, and the excess pressure energy is converted into electrical energy through the motor, which further improves the utilization rate of heating steam.

[0028] 3. Based on the changes in heating load, establish a motor control optimization model to obtain the optimal control parameters predicted within the cycle to control the motor operation. This enables the system to reduce the delayed response of the heating load under constantly changing heating load conditions, thereby ensuring stable and efficient system operation and flexible switching of the frequency converter between power generation and transmission states. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating one method of the present invention.

[0030] Figure 2 This is a schematic diagram of the structure of the system of the present invention.

[0031] 1-Steam generator, 2-Main steam valve, 3-High-pressure cylinder of steam turbine, 4-Low-pressure cylinder of steam turbine, 5-Generator, 6-Condenser, 7-Condensate pump, 8-Low-pressure heater, 9-Deaerator, 10-Feed water pump, 11-High-pressure heater, 12-Residual pressure steam turbine inlet valve, 13-Residual pressure steam turbine, 14-Automatic synchronous clutch, 15-Four-quadrant frequency converter, 16-Motor, 17-Steam compressor inlet valve, 18-Steam compressor, 19-Steam electric heater, 20-Steam-water heat exchanger. Detailed Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0033] Example 1: This embodiment presents a nuclear power unit coupled steam supply method based on heat load variation. The method is applied to a nuclear power unit coupled steam supply system, which includes a residual pressure steam turbine and a steam compressor connected to a motor. The residual pressure steam turbine is connected to the motor via an automatic clutch. Figure 1 As shown, the method includes the following steps: S1. Obtain heating status.

[0034] In this embodiment, the heating status is divided into heating season and non-heating season, and time is generally used to determine whether it is a heating season or not. The system obtains the current time to determine which heating status is currently in.

[0035] S2. During the heating season, control the valve to allow steam to enter the residual pressure steam turbine, calculate the heating load corresponding to the ambient temperature at the current cycle time step to reach the required heating flow rate, and control the valve opening until the steam flow rate reaches the heating load.

[0036] As a preferred embodiment, when it is determined that the current state is the heating season, the valve on the pipeline leading to the residual pressure steam turbine is slowly opened to allow steam in the high-pressure cylinder of the steam turbine to enter the residual pressure steam turbine until the residual pressure turbine speed reaches the rated speed.

[0037] Continue opening the valve until the steam flow reaches the heating load. The steam flow and heat load are converted using a related formula, and then compared after conversion to load. The heating load mentioned here refers to the heating load required to reach the desired heating flow at the ambient temperature corresponding to the current cycle time step. The system controls motor operation using periodic sampling data. Each cycle is divided into several time steps. The heating load is related to the ambient temperature and changes continuously over time. The heating load is calculated at each time step, and the valve is controlled to ensure the steam flow reaches the required heating load. At this point, the ambient temperature of the current time step needs to be obtained to calculate the heating load. Specifically, the temperature difference between the indoor and ambient temperatures is obtained. The product of the temperature difference and the overall heat transfer coefficient, plus the minimum heating load, yields the heating load at the current ambient temperature. The specific form of the heating load is expressed as follows: Heating load = Comprehensive heat transfer coefficient * (Indoor temperature - Ambient temperature) + Minimum heating load.

[0038] In this scheme, both the overall heat transfer coefficient and the minimum heating load (e.g., used to maintain the pipe network temperature) are related to the current ambient temperature. Obtaining the overall heat transfer coefficient and minimum heating load involves fitting functions for the overall heat transfer coefficient and the minimum heating load under different ambient temperatures based on historical operating data. The overall heat transfer coefficient and minimum heating load at the current ambient temperature are then calculated using these two functions. Finally, the heating load is calculated based on the overall heat transfer coefficient, minimum heating load, ambient temperature, and indoor temperature.

[0039] S3. The residual pressure steam turbine and the motor are connected by an automatic clutch, and the motor drive or generator is controlled according to the work done by the residual pressure steam turbine.

[0040] In a preferred embodiment, when it is determined that the current state is the heating season, the automatic clutch can be controlled to connect the residual pressure steam turbine and the motor, allowing the residual pressure steam turbine to drive the motor. In another implementation, the timing for the automatic clutch to connect the residual pressure steam turbine and the motor can be after a certain period following the determination that the heating season has begun, such as the time it takes for the valve to open until the steam flow reaches the required heating load at the current ambient temperature, or the time it takes for the residual pressure steam turbine to reach its rated speed. After connecting the residual pressure steam turbine and the steam compressor via the automatic clutch, the motor is controlled to drive or generate electricity by comparing the work done on both sides of the motor, i.e., the residual pressure steam turbine and the steam compressor. The specific process of determining whether to drive or generate electricity includes: Set the required work output of the steam compressor and obtain the current work output of the residual pressure steam turbine; Determine whether the work done by the residual pressure steam turbine is greater than the work required by the steam compressor. If so, the motor switches to generator mode to convert the excess work into electrical energy. If not, the motor switches to drive mode to convert electrical energy into work to drive the steam compressor.

[0041] The steam compressor increases the steam pressure to the level required by industrial users. After being heated by an electric heater, the steam is supplied to industrial users through heating pipes. The amount of steam required by industrial users remains relatively constant, meaning the amount of work done by the steam compressor also remains relatively constant. This work requirement can be determined by setting the appropriate parameters. During the heating season, the amount of heating steam supplied varies with the ambient temperature. Lower ambient temperatures require more heating steam, and higher ambient temperatures require less. The amount of heating steam supplied affects the amount of work done by the residual pressure steam turbine. When the work done by the residual pressure steam turbine exceeds the work required by the steam compressor, the motor switches to generator mode, converting the excess work into electrical energy, which is then fed into the power plant's auxiliary power system via a four-quadrant frequency converter. When the work done by the residual pressure steam turbine is not greater than the work required by the steam compressor, the motor switches to drive mode, converting electrical energy into work to drive the steam compressor, thus stabilizing the steam pressure at the compressor outlet.

[0042] S4. Predict the turbine power at each time step within the current cycle, establish a motor control optimization model, calculate the optimal control sequence within the cycle, and control the motor operation.

[0043] As a preferred embodiment, a motor control optimization model is established based on the predicted turbine power, where the predicted turbine power is related to the heating load at the current time step. The ambient temperature is determined based on the predicted time step; this ambient temperature can be determined by obtaining weather forecast information or by predicting based on historical data. After obtaining the ambient temperature corresponding to the predicted time step, the heating load corresponding to the predicted time step can be obtained according to the heating load calculation method described above.

[0044] As a preferred embodiment, turbine power prediction acquisition includes: The heating steam flow rate is calculated based on the relationship between heating load and heating steam flow rate. The calculation process is as follows: Divide the heating load by the difference between the heating steam enthalpy and the heating return water enthalpy to obtain the heating steam flow rate. The heating steam flow rate is expressed as follows: Heating steam flow rate = heating load / (heating steam enthalpy - heating return water enthalpy).

[0045] In this embodiment, the residual pressure steam turbine is connected in series with a heat exchanger. The turbine flow rate is equal to the heating steam flow rate. The turbine flow rate is obtained by calculating the heating steam flow rate. Further, the predicted turbine power is calculated based on the turbine flow rate, the inlet and outlet parameters of the residual pressure steam turbine, and the turbine efficiency. The predicted turbine power is calculated as follows: the predicted turbine power is obtained by multiplying the turbine flow rate, turbine efficiency, and the enthalpy drop of the steam at the turbine inlet and outlet. The specific form of the predicted turbine power is as follows: Turbine predicted power = turbine efficiency * turbine inlet and outlet * steam enthalpy drop.

[0046] Then, the turbine prediction power of each time step in the period is calculated using this method. In this embodiment, the period is divided into Np time steps as an example to obtain the turbine prediction power of the next Np time steps, which is expressed as: turbine prediction power (1), turbine prediction power (2), ..., turbine prediction power (Np).

[0047] As a preferred embodiment, a motor control optimization model is established, including: Construct the objective function and constraints; The objective function is constructed by using the difference between the DC bus voltage, the motor speed and the set value, the motor power and the rate of change of motor torque to form a control value function.

[0048] Specifically, the settings include the period, time step, control time domain, and weighting coefficients. The control value function is the sum of the weighted squares of the differences between the DC bus voltage and the setpoint at each time step of the period, the differences between the motor speed and the setpoint, the motor power, and the rate of change of motor torque. The setpoints are the corresponding DC bus voltage setpoint and motor speed setpoint.

[0049] Based on the power balance and torque balance relationships, we construct equations relating motor power to DC bus voltage and electromagnetic torque to motor speed.

[0050] The relationship between motor power and DC bus voltage is expressed as follows: the product of the derivative of DC bus voltage with respect to time and DC bus capacitance equals the ratio of motor power plus steam compressor power, minus turbine predicted power, minus converter power losses, to the DC bus voltage. The specific expression is as follows: DC bus capacitance * d DC bus voltage / dt = (motor power + steam compressor power - turbine predicted power - converter power loss) / DC bus voltage.

[0051] The relationship between electromagnetic torque and motor speed is expressed as follows: the product of the derivative of motor speed with respect to time and the motor's moment of inertia equals the difference between the turbine torque and the torques of the steam compressor, motor, and friction. The specific expression is as follows: Motor rotational inertia * d = motor speed / dt = turbine torque - steam compressor torque - motor torque - friction torque.

[0052] Substituting the relational expression into the control value function yields the objective function.

[0053] Based on the above-mentioned relationships between motor power and DC bus voltage and electromagnetic torque and motor speed, the corresponding relationships between motor power and DC bus voltage and electromagnetic torque and motor speed for each time step are obtained. Then, these relationships are substituted into the DC bus voltage and motor speed of the control value function to obtain the value function, i.e., the objective function, regarding motor power, electromagnetic torque, motor power change rate, and motor torque change rate.

[0054] The constraints include motor power limits, motor torque limits, DC bus voltage limits, motor speed limits, and motor power change rate limits.

[0055] Set the maximum and minimum motor power values, where the minimum motor power ≤ the maximum motor power.

[0056] Set the maximum and minimum values ​​of the electric torque, where the minimum motor torque ≤ the maximum motor torque.

[0057] Set the maximum and minimum values ​​of the DC bus voltage, where the minimum DC bus voltage ≤ the maximum DC bus voltage.

[0058] Set the maximum and minimum motor speeds, where the minimum motor speed ≤ the maximum motor speed.

[0059] Set the maximum and minimum values ​​for the motor power change rate, where the minimum motor power change rate ≤ the maximum motor power change rate.

[0060] A motor control optimization model is constructed based on the objective function and constraints.

[0061] As a preferred embodiment, calculating the optimal control sequence within the cycle to control the motor operation specifically includes: With the objective function minimization as the goal, and under all constraints, the motor power control sequence and motor torque control sequence in the control time domain [t, t+Np] are obtained within the period, i.e. the prediction time domain [t, t+Nc]. Typically, Nc is less than Np.

[0062] The calculated motor power control sequence and motor torque control sequence are used as control commands. The motor power control sequence is sent to the grid-side converter to control the power it interacts with the grid, and the motor torque control sequence is sent to the motor-side converter to control the electromagnetic torque of the motor.

[0063] S5. Proceed to the next cycle and repeat steps S1-S4.

[0064] S6. During the non-heating season, the connection between the residual pressure steam turbine and the motor is disconnected by an automatic clutch, and the motor drives the steam compressor.

[0065] During the non-heating season, when there is no demand for heating steam, the automatic clutch can be disengaged, and the steam compressor can be directly driven by the motor. During the non-heating season, the inlet valve of the residual pressure steam turbine is closed, while the inlet valve of the steam compressor is open. Exhaust steam from the high-pressure cylinder of the turbine enters the steam compressor, increasing the steam pressure. After being heated by the steam electric heater, the steam enters the external industrial steam pipeline. The automatic clutch then disconnects the residual pressure steam turbine from the motor, and the motor drives the steam compressor to perform its work.

[0066] The method in this embodiment has the following advantages: 1. By increasing the work done by the residual pressure steam turbine, the steam pressure is reduced, and the residual steam pressure is utilized to simultaneously supply heating steam. By adding a steam compressor, driven by the residual pressure steam turbine, the residual steam pressure is utilized, and industrial steam is supplied at the same time.

[0067] 2. A detachable motor is installed between the residual pressure steam turbine and the steam compressor. The motor compares the work done on both sides to control the motor drive or generate electricity. The pressure difference of the heating steam is used to drive the motor to do work for the steam compressor, and the excess pressure energy is converted into electrical energy through the motor, which further improves the utilization rate of heating steam.

[0068] 3. Based on the changes in heating load, establish a motor control optimization model to obtain the optimal control parameters predicted within the cycle to control the motor operation. This enables the system to reduce the delayed response of the heating load under constantly changing heating load conditions, thereby ensuring stable and efficient system operation and flexible switching of the frequency converter between power generation and transmission states.

[0069] Example 2: This embodiment describes a nuclear power unit coupled steam supply system based on heat load variation, used to implement the method in Embodiment 1, such as... Figure 2As shown, the system includes a steam generator 1 and a high-pressure turbine cylinder 3 connected to it. A main steam valve 2 is connected to the pipeline between the steam generator 1 and the high-pressure turbine cylinder 3. The exhaust of the high-pressure turbine cylinder 3 includes three paths. The first outlet of the high-pressure turbine cylinder 3 is connected to a residual pressure steam turbine 13. The outlet of the residual pressure steam turbine is connected to a steam-water heat exchanger 20, and then to the third path, which is connected to the steam generator 1. A residual pressure steam turbine inlet valve 12 is connected to the first outlet pipeline of the high-pressure turbine cylinder 3. The second outlet of the high-pressure turbine cylinder 3 is connected to a steam compressor 18. The outlet of the steam compressor is connected to an industrial steam pipeline via a steam heater 19. The residual pressure steam turbine 13 is connected to a motor 16 via an automatic clutch 14. The motor 16 drives the steam compressor 18. The motor is connected to the power plant's auxiliary power system via a four-quadrant frequency converter 15. A steam compressor inlet valve 17 is connected to the second outlet pipeline of the high-pressure turbine cylinder 3. The third outlet of the high-pressure cylinder 3 of the steam turbine is connected to the low-pressure cylinder 4 of the steam turbine. The generator 5 drives both the low-pressure and high-pressure cylinders of the steam turbine. The low-pressure cylinder 4 is connected to the condenser 6. The condenser 6 is connected to the steam generator after passing through the condensate pump 7, the low-pressure heater 8, the deaerator 9, the feedwater pump 10, and the high-pressure heater 11. The steam-water heat exchanger 20 is connected to the condenser 6.

[0070] This embodiment utilizes a nuclear power plant's coupled steam supply system to simultaneously supply heating and industrial steam from nuclear power plant extraction. Steam generator 1 produces saturated steam. The high-pressure cylinder 3 of the steam turbine performs work on the incoming saturated steam. The exhaust outlet of the high-pressure cylinder is divided into three paths. The first path leads to a residual pressure steam turbine, which drives a steam compressor. The steam, after passing through the residual pressure steam turbine, utilizes its excess pressure energy. After depressurization, it exchanges heat with the heating network water through a steam-water heat exchanger. The heating network water is used for urban heating. The residual pressure steam turbine is connected to a motor via an automatic clutch, utilizing the pressure energy in the steam turbine to drive the motor. The motor is connected to the steam compressor and to the power grid via a four-quadrant frequency converter. The four-quadrant frequency converter supports the motor in four states: forward motoring, regenerative braking, reverse motoring, and reverse braking (i.e., the operating mechanical characteristic curve covers the four quadrants of the mathematical coordinate axis). The motor selects to generate or consume electricity based on the work done by the residual pressure steam turbine and the steam compressor, achieving bidirectional flow of electrical energy. Simultaneously, the motor can also disconnect from the residual pressure steam turbine via an automatic clutch, allowing it to drive the steam compressor independently. The second outlet of the high-pressure cylinder of the steam turbine enters the steam compressor, increasing the steam pressure to the level required by industrial users. It then passes through an electric heater to reach the temperature required by heat users, and is subsequently connected to external heating pipelines to supply heat to users outside the plant. The third outlet of the high-pressure cylinder of the steam turbine enters the low-pressure cylinder to continue working. The steam exiting the low-pressure cylinder passes through the condenser, condensate pump, low-pressure heater, deaerator, feedwater pump, and high-pressure heater before returning to the steam generator.

[0071] During the heating season, the amount of heating steam required varies with ambient temperature; lower temperatures require more steam, and higher temperatures require less. The amount of heating steam also affects the work done by the steam pressure turbine, while the amount of industrial steam remains relatively constant. When the work done by the steam pressure turbine exceeds the work required by the steam compressor, the excess work is converted into electrical energy by a motor and fed into the power plant's auxiliary power system via a four-quadrant frequency converter. When the work done by the steam pressure turbine is less than the work required by the steam compressor, the electrical energy is converted back into work by the motor, thus stabilizing the steam pressure at the compressor outlet. During the heating season, the inlet valve 12 of the residual pressure steam turbine is opened, and the exhaust steam from the high-pressure cylinder 3 enters the residual pressure steam turbine 13 to perform work. The steam that has completed its work passes through the steam-water heat exchanger 20 to exchange heat with the heating network water. After heat exchange, the steam becomes water and enters the condenser 6. The inlet valve 17 of the steam compressor is opened, and the exhaust steam from the high-pressure cylinder 3 enters the steam compressor 18 to increase the steam pressure. Then, after being heated by the steam electric heater 19, it enters the external industrial steam pipeline. The automatic synchronization clutch 14 is engaged, and the motor 16 can drive or generate electricity depending on the work done on both sides.

[0072] During the non-heating season, when there is no demand for heating steam, the automatic synchronization clutch 14 is disconnected, and the steam compressor is directly driven by the motor 16. During the non-heating season, the residual pressure steam turbine inlet valve 12 is closed; the steam compressor inlet valve 17 is opened, and the exhaust steam from the high-pressure cylinder 3 of the steam turbine enters the steam compressor 18 to increase the steam pressure. After being heated by the steam electric heater 19, the steam enters the external industrial steam supply pipeline.

[0073] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0074] Although this document uses terms such as steam generator, residual pressure steam turbine, steam compressor, electric motor, steam electric heater, and high-pressure cylinder of steam turbine frequently, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention.

Claims

1. A method for coupled steam supply to a nuclear power unit based on changes in heat load, characterized in that, Includes the following steps: Get heating status; During the heating season, control the valve to allow steam to enter the residual pressure steam turbine, calculate the heating load corresponding to the ambient temperature at the current cycle time step to reach the required heating flow rate, and control the valve opening until the steam flow rate reaches the heating load. The residual pressure steam turbine and the motor are connected by an automatic clutch, and the motor drive or generator is controlled according to the work done by the residual pressure steam turbine. Predict the turbine power at each time step within the current cycle, establish a motor control optimization model, calculate the optimal control sequence within the cycle, and control the motor operation. During the non-heating season, the connection between the residual pressure steam turbine and the motor is disconnected by an automatic clutch, and the motor drives the steam compressor.

2. The nuclear power unit coupled steam supply method based on heat load variation according to claim 1, characterized in that, Calculating the heating load includes: Get the ambient temperature at the current time step and set the indoor temperature; The temperature difference between indoor temperature and ambient temperature is the temperature difference value. The sum of the product of the temperature difference value and the comprehensive heat transfer coefficient and the minimum heating load is the heating load at the current ambient temperature.

3. The nuclear power unit coupled steam supply method based on heat load variation according to claim 1, characterized in that, Controlling valves to allow steam to enter the residual pressure steam turbine includes: Slowly open the inlet valve of the residual pressure turbine until the turbine speed reaches the rated speed.

4. A method for coupled steam supply to a nuclear power unit based on changes in heat load, as described in claim 1, 2, or 3, characterized in that: Set the required work output of the steam compressor and obtain the current work output of the residual pressure steam turbine; Determine whether the work done by the residual pressure steam turbine is greater than the work required by the steam compressor. If so, the motor switches to generator mode to convert the excess work into electrical energy. If not, the motor switches to drive mode to convert electrical energy into work to drive the steam compressor.

5. A method for coupled steam supply to a nuclear power unit based on changes in heat load, as described in claim 1, 2, or 3, characterized in that... Turbine power prediction acquisition includes: The heating steam flow rate is obtained by dividing the heating load by the difference between the heating steam enthalpy and the heating return water enthalpy. The predicted power of the turbine is obtained by multiplying the turbine flow rate, turbine efficiency, and enthalpy drop of steam at the turbine inlet and outlet, where the heating steam flow rate is equal to the turbine flow rate.

6. A method for coupled steam supply to a nuclear power unit based on changes in heat load, as described in claim 5, is characterized in that... Establish a motor control optimization model, including: Construct the objective function and constraints; A control value function is constructed based on the difference between the DC bus voltage, the motor speed and the set value, the motor power, and the rate of change of motor torque. Based on the power balance and torque balance relationships, we construct equations relating motor power to DC bus voltage and electromagnetic torque to motor speed. Substituting the relational expression into the control value function yields the objective function.

7. A method for coupled steam supply to a nuclear power unit based on changes in heat load, as described in claim 6, characterized in that: The constraints include motor power limits, motor torque limits, DC bus voltage limits, motor speed limits, and motor power change rate limits.

8. A method for coupled steam supply to a nuclear power unit based on changes in heat load, as described in claim 7, characterized in that: With the objective function minimization as the goal and all constraints satisfied, the motor power control sequence and motor torque control sequence in the control time domain are obtained by solving.

9. A nuclear power unit coupled steam supply system based on heat load variation, implementing the method according to any one of claims 1-8, characterized in that: It includes a steam generator and a high-pressure cylinder of a steam turbine connected to it. The first outlet of the high-pressure cylinder of the steam turbine is connected to a residual pressure steam turbine. The outlet of the residual pressure steam turbine is connected to a steam-water heat exchanger and then to the steam generator. The second outlet of the high-pressure cylinder of the steam turbine is connected to a steam compressor. The outlet of the steam compressor is connected to an industrial steam pipeline through a steam heater. The residual pressure steam turbine is connected to a motor through an automatic clutch. The motor drives the steam compressor and is connected to the power grid through a four-quadrant frequency converter.

10. A nuclear power unit coupled steam supply system based on heat load variation according to claim 9, characterized in that: The third outlet of the high-pressure cylinder of the steam turbine is connected to the low-pressure cylinder of the steam turbine. The low-pressure cylinder of the steam turbine is connected to the condenser. The condenser is connected to the steam generator after passing through the condensate pump, the low-pressure heater, the deaerator, the feedwater pump, and the high-pressure heater.

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