A control method of an electric heating molten salt energy storage system

Abstract

This invention discloses a control method for an electrically heated molten salt energy storage system, belonging to the field of energy storage technology. The method includes: determining the percentage of the design power of the first and second stage heaters relative to the total design power using a comprehensive weighted method based on the per-unit value of the power plant's annual output data; calculating the design volume of the intermediate tank based on the flow rate and buffer time under the system's design operating conditions; formulating flow control strategies for the first and second stage heaters and input power allocation strategies: stabilizing the outlet temperature of the second stage heater using a proportional-integral-derivative controller, based on the outlet temperature of the first stage heater, the liquid level in the intermediate tank, and the safe flow rate of the first stage heater; and implementing the input power allocation strategy based on the matching relationship between the total system input power and the design power of the second stage heater, with the first stage heater absorbing all fluctuations in the system's input power and the second stage heater operating at its design power. This invention improves the system's adaptability in scenarios with high proportions of renewable energy fluctuations.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology, and specifically relates to a control method for an electrically heated molten salt energy storage system. Background Technology

[0002] With the continuous expansion of installed capacity of new energy power generation such as wind power and photovoltaics, their output exhibits strong intermittency and high random fluctuations, posing a severe challenge to grid frequency stability and power balance. Energy storage technology is considered a key support for smoothing out new energy fluctuations and improving the grid's absorption capacity. Molten salt energy storage, as a technology route that combines energy time shifting and thermoelectric decoupling potential, can convert fluctuating electrical energy into thermal energy for storage and regenerate it through a steam turbine when needed, making it one of the effective paths to achieve deep substitution of new energy sources.

[0003] However, the output of new energy sources is characterized by large and rapid fluctuations on a minute or even second basis. Existing electric heating energy storage systems have fundamental technical shortcomings in dealing with such fluctuating conditions: mainstream molten salt electric heating devices adopt a fixed-power tube structure, which has large thermal inertia and slow adjustment response, making it difficult to track the sharp rises and falls of wind and solar power in real time, resulting in continuous fluctuations in the molten salt outlet temperature; if forced to operate under different loads in pursuit of rapid response, it is easy to cause problems such as local overheating of the electric heating tube, uneven thermal stress of the molten salt, and even decomposition failure. This bottleneck directly restricts the adjustment capability and operational safety of molten salt energy storage systems in scenarios with a high proportion of new energy sources.

[0004] To address the aforementioned issues, Chinese patent application CN119617936A (An Array Molten Salt Electric Heating Energy Storage System) attempts to balance rapid power point tracking at the front end and precise temperature control at the back end by deploying electric heating units in sections before and after the buffer tank. However, this solution lacks a design basis for power allocation between the front and back ends and does not establish a specific control strategy to cope with continuous large fluctuations in operating conditions. Specifically, it does not clarify the matching relationship between power allocation between the front and back ends and the fluctuation characteristics of new energy sources, resulting in unreasonable power allocation under different fluctuation conditions. At the same time, it lacks a specific control strategy for continuous large fluctuations (such as a sudden increase of 50% or a sudden decrease of 30% in wind power output), causing the system to still have the risk of excessive temperature fluctuations and local overheating under extreme fluctuation conditions. This makes it unable to meet the actual needs of high-proportion new energy grid connection, and the system's adaptability and reliability in multiple scenarios are still insufficient.

[0005] In summary, the core bottleneck of existing electrically heated molten salt energy storage technology lies in its inability to simultaneously achieve the following three objectives under conditions of highly fluctuating power input: 1. Rapidly tracking fluctuations in renewable energy power; 2. Stably controlling the molten salt outlet temperature; and 3. Avoiding safety risks such as localized overheating of the electric heating element and molten salt decomposition. There are irreconcilable contradictions among these three objectives, necessitating new solutions at the control method level. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A control method for an electrically heated molten salt energy storage system includes:

[0008] The system parameters are designed, including: the design power of the first-stage heater. Design power of the second-stage heater The design volume V of the intermediate tank surge Design is carried out; per-unit values ​​based on the power plant's annual output data. The percentage of the design power of the first-stage heater and the second-stage heater relative to the total design power is determined by a comprehensive weighted method; based on the flow rate under the system design conditions... and buffer time Calculate the design volume of the intermediate tank;

[0009] Develop flow control strategies and input power distribution strategies for the first-stage and second-stage heaters:

[0010] The flow control strategy for the second-stage heater is to stabilize the outlet temperature of the second-stage heater through a proportional-integral-derivative controller; the flow control strategy for the first-stage heater is based on the outlet temperature of the first-stage heater, the liquid level in the intermediate tank, and the safe flow rate of the first-stage heater.

[0011] The power input distribution strategy is based on the total system input power P. t With the design power P of the second-stage heater 2,rated The matching relationship is such that the first-stage heater absorbs all fluctuations in the system's input electrical power, while the second-stage heater operates at the designed power.

[0012] In the electrically heated molten salt energy storage system, the first molten salt pump pumps low-temperature molten salt out of the low-temperature salt tank, flows through the first regulating valve into the first-stage heater for heat exchange, and flows into the intermediate tank. The molten salt in the intermediate tank is pumped out by the second molten salt pump, flows through the second regulating valve into the second-stage heater for heat exchange, and finally flows into the high-temperature salt tank.

[0013] The present invention has the following beneficial effects:

[0014] (1) Based on the two-stage heater, this invention combines the fluctuation characteristics of the power plant’s annual output data and determines the power allocation of the two-stage heater through a comprehensive weighting method, thereby achieving a decoupled design of stable power and fluctuating power. This allows the second-stage heater to maintain stable operation at the design power and ensure that the high-temperature molten salt temperature remains constant, while the first-stage heater takes on all input power fluctuations, shortening the system’s response delay to power plant output fluctuations and solving the problem of power response lag in the prior art.

[0015] (2) The method for determining the volume of the intermediate tank proposed in this invention is to calculate the reasonable volume of the intermediate tank based on the flow rate and buffer time under the system design conditions. By reasonably designing the volume of the intermediate tank to buffer the molten salt temperature fluctuation, the decoupled control of the molten salt temperature fluctuation caused by the input power fluctuation is realized.

[0016] (3) This invention proposes a flow control method and input power distribution strategy for two-stage heaters. Based on the safety flow constraint of the first-stage heater, a multi-level unit collaborative closed-loop control strategy is constructed, which not only ensures the rapid response of the electric heating molten salt energy storage system to the grid frequency regulation and scheduling, but also avoids the risk of local overheating of the electric heating tube and molten salt decomposition failure, thus improving the safety and reliability of the system operation. Compared with the prior art, this invention clarifies the quantitative basis of the power distribution of the two-stage heaters and the specific control logic under the continuous large fluctuation of the power plant output, thus improving the adaptability of the system in the high proportion of new energy fluctuation scenario. Attached Figure Description

[0017] Figure 1 This is a structural diagram of a first embodiment of the molten salt energy storage system for heating with high fluctuations in electrical energy according to the present invention; wherein, 1-low temperature salt tank, 2-high temperature salt tank, 3-intermediate tank, 4-first stage heater, 5-second stage heater, 6-first molten salt pump, 7-second molten salt pump, 8-first regulating valve, 9-second regulating valve, 10-first temperature measuring point, 11-second temperature measuring point, 12-level gauge. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0019] To overcome the shortcomings of existing electrically heated molten salt energy storage systems, such as slow response to large fluctuations in renewable energy power, poor reliability under varying loads, and difficulty in simultaneously achieving rapid tracking and stable temperature control, this invention proposes an electrically heated molten salt energy storage system (or simply the system) based on a two-stage heating, intermediate buffer, and graded control architecture.

[0020] Low-temperature salt container 1, used for storing low-temperature molten salt;

[0021] High-temperature salt tank 2 is used to store high-temperature molten salt from the outlet of the second-stage heater 5;

[0022] Intermediate tank 3 is used to store molten salt from the outlet of the first-stage heater 4;

[0023] The first-stage heater 4 is used to convert electrical energy into heat energy and transfer it to the molten salt. The outlet molten salt enters the intermediate tank 3.

[0024] The second-stage heater 5 is used to convert electrical energy into heat energy and transfer it to the molten salt, and the outlet molten salt enters the high-temperature tank 2;

[0025] The first molten salt pump 6 is located inside the cryogenic salt tank 1 and is used to pump cryogenic molten salt to the first stage heater 4;

[0026] The second molten salt pump 7, located inside the intermediate tank 3, is used to pump molten salt to the second-stage heater 5;

[0027] The first regulating valve 8 is located at the inlet of the first stage heater 4 and is used to regulate the molten salt flow rate to control the molten salt temperature at the outlet of the first stage heater 4.

[0028] The second regulating valve 9 is located at the inlet of the second-stage heater 5 and is used to regulate the molten salt flow rate to control the molten salt temperature at the outlet of the second-stage heater 5.

[0029] Connecting pipes are used to connect the above components. All pipes are equipped with insulation to reduce heat loss. Backup pipes and valves are also provided to ensure continuous system operation.

[0030] The first temperature measuring point 10 is set at the outlet of the first stage heater 4 to provide feedback temperature signals to control the opening of the first regulating valve 8 and the speed of the molten salt pump.

[0031] The second temperature measuring point 11 is set at the outlet of the second stage heater 5 and is used to feed back temperature signals to control the opening of the second regulating valve 9 and the speed of the molten salt pump.

[0032] A level gauge 12 is installed inside the intermediate tank 3 to provide feedback on the liquid level signal in order to control the opening of the first regulating valve 8 and the rotation speed of the first molten salt pump 6.

[0033] The control method for the electrically heated molten salt energy storage system of the present invention includes:

[0034] The system parameters are designed, including: the design power of the first-stage heater 4. The design power of the second-stage heater 5 The design volume V of intermediate tank 3 surge Design; per-unit values ​​based on the annual power plant output data The percentage of the design power of the first-stage heater 4 and the second-stage heater 5 to the total design power is determined by a comprehensive weighted method; based on the flow rate under the system design conditions. and buffer time Calculate the design volume of the intermediate tank.

[0035] The flow control strategy and input power distribution strategy of the first-stage heater 4 and the second-stage heater 5; the flow control of the second-stage heater 5 is stabilized by a proportional-integral-derivative controller to stabilize the outlet temperature of the second-stage heater 5; the flow control of the first-stage heater 4 is based on the outlet temperature of the first-stage heater 4, the liquid level of the intermediate tank 3, and the safe flow rate of the first-stage heater 4; specifically, the flow rate of the first-stage heater 4 is controlled by the temperature control unit, the liquid level control unit, the signal processing unit, the safety protection unit, and the nonlinear compensation unit in a coordinated manner.

[0036] The power input distribution strategy is based on the total system input power P. t With the design power P of the second-stage heater 2,rated The matching relationship is such that the first-stage heater 4 absorbs all fluctuations in the system's input power, while the second-stage heater 5 operates at its designed power. Specifically, the total system input power P... t ≥P 2,rated At that time, the input power of the second-stage heater 5 is maintained at P. 2,rated The power remains unchanged; the first-stage heater 4 carries the remaining power. t <P 2,rated At that time, the input power of the second-stage heater 5 is equal to P. t The input power of the first-stage heater 4 is zero.

[0037] The specific system parameter design is as follows:

[0038] The parameters of this system that differ from traditional electrically heated molten salt energy storage systems during the design phase include: the design power of the first-stage heater 4. The design power of the second-stage heater 5 The design volume of intermediate tank 3 is V surge .

[0039] Among them, the design power P of the first-stage heater 4 1,rated Design power of the second stage heater 5 The determination method is as follows:

[0040] (1) Determine the total electric heating power of the system based on project requirements. ;

[0041] (2) Obtain annual meteorological data for a typical year at the project construction site, and determine the annual power output data of the wind and solar power stations to be connected through simulation calculations. ;

[0042] (3) The annual power output data of wind and solar power stations Normalization was performed to obtain the per-unit values ​​of the annual output data. :

[0043] ;

[0044] in, Annual power output data for wind and solar power plants The maximum value;

[0045] (4) Standardize the annual output data to per unit value Divided into 0 to 1 Each interval is used to calculate the percentage of data points within that interval relative to the total number of data points for the entire year. ,in, For interval numbering;

[0046] (5) Calculate the weighted average per-unit value using the comprehensive weighting method. The design power of the second-stage heater 5 Percentage of total design power:

[0047] ;

[0048] in, For interval per unit value The average value;

[0049] The design power of the second-stage heater 5 for:

[0050] ;

[0051] The design power of the first-stage heater 4 for:

[0052] .

[0053] Design volume of intermediate tank 3 The determination method is as follows:

[0054] (1) Based on the total electric heating power of the system Calculate the system design flow rate ;

[0055] (2) Calculate or set the buffer time Buffer time The value is determined based on the maximum duration of new energy fluctuations and the allowable rate of change of molten salt temperature, and is generally taken as 15 minutes or more.

[0056] (3) Calculate the design volume of intermediate tank 3 for:

[0057] ;

[0058] in, The density of the fluid.

[0059] The flow control strategies for the first-stage heater 4 and the second-stage heater 5 are as follows:

[0060] The flow control system of the second-stage heater 5 includes a second temperature measuring point 11, a second regulating valve 9, and a proportional-integral-derivative (PID) controller, respectively located at the outlet and inlet ends of the second-stage heater 5. The first input parameter of the PID controller is the outlet temperature T of the second-stage heater 5. fo,2 The second input parameter is the target outlet temperature T of the second-stage heater 5. fo,2,target Based on the difference between the first and second input parameters, the proportional-integral-derivative controller adjusts the opening of the second regulating valve 9 to stabilize the outlet temperature T of the second-stage heater 5. fo,2 Make it equal to the target outlet temperature T of the second-stage heater 5. fo,2,target .

[0061] The flow control system of the first-stage heater 4 differs from traditional molten salt energy storage systems. It includes a first temperature measuring point 10 and a first regulating valve 8, a level gauge 12, a temperature control unit, a level control unit, a signal processing unit, a safety protection unit, and a nonlinear compensation unit, all located at the outlet and inlet ends of the first-stage heater 4, respectively. Specifically, the first temperature measuring point 10 is connected to the input of the temperature control unit; the level gauge 12 is located inside the intermediate tank 3 and is connected to the input of the level control unit; the outputs of both the temperature control unit and the level control unit are connected to the signal processing unit; the output of the signal processing unit is sequentially connected to the safety protection unit and the nonlinear compensation unit; and the output of the nonlinear compensation unit is connected to the drive end of the first regulating valve 8, used to adjust the opening of the first regulating valve 8 to control the flow rate of the first-stage heater 4.

[0062] The first input parameter of the temperature control unit is the measured outlet temperature of the first-stage heater 4. The second input parameter is the upper limit temperature of the outlet temperature of the first-stage heater 4. The third input parameter is the lower limit temperature of the outlet temperature of the first-stage heater 4. ,and and Input power for the second-stage heater 5 and range of flow variation Functions:

[0063] ;

[0064] ;

[0065] in, This represents the maximum flow rate of the electrically heated molten salt energy storage system. This is the minimum flow rate for an electrically heated molten salt energy storage system. For specific heat of fluid, The maximum operating temperature of the fluid. The minimum operating temperature of the fluid; max() is the function to get the maximum value; min() is the function to get the minimum value.

[0066] when < < The output parameter of the temperature control unit is zero; when > ,or < The target outlet temperature of the first-stage heater 4 is set to T. fo,1,target =0.5×( + ), calculate the measured outlet temperature of the first-stage heater 4. With the target outlet temperature T fo,1,target The deviation ΔT=T fo,1 -T fo1,target The output parameter of the temperature control unit is the target flow correction value of the first-stage heater 4 based on ΔT, which is output by a proportional-integral-derivative controller. .

[0067] The first input parameter of the liquid level control unit is the actual liquid level L of intermediate tank 3. surge The second input parameter is the target liquid level L in intermediate tank 3. surge,target A proportional-integral-derivative controller is used to calculate the target flow correction value of the first-stage heater 4 output by the level control unit based on the difference between the first input parameter and the second input parameter. This ensures that the actual liquid level in the intermediate tank remains within a defined range, preventing the internal fluid from overflowing or being depleted.

[0068] The first input parameter of the signal processing unit is the rated flow rate of the first-stage heater 4. The second input parameter is The third input parameter is The fourth input parameter is Weight parameters The fifth input parameter is Weight parameters Output the initial target flow :

[0069] ;

[0070] The first input parameter of the safety protection unit is the initial target flow rate. The second input parameter is the safe flow rate. Output parameters: the final target flow rate of the first-stage heater 4. for:

[0071] ;

[0072] Where max() is the maximum value function, and safe flow rate is... Input power for the first stage heater 4 and the inlet temperature of the first stage heater 4 Functions:

[0073] ;

[0074] Among them, the function Based on the structure and input power of the first-stage heater 4 and inlet temperature Determined through three-dimensional simulation or experimental testing.

[0075] The input parameters of the nonlinear compensation unit are: The nonlinear function F of flow rate and valve opening fv (This function is obtained by experimentally measuring the relationship between flow rate and valve opening), and the output parameter is the target opening OV of the first regulating valve 8. target :

[0076] OV target =F fv ( );

[0077] By adjusting the opening of the first regulating valve 8 to 0V target The flow control system of the first-stage heater 4 can adjust the flow of the first-stage heater 4 according to the above control logic.

[0078] The specific energy distribution strategy for the first-stage heater 4 and the second-stage heater 5 is as follows:

[0079] (1) The system's input electrical power P t Greater than the design power of the second-stage heater 5 At this time, the input power of the second-stage heater 5 is maintained at the design power. The fluctuations in input electrical energy remain unchanged, and are all borne by the first-stage heater 4;

[0080] (2) The system's input electrical power P t Less than the design power of the second-stage heater 5 At that time, the input power of the second-stage heater 5 is equal to the system's input electrical power P. t The input power of the first-stage heater 4 is zero.

[0081] The flow control system of the first-stage heater 4 and the flow control system of the second-stage heater 5 are strongly coupled, and their coordination is as follows:

[0082] Step 1: Execute the power distribution strategy in real time;

[0083] The total input electrical power Pt of the acquisition system is allocated to the power of the two-stage heaters according to the following rules:

[0084] If P t ≥ The power P2 of the second-stage heater 5 is set to P2= (Constant), the power of the first-stage heater 4 is set to P1=P t - (Accepting all fluctuations);

[0085] If P t < The power P2 of the second-stage heater 5 is set to P2=P t The power P1 of the first-stage heater 4 is set to P1=0.

[0086] Step 2: Regulate the flow rate of the first-stage heater 4;

[0087] Step 2.1: Calculate in real time the change in the safe flow rate of the first-stage heater 4 as a function of the power P1 of the first-stage heater;

[0088] Based on the current power P1 of the first-stage heater 4 and the inlet temperature of the first-stage heater 4 Real-time calculation of the safe flow rate of the first-stage heater 4 :

[0089] ;

[0090] Safe traffic It is power The function, Changes in safe flow It also changes immediately;

[0091] Step 2.2: Collect the outlet temperature of the first-stage heater 4. The temperature control unit outputs the target flow correction value for the first-stage heater 4. ;

[0092] Step 2.3: Collect the actual liquid level L in the intermediate tank. surge The liquid level control unit outputs the target flow correction value for the first-stage heater 4. ;

[0093] Step 2.4, the signal processing unit calculates the initial target flow rate of the first-stage heater 4:

[0094] ;

[0095] Step 2.5, calculate the output parameters of the safety protection unit. :

[0096] ; Ensure the target flow rate of the first-stage heater 4 Always above safe flow The first-stage heater 4 will not overheat;

[0097] Step 2.6: Adjust the first regulating valve 8 based on the output signal of the nonlinear compensation unit;

[0098] The nonlinear compensation unit uses the nonlinear function F of flow rate and valve opening. fv Get target traffic The target opening degree OV of the corresponding first regulating valve 8 target And perform adjustments.

[0099] Step 3: Regulate the flow rate of the second-stage heater 5;

[0100] The outlet temperature of the first-stage heater 4 fluctuates with the power P1, so the fluid temperature in the intermediate tank 3 also fluctuates, which affects the inlet temperature of the second-stage heater 5. Therefore, the second-stage heater 5 is affected by the disturbance of the first-stage heater 4.

[0101] Independent closed-loop temperature control of the second-stage heater 5 includes: collecting the outlet temperature T of the second-stage heater 5 at the second temperature measuring point 11. fo,2 , will T fo,2 With the target outlet temperature T of the second-stage heater 5 fo,2,target By adjusting the opening of the second regulating valve 9 via a proportional-integral-derivative controller, the molten salt flow rate of the second-stage heater 5 is changed, thus affecting T. fo,2 Stable at T fo,2,target .

[0102] It should be noted that steps 1 to 3 above are not strictly performed in chronological order. The overall control effect of the above steps is as follows: The power distribution strategy determines the power allocation between the first-stage heater 4 and the second-stage heater 5, with all input power fluctuations being borne by the first-stage heater 4; the flow rate control of the first-stage heater 4 achieves real-time adjustment of the target flow rate of the first-stage heater 4 according to the input power, ensuring that the first-stage heater 4 does not overheat; the second-stage heater 5 maintains a constant outlet temperature by adjusting the second regulating valve 9, offsetting the disturbances caused by changes in the inlet temperature and input power of the second-stage heater 5, and finally outputs constant-temperature high-temperature molten salt to the high-temperature salt tank 2.

[0103] Preferably, the input electrical energy for the first-stage heater 4 and the second-stage heater 5 can come from the power grid or various power generation equipment such as photovoltaic and wind power.

[0104] Preferably, the first-stage heater 4 can be arranged in a series-parallel configuration using multiple heaters.

[0105] Preferably, the second-stage heater 5 can be arranged in series and parallel.

[0106] Preferably, the intermediate tank 3 can be arranged in a series or parallel configuration.

[0107] Preferably, the flow control system of the second-stage heater 5 in this system can use other control methods known in the art, such as feedforward-feedback composite control, to replace the aforementioned control method in order to stabilize the outlet temperature of the second-stage heater 5.

[0108] Preferably, the flow control system of the first-stage heater 4 in this system can use other control methods known in the art, such as cascade control, to change the positional relationship of existing units to adjust the outlet temperature of the first-stage heater 4.

[0109] Preferably, the flow rate regulation of the first-stage heater 4 and the second-stage heater 5 can also be achieved by adjusting the rotation speed of the first molten salt pump 6 and the second molten salt pump 7.

[0110] Preferably, a dead zone can be added to the input signal of each proportional-integral-derivative controller to avoid frequent signal fluctuations and adjustments.

[0111] Example 1:

[0112] like Figure 1 As shown, an electrically heated molten salt energy storage system of the present invention includes a low-temperature salt tank 1, a high-temperature salt tank 2, an intermediate tank 3, a first-stage heater 4, a second-stage heater 5, a first molten salt pump 6, a second molten salt pump 7, a first regulating valve 8, and a second regulating valve 9. During system operation, the first molten salt pump 6 pumps low-temperature molten salt from the low-temperature salt tank 1, flows through the first regulating valve 8 into the first-stage heater 4 for heat exchange, and then flows into the intermediate tank 3. The molten salt in the intermediate tank 3 is pumped out by the second molten salt pump 7, flows through the second regulating valve 9 into the second-stage heater 5 for heat exchange, and finally flows into the high-temperature salt tank 2.

[0113] System design parameters determined: Project requirement: Total electric heating power P of the system t,rated= 50MW; Obtain typical annual meteorological data of the project construction site and simulate the maximum annual output P of the wind and solar power station. plant,max =100MW, per-unit value of annual power output data Divided into 10 intervals, the weighted average per-unit value α = 0.6 was obtained; therefore, the design power P of the second-stage heater 5 is...2,rated =0.6×50MW=30MW, the design power P of the first-stage heater 4 1,rated =50MW-30MW=20MW.

[0114] Intermediate tank 3 is designed with a volume of V surge Calculate: Specific heat capacity of molten salt at constant pressure, c p =1.5kJ / (kg·K), the system design molten salt temperature rise ΔT=270K, then the system design flow rate is... =50MW / (1.5kJ / (kg·K)×270K)≈123kg / s; take the buffer time t surge =10 minutes = 600 seconds, molten salt density ρ = 1900 kg / m³, then the design volume V of the intermediate tank surge =2×123kg / s×600s / 1900kg / m³≈77.68m³;

[0115] Implementation of the flow control system for the second-stage heater 5: Target outlet temperature T of the second-stage heater 5 fo,2,target =560℃, using a proportional-integral-derivative controller to adjust the opening of the second regulating valve 9 based on the temperature signal fed back from the second temperature measuring point 11, so that the temperature fluctuation of the outlet of the second stage heater 5 is controlled within ±3℃.

[0116] The flow control system for the first-stage heater 4 operates as follows:

[0117] Temperature control unit implementation: Set the upper limit T of the outlet temperature of the first-stage heater 4. fo,1,max =426℃, lower limit T fo,1,min =290℃ (the two are calculated and determined based on the input power of the second-stage heater 5 of 30MW, the maximum flow rate of 150kg / s, the minimum flow rate of 24.6kg / s, the highest operating temperature of molten salt of 580℃ and the lowest operating temperature of 290℃); the first temperature measuring point 10 collects the outlet temperature T of the first-stage heater 4 in real time. fo,1 When 290℃ <T fo,1 At temperatures below 426℃, the temperature control unit outputs the target flow correction value. =0; when T fo,1 ≥426℃ or T fo,1 At ≤290℃, based on the deviation [T] fo,1 -0.5 × (426℃ + 290℃)] = T fo,1 At -358℃, a proportional-integral-derivative (PID) controller (proportional coefficient Kp=2.5, integral time Ti=60s, derivative time Td=15s) is used to output the target flow correction value. For example, when T fo,1 At 455℃, =+8kg / s; when T fo,1At 285℃, =-6kg / s.

[0118] Liquid level control unit implementation: Set the target liquid level L of intermediate tank 3 surge,target =1.8m, level gauge 12 collects the actual liquid level L of intermediate tank 3 in real time. surge The target flow correction value is calculated using a proportional-integral-derivative controller (proportional coefficient Kp=3.0, integral time Ti=80s, derivative time Td=20s). For example, when L surge When the liquid level is 1.9m (above the target liquid level), =-5kg / s; when L surge =1.7m (below the target liquid level), =+4kg / s.

[0119] Signal processing unit implementation: Set the rated flow rate of the first-stage heater 4. =123kg / s, weighting parameter W tem =0.8, W level =0.7 (Given the current large fluctuations in wind and solar power output, temperature control is given priority), according to the formula Calculate the target traffic, for example when =+8kg / s、 When = +5kg / s, m target =123+0.8×8+0.7×5=123+6.4+3.5=132.9kg / s.

[0120] Safety protection unit implementation: safe flow The structure, input power P1, and inlet temperature of the first-stage heater 4 are determined through three-dimensional simulation or experimental testing; combined with the parameters of this embodiment, for example, when the input power P1 of the first-stage heater 4 is 20MW (rated power) and the inlet temperature T... fi,1 =290℃, determined by three-dimensional simulation. ≈95.8 kg / s; the calculated value is... and Compare and take the maximum value as For example, when When =132.9kg / s, =132.9kg / s; when =90kg / s (lower than) )hour, =95.8kg / s, to avoid local overheating caused by excessively low flow rate.

[0121] Implementation of nonlinear compensation unit: Nonlinear function F of flow rate and valve opening fvA piecewise polynomial function is used, with calibration coefficients based on the model of the first regulating valve 8, for example: when ≤0.5 When (≤61.5kg / s), F fv =0.002× 2 +0.15× +5; when 0.5 < ≤1.5 When (61.5~184.5 kg / s), F fv =0.003× +0.1; when >1.5m When F > 184.5 kg / s, fv =0.001× 2 +0.2× +8; for example, when When =132.9kg / s, OV target =0.003×132.9+0.1=49.87%, that is, the opening of the first regulating valve 8 is adjusted to 49.87%, thus achieving precise control of the flow rate of the first stage heater 4.

[0122] System input power distribution strategy implementation:

[0123] Operating Condition 1: The system's input electrical power is greater than the design power (P) of the second-stage heater. 2,rated =30MW). When the output of the wind and solar power station increases and the system input power rises to 45MW (greater than 30MW), the input power of the second-stage heater 5 remains unchanged at the design power of 30MW. The fluctuation of input power (45MW-30MW=15MW) is entirely borne by the first-stage heater 4. At this time, the input power of the first-stage heater 4 is adjusted to 15MW (not exceeding its rated design power of 20MW). In conjunction with the flow control system of the first-stage heater 4, the outlet temperature of the first-stage heater 4 is kept stable at 290~426℃ to ensure stable system operation and realize the rapid acceptance of new energy fluctuations.

[0124] Operating Condition 2: The system's input electrical power is less than the design power (P) of the second-stage heater. 2,rated=30MW). When the output of the wind and solar power station decreases and the system input power drops to 25MW (less than 30MW), the input power of the second-stage heater 5 is adjusted to the actual system input power of 25MW, and the load is reduced to match the input power. At the same time, the input power of the first-stage heater 4 is set to zero. At this time, the second-stage heater 5 adjusts the opening of the second regulating valve 9 through its own flow control system proportional-integral-derivative controller to maintain the outlet temperature at 560±3℃, ensuring that the high-temperature molten salt temperature is constant and meeting the subsequent energy storage and power generation needs.

[0125] Through the above power distribution strategy, the system can flexibly adapt to fluctuations in input power. When the input power fluctuates, there is no need to adjust the operating status of the two-stage heaters as a whole. The dual goals of fluctuation tracking and stable temperature control can be achieved simply by grading the power. The system is fast-responding and reliable in operation, and adapts to the needs of scenarios with high proportion of new energy power output fluctuations.

[0126] The above description is merely an embodiment of the present invention and does not limit the scope of the invention. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related system fields, are similarly included within the protection scope of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A control method for an electrically heated molten salt energy storage system, characterized in that, include: The system parameters are designed, including: the design power of the first-stage heater. Design power of the second-stage heater The design volume V of the intermediate tank surge Design is carried out; per-unit values ​​based on the power plant's annual output data. The percentage of the design power of the first-stage heater and the second-stage heater relative to the total design power is determined by a comprehensive weighted method; based on the flow rate under the system design conditions... and buffer time Calculate the design volume of the intermediate tank; Develop flow control strategies and input power distribution strategies for the first-stage and second-stage heaters: The flow control strategy for the second-stage heater is to stabilize the outlet temperature of the second-stage heater through a proportional-integral-derivative controller; the flow control strategy for the first-stage heater is based on the outlet temperature of the first-stage heater, the liquid level in the intermediate tank, and the safe flow rate of the first-stage heater. The power input distribution strategy is based on the total system input power P. t With the design power P of the second-stage heater 2,rated The matching relationship is such that the first-stage heater absorbs all fluctuations in the system's input electrical power, while the second-stage heater operates at the designed power. In the electrically heated molten salt energy storage system, the first molten salt pump pumps low-temperature molten salt out of the low-temperature salt tank, flows through the first regulating valve into the first-stage heater for heat exchange, and flows into the intermediate tank. The molten salt in the intermediate tank is pumped out by the second molten salt pump, flows through the second regulating valve into the second-stage heater for heat exchange, and finally flows into the high-temperature salt tank.

2. The control method for the electrically heated molten salt energy storage system according to claim 1, characterized in that, in, The design power of the first-stage heater Design power of the second stage heater The determination method is as follows: Based on project requirements, the total electric heating power of the system is determined to be: ; Obtain annual meteorological data for a typical year at the project construction site, and determine the annual power output data of the proposed wind and solar power stations through simulation calculations. ; The annual power output data of wind and solar power stations Normalization was performed to obtain the per-unit values ​​of the annual output data. : ； in, Annual power output data for wind and solar power plants The maximum value; Standardize the annual output data to per unit value Divided into 0 to 1 Each interval is used to calculate the percentage of data points within that interval relative to the total number of data points for the entire year. ,in, For interval numbering; The weighted average per-unit value is calculated using the comprehensive weighting method. Design power for the second-stage heater Percentage of total design power: ； in, For interval per unit value The average value; The design power of the second-stage heater for: ； The design power of the first-stage heater for: 。 3. The control method for the electrically heated molten salt energy storage system according to claim 1, characterized in that, Design volume of intermediate tank for: Based on the total electric heating power of the system Calculate the system design flow rate ; The buffer time is determined based on the maximum duration of new energy fluctuations and the allowable rate of change in molten salt temperature. ; Calculate the design volume of the intermediate tank for: ； in, The density of the fluid.

4. The control method for the electrically heated molten salt energy storage system according to claim 1, characterized in that, In the flow control strategy of the second-stage heater, the flow control system of the second-stage heater includes a second temperature measuring point, a second regulating valve, and a proportional-integral-derivative (PID) controller, respectively installed at the outlet and inlet ends of the second-stage heater; wherein, the first input parameter of the PID controller is the outlet temperature T of the second-stage heater. fo,2 The second input parameter is the target outlet temperature T of the second-stage heater. fo,2,target Based on the difference between the first and second input parameters, the proportional-integral-derivative controller adjusts the opening of the second regulating valve to stabilize the outlet temperature T of the second-stage heater. fo,2 Make it equal to the target outlet temperature T of the second-stage heater. fo,2,target .

5. The control method for the electrically heated molten salt energy storage system according to claim 4, characterized in that, In the flow control strategy of the first-stage heater, the flow control system of the first-stage heater includes a first temperature measuring point and a first regulating valve, a level gauge, a temperature control unit, a level control unit, a signal processing unit, a safety protection unit, and a nonlinear compensation unit, respectively set at the outlet and inlet ends of the first-stage heater. The first temperature measuring point is connected to the input end of the temperature control unit; the level gauge is located inside the intermediate tank and connected to the input end of the level control unit; the output ends of both the temperature control unit and the level control unit are connected to the signal processing unit; the output end of the signal processing unit is sequentially connected to the safety protection unit and the nonlinear compensation unit; the output end of the nonlinear compensation unit is connected to the drive end of the first regulating valve, used to adjust the opening of the first regulating valve to control the flow rate of the first-stage heater.

6. The control method for the electrically heated molten salt energy storage system according to claim 5, characterized in that, The first input parameter of the temperature control unit is the measured outlet temperature of the first-stage heater. The second input parameter is the upper limit temperature of the outlet temperature of the first-stage heater. The third input parameter is the lower limit temperature of the outlet temperature of the first-stage heater. ,and and Input power for the second-stage heater and range of flow variation Functions: ； ； in, This represents the maximum flow rate of the electrically heated molten salt energy storage system. This is the minimum flow rate for an electrically heated molten salt energy storage system. For specific heat of fluid, The maximum operating temperature of the fluid. This represents the minimum operating temperature of the fluid; max() is the function to retrieve the maximum value; min() is the function to retrieve the minimum value. when < < The output parameter of the temperature control unit is zero; when > ,or < The target outlet temperature of the first-stage heater is set to T. fo,1,target =0.5×( + ), calculate the measured outlet temperature of the first-stage heater. With the target outlet temperature T fo,1,target The deviation ΔT=T fo,1 -T fo1,target The temperature control unit outputs a target flow correction value for the first-stage heater based on ΔT, using a proportional-integral-derivative controller. .

7. The control method for the electrically heated molten salt energy storage system according to claim 6, characterized in that, The first input parameter of the level control unit is the actual liquid level L in the intermediate tank. surge The second input parameter is the target liquid level L in the intermediate tank. surge,target A proportional-integral-derivative controller is used to calculate the target flow correction value of the first-stage heater output by the level control unit based on the difference between the first and second input parameters. This ensures that the actual liquid level in the intermediate tank remains within a specified range. The first input parameter of the signal processing unit is the rated flow rate of the first-stage heater. The second input parameter is The third input parameter is The fourth input parameter is Weight parameters The fifth input parameter is Weight parameters Output the initial target flow : 。 8. The control method for the electrically heated molten salt energy storage system according to claim 7, characterized in that, The first input parameter of the safety protection unit is the initial target flow rate. The second input parameter is the safe flow rate. The output parameter is the final target flow rate of the first-stage heater. for: ； Where max() is the function to find the maximum value; The input parameters of the nonlinear compensation unit are: The nonlinear function of flow rate and valve opening, with output parameters as follows: The target opening degree OV of the corresponding first regulating valve target : OV target =F fv ( ); The flow control system of the first-stage heater adjusts the opening of the first regulating valve to 0V. target Adjust the flow rate of the first-stage heater.

9. The control method for the electrically heated molten salt energy storage system according to claim 8, characterized in that, The energy distribution strategy for the first-stage heater and the second-stage heater is as follows: The system's input electrical power P t Greater than the design power of the second-stage heater At that time, the input power of the second-stage heater is maintained at the design power. The input electrical energy fluctuations remain unchanged and are all absorbed by the first-stage heater. The system's input electrical power P t Less than the design power of the second-stage heater At that time, the input power of the second-stage heater is equal to the system's input electrical power P. t The input power of the first-stage heater is zero.

10. The control method for the electrically heated molten salt energy storage system according to claim 9, characterized in that, The energy distribution strategy for the first-stage heater and the second-stage heater includes: Real-time execution of power distribution strategies, specifically including: acquiring the total input power Pt of the system, if P t ≥ The power P2 of the second-stage heater is set to P2= The power of the first-stage heater is set to P1=P t - The first-stage heater absorbs all fluctuations; if P t < The power P2 of the second-stage heater is set to P2 = P t The power P1 of the first-stage heater is set to P1=0; Flow control of the first-stage heater includes: Step 2.1: Calculate in real-time the change in the safe flow rate of the first-stage heater as the power P1 of the first-stage heater changes; based on the current power P1 of the first-stage heater and the inlet temperature of the first-stage heater... Real-time calculation of the safe flow rate of the first-stage heater ; Step 2.2: Collect the outlet temperature of the first-stage heater. The temperature control unit outputs the target flow correction value for the first-stage heater. ; Step 2.3: Collect the actual liquid level L in the intermediate tank. surge The level control unit outputs the target flow correction value for the first-stage heater. ; Step 2.4: The signal processing unit calculates the initial target flow rate of the first-stage heater. ； Step 2.5, calculate the output parameters of the safety protection unit. : ; Ensure the target flow rate of the first-stage heater Always above safe flow The first-stage heater will not overheat; Step 2.6, the nonlinear compensation unit uses the nonlinear function F of flow rate and valve opening. fv Get target traffic The target opening degree OV of the corresponding first regulating valve 8 target And adjust the first regulating valve to the target opening degree OV. target ; Flow control of the second-stage heater is performed, including: collecting the outlet temperature T of the second-stage heater at the second temperature measuring point 11. fo,2 , will T fo,2 With the target outlet temperature T of the second-stage heater fo,2,target By comparing and adjusting the opening of the second regulating valve, the molten salt flow rate of the second-stage heater is changed, so that T fo,2 Stable at T fo,2,target .

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