Multi-element variable-frequency water replenishing control method and system for boiler and storage medium

Abstract

The embodiment of the invention discloses a boiler multi-element frequency conversion water supplementing control method and system and a storage medium. The water supplementing control method comprises the steps that the theoretical fuel flow is obtained based on the current load of a boiler; obtaining a theoretical water supplementing flow based on the current power of the water supplementing frequency converter; on the basis of a preset time interval, switching value states corresponding to the low-position probe, the middle-position probe and the high-position probe are repeatedly obtained, and the current liquid level height is updated; when the current liquid level height is higher than the low-level probe and lower than the high-level probe, the current working frequency of the water supplementing frequency converter is adjusted based on the magnitude relation between the theoretical fuel flow and the theoretical water supplementing flow and the high-low relation between the current liquid level height and the middle-level probe, and the output working frequency of the water supplementing frequency converter is obtained; the boiler controls the make-up pump to make up water through the output working frequency of the frequency converter. The boiler does not need to be provided with a flowmeter, a modulus liquid level meter and other high-cost sensors, the production cost is reduced with certain liquid level control precision, and the economical efficiency of small and medium-sized boilers is improved.

Description

Technical Field

[0001] Multiple embodiments of this specification relate to the technical field of boiler make-up water control, specifically to cost optimization of the variable-frequency make-up water control method for boilers. Background Art

[0002] Boiler multi-variable frequency make-up water control is an automated system based on variable-frequency speed regulation technology that achieves precise control of the boiler steam drum level through coordinated adjustment of multiple parameters. Its core objective is to maintain the stability of the steam drum level by dynamically adjusting the operating frequency of the make-up water pump or the valve opening, thereby ensuring the safe operation of the boiler and improving energy efficiency. With the rapid development of industrial automation and variable-frequency technology, this technology has gradually evolved from early single-loop control to a multi-variable coordinated control mode and is widely used in power station boilers, industrial boilers and other fields.

[0003] Currently, the mainstream boiler multi-variable frequency make-up water control strategy is mainly based on a PID control architecture that combines multi-parameter feedback and feedforward. Three-impulse control: Using the steam drum level as the main adjustment quantity, the make-up water flow as the secondary adjustment quantity, and the steam flow as the feedforward quantity, the frequency of the make-up water pump or the valve opening is adjusted by comprehensively considering the deviations of the three through the PID algorithm. Dual-impulse simplified control: In some scenarios, to reduce complexity, only the steam drum level and the steam flow (or make-up water flow) are used as input quantities, and the level stability is achieved through feedforward-feedback composite control.

[0004] However, the above make-up water control methods have high-cost and reliability problems: 1. The system needs to be equipped with high-precision flow meters and analog level gauges. Such sensors are costly, and the analog level gauges are easily interfered by water quality and pressure fluctuations, with poor long-term stability and high failure rates. 2. Maintenance complexity: The redundant design of sensors increases the system complexity, and the troubleshooting and maintenance costs increase accordingly, which is particularly uneconomical for small and medium-sized boiler users. Summary of the Invention

[0005] Embodiments of this specification provide a boiler multi-variable frequency make-up water control method, system and storage medium, aiming to reduce the production cost and maintenance difficulty of boilers compared with the make-up water control method that relies on sensors.

[0006] The technical solutions are as follows: In a first aspect, embodiments of this specification provide a boiler multi-variable frequency make-up water control method. A low probe, a middle probe and a high probe are arranged in the boiler. The make-up water control method includes the following steps: Obtain the current load of the boiler, the current operating frequency and the current power of the make-up water frequency converter; Obtain the theoretical fuel flow based on the current load of the boiler; Obtain the theoretical make-up water flow based on the current power of the make-up water frequency converter; Repeatedly obtain the digital input states corresponding to the low-level probe, middle-level probe, and high-level probe at preset time intervals, and update the current liquid level height. When the current liquid level height is higher than the low-level probe and lower than the high-level probe, determine the first frequency change amount based on the magnitude relationship between the theoretical fuel flow rate and the theoretical make-up water flow rate, determine the second frequency change amount based on the height relationship between the current liquid level height and the middle-level probe, and adjust the current operating frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter. Among them, the absolute value of the first frequency change amount is greater than the absolute value of the first frequency change amount. The boiler controls the make-up water pump to supply water through the output operating frequency of the frequency converter.

[0007] As a preferred solution, the obtaining of the theoretical fuel flow rate based on the current load of the boiler includes: Obtain a pre-calibrated fuel flow rate-load mapping table. Look up the table based on the current load of the boiler, and use the linear interpolation formula to obtain the theoretical fuel flow rate.

[0008] As a preferred solution, the obtaining of the theoretical make-up water flow rate based on the current power of the make-up water frequency converter includes: Obtain a pre-calibrated compensation coefficient. Based on the flow formula, obtain the estimated make-up water flow rate corresponding to the current power of the make-up water frequency converter. Based on the compensation coefficient and the estimated make-up water flow rate, obtain the theoretical make-up water flow rate.

[0009] As a preferred solution, the make-up water control method further includes: Obtain the current pressure of the boiler and a pre-calibrated frequency-pressure mapping table. Based on the pre-calibrated frequency-pressure mapping table, obtain the output frequency range of the make-up water frequency converter corresponding to the current pressure of the boiler. The adjusting of the current operating frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter includes: Adjust the current operating frequency of the make-up water frequency converter within the output frequency range based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter.

[0010] As a preferred solution, the make-up water control method further includes: When the current liquid level height is lower than the low-level probe, use the maximum output frequency of the output frequency range as the output operating frequency of the make-up water frequency converter. When the current liquid level height is higher than the high-level probe, use the minimum output frequency of the output frequency range as the output operating frequency of the make-up water frequency converter.

[0011] As a preferred solution, determining the first frequency change amount based on the magnitude relationship between the theoretical fuel flow rate and the theoretical make-up water flow rate includes: When the absolute value of the difference between the theoretical fuel flow rate and the theoretical make-up water flow rate is greater than a preset value, determining the first frequency change amount based on the magnitude relationship between the theoretical fuel flow rate and the theoretical make-up water flow rate.

[0012] As a preferred solution, the make-up water control method further includes: When the second frequency change amounts for consecutive preset times are all positive or all negative, the second frequency change amount increases successively; When the positive and negative of the second frequency change amounts for two adjacent times are different, the second frequency change amount is reset to the initial value.

[0013] As a preferred solution, adjusting the current working frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output working frequency of the make-up water frequency converter further includes: Outputting a third frequency change amount based on the change trend of the theoretical fuel flow rate; Adjusting the current working frequency of the make-up water frequency converter based on the first frequency change amount, the second frequency change amount, and the third frequency change amount to obtain the output working frequency of the make-up water frequency converter.

[0014] In a second aspect, an embodiment of the present specification provides a boiler multi-variable frequency make-up water control system. A low-level probe, a middle-level probe, and a high-level probe are arranged in the boiler. The make-up water control system includes: an acquisition module, a flow calculation module, a liquid level judgment module, and a frequency control module; The acquisition module acquires the current load of the boiler, the current working frequency, and the current power of the make-up water frequency converter; The flow calculation module acquires the theoretical fuel flow rate based on the current load of the boiler; and acquires the theoretical make-up water flow rate based on the current power of the make-up water frequency converter; The liquid level judgment module repeatedly acquires the switch quantity states corresponding to the low-level probe, the middle-level probe, and the high-level probe respectively at a preset time interval, and updates the current liquid level height; When the current liquid level height is higher than the low-level probe and lower than the high-level probe, the frequency control module determines a first frequency change amount based on the magnitude relationship between the theoretical fuel flow rate and the theoretical make-up water flow rate, determines a second frequency change amount based on the height relationship between the current liquid level height and the middle-level probe, and adjusts the current working frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output working frequency of the make-up water frequency converter; wherein, the absolute value of the first frequency change amount is greater than the absolute value of the first frequency change amount; The boiler controls the make-up water pump to supply water through the output working frequency of the frequency converter.

[0015] In a third aspect, an embodiment of this specification provides a computer-readable storage medium storing multiple instructions, which are adapted to be loaded and executed by a processor to perform the steps described in the first aspect of the above embodiments.

[0016] The beneficial effects brought by the technical solutions provided in some embodiments of this specification at least include: 1. The boiler does not need to be equipped with high-cost sensors such as flow meters and modulus liquid level gauges, reducing the number of failure points. During factory acceptance debugging or initial installation, the non-linear relationship between the calibrated load and fuel flow can be stored in the boiler system through a flow meter. Then, the calibrated data can be directly called for variable-frequency water replenishment control during use. Calculate the theoretical values of the corresponding fuel flow and water replenishment flow based on the boiler load and the power of the water replenishment frequency converter, and then combine the switch quantity state of the probe to judge the approximate height of the liquid level, and perform dynamic variable-frequency control on the water replenishment frequency converter to keep the water level near the middle probe. Thus, sacrificing a certain liquid level control accuracy in exchange for a reduction in the production cost of the boiler, balancing cost and accuracy, and improving the economy of small and medium-sized boilers.

[0017] 2. Adjust the water replenishment flow within the optimal operating frequency range corresponding to the steam pressure in the boiler to avoid the water pump operating in a non-efficient area, resulting in situations such as inability to replenish water or large-flow water replenishment.

[0018] 3. Dynamically adjust the magnitude of the second frequency change according to the change of the second frequency change to compensate for the "false water level" phenomenon of the boiler and reduce the amplitude of liquid level fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 is a schematic diagram of the architecture of a commonly used existing boiler system.

[0021] Figure 2 is a schematic flow diagram of a boiler multi-variable frequency water replenishment control method provided by an embodiment of this specification.

[0022] Figure 3 is a schematic structural diagram of a boiler multi-variable frequency water replenishment control system provided by an embodiment of this specification. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Next, the technical solutions in the embodiments of this specification will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of this specification.

[0024] In this specification, terms such as "first", "second", "third", etc. in the description and claims and the above accompanying drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products, or devices.

[0025] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes can be made to the functions and arrangements of the described elements without departing from the scope of the content of this specification. Various processes or components can be appropriately omitted, substituted, or added in each example. For example, the described method can be executed in a different order from the described order, and various steps can be added, omitted, or combined. In addition, the features described in some examples can be combined into other examples.

[0026] In view of the strong dependence on high-cost sensors and the maintenance problems in the existing boiler multi-variable frequency water replenishment control method, there is an urgent need for an innovative control scheme that eliminates sensors, has low cost, and is more robust. Therefore, this application is proposed.

[0027] As Figure 1 shown, Figure 1 is a schematic diagram of the architecture of a commonly used existing boiler system. The accurate liquid level in the boiler steam drum is obtained according to the modulus liquid level gauge, the water replenishment flow rate and the steam flow rate are obtained according to the flow meter, and two or three of the boiler steam drum liquid level, water replenishment flow rate, and steam flow rate are selected for water replenishment control. Generally, the steam drum liquid level is the main regulated quantity, the water replenishment flow rate is the secondary regulated quantity, and the steam flow rate is the feedforward. Then, through PID calculation, the opening of the feed water valve or the variable frequency of the variable frequency converter input to the water replenishment pump is adjusted, so as to achieve the purpose of automatically controlling the steam drum liquid level.

[0028] The three probes can only determine the approximate height range of the liquid level, and cannot know the accurate liquid level height. They can only know whether the water replenishment flow rate needs to be increased or decreased, and cannot determine the increase or decrease amplitude of the water replenishment flow rate. When using PID control, it is usually used as an emergency protection, and the liquid level is mainly obtained through the modulus liquid level gauge.

[0029] Analog liquid level gauge: linearly converts the liquid level height into an electrical signal.

[0030] Probe (switching liquid level gauge): When the liquid level contacts the electrode, the circuit is turned on and the switch signal is triggered.

[0031] Refer to Figure 2 as shown Figure 2 which is a schematic flow chart of a boiler multi-variable frequency water replenishment control method provided by an embodiment of this specification. Among them, a low-level probe, a middle-level probe, and a high-level probe are arranged in the boiler, and the boiler replenishes water through a water replenishment pump controlled by an inverter.

[0032] The water replenishment control method may at least include the following steps: Step 202, obtain the current load of the boiler, the current working frequency, and the current power of the water replenishment inverter; Step 204, obtain the theoretical fuel flow based on the current load of the boiler; Step 206, obtain the theoretical water replenishment flow based on the current power of the water replenishment inverter; Step 208, repeatedly obtain the digital input states corresponding to the low-level probe, the middle-level probe, and the high-level probe respectively at preset time intervals, and update the current liquid level height; Step 210, when the current liquid level height is higher than the low-level probe and lower than the high-level probe, determine the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical water replenishment flow, determine the second frequency change amount based on the height relationship between the current liquid level height and the middle-level probe, and adjust the current working frequency of the water replenishment inverter based on the first frequency change amount and the second frequency change amount to obtain the output working frequency of the water replenishment inverter wherein, the absolute value of the first frequency change amount is greater than the absolute value of the first frequency change amount; The boiler controls the water replenishment pump to replenish water through the output working frequency of the inverter.

[0033] Explanatorily, the load of the boiler refers to the actual steam output per unit time of the boiler, reflecting the output capacity of the boiler. In the control system, it is often expressed as the percentage of the current output relative to the maximum design production capacity. The heat released by fuel combustion is transferred to water through the boiler heating surface to generate steam. The fuel flow is positively correlated with the steam output. Therefore, there is a corresponding relationship between the load of the boiler and the fuel flow, and the approximate theoretical fuel flow can be obtained through the load. The real-time power of the water replenishment inverter is accessed through a 4 - 20 mA signal, and the theoretical water replenishment flow can be calculated through the shaft power formula.

[0034] Illustratively, the current liquid level height refers to the approximate height determined according to the digital input states of each probe, including below the low-level probe (i.e., the low-level probe, the middle-level probe, and the high-level probe are all open), between the middle-level probe and the low-level probe (i.e., the low-level probe is closed, and the middle-level probe and the high-level probe are open), between the middle-level probe and the high-level probe (i.e., the low-level probe and the middle-level probe are closed, and the high-level probe is open), and above the high-level probe (i.e., the low-level probe, the middle-level probe, and the high-level probe are all closed).

[0035] The adjustment range of the output frequency of the water make-up frequency converter corresponds to the flow rate change rate of the make-up water pump. For example, for a 50Hz water pump, the first frequency change is +5% or -5%, the second frequency change is +3% or -3%. A ±5% frequency change is approximately ±2.5Hz, and according to the similarity law, the flow rate change is approximately ±5%.

[0036] It should be noted that the heat released by fuel combustion is transferred to water through the boiler heating surface to generate steam. The fuel flow rate indirectly determines the make-up water volume through the steam output. The make-up water flow rate and the fuel flow rate are dynamically matched according to the energy-mass transfer coefficient (determined by fuel calorific value, boiler efficiency, etc.). The relationship between the theoretical fuel flow rate and the theoretical make-up water flow rate is the equivalent relationship between the two after thermodynamic conversion, so as to roughly judge the increase or decrease of the net make-up water volume.

[0037] The purpose of comparing the current liquid level height with the height of the middle probe is to maintain the liquid level in the boiler steam drum near the height corresponding to the middle probe. When it is lower than the middle level, increase the make-up water flow rate, that is, determine the second frequency change as +3%. When it is higher than the middle level, reduce the make-up water flow rate, that is, determine the second frequency change as -3%. Combine with the rough judgment of the increase or decrease of the net make-up water volume to jointly adjust the output frequency of the make-up water frequency converter. The larger first frequency change is responsible for quickly adjusting the increase or decrease of the net make-up water volume, and the smaller second frequency change is responsible for maintaining the liquid level near the middle height. The stepped output frequency adjustment strategy can not only reduce the fluctuation amplitude of the liquid level near the middle level but also ensure the speed of adjusting the liquid level to the middle height.

[0038] It should be noted that when the actual fuel flow rate increases, there is a certain delay in the change of steam volume. Therefore, there will be a deviation between the theoretical fuel flow rate calculated according to the boiler load and the actual fuel flow rate. At the moment when the fuel increases (0 seconds): the steam flow rate has not changed yet (remains the original value), but the furnace heat load increases, the heat absorption in the water wall increases, and more steam bubbles are generated. The expansion of the bubble volume causes the water level to rise (false water level rising stage). At this time, if the make-up water flow rate is reduced only based on the rising water level, it will exacerbate the subsequent water level drop. After a delay of 15 - 30 seconds: the steam flow rate begins to increase (greater than the original steam flow rate). At this time, since the steam outflow is greater than the feed water inflow (because the make-up water flow rate did not increase in time due to the false water level), the actual water level will begin to drop. The feed water regulation system responds (2 - 5 seconds): when the control system detects the water level change (first rising and then falling), it will adjust the make-up water flow rate. However, due to the existence of the false water level, the initial rising water level may lead to a reduction in the make-up water flow rate, and then when the water level begins to drop, it is necessary to open it wide, which will cause large fluctuations.

[0039] This solution combines the first frequency change amount and the second frequency change amount. When the actual fuel flow increases but the calculated theoretical fuel flow remains unchanged, only a small adjustment is made in response to the liquid level change, limiting the intensity of false actions caused by false water levels. When the steam flow starts to increase, causing a load change and a rapid water level drop, the theoretical fuel flow is greater than the theoretical make-up water flow. Then, for the small frequency reduction adjustment previously made in response to the liquid level rise, a small frequency increase adjustment in response to the liquid level drop and a large frequency increase adjustment in response to the reduction in net make-up water volume are jointly carried out to accelerate the make-up water recovery. Exemplarily, in the false water level rising stage, it is -2%, and in the false water level fading (water level dropping) stage, it is +2% + 5% = +7%.

[0040] Illustratively, during the pre-delivery commissioning and acceptance, the mapping relationships between the boiler load and the fuel flow, and between the power of the make-up water frequency converter and the make-up water flow can be obtained in advance through a modulus liquid level gauge, a flow sensor, etc., and stored in the boiler system. When the boiler is in use, the mapping data is directly called for variable frequency make-up water control, so that the boiler does not need to be equipped with a liquid level gauge and a sensor, balancing the production cost and the control accuracy, and improving the economy of small and medium-sized boilers. It is especially suitable for the transformation of old systems or the scenarios of emerging small boilers.

[0041] In an embodiment of this specification, step 204, obtaining the theoretical fuel flow based on the current load of the boiler, includes: Step 2041, obtaining a pre-calibrated fuel flow-load mapping table; Step 2042, looking up the table based on the current load of the boiler and using the linear interpolation formula to obtain the theoretical fuel flow.

[0042] Explanatorily, the boiler load usually refers to the percentage of the heat generation or steam generation capacity of the boiler relative to its maximum design capacity. Considering the heat balance of the boiler. The heat released by fuel combustion is absorbed by water to generate steam. Assuming a constant boiler efficiency, the fuel flow is proportional to the heat generated, and the heat is proportional to the steam output. Therefore, there may be a direct proportional relationship between the fuel flow and the boiler load. However, in practice, the boiler efficiency may decrease at low loads, resulting in an increase in the fuel consumption rate, so non-linear adjustment is required.

[0043] Exemplarily, the following fuel flow-load mapping table is established, and the real-time flow values of the fuel corresponding to the boiler load changing from 0 to 100% are entered into the table. Load % <![CDATA[Fuel flow rate m 3 > Load % <![CDATA[Fuel flow rate m 3 > 0-10 0-R1 50-60 R5 - R6 10-20 R1 - R2 60-70 R6 - R7 20-30 R2 - R3 70-80 R7 - R8 30-40 R3 - R4 80-90 R8 - R9 40-50 R4 - R5 90-100 R9 - R10

[0044] Overall, a piecewise linear relationship is formed. The linear interpolation formula is used to approximately obtain the theoretical fuel flow for the current load within a certain load range.

[0045] Isl and Ish represent the lower and upper limits of the input range, Osl and Osh are the lower and upper limits of the output range, Ov is the current input value, and Os is the converted output value.

[0046] Through the lightweight method of "table + scaling", the dynamic matching between the boiler load and the theoretical fuel flow is realized, which has both practicality and flexibility.

[0047] In an embodiment of this specification, step 206, obtaining the theoretical makeup water flow based on the current power of the makeup water frequency converter, includes: Step 2061, obtaining a pre-calibrated compensation coefficient; Step 2062, obtaining the estimated makeup water flow corresponding to the current power of the makeup water frequency converter based on the flow formula; Step 2063, obtaining the theoretical makeup water flow based on the compensation coefficient and the estimated makeup water flow.

[0048] Illustratively, the shaft power formula: P = Q×H×ρ×g / 3600 / η, where: P: shaft power (kW), Q: flow rate (m / h), H: head (m), ρ: medium density (taking 1000 kg / m³ for water), g: acceleration due to gravity (9.81 m / s²), η: pump efficiency (%).

[0049] After transformation, we get: Q = P×η×3600 / ρ / g / H = P×η / 2.73 / H.

[0050] Explanatorily, when the frequency of the frequency converter decreases, the pump efficiency η will decrease non-linearly. In this solution, the actual makeup water flow obtained through the measured flowmeter is calibrated with the Q calculated by the above formula to obtain the compensation coefficient LJ. For example, measure the actual makeup water flow at three frequency points of 80%, 50%, and 30%, and fit the correction curve of η changing with frequency. That is, Qb = P×η / 2.73 / H×LJ.

[0051] In an embodiment of this specification, the makeup water control method further includes: Obtaining the current pressure of the boiler and a pre-calibrated frequency-pressure mapping table; Obtaining the output frequency range of the makeup water frequency converter corresponding to the current pressure of the boiler based on the pre-calibrated frequency-pressure mapping table.

[0052] Adjusting the current operating frequency of the makeup water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the makeup water frequency converter, includes: Adjusting the current operating frequency of the makeup water frequency converter within the output frequency range based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the makeup water frequency converter.

[0053] Explanatory, the frequency range of the make-up water pump is limited by the steam pressure in the boiler, so as to avoid the pump running in the non-efficient area and the situation of unable to make up water or large-flow make-up water. When the output frequency of the make-up water frequency converter is greater than the highest frequency of the output frequency range corresponding to the current pressure of the boiler, the highest frequency of the output frequency range is used as the adjusted output frequency; similarly, when the output frequency of the make-up water frequency converter is less than the lowest frequency of the output frequency range corresponding to the current pressure of the boiler, the lowest frequency of the output frequency range is used as the adjusted output frequency.

[0054] Exemplarily, the following fuel flow-load mapping table is established, and the real-time flow values of the fuel corresponding to the change process of the boiler load from 0 to 100% are entered into the table.

[0055] In an embodiment of the present specification, the make-up water control method further includes: Step 210A, when the current liquid level height is lower than the low probe, the maximum output frequency of the output frequency range is used as the output operating frequency of the make-up water frequency converter; Step 210B, when the current liquid level height is higher than the high probe, the minimum output frequency of the output frequency range is used as the output operating frequency of the make-up water frequency converter.

[0056] Explanatory, once the theoretical fuel flow is incorrect, it may lead to insufficient or excessive make-up water. Therefore, it is necessary to combine the switch-type liquid level gauge as a safety backup, such as triggering a protection action at extremely low or high liquid levels.

[0057] In an embodiment of the present specification, determining the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical make-up water flow includes: When the absolute value of the difference between the theoretical fuel flow and the theoretical make-up water flow is greater than a preset value, the first frequency change amount is determined based on the magnitude relationship between the theoretical fuel flow and the theoretical make-up water flow.

[0058] It can be understood that when the make-up water flow is less than the fuel flow or the liquid level is lower than the height of the middle probe, the make-up water frequency needs to be increased to maintain the liquid level stable near the height of the middle probe, and vice versa, the make-up water frequency is reduced. Therefore, when the theoretical fuel flow is greater than the theoretical make-up water flow, the output first frequency change amount is positive, and when the theoretical fuel flow is less than the theoretical make-up water flow, the output first frequency change amount is negative. When the current liquid level height is lower than the middle probe, the output second frequency change amount is positive, and when the current liquid level height is higher than the middle probe, the output second frequency change amount is negative.

[0059] Explanatory, a dead zone is set for the frequency adjustment according to the net make-up water flow, such as triggering an adjustment only when the flow deviation between the theoretical fuel flow and the theoretical make-up water flow exceeds a preset value (such as ±2%).

[0060] Exemplary: At a certain moment, if the theoretical fuel flow rate is greater than the theoretical make-up water flow rate and the current liquid level is higher than the median probe, then the operating frequency is adjusted by +5% + (-3%) = +2%; At a certain moment, if the theoretical fuel flow rate is greater than the theoretical make-up water flow rate and the current liquid level is lower than the median probe, then the operating frequency is adjusted by +5% + 3% = +8%; At a certain moment, if the theoretical fuel flow rate is less than the theoretical make-up water flow rate and the current liquid level is higher than the median probe, then the operating frequency is adjusted by -5% + (-3%) = -8%; At a certain moment, if the theoretical fuel flow rate is less than the theoretical make-up water flow rate and the current liquid level is lower than the median probe, then the operating frequency is adjusted by -5% + 3% = -2%.

[0061] Explanatory, when the flow rate deviation is small, only a small frequency adjustment is made based on the relationship between the liquid level and the height where the median probe is located to maintain the liquid level stability, avoiding a small change in the theoretical make-up water flow rate caused by a small frequency adjustment to maintain the liquid level at the median height, which triggers a large frequency adjustment based on the net make-up water flow rate and results in an increase in the liquid level fluctuation amplitude.

[0062] In an embodiment of the present specification, the make-up water control method further includes: When the second frequency change amounts for consecutive preset times are all positive or all negative, the second frequency change amount increases successively; When the positive and negative of the second frequency change amounts for two adjacent times are different, the second frequency change amount is reset to the initial value.

[0063] Explanatory, there is a delay of about 15 - 30 seconds from the fuel change to the steam flow rate change. After the actual fuel flow rate increases, since the steam flow rate has not changed yet and the boiler load has not changed, the calculated theoretical fuel flow rate has not changed either. However, at this time, the actual required make-up water volume increases. When the liquid level suddenly drops rapidly, a larger second frequency change amount as a compensation mechanism helps to quickly restore the liquid level to the median.

[0064] In an embodiment of the present specification, adjusting the current operating frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter further includes: Outputting a third frequency change amount based on the change trend of the theoretical fuel flow rate; Adjusting the current operating frequency of the make-up water frequency converter based on the first frequency change amount, the second frequency change amount, and the third frequency change amount to obtain the output operating frequency of the make-up water frequency converter.

[0065] Explanatory, when the theoretical fuel flow rate shows a continuous upward / downward trend, an additional third frequency change amount is added to compensate for the large make-up water volume gap or surplus generated during the continuous adjustment of the fuel flow rate, thereby accelerating the adjustment of the make-up water frequency.

[0066] The above describes specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in a different order than in the embodiments and still achieve the desired results. Additionally, the processes depicted in the drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0067] Next, please refer to Figure 3 , Figure 3 which is a schematic structural diagram of a boiler multi-variable frequency water replenishment control system provided by an embodiment of this specification.

[0068] The water replenishment control system includes an acquisition module 301, a flow calculation module 302, a liquid level judgment module 303, and a frequency control module 304; The acquisition module 301 acquires the current load of the boiler, the current operating frequency, and the current power of the water replenishment frequency converter. The flow calculation module 302 obtains the theoretical fuel flow based on the current load of the boiler; and obtains the theoretical water replenishment flow based on the current power of the water replenishment frequency converter. The liquid level judgment module 303 repeatedly acquires the digital quantity states corresponding to the low probe, the middle probe, and the high probe at preset time intervals and updates the current liquid level height. The frequency control module 304, when the current liquid level height is higher than the low probe and lower than the high probe, determines the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical water replenishment flow, determines the second frequency change amount based on the height relationship between the current liquid level height and the middle probe, and adjusts the current operating frequency of the water replenishment frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the water replenishment frequency converter; wherein, the absolute value of the first frequency change amount is greater than the absolute value of the first frequency change amount; The boiler controls the water replenishment pump to replenish water through the output operating frequency of the frequency converter.

[0069] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the key points of each embodiment are the differences from other embodiments. In particular, for the embodiment of the water replenishment control system, since it is basically similar to the embodiment of the water replenishment control method, the description is relatively simple, and the relevant parts can be referred to the corresponding description in the embodiment of the water replenishment control method.

[0070] The embodiments of this specification also provide a computer-readable storage medium. Instructions are stored in the computer-readable storage medium. When the instructions run on a computer or a processor, the computer or the processor is caused to execute one or more steps in the above-described embodiment of the water replenishment control method. If each component module of the above electronic device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium.

[0071] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions according to the embodiments of this specification are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted through a computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center in a wired manner (such as coaxial cable, optical fiber, Digital Subscriber Line (DSL)) or a wireless manner (such as infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or a data center that integrates one or more available media. The available medium can be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a Digital Versatile Disc (DVD)), or a semiconductor medium (for example, a SolidState Disk (SSD)), etc.

[0072] Those of ordinary skill in the art can understand that all or part of the processes in the above-described embodiment methods can be completed by instructing relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above-described method embodiments. The foregoing storage medium includes various media that can store program codes, such as ROM, RAM, magnetic disks, or optical discs. Without conflict, the technical features in this embodiment and the implementation solutions can be combined arbitrarily.

[0073] The above embodiments are only described in the preferred embodiment manner of this specification, and do not limit the scope of this specification. Without departing from the design spirit of this specification, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of this specification shall fall within the protection scope determined by the claims of this specification.

Claims

1. A multi-variable frequency conversion water replenishment control method for a boiler, wherein a low-level probe, a middle-level probe, and a high-level probe are arranged in the boiler, and it is characterized in that, It includes the following steps: Obtain the current load of the boiler, the current operating frequency, and the current power of the make-up water frequency converter; Obtain the theoretical fuel flow based on the current load of the boiler; Obtain the theoretical make-up water flow based on the current power of the make-up water frequency converter; Repeat obtaining the digital input states corresponding to the low-level probe, the middle-level probe, and the high-level probe respectively at preset time intervals, and update the current liquid level height; When the current liquid level height is higher than the low-level probe and lower than the high-level probe, determine the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical make-up water flow, determine the second frequency change amount based on the height relationship between the current liquid level height and the middle-level probe, and adjust the current operating frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter; Wherein, the absolute value of the first frequency change amount is greater than the absolute value of the first frequency change amount; The boiler controls the make-up water pump to supply water through the output operating frequency of the frequency converter.

2. The boiler multi-variable frequency water replenishment control method according to claim 1, characterized in that The obtaining the theoretical fuel flow based on the current load of the boiler includes: Obtain the pre-calibrated fuel flow-load mapping table; Look up the table based on the current load of the boiler, and use the linear interpolation formula to obtain the theoretical fuel flow.

3. A method for controlling multi-variable frequency water replenishment of a boiler according to claim 1, characterized in that, The obtaining the theoretical make-up water flow based on the current power of the make-up water frequency converter includes: Obtain the pre-calibrated compensation coefficient; Obtain the estimated make-up water flow corresponding to the current power of the make-up water frequency converter based on the flow formula; Obtain the theoretical make-up water flow based on the compensation coefficient and the estimated make-up water flow.

4. A boiler multi-variable frequency water replenishment control method according to claim 1, characterized in that, It also includes: Obtain the current pressure of the boiler and the pre-calibrated frequency-pressure mapping table; Obtain the output frequency range of the make-up water frequency converter corresponding to the current pressure of the boiler based on the pre-calibrated frequency-pressure mapping table; The adjusting the current operating frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter includes: Adjust the current operating frequency of the make-up water frequency converter within the output frequency range based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter.

5. A boiler multi-variable frequency water replenishment control method according to claim 4, characterized in that, It also includes: When the current liquid level height is lower than the low-level probe, use the maximum output frequency of the output frequency range as the output operating frequency of the make-up water frequency converter; When the current liquid level height is higher than the high-level probe, use the minimum output frequency of the output frequency range as the output operating frequency of the make-up water frequency converter.

6. A method for controlling multi-variable frequency water replenishment of a boiler according to claim 1, characterized in that, The determining the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical make-up water flow includes: Determine the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical make-up water flow when the absolute value of the difference between the theoretical fuel flow and the theoretical make-up water flow is greater than a preset value.

7. A boiler multi-variable frequency water replenishment control method according to claim 6, characterized in that It also includes: When the second frequency change amounts for consecutive preset times are all positive or all negative, the second frequency change amount increases successively; When the positive and negative signs of the second frequency change amounts for two adjacent times are different, the second frequency change amount is reset to the initial value.

8. A method for controlling multi-variable frequency water replenishment of a boiler according to claim 1, characterized in that, The adjusting the current operating frequency of the make-up water frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the make-up water frequency converter also includes: Output a third frequency change amount based on the change trend of the theoretical fuel flow; Adjust the current operating frequency of the water replenishment frequency converter based on the first frequency change amount, the second frequency change amount, and the third frequency change amount to obtain the output operating frequency of the water replenishment frequency converter.

9. A control system applying the boiler multi-variable frequency water replenishment control method as described in claim 1, wherein a low-level probe, a middle-level probe and a high-level probe are arranged in the boiler, characterized in that, It includes an acquisition module, a flow calculation module, a liquid level judgment module, and a frequency control module; The acquisition module acquires the current load of the boiler, the current operating frequency, and the current power of the water replenishment frequency converter; The flow calculation module obtains the theoretical fuel flow based on the current load of the boiler; obtains the theoretical water replenishment flow based on the current power of the water replenishment frequency converter; The liquid level judgment module repeatedly acquires the digital input states corresponding to the low probe, the middle probe, and the high probe respectively at preset time intervals and updates the current liquid level height; The frequency control module, when the current liquid level height is higher than the low probe and lower than the high probe, determines the first frequency change amount based on the magnitude relationship between the theoretical fuel flow and the theoretical water replenishment flow, determines the second frequency change amount based on the height relationship between the current liquid level height and the middle probe, and adjusts the current operating frequency of the water replenishment frequency converter based on the first frequency change amount and the second frequency change amount to obtain the output operating frequency of the water replenishment frequency converter; wherein, the absolute value of the first frequency change amount is greater than the absolute value of the first frequency change amount; The boiler controls the water replenishment pump to replenish water through the output operating frequency of the frequency converter.

10. A computer-readable storage medium, on which a computer program is stored, and instructions are stored in the computer-readable storage medium. When the instructions are run on a computer or a processor, the computer or the processor is caused to execute the steps of the method according to any one of claims 1-8.

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