Heat balance heating method for dynamic water inlet and outlet of water storage type boiler

Abstract

The invention belongs to the technical field of boiler temperature control, and particularly relates to a water storage type boiler dynamic water inlet and outlet heat balance heating method which comprises the steps that the heating state of a boiler is judged, the situation that the boiler is in a two-time heating balance steady state is obtained, and the accumulated water inlet amount and the accumulated heating duration when the boiler is in the two-time heating balance steady state are calculated; calculating the continuous heating time required for reaching the preset temperature at present according to the water inlet temperature, the dynamic water inlet amount and the preset temperature of the boiler by utilizing a heat balance principle; and calculating the basic heating power of the boiler according to the calculated continuous heating time. The accuracy and the stability of the boiler temperature are ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of boiler temperature control, and in particular relates to a heat balance heating method for dynamic inlet and outlet water of a water storage boiler. Background Art

[0002] The PID algorithm in the hot water heating process is a very commonly used control algorithm. The basic principle is to calculate the output control signal of the heating equipment based on the current actual detection temperature and the preset temperature through proportional-deviation value, integral-deviation accumulation, and differential-deviation slope. In controlling the dynamic water inlet and outlet and heating of the boiler, the conventional PID algorithm has some obvious disadvantages:

[0003] 1. The PID control algorithm uses only temperature as the signal feedback, and does not make good use of other variables in the dynamic water inlet and heating process, affecting the overall performance;

[0004] 2. The differential part predicts the temperature change trend and responds in advance; however, due to differences in temperature distribution, heat conduction, temperature detection elements, etc. inside the boiler, high-frequency interference may occur, resulting in instability in actual control;

[0005] 3. Due to the large setting range of boiler temperature, the deviation in the actual control process may also be large, which may easily lead to saturation overshoot and large overshoot.

[0006] In this regard, the current general platform coffee machine water storage boiler heating control mainly adopts the "improved PID + flow rate compensation" algorithm, which is an adjustment of the conventional PID algorithm in a specific application environment. The main improvements are as follows:

[0007] 1. For the problem of sudden interference of differential items, a longer filtering and averaging time is used to reduce interference and limit the maximum differential value;

[0008] 2. Weak integral calculation, only when the deviation is small and exists for a long time, the integral calculation is performed to eliminate the static error and avoid excessive overshoot caused by premature integration. (The early algorithm did not have an integral term, mainly considering the simplicity of the algorithm and reducing overshoot; later it was found that sometimes small deviations took a long time to eliminate, so the separated integration method was adopted);

[0009] 3. For the case where the temperature detection lag is obvious and the feedback signal of the control process is only the temperature problem, the heating compensation of flow rate is added. That is, according to the current flow rate of the water entering the boiler, a relatively safe proportion of heating output is made in advance before the temperature is detected to increase the response speed of the system.

[0010] For the water storage boiler heating system, the "improved PID + flow rate compensation" improves the response speed and reduces the degree of overshoot to a certain extent compared with the traditional PID. It is an adaptation and improvement of the conventional PID in the application environment of hot water boilers; it can speed up the response speed and optimize the control deviation to a certain extent, making it significantly more practical in a specific environment. However, the current "improved PID + flow rate compensation" heating method still has some unsatisfactory aspects:

[0011] 1. The actual temperature still has a large overshoot phenomenon;

[0012] 2. Since the flow rate compensation is based on the current flow rate, it will not work after the water inlet stops and cannot cover the entire process. That is, after the water stops, heating cannot be performed when the temperature detection reaches the set value but the actual temperature of the water below the sensor is lower;

[0013] 3. The flow rate compensation heating control output is based on the preset inlet water temperature, which may be significantly different from the actual water temperature; and for the sake of the safe and controllable range of heating, a relatively conservative proportional coefficient is set, which weakens the actual compensation effect.

[0014] The data is roughly as follows:

[0015] 1. In the continuous production process, the temperature is prone to overshoot by more than 3° (the actual temperature exceeds the preset temperature, and the excess value reaches 3°), and in some cases it may be 4-5° (Note: When the product is on standby or intermittently produced, such as making a cup every few minutes, the boiler temperature control accuracy is very high, and the general error is within 1°).

[0016] 2. In terms of heating timeliness, the effective utilization rate is generally expected to be around 80%-90% (the utilization rate is closely related to the water volume and flow rate of a single product; if the single cup is more than 200ml each time, the heating time utilization rate can be as high as over 90%).

[0017] 3. The fluctuation of water volume is due to uneven heating, and an error of about 5-10 ml may occur. Summary of the invention

[0018] The problem to be solved by the present invention is: to optimize the shortcomings of the heating method of the background technology "improved PID+flow rate compensation" and to improve the stability, timeliness and uniformity of heating.

[0019] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0020] A heat balance heating method for dynamic inlet and outlet water of a water storage boiler comprises the following steps:

[0021] Determine the heating state of the boiler, obtain the boiler in two heating equilibrium steady states, and calculate the cumulative water intake and cumulative heating time between the two heating equilibrium steady states;

[0022] Using the heat balance principle, the continuous heating time required to reach the preset temperature is calculated through the inlet water temperature, dynamic inlet water volume and the preset temperature of the boiler.

[0023] Based on the calculated continuous heating time, the basic heating power of the boiler is calculated.

[0024] Furthermore, the heating state of the boiler is determined based on parameters including the current temperature, water intake, and heating time of the boiler.

[0025] Furthermore, the heating state of the boiler includes an initialization state, an initial water inlet state, a heating balance steady state, a water inlet not reaching a threshold state, and a water inlet sufficient state.

[0026] Furthermore, the heating balance steady state indicates that the water inlet of the boiler has reached the set water level threshold, and the heating and heat dissipation of the boiler have reached a balance, and the temperature is stable within the expected range.

[0027] Furthermore, the method further comprises the following steps:

[0028] Calculate the difference between the actual boiler temperature and the preset temperature as the proportional part of the PID controller;

[0029] Calculate the rising slope of boiler temperature as the differential part of PID controller;

[0030] Calculate the boiler inlet water flow rate heating power according to the boiler inlet water flow rate and the characteristics of the hot and cold channels of the inlet water;

[0031] According to the PD algorithm, the heating output power of the boiler is calculated by combining the proportional part P and the differential part D, as well as the heating power of the inlet water flow rate;

[0032] Using the heat balance principle, the required comprehensive heating power is calculated based on the continued heating time required to reach the preset temperature and the heating output power.

[0033] Furthermore, heating output power = Kp×P+Kd×D+inlet water flow rate heating power, where Kp and Kd are proportional and differential control coefficients, respectively.

[0034] Furthermore, the method further comprises the following steps:

[0035] When the boiler temperature rises slowly and is in a non-water-intake state, the integral part I of the boiler temperature difference is calculated, and the integral part I is used to perform heating compensation as the error integral compensation of the boiler temperature difference.

[0036] Furthermore, the integral part I represents the cumulative effect of the difference between the actual boiler temperature and the preset temperature. Through integral control, the heating power is gradually adjusted to eliminate the temperature deviation.

[0037] Furthermore, the method further comprises the following steps: calculating the final executed heating power according to the flicker limit, the maximum temperature limit, the minimum heating time limit, the heating stagger requirement, and the error integral compensation of the boiler.

[0038] Further, the heating power is expressed as a heating duty cycle, that is, the ratio of the time the heating element is turned on to the total time.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The present invention is based on the principle of "heat balance". It uses real-time judgment of the inlet water temperature and the amount of water to be heated, performs heating before the temperature detection reaction, and stops heating before the temperature judgment. "Heat balance" has the characteristics of "full process, closed-loop feedback, and main algorithm". It calculates the cumulative inlet water volume and cumulative heating time between two heating equilibrium steady states of the boiler, and uses the heat balance principle to calculate the continued heating time required to reach the preset temperature, ensuring the accuracy and stability of the boiler temperature.

[0041] Through the "heat balance" algorithm, the present invention achieves uniform heating of the incoming water, thereby improving the stability of the outgoing water volume. In the continuous production process, the temperature overshoot is basically controlled within 2°, occasionally reaching about 3°; in standby or intermittent production, the temperature error is kept within 1°.

[0042] 2. Due to the higher advance heating reaction speed and effective utilization of relevant data, it brings higher heating time window utilization (faster continuous production capacity) and smaller temperature fluctuation. The comprehensive effective time window utilization rate reaches about 85%-95%. It realizes precise control of the boiler heating process. It avoids overheating or underheating and improves heating efficiency.

[0043] 3. According to the required continuous heating time, combined with the heating output power, the required heating power is comprehensively calculated. The accuracy and stability of the boiler outlet water temperature are ensured by dynamically adjusting the heating output power and calculating the required continuous heating time.

[0044] 4. The present invention calculates the heating output power of the boiler through the PD algorithm and the water inlet conditions. The heating output power is dynamically adjusted according to the current heating demand and water inlet conditions, making the heating process more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of a PID algorithm of the prior art;

[0046] Figure 2 It is a flow chart of the heat balance heating method of the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be clearly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the protection scope of the present invention.

[0048] The present invention is based on the PID algorithm. The logic module of the PID algorithm consists of three parts: a proportional part (P), an integral part (I), and a differential part (D). Figure 1 As shown,

[0049] Proportional parameter: The output of the controller is proportional to the input deviation value. Once the system has a deviation, the proportional adjustment will immediately take effect to reduce the deviation. The process is simple and fast, and the proportional effect is large, which can speed up the adjustment and reduce the error; however, it will reduce the stability of the system, causing instability and residual error.

[0050] Integral parameters: The integral link is mainly used to eliminate static error. The so-called static error is the difference between the output value and the set value after the system stabilizes. The integral link is actually a process of accumulating deviations. The accumulated error is added to the original system to offset the static error caused by the system.

[0051] Differential parameter: The differential signal reflects the changing law, or changing trend, of the deviation signal. Advance adjustment is performed based on the changing trend of the deviation signal, thereby increasing the rapidity of the system.

[0052] The PID control algorithm is a widely adaptable algorithm. For occasions with large time constants or large lags, it is a control method with good versatility, relatively simple logic, and guaranteed basic performance.

[0053] Example

[0054] like Figure 2 As shown, the present invention provides a heat balance heating method for dynamic inlet and outlet water of a water storage boiler, comprising the following steps:

[0055] The difference between the actual temperature of the boiler and the preset temperature is calculated as the ratio P of the PID controller.

[0056] Calculate the rising slope of the boiler temperature as the differential part D of the PID controller.

[0057] According to the boiler inlet water flow rate, the cold and hot channels of the inlet water are distinguished, and the characteristics of the cold and hot channels, such as heat transfer coefficient, heat capacity, etc., are determined to calculate the boiler inlet water flow rate heating power.

[0058] According to the PD algorithm, the heating output power of the boiler is calculated by combining the proportional part P and the differential part D, as well as the heating power of the inlet water flow rate; that is, the heating output power = Kp×P+Kd×D+inlet water flow rate heating power, where Kp and Kd are the control coefficients of the proportion and differential respectively.

[0059] According to the current temperature, water inlet, heating time and other parameters of the boiler, the heating state of the boiler is judged, and the initialization state of the boiler is set to 0, the initial water inlet state is set to 1, the heating balance steady state is set to 2, the water inlet does not reach the threshold state is set to 3, and the water inlet is sufficient state is set to 4.

[0060] The initialization state (0) means that the boiler has just started to work and all parameters are not set or are at default values;

[0061] The judgment condition is that all relevant parameters (such as temperature, water intake, heating time) are initial values ​​or undefined values.

[0062] The initial water inflow state (1) indicates that the boiler begins to inflow water, but has not yet reached the set water level threshold;

[0063] The judgment condition is that the water inflow is less than the set water level threshold and the boiler has not started heating (or the heating time is very short and can be regarded as not started).

[0064] The water inflow not reaching the threshold state (3) means that the boiler is in the heating process, but the water inflow has not yet reached the set water level threshold;

[0065] The judgment condition is that the water inflow is less than the set water level threshold and the boiler has been heated for a period of time (the heating time exceeds a certain threshold).

[0066] The sufficient water inflow state (4) indicates that the water inflow of the boiler has reached or exceeded the set water level threshold and the boiler is heating;

[0067] The judgment condition is that the water inflow reaches or exceeds the set water level threshold and the boiler is heating (the heating time exceeds a certain threshold).

[0068] Heating equilibrium steady state (2) means that the water inflow of the boiler has reached the set water level threshold, and the heating and heat dissipation of the boiler have reached a balance, and the temperature is stable within a certain range;

[0069] The judgment conditions are that the water intake reaches or exceeds the set water level threshold, the boiler has been heated for a period of time (the heating time is long enough to make the temperature change tend to be stable), and the current temperature is within a preset stable range.

[0070] The state of boiler heating twice is obtained as a heating equilibrium steady state. Between the two heating equilibrium steady states, the cumulative water intake and the cumulative heating time are recorded and calculated.

[0071] Using the heat balance principle, the inlet water temperature is calculated through the cumulative water inflow between two heating equilibrium steady states, the cumulative heating time, the boiler power and the actual temperature of the boiler at heating equilibrium.

[0072] Using the heat balance principle, the continuous heating time required to reach the preset temperature is calculated through the inlet water temperature, dynamic inlet water volume and the preset temperature of the set boiler.

[0073] The required heating power is calculated based on the required continuous heating time and the heating output power provided by the PD algorithm.

[0074] When the boiler temperature rises slowly and is not in the water-intake state, the integral part I of the boiler temperature difference is calculated and used for heating compensation. The integral part I represents the cumulative effect of the difference between the actual boiler temperature and the preset temperature, which serves as the error integral compensation of the boiler temperature difference. Through integral control, the heating power is gradually adjusted to eliminate temperature deviation.

[0075] The final heating power (reflected as the heating duty cycle) is calculated based on the boiler's flicker limit, maximum temperature limit, minimum heating time limit, heating stagger requirements, etc., as well as error integral compensation.

[0076] The temperature deviation is corrected according to the flicker limit, maximum temperature limit, minimum heating time limit, heating staggered requirements, etc., as well as error integral compensation, and the final executed heating power (reflected as the heating duty cycle) is calculated. This heating power is expressed as the heating duty cycle, that is, the ratio of the time the heating element is turned on to the total time.

[0077] Flicker limiting, or flicker limiting, is intended in a heating system to prevent frequent changes in heating power, thereby avoiding unnecessary shocks to the system and reducing possible flickering or instability.

[0078] The present invention dynamically calculates the inlet water temperature according to the boiler temperature, boiler power, heating time, temperature overshoot and other conditions, and then conversely calculates the required heating time according to the inlet water temperature, inlet water volume and other conditions; and the two form a closed-loop feedback, which can correct the actual situation (such as changes in ambient temperature, differences in the actual effective power of the boiler, etc.).

[0079] Preliminary self-test, comparing the "heat balance + PID correction" of the present invention with the original "improved PID + flow compensation", tested in terms of "temperature stability, heating speed", the test results are shown in Table 1, it can be seen that the temperature overshoot has been significantly reduced. A simple test was conducted on the heating speed (timeliness), in which, for the machine model ESFB4C instant 100ml, the maximum speed was used to continuously make 10 cups, the total time using the original heating logic was 2 minutes and 21 seconds, and the new heating logic was 2 minutes and 10 seconds.

[0080] Table 1

[0081]

[0082] The machine model is BTC7C instant 100ml, and the maximum speed is to make 8 cups continuously. The total time of the original heating logic is 2 minutes and 20 seconds; the new heating logic is 1 minute and 50 seconds. The test results are shown in Table 2.

[0083] Table 2

[0084]

[0085]

[0086] The improved PID+flow rate compensation, through adaptation and improvement, also has obvious limitations in overall performance in terms of "temperature stability, water volume fluctuation, and heating speed". The "heat balance+PID correction" of the present invention is another idea. The core algorithm is directly based on the dynamic balance of heat input and output. It is a precise control method, so the upper limit of performance is higher.

[0087] The heating method of the present invention is based on the principle of "heat balance" and realizes precise regulation of the heating process through real-time monitoring and control. Compared with the current heating method, this method shows significant performance improvement in temperature stability, heating timeliness and water volume accuracy.

[0088] The above technical features constitute the best embodiment of the present invention, which has strong adaptability and best implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the needs of different situations.

[0089] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A heat balance heating method for dynamic inlet and outlet water of a water storage boiler, characterized in that: The steps include: Determine the heating state of the boiler, obtain the boiler in two heating equilibrium steady states, and calculate the cumulative water intake and cumulative heating time between the two heating equilibrium steady states; Using the heat balance principle, the continuous heating time required to reach the preset temperature is calculated through the inlet water temperature, dynamic inlet water volume and the preset temperature of the boiler. Based on the calculated continuous heating time, the basic heating power of the boiler is calculated.

2. The heat balance heating method according to claim 1, characterized in that: The heating status of the boiler is determined based on parameters including the current temperature, water intake, and heating time of the boiler.

3. The heat balance heating method according to claim 1, characterized in that: The heating state of the boiler includes the initialization state, the initial water inlet state, the heating balance steady state, the water inlet not reaching the threshold state and the water inlet sufficient state.

4. The heat balance heating method according to claim 1, characterized in that: The heating balance steady state means that the water inlet of the boiler has reached the set water level threshold, and the heating and heat dissipation of the boiler have reached a balance, and the temperature is stable within the expected range.

5. The heat balance heating method according to claim 1, characterized in that: The following steps are also included: Calculate the difference between the actual boiler temperature and the preset temperature as the proportional part of the PID controller; Calculate the rising slope of boiler temperature as the differential part of PID controller; Calculate the boiler inlet water flow rate heating power according to the boiler inlet water flow rate and the characteristics of the hot and cold channels of the inlet water; According to the PD algorithm, the heating output power of the boiler is calculated by combining the proportional part P and the differential part D, as well as the heating power of the inlet water flow rate; Using the heat balance principle, the required comprehensive heating power is calculated based on the continued heating time required to reach the preset temperature and the heating output power.

6. The heat balance heating method according to claim 5, characterized in that: Heating output power = Kp×P+Kd×D+inlet water flow rate heating power, where Kp and Kd are the proportional and differential control coefficients respectively.

7. The heat balance heating method according to claim 5, characterized in that: The following steps are also included: When the boiler temperature rises slowly and is in a non-water-intake state, the integral part I of the boiler temperature difference is calculated, and the integral part I is used to perform heating compensation as the error integral compensation of the boiler temperature difference.

8. The heat balance heating method according to claim 7, characterized in that: The integral part I represents the cumulative effect of the difference between the actual boiler temperature and the preset temperature. Through integral control, the heating power is gradually adjusted to eliminate the temperature deviation.

9. The heat balance heating method according to claim 7, characterized in that: The method also includes the following steps: calculating the final heating power according to the flicker limit, the maximum temperature limit, the minimum heating time limit, the heating stagger requirement, and the error integral compensation of the boiler.

10. The heat balance heating method according to claim 9, characterized in that: The heating power is expressed as the heating duty cycle, which is the ratio of the time the heating element is on to the total time.

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