An automatic control system for a central heating heat exchange station and its design method

Abstract

The present invention belongs to the technical field of heat exchange station control systems, and particularly relates to a centralized heating heat exchange station automatic control system and its design method. The system is composed of a primary heat network circulation system, a secondary heat network circulation system, a data acquisition and processing module, and an automatic control module. The design method realizes the automatic switching of the feed-forward - feedback control quantity adjustment and the feedback control quality adjustment of the secondary side heat network through a switching switch according to the changes in weather conditions by collecting and analyzing analog quantity parameters such as meteorological parameters, fluid pressure, and fluid temperature in the weather forecast in real time. The automatic control of the constant temperature difference between the supply and return water of the secondary side heat network of the heat exchange station is realized through a PID controller, so as to keep the heat supply matched with the heating load, ensure the thermal balance of the heat network, and realize the economic and reliable operation of the heat exchange station.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat exchange station control systems, and particularly relates to a centralized heating heat exchange station automatic control system and its design method. Background Art

[0002] The heat exchange station is the hub and core of the centralized heating system, and is the bridge and link between the heat source and heat users. The main task of the heat exchange station control system is to timely adjust the operating state of the heat exchange station according to the change of the heat load, meet the heat demand of users, and ensure that the indoor temperature of heat users is maintained within a certain range.

[0003] In the past, in order to make up for a series of heating quality problems such as local overheating, local non-heating, and vertical thermal imbalance in the heating area caused by hydraulic imbalance, the heat exchange station usually adopted the "large flow rate and small temperature difference" operation mode, resulting in low efficiency of the heating system and high heating energy consumption. At present, the heat exchange station is basically equipped with an automatic control system, but most heat exchange stations still rely on the experience of operating personnel to manually set various adjustment parameters. When the climate changes abnormally and the temperature fluctuates greatly, the phenomenon that the heat supply does not match the demand of heat users still widely exists.

[0004] Therefore, on the premise of ensuring the comfort of heat users, scientifically and reasonably adjusting and controlling the operation of the heat exchange station can effectively improve the heating efficiency, reduce the energy consumption of the heating system, reduce energy waste, and has great economic value and social benefits. Summary of the Invention

[0005] The present invention proposes a centralized heating heat exchange station automatic control system. The control system is composed of a primary side circulation system of the heat network, a secondary side circulation system of the heat network, a data acquisition and processing module, and an automatic control module; wherein, the data acquisition and processing module is composed of an air temperature and flow conversion unit and two subtractors; the automatic control module is composed of a subtractor, an adder, a changeover switch, and two PID controllers.

[0006] In the described primary side circulation system of the heat network, the high-temperature hot water provided by the heat source is transported to the heat exchange station through the primary side supply pipeline of the heat network. An electric control valve is installed on the primary side supply pipeline of the heat network, which can change the flow rate of the high-temperature hot water in the primary side supply pipeline of the heat network; in the heat exchange station, the high-temperature hot water transported by the primary side supply pipeline of the heat network enters the plate heat exchanger, and exchanges heat with the circulating water on the secondary side of the heat network in the plate heat exchanger. The cooled primary side return water of the heat network passes through the primary side circulation water pump installed on the primary side return pipeline of the heat network, and returns to the heat source through the primary side return pipeline of the heat network.

[0007] In the described secondary side circulation system of the heat network, after the secondary side circulating water of the heat network absorbs heat in the plate heat exchanger, the heat is transferred to heat users through the secondary side supply water pipeline of the heat network from the outlet of the plate heat exchanger. Temperature sensors and pressure sensors are installed on the secondary side supply water pipeline of the heat network to measure the temperature and pressure of the circulating water in the supply water pipeline; the cooled return water returns to the plate heat exchanger via the secondary side return water pipeline through the secondary side circulating water pump installed on the secondary side return water pipeline of the heat network. Temperature sensors and pressure sensors are installed on the secondary side return water pipeline of the heat network to measure the temperature and pressure of the circulating water in the secondary side return water pipeline of the heat network.

[0008] The described data acquisition and processing module collects in real time the temperature and pressure signals of the secondary side supply water and return water of the heat network, as well as obtains the outdoor atmospheric temperature and wind speed information from the weather forecast by connecting to the Internet; the temperature sensors on the secondary side supply water pipeline and return water pipeline of the heat network are connected to the first subtractor to obtain the secondary side supply-return water temperature difference signal Δt; the pressure sensors on the secondary side supply water pipeline and return water pipeline of the heat network are connected to the second subtractor to obtain the secondary side supply-return water pressure difference signal Δp; the outdoor atmospheric temperature and wind speed information are connected to the air temperature and flow conversion unit to obtain the flow rate of the secondary side circulation loop of the heat network required to meet the heat supply of heat users, which is used as the adjustment amount of the feedforward loop for the quantity adjustment control of the heat exchange station system; the outputs OUT1, OUT2, and OUT3 of the data acquisition and processing module are respectively connected to the automatic control module IN1, IN2, and IN3.

[0009] The described automatic control module connects the secondary side supply-return water temperature difference signal Δt output by the data acquisition module and the set value of the secondary side supply-return water temperature difference of the heat network to the third subtractor to obtain the automatic control feedback deviation signal Error; the secondary side supply-return water pressure difference signal Δp output by the data acquisition module is connected to the switching switch. When the secondary side supply-return water pressure difference signal Δp is within the normal value range, the output terminal OUT4 of the switching switch is connected to the input terminal of the first PID controller. The output of the first PID controller is connected to the frequency converter, and the output of the frequency converter is connected to the secondary side circulating water pump to realize the quantity adjustment control of the heat exchange station system; when the secondary side supply-return water pressure difference signal Δp reaches the upper limit value or the lower limit value, the output terminal OUT5 of the switching switch is connected to the input terminal of the second PID controller, and the output of the second PID controller is connected to the primary side electric control valve of the heat network to realize the quality adjustment control of the heat exchange station system.

[0010] A design method for an automatic control system of a central heating heat exchange station proposed by the present invention is to collect analog parameters such as meteorological parameters, fluid pressure, and fluid temperature in the weather forecast in real time. After analyzing and processing these real-time collected analog parameters, the automatic switching between the feed-forward-feedback quantity regulation control and the feedback quality regulation control on the secondary side of the heat network is realized through a switching switch, and the automatic control of the constant temperature difference between the supply and return water of the secondary side of the heat network of the heat exchange station is realized through a PID controller. The specific steps include:

[0011] (1) Quantity regulation control of the heat exchange station system

[0012] 1. Feed-forward control

[0013] Since there is a large thermal inertia in the heat supply source, the heat supply network, and the building, the influence of the changes in meteorological parameters and heat supply parameters such as the supply water temperature and supply water flow on the room temperature of heat users will have a long lag time. To ensure the design requirements of the room temperature of heat users, when adjusting the operation of the heat supply network, pre-adjustment must be considered, that is, there is a reasonable time difference between the change of the adjustment plan and the change of the indoor temperature. According to the weather forecast information, predict the heat supply load, adjust the operation conditions of the heat exchange station in a timely and reasonable manner, realize the optimal dispatching of the system, reduce the lag time of the heat network, ensure the heating quality, and achieve the purpose of energy conservation and environmental protection.

[0014] Meteorological parameters are the basis for the design and adjustment of the entire central heating system. The main meteorological parameters affecting the building heat load and the operation adjustment strategy of the heat supply system are the outdoor air temperature and wind speed, etc. With the continuous development of meteorological prediction technology, the prediction accuracy has been steadily improved, and the meteorological forecast information service based on Internet technology has become increasingly perfect. The outdoor comprehensive temperature is obtained by correcting the outdoor air temperature with the wind speed information in the weather forecast

[0015] t w = 35.74 + 0.6215×t - 35.75×v 0.16 + 0.4275×t×v 0.16 (1)

[0016] Among them, t w is the outdoor comprehensive temperature, in °C; t is the air temperature in the weather forecast, in °C; v is the wind force level in the weather forecast, in m / s.

[0017] Under stable conditions, the heat supply delivered by the heat exchange station is equal to the heating load of the heat users

[0018] cG(t g - t h ) = q v V(t n - t w ) (2)

[0019] Among them, c is the specific heat capacity of hot water, with the unit J / (kg·℃); G is the circulating flow rate on the secondary side of the heat network, with the unit kg / s; t g is the supply water temperature on the secondary side of the heat network, with the unit ℃; t h is the return water temperature on the secondary side of the heat network, with the unit ℃; q v is the building heating volume, with the unit W / m 3 ·℃; V is the external surface volume of the building, with the unit m 3 ; t n is the indoor calculated temperature for winter heating, with the unit ℃.

[0020] Under the condition of constant temperature difference between the supply and return water on the secondary side of the heat network, that is, (t g -t h ) remains unchanged. When the outdoor comprehensive temperature t w changes, to keep the heat supply and heat load balanced, only the circulating flow rate G on the secondary side of the heat network needs to be adjusted, that is, through frequency conversion adjustment, the method of changing the flow rate of the secondary side circulating water pump is used to achieve energy saving.

[0021] Through Equation (1) and Equation (2), the change relationship between meteorological parameters and the flow rate of the secondary side circulating water pump can be obtained. The outdoor air temperature and wind speed information in the weather forecast are connected to the data acquisition and processing module. After being converted by the temperature-flow conversion unit, the output end OUT1 of the data acquisition and processing module is connected to the automatic control module IN1. After passing through the adder, the output end OUT6 of the automatic control module is connected to the frequency converter, serving as the feedforward control in the control loop of the secondary side circulating water pump, adjusting the output frequency of the frequency converter, and then changing the circulating flow rate on the secondary side of the heat network; adjusting the secondary side of the heat network in advance through the meteorological parameters in the weather forecast can effectively reduce the comfort of the indoor environment of heat users caused by the hysteresis of the heating system.

[0022] 2. Feedback control

[0023] When the weather forecast information does not match the actual meteorological parameters, through the rough adjustment of the feedforward control, the temperature difference between the supply and return water on the secondary side of the heat network changes, generating a deviation Error from the set value of the temperature difference between the supply and return water. The deviation Error is connected to the input end of the first PID controller via the changeover switch. After operations of proportional P, integral I, and differential D, the output of the first PID controller passes through the adder, and the output end OUT6 of the automatic control module is connected to the frequency converter, changing the output frequency of the frequency converter, and then adjusting the circulating flow rate on the secondary side of the heat network to eliminate the deviation Error, and finally making the temperature difference between the supply and return water on the secondary side of the heat network equal to the set value.

[0024] When the operating conditions of the primary side of the heat network change or are disturbed, the supply water temperature of the primary side of the heat network changes, and the supply water temperature of the secondary side of the heat network also changes, which in turn leads to a change in the temperature difference between the supply and return water on the secondary side of the heat network. The deviation Error generated between the temperature difference between the supply and return water on the secondary side of the heat network and the set value enters the first PID controller via the changeover switch. After proportional P, integral I, and derivative D operations, the output of the first PID controller passes through an adder, and the output terminal OUT6 of the automatic control module is connected to the frequency converter, changing the output frequency of the frequency converter, thereby changing the flow rate of the circulating water pump on the secondary side of the heat network. After adjustment and stabilization, the deviation Error is eliminated, and the temperature difference between the supply and return water on the secondary side of the heat network is consistent with the set value.

[0025] (2) Quality regulation control of the heat exchange station system

[0026] In the early cold period or the late cold period, when the outdoor temperature is relatively high and the circulating flow rate on the secondary side of the heat network is small, to ensure that there is no thermal imbalance in the indoor heating system, when the pressure difference between the supply and return water pipes on the secondary side of the heat network reaches the lower limit set value, the secondary side circulating water pump will maintain a certain rotational speed unchanged, the changeover switch acts, and the adjustment object of the automatic control system of the heat exchange station changes from the secondary side circulating water pump to the electric control valve on the supply water pipe of the primary side of the heat network. The automatic control of the heat exchange station system is converted from quantity regulation to quality regulation. The deviation Error between the measured value of the temperature difference between the supply and return water pipes on the secondary side of the heat network and the set value of the temperature difference between the supply and return water pipes on the secondary side of the heat network is connected to the second PID controller from the output terminal OUT5 of the changeover switch. After proportional P, integral I, and derivative D operations, the output terminal of the second PID controller is connected to the electric control valve on the supply water pipe of the primary side of the heat network, reducing the opening of the electric control valve on the primary side of the heat network, reducing the flow rate of the supply water pipe on the primary side of the heat network, and thereby reducing the supply water temperature on the secondary side of the heat network to ensure the balance between the heat supply delivered by the heat exchange station and the heating heat load of the heat users.

[0027] In the severe cold period, when the outdoor temperature is low, the secondary side circulating water pump reaches the rated rotational speed, the pressure difference between the supply and return water pipes on the secondary side of the heat network reaches the upper limit set value, and the actual measured value of the temperature difference between the supply and return water is still lower than the set value, and the heat supply delivered by the heat exchange station cannot meet the heating heat load of the heat users. The changeover switch acts, and the adjustment object of the automatic control system of the heat exchange station changes from the secondary side circulating water pump to the electric control valve on the supply water pipe of the primary side of the heat network. The automatic control of the heat exchange station system is converted from quantity regulation to quality regulation. The deviation Error between the measured value of the temperature difference between the supply and return water pipes on the secondary side of the heat network and the set value of the temperature difference between the supply and return water pipes on the secondary side of the heat network is connected to the second PID controller from the output terminal OUT5 of the changeover switch. After proportional P, integral I, and derivative D operations, the output terminal of the second PID controller is connected to the electric control valve on the supply water pipe of the primary side of the heat network, increasing the opening of the electric control valve on the primary side of the heat network, increasing the flow rate of the supply water pipe on the primary side of the heat network, and thereby increasing the supply water temperature on the secondary side of the heat network to ensure the balance between the heat supply delivered by the heat exchange station and the heating heat load of the heat users.

[0028] The automatic control system of the heat exchange station of the present invention adopts a feedforward-feedback control method to keep the heat supply matching the heating load, ensure the thermal balance of the heat network, and achieve the economic and reliable operation of the heat exchange station. Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages: 1. The heat exchange station system operates with a constant temperature difference between the supply and return water, and a variable-frequency circulating water pump is used to adjust the flow rate of the heating system to achieve the purpose of energy conservation; 2. The weather forecast information is used as feedforward control to pre-adjust the heating system of the heat exchange station, and the heat supply is adjusted in advance to reduce the influence of the large inertia and large lag of the heating system on the comfort of heat users; 3. Feedback control is adopted to achieve a constant temperature difference operation between the supply and return water on the secondary side of the heat network, improve the heating efficiency, and reduce energy waste; 4. In extreme weather conditions, to ensure the heating quality of heat users, according to the size of the pressure difference between the supply and return water, the automatic control system of the heat exchange station is switched from the quantity adjustment control mode to the quality adjustment control mode to rationally utilize resources. Brief Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of the heat exchange station control system;

[0030] Figure 2 It is a partial schematic diagram of the data acquisition and processing module;

[0031] Figure 3 It is a partial schematic diagram of the automatic control module;

[0032] Figure 4 It is a block diagram of the working principle of the automatic control of the heat exchange station. Detailed Embodiment

[0033] The present invention provides an automatic control system for a centralized heating heat exchange station, as Figure 1 shown, the control system is composed of a primary side circulation system of the heat network, a secondary side circulation system of the heat network, a data acquisition and processing module, and an automatic control module; among them, the data acquisition and processing module is composed of an air temperature and flow conversion unit and two subtractors; the automatic control module is composed of a subtractor, an adder, a changeover switch, and two PID controllers.

[0034] For the primary side circulation system of the heat network, the high-temperature hot water provided by the heat source is transported to the heat exchange station through the primary side supply water pipeline of the heat network. An electric control valve is installed on the primary side supply water pipeline of the heat network, which can change the flow rate of the high-temperature hot water in the primary side supply water pipeline of the heat network; in the heat exchange station, the high-temperature hot water transported by the primary side supply water pipeline of the heat network enters the plate heat exchanger, and heat exchange is carried out with the circulating water on the secondary side of the heat network in the plate heat exchanger. The cooled primary side return water of the heat network passes through the primary side circulating water pump installed on the primary side return water pipeline of the heat network and returns to the heat source through the primary side return water pipeline of the heat network.

[0035] In the described secondary side circulation system of the heat network, after the secondary side circulating water of the heat network absorbs heat in the plate heat exchanger, the heat is transferred to the heat users through the secondary side supply water pipeline of the heat network from the outlet of the plate heat exchanger. Temperature sensors and pressure sensors are installed on the secondary side supply water pipeline of the heat network to measure the temperature and pressure of the circulating water in the supply water pipeline; the cooled return water returns to the plate heat exchanger via the secondary side return water pipeline through the secondary side circulating water pump installed on the secondary side return water pipeline of the heat network. Temperature sensors and pressure sensors are installed on the secondary side return water pipeline of the heat network to measure the temperature and pressure of the circulating water in the secondary side return water pipeline of the heat network.

[0036] The described data acquisition and processing module, such as Figure 2 shown, real-time collects the temperature and pressure signals of the secondary side supply water and return water of the heat network and obtains the outdoor atmospheric temperature and wind speed information from the weather forecast by connecting to the Internet; the temperature sensors on the secondary side supply water pipeline and return water pipeline of the heat network are connected to the first subtractor, and the output end of the first subtractor is connected to the output end OUT1 of the data acquisition and processing module; the pressure sensors on the secondary side supply water pipeline and return water pipeline of the heat network are connected to the second subtractor, and the output end of the second subtractor is connected to the output end OUT2 of the data acquisition and processing module. The outdoor atmospheric temperature and wind speed information are connected to the input end of the air temperature and flow conversion unit, and the output end of the air temperature and flow conversion unit is connected to the output end OUT3 of the data acquisition and processing module.

[0037] The described automatic control module, such as Figure 3 shown, the output end OUT1 of the data acquisition module is connected to the input end IN1 of the automatic control module, the OUT2 of the data acquisition module is connected to the input end IN2 of the automatic control module, and the OUT3 of the data acquisition module is connected to the input end IN3 of the automatic control module; the input end IN2 of the automatic control module and the set value of the temperature difference between the secondary side supply water and return water of the heat network are connected to the third subtractor together; the output end of the third subtractor and the input end IN3 of the automatic control module are connected to the changeover switch together, the output end OUT4 of the changeover switch is connected to the input end of the first PID controller, the output end of the first PID controller and the input end IN1 of the automatic control module are connected to the adder together, the output end of the adder is connected to the output end OUT6 of the automatic control module, the output end OUT6 of the automatic control module is connected to the frequency converter, and the output of the frequency converter is connected to the secondary side circulating water pump; the output end OUT5 of the changeover switch is connected to the input end of the second PID controller, and the output end of the second PID controller is connected to the output end OUT7 of the automatic control module; the output end OUT7 of the automatic control module is connected to the primary side electric control valve.

[0038] A design method for the automatic control system of a central heating heat exchange station proposed by the present invention, such as Figure 4As shown, analog parameters such as meteorological parameters, fluid pressure, and fluid temperature in the weather forecast are collected in real time. After analyzing and processing these real-time collected analog parameters, the automatic switching of the feed-forward - feedback control quantity adjustment and the feedback control quality adjustment on the secondary side of the heat network is realized through a switching switch. The automatic control of the constant temperature difference between the supply and return water on the secondary side of the heat network in the heat exchange station is realized through a PID controller. The specific steps include:

[0039] (I) Quantity adjustment of the heat exchange station system

[0040] 1. Feed-forward control

[0041] Since there is a large thermal inertia in the heat supply source, heat supply network, and buildings, the change of meteorological parameters and heat supply parameters such as supply water temperature and supply water flow rate will have a long lag time on the room temperature of heat users. To ensure the design requirements of the room temperature of heat users, when adjusting the operation of the heat supply network, pre-adjustment must be considered, that is, there is a reasonable time difference between the change of the adjustment scheme and the change of the indoor temperature. According to the meteorological forecast information, the heat supply load is predicted, and the operation conditions of the heat exchange station are adjusted in a timely and reasonable manner to realize the optimal dispatching of the system, reduce the lag time of the heat network, ensure the heating quality, and achieve the purpose of energy conservation and environmental protection.

[0042] Meteorological parameters are the basis for the design and adjustment of the entire central heating system. The main meteorological parameters affecting the building heat load and the operation adjustment strategy of the heat supply system are outdoor air temperature and wind speed, etc. With the continuous development of meteorological prediction technology, the prediction accuracy has been steadily improved, and the meteorological forecast information service based on Internet technology has become increasingly perfect. The outdoor comprehensive temperature is obtained by correcting the outdoor air temperature with the wind speed information in the weather forecast

[0043] t w =35.74 + 0.6215×t - 35.75×v 0.16 + 0.4275×t×v 0.16 (1)

[0044] Among them, t w is the outdoor comprehensive temperature, in °C; t is the air temperature in the weather forecast, in °C; v is the wind force level in the weather forecast, in m / s.

[0045] Under stable conditions, the heat supply delivered by the heat exchange station is equal to the heating load of heat users

[0046] cG(t g - t h ) = q v V(t n - t w ) (2)

[0047] Among them, c is the specific heat capacity of hot water, with the unit J / (kg·℃); G is the circulating flow rate on the secondary side of the heat network, with the unit kg / s; t g is the supply water temperature on the secondary side of the heat network, with the unit ℃; t h is the return water temperature on the secondary side of the heat network, with the unit ℃; q v is the heating volume of the building, with the unit W / m 3 ·℃; V is the external surface volume of the building, with the unit m 3 ; t n is the indoor calculated temperature for winter heating, with the unit ℃.

[0048] Under the condition of constant temperature difference between the supply and return water on the secondary side of the heat network, that is, (t g -t h ) remains unchanged. When the outdoor comprehensive temperature t w changes, to keep the heat supply and heat load balanced, only the circulating flow rate G on the secondary side of the heat network needs to be adjusted, that is, through frequency conversion regulation, the flow rate of the secondary side circulating water pump is changed to achieve energy saving.

[0049] Through Equation (1) and Equation (2), the change relationship between meteorological parameters and the flow rate of the secondary side circulating water pump can be obtained. The outdoor air temperature and wind speed information in the weather forecast are connected to the data acquisition and processing module. After being converted by the temperature-flow conversion unit, the output end OUT1 of the data acquisition and processing module is connected to the input end IN1 of the automatic control module. After passing through the adder, the output end OUT6 of the automatic control module is connected to the frequency converter, serving as the feedforward control in the control loop of the secondary side circulating water pump, adjusting the output frequency of the frequency converter, and then changing the circulating flow rate on the secondary side of the heat network; adjusting the secondary side of the heat network in advance through the meteorological parameters in the weather forecast can effectively reduce the comfort of the indoor environment of heat users caused by the hysteresis of the heating system.

[0050] 2. Feedback control

[0051] When the weather forecast information does not match the actual meteorological parameters, through the rough adjustment of the feedforward control, the temperature difference between the supply and return water on the secondary side of the heat network changes, generating a deviation Error from the set value of the temperature difference between the supply and return water. The deviation Error is connected to the input end of the changeover switch, and the output end OUT4 of the changeover switch is connected to the input end of the first PID controller. After operations of proportional P, integral I, and derivative D, the output of the first PID controller passes through the adder, and the output end OUT6 of the automatic control module is connected to the frequency converter, changing the output frequency of the frequency converter, and then adjusting the circulating flow rate on the secondary side of the heat network to eliminate the deviation Error, and finally making the temperature difference between the supply and return water on the secondary side of the heat network equal to the set value.

[0052] When the operating conditions of the primary side of the heat network change or are disturbed, the supply water temperature of the primary side of the heat network changes, and the supply water temperature of the secondary side of the heat network also changes, which in turn leads to a change in the temperature difference between the supply and return water of the secondary side of the heat network. The deviation Error generated between the temperature difference between the supply and return water of the secondary side of the heat network and the set value is connected to the input end of the changeover switch. The output end OUT4 of the changeover switch is connected to the input end of the first PID controller. After operations of proportional P, integral I, and derivative D, the output of the first PID controller passes through an adder, and the output end OUT6 of the automatic control module is connected to the frequency converter to change the output frequency of the frequency converter, thereby changing the flow rate of the circulating water pump on the secondary side of the heat network. After adjustment and stabilization, the deviation Error is eliminated, so that the temperature difference between the supply and return water of the secondary side of the heat network is equal to the set value.

[0053] (2) Quality regulation control of the heat exchange station system

[0054] When the weather is abnormal during the heating season, the upper and lower limits reached by the pressure difference between the supply and return water on the secondary side of the heat network cannot meet the heating requirements of heat users through the quantity regulation method of adjusting the flow rate of the circulating water pump on the secondary side. To ensure that there is no problem of thermal imbalance in the heating system, the quantity regulation control loop is switched to the quality regulation control loop through the changeover switch. By adjusting the opening degree of the electric control valve on the primary side of the heat network, the supply and return water flow rates on the primary side of the heat network are changed, thereby changing the fluid temperature of the supply water pipeline on the secondary side and adjusting the heat supply delivered by the heat exchange station to heat users.

[0055] During the early cold period or the late cold period, when the outdoor temperature is relatively high, the circulating flow rate on the secondary side of the heat network is small, and when the pressure difference between the supply and return water pipelines on the secondary side of the heat network reaches the lower limit set value, the circulating water pump on the secondary side will maintain a certain rotational speed unchanged, and the changeover switch will act. The automatic control of the heat exchange station system is switched from quantity regulation to quality regulation. The deviation Error between the measured value of the temperature difference between the supply and return water pipelines on the secondary side of the heat network and the set value of the temperature difference between the supply and return water pipelines on the secondary side of the heat network is connected to the input end of the changeover switch. The output end OUT5 of the changeover switch is connected to the second PID controller. After operations of proportional P, integral I, and derivative D, the output end of the second PID controller is connected to the electric control valve on the supply water pipeline of the primary side of the heat network to reduce the opening degree of the electric control valve on the primary side of the heat network and lower the supply water temperature on the secondary side of the heat network to ensure the balance between the heat supply delivered by the heat exchange station and the heating load of heat users.

[0056] During the severe cold period, when the outdoor temperature is relatively low, the secondary circulation pump reaches the rated speed, but the actual measured value of the temperature difference between the supply and return water on the secondary side of the heat network is still lower than the set value. The heat supply delivered by the heat exchange station cannot meet the heating load of the heat users. When the pressure difference between the supply and return water pipes on the secondary side of the heat network reaches the upper limit set value, the switching switch operates, and the automatic control system of the heat exchanger switches to mass regulation control. The deviation Error between the measured value of the temperature difference between the supply and return water pipes on the secondary side of the heat network and the set value of the temperature difference between the supply and return water pipes on the secondary side of the heat network is connected to the input end of the switching switch. The output end OUT5 of the switching switch is connected to the second PID controller. After proportional P, integral I, and derivative D operations, the output end of the second PID controller is connected to the electric control valve of the supply water pipe on the primary side of the heat network, increasing the opening of the electric control valve on the primary side of the heat network, raising the supply water temperature on the secondary side of the heat network, and ensuring the balance between the heat supply delivered by the heat exchange station and the heating load of the heat users.

[0057] As mentioned above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An automatic control system for a central heating heat exchange station, characterized in that, the control system is composed of a primary side circulation system of the heat network, a secondary side circulation system of the heat network, a data acquisition and processing module, and an automatic control module; among them, the data acquisition and processing module is composed of an air temperature and flow conversion unit and two subtractors; the automatic control module is composed of a subtractor, an adder, a changeover switch, and two PID controllers; the said data acquisition and processing module real-time collects the temperature and pressure signals of the supply water and return water on the secondary side of the heat network, as well as obtains the outdoor atmospheric temperature and wind speed information from the weather forecast through connecting to the Internet; the temperature sensors on the supply water pipeline and return water pipeline on the secondary side of the heat network are connected to the first subtractor to obtain the supply-return water temperature difference signal Δt and are connected to the output terminal OUT1 of the data acquisition and processing module; the pressure sensors on the supply water pipeline and return water pipeline on the secondary side of the heat network are connected to the second subtractor to obtain the supply-return water pressure difference signal Δp and are connected to the output terminal OUT2 of the data acquisition and processing module; the outdoor atmospheric temperature and wind speed information are connected to the input terminal of the air temperature and flow conversion unit, and the output terminal of the air temperature and flow conversion unit is connected to the output terminal OUT3 of the data acquisition and processing module; the output terminal OUT1 of the data acquisition module is connected to the input terminal IN1 of the automatic control module, the OUT2 of the data acquisition module is connected to the input terminal IN2 of the automatic control module, and the OUT3 of the data acquisition module is connected to the input terminal IN3 of the automatic control module; the said automatic control module, the input terminal IN2 of the automatic control module and the set value of the supply-return water temperature difference on the secondary side of the heat network are connected to the third subtractor together; the output terminal of the third subtractor and the input terminal IN3 of the automatic control module are connected to the changeover switch together, the output terminal OUT4 of the changeover switch is connected to the input terminal of the first PID controller, the output terminal of the first PID controller and the input terminal IN1 of the automatic control module are connected to the adder together, the output terminal of the adder is connected to the output terminal OUT6 of the automatic control module, the output terminal OUT6 of the automatic control module is connected to the frequency converter, and the output of the frequency converter is connected to the secondary side circulation water pump; the output terminal OUT5 of the changeover switch is connected to the input terminal of the second PID controller, and the output terminal of the second PID controller is connected to the output terminal OUT7 of the automatic control module; the output terminal OUT7 of the automatic control module is connected to the electric control valve on the primary side of the heat network.

2. The system according to claim 1, characterized in that, for the said primary side circulation system of the heat network, the heat source outlet is connected to the inlet of the electric control valve via the primary side supply water pipeline of the heat network, the outlet of the electric control valve is connected to the inlet of the hot end of the plate heat exchanger via the primary side supply water pipeline of the heat network, the outlet of the hot end of the plate heat exchanger is connected to the inlet of the primary side circulation water pump of the heat network via the primary side return water pipeline of the heat network, and the outlet of the primary side circulation water pump of the heat network is connected to the inlet of the heat source via the primary side return water pipeline of the heat network.

3. The system according to claim 1, characterized in that, For the secondary-side circulation system of the heat network, the outlet at the cold end of the plate heat exchanger is connected to the inlet of the heat user through the secondary-side supply water pipeline of the heat network. The outlet of the heat user is connected to the inlet of the secondary-side circulation pump of the heat network through the secondary-side return water pipeline of the heat network. The outlet of the secondary-side circulation pump of the heat network is connected to the inlet of the cold end of the plate heat exchanger through the secondary-side return water pipeline of the heat network. Temperature sensors and pressure sensors are installed on the secondary-side supply water pipeline of the heat network to measure the temperature and pressure of the circulating water in the supply water pipeline. Temperature sensors and pressure sensors are installed on the secondary-side return water pipeline of the heat network to measure the temperature and pressure of the circulating water in the return water pipeline.

4. A design method for the automatic control system of a central heating heat exchange station. By collecting analog parameters such as meteorological parameters, fluid pressure, and fluid temperature in the weather forecast, after analyzing and processing these real-time collected analog parameters, the automatic switching of the feedforward-feedback control quantity adjustment and feedback control quality adjustment of the secondary side of the heat network is realized through a changeover switch. The automatic control of the constant temperature difference between the supply and return water on the secondary side of the heat network of the heat exchange station is realized through a PID controller. The specific steps include: (1) Quantity adjustment of the heat exchange station system 1. Feedforward control Since there is a large thermal inertia in the heat supply source, the heat supply network, and the building, the influence of the changes in meteorological parameters and heat supply parameters such as the supply water temperature and supply water flow on the indoor temperature of the heat user will have a long lag time. To ensure the design requirements of the indoor temperature of the heat user, when adjusting the operation of the heat supply network, it is necessary to consider pre-adjustment, that is, there is a reasonable time difference between the change of the adjustment plan and the change of the indoor temperature. According to the meteorological forecast information, predict the heat supply load, timely and reasonably adjust the operation conditions of the heat exchange station, realize the optimal dispatching of the system, reduce the lag time of the heat network, ensure the heating quality, and achieve the purpose of energy conservation and environmental protection; Meteorological parameters are the basis for the design and adjustment of the entire central heating system. The main meteorological parameters affecting the building heat load and the operation adjustment strategy of the heat supply system are the outdoor air temperature and wind speed, etc. With the continuous development of meteorological prediction technology, the prediction accuracy has steadily improved, and the meteorological forecast information service based on Internet technology has become increasingly perfect. The outdoor comprehensive temperature is obtained by correcting the outdoor air temperature with the wind speed information in the weather forecast t w = 35.74 + 0.6215×t - 35.75×v 0.16 + 0.4275×t×v 0.16 (1) Among them, t w is the outdoor comprehensive temperature, with the unit of °C; t is the atmospheric temperature in the weather forecast, with the unit of °C; v is the wind force level in the weather forecast, with the unit of m / s; Under stable conditions, the heat supply delivered by the heat exchange station is equal to the heating load of the heat user cG(t g -t h ) = q v V(t n -t w ) (2) Among them, c is the specific heat capacity of hot water, with the unit J / (kg·℃); G is the secondary side circulation flow rate of the heat network, with the unit kg / s; t g is the supply water temperature on the secondary side of the heat network, with the unit ℃; t h is the return water temperature on the secondary side of the heat network, with the unit ℃; q v is the heating volume of the building, with the unit W / m 3 ·℃; V is the external surface volume of the building, with the unit m 3 ; t n is the indoor calculated temperature for winter heating, with the unit ℃; Under the condition of constant temperature difference between the supply and return water on the secondary side of the heat network, that is, (t g -t h ) remains unchanged. When the outdoor comprehensive temperature t w changes, to keep the heat supply balanced with the heat load, only the circulating flow rate G on the secondary side of the heat network needs to be adjusted, that is, through frequency conversion regulation, the energy saving is achieved by changing the flow rate regulation method of the secondary side circulating water pump; Through formulas (1) and (2), the change relationship between meteorological parameters and the flow rate of the secondary-side circulation pump can be obtained. The outdoor air temperature and wind speed information in the weather forecast are connected to the data acquisition and processing module. After being converted by the temperature-flow conversion unit, it is connected to the automatic control module by the data acquisition and processing module. After passing through the adder, it is connected to the frequency converter by the automatic control module, serving as the feedforward control in the control loop of the secondary-side circulation pump, adjusting the output frequency of the frequency converter, and then changing the circulation flow rate on the secondary side of the heat network; By adjusting the secondary side of the heat network in advance through the meteorological parameters in the weather forecast, the comfort of the indoor environment of the heat user caused by the lag of the heat supply system can be effectively reduced; 2. Feedback control When the weather forecast information does not match the actual meteorological parameters, through the rough adjustment of feedforward control, the temperature difference between the supply and return water on the secondary side of the heat network changes, generating a deviation Error from the set value of the supply-return water temperature difference. The deviation Error is connected to the input end of the first PID controller via a switching switch. After proportional P, integral I, and derivative D operations, the output of the first PID controller passes through an adder and is connected to a frequency converter by an automatic control module, changing the output frequency of the frequency converter, thereby adjusting the circulating flow rate on the secondary side of the heat network, eliminating the deviation Error, and finally making the supply-return water temperature difference on the secondary side of the heat network equal to the set value; When the operating conditions on the primary side of the heat network change or are disturbed, the supply water temperature on the primary side of the heat network changes, and the supply water temperature on the secondary side of the heat network also changes, thereby causing the supply-return water temperature difference on the secondary side of the heat network to change. The deviation Error generated between the supply-return water temperature difference on the secondary side of the heat network and the set value is connected to the first PID controller via a switching switch. After proportional P, integral I, and derivative D operations, the output of the first PID controller passes through an adder and is connected to a frequency converter by an automatic control module, changing the output frequency of the frequency converter, thereby changing the flow rate of the circulating water pump on the secondary side of the heat network. After adjustment and stabilization, the deviation Error is eliminated, and the supply-return water temperature difference on the secondary side of the heat network remains consistent with the set value; (2) Quality adjustment control of the heat exchange station system When the weather is abnormal during the heating season, the upper and lower limits reached by the supply-return water pressure difference on the secondary side of the heat network cannot meet the heating requirements of heat users through the quantity adjustment method of adjusting the flow rate of the secondary side circulating water pump. Through the switching switch, the quantity adjustment control loop is switched to the quality adjustment control loop. By adjusting the opening degree of the electric control valve on the primary side of the heat network, the supply-return water flow rate on the primary side of the heat network is changed, thereby changing the fluid temperature of the secondary side supply water pipeline and adjusting the heat supply delivered by the heat exchange station to heat users; During the early cold period or the late cold period, when the outdoor temperature is relatively high and the circulating flow rate on the secondary side of the heat network is small, to ensure that there is no thermal imbalance in the indoor heating system, when the pressure difference between the supply and return water pipelines on the secondary side of the heat network reaches the lower limit set value, the secondary side circulating water pump will maintain a certain rotational speed unchanged, the switching switch acts, and the adjustment object of the automatic control system of the heat exchange station changes from the secondary side circulating water pump to the electric control valve on the supply water pipeline on the primary side of the heat network. The automatic control of the heat exchange station system is converted from quantity adjustment to quality adjustment. The deviation Error between the measured value of the supply-return water temperature difference on the secondary side of the heat network and the set value of the supply-return water temperature difference on the secondary side of the heat network is connected to the second PID controller via a switching switch. After proportional P, integral I, and derivative D operations, the output end of the second PID controller is connected to the electric control valve on the supply water pipeline on the primary side of the heat network, reducing the opening degree of the electric control valve on the primary side of the heat network, reducing the flow rate of the supply water pipeline on the primary side of the heat network, and thereby reducing the supply water temperature on the secondary side of the heat network to ensure the balance between the heat supply delivered by the heat exchange station and the heating load of heat users; During the severe cold period, when the outdoor temperature is low, the secondary-side circulation pump reaches its rated speed, the pressure difference between the supply and return water pipelines on the secondary side of the heat network reaches the upper limit set value, and the actual measured value of the temperature difference between the supply and return water is still lower than the set value. If the heat supply delivered by the heat exchange station cannot meet the heating load of the heat users, the switching switch operates, and the control object of the automatic control system of the heat exchange station changes from the secondary-side circulation pump to the electric control valve on the supply water pipeline of the primary side of the heat network. The automatic control of the heat exchange station system changes from quantity regulation to quality regulation. The deviation Error between the measured value of the temperature difference between the supply and return water pipelines on the secondary side of the heat network and the set value of the temperature difference between the supply and return water pipelines on the secondary side of the heat network is connected to the second PID controller via the switching switch. After proportional P, integral I, and derivative D operations, the output end of the second PID controller is connected to the electric control valve on the supply water pipeline of the primary side of the heat network, increasing the opening of the electric control valve on the primary side of the heat network and the flow rate of the supply water pipeline on the primary side of the heat network, thereby increasing the supply water temperature on the secondary side of the heat network and ensuring the balance between the heat supply delivered by the heat exchange station and the heating load of the heat users.

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