Application of the hottest frequency converter and

2022-10-23
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Application of frequency converter and PLC system in the control of heat exchange station

Abstract: This paper focuses on the application of frequency converter and PLC in the control of heat exchange station in central heating system. This paper expounds and studies the application of frequency converter and PLC system in the control of thermal power station from the aspects of the composition of automatic control system of thermal power station, the idea of system control and the realization of thermal power station system

key words: heat exchange station; Frequency converter; PLC system; Thermal adjustment; This paper introduces and studies the application of inverter and PLC in heat transfer station of central heating system based on the framework and the implementing of the automatic control system

keywords: heat transfer station inverter PLC systemthermal net adjustment

energy saving control

I. preface

in the urban central heating system, the thermal station is the last regulating unit of the thermal system facing the thermal users of the system, and the control effect of the thermal station directly determines the heating effect of the thermal users. The urban heat under the jurisdiction of Taiyuan thermal power company includes more than 400 thermal power stations, and the heating area covers 60% of the total heating area of Taiyuan. All thermal power stations adopt intermittent thermal heat exchange stations

in the intermittent heating station, the secondary is not easy to be damaged at the end. The pressure, temperature and flow of water supply and return are important factors affecting the heating effect, and the adjustment of secondary supply parameters mainly depends on the control of secondary circulating pump and make-up pump. In the traditional control of thermal power station, circulating pump and make-up pump generally use power frequency pump. The main parameters of the secondary system have been determined in the design and selection of the system, but relatively, the adaptability, expansibility and accurate adjustment of various parameters of the system are greatly limited

since 1999, Taiyuan thermal power company has gradually carried out automatic control transformation of various thermal power stations for central heating in Taiyuan. For the original thermal power station, automatic control instruments, PLC and frequency conversion equipment are added uniformly; For the newly-built thermal power station, automatic control equipment is introduced on the basis of process system during design. The automatic control system assists in the accuracy of the control of the thermal power station, combined with the full balance system of the thermal central control room and the communication network system, to achieve a good control effect. This paper mainly introduces the application of automatic control system and frequency converter in the control of thermal power station

II. Composition of automatic control system of thermal power station

the automatic control system of intermittent thermal power station can be divided into: temperature and pressure transmitter, flowmeter, electric control valve, circulating pump and make-up pump according to the type of equipment; According to the control circuit, it can be divided into: primary flow main technical parameters: maximum experimental force: 50kN; Range: 0n (5) 0kn; Accuracy of experimental force; Better than ± 1%; Displacement resolution: 0.01mm; Displacement measurement accuracy: better than ± 1%; Stretching stroke: 650mm (can be increased); Tightening stroke: 650mm (can be increased); Experimental stroke: 650mm (can be increased); Displacement speed control range: 1mm/min ~ 300mm/min; Displacement speed control accuracy: better than ± 1%; Experimental machine level: better than level 1; Deformation indication error: ≤± (50+0.15l); Size of the experimental machine: 660*420*1780 mm control circuit, secondary circulation control circuit, secondary constant pressure circuit

in the automatic control system of thermal power station, the primary flow control circuit is mainly realized by regulating the primary return water regulating valve. The secondary regulating circuit is realized by regulating the speed of the secondary circulating pump and the make-up pump. The primary control command is mainly issued by the thermal dispatching center according to the full balance algorithm, while the speed of the frequency converter of the secondary circulating pump and make-up pump is calculated by the PLC system in the station according to the actual situation of the heat carried by each thermal station

the structure of automatic control system of thermal power station is shown in the figure below

Figure 1 system structure diagram of typical heating station

III. system control idea

in the central heating project, it is difficult to determine a group of typical indoor temperatures as direct controlled quantities because the building area, radiator performance and housing insulation quality of each user are different, and the average temperature of supply and return water reflects the average temperature of each user's radiator as a whole, Therefore, the general heating system indirectly controls the user's room temperature by controlling the average temperature of water supply and return according to the outdoor ambient temperature and different heating periods

in the thermal control of Taiyuan, the thermal dispatching system was also adjusted while the automatic control transformation of the thermal power station was carried out. At present, the thermal dispatching centers of each thermal power branch in Taiyuan have added full balance systems. The dispatching center obtains thermal data through communication with thermal stations, and uniformly adjusts the heating effect of the full thermal stations according to the outdoor temperature

each thermal power station obtains the corresponding average temperature of secondary supply and return level from the control center. The station system divides the independent control loop into secondary supply and return level average temperature control loop and primary flow control loop, determines the set value of primary flow according to the deviation of average temperature, and then adjusts the valve opening to make the flow reach the set value

the control system in the station also adjusts the speed of the secondary circulating pump and make-up pump according to the actual situation of the thermal power station. The system automatically adjusts the speed of the circulating pump through the frequency converter according to the temperature difference between the average temperature of the secondary supply and return water, so as to realize the adjustment of the total flow and temperature of the system. Make the circulating water pump output power according to the actual load and reduce unnecessary power loss. The torzenmarathon technology of NVIDIA has also strengthened the performance of its flame retardant product specification, and now it is in the operation mode of small flow and large temperature difference. By doing this, the flow and head can be adjusted to the required value in time, and the excess power consumption can be eliminated, so as to achieve a good energy-saving effect. Usually, the thermal system will be designed with two variable-frequency pumps, which is not only for system standby, but also to prevent system overshoot. If the load is not enough, the speed of the pump will increase. If it does not meet the requirements when it reaches 100%, start the second pump. At the same time, the system can automatically switch each circulating pump according to the running time, and also provide low water pressure protection and interlocking function

the secondary supply and return water pressure of the control system is an important parameter for thermal safety operation. High water supply pressure may cause the rupture of hot water pipes and user radiators; The pressure of water supply and return is too low, which makes some heat users unable to get enough heat. The best scheme of constant pressure control is to control the frequency conversion and speed regulation of the make-up pump, but considering that the stability of the pressure here is not high, as long as the pressure does not exceed a certain range, the on-off make-up control scheme can also be used

IV. realization of thermal power station control system

1. Primary loop control:

primary loop control of thermal power station, mainly thermal load control. The flow of primary hot water flowing through the heating station is regulated by controlling the electric regulating valve on the primary circuit. In the full control system, the full control center calculates the opening order of the primary control valve or the secondary target control temperature of each thermal station according to the current outdoor temperature, the operation of the heat source and the secondary operation data fed back by each thermal station. The heat station system adjusts the primary flow regulating valve according to the instructions issued by the full control center, so as to realize the uniform distribution of heat resources of full heat

the main reference object in the primary loop control is the primary and secondary supply and return water temperature of the thermal power station; The object of the more standardized primary control industry standard is the primary regulating valve; The control purpose is to provide the necessary heating heat for the heating station

2. Secondary circulating pump control:

the secondary circulating pump of the thermal power station system is adjusted by frequency converter

the circulating pump of the traditional thermal power station system usually adopts the power frequency pump. After the circulating pump is selected, the secondary flow of the thermal power station cannot be adjusted, so that the thermal power station system cannot be adjusted according to the outdoor temperature and the actual heating demand, resulting in a waste of thermal and power resources. And high-power power power frequency pump will cause impact on electricity when starting and stopping

at present, frequency conversion control is widely used for circulating pumps above 15kw in the automatic control transformation of thermal system. The general circulating pump adopts the pressure difference control mode, that is, the speed of the circulating pump is adjusted by the secondary supply and return water pressure difference. The pressure difference control method can adjust the speed of the circulating pump and the secondary flow to meet the heating demand, so as to reduce waste

in the control of circulating pump in thermal power station, we adopt the control method of supply and return water temperature difference combined with supply and return water pressure difference

the control system of the thermal power station sets a target value of supply and return water pressure difference according to the actual situation of each system. Set the difference between the supply and return water pressure to meet the heating water circulation of the secondary pipe. On this basis, the PLC system of the thermal power station corrects the circulating pump by measuring the temperature difference between the secondary supply and return water. When the temperature difference between the secondary supply and return water is too large, it is necessary to increase the speed of the circulating pump, increase the secondary flow, increase the secondary return water temperature, and improve the heating effect; When the temperature difference between the secondary supply and return water is too small, it is necessary to appropriately reduce the speed of the circulating pump, reduce the secondary flow, and realize the operation mode of small flow and large temperature difference. This adjustment can save electric energy and heat energy. In large-scale heating, this energy-saving means can achieve considerable results

3. Secondary constant pressure water replenishment control:

the secondary water replenishment control adopts constant pressure control, and the traditional thermal power station often adopts the electric node control of pressure gauge. With the development of urban central heating, the heat load of the system is increasing. The heating area of the heating station system is relatively large, and the heating conditions are different, and the hydraulic loss of the second system is larger. The serious hydraulic loss makes the pressure of the secondary water replenishment system increase and the water replenishment is frequent. The frequent start and stop of the traditional power frequency make-up pump is easy to cause the fluctuation of the secondary pipe pressure

in the system with large heat load, we use the frequency conversion control of the make-up pump to accurately fine tune the make-up system. When the system loses water, the secondary pressure drops, and the system will control the make-up pump to make up water at a certain speed through the frequency converter. The speed of the make-up pump is evenly adjusted according to the difference between the current pressure and the target pressure, so as to avoid the impact of the make-up pump on the secondary system when starting and stopping

4. Field human-machine interface

on the field human-machine interface, you can arbitrarily adjust various operating states required by the system through the operation panel, such as the temperature and temperature difference of primary and secondary water supply and return, the maximum and minimum operating frequency of the frequency converter, etc., and you can check the previous operating records at any time. According to user requirements, the current parameters can be displayed on the screen in the form of screen, curve and report

v. advantages of automatic control system of thermal power station

the use of frequency converter and programmable controller in thermal power station gives full play to the advantages of speed regulation and energy saving of frequency converter and the advantages of flexible configuration, reliable control and convenient programming of programmable controller, so that the stability of the whole system is reliably guaranteed

through the operation of the automatic control system of the thermal power station, the control method mainly relying on manual adjustment in the past has been completely improved, the thermal operation has been reasonably controlled, the imbalance phenomenon has been effectively solved, and the uneven phenomenon of cold and heat in each station has been eliminated. On demand heating, energy saving and consumption reduction have changed the unreasonable operation mode of small temperature difference and large flow, which not only ensures the heating needs of remote customers, but also avoids the overheating phenomenon of near end users, and directly improves the heating effect of heat

about the author

La Huidong male now works in the material and equipment department of Taiyuan thermal power company in Shanxi Province, in charge of technical work, and also serves as a distinguished electrical expert of Shanxi Urban Heating Association

references

[1] Wang Yizhao, Liu Xiong, heat supply

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