【正文】 ut value to adjust the control the speed of the pump motor, to ensure that the pipe network pressure constant requirements.The application of inverter in the constant pressure water supply一．The characteristic and analysis of variable frequency speed regulationThe water users in general is dynamic, so the water supply is insufficient or excess water supply situation has occurred. The water supply and the imbalance between the concentrated reflection in water supply pressure, namely water and water supply is less, the low pressure。 less water consumption and water supply, the pressure. Keep the water pressure constant, can make the water supply and water balance between water supply and water for a long time, that is, less water when the water is less, so as to improve the quality of water supply.Constant pressure water supply system for the user is very important. In production and living water, if water supply due to insufficient pressure or short of water, may affect the quality of life, serious when can influence the survival safety, such as when a fire occurs, if the water pressure is insufficient or water supply, can quickly fire, may cause significant economic losses and casualties. Therefore, water area by means of Arts is the constant pressure water supply system, can produce great economic benefit and social benefit.With the development of electric power technology, frequency conversion technology perfected, with variable frequency speed control as the core of the intelligent water control system replaced the previous high level water tank and a pressure tank and water supply equipment, stable starting, the starting current can be limited within specified current, thereby avoiding the starting time of the impact of power grid。 because the average rotational speed of pump is reduced, which can extend the pumps and valves and other things of life。 to eliminate the start and stop of the water hammer effect. The stable and safe performance, simple and convenient operation, and plete and thoughtful function, will make the water supply and water conservation, energy saving, labor saving, ultimately achieve efficient operation.二． The application of variable frequency control constant pressure water supply modeUsually in the same way in the water supply system, setting multiple mon pump, water supply when the quantity of multi pump full open, water supply on one or two hours. In the variable frequency speed control for constant pressure water supply, in two ways, one is all pumps with a frequency converter。 and each water pump with a frequency converter. After a method based on pressure feedback signal, operated by PID automatically adjusts the output frequency of the inverter, change the speed of the motor, eventually reaching the purpose of network voltage, a closed loop, is relatively simple, but the cost is high. The previous method of low cost, less than kind of poor performance, but the control program is plex, is the future direction of development, such as the Shanghai arts and science and technology of constant pressure water supply control system can realize a inverter control any number of motor function. The principle mentioned below are multiple motor inverter drive system.三．The PID control principleAccording to the feedback principle: to maintain a physical quantity unchanged or essentially unchanged, it should bring the physical quantity and the constant parison, to form a closed loop system. We want to keep the pressure constant, so we must introduce the hydraulic feedback value with a given value, thereby forming a closed loop system. But the control system is characterized by nonlinear, inertial system, now the control method bined with PID in the large pressure fluctuation, using fuzzy control, in order to accelerate the response speed in the pressure range。 using PID to maintain static accuracy. This through the PLC and intelligent instrument can show the algorithm, while the PLC programming to show when the pump frequency and inverter switching between. Practice has proved that, using this method is feasible, and the cost is not high.To maintain the constant pressure water supply network, according to the feedback theorem in network management system installed on the pressure transmitter as a feedback element, because of long, large diameter pipe system of water supply, pipeline pressure charging are slower, so the system is a big time lag system, is not easy to directly with PID regulator for control, and adopts PLC is involved in the control of the way to achieve the control system regulates the effect.四．Frequency controlUsing frequency control to realize constant pressure water supply, with adjustable valve to realize constant pressure water supply, energysaving effect is very significant ( according to the specific circumstances calculated ). The utility model has the advantages of:1, starting balance, the starting current can be limited within specified current, thereby avoiding the starting time of the impact of power grid。2, because the average rotational speed of pump is reduced, thereby prolonging the service life of pump and valve etc.。3, can eliminate the start and stop of the water hammer effect。Generally speaking, when performed by a frequency converter to control a motor, just make the inverter motor capacity and the actual capacity of the motor can be. When one inverter control two motors, principle of inverter motor capacity should be equal to the capacity of the two motors. But if the peak load of water more than two pumps at full supply a lot of difference, Shanghai arts and science and technology engineers suggested, may be considered appropriate to reduce the capacity of the frequency converter, but attention should be paid to leave enough capacity.Although the pump at low speed, small working current of the motor. However, when the user with the water volume changes frequently, the motor will be in frequent ascending, de