Application of the hottest delta frequency convert

Application of delta inverter in constant pressure water supply control system

1 introduction

in water supply engineering, in order to maintain constant pressure water supply and save energy, in addition to maintaining constant pressure without using large barrel tanks or throttles that waste drying conditions: 130 ℃ and 4 hours of energy, it is also necessary to prevent pressure surges caused by rapid start and stop of the pump. Using frequency converter is a good solution, but it requires skills in control. Generally, the external PLC or PID controller receives the operation instructions of the frequency converter, so the integration and adjustment is difficult and time-consuming. Delta vfd-f pump special inverter uses built-in pump control logic, which greatly simplifies the variable speed control of the water supply system

2 variable frequency speed regulation characteristics

according to the motor theory, the motor speed formula is:

where: P is the pole number of the motor, s is the slip rate, f is the power supply frequency, and N is the actual speed of the motor. From the formula, it can be seen that the speed of the motor is in direct proportion to the frequency, and the reuse of plastic waste materials seems to be strengthened. Changing the frequency can smoothly adjust the speed of the motor, so as to continuously and conveniently change the air volume of the fan. The fan is a pump load, which belongs to square torque load. Its speed n, flow Q, pressure h and shaft power P have the following relations: Q ∝ n, H ∝ N2, P ∝ N3, that is, the flow is proportional to the speed, the pressure is proportional to the square of the speed, and the shaft power is proportional to the cubic of the speed. From the above analysis, it can be seen that by changing the motor speed, the air volume of the fan can be easily changed to ensure the optimization of the air-fuel ratio; By changing the motor speed, the expected working condition of the system can be effectively guaranteed and the electric loss of the system can be reduced. Using variable frequency speed regulation technology (frequency converter) in the monitoring system has the following advantages:

(1) it is convenient to realize the soft start and free stop of the motor. The motor is slowly accelerated from 0-50Hz through frequency converter or soft start, which reduces the impact of sudden high-speed start of the pump and the impact of starting current on electricity during direct start

(2) it can improve the power factor, improve the power quality of the motor, ensure that the power of the motor matches the actual load, and achieve the purpose of energy-saving operation of the system

(3) it can eliminate the surge phenomenon of the pump and make the pump run in the best working condition

(4) it can easily realize automatic control, make the regulated quantity regulated more smoothly, and enhance the stability and reliability of the system

using variable frequency speed regulation technology is not only convenient to adjust, but also has obvious energy-saving effect. If the rated power of the motor is PN, the rated speed is NN, and the actual output power is p when the speed is n, then energy saving (expressed in power) △ P can be expressed as:

, then △ p=0.67pn, that is, the energy-saving effect can reach 67% under ideal conditions. It can be seen that as long as variable frequency speed regulation technology is used, the energy-saving effect of variable frequency speed regulation is very significant

3 constant pressure water supply control system based on variable frequency speed regulation

constant pressure water supply control system based on variable frequency speed regulation is shown in Figure 1. In the control system of Figure 1, pressure and flow are two important parameters of pump control. Vfd-f can continuously track the pressure and flow with the help of the voltage or current signal returned by the pressure or flow sensor. The pump works or stops according to the preset operation mode, which can greatly save electricity and prolong the service life of the motor and pump. Control multiple pumps

in order to improve the flow, more than one pump can be used to form a control system. Vfd-f can use the built-in relay (widely used in automobile, aviation, medical devices, furniture, machinery manufacturing and other industries such as the production and utilization of springs and shock absorbers, or the purchase of relay cards) to control the start or stop of additional pumps when necessary, so as to maintain constant pressure. The special setting of vfd-f frequency converter parameters can prevent disturbing start and stop, provide smooth transfer between pumps and maintain the pressure within the allowable error range. Vfd-f can control any pump driven by motor, and the built-in minimum speed setting can meet the minimum speed requirements of deep well pump motor manufacturers. Because vfd-f frequency converter can use v/f curve, it is set to provide 100% rated torque at low speed and provide the torque required for positive displacement pump at low speed. Users do not need to increase the capacity of frequency converter and motor, and dangerous speed can be eliminated when using line shaft turbine pump

4 conclusion

pump control system is widely used in various types of water stations and water supply and distribution stations. This paper discusses only the simplest application. As delta vfd-f frequency converter is a series of products with wide adaptability, users interested in products are welcome to cooperate with us