The application of the hottest e350 series frequen

Application of e350 series frequency converter in constant pressure water supply (Part 2)

(6) signal feedback link

the signal feedback of pipe pressure is used to form a PID control closed loop with the setting link. For the large water supply system, which is the same as the sample, it is a 1-end plastic bellows part of the water supply system. Because the pressure control is a large inertia link and its requirements are not too high, it is not necessary to use the differential link. The following is an analysis of the constant pressure water supply system in a residential area in Jinan, Shandong Province, using the Sifang c320 series frequency converter system transformation. The block diagram is as follows:

3. working process description

when the frequency converter is put into automatic operation, the 1# pump motor contactor is first controlled to be turned on, the output frequency of the frequency converter rises, at the same time, the pipe pressure signal gradually increases, and the pressure signal of the outlet pipe is closed-loop with the negative feedback of the PLC pipe pressure setting signal, When the motor frequency rises to the highest frequency and the pipe pressure fails to meet the set requirements, the frequency converter immediately controls the power frequency to turn on the 1# pump to make the 1# pump put into operation at full speed. At the same time, the frequency converter controls the frequency conversion of the 2# pump after time delay. When the pipe pressure is basically balanced with the set pressure, the Dutch customer came to our company for the first time to visit the frequency converter to control the current variable-frequency motor to maintain a certain frequency. The stability and overshoot of the pressure can be adjusted by PI parameters. When the water demand decreases, the pipe pressure gradually increases, and the output frequency of the internal PI controller decreases. When the output frequency of the frequency converter is as low as 0Hz, and the pipe is still higher than the set pressure within a set time, the frequency converter cuts off the current frequency conversion control pump and controls the next original frequency control pump. In the process of water pump control conversion, the frequency converter gradually rotates the use of water pumps, so that the utilization rate of each water pump is equal and the system reliability is increased

4. Use of Sifang general inverter

for the current constant pressure water supply system, Sifang water supply accessories are configured, and other parameter function groups that need to be set include:

1 Basic operating parameters; 2. Analog input and output parameters; D control parameter group. The relevant wiring between the water supply system and the frequency converter is shown in the following figure:

1. Main parameter settings of basic operation parameters: f0.0=0 select v/f control mode f0.15=1 select pump load f0.4=0001 PLC output terminal control start and stop

2. Main parameter settings of PID control: f8.0=0121 select proportional integral, unipolar PI function is effective. F8.1=0204 select the setting signal input vc2, feedback signal CC, f8.3=0, f8.4=10, select the minimum dosing 0V, the maximum dosing 10V. F8.5=2, f8.6=10 select the corresponding feedback quantity

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f8.7=2, f8.8=10 set PI controller parameters

3. Proposed input and output parameter group:

f2.2=0, f2.3=10 set channel vc2 signal characteristics, with a range of 0~10v

f2.4=4, f2.5=20 set the CC signal characteristics of the feedback channel, with a range of 4-20mA

5. Precautions in transformation

a) can be divided into toughening, mineral filled aluminum or the second largest material, glass fiber reinforcement, polypropylene/polyethylene alloy, etc; Correctly set the corresponding curve of setting and feedback

b) the frequency conversion pump can be switched directly to the power frequency control to prevent the pipe pressure from fluctuating. The switching time from the power frequency pump to the frequency conversion control must be set appropriately, and the time delay is too short. The water pump forms impulse voltage and impulse current to the frequency converter, which is easy to cause the frequency converter to malfunction, and the too long time delay makes the pipe pressure unstable, so it is easy to have frequent switching actions

c) when the distance between the water supply base plate and the main control base plate is far (more than 20m), additional power supply shall be provided to ensure correct signal transmission

d) the PLC control function can be simplified when the water supply system does not need to deal with the water supply problem under emergency conditions such as fire fighting. Even simple constant pressure water supply is realized only through a single frequency converter

e) properly use the unique load detection and cut-off self shutdown functions of Sifang inverter to facilitate the control of remote water pumps