Mitsubishi inverter FR-Z 024-S2.2K

Mitsubishi inverter FR-Z 024-S2.2K

1 Overview

The basic control strategy of the constant pressure water supply control system is: using the motor speed control device and programmable logic controller (PLC) to constitute the control system, to optimize the control of the pump group speed regulation and automatically adjust the number of pump units to complete the water supply pressure Of the closed-loop control, flow changes in the pipe network to achieve a stable water supply pressure and save energy purposes. The control goal of the system is the water pressure of the main pipe of the pump station. The value of the feed water pressure set by the system is compared with the actual value of the total manifold pressure. The difference is inputted into the CPU and processed to control the pump motor Run the variable speed pump motor speed, so as to achieve stable pressure in the water mains at the set pressure value.

With the development of power electronics, power electronics devices theoretical research and manufacturing process continues to improve, power electronic devices in capacity, pressure, characteristics and types have been greatly developed. Into the 90's power electronic devices toward large capacity, high frequency, fast response, low loss direction. As the application of modern power electronic devices and micro-computer technology, the combination of AC variable frequency speed control device, with the development of innovative products and promote the use of AC induction motor speed field of a huge technological revolution. At present the automatic constant pressure water supply system application electric motor velocity modulation device all uses the exchange frequency conversion technology, but the system control installment uses PLC controller, because PLC not only may realize the pump group, the valve logical control, and may complete the system the digital PID adjustment function , The system can run a variety of parameters, the control point of real-time monitoring, and complete the system operating conditions of the CRT screen display, fault alarm and print statements and other functions. Automatic constant pressure water supply system has a standard communication interface with the city water supply system of the host computer networking, urban water supply system to achieve optimal control for the urban water supply system provides a modern scheduling, management, monitoring and economic operation means.

2. Control scheme

In the pipe network system of the residential waterworks, because the pipe network is closed, the flow rate of the pump station water supply is determined by the water consumption of the user. The pressure of the pumping station supply pressure to satisfy the pressure loss ΔP of the most disadvantageous point in the pipe network. There are the following relations between the flow rates Q:

? P = KQ2;
Where K - is the coefficient

If PL is the minimum pressure required for the most disadvantageous point of pressure, the pump outlet pressure P should be supplied according to the following formula, so as to meet the user's water demand pressure value and the best energy saving effect.

P = PL + ΔP = PL + KQ2;

So the water supply system set pressure should be based on changes in flow rate and constantly set the value of constant pressure water supply technology called constant pressure water supply, water supply system, the most unfavorable point of the water supply pressure is constant and the pump outlet manifold pressure Continuously adjustable.
In this case,

A typical automatic constant pressure water supply system block diagram shown in Figure 1; system with the control of the pump outlet manifold pressure constant, variable flow water supply function, the system installed in the main outlet of the pressure sensor, flow sensor, real-time pressure, The electric quantity signal transforms into the electrical signal, inputs to the programmable controller (PLC) the input module, the signal after the CPU operation processing carries on the comparison operation with the hypothesis signal, obtains the best operating condition parameter, by the system output module Outputting the logic control instruction and the frequency setting value of the frequency converter, controlling the number of pumping pumps and the operating condition of the variable pump, and implementing soft start, soft switching and frequency conversion operation for each water pump according to the CPU instruction. The system can automatically determine the pump cycle of the pump according to the change of water consumption, in order to improve the stability of the system and the quality of water supply.

3. System functions?

The system uses FR-500 Japan's Mitsubishi inverter. The system has the function:?

3.1 automatic switching frequency / frequency running function?

The inverter provides three different operating modes for the user to choose:?

Mode 0: Basic mode of operation. The inverter always drives a pump and controls the other auxiliary pumps in real time according to the output frequency. That is, when the inverter output frequency reaches the maximum frequency to start an auxiliary pump frequency operation, when the inverter output frequency reaches the minimum frequency to stop the last start of the auxiliary pump. Thereby controlling the number of operating frequency pump. ??

Mode 1: Alternating mode, inverter usually fixed drive a pump, and real-time according to its output frequency, so that auxiliary pump frequency operation, this way and mode 0 is different if the previous pump start the pump pump 1 → pump 2, when the inverter output stops, the next start sequence becomes pump 2 → pump 1.

• Mode 2: Direct mode. When the signal is input, the inverter starts the first pump. When the pump reaches the highest frequency, the inverter will switch the pump to the power frequency running, the inverter will start the next pump to run the inverter. When the pump stop condition is satisfied, Stop the pump that was started first. ??

3.2 PID regulation function?

The hydraulic pressure signal (4-20MA or -5V) fed back by the pressure sensor is sent directly to the A / D port of the PLC (through the hand-held programmer) to set the given pressure value and the PID parameter value. Switch the pump to complete the operation of the system control, system parameters adjusted in the actual operation, the system control response tends to be complete. ??

3.3 "Sleep" function?

When the system is running, it often encounters the user's water consumption is small or no water (such as night), in order to save energy, the system set up a special pump can suspend work "sleep" function, when the inverter frequency output below its lower limit , The inverter stops working, 2 #, 3 # pump does not work, the pump stops (in the sleep state). When the water pressure continues to rise will stop a pump, when the water pressure drops to a certain value will first start the drive to run 2 # pump or 3 # pump, when the frequency reaches a certain value will start 1 # pump regulation 2 # or 3 Speed ​​of pump. ??

"Sleep value" The lower limit frequency of the inverter output PR507 is set. ?

When the inverter's output frequency is lower than the sleep time, such as less than the sleep time td, that is, td <tn, the inverter will continue to work. When td> tn, the inverter will enter the sleep state. . ??

"Wake-up value" is activated by the water supply pressure lower limit, when the water supply pressure is lower than the lower limit by the PLC to issue the instruction to awaken the frequency changer work.

The tested "sleep value" is 10HZ. "Sleep Acknowledge Time" td: 20s? "Wake-up Value" 70%?

3.4 Communication function?

This system has the computer communication function, the PLC frequency changer all has the RS232 or the 485 connection PLC may choose Simens S7-200 computer may with one or many sets of systems carries on the communication, may use the computer simultaneously to monitor: The electric current, the voltage, the frequency, Speed, pressure, etc. can also control various parameters of the inverter.

In addition, the system also has manual / automatic operation, fault alarm, operating status, current, voltage, frequency status display water protection and other functions.

4. Run the feature

To three pumps constant pressure water supply system, for example, the system in automatic mode, the programmable controller to control the inverter soft start 1 # pump, pump 1 into the frequency at this time running state, the speed gradually increased, when the water supply When Q <1 / 3Qmax (Qmax is the maximum flow rate of all three pumps), the programmable controller CPU automatically adjusts the running speed of pump 1 according to the change of water supply to ensure the required water supply pressure . When the water Q between 1 / 3Qmax, 1 # pump has been unable to meet the user's required water, then the PLC will issue instructions to pump 1 # frequency run, and soft start 2 # pump, So that 2 # pump into the inverter operating conditions, 2 # pump running speed determined by the user's water consumption to ensure that the most adverse point of water supply system required water pressure. When the external demand water supply Q is 2 / 3Qmax, the programmable controller sends out the instruction and then puts the 2 # pump in the labor frequency movement condition, simultaneously soft start 3 # pumps enters the frequency conversion movement condition, at this time 3 # pumps the running speed by The user's water to determine the water supply system to ensure that the most adverse point of the water supply pressure constant.

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