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Application of ABB frequency converter in the control system of variable frequency stabilized water supply equipment
Time: 2020-01-08 09:17 Source: win of Water: Water factory in winning hits: Times

Application of ABB frequency converter in the control system of variable frequency stabilized water supply equipment

The composition and principle of variable frequency stabilized water supply equipment system

The frequency conversion stabilized water supply equipment control system adjusts the output frequency through the measured pressure of the pipe network and calculates by the built-in PID regulator of the frequency converter to achieve constant pressure water supply of the pipe network. The frequency over-frequency signal of the inverter (usually used as the pressure signal of the pipe network) can timely inform the PLC to perform logic switching of the inverter pump. To prevent the occurrence of water hammer, the start and stop of the pump will be linked to its outlet valve.

Selection instructions of variable frequency stabilized water supply equipment

The water supply system of frequency conversion and stabilized water supply equipment is mainly composed of frequency conversion control cabinet, pressure sensor, water pump and so on. Frequency conversion control cabinet consists of circuit breaker, inverter, contactor, intermediate relay, PLC and so on.

Selection principle of water supply system

(1) The storage tank capacity should be greater than the peak water supply per hour.

(2) The pump lift should be greater than the actual water supply height.

(3) The sum of the pump flow should be greater than the actual peak water supply.

(4) Selection of inverter control cabinet:

Users can determine the model and number of pumps according to the water supply volume and water supply height, and then select the control cabinet.

Frequency converter

According to process requirements, it is recommended to use ABB ACS600 series inverter. ACS 600 series inverters are high-performance inverters introduced by ABB company using direct torque control (DTC) technology combined with many advanced manufacturing processes. It has a wide power range, excellent speed control and torque control characteristics, complete protection functions, flexible programming capabilities, high reliability and small size.

Main technical data of variable frequency stabilized water supply equipment:

· Power range: 2.2-3000kW

Power supply voltage: 380/400/415/440/460/480 / 500VAC 3 phases ± 10%;

· Power frequency: 48-63Hz

Control connection: 2 programmable analog inputs (AI); 1 programmable analog output (AO); 5 programmable digital inputs (DI); 2 programmable digital outputs (DO).

Continuous load capacity: 150% In, 1 minute allowed every 10 minutes

· Serial communication capability: The standard RS-485 interface enables the inverter to be easily connected to a computer.

· Protection characteristics: overcurrent protection, I2t, overvoltage protection, undervoltage protection, overheat protection, short circuit protection, ground protection, undervoltage buffering, motor under / overload protection, stall protection, serial communication fault protection, AI signal loss Protection, etc.

Compact appearance and easy installation. The product has been certified by various electrical specifications, and complies with GE, UL and ISO9001 and ISO4001 quality certification systems.

The direct torque control (DTC) function of the ABB inverter is currently a better motor control method. It can directly control the core variables of all AC motors, and can achieve accurate control of motor speed and torque without speed feedback.

ACS600 inverter has built-in eight application macros such as PID, PFC and pre-flux. Just select the required application macro, all corresponding parameters are automatically set, and the input and output terminals will be automatically configured. These preset application macro configurations greatly save Reduce debugging time and reduce errors.

Programmable controller

PLC recommends Siemens S7-200. SIMATIC S7-200 programmable controller is a modular small and medium-sized PLC system, which can meet the application of medium performance requirements; a wide range of various functional modules can very well meet and adapt to automatic control tasks. Combined for expansion; simple and practical decentralized structure and multi-interface network capabilities make the application very flexible; user-friendly and simple fanless design; when control tasks increase, it can be expanded freely; a wide range of integrated functions makes it Very powerful.

A variety of CPUs with increasing performance and rich I / O expansion modules with many convenient functions enable users to choose the appropriate module according to the actual application. 随时使用附加模块对PLC进行扩展。 When the task scale expands, the PLC can be expanded at any time with additional modules.

Application range of variable frequency stabilized water supply equipment

1. The system can be used for production and domestic water, as well as hot water supply, constant pressure spraying and other systems.

a. Can be widely used in industrial enterprises, living, production and water supply systems and enterprises to prepare and transform projects, water plants, living quarters and fire water supply systems.

b. Constant pressure, variable pressure, cooling water and circulating water supply systems that can be used in various occasions.

c. Can be used in sewage pumping stations, sewage treatment and sewage lifting systems.

d. Can be used in agricultural irrigation and drainage, garden sprinkler, water feature and music fountain system.

e. It can be used in water supply and fire protection systems of hotels and large public buildings.

2. Technical indicators

a. Water supply height: 200 meters

b. Flow: 1000 cubic meters / hour

c. Pressure fluctuation: ≤ 0.25 MPa

d. Water pump motor power: 0.75KW-280KW

Overview of variable frequency stabilized water supply equipment

Since its establishment, Changsha Zhongying Water Supply Equipment Co., Ltd. has been engaged in the research, development, and production of variable frequency stabilized water supply equipment. 不锈钢无负压变频稳压给水设备 ,无负压供水设备,自来水供水设备。 Professional production and operation of variable frequency stabilized water supply equipment, constant pressure water supply equipment, towerless water supply equipment, pipe network laminated water supply equipment, variable frequency speed regulating water supply equipment, stainless steel non-negative pressure variable frequency stabilized water supply equipment , non-negative pressure water supply equipment, tap water supply device.

The outstanding advantages of this variable-frequency voltage-stabilizing water supply equipment are that it does not need to build a water tower, has a small investment and occupies a small amount of land. It adopts automatic adjustment of water and gas, automatic operation, and automatic grid connection with tap water. It can still supply water after power failure. Need care. It saves 70% of investment compared with the construction of water towers and 60% of investment compared with the construction of high-level water tanks. Water supply households are in the 20-20000 households. The daily water supply is 20-50,000m3, and the water supply height is 150 meters, that is, 50-story building.

The use of our company's variable frequency water supply equipment can be installed only in the boiler room or basement, squeeze out a little place, units with tap water, use this equipment can adjust the peak water consumption, increase water pressure, can meet Water for large areas and high floors. Units, factories or rural areas without running water, just use this equipment to connect the water source to get the same effect as the water tower, so that you can use tap water satisfactorily. The equipment produced by our company is an integrated equipment, which guarantees 5 days of installation on site Done. Users are welcome to come to the company to see samples and order.

Characteristics of variable frequency stabilized water supply equipment

■ It adopts three different control methods such as microcomputer control, pressure classification control and manual control to ensure the reliability of the equipment.

■ It can realize soft start of the motor, greatly reduce the starting load and pressure fluctuation, and realize constant pressure water supply, which has significant energy saving effect.

■ Adopting high-reliability pipeline accessories and non-contact control of electrical appliances, which greatly improves the service life of the equipment.

■ The system is equipped with a small buffer pressure regulating tank, which greatly reduces the water hammer in the pipe network. It is also equipped with a small-flow constant-pressure pump, which plays the role of supplying water in a small flow range and ensuring the constant pressure of the fire protection system.

■ Equipped with various protection functions such as phase failure, over-voltage, over-current, overload, stall and no water, as well as fault display and alarm devices.

■ The equipment covers a small area and height, is flexible and mobile, convenient to install and debug, saves labor and time, and saves investment.

Application range of variable frequency stabilized water supply equipment:

● Production water: water supply 1 ~ 1300m3 / h

● Domestic water: water for 1 to 120,000 households

● Fire-fighting water: it can be used for fire-fighting water of Class 1-3 buildings

Frequency conversion application of water supply equipment

Usually in the same water supply system, multiple commonly used pumps are set. When the water supply is large, multiple pumps are fully turned on, and when the water supply is small, one or two pumps are turned on. When using constant frequency water supply equipment for constant pressure water supply, two methods are used. One is to use one inverter for all pumps; the other is to use one inverter for each pump. In the latter method, the output frequency of the inverter is automatically adjusted through PID calculation based on the pressure feedback signal, and the motor speed is changed to achieve the purpose of constant voltage in the pipe network. A closed loop circuit is simpler but more costly. The former method is low in cost and performance is not worse than the latter, but the control program is more complicated and is the future development direction. Our company developed the NKL-A series of frequency conversion and stabilized water supply equipment system to achieve the function of an inverter to control any number of motors. The principles described below are all systems where one inverter drives multiple motors.

Principle of variable frequency control of variable frequency and stabilized water supply equipment

The use of variable frequency speed regulation to achieve constant pressure water supply, compared with the use of regulating valves to achieve constant pressure water supply, the energy saving effect is very significant (can be calculated according to specific circumstances). Its advantages are:

a. Starting balance, starting current can be limited to the rated current, thereby avoiding the impact on the power grid during starting;

b. As the average speed of the pump is reduced, the service life of pumps and valves can be extended;

c. It can eliminate the water hammer effect during starting and stopping;

Generally speaking, when a motor is controlled by a frequency converter, it is only necessary to make the capacity of the matched motor of the frequency converter consistent with the actual motor capacity. When one inverter controls two motors at the same time, in principle, the capacity of the matched motor of the inverter should be equal to the sum of the capacities of the two motors. However, if the water consumption at peak load is much different than the full-speed water supply of the two pumps, you can consider appropriately reducing the capacity of the inverter, but you should pay attention to leaving enough capacity.

Although the water pump runs at low speed, the working current of the motor is small. However, when the user's water consumption changes frequently, the motor will be in a state of frequent rise and fall, and the current of the rise and fall may slightly exceed the rated current of the motor, causing the motor to overheat. Therefore, thermal protection of the motor is necessary. The electronic thermal protection function in the inverter is difficult to protect against the temperature rise accumulated due to frequent rises and falls, so a thermal relay should be used to perform thermal protection of the motor.

In terms of main function presets, the frequency should be the rated frequency of the motor as the operating frequency of the inverter. In the case of adopting PID regulator, the time of raising and lowering speed should be set as short as possible, so as not to affect the dynamic response process determined by PID regulator. For example, when the inverter has PID adjustment function, as long as the PID function is set to be valid during the preset, the set speed-up and speed-down time will be automatically invalidated.

Principle of PID control of variable frequency stabilized water supply equipment

According to the feedback principle: if you want to maintain a physical quantity unchanged or basically unchanged, you should draw a comparison between this physical quantity and a constant value to form a closed loop system. If we want to keep the water pressure constant, we must introduce a comparison of the water pressure feedback value with a given value to form a closed-loop system. However, the controlled system is characterized by a non-linear, large inertia system. Now the method of combining control and PID uses fuzzy control when pressure fluctuations are large to speed up the response speed; PID is used to maintain static accuracy when the pressure range is small. This algorithm can be realized by PLC and intelligent instrument, and the PLC can be switched between the power frequency and the frequency conversion of the pump. Practice has proved that using this method is feasible and the cost is not high.

  要想维持供水网的压力不变,根据反馈定理在管网系统的管理上安装了压力变送器作为反馈元件,由于供水系统管道长、管径大,管网的充压都较慢,故系统是一个大滞后系统,不易直接采用PID调节器进行控制,而采用PLC参与控制的方式来实现对控制系统调节作用。 In order to maintain the pressure of the water supply network constant, the frequency conversion stabilized water supply equipment is installed with a pressure transmitter as a feedback element on the management of the pipe network system according to the feedback theorem. Both are slow, so the system is a large lagging system. It is not easy to directly control it with a PID regulator, and PLC is used to control the control system to achieve the adjustment of the control system.

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