I. Review
Generally speaking, it is stipulated that the water pressure of urban pipe network only guarantees the building water below 6 floors, and the water pressure of other upper floors must be "upgraded" to meet the water demand. In the past, most of the traditional water towers, high-level water tanks, or air pressure tank pressurization equipment were used, but all of them had to be "lifted" by the water pump at a pressure higher than the actual water height, which increased the shaft power and energy loss of the water pump.
Since the advent of universal frequency converter, frequency conversion speed regulation technology has been widely used in various fields. Frequency conversion speed regulation technology has been widely used in various fields. With the advantages of energy-saving, safe and high-quality water supply, the technical equipment level of China's water supply industry has experienced a leap since the early 1990s. Constant pressure water supply speed regulation system realizes stepless speed regulation of water pump motor, automatically adjusts the operating parameters of the system according to the change of water consumption, and keeps the water pressure constant when the water consumption changes to meet the water demand. It is the most advanced and reasonable energy-saving water supply system at present. It has been greatly developed in practical application. With the rapid development of power electronics technology, the function of frequency converter is getting stronger and stronger. It is of great significance to make full use of the built-in function of frequency converter to reasonably design frequency conversion speed regulation constant pressure water supply equipment, reduce cost and ensure product quality.
Compared with the previous water tower or high-level water tank and pneumatic water supply mode, the new water supply mode has incomparable advantages in equipment investment, operation economy, stability, reliability and automation degree of the system, and the energy saving effect is remarkable. These advantages of constant pressure water supply speed regulation system have attracted great attention of almost all domestic water supply equipment manufacturers, who have been continuously investing in the research and development and production of this high-tech product.
At present, the products are developing towards high reliability, full digital microcomputer control and multi-variety serialization. Pursuing high intelligence and series standardization is an inevitable trend for water supply equipment to meet the requirements of future urban construction, intelligent building, networked water supply dispatching and overall planning.
In just a few years, the variable speed and constant pressure water supply system has experienced a gradual development process, and the early single pump variable speed and constant pressure system has been gradually replaced by multi-pump system. Although the design of single-pump product system is simple and reliable, due to the deep speed regulation of single-pump motor, the operation efficiency of water pump and motor is low, while the multi-pump product is more economical in investment and high in operation efficiency. Practice has proved that it is the optimal system design and has quickly developed into a leading product.
Second, frequency conversion control constant pressure water supply control mode
As we all know, the power consumption of water pump is directly proportional to the cubic power of rotation speed. That is, n = k3n: power consumption of water pump; N: the rotating speed of the water pump when it is running; K is the proportional coefficient. The design of the water pump is designed according to the power frequency operation, but the flow rate is small most of the time except the peak. Because the naming adopts frequency conversion technology and microcomputer technology controlled by microcomputer, the running speed of the pump can change with the change of flow, and finally achieve the purpose of energy saving. Practice has proved that the use of frequency conversion equipment can reduce the average running speed of water pump by 20% compared with the power frequency speed, thus greatly reducing energy consumption, and the energy saving rate can reach 20%-40%.
At present, the electric control cabinets of water supply equipment produced by domestic manufacturers are roughly divided into the following four categories, except for the backward control mode of relays and contactors:
Logic electronic circuit control mode:
This control loop is difficult to realize full soft start and full flow frequency conversion regulation of water pump unit. Often one pump is fixed in frequency conversion state, and other pumps are in power frequency state. Therefore, the control accuracy is low, the water pressure fluctuates greatly when the water pump is switched, the debugging is troublesome, the starting of the power frequency pump has an influence, and the anti-interference ability is weak. But the cost is lower.
Single chip microcomputer circuit control mode:
This control circuit is superior to logic circuit, but it is troublesome to debug when dealing with different pipe networks and different water supply situations, and it is often inflexible and inconvenient to modify the circuit when adding functions. The reliability and anti-interference ability of the circuit are not very high.
Control mode of PID loop regulator and/or PLC:
The purpose of this inverter is to provide variable frequency power supply for the motor, realize stepless speed regulation of the motor, and thus make the water pressure in the pipe network change continuously. The task of the sensor is to detect the water pressure in the pipe network. The pressure setting unit provides the system with the expected value of water pressure to meet the needs of users. After the pressure setting signal and pressure feedback signal are input into the programmable controller, they are calculated by the PID control program inside the programmable controller and output to the frequency converter as speed control signals. Another way is to send the pressure setting signal and pressure feedback signal to the PID loop regulator, which will be calculated in the regulator and input into the frequency converter as the speed regulating signal.
Because the speed control signal of frequency converter is given by programmable controller or PID loop regulator, it is necessary to have both analog input interface and analog output interface for the programmable controller to time. Due to the high price of programmable controller with analog input/output interface, this invisibly increases the cost of water supply equipment. If a programmable controller with analog input/digital output is adopted, a PWM modulation board should be connected to the digital output port of the programmable controller, which will not only reduce the cost of converting the digital signal output by the programmable controller into the controller, but also increase wiring and additional equipment, reducing the reliability of the whole set of equipment. If you use a programmable controller with switch input/output and a PID loop regulator, the cost is similar to that of a programmable controller with analog input/output. Therefore, in the constant pressure water supply control equipment with frequency conversion and speed regulation, the generation and output of PID control signals become the key link to reduce the cost of water supply equipment.
New water supply equipment with frequency conversion and speed regulation;
In view of the shortcomings of traditional frequency conversion water supply equipment, many domestic and foreign manufacturers have introduced a series of new products in recent years, such as TD 2100; Huawei; Altivar58 pump switching card of Schneider Company; SANKEN's SAMCO-I series; ABB's ACS600 and ACS400 series products; Fuji g11s/p11s series products; Wait a minute. These products integrate the functions of PID regulator and simple programmable controller into frequency converter, forming a new type of frequency converter with various application macros. Because the PID operation is inside the frequency converter, the storage capacity of the programmable controller is saved, and the requirements for the storage capacity of the programmable controller and the programming of PID algorithm are saved. Moreover, the online debugging of PID parameters is very easy, which not only reduces the production cost, but also greatly improves the production efficiency. Because the PID regulator inside the frequency converter adopts the optimization algorithm, the adjustment of water pressure is very smooth and stable. At the same time, in order to ensure the accuracy of the water pressure feedback signal, the filtering time constant can be set for the signal and the feedback signal can be converted, which makes the debugging of the system very simple and convenient. The price of this inverter is only slightly higher than that of the general inverter, but its function is much stronger. Therefore, the constant pressure water supply equipment produced by the inverter with built-in PID function reduces the equipment cost, improves the production efficiency and saves the installation and debugging time. In the case of meeting the process requirements, priority should be given.
Third, the function of special frequency converter for water supply
Special frequency converter for water supply = ordinary frequency converter PLC, which is a system integrating water supply control and water supply management. Built-in special PID regulator for water supply can form a closed-loop control system for water supply with only one pressure sensor. The water pressure signal fed back by the sensor is directly sent to the input port of the PID regulator of the frequency converter, and the pressure setting can be set by the keyboard of the frequency converter or by an analog potentiometer. Multi-stage pressure operation can be set daily to meet the needs of water supply pressure. You can also set the daily water supply pressure that needs to be specified. You can also set the specified daily water supply pressure control. The panel can directly display the pressure feedback value (Mpa).
The system has two basic water supply modes: variable frequency pump fixed mode and variable pump circulation mode. The fixed mode of variable frequency pump can control up to 7 pumps, and you can choose two pump closing sequences: "Turn on first and then turn off" and "Turn on first and then turn off" (suitable for occasions where the pump capacity is not used). The frequency conversion pump circulation mode can control up to 4 pumps, and the system turns off the pumps in the order of "turn on first and then turn off". Flexible configuration of conventional pumps, fire pumps, sewage pumps, eyewash pumps, to facilitate the full automation of pump room water supply. The working pump and standby pump are not fixed, so they can be rotated automatically and regularly. It can effectively prevent the standby pump from rusting when it is not used for a long time, improve the comprehensive utilization rate of the equipment and reduce the maintenance cost. The automatic accumulation function of working hours is convenient for energy saving analysis and equipment state maintenance. When the water supply decreases sharply at night, it is convenient to specify the start and end time of closing eyes every day and set the given pressure value when closing eyes. During the rest period, only the rest pump works, and the frequency converter only monitors the pipe network pressure. When the pressure is lower than the set pressure, the system will wake up automatically. When the variable frequency pump is put into operation, when the pressure is higher than the set value, the system enters the dormant state again, and only the dormant pump runs. In this way, water and electricity can be saved to the maximum extent. It has the function of timing shutdown, and the user will automatically stop when not using water. Fault pump exit function, when the pump is damaged, the fault pump will automatically quit working. The fire signal has an external input interface. When a fire alarm or fire signal comes, the system can automatically switch to fire mode. There are a variety of fire fighting modes to choose from, mainly depending on whether to use the fire fighting and living pipe network and whether to use the water inlet tank. There is also an automatic inspection function of fire pump, which can set a regular inspection cycle.
With the communication function, network control can be realized. Convenient for building automation and management.
In addition, there are some functions, such as sewage pump control function, water level detection and control of inlet tank, over-voltage and under-voltage protection function of pipe network, temperature difference and pressure difference control, and automatic telephone dialing in case of failure (when the water supply system or frequency converter fails, it is connected with external MODEM equipment through the built-in RS232C serial communication interface to automatically start the preset telephone number and information, and notify the equipment maintenance personnel to deal with it in time, which can conveniently realize unattended pump room).
It can be seen that the special frequency converter for water supply is powerful and can meet various control schemes of water supply system. If a small PLD is added, more complex process requirements can be met.
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