Abstract: This paper introduces several methods of FFU control in clean room, and lists its advantages and disadvantages and the functional characteristics of intelligent FFU control system with AC motor.
1. introduction
With the development of economy and the improvement of people's living standard, people have higher and higher requirements for product quality. The production technology and production environment determine the product quality, which forces manufacturers to pursue better production technology and higher production environment. Especially in the fields of electronics, pharmacy, food, bioengineering, medical treatment, laboratory and so on, there are strict requirements for the production environment. It integrates technology, architecture, decoration, water supply and drainage, air purification, HVAC, air conditioning, automatic control and other technologies. The main technical indicators to measure the production environment quality of these industries are temperature, humidity, cleanliness, air volume, indoor positive pressure, etc.
Therefore, the reasonable control of each technical index of production environment to meet the requirements of special production process has become one of the research hotspots of clean engineering. As a kind of purification equipment, FFU is widely used in various cleaning projects. The full name of FFU is fan filter unit, "fan filter unit", that is, the clean equipment that the fan and filter are connected together and can provide their own power. As early as the 1960s, the establishment of the first laminar flow clean room in the world has begun to appear the application of FFU.
Design scheme of FFU in clean room
2. Status quo of FFU control mode
At present, FFU generally adopts single-phase multi speed AC motor, three-phase multi speed AC motor and DC motor. The power supply voltage of the motor is about 110V, 220V, 270V and 380V. Its control mode is mainly divided into the following: 1. Multi gear switch control; 2. Continuous speed regulation control; 3. Computer control; 4. Remote control;
The following is a simple analysis and comparison of the above four control methods:
2.1 multi gear switch control
The multi gear switch control system only includes a speed regulating switch and a power switch provided by FFU. As the control element is provided by FFU, which is distributed in each position of the ceiling of the clean room, the staff must adjust FFU through the shift switch on site, which is very inconvenient to control, and the adjustable range of FFU's wind speed is limited to several gears. We once did a project, in order to overcome the inconvenient factors of FFU control and operation, through the design of electrical circuit, we concentrated all the multi gear switches of FFU and put them in a cabinet on the ground to realize centralized operation, but there are limitations in appearance and function. The advantages of multi gear switch control are simple control and low cost, but there are many defects: large energy consumption, no smooth speed regulation, no feedback signal, no flexible group control, etc.
2.2 continuous speed regulation control
Compared with the multi gear switch control mode, the continuous speed regulation control mode has one more continuous speed regulator, which makes the speed of FFU fan continuously adjustable, but at the same time, the motor efficiency is sacrificed, making its energy consumption higher than the multi gear switch control mode.
2.3 computer control
Generally, the computer control mode adopts DC motor. Compared with the former two modes, the computer control mode has the following advanced functions: 1. Adopting distributed control mode, it can easily realize the centralized monitoring and control of FFU. 2. It is convenient to realize single, multiple and zone control of FFU. 3. Intelligent control system has energy-saving function. 4. Optional remote control mode can be used for monitoring and control. 5. The control system reserves the communication interface, which can communicate with the upper computer or network, so as to realize the remote communication and management functions.
The outstanding advantages of controlling DC motor are easy to control and wide speed range. However, there are some fatal defects in the control mode: 1. As the FFU motor is not allowed to have brushes in the clean workshop, the motor of FFU adopts the BLDCM, and the problem of commutation is solved by the electronic phase changer. The short service life of the electronic phase changer greatly reduces the service life of the whole control system. 2. The whole system is expensive. 3. High maintenance cost in later period.
2.4 remote control mode
As a supplement of computer control mode, remote control mode can be used to control each FFU, which is complementary to computer control mode.
To sum up: the former two control methods have high energy consumption and inconvenient control; the latter two control methods have short life and high cost. Is there a control method that can not only achieve low energy consumption and convenient control, but also ensure the service life and low cost? That is to use the computer control mode of AC motor.
Compared with DC motor, AC motor has a series of advantages, such as simple structure, small size, convenient manufacture, reliable operation, low price, etc. its service life is far longer than DC motor because it does not have commutation problem. For a long time, because of its poor speed regulation performance, the speed regulation mode has been occupied by the DC speed regulation mode. However, with the emergence and development of new power electronic devices and large-scale integrated circuits, as well as the continuous emergence and application of new control theory, the AC control mode has gradually developed, and will eventually replace the DC speed control system.
