SEVICON Cleanroom FFU Control System
SEVICON introduces several ways of cleanroom FFU control, and lists its advantages and disadvantages and the functional characteristics of the intelligent FFU control system using AC motors.FFU is also known as Fan Filter Unit. The fan and the filter are connected together to provide their own power to the clean equipment.As a purification equipment, FFU is now widely used in various clean projects. With the development of the economy and the improvement of people\'s living standard, people\'s demand for product quality is also higher and higher.The production technology and environment determine product quality, forcing manufacturers to pursue better production technology and a higher production environment.Especially in electronics,
pharmaceuticals, food, bio-engineering, medical, laboratory and other production environment that has harsh requirements, which integrates the process, construction, decoration, water supply and drainage, air purification, HVAC, air conditioning, automatic control and other aspects of technology.The main technical indicators for measuring the quality of the production environment in these industries are temperature, humidity, cleanliness, airflow, positive indoor pressure, etc.Therefore, it has become one of the research hotspots of clean engineering nowadays to carry out reasonable control of each technical index of the production environment to meet the requirements of special production processes.
2. FFU control mode status
Currently FFU generally use single-phase multi-speed AC motors, three-phase multi-speed AC motors and DC motors.There are roughly four types of motor supply voltages: 110V, 220V, 270V and 380V. Their control methods are mainly categorized as follows,
◆ Multi-position switch control
◆ Continuous speed adjustment control
◆ Computerized control
◆ Remote control
The following is a brief analysis and comparison of the above four control methods:
2.1 Multi-position switch control
The multi-position switch control system includes only one speed control switch and one power switch that come with the FFU.Since the control elements are self-contained for the FFU and are distributed in various locations within the cleanroom ceiling. Operators must adjust the FFUs on-site with dip switches, which is extremely inconvenient to control, and the FFUs have a limited range of adjustable air speeds.We have done a project. To overcome the inconvenient factor of FFU control operation, after designing the electrical wiring, all the FFU multi-speed switches are centralized and put into a cabinet on the ground to achieve centralized operation, but there are limitations in appearance and function.The advantage of using multi-speed switching control is simple operation, low cost, but there are many defects. For example, huge energy consumption, unable to regulate speed smoothly, no feedback signal, unable to achieve the flexible group control and so on.
2.2 Continuous speed adjustment control
Compared with multi-position switch control mode, continuous speed regulation control has one more continuous speed regulator, so that the FFU fan speed is continuously adjustable. But at the same time, it also sacrifices the efficiency of the motor, its energy consumption is higher than the multi-position switch control mode.
2.3 Computerized control
The computerized control method generally uses DC motors, and compared to the previous two methods, the computerized control method has the following advanced features:
◆ Adopting centralized control mode, which is easy to achieve the centralized monitoring and control FFU.
◆ easy to achieve single, multiple and partition control of FFU.
◆ Intelligent control system with energy saving function.
◆ Optional remote control can be used for monitoring and control.
◆ The control system reserves the communication interface, which can communicate with the upper computer or the network, so as to realize the remote communication and management function.
The outstanding advantages of controlling DC motors are easy control and wide speed range.
However, the control has some flaws:
◆ Due to the clean plant does not allow FFU motor with brushes, the FFU motors are brushless DC motors. Commutation problems are solved by electronic shifters. The short lifespan of the electronic commutator greatly reduces the service life of the entire control system.
◆ Expensive system cost
◆ High maintenance cost
2.4 Remote control
Remote control is a way to support the computer control, you can use the remote control to control each FFU with computer.In a word, the first two control methods is high energy consumption and inconvenient; the latter two are short life and high cost. Is there a control method that can achieve both low energy consumption with convenient control, but also to ensure low cost service life? There is, that is computer control using AC motor.AC motor has a bunch of advantages such as simple structure, small size, convenient manufacture, easy operation and low price, comparing with DC motor. Its service life is longer than DC motor because of its non-existence of commutator shift.The speed control method has been replaced by the DC speed control for a long time due to its poor speed control performance.However, AC control mode is gradually developed due to the new electronic devices and large-scale integrated circuits,and will eventually replace the DC speed control system.
It’s mainly divided into two control modes in the FFU AC control mode, voltage regulation control and frequency conversion control.The so-called voltage regulation control method is to adjust the motor speed by directly changing the size of the motor stator voltage.The disadvantages of the voltage regulation method are low efficiency in speed regulation, serious motor heating when the speed is low and limited speed range.However, the drawbacks of the voltage regulation method for FFU fan loads are not very obvious and there are some advantages in the current situation,
◆ The speed control program is well established and the speed control system is stable, which can ensure trouble-free operation for a long time.
◆ Easy operation and low cost of control system
◆ As the FFU fan load is very light, the motor heating is not very serious at low speeds.
◆ The voltage regulation is especially suitable for fan loads, because the FFU fan responsible curve is a unique damping curve, the speed regulation range can be very wide.Therefore, the voltage regulation will remain a major speed regulation method for a long time.Frequency control mode is to speed up the motor by changing the power supply frequency F. At the same time, the input voltage of the whole motor is adjusted by a certain proportion.Variable frequency control method has excellent performance, such as large speed range, high smoothness and high speed control efficiency, etc.Inverter generally uses the more advanced SPWM control method and uses a microcontroller to generate the SPWM waveform.
Compared with other inverter methods, the SPWM inverter method has the following characteristics,
1）Simple structure and easy control
2）High power factor input
3）Fast system dynamic response
4）Low harmonic output
The frequency conversion method also has some disadvantages compared to the voltage regulation method, which are mainly reflected in the following two aspects，
◆ Higher cost of inverter method
◆ Lifespan is not as long as the regulator method
With the continuous development of semiconductor technology, it can be expected that a number of simple, reliable, high-performance, inexpensive frequency control system will continue to appear. Asynchronous motor frequency conversion speed control method will be widely used, and will replace DC speed control and voltage regulation speed control method.
3.FFU intelligent control system
Currently, the application rate of its control system is still relatively low in the FFU application, FFU intelligent control system, generally only for the FFU equipped with brushless DC motor is popular in the international market. Especially in energy shortage, the energy-saving benefits of control systems are increasingly being emphasized.Each cleanroom depends on the product\'s production process and determines the appropriate airspeed while considering energy consumption.The general control system can adjust the limited wind speed range. Still, it can not provide specific wind speeds according to particular requirements, especially besides 8-hour resting time, which undoubtedly brings a massive waste of energy maintaining a high wind speed.The HH-F series of FFU intelligent control system is launched with digitally adjusting fan
speed for this specific situation.
The system is easy to operate and has a friendly interface, especially since it can be set digitally according to the specific airspeed requirement of the clean room (e.g., 0.37m/s,0.28m/s).
HH-F series of FFU control systems is a set of centralized control systems that can conveniently achieve on-site decentralized control and centralized, unified management functions.
It can flexibly control the starting and stopping of each fan and wind speed in the clean room. The control system utilizes the repeater technology to solve the problem of limited 485 driving capacity and can control unlimited fans.
This control system consists of the following four parts,
◆ On-site intelligent controller
◆ Integrated wiring control method
◆ Remote control method
◆ Systematic integration function
The control system chart is shown below:
3.1 On-site intelligent control module
The on-site intelligent control module realizes the control function with microcontroller as the core processor. One intelligent module controls one FFU.
The on-site intelligent control module is divided into a voltage regulator module and a frequency converter module, and the two intelligent control modules can achieve the following control functions:
1）The intelligent modules are highly open and can be controlled in the field using an optional hand operator (pluggable). Remote centralized control and fault diagnosis and setting can be achieved through the reserved RS485 interface. Remote control is possible with an optional remote control kit (pluggable).
2）can control the FFU start and stop, providing accurate step-less speed shift, and display the FFU outlet air speed value.
3）This intelligent module enables the FFU to have an energy-saving function.
4）Overload and short-circuit protection: when overloaded, prompt the unit alarm ; when short-circuited, prompt the alarm and automatically cut off the power supply of FFU.
3.2 Wired control system
The wired control method is optional, which is implemented through the RS485 interface reserved for the field intelligence module.To meet the needs of different users, we use the control panel and touch screen, which are two kinds of control modes. The control panel is easy to operate, but the display is not intuitive, and the function is limited.The touch screen cost is easy to operate, and the display screen is rich and powerful.The touch screen control method mainly comprises three parts: 1) central control unit, 2) human-machine interface unit, and 3) alarm control unit.
(1)Central control unit with PLC controller. It is capable of realizing the following control functions:
◆ It adopts the RS485 bus system to connect with the on-site intelligent control module to analyze and process the collected on-site data and realize the control function of the on-site equipment. Thus, it achieves the centralized monitoring and control of all FFUs on site.
◆ Communicates with the alarm control unit.
◆ Communicates with the HMI unit.
2）The human-machine interface unit uses a touch screen to realize the monitor and adjust the FFU from a distance. It can recognize the following control functions:
◆ It is easy to realize single, multiple, and partition control of FFU. In other words, it can
control any number of FFUs at the same time.
◆ It can realize the start-stop and speed regulation function of any number of FFUs, and the speed regulation function can be digitized, i.e., directly inputting the expected wind speed value (e.g., 0.25, 0.31, etc.) to achieve the purpose of speed regulation.
◆ Able to monitor the air velocity value of any FFU.
◆ When there is a faulty FFU alarm, it can display the faulty FFU in real time.
The alarm control unit uses a sound and light alarm device through communication with the central processing unit; when FFUs fail, the control unit uses real-time sound and light alarm with the human-computer interface unit to cooperate and quickly identify the faulty FFU to ensure that the monitoring staff to deal with the problem promptly.
Control panel： according to the needs of the actual system, the repeater has a corresponding number of 485 communication sockets; each socket corresponds to a group of FFU controllers.Each controller can be controlled via the control panel. The control functions are as follows:
1）It controls the starting and stopping of a particular group of fans in the whole clean room, and the air speed of a specific group of fans can be set uniformly.
2）It controls the starting and stopping of a particular fan in the entire clean room, and allows you to set the air speed of a particular fan.
3）The number of fans in a group can be set. (The system specifies 16 fans per group).
4）Query the operation status of a fan in the entire cleanroom, such as the start and stop status of the fan and the fan\'s operating airspeed.
5）Short-circuit protection: When a short-circuit occurs, the power supply of the FFU can be cut off automatically to protect the equipment.
3.3 Remote control method
The remote control method is optional.
It realizes the remote control mode through the on-site intelligent module reserved interface and the pluggable communication module. The hand instrument realizes the specific function and adopts a one-to-many control mode for control.
The hand instrument is capable of the following control functions,
1）It is easy to realize the start/stop and speed regulation function of each FFU. The speed control function can be digitized, i.e., directly inputting the expected wind speed value to achieve the purpose of speed control.
2）Able to monitor the air velocity value of each FFU.
3.4 Systematic integration functions
The control system is also capable of performing the following functions:
1）The AC voltage regulating mode control system can guarantee a long time, trouble-free, continuous operation under normal use conditions, and more than 80,000 hours can be guaranteed under normal use conditions.
2）The whole set of control systems has a reasonable layout and simple wiring.
3）The wind speed can be set according to the actual situation to minimize the fan\'s power consumption and achieve energy savings.
4）Timing control of the fan speed during non-working hours automatically reduces the fan speed to maintain indoor clean requirements and achieve the purpose of energy saving.
SEVICON can professionally design customized products with purifying equipment according to specific requirements. It also provides:
Strict product testing.
Multi-channel product commissioning.
Installation control.
Pre-sale and after-sale professional support services.
