SEVICON Cleanroom FFU Control System

The full name of FFU is Fan Filter Unit, which is a clean device where the fan and filter are connected together and can provide its own power. As a type of purification equipment, FFU is currently widely used in various cleanroom engineering projects. With economic development and the improvement of people\\\'s living standards, there is an increasing demand for product quality. The production technology and production environment determine product quality, which compels manufacturers to pursue better production technology and higher production standards. Especially in fields such as electronics, pharmaceuticals, food, bioengineering, medical, and laboratories, strict requirements are placed on the production environment, encompassing multiple technologies including process, construction, decoration, water supply and drainage, air purification, heating, ventilation, air conditioning, and automatic control. The main technical indicators for measuring the quality of production environments in these industries include temperature, humidity, cleanliness, air volume, and indoor positive pressure. Therefore, rational control of various technical indicators of the production environment to meet the requirements of special production processes has become one of the current research focuses in cleanroom engineering.

2.Current Status of FFU Control Methods

At present, FFUs generally use single-phase multi-speed AC motors, three-phase multi-speed AC motors, and DC motors. The motor supply voltages are roughly 110V, 220V, 270V, and 380V. The control methods are mainly divided into the following categories:

◆ Multi-position switch control

◆ Continuous speed regulation control

◆ Computer control

◆ Remote control

Below is a brief analysis and comparison of the above four control methods:

2.1 Multi-Position Switch Control

The multi-position switch control system only includes a single speed control switch and a power switch built into the FFU itself. Since the control components are integrated within the FFU and distributed in various positions within the cleanroom ceiling, personnel must adjust the FFU on-site using the toggle switches, making control extremely inconvenient. Moreover, the adjustable range of the FFU fan speed is limited. We once carried out a project where, in order to overcome the inconvenience of FFU control operations, through the design of electrical circuits, all FFU multi-position switches were centralized and placed in a cabinet on the ground, allowing for centralized operation. However, there were limitations both in terms of appearance and functionality. The advantages of using a multi-position switch control method are its simplicity and low cost, but it has many shortcomings: for example, high energy consumption, inability for smooth speed regulation, lack of feedback signals, and inability to achieve flexible group control.

2.2 Continuous Speed Regulation Control

Compared with the multi-position switch control method, continuous speed regulation control adds a continuous speed regulator, allowing the FFU fan speed to be continuously adjustable. However, this also sacrifices motor efficiency, resulting in energy consumption that is even higher than that of the multi-position switch control method.

2.3 Computer Control

Computer control methods generally use DC motors. Compared with the previous two methods, computer control has the following advanced features:

◆ Adopts a distributed control method, which can easily achieve centralized monitoring and control of FFUs.

◆ Can conveniently implement single-unit, multiple-unit, and zoned control of FFUs.

◆ Intelligent control systems have energy-saving functions.

◆ Optional remote control methods can be used for monitoring and control.

◆ The control system reserves communication interfaces, allowing communication with a host computer or network to enable remote communication and management functions.

The outstanding advantages of controlling DC motors are that they are easy to control and have a wide speed adjustment range. However, this control method also has some critical drawbacks:

◆ Since cleanrooms do not allow FFU motors to have brushes, all FFU motors use brushless DC motors. The commutation issue is solved by electronic commutators, but the short lifespan of electronic commutators greatly reduces the overall lifespan of the control system.

◆ The entire system is expensive.

◆ Maintenance costs are high.

2.4 Remote Control Method

As a supplement to computer control methods, the remote control method can be used to control each FFU via a remote controller, complementing the computer control method.

In summary: the first two control methods have high energy consumption and are inconvenient to operate; the latter two control methods have short lifespans and high costs. So, is there a control method that can achieve low energy consumption, convenient operation, and also ensure long service life and reasonable cost? Yes, that is the computer control method using AC motors.

Compared with DC motors, AC motors have a series of advantages such as simple structure, small size, ease of manufacturing, reliable operation, and low cost. Since they do not have commutation problems, their service life far exceeds that of DC motors. For a long time, due to their poor speed regulation performance, speed regulation has been dominated by DC methods. 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 theories, AC control methods have gradually developed and will eventually replace DC speed regulation systems.

In FFU (Fan Filter Unit) variable speed control, there are mainly two control methods: voltage regulation control and frequency conversion control. Voltage regulation control refers to adjusting the speed of the motor by directly changing the voltage of the motor stator. The disadvantages of voltage regulation include lower efficiency during speed regulation, significant motor heating at low speeds, and a relatively narrow speed adjustment range. However, for the FFU fan load, these drawbacks are not very prominent, and under current conditions, there are still several advantages:

◆ The speed control solution is mature, and the speed control system is stable, ensuring long-term continuous operation without failure.

◆ The operation is simple, and the control system is cost-effective.

◆ Since the FFU fan load is very light, motor heating at low speeds is not severe.

◆ Voltage regulation is particularly suitable for fan loads. Because the FFU fan load curve is a unique damping curve, the speed adjustment range can be very wide.

Therefore, for the foreseeable future, voltage regulation will continue to be one of the main speed control methods.

Variable frequency control is a method of adjusting the speed of an electric motor by changing the frequency f of the power supply, while proportionally adjusting the input voltage of the entire motor. Variable frequency control offers excellent performance, a wide speed regulation range, high smoothness, and high speed regulation efficiency. Variable frequency control generally uses the more advanced SPWM control method and employs a microcontroller to generate the SPWM waveform. Compared with other variable frequency methods, the SPWM variable frequency method has the following characteristics:

(1) Simple structure and convenient control;

(2) High input power factor;

(3) Fast dynamic response of the system;

(4) Low output harmonics.

Under the current circumstances, compared with the voltage regulation method, the variable frequency method also has some disadvantages, mainly reflected in the following two aspects:

◆ The variable frequency method is relatively expensive.

◆ Its service life is not as long as that of the voltage regulation method.

With the continuous development of semiconductor technology, it can be anticipated that simple, reliable, high-performance, and cost-effective variable frequency speed control systems will continue to emerge. The application of variable frequency speed control methods for asynchronous motors will become increasingly widespread and will eventually replace both DC speed control methods and voltage regulation speed control methods.

3. FFU Intelligent Control System

Currently, in the field of FFU applications, the utilization rate of control systems is still relatively low. Moreover, among the intelligent control systems for FFUs popular in the international market, they generally only target FFUs equipped with brushless DC motors. Especially in today\\\'s world, where global energy is becoming increasingly scarce, the energy-saving benefits of control systems are receiving more attention. Each cleanroom determines the corresponding airspeed according to its production process, while also having to consider energy consumption issues. However, the wind speed range that general control systems can adjust is limited and cannot provide the exact airspeed required. Particularly during non-production periods beyond 8 hours of rest time, when airspeed remains high, this undoubtedly leads to significant energy waste. In response to this situation, Jijin has launched the HH-F series FFU intelligent control system, which enables digital adjustment of airspeed. This system is easy to operate, has a user-friendly interface, and can digitally set airspeed according to the specific requirements of the cleanroom (e.g., 0.37 m/s, 0.28 m/s).

The HH-F series FFU control system is a distributed control system that conveniently achieves both on-site decentralized control and centralized management functions. It can flexibly control the start/stop and airspeed of each fan in the cleanroom. This control system utilizes repeater technology to solve the limitation of 485 drive capacity, allowing control of an unlimited number of fans.

This control system includes the following four components:

◆ On-site intelligent controller

◆ Wired centralized control method

◆ Remote control method

◆ Comprehensive system functions

The control system topology diagram is shown below:

3.1 On-site Intelligent Control Module

The on-site intelligent control module uses a microcontroller as the core processor to perform control functions. One intelligent module controls one FFU. The on-site intelligent control module is divided into a voltage regulation module and a frequency conversion module. Both types of intelligent control modules can achieve the following control functions:

(1) The intelligent module has strong openness. By using an optional handheld operator (plug-in type), on-site control can be realized; through the reserved RS485 interface, remote centralized control, fault diagnosis, and setting adjustments can be achieved; by using an optional remote control component (plug-in type), remote control can be realized.

(2) The plug-in handheld operator can be used to start and stop the FFU and accurately perform stepless speed regulation, and it can display the FFU outlet airspeed.

(3) This intelligent module enables the FFU to have energy-saving functions.

(4) It has overload and short-circuit protection functions: in case of overload, the alarm unit will alert; in case of a short circuit, the alarm unit will alert and automatically cut off the FFU power supply.

3.2 Wired Control Method

The wired control method is an optional control mode, which is realized through the RS485 interface reserved by the on-site intelligent module. To meet the needs of different users, we use two control methods: control panel and touchscreen. The control panel is easy to operate but the display is not very intuitive and the functions are limited; the touchscreen is cost-effective and convenient to operate, with rich display screens and powerful functions.

The touchscreen control method mainly consists of the following three parts: (1) Central Control Unit; (2) Human-Machine Interface Unit; (3) Alarm Control Unit.

(1) Central Control Unit, using a PLC controller, can achieve the following control functions:

◆ Connect with the on-site intelligent control modules via an RS485 bus system to analyze and process the collected on-site data; implement control functions for on-site equipment, thereby realizing centralized monitoring and control of all on-site FFUs.

◆ Communicate with the alarm control unit.

◆ Communicate with the human-machine interface unit.

(2) Human-Machine Interface (HMI) unit: Uses a touchscreen to achieve remote monitoring and adjustment of FFUs. It can perform the following control functions:

◆ Convenient control of single, multiple, or zoned FFUs. In other words, it can control any number of FFUs simultaneously.

◆ Ability to start, stop, and adjust the speed of any number of FFUs, with speed adjustment capable of digital input, i.e., directly entering the desired air velocity values (e.g., 0.25, 0.31, etc.) to achieve speed control.

◆ Monitoring of the air velocity of any individual FFU.

◆ Real-time display of faulty FFUs when there is an alarm.

(3) Alarm Control Unit: Uses audible and visual alarm devices. Through communication with the central processing unit, this control unit triggers audible and visual alarms in real time when any one or multiple FFUs fail and coordinates with the HMI unit to quickly identify the faulty FFU, ensuring that monitoring personnel can handle the fault promptly.

Control Panel Control Method: According to the actual needs of the system, the repeater has a corresponding number of 485 communication sockets, each socket corresponding to a set of FFU controllers. Each controller can be controlled through the control panel. The control functions are as follows:

(1) Control the start and stop of a set of fans in the entire cleanroom and uniformly set the airspeed of a set of fans.

(2) Control the start and stop of a single fan in the entire cleanroom and set the airspeed of that fan.

(3) Set the number of fans in a certain group. (The system stipulates that the maximum number of fans per group is 16.)

(4) Query the operating status of a single fan in the entire cleanroom, such as the start/stop status and operating airspeed of the fan.

(5) Short-circuit protection function: In the event of a short circuit, the power to the FFU can be automatically cut off to protect the equipment.

3.3 Remote Control Method

The remote control method is an optional control method. It is implemented through the reserved interface of the on-site intelligent module and a pluggable communication module. The specific functions are realized by a manual controller, which operates using a one-to-many control approach. The manual controller can achieve the following control functions:

(1) It can easily control the start, stop, and speed adjustment of each FFU. The speed adjustment function can be digitalized, allowing the direct input of the desired airspeed to achieve speed control.

(2) It can monitor the airspeed of each FFU.

3.4 System Comprehensive Functions

The control system can also achieve the following functions:

(1) The AC voltage regulation control system can ensure long-term fault-free continuous operation under normal usage conditions, with a guarantee of over 80,000 hours under normal usage conditions.

(2) The entire control system layout is reasonable and wiring is simple.

(3) Under the premise of meeting cleanliness requirements, wind speed and rotation speed can be set according to actual conditions to minimize fan power consumption and achieve energy savings.

SEVICON conducts rigorous product testing, multiple stages of product debugging and installation adjustments, and provides professional full-process pre-sales and after-sales support. According to customer requirements, it can design personalized products as needed and efficiently deliver more professional purification equipment solutions.