Scenery converter application in the pharmaceutical industry and electromagnetic compatibility
Shandong New Scenery Electronic Technology Development Co., Ltd. Zhao Xinjun
Zhao Xinjun
Abstract: This paper introduces the application of frequency converter in DCS system of fermentation industry, the selection of filter components, and the matters needing attention in installation.
Keywords: frequency converter electromagnetic interference electromagnetic compatibility
Abstract:This article introduces the application of inverter in the yeast- industry DCS system, the choice of the filter, and some items in installation should pay attention to.
Key words: Inverter EMI EMC
1 Introduction
Fermentation industry is an important part of modern bio-engineering, especially the new fermentation industries such as pharmaceuticals, monosodium glutamate, citric acid, and xanthan gum, which have been rapidly developed in recent years. Since the raw materials are produced, they are inseparable from the fermenter. At the core, with the continuous increase of product output and new varieties, the stirring speed of the fermenter is also required to be different, and different adjustments are required at different times. In view of the large load, relatively large power consumption, and long fermentation cycle, we have done a lot of equipment transformation in the national fermentation industry in recent years, that is, to meet the production process requirements and save a lot of resources.
The application of frequency converters in fermentation tanks has become increasingly popular, providing good production and process benefits for industrial automation control in the industry. However, with the continuous improvement of the degree of automation, the degree of pollution of power supplies from automation equipment is getting deeper and deeper, and the corresponding interference with automatic control systems is becoming stronger and stronger, and the requirements for relatively stable green power supply for filtering and purifying power supplies have been achieved. It is also getting higher and higher.
With the development of power electronics, household appliances, industrial appliances, and computer networks are increasingly developed. The electromagnetic environment is increasingly complex and deteriorating, making electromagnetic compatibility (EMC), electromagnetic interference (EMI), and electromagnetic immunity (EMS) of electrical and electronic products subject to various governments and production. The company attaches great importance to electromagnetic compatibility (EMC) of electrical and electronic products. EMC is a very important quality indicator. It not only concerns the reliability and safety of the product itself, but also may affect the normal operation of other equipment and systems. To protect the electromagnetic environment, in order to ensure the stable and reliable operation of electronic equipment and reduce electromagnetic pollution, more and more countries have begun to implement EMC standards, especially in European countries, EMC's performance has become a legal indicator, become electronic One of the indicators that product manufacturers must pass.
Internationally, there are relatively clear laws and regulations on the design and application of electromagnetic compatibility (EMC or EMI). There are clear regulations on the interference and interference of electronic devices and the harmonic content of power supplies. Due to the late start of EMC technology in China, both the theory and technology level and related products (test equipment, shielding materials, filters, etc.) are far from developed countries, so they are relatively backward in practice. However, in some In industries where the degree of industrial automation is relatively high, the significance of electromagnetic compatibility has become relatively obvious. Some electronic devices are very sensitive to electromagnetic interference and have been unable to work properly.
2 Types of noise and countermeasures
1) The main ways of interference spread are conduction and radiation
Conducted interference: The root cause of interference is an unwanted change in voltage/current. This change is caused by direct transmission of the wire to other devices.
Radiated interference: The generation of phenomena is inseparable from the antenna. According to the “antenna principleâ€, if the length of the wire is equal to the wavelength, it is easy to generate electromagnetic waves.
In short, when the length of equipment and wires is shorter than the wavelength, the main problem is conducted interference. When their size is longer than the wavelength, the main problem is radiated interference.
In addition, there are some short-lived high-energy pulse interferences in the environment. These interferences are very harmful to electronic devices. Generally speaking, these interferences are transient interferences. Transient interference can enter the device through cables, and can also be in the form of broadband radiation interference. Affect the device.
2) Voltage/current changes There are two states when transmitting over the wire, common mode and differential mode.
The communication lines that exchange power lines, signal lines, etc. between the equipment and other equipment or peripheral equipment have at least two conductors. These two conductors transmit power or signals as a round-trip line, but they are There is another kind of lead wire.
There are two ways to interfere with the voltage and current:
A two-wire transmission as a round trip line is differential mode;
The other is the two wires to do the way, the ground return transmission is common mode.
For the differential mode voltage, one wire is (line voltage)/2, and the other wire is (line voltage)/2, and thus is balanced. However, the common mode voltage is the same on both wires. When two modes exist at the same time, the voltages of the two wires to the ground are different.
Therefore, when the two wires have different voltages or currents from the ground, the following two methods can be used to determine the composition of the two modes:
UN=(U1-U2)/2UC=(U1+U2)/2
IN=(I1-I2)/2IC=(I1+I2)/2
3) Grounding is an important issue for electronic devices:
1. Grounding makes all the circuits in the entire circuit system have a common reference zero potential, that is, there is no potential difference between the grounds of each circuit to ensure that the circuit system can work stably.
2, to prevent external electromagnetic interference, the chassis ground provides a relief channel for transient interference, but also can cause a large amount of charge accumulated in the chassis due to electrostatic induction through the earth to discharge, in addition, for the circuit shield, if you choose Proper grounding can achieve good shielding effect.
3, to ensure safe operation, when direct lightning electromagnetic induction occurs, can avoid damage to electronic equipment, when the equipment is not well insulated caused by grounding equipment, can avoid artificial electric shock.
In short, grounding is one of the main ways to suppress noise and prevent interference. A well-designed grounding system prevents undesired interference and emissions at a very low cost.
4) The cable is a highly efficient electromagnetic wave receiving antenna and radiating antenna, and it is also a good channel for interference. The use of shielded cables may solve the problem of cable radiation. However, in the case of shielded cables, a reasonable grounding of the shield is an important issue to solve the cable interference. Incorrect selection of grounding points will cause interference problems with the shielded lines. .
In addition, the layout of the cable also has a significant impact on the electromagnetic interference of the product. The coupling between the cables and the loop formed by the cable routing are important components of the electromagnetic interference design of the cable.
3 EMC filter and filter selection
a) Resistance
Resistance is the most commonly used device on a PCB, and resistance is also a limitation of EMI use. The limitations imposed on the frequency domain requirements depend on the resistive material used. Wire wound resistors are not suitable for high frequency applications due to the additional inductance of the wire wound. The thin film resistors contain some inductance, but due to their low lead inductance, they can sometimes be used in high frequency applications.
b) Capacitance
Capacitors are commonly used for power bus decoupling, filtering, bypassing, and regulation. Below the self-resonant frequency, the capacitor maintains capacitance. Above the self-resonant frequency, the capacitance range is inductive, and can be described by the formula Xc=1/2 лƒC, where Xc is capacitive reactance and the unit is ohm (Ω); F is frequency, The unit is Hertz (HZ); C is a capacitor and the unit is Farad (F).
c) Inductor
Inductors are also commonly used to control EMI. As the frequency increases, the inductance of the inductor increases linearly and can be described by the formula XL = 2 лƒL.
Common Mode Choke is also called common mode choke.
The common mode inductor is connected to the interference source at one end and to the interfered device at the other end. It is usually used together with a capacitor to form a low-pass filter, which allows the common-mode EMI signal on the line to be controlled at a very low level. The circuit can not only inhibit the incoming of external EMI signals, but also attenuate the EMI signals generated when the circuit itself works, and can effectively reduce the intensity of EMI.
d) Ferrite ring
When the inductor cannot be used for high frequencies, it is a good idea to use ferrite beads. The ferrite material is a ferromagnetic or iron-nickel alloy. This material has a very high frequency permeability and high frequency impedance, and at the same time it has the smallest wire-wound capacitance and is suitable for high frequency applications. At low frequencies, the inductance is small and the line loss is small. At high frequencies, it is basically reactive, and it is related to the frequency.
Ferrite magnetic ring is "energy-consuming equipment." It consumes high-frequency energy in the form of heat and can only be explained by the characteristics of a resistor rather than an inductor.
e) Filter
The filter is a two-port network. It has inductance, capacitance, and common-mode inductance components to form a passive low-pass network. The basic circuit diagram is as follows:
In a general filter, the role of the common mode choke is to filter out low frequency common mode interference. Due to the presence of parasitic capacitance at high frequencies, common-mode chokes have less interference suppression and rely mainly on common-mode filter capacitors.
4 System Introduction
Henan Xinxiang Huaxing Pharmaceutical Co., Ltd. adopts the automatic DCS control system produced by Beijing Kangtuo Bioengineering Co., Ltd. to conduct comprehensive monitoring of the temperature, pressure, flow rate, dissolved oxygen (DO), and pH (pH) of each fermentation tank. And in the fermentation process of feeding, discharging, including liquid sugar, phenylacetic acid, sulfur ammonia, etc. for automatic control, there are three sensors to detect and send electrical signals to the computer control system. The microcomputer control system timely sends a pulse signal (+5V) according to the detected voltage (or current) value to control the opening and closing of the solenoid valve (the solenoid valve operating voltage is +36V) to achieve the replenishment of the material in and out. In this way, there are three solenoid valves, three sensors, and two detection instruments for each fermentation tank. All remote monitoring is performed on the microcomputer and all data is displayed on a large screen wall. The system diagram is as follows :
5 Electromagnetic Interference Problem Analysis and Solution The input power supply of the inverter adopts the filter manufactured by Taiyuan Ford Electronics Co., Ltd. The internal ferrite core and iron powder core with high magnetic permeability are used, and a certain capacitance is combined to constitute the LC. The filter filters out the higher harmonics (in a certain frequency band) generated by the frequency converter, so that the electrical equipment in the vicinity or in the same power grid can operate normally without interference. The schematic is shown below.
Figure 1 shows the schematic diagram of the input filter circuit. The power filter at the output of the inverter adopts inductance (L) filtering to suppress the conduction interference from the inverter output and reduce the low-frequency radiation interference on the output line, so that the electromagnetic noise of the directly driven motor is reduced. The copper loss and iron loss of the motor are greatly reduced. The schematic diagram is shown in Figure 2.
Figure 2 shows the schematic of the output filter circuit.
Figure 3 is the inverter main circuit diagram Inverter main circuit is generally AC - DC - AC mode shown in Figure 3, the external input 380V/50Hz power frequency power supply is not controlled by the three-phase bridge rectifier into a DC voltage signal, the filter capacitor filtering and The high power transistor switching element is inverted to a variable frequency AC signal. In the rectifying circuit, the waveform of the input current is an irregular rectangular wave, and the waveform is decomposed into the fundamental wave and each harmonic wave according to the Fourier series. Among them, the higher harmonic wave will interfere with the input power supply system. In the inverter output circuit, the output current signal is a pulse waveform modulated by the PWM carrier signal. For the GTR high power inverter component, the PWM carrier frequency is 2 to 3 kHz, and the PWM highest carrier frequency of the IGBT high power inverter component Up to 15kHz. Similarly, the output loop current signal can also be decomposed into a fundamental wave containing only a sine wave and other harmonics, and the higher harmonic current directly interferes with the load. In addition, high-order harmonic currents also radiate into the space through cables and interfere with nearby electrical equipment.
6 Speed ​​words
Through the approval of many companies, the scenery converter has been widely used in the fermentation industry, and it has solved the issues related to the electromagnetic compatibility of the automation industry and the inverter in the fermentation industry. As China's inverter market is expanding, the significance of electromagnetic compatibility will be more extensive, and its application prospects will be very optimistic.
references
Yu Lv Youkang Mingdian Electric Co., Ltd. Consideration of Electromagnetic Wave Noise in Frequency Inverter Application Inverter World 2006.08
About the Author
Zhao Xinjun (1978-) Male Engineer Currently working with the Technical Support Department of Shandong Xinfeng Optoelectronics Technology Development Co., Ltd., the main direction: the DCS system automation control and inverter EMC design and development in the fermentation industry.
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