Power filter must be familiar to everyone, how much do you know about it? What brand is better in the field of power filters at present? This article will discuss the selection of power supply filters.
Power filterThe power filter is a filter circuit composed of capacitors, inductors and resistors, also known as "power EMI filter" or "EMI power filter", a passive two-way network, one end of which is the power supply and the other end is the load . The principle of the power filter is one kind-impedance adaptation network: the greater the impedance adaptation between the input and output sides of the power filter and the power supply and load side, the more effective the attenuation of electromagnetic interference. The filter can effectively filter out the frequency point of a specific frequency in the power line or the frequency other than the frequency point to obtain a power signal of a specific frequency, or eliminate a power signal of a specific frequency.
The power filter is a passive two-way network, one end of which is the power source, and the other end is the load. The principle of the power filter is one kind-impedance adaptation network: the greater the impedance adaptation between the input and output sides of the power filter and the power and load sides, the more effective the attenuation of electromagnetic interference.
What brand of power filter is good (ranking)1. Honeywell
Honeywell SmartWave series active power filter is a truly effective harmonic control solution, using the most advanced active harmonic compensation technology to dynamically eliminate grid harmonics. SmartWave detects the current waveform generated by the non-linear load in real time, separates the harmonic part, and then outputs the equivalent harmonic current through the IGBT inverter circuit to offset the load harmonic, ensure that the current drawn from the grid is a sine wave, and achieve harmonic filtering In addition to the function. In addition, SmartWave can also provide leading or lagging reactive current to improve the power factor of the grid and achieve dynamic reactive power compensation.
Star product: SmartWave series active power filter
2. Nokia
The establishment of Nuoqi Capacitor (Shanghai) Co., Ltd. not only brought international advanced power products to the country, but also changed the domestic power industry's usage of reactive power compensation and harmonic filtering. It has not only promoted the development of the domestic capacitor industry towards high quality, high stability and high safety. Provide solutions to customers through a professional sales team.
Star product: Low-voltage active filter (NCSA)
3. ABB
The ABB filter is a dynamic filter with an unprecedented ability to filter out harmonics in the power grid. It is the only product in the world that can filter out harmonics with closed-loop feedback. Applicable to the industrial field, it can effectively control the high-order harmonics of the power grid, improve the quality of the power grid, and increase the power factor. It is widely used in metallurgy, communication, process control and other industrial fields. PQF is a controllable dynamic way to filter out the harmonics appearing in the power supply system. It is not affected by changes in the operation structure of the power grid, such as the impact of changes in system impedance caused by different power supply conditions such as parallel power supply, grid power supply and switching power supply between standby generators.
Star product: PQF series active filter
4. Schneider
Schneider Electric's Accusine active power filter is the perfect solution for harmonic control. Accusine uses the most advanced analog logic method to eliminate grid harmonics. Accusine detects the current waveform generated by the non-linear load in the power grid in real time, separates the harmonic part, reverses it, and then injects the reverse current into the power grid through the IGBT inverter to achieve the function of filtering harmonics. In addition, Accusine can also provide leading or lagging reactive current to improve the power factor of the grid and realize dynamic reactive power compensation.
Star product: AccuSine active power filter
5. Chasing Sun Electric
The ZAPF parallel active power filter device of Zhui Ri Electric integrates the most advanced technology in the world in this field, and it was selected for the 2010 Shanghai World Expo and the Guangzhou Games. Not only that, Chairi Electric also combines fate and passive, filtering and compensation, and develops a variety of power quality optimization control products to meet the different needs of different industries, different working conditions, and different customers.
Star products: ZAPF three-phase three-wire parallel active power filter device (active filter), ZAPF three-phase four-wire parallel active power filter device (active power filter)
6. Maxwell Electric
As an early expert in harmonic control, Maxwell Electric's team has independently developed, produced and sold a full range of active power filters based on multiple project experience and years of technical precipitation. Maxwell Electric’s METAPF series of harmonic control products cover a wide range. The maximum harmonic control capacity of a single set of equipment can reach 1200A, reaching the most advanced international technical level. The harmonic control capacity of a single active power filter cabinet can reach 200A, and the products include wall mounts. Various product models such as model type, cabinet type, 3P3L, 3P4L, etc., to meet the different market needs of different end customers.
Star product: GEMActive active power filter
7. Shenzhen Shenghong
The advantage of Shenghong Electric's power electronic technology is the modular high-power power product technology. Various products of power quality and renewable energy use this as a platform technology to maximize the effectiveness of modular technology. Sinexcel APF series products have a variety of compensation functions such as harmonic compensation, power factor compensation and three-phase unbalance compensation. They can filter out 2-50 harmonics and improve the power factor of the power grid. It is a perfect solution for power quality problems.
Star product: 400V APF product capacity series active power filter
8. Shanghai Siyuan
Shanghai Siyuan Electric is a well-known domestic listed company specializing in power technology research and development, equipment manufacturing, and engineering services. The company has seven wholly-owned and holding subsidiaries. The product line covers multiple power transmission and distribution technologies and professional fields of power transmission and distribution primary and secondary equipment. The company’s leading products and core technologies are at an advanced level in the world, and provide users Provide complete solutions for substations.
Star product: APF active power filter
9. Cyber ​​Electric
Xi’an Cyber ​​Electric Co., Ltd. is a high-tech enterprise specializing in the research and development, production, sales and service of power quality products with active power filters and static reactive power generators as the core. It is a first-class provider of overall power quality solutions Quotient.
Star product: Active Power Filter APF
10. Shenzhen INAST
Insex Active Power Filter APF module is a supporting optimization solution specially launched for low-voltage complete sets of manufacturers. Under the premise of ensuring high-quality harmonic control effects, it can greatly reduce the supporting costs of low-voltage complete sets of manufacturers and improve the competitiveness of enterprises.
Star product: Modular products of active power filter, APF (cabinet type) of active power filter
What should be paid attention to when choosing a power supply filter?There are many kinds of filters, and power filters and signal filters are commonly used in equipment. Other types of power filters for reactive power compensation and microwave frequency filters are not discussed here.
1. Voltage
This voltage value requirement is a range, which is the synthesis of steady-state voltage ± ripple voltage.
2. Current
The current index is very important, it determines the wire diameter of the winding copper wire and the lead wire of the inductance inside the filter. If you choose a thinner wire, running a large current on the thin wire, such as a small horse-drawn cart, will cause severe heat and even burn. This current is also a range, the maximum value of steady-state current + fluctuating current.
3. Electromagnetic compatibility standard requirements
Since it is a filter, the purpose is to filter out some undesired frequency bands, and the filtering effect is generally determined by the intuitive results of EMC test standards and field applications. Especially for power supply filters, it is best to determine which standard the product using this filter needs to pass. According to the different standard requirements, there are also specific test frequency band requirements when selecting.
The main indicators of the power filter are the conducted emission CE and the conducted anti-interference CS, and the signal filter mainly depends on the requirements for the undesired input frequency band and the undesired output frequency band in the EMC standard.
For example, the rectifier used in induction lamps is a switching state and will have external emission. During EMC testing, the switching frequency and the conduction interference of its high-order harmonic components will be checked. The filter needs to be targeted at these specific frequency bands or frequencies. The point has sufficient filtering effect.
4. Safety standard requirements
Readers may find it strange to choose a filter and say what safety standards do? This is because the filter is generally used at the power input terminal and the interface of the board. These parts are the hardest hit areas for safety issues. It is equivalent to the filter itself has undertaken multiple requirements. The focus of safety regulations related to filters are three indicators: insulation withstand voltage, leakage current, residual voltage and residual energy.
The insulation strength of LN to ground is tested by the withstand voltage value of the Y capacitor. If the Y capacitor is large, the leakage current will be large, which will easily cause the leakage current in the safety requirements to exceed the standard. Now some manufacturers design it A design with no Y capacitor at the input is adopted (as shown in the figure). In this way, LN to G becomes LN through L1, Cy1, Cy2, G'to G, and G and G'are not connected. If the input terminal is connected to the Y capacitor, that is, Cy1 and Cy2 are placed on the left side of the front R, the insulation withstand voltage setting and the leakage current are positively correlated during the test, and the maximum is not more than 20mA. I have encountered a situation where the filter was almost returned and said the safety of the filter was unqualified. Finally, it was checked that the leakage current was set to 2mA (should be 5mA) at 1500V, and the test instrument alarm was normal.
Another problem is the choice of R. There are many manufacturers’ filters that do not install this resistor. After unplugging, touch the power socket within a short period of time. If there is a feeling of being charged, the problem lies in it. This resistor is not installed. This is a power resistor with high withstand voltage and a role of bleeder and discharge.
5. Filter circuit structure
The choice of circuit structure and period parameters is the core of the filter, but it is in this part that application engineers often choose with a blind eye. Although it can be used most of the time, they do not know their own or other design methods. , The possibility of wasting resources and burying hidden dangers is greatly increased. This is out of date in the electronics manufacturing industry that requires lean design, from Chinese manufacturing to Chinese creation, and from the growth expectations of junior engineers to senior engineers.
The function of the filter is to have different amplification effects on the different frequencies passing through it. It does not attenuate the frequency band within the passband, and attenuates the frequency band outside the passband at the level of tens of dB, so as to achieve the sieve. purpose. But even when the filter adopts different magnifications for the voltage amplitude of different frequencies, the phase of the electromagnetic wave is also changing, because the phase is also related to the frequency, so the selection of the filter structure is still somewhat knowledgeable.
There are three commonly used filter structures:
a. Butterworth filter: The characteristic is that the magnification in the passband is flat, and in the passband, with the change of frequency, the magnification of the filter basically remains unchanged; but the disadvantage is that the transition section from the passband to the cutoff section is transitional. More gentle. It means that the boundary between the enemy and the friend is not very clear. Some of our friends are also doing the enemy's things, and some of the enemies are also helping us. It is very entangled to kill this part or stay in the organization. If the useful frequency and the interference frequency are very close, the function of this kind of filter is very problematic.
b. Chebyshev filter: It can solve the shortcomings of the smooth transition zone of Butterworth. In this form of filter, the transition zone is very steep, even if the useful frequency and the interference frequency are very close, because the transition zone is very close. It is steep, so the difference in the magnification of the two frequency bands before and after the cutoff frequency point is very big. It is easy to distinguish whether it is a friend or an enemy. If it is a friend, it has never done something sorry for us, and if it is an enemy, it has never done a good thing for us. , So friends are drawn into the organization and treated well, but the enemy is wiped out cleanly. There must be deep valleys on the side of the mountain. One advantage must be accompanied by a disadvantage. The disadvantage of the Chebyshev filter is that at the end of the passband frequency, the magnification will have strong fluctuations, that is, in the passband, with the frequency Change, although the magnification is much larger than the filtered frequency band, the magnification of the frequency in the passband is not stable, that is, the mood of friends is not stable, and not all friends are the same as before. Give help. (Just give an example, don’t misunderstand it as dissatisfaction with friends)
c. Bessel filter: This type of filter is not very versatile, and it is more specialized because its characteristic is phase linearity. The first two focus on the magnification, but for voice signals, such as songs, although the magnification in the passband has not changed, the melody is no longer melodious. Because of the change in phase, the song chuckles and is unpleasant to listen to. At this time, the Bessel filter will have its effect.
As to which filter circuit structure to choose, circuit engineers may not do in-depth research, but they must know the characteristics they want and provide them to the filter manufacturer, who will help you make the choice.
The current power filters are all low-pass filters, passing the power frequency 50Hz or 60Hz, which is a useful frequency, and the others are all useless, so it is more than enough to use a cut-off frequency above 1KHz. Therefore, blind people ride Choose the filter randomly, and there is no problem in many cases. Therefore, more attention should be paid to the selection of power supply filters in terms of technology and safety regulations. However, when there is a specific output or input, the selection of the power supply filter must be cautious. For example, the operating frequency of electrosurgical products during medical surgery is 500KHz, which will cause interference to the network power supply. Therefore, the external conduction interference of electrosurgicals needs to be suppressed; at the same time, equipment that shares power with electrosurgicals should also be vigilant, and its 500KHz is also It may interfere with you.
6. Insertion loss curve
The insertion loss measurement of the filter must not be true. For example, if we find that 100KHz exceeds the standard by 13dB, we choose a filter, and we can see from the insertion loss curve that its insertion loss at 100KHz is 20dB. If we think that this filter will definitely be no problem when it is used, it is wrong. , Because the manufacturer’s insertion loss curve is measured under the standard impedance of 50Ω-50Ω, the actual application site is basically certain that the source impedance and load impedance characteristics are not so standard, so the attenuation effect of the filter will be greatly reduced. Therefore, when selecting the frequency point to be suppressed, a margin of at least 20dB must be left. As in the above example, it is necessary to select a filter with an insertion loss of not less than 33dB at 100KHz.
In addition, the insertion loss is divided into common mode insertion loss and differential mode insertion loss. Generally, for interference above 30MHz, select a filter with common mode insertion loss that meets the above requirements, and for interference below 10MHz, select a filter with differential mode insertion loss that meets the requirements. For example, 100KHz, choose a filter with a 33dB differential mode insertion loss.
7. The installation form of the filter
This problem is easy to understand. Generally, there are plate type (with solderable pin pins), screw fixed installation, IEC standard (with single-phase 220V three-pin input), and IEC with switch. This can be selected according to the actual structure and function requirements.
8. Installation process specification
The installation of the filter is the technical element second only to the circuit structure and the component index. Mainly reflected in the location of the filter and grounding measures. The location is required to be close to the input or output end, in order to avoid the high-frequency interference on the input end and output end cables from radiating out and affecting other circuits; the input line and output line must not run in parallel or close to the line, so as to avoid mutual crosstalk causing the clean Cannot be cleaned; the subject of the filter is a metal shell. Grounding requires surface grounding instead of line grounding. The entire surface must be in good contact with the ground. It cannot be grounded only by the screw that fixes the pin or the grounding wire drawn from it. The lead of the wire is grounded. Large inductance and high high-frequency grounding impedance lead to poor high-frequency grounding and poor filtering; the grounding cable is not suitable for screwing, and welding must be used.
9. The Q value of the filter
The Q value has little effect on the actual filtering effect, but the Q value represents the loss/input power. The higher the Q value, the greater the loss, which means that part of the energy will be lost in the inductance of the filter. In general low-power power supply filters and signal filters, this problem will not be too prominent. However, this loss should not be underestimated in a filter with higher power. First, it will cause heat, and the capacitor after heat will cause a greater negative effect. Leakage current, withstand voltage, capacitance, etc. will all change with temperature; It is the power consumption that causes unnecessary power loss.
10. Other
The other content is the inside of the filter, which is invisible to the user. The uniformity and density of the potting compound and the thickness of the insulating paper between the device and the metal can only be understood by users through interrogation. If the manufacturer tells the truth, it depends on destiny.
ConclusionThat's it for the introduction of power supply filters. I hope this article will give you a deeper understanding of power supply filters.
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