Active power filter

Active Power Filter (APF) is a new type of power electronic device for dynamically suppressing harmonics and compensating for reactive power. It can compensate for harmonics and varying reactive powers that vary in size and frequency. Active,
First, the basic concept:
As the name suggests, the device needs to provide power (to compensate for the harmonics of the main circuit), and its application can overcome the shortcomings of traditional harmonic suppression and reactive compensation methods such as LC filters (traditional only fixed compensation), realizing dynamic tracking Compensation, and can complement both harmonic and reactive; three-phase circuit instantaneous reactive power theory is the main basic theory of APF development; APF has two types of parallel and series, the former uses more; parallel active filter mainly It is to control the current harmonics, and the series active filter is mainly to solve the problems caused by voltage harmonics. Compared with the passive filter, the active filter has good control effect. It can filter out multiple and higher harmonics at the same time, and will not cause resonance, but the price is relatively high!

Second, the basic principle:
The active power filter is a new type of power harmonic control special equipment made by modern power electronics technology and digital signal processing technology based on high-speed DSP devices. It consists of two main parts: the command current operation circuit and the compensation current generation circuit. The command current operation circuit monitors the current in the line in real time, converts the analog current signal into a digital signal, and sends it to a high-speed digital signal processor (DSP) to process the signal, separate the harmonic from the fundamental wave, and pulse width modulation ( The PWM signal form sends a drive pulse to the compensation current generating circuit to drive the IGBT or IPM power module to generate a compensation current equal to the harmonic current amplitude of the grid and opposite in polarity, which is injected into the grid to compensate or cancel the harmonic current and actively eliminate Power harmonics.
The technical advantage green efficiency is 97.2%, and the energy saving of the active filter is about 6,500kwh.
More efficient topology-enhanced control algorithm based on accurate model thermal design and structural optimization. The miniaturized volume is only 1/6 of the mainstream mainstream brands, taking up less space.
Adapt to different working conditions, install and innovate, use less raw materials for wall-mounted or rack-mounted installation, protect the environment, intelligently compensate for the specified number of harmonics, adjust the sensitivity, capacitive reactive compensation system, unbalanced load automatic detection and suppression system Resonant full-featured monitoring system modular N+1 redundancy, significantly improve system reliability pipeline production, better quality assurance, reduce system single fault point, flexible parallel connection, adapt to different operating conditions and features 2 to 50 harmonics at the same time, or Select any number of harmonics within 2~50 times to compensate the response time is less than 300μs
It adopts 3DSP+CPLD full digital control mode and international famous brand high-speed IGBT, closed-loop control, precise filtering of harmonic application four-phase line technology, eliminating neutral line current to automatically eliminate resonance, and is not affected by grid impedance and system impedance variation. Wave; compensate for harmonics and reactive power at the same time; compensate harmonics at the same time, reactive power and load three-phase current imbalance three working modes electronic overload protection inverter control with machine fast FPGA, power digital signal processing function module Design, easy to expand multi-machine parallel centralized monitoring function Remote network monitoring function is easy to maintain, work in the required working environment, non-machine failure no maintenance product design and production follow the domestic, international standard international standard EN50091-3, EN61000- 6-2, EN55011, EN50178:1997, IEC62040-3, IEC50178:1997, AS62040-3 (VFISS111), CISPR11
National Standard GB/T14549-93 "Power Quality: Harmonics in Utility Grid"
GB/T15543-1995 "Power quality: three-phase voltage allowable imbalance"
GB/T15945-1995 "Power Quality: Power System Frequency Allowance"
GB/T12326-2000 "Power Quality: Voltage Fluctuation and Flicker"
GB/T12325-2003 "Power Quality: Supply Voltage Allowance Bias"
GB/T18481-2001 "Power Quality: Temporary Overvoltage and Transient Overvoltage"
GB/T15576-2008 "Low-voltage complete set of reactive power compensation device"
GB7625.11998 "Harmonic Current Limits from Low Voltage Electrical and Electronic Products"
GB4208-2008 "Shell protection grade (IP code)"
Extremely wide voltage input range rated operating voltage is 380V, can withstand -40% to +20% voltage fluctuations, frequency is 50/60Hz, can withstand +/-5% frequency fluctuations, adapt to the power quality of various working conditions surroundings. At the same time, if the voltage fluctuation exceeds the upper and lower limits, the machine automatically blocks the output and issues an alarm.
The automatic current limiting is automatically limited to 100% of the output within the rated capacity. If the load side harmonic current is greater than the rated capacity of the machine, the machine will continue to output current compensation harmonics within the rated capacity, without overloading causing its own overload or exiting operation.
The load short circuit protection can withstand the impact of the load short-circuit short circuit and restart after the short circuit is eliminated.
Parallel independent control is connected in parallel to the power grid, and there will be no power failure in the power grid due to machine failure. Multiple YW-APF active power filter parallel systems, if one is out of operation due to a fault, the remaining machines can still work normally to achieve the filtering function.
The three-phase current independently controls the phase currents to be independently controlled, and the single-phase injection current is not affected by the system three-phase current imbalance, and the neutral line filtering capability is three times that of the phase line.
IP protection level and lightning protection IP protection level is IP20; lightning protection capacity is 20kA.
The monitoring system has fast and complete fault self-test functions, including mains undervoltage or overvoltage, bus overvoltage or overcurrent, fan fault, power device over temperature, input fuse blown, and other fault self-tests. The alarm signal is sent through the LCD display and the LED running status light, and the machine automatically takes the corresponding operation protection system. The monitoring system can save 500 fault records under power supply or power failure, which is convenient for analyzing the causes and troubleshooting.
Third, the basic application:
Harmonic main hazards:
· Increase power plant load, reduce system power factor, reduce effective capacity and efficiency of power generation, transmission and power equipment, resulting in equipment waste, line waste and power loss;
·Causing reactive power compensation capacitor resonance and harmonic current amplification, causing the capacitor bank to be damaged or unable to be put into operation due to overcurrent or overvoltage;
· Generate pulsating torque to cause motor vibration, affecting product quality and motor life;
· Due to eddy current and skin effect, the motor, transformer, transmission line, etc. generate additional power loss and overheat, waste power and accelerate insulation aging;
· The harmonic voltage enhances the electric field strength of the insulating medium in a form proportional to its peak voltage, reducing the service life of the device;
· Zero sequence (multiple times of 3) harmonic current will cause the neutral line of the three-phase four-wire system to be overloaded, and a circulating current will be generated in the transformer winding of the delta connection, so that the winding current exceeds the rated value, and even an accident may occur in severe cases.
· Harmonics will change the operating characteristics of the protection relay, causing malfunction of the relay protection facility, causing disorder of the automatic device such as relay protection;
· Harmonic changes change the rate and peak value of voltage or current, delay arc extinction, and affect the breaking capacity of the circuit breaker;
·Making metering instruments, especially inductive energy meters, produce metering errors;
· Interfere with nearby power electronic equipment, industrial control equipment and communication equipment, affecting the normal operation of the equipment.
Harmonic treatment economic efficiency energy saving 5% to 8%
7 sets of 400KVAUPS uninterruptible power supply in an IDC engine room, the electricity cost in 2008 is about 15 million yuan, and the electricity saving fee is 1.1 million yuan after the harmonics are controlled. The energy saving effect is 7.3%.
Derating reduces transformers, circuit breakers, and cable investment. A factory installs self-active filters in the national power supply, and returns a transformer to the power supply bureau, saving more than 1 million investment protection equipment and reducing equipment investment. Harmonics generated by a paper mill in Henan. Burning two wind turbines every month, losing 30,000 yuan per month to increase productivity and maintaining continuous power supply. The daily output of Daqing Acrylic Fiber Factory has increased from 197 tons to 210 tons. The advantages and disadvantages of active filtering are:
Advantages: The harmonics can be dynamically filtered out, and the harmonics in the system can be completely absorbed; no resonance will occur.
Disadvantages: the cost is too high; limited by hardware, can not be used in large-capacity occasions: the active filter capacity single set does not exceed 100KVA, the current maximum applicable grid voltage does not exceed 690V.
V. Applications Active power filters can be widely used in industrial, commercial and institutional distribution networks, such as: power systems, electrolytic plating companies, water treatment equipment, petrochemical enterprises, large shopping malls and office buildings, precision electronics companies. , airport/port power supply system, medical institutions, etc. Depending on the application, the application of the HTAPF-I active power filter will ensure power supply reliability, reduce interference, improve product quality, increase equipment life and reduce equipment damage.
â– Communication industry In order to meet the operational needs of large-scale data center equipment rooms, the UPS usage capacity in communication distribution systems has increased significantly. According to the survey, the main harmonic source equipment of the communication low-voltage power distribution system is UPS, switching power supply, inverter air conditioner and so on. The harmonic content produced is high, and the displacement power factor of these harmonic source devices is extremely high. By using active filters, the stability of communication systems and power distribution systems can be improved, the service life of communication equipment and power equipment can be extended, and the power distribution system can be more in line with the design specifications of harmonic environments.
â–  The third harmonic of most semiconductor industries in the semiconductor industry is very serious, mainly due to the large number of single-phase rectifier devices used in the enterprise. The 3rd harmonic belongs to the zero-order harmonic, which has the characteristics of gathering in the neutral line, causing the neutral line pressure to be too large, and even sparking phenomenon, which has great production safety hazards. Harmonics can also cause the circuit breaker to trip, delaying production time. The 3rd harmonic forms a circulation in the transformer, which accelerates the aging of the transformer. Severe harmonic pollution will inevitably affect the efficiency and longevity of equipment used in power distribution systems.
â– In the petrochemical industry, due to the production needs, there are a large number of pump loads in the petrochemical industry, and many pump loads are equipped with frequency converters. The large number of applications of frequency converters has greatly increased the harmonic content in the distribution system of the petrochemical industry. At present, most of the inverter rectification links use 6 pulses to convert AC into DC, so the harmonics generated are mainly 5, 7 and 11 times. The main hazards are manifestations of hazards to electrical equipment and deviations in metering. This problem can be well solved by using an active filter.
â– In the chemical fiber industry, in order to greatly increase the melting rate, improve the melting quality of the glass, and extend the age of the furnace and save energy, electric flux heating equipment is commonly used in the chemical fiber industry, and the electricity is directly sent to the fuel-heated glass tank kiln by means of electrodes. These devices generate a large amount of harmonics, and the difference in spectrum and amplitude of the three-phase harmonics is relatively large.
â– The medium frequency furnace, rolling mill, electric arc furnace and other equipment commonly used in the iron and steel/intermediate frequency heating industry will have a major impact on the power quality of the power grid, making the capacitor compensation cabinet overload protection action frequent, the transformer and power supply line heating is serious, and the fuse Frequent blows, etc., even causing voltage drops and flicker.
â– The welding machine in the automobile manufacturing industry is an indispensable equipment in the automobile manufacturing industry. Due to the randomness, rapidity and impact characteristics of the welding machine, the use of the welding machine causes serious power quality problems, resulting in unstable welding quality and automation. A high degree of robot cannot work due to voltage instability, and the reactive power compensation system cannot be used normally.
â–  DC motor harmonic control Large DC motor places need to convert AC power to DC power through rectification equipment. Due to the large load capacity of such projects, there are serious harmonic pollution on the AC side, causing voltage distortion, serious It can cause an accident.
â– Automatic production lines and the use of precision equipment In the case of automated production lines and precision equipment, harmonics can affect their normal use, causing faults in intelligent control systems, PLC systems, etc.
■Hospital system hospitals have very strict requirements on the continuity and reliability of power supply. Class 0 places automatically restore power supply time T≤15S, Class 1 places automatically restore power supply time 0.5S≤T≤15S, Class 2 places automatically restore power supply time T≤0.5S, voltage total harmonic distortion rate THDu≤3%, X-ray machine, CT machine, nuclear magnetic resonance are loads with extremely high harmonic content.
â–  Theater/sports thyristor dimming system, large LED equipment, etc. are all harmonic sources. During the operation, a large number of third harmonics will be generated, which will not only cause the power equipment of the power distribution system to be inefficient, but also cause the frequency of the light. Flashing, causing noise or even malfunction to weak electrical circuits such as communication and cable TV.
Sixth, the main development status:
Due to the shortcomings and shortcomings of active filtering, passive filtering is mainly used in the domestic market; internationally, ABB, ABLEREX, Nokia, Schneider, and Siemens are the domestic representatives. The Shanda Huatian, Harbin Institute of Technology, Xi'an Saibo, Anhui Yousai, and Nanjing Yapai are the representatives. In addition, the CleanPower series of active power filters developed by the Department of Electrical Engineering of Tsinghua University are the most adaptive, stable and reliable for various delays. The compensation has made great progress and has become one of the most advanced products. With the advancement of power electronics technology, active power filters will eventually replace the traditional capacitive reactive power compensation devices with their huge technical advantages, powerful functions, and gradually decreasing prices, occupying the mainstream of the market.

Active Power Filter Active Filter Field Application Active Power Filter (APF) is a new type of power electronic device for dynamically suppressing harmonics and compensating for reactive power. It is capable of harmonics that vary in size and frequency, and The variable reactive power is compensated. It is called active. As the name suggests, the device needs to provide power. Its application can overcome the shortcomings of traditional harmonic suppression and reactive compensation methods such as LC filters (traditional only fixed compensation). Realized dynamic tracking compensation, and can complement both harmonics and reactive power.

Active filter field application

The three-phase circuit instantaneous reactive power theory is the main basic theory of APF development; APF has two types of parallel type and series type, the former uses more; the parallel active filter mainly controls current harmonics, and the series active filter is mainly Control problems caused by voltage harmonics, etc.
The theoretical basis active filter is better than the passive filter. The control effect is good. It can mainly filter out multiple and higher harmonics at the same time, and will not cause resonance, but the price is relatively high! The current active filters are mainly low voltage, and the high voltage active filter technology has matured, but the practical application safety factor is very low. The international common practice is to boost the transformer to ensure the reliability. The relevant national departments also require transformers. The boosted form is combined with an active filter to handle high voltage harmonics!
Working principle The active power filter detects the load current through the current transformer, and extracts the harmonic component in the load current through the internal DSP calculation, and then sends it to the internal IGBT through the PWM signal to control the inverter to generate a load harmonic. The currents of equal magnitude and opposite harmonic currents are injected into the grid for filtering purposes.
Domestic and international standards for product design and production are in accordance with international standards EN50091-3, EN61000-6-2, EN55011, EN50178:1997, IEC62040-3, IEC50178:1997, AS62040-3 (VFISS111), CISPR11
National Standard GB/T14549-93 "Power Quality: Harmonics in Utility Grid"
GB/T15543-1995 "Power quality: three-phase voltage allowable imbalance"
GB/T15945-1995 "Power Quality: Power System Frequency Allowance"
GB/T12326-2000 "Power Quality: Voltage Fluctuation and Flicker"
GB/T12325-2003 "Power Quality: Supply Voltage Allowance Bias"
GB/T18481-2001 "Power Quality: Temporary Overvoltage and Transient Overvoltage"
GB/T15576-1995 "General technical conditions for low voltage reactive power static compensation device"
GB7625.11998 "Harmonic Current Limits from Low Voltage Electrical and Electronic Products"
GB4208-93 "Classification of enclosure protection grade"
The three-level technology diode clamp three-level topology was proposed by Japanese scholar Nabae.A and others in 1980. After nearly 30 years of development, it is widely used in various fields of power electronics technology. The advantage of the diode-clamped three-level topology is that each switch tube is subjected to a reverse voltage of half the DC bus voltage, and a lower voltage class switch can be used to form a higher voltage class converter. This technology is now widely used in medium voltage high power AC drive systems. The 6500V class IGBT or IGCT three-level medium voltage inverter has been widely used in 4.2kV motor drive systems. Generally, three-level technology is generally applied to systems with higher voltage and higher power, which is determined by the contradiction between the limited voltage of the power device and the high voltage demand of the converter system. But we should see some of the inherent advantages of diode-clamped three-level topologies.
Technical advantages (1) Using a switch with a lower voltage level to form a converter with a higher voltage level. With the continuous development of power device technology, there are already 6500V IGBTs on the market, but the higher the withstand voltage, the IGBT is switched. The higher the loss, the lower the switching frequency. The IGBT switching frequency above 3300V will not exceed 5kHz, and the switching loss of 1200V IGBT is much larger than that of 600V. The switching loss of a three-level converter using a low-voltage IGBT is much lower than that of a two-level converter using a high-voltage IGBT of the same voltage level, and the former can achieve a higher switching frequency than the latter.
(2) It is possible to output three levels. The diode clamped three-level converter can output positive bus voltage, negative bus voltage and zero voltage (referred to as P, N, O). Under normal circumstances, the output voltage jumps between PO and ON. In special cases, PN will appear. The transition, while the two-level converter can only jump between PNs. That is to say, the three-level voltage jump amplitude is half of the DC bus voltage, and the two levels are the DC bus voltage. The high voltage jump amplitude brings high ripple current to the grid-connected inverter or active power filter. In order to suppress the ripple current, a large output inductor and filter capacitor are required, which brings Higher ripple current loss. At the same time, the output filter inductor capacitance also reduces the current response speed, or has a certain limit on the ability to output current. What the inverter brings is the impact on the motor and the large shaft current, which seriously affects the life of the motor. In addition, higher voltage jump amplitudes can also cause severe electromagnetic interference, which is also a serious hazard to peripheral electronic devices. The three levels solve the above problems to a large extent with their inherent advantages.
With the continuous development of technology, three-level technology has been paid more and more attention by people, and it has also been introduced into the low-voltage and low-power applications of 400V from the medium-voltage and high-power fields. Various internationally renowned power device manufacturers have launched A large number of integrated diode-clamped three-level power modules for 400V system applications have a tendency to gradually replace traditional two-level converters. Successful three-level products for the 400V field are as follows:
(1) In 2008, Yaskawa Electric of Japan introduced the Varispeed G7 series of universal vector inverters. Its 400V products use Mitsubishi's three-level power modules and have achieved great success in applications.
(2) In 2009, Dezhou Heneng Industrial Automation Co., Ltd. launched the HEINV series of three-level photovoltaic grid-connected inverters based on the self-developed three-level converter control technology. The front end uses symmetric BOOST for maximum power point. Tracking, the inverter uses a diode-clamped three-level topology, and the two cooperate with each other. Semikron's three-level power module is used, and each index is superior to similar two-level products.
(3) In 2009, Texas Hold'em Industrial Automation Co., Ltd. launched the industry's first three-level active power filter HESINE series, and achieved great success. This article will give a more detailed description of this series of products.
Active power filter uses diode clamped three-level technology in the field of active power filters. Many domestic and foreign literatures are involved. Many experts and scholars at home and abroad have conducted in-depth research on this and also proposed many new ones. Algorithm. However, three-level active power filters have never moved from the laboratory to the market. The reason may be that the technology is not mature enough, the control algorithm is too complicated, and the application cost is high. It may also be that the enterprise community pays insufficient attention to this and has not yet realized the advantages of the technology. Dezhou Heneng Industrial Automation Co., Ltd. first introduced a three-level active power filter product in the industry through in-depth research on three-level technology and correct grasp of market trends.
The three-level active power filter has the following advantages over the traditional two-level active power filter:
Low ripple current ripple current and current response speed are two contradictory indicators. As an active power filter, the basic principle is to detect the load harmonics, inject the inverting harmonics, and cancel the harmonics to achieve the purpose of filtering. A typical active power filter is a current mode controlled voltage source inverter. The output current is generated by the voltage output from the inverter acting on the output inductor. The inverter uses pulse width modulation. According to the basic principle of the electrician, the ripple current is determined by the switching frequency, the DC bus voltage, and the output inductance, regardless of the current loop control. The higher the switching frequency, the smaller the ripple current, the higher the DC bus voltage, the larger the ripple current; the larger the output inductance, the smaller the ripple current. The desired output current of the inverter is controlled by the current loop. The active power filter outputs harmonic current. If the fundamental wave is 50Hz and the 50th harmonic is calculated, the highest harmonic frequency will reach 2.5kHz. Active power filters have high requirements for current response speed.
Technical Analysis The current response speed is related to the DC bus voltage and the output inductor. The higher the DC bus voltage, the faster the current response; the larger the output inductance, the slower the current response. We expect the output ripple current to be as small as possible, and the faster the current response, the better. This is a contradiction. It can be seen from the above analysis that the two-level active power filter can only solve this contradiction by increasing the switching frequency. Some manufacturers' two-level active power filter products now have a switching frequency of 20 kHz. However, the increase in switching frequency results in higher switching losses and drive losses. The stand-alone capacity of the active power filter is limited, while for higher voltage rated active power filters, the high voltage IGBT is not at all. Allow such a high switching frequency. However, the three-level active power filter is in principle a solution to the above problem. The three-level inverter can output positive, negative and zero voltages. When calculating the ripple current, it only needs to calculate half of the DC bus voltage. Thus, under the premise of the same switching frequency, the same DC bus voltage, and the same ripple current requirement, the three-level output inductor is half of the two levels, and the switching loss of the device and the ripple loss on the inductor are also reduced. . When calculating the current response speed, all DC bus voltage will be active, and the output inductor will be halved, which will speed up the response of the current, enhance the filtering effect and increase the capacity of the single unit.
Improve the system withstand voltage usually 400V domestic low-voltage power grid, but for some industries, its low-voltage power grid will be relatively high, such as the oil rig drive is 600V, the mine power may be 690V or 1140V, and the voltage level of some industries may More diverse, but generally more than 500V. How to solve the harmonic control needs of these industries is a problem. Generally, in order to improve the current response speed and ensure the compensation effect, the active power filter that processes the harmonics requires a higher DC bus voltage than the inverter or the grid-connected inverter that processes the fundamental wave. Usually the DC bus voltage of a two-level inverter is twice the rms voltage of the AC grid. For 380V applications, the DC bus voltage is typically between 700V and 750V, while for 600V, the DC bus voltage needs to be 1200V. The practice of many companies is to add a transformer to change the voltage of other grades to 400V. The transformers that pass the harmonics are specially designed, the price is relatively high, the volume is relatively large, and the loss of the transformer will be relatively large. The three-level technology can be used to form a converter system with high withstand voltage, which can be directly connected to a higher voltage grid, while ensuring better filtering effect and stand-alone capacity.
Active power filter parameters and basic applications
SPA3 series active power filter performance description can simultaneously filter the response load change within 40μs from 2nd to 60th harmonics, and the total response time is less than 10ms (1/2 cycle)
Single-phase dynamic compensation, independent of system imbalance, 3.8-inch QVGA display,
MODBUS communication interface adopts IGBT with speed up to 20KHz, which perfectly eliminates harmonic parallel installation. It is simple, convenient and easy to expand. Up to 10 parallel designs can be selected easily. No detailed grid analysis is needed, only harmonic current measurement is needed. The size advantage SPA3 is the perfect solution for harmonic control. Dynamic current compensation eliminates harmonics and improves power factor. Reduces harmonics in cables, switches, transformers. Reduces harmonics caused by power failures and time increases power utilization and reduces operating costs. Application range SPA3 is suitable for industrial load applications
The SPA4 series active power filter performance description effectively eliminates the neutral line current generated by the zero-order harmonics and can simultaneously filter all or a selected number of harmonic single-phase dynamic compensation in the range of 2 to 25 times, regardless of the system. Balanced effect Parallel installation, easy to install, easy to expand, up to 4 parallel design options, no need for detailed grid analysis, only need to measure the harmonic current size and volume, can be wall mounted standard communication Interface, convenient access to users' existing communication system advantages SPA4 series is the perfect solution for harmonic control. Dynamic current compensation eliminates harmonics and improves power factor. Reduces harmonics caused by heat generation in cables, switches and transformers. Power failure and time increase power utilization reduce operating cost Application range Three-phase four-wire is suitable for commercial building load applications Main applications 1. Application of frequency conversion equipment With the advancement of technology, frequency conversion equipment is widely used in various occasions, frequency conversion equipment A large number of harmonics are generated, so such an occasion is one of the main target markets for active filters. 2. Unstable load applications Unstable load is not the main market for active filters, but it is an extremely important aspect of power systems, because unstable loads, although not a large proportion, are generated by the power system. The impact is far greater than the impact of other loads, so it should be one of the main market directions for active filters for such applications. 3. The electric arc furnace and rolling mill of the steel plant of the steel plant are the main harmonic generating equipment, and mainly the impact load, which has a great influence on other loads near the steel plant. At the same time, the harmonic problem has a great influence on the reactive power compensation of the steel plant, so the simultaneous treatment of reactive power compensation and harmonic control should be the target. 4. Non-ferrous metallurgical non-ferrous metallurgical load In addition to the load of the electric arc furnace nature, a large amount of DC components are generated due to the use of direct current hydrometallurgy. 5. The port machinery port machine is a large-scale lifting device, which generally uses a large frequency converter, so it is the main source of harmonic generation of port machinery. Therefore, it should be used as one of the market directions of active filters for such applications. . 6. Electrified railways Electrified railways are generally driven by DC motors and are therefore a major source of harmonics in the municipal sector. According to the existing operation of electrified railways in Shanghai and Beijing, most systems are equipped with filters. This product is expected to achieve the role of localization of electrical railway filters. 7. High-precision automated production line The high-precision automated production line itself does not generate harmonics, but it has high requirements for power quality. Therefore, it is necessary to install an active filter on the power supply side of the high-precision automated production line to reduce the influence of harmonics on the production line. 8. Office buildings, large commercial areas and other energy-saving lamps and air-conditioning centralized office buildings, large commercial areas and other energy-saving lamps and air-conditioning concentrated places are also very serious harmonics, governance methods should adopt centralized management methods to save costs.

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