Filtering is an operation that filters out specific band frequencies in a signal and is an important measure to suppress and prevent interference. Harmonic control must first control the source of harmonic generation, and secondly we must eliminate the harmonics by adding filtering devices. How to choose the right harmonic quality scheme is very important.
First, passive filtering
definition
Passive filter, also known as LC filter, is a filter circuit composed of a combination of inductor, capacitor and resistor. It can filter out one or more harmonics. The most common passive filter structure is the inductor. In series with the capacitor, it can form a low impedance bypass for the main subharmonics (3, 5, 7); single tuned filters, double tuned filters, and high pass filters are all passive filters. The passive filter is composed of passive components such as LC. It is designed to be very low impedance at a certain frequency, and the corresponding frequency harmonic current is shunted. The behavior mode is to provide a passive harmonic current bypass channel. Figure 1 shows the passive filter schematic.
Figure 1 Passive filter schematic
Advantages and disadvantages
Advantages: The passive filter has the advantages of simple structure, low cost, high operational reliability and low operating cost.
Disadvantages: The signal in the passband has energy loss, and the load effect is obvious. When the inductor element is used, the electromagnetic induction is easily caused. When the inductance L is large, the volume and weight of the filter are relatively large, and it is not applicable in the low frequency domain.
application
Due to the advantages of passive filtering with large capacity and low price, the filtering of the steel industry adopts passive filtering. At present, the domestic filtering market (power harmonic control market) mainly uses passive filtering. Internationally represented by ABB, Schneider and Siemens, the country is represented by Satons, Wenzhou Tsinghua Electronics, Shanda Huatian, Harbin Institute of Technology, Xi'an Saibo and Greenbojie. The development situation is reflected quickly, harmonic control is thorough, and comprehensive control is the main.
Second, active filtering
definition
Active Power Filter (APF) is a new type of power electronic device for dynamically suppressing harmonics and compensating for reactive power. It can compensate harmonics with varying magnitude and frequency as well as varying reactive power. It is called active, as the name implies, the device needs to provide power (to compensate the harmonics of the main circuit), and its application can overcome the shortcomings of traditional harmonic suppression and reactive compensation methods such as LC passive filters (traditional only Can be fixed compensation), realize dynamic tracking compensation, and can complement both harmonics and reactive power.
The three-phase circuit instantaneous reactive power theory is the main basic theory of APF development. APF has two types: parallel type and series type. The former uses more. The parallel active filter mainly controls current harmonics. The series active filter is mainly Control problems caused by voltage harmonics, etc. Compared with the passive filter, the active filter has good control effect, and can mainly filter out multiple times and higher harmonics at the same time, and does not cause resonance, but the price is relatively high. Figure 2 shows the active filter structure.
Figure 2 Active filter structure
Advantages and disadvantages
Advantages: The harmonics can be dynamically filtered out, and the harmonics in the system can be completely absorbed; no resonance will occur. The signal in the passband not only has no energy loss, but also can be amplified, the load effect is not obvious, and the mutual influence is small when the multi-level is connected. The high-order filter is easily formed by the simple method of cascading, and the filter is small in size. Light weight, no magnetic shielding is required.
Disadvantages: The passband range is limited by the bandwidth of active devices. It needs DC power supply, and the reliability is not as high as that of passive filters. It is not suitable for high voltage, high frequency and high power.
application
Active filters can be widely used in distribution networks of industrial, commercial and institutional groups, such as: power systems, electrolytic plating companies, water treatment equipment, petrochemical enterprises, large shopping malls and office buildings, precision electronics companies, airports/ports. Power supply systems, 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.
Communications industry;
Semiconductor Industry;
Automotive Manufacturing;
DC motor harmonic control;
Hospital system
Theater and gymnasium.
Third, the comparison of active filtering and passive filtering
working principle
The passive filter consists of passive components such as LC. It is designed to be very low impedance at a certain frequency, and the corresponding frequency harmonic current is shunted. The behavior mode is to provide a passive harmonic current bypass channel. The active filter is composed of A power conversion device composed of a power electronic component and a DSP detects a load harmonic current and actively provides a corresponding compensation current. The compensated source current is almost a pure sine wave, and the behavior mode is an active current source output.
Impedance effect
Passive filters are severely affected by system impedance, and there is a danger of harmonic amplification and resonance; active filtering is not affected.
Frequency effect
Passive filter resonance point offset, the effect is reduced; active filter is not affected.
Load impact
The passive filter may be damaged due to overload; the active filter is not damaged, and when the harmonic amount is greater than the compensation capability, only the compensation effect is insufficient. The passive filter compensation effect varies with load; the active filter is unaffected by load changes.
Equipment cost
The passive filter is low; the active filter is too high.
Fourth, the application of E6500 in harmonic processing
Harmonic hazards have been self-evident, such as increasing power plant load, reducing system power factor, reducing the effective capacity and efficiency of power generation, transmission, and electrical equipment, resulting in equipment waste, line waste, and power loss; causing reactive compensation capacitors Resonance and harmonic current amplification causes the capacitor bank to be damaged or out of operation due to overcurrent or overvoltage... and so on.
Figure 3 E6500 harmonic measurement map
Since the harmonics appear, we have to find a way to filter it out, but only if we can accurately measure the harmonics. The Zhiyuan E6500 Power Quality Analyzer adopts anti-aliasing core technology. Each channel is equipped with a separate anti-aliasing filter, which is a second-order active filter. The cutoff frequency is 14KHz in the normal range and is cut off in the full-scale range. The frequency is 22KHz, which fully complies with the power quality input signal range (up to 10KHz), thus ensuring the accuracy of measurement calculation in hardware.
Figure 4 Harmonic measurement analysis diagram
There may be many high-frequency interferences at the measurement site, such as power signals, radio signals, etc., which may introduce high-frequency interference inputs, causing frequency aliasing. If no aliasing is done, an error will occur. For example, the first picture in Figure 3 is not subjected to aliasing processing, and the harmonic analysis result is that the 7th harmonic is exceeded, which is wrong;
The only reliable method is to do anti-aliasing before the analog-to-digital conversion of the signal to ensure the correctness of the measurement results. For example, the second picture in Fig. 3 is subjected to aliasing processing, and the harmonic analysis result is that the 9th harmonic exceeds the standard, which is consistent with the original signal analysis result.
Stator and rotor laminations are an important part of motors and generators. For large-size and small-batch punching sheets, we usually use the notching method to produce them. The advantages of notching are that the cost of the notching die is low and the production cycle of the notching die is short. It is suitable for producing large size laminations, usually the outer diameter is from 500mm-1250mm. The slot size is more accurate than Laser Cutting.
Stator And Rotor Lamination By Single Notching,Stator Core Laminations,Generator Stator Laminations,Electric Motor Rotor Laminations
Henan Yongrong Power Technology Co., Ltd , https://www.hnyongrongglobal.com