Differences between active and passive filters Passive filters: This circuit consists mainly of passive components R, L and C.
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Apf active filter: integrated operational amplifier and R, C components, with no inductance, small size, light weight and so on.
Apf active filter device: It consists of a set of switching devices and passive energy storage components such as inductors and capacitors. The system consists of two parts: the command current calculation circuit and the compensation current generation circuit. A new type of power electronic device for dynamically suppressing harmonics and compensating for reactive power. It can compensate for harmonics of varying magnitude and frequency as well as varying reactive power. 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 power compensation methods such as LC filters (traditional only fixed compensation), realize dynamic tracking compensation, and can complement both harmonics and reactive power.
The types of filters widely used in the world include: single-order single-tuned filters, double-tuned filters, second-order wide-band and third-order wide-band high-pass filters.
1. Single-tuned filter: The advantage of the first-order single-tuned filter is that the filtering effect is good and the structure is simple; the disadvantage is that the power loss is relatively large, but decreases with the improvement of the quality factor, and increases with the decrease of the harmonic order. The electric furnace is just a low-order harmonic, mainly 2 to 7 times, and therefore, the fundamental wave loss is large. Second-order single-tuned filter When the quality factor is below 50, the fundamental loss can be reduced by 20 to 50%, which is energy-saving and the filtering effect is equivalent. The third-order single-tuned filter is the filter with the least loss, but the composition is more complicated and the investment is higher. It is used in the electric arc furnace system. The second-order filter is better for the second-order filter, and the second-order single-tuning filter is used for the other. Device.
2. High-pass (wideband) filter, generally used for harmonic suppression of one time and above. When it is used in a nonlinear load system such as an electric arc furnace, when filtering for 5 or more times, a low-impedance path of the filter circuit to the 5th and upper harmonics can be formed by parameter adjustment. Although the passive filter has the advantages of low investment, high efficiency, simple structure and convenient maintenance, it is widely used in the distribution network at this stage. However, since the filter characteristics are greatly affected by the system parameters, only a few harmonics can be eliminated. Waves, and for some subharmonics will produce amplification, even resonance phenomena and other factors, with the development of power electronics technology, people gradually turn the research direction of the filter to active power (Active PowerFliter, abbreviated as APF).
The APF active filter uses a controllable power semiconductor device to inject a current equal to the amplitude of the harmonic source current and the opposite phase to the grid, so that the total harmonic current of the power supply is zero, and the harmonic current is compensated in real time. It is equivalent to providing a very low impedance path close to zero for harmonic currents to avoid harmonic current injection into the system.
Compared with passive filters, it has the following characteristics:
1. Not only can compensate for each harmonic, but also can suppress flicker, compensate for reactive power, unbalance compensation and other compensation functions, which is more reasonable in cost performance;
2. The filtering characteristics are not affected by the system impedance, etc., independent of the grid system, resonance and harmonic voltage amplification do not occur, and the safety is high.
3. Adaptive function to dynamically compensate for harmonic changes in real time
Puyang Yuanchuang Electric has a professional manufacturer of electrical products for ten years. It cooperates with universities such as Wuhan University in the field of apf active filter technology to develop and produce. The performance has reached international standards and has been well received by everyone.
Puyang Yuanchuang Electric Main: dynamic reactive power compensation cabinet|reactive power compensation cabinet|high and low voltage reactive power compensation cabinet|apf active filter compensator|water resistance cabinet|phaser|high and low voltage soft starter|electrolytic powder
Source: Yanyang Yuanchuang Industrial Control Co., Ltd.
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