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Low-order harmonic filtering method for three-phase alternating-current signal

A three-phase AC, low-order harmonic technology, applied in the AC network to reduce harmonics/ripples, harmonic reduction devices, etc. The effect of controlling performance and improving system stability

Inactive Publication Date: 2020-06-05
SOUTHWEST JIAOTONG UNIV +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] Aiming at the shortcomings of large signal time delay and low precision in the above-mentioned traditional filtering methods, the present invention proposes a low-order harmonic filtering method for three-phase AC signals, which uses the idea of ​​multi-pulse rectification to improve the power quality of the AC side, and converts the to-be-filtered The three-phase AC signal is virtualized as the secondary side current of one of the rectifier transformers for multi-pulse rectification. After time delay, the multi-pulse rectification and other transformer secondary side output current signals are constructed, and then the primary winding and secondary winding of the rectifying transformer are used. Corresponding relationship, constructing the current signal of the primary side corresponding to the secondary winding of each transformer. After the primary side current signals of multiple rectifier transformers are synthesized, part of the low-order characteristic harmonics in the signal are cancelled, thereby achieving the purpose of reducing the harmonics.

Method used

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  • Low-order harmonic filtering method for three-phase alternating-current signal
  • Low-order harmonic filtering method for three-phase alternating-current signal
  • Low-order harmonic filtering method for three-phase alternating-current signal

Examples

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Embodiment 1

[0025] like figure 1 Shown is the schematic diagram of a typical 12-pulse rectifier circuit, in which TR1 and TR2 are two rectifier transformers with the same voltage ratio, and the winding connections are Y / Y connection and Y / △ connection respectively. The primary sides of the two transformers TR1 and TR2 are connected in parallel and then connected to the AC power grid, and the secondary sides are respectively connected in parallel through two rectifiers RT1 and RT2 to supply power to the load.

[0026] The primary winding currents of the two transformers TR1 and TR2 are respectively i A1 i B1 i C1 and i A2 i B2 i C2 , the secondary winding currents are respectively i a1 i b1 i c1 and i a2 i b2 i c2 . In addition to the fundamental current in the secondary side current, there are 5 times, 7 times, 11 times, 13 times, 17 times, 19 times, 23 times, 25 times, etc. 6k±1 (where k is the number of positive rectification) times and other characteristic harmonic compone...

Embodiment 2

[0041] like Figure 4 Shown is an implementation of the 18-pulse rectifier circuit, TR1, TR2 and TR3 are three rectifier transformers, the primary is connected to the AC grid in parallel. In this embodiment, the primary windings of the three rectifier transformers are Y-connected, the secondary windings of TR2 are Y-connected, and the secondary windings of TR1 and TR3 are all extended-edge delta-connected (the secondary has two sets of windings, which can form different phases ). In this embodiment, the phase relationship between the secondary current of the three transformers and the primary current is 20° ahead, the same phase, and 20° behind. The detailed connection of the windings is as follows Figure 5 shown. The 18-pulse rectification takes the current from the AC grid only including the fundamental wave and 18k±1 (k is the positive rectification number), and other harmonics are filtered out and do not appear in the AC grid current, especially the 5th, 7th, 11th, 13 ...

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Abstract

The invention provides a low-order harmonic filtering method for a three-phase alternating-current signal. The method comprises the steps of firstly, constructing a multi-pulse-wave rectifying circuitcomprising a first transformer to an Nth transformer according to the harmonic order of a to-be-filtered three-phase alternating current signal, and virtualizing the to-be-filtered three-phase alternating current signal into a secondary side current signal of the first transformer; respectively translating the secondary side current signals of the first transformer according to the phase relationship between the first transformer and the currents of the second transformer to the Nth transformer to obtain secondary side current signals of the second transformer to the Nth transformer; according to the relationship between the primary winding and the secondary winding of each transformer, converting the secondary side current signals of the N transformers to obtain primary side current signals; and finally, adding the primary side current signals of the N transformers and then dividing by N to obtain a filtered signal. According to the filtering method provided by the invention, the low-order harmonic component in the three-phase signal is completely filtered with smaller time delay, and the precision of an effective signal is not influenced.

Description

technical field [0001] The invention relates to a method for filtering low-order harmonics of three-phase AC signals, which is suitable for filtering voltage and current signals of three-phase circuits. Background technique [0002] Three-phase systems are the most widely used in industrial electrical energy applications. In the process of three-phase power quality detection and control, it is often necessary to extract the fundamental wave signal of three-phase voltage or current. In a three-phase system, usually the voltage and current do not contain multiple harmonics of 3 or even harmonics, but only 5th, 7th, 11th, 13th, 17th, 19th, 23rd, and 25th Etc. 6k±1 (where k is the number of positive rectification) harmonic components, and the lower the harmonic order, the higher its content. First-order or second-order filters are commonly used to filter signals containing low-order harmonics. To obtain a good filtering effect, the cut-off frequency should be lower than 1 / 10-1...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/01
CPCH02J3/01Y02E40/40
Inventor 郭育华卢国涛余胜罗锐
Owner SOUTHWEST JIAOTONG UNIV