Active power filter device for specific sub-harmonics

Abstract

The invention discloses an active power filter device for specific sub-harmonics. The device is applicable to a circuit comprising a system power supply and a harmonic load, and comprises a transformer, an inverter and a modulation signal generation module; the primary winding of the transformer is connected in series with the harmonic load, and connected to a circuit formed by the system power supply and the harmonic load; the modulation signal generation module is used for generating modulation signals for the inverter, and the modulation signals are generated by superposing primary fundamental wave current amplified reversely and primary specific n sub-harmonic current amplified positively; the inverter is used for converting direct current signals into alternating current signals having the same frequency as the modulation signals and injecting the alternating current signals into the secondary winding of the transformer, so that the primary fundamental wave equivalent impedance of the transformer is Z1+(1-a)Zm, and the primary n sub-harmonic equivalent impedance of the transformer is nZ1+(1+beta)nZm. Based on fundamental wave and specific sub-harmonic flux hybrid control, the primary side of the transformer is short-circuited relative to fundamental waves and open-circuited relative to specific sub-harmonics.

Description

technical field [0001] The invention belongs to the technical field of active power filtering, and more particularly, relates to an active power filtering device for specified harmonics. Background technique [0002] As power electronic nonlinear loads are more and more widely used in industrial and civil fields, the current waveform distortion in the power grid is more serious, and the harmonic and reactive power problems are becoming more and more significant. For the problem of harmonics and power factor, the industry has proposed a variety of solutions, among which the main filtering solutions include traditional passive LC filters, traditional parallel active power filters, series hybrid active power filters, and injection hybrid active power filters. Active power filters and unified power quality conditioners. [0003] Passive filters are large in size and weight, and can only filter out harmonics of a specific frequency; among all power filters, series hybrid active ...

AI Technical Summary

Problems solved by technology

The inverter components are connected in series between the power supply and the load, and cannot be directly protected by devices such as power contactors, circuit breakers or fuses;

[0005] 2) The filter performance of the device conflicts with the transformer capacity

The traditional series hybrid active power filter based on fundamental magnetic flux compensation only compensates the fundamental magnetic flux, which can only reduce the fundamental equivalent impedance. Impedance; the design of the rated capacity of the transformer depends on the magnitude of the excitation impedance under the consideration of the system protection strategy. Considering the extreme case where the fundamental magnetic flux of the transformer is not compensated at all, the design capacity of the series transformer is In order to reduce the rated capacity, the excitation impedance of the transformer must be reduced; in summary, better filtering performance requires a larger capacity transformer

[0006] 3) The protection strategy and reliability of the device conflict with the transformer capacity

[0007] 4) When the harmonic current is fully compensated, the system stability is reduced

But on the one hand, it only compensates the fundamental magnetic flux, so it can only reduce the fundamental equivalent impedance. When the transformer used is determined, its harmonic equivalent impedance is a fixed value. In order to obtain a better filtering effect, a larger Capacity transformer; on the other hand, the existing series hybrid active power filter adopts the method of full current compensation, which greatly reduces the stability of the system, and increases the cost due to the increase of the capacity of the transformer and each switching device of the system

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