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In this paper, a novel transformer structure is proposed in order to manufacture a high-power active filtering device. The novel transformer structure contains one primary and multiple secondary windings. The system configuration and compensation principle are addressed in detail. The fundamental magnetic flux compensation in the case of the transformer with multiple secondary windings is fulfilled. In addition, a three-phase active power filter topology consisting of three independent transformers with multiple secondary windings is presented so that the filter can run under unbalanced loads. The parameters of hysteresis current control are also analyzed in detail. A simple and practical fundamental detecting approach is discussed. Transient response and fault protection schemes are explained. A set of automatic three-phase active power filtering devices has been constructed and operated in the field. The field test results verify the validity of the novel transformer structure and the active power filtering system. [ABSTRACT FROM AUTHOR]

In this paper, a novel practical principle of series hybrid active power filter based on the fundamental magnetic flux compensation (FMFC) of a series transformer is proposed. In the active power filter, the fundamental current component of power utility is detected and tracked to produce a fundamental compensation current, which is injected into the secondary winding. According to the law of superposition, when the injected fundamental current and the fundamental current component of the power utility satisfy the FMFC, the series transformer can really exhibit very low impedance to fundamental and naturally magnetizing impedance to harmonics. As a result, the series hybrid active power filter with FMFC really acts as a "harmonic isolator". The current control scheme and fundamental detecting method are analyzed. The validity of the novel principle and excellent filtering characteristics are verified by the experimental results of the two kinds of typical harmonic-producing loads. [ABSTRACT FROM AUTHOR]

In this paper, a novel principle of an active power filter based on the harmonic impedance control of a transformer is proposed for high-voltage power distribution systems application. A linear transformer with multiple secondary windings is adopted. The primary winding is shunted with harmonic-producing loads, while the secondary windings are connected with inverters. The primary harmonic current is detected and then tracked by the inverters with fixed compensation coefficient. When the harmonic current compensation condition is satisfied, the transformer can really exhibit nearly zero impedance to harmonic current and primary self-impedance to fundamental current. As a result, the harmonic currents in power systems can be led to flow into the transformer branch. The operation principle, the control scheme, and the harmonic current detection method are discussed in detail. Finally, simulated waveforms and experimental results are presented to verify the effectiveness of the active power filter. [ABSTRACT FROM AUTHOR]