Research On Background Harmonic Propagation Suppression In Distribution Systems

Along with the development of national economy, the demand for power is growingrapidly, and the scale of power system has been continuously expanded. In the process oflong distance power transmission and distribution in the large-scale power system, due tothe structural characteristics of transmission line, the harmonic resonance may cause theproliferation or amplification of harmonic voltage in transmission line, and cause somelocal accident, even trigger widespread blackouts of the whole power system.Based on the uniform transmission line theory, two kinds of parameter models of thetransmission line are set up in the power distribution system: the distributed-parametermodel and the lumped-parameter model. According to the two parameter model, thecauses of the background harmonic proliferation or amplification in transmission line areanalysed. At the same time, some theoretical derivations are made for the causes of theharmonic voltage amplification based on the actual two kinds of the transmission lines(radial line and loop line).In this paper the principle of harmonic suppression scheme R-APF which is installedin different transmission lines is introduced. Based on the theory of installing R-APF atthe end of the radial line, which is pointed out in the paper that the optimal installationposition of installing R-APF in loop line is the midpoint.In order to solve the mismatches between the resistive gain of R-APF and thecharacteristic impedance of the line in most cases, the over compensation plus resistiveAPF is proposed which detects the harmonic voltage and source side harmonic current atthe end of the radial line, and selects the appropriate voltage and current gains to suppressthe harmonic of the radial line through injecting corresponding harmonic current into theline. In theory，impedance analysis of the control scheme is studied. Simulation andexperiments verify the effectiveness of the control strategy in terms of compensating thegrid harmonic voltage.According to the lumped parameter model of the radial transmission line, the9kmtransmission line has been built imitatively. For the purpose of filtering the harmonic in the transmission line, experiments platform based on TMS320F2812DSP have been set upand experiments have been performed to demonstrate and verify the feasibility andeffectiveness of R-APF and OCR-APF.