Research on a shunt active filter for damping of harmonic propagation in power distribution systems

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The serious status of harmonic pollution in Japan has been reported : The maximum value of 5th harmonic voltage in the downtown area of a 6.6-kV power distribution system exceeds 7% under light-load conditions at night. These observations, which are based on the actual measurements, suggest that the increase of 5th harmonic voltage on the 6.6-kV bus at night is due to "harmonic propagation" resulting from harmoni resonance between line inductors and shunt capacitors installed on the distribution system for power factor correction.Research has been done on a shunt active filter based on voltage detection, which is controlled in such a way as to present infinite impedance to the external circuit for the fundamental frequency, and as to exhibit a low resistance for harmonic frequencies. A power distribution feeder rated at 200 V and 20 kW has been designed and constructed to verify the practical viability and justification of the active filter rated at 0.67 kVA.Experimental results obtained from the laboratory system, along with theoretical results, are summarized as follows.・Installation of the active filter on the end bus of a power distribution line is more effective in harmonic damping than installation on the beginning bus or in the vicinity of a primary ditribution transformer.・Installation on the end bus makes the required current ration of the active filter smaller than installation at the beginning bus.・Harmonic mitigation ofvoltage and current is a welcome "byproduct, " as a result of harmonic damping throughout the power distribution line.