Research On Harmonic Damping Of The Loop Power Distribution System Based On A Site Selection Straregy Of The Discrete Frequency Tuned RAPF

Harmonic voltages and currents along the loop feeder are magnified owing to the harmonic resonance between power factor correction capacitors and system inductors, thus deteriorating power quality. The RAPF(Resistive Active Power Filter), which is installed at the middle point of the loop feeder, can effectively damp harmonic resonance along the loop feeder only when its equivalent impedance is Z/2, where Z represents the characteristic impedance of the loop feeder. In this case, impedance matching is satisfied. However, system parameters are changeable in practice, which may break the impedance matching condition and affect the harmonic damping capability of the RAPF.In order to find a method which can mitigate the harmonic resonance effectively at the same time of showing better adaptability to system parameter variations, the distributed parameter models of the loop feeder with the RAPF installed on the middle bus and with the RAPFs symmetrically deployed on different locations are established respectively in this paper. And the harmonic voltage standing wave expressions are derived accordingly, based on which the harmonic magnification theory is analyzed. By comparing the harmonic damping effects with the RAPF installed on the middle bus and the RAPFs symmetrically deployed on different locations, a site selection strategy of discrete frequency tuned RAPF is proposed to damp the harmonic propagation in loop power distribution systems. To be specific, the proposed site selection strategy notes that if the feeder length is shorter than the half wavelength, the optimal installation location should be symmetrical locations close to the middle point; and that if the feeder length is longer than the half wavelength, the optimal installation location should be symmetrical positions which are a quarter wavelength away from the source. Furthermore, the influence of conductance variations on the damping effects are discussed when the RAPF is located on the middle point of the loop line or the RAPFs are symmetrically installed according to the proposed site selection strategy, which illustrates that the proposed discrete frequency tuned RAPF can achieve good damping results as long as the equivalent conductance is not less than the matching conductance 2/Z and therefore shows better adaptability to parameter changes.The simulation circuit and experimental platform are established according to the lumped-parameter model of the loop line in this paper. Then, simulations and experiments are performed under conditions when system parameters remain constant, system parameters change and nonlinear loads exist in the loop feeder. Simulation and experimental results verify the validity of the proposed strategy.