Investigation On Harmonic Damping Characteristics Of Single-phase Nonlinear Load

Electrical load with single-phase bridge rectifier circuit as the front end is the main nonlinear load form in low-voltage distribution system nowadays.This sort of load power is low but numerous in quantity,with rich harmonic content and wide distribution in low-voltage distribution system.Replacing original linear load,the nonlinear load has changed the impedance characteristics at harmonic frequencies in power system.Harmonic resonance is suppressed somehow when linear load exhibits a resonant state in local system because of damping.When such linear load is replaced by nonlinear load,the damping characteristics for harmonic resonance are urgent problems to be studied.This thesis researched this problem to find out harmonic damping characteristics of nonlinear load at low harmonic frequencies by analysis,simulation and tests,based on analytical harmonic frequency domain model for single-phase bridge rectifier load.The specific work was as follows:(1)The key admittance elements in the harmonic coupling admittance model of single-phase bridge rectifier load were compared and analyzed,and the decoupling model expression for harmonic damping analysis was proposed.The contribution of the fundamental voltage component and the harmonic voltage component to the total harmonic current in the model and the correlation between each other were studied respectively.(2)According to the decoupling harmonic model and the relatively constant contribution of the fundamental voltage to the harmonic current,when considering the characteristics of the harmonic current source inherent in the nonlinear load,the equivalent impedance representation method for characterizing the nonlinear load harmonic damping was defined and the concept of damping attenuation for nonlinear load harmonic damping evaluation was proposed.(3)Two impedance calculation methods without power source to obtain the harmonic equivalent impedance were proposed and compared with each other.The influences what harmonic voltage amplitude and phase would make on harmonic equivalent impedance and damping attenuation were studied by theoretical analysis and computational simulation.The experimental platform was built and simulation results were verified experimentally.