Investigation On The Influence Of Single-phase Nonlinear Load Harmonic Damping At System Local Harmonic Resonance

As the proportion of single-phase nonlinear loads in the power distribution system continues to increase,not only the harmonic injection level of the system is increased,but the original damping properties of the system are also changed,which may cause the power distribution system to experience more serious harmonic resonance and weakly damped transients,that means it brings challenges to the division of harmonic responsibilities.This paper takes single-phase nonlinear load as the research object,reveals the cause of nonlinear load damping,studies its damping characteristics,and analyzes its damping effect at local harmonic resonance.Aiming at the 3^rd harmonic,a preliminary exploration and proposal of a basic method for distinguishing between harmonic sources and harmonic resonances based on PCC point current and voltage are proposed.The main work of the dissertation is as follows:a)Reveal the cause and characteristics of harmonic damping through the element expression of frequency domain harmonic coupling admittance matrix of single-phase nonlinear load;Propose the expression method of fundamental wave and harmonic damping;Analyze fundamental wave and harmonic damping characteristics through theory and simulation;Set up experiments to verify the single-phase nonlinear load damping characteristics;b)Analyze its influence on local resonance through the equivalent circuit of single-phase nonlinear load at local resonance;Propose a method to express the damping effect of local harmonic resonance,namely resonance damping index;Analyze resonance damping characteristics through theory and simulation;Set up experiments to verify the resonant damping characteristics of single-phase nonlinear loads;c)For the 3^rd harmonic,study the two causes of the increase in the harmonic level of the PCC point of the power distribution system:harmonic source and harmonic resonance,which affect the harmonic current and voltage of the PCC point;A method is proposed based on the PCC point current and voltage measurement values,with the user-side harmonic current phase and the PCC point harmonic impedance’s change relationship at resonance,to make a preliminary identification of the leading factors for the increase of the third harmonic level;The method is verified by simulation examples of power distribution system.