Modeling and analysis of impedance for uncontrolled rectifier based nonlinear load

Uncontrolled Rectifier is widely applied in power supply, HVDC, et al, which could be regarded as the typical nonlinear device in power system. It injects a mass of harmonic current into power system and dramatically leads to voltage distortion. The relationship between the harmonic voltage and current, namely called input impedance, is nonlinear. Conversional system voltage control is based on the harmonic currents compensation. However, the harmonic currents changes with the voltage control, namely the harmonic currents compensation reference are shifty in real time, which degrade voltage control performance. Therefore, it is necessary to analysis the impedance character of nonlinear loads, and applies it to the control system to realize the harmonic current dynamic compensation and improve the voltage control performance. In this paper, a time domain input impedance model for uncontrolled rectifier is developed, and then the nonlinear character of the input impedance is analyzed. Finally, a simulation model is implemented, the simulation results validate the theoretical analysis.