Mathematical Analysis of Grid Impedance Effects on Grid Harmonics and Commutations in a Distribution Network with a Three-phase Diode-Rectifier

Adjustable Speed Drives which are employed in a variety of industrial applications, consist of a three-phase diode-rectifier. Due to the utilization of nonlinear devices, the performance of this diode-rectifier is impacted by harmonic distortion in distribution systems. Previously, the effects of background voltage harmonics on the amplitude and phase angle of current harmonics have been investigated. However, the impacts of grid impedance, which are commutation and filtering effects, have not been explored. In this paper, grid impedance effect on a three-phase diode-rectifier and its impacts on the voltage and current harmonics have been investigated. Additionally, a simulation test has been done to verify the impacts of grid impedance on the current harmonic emissions. The results show that when the grid impedance value is small, the commutation does not have significant impact on the current harmonics; however, as the grid impedance increases, the commutation will have a big impact on the voltage harmonic distortions so that it will affect the current harmonic emissions.