Harmonic Issues in a Multi-drive Network with Resonances at the Grid Impedance Under Low and High Damping Cases

Resonances can cause relatively high voltage harmonics at the Point of Common Coupling (PCC) with regards to the value of current harmonics at the resonant frequencies. These current harmonics are mainly generated by the full-bridge Diode Rectifiers (DRs) utilised in Adjustable Speed Drives (ASDs). To decrease the magnitude of voltage harmonics at the resonant frequencies, the phase angle of ASDs current harmonics could be determined in a way that they cancel out each other at the system level. This needs the ASDs to generate current harmonics with different phase angles by some modifications across their dc-link. An alternative method could also be increasing the damping factor of system at the resonant frequency to limit the resonance effect. Thus, this paper first analyses the harmonic issues of multiple parallel ASDs when the grid has resonant frequencies. Then, the impact of system damping on the voltage harmonics due to the resonance at the PCC is investigated. Simulation and experimental case studies show that the amplitude of voltage harmonics at PCC depends on the value of damping resistors at the grid side.