Dynamic Online Grid Impedance Estimation and Its Effects on DC Capacitor Lifetime in Variable Frequency Drive

Grid impedance plays a significant role in the performance and design considerations of nonlinear devices like Variable Frequency Drive (VFD). VFD operates across domestic, industrial, and residential applications under different grid configurations and capacities including renewables. IEEE 519 standard recommends grid short circuit ratio and thereby grid impedance as an index for the individual and overall current harmonic performance of the connected utilities. This research investigation details a comprehensive approach for an online dynamic grid impedance estimation and may also give an insight into the hardware implementation within a VFD to achieve optimum performance and reliability during installation. A VFD of 250 kW is used for real-time measurements and simulation with varying grid configurations to determine grid impedance and lifetime of the DC capacitors. A fuzzy model is developed based on the established knowledge base for the estimation of the grid impedance of a generic grid. The fuzzy model is further enhanced to estimate the lifetime of the DC capacitor.