Power Electronic Systems continue to be increasingly deployed in the electrical networks in industrial, commercial and residential zones. These devices are basically used to improve the application performance and to save energy, but the presence of these devices may deteriorate the power quality and may in turn have adverse effects on other loads which are more sensitive to the PQ disturbances. A further application in recent times is an expansion of renewable energy sources and non-linear loads with inbuilt power electronic systems. The presence of such non-linear devices in the residential low voltage network can also cause resonance and stability issues apart from the detrimental effects of harmonics. Studies of such systems typically involve detailed time domain simulations incorporating the switching models of power electronic interfaces, their filters and other loads, which could be time consuming in switching networks and dependent on the stability and accuracy of numerical integration algorithms. The performance of these nonlinear power electronic interfaces is also dependent on the level of background distortion present in the system. In this work, exploration to develop frequency domain models for three-phase power electronic interfaces is attempted. An extensive study of power quality status at various locations is undertaken to understand the nature of background distortion levels and trends. A coupled frequency Norton description is developed for the case of a three-phase diode bridge used in a Variable Frequency Drive (VFD) as a specific example, and an approach to predicting the steady state system response is studied. Simulation results to validate the model performance in the presence of background distortion types observed in the field, are presented. While studies show that the model is fast and has good accuracy in estimating the steady state performance and harmonic emission, further work is being done to include the effects of grid impedance, multiple power electronic interfaces and other loads.

The seminar presents the results of the extensive power quality study followed by the development of frequency domain model for the VFD under consideration.