Online Determination of Grid Impedance Spectrum through Pseudo-Random Excitation of a Pulse Width Modulator

The last decade has seen a dramatic rise in renewable energy converters connected to the grid, consisting mostly of intermittent distributed generators on the medium or low voltage grid. Due to this evolution in energy transmission, improved monitoring and control of the distribution grid is becoming mandatory in order to efficiently integrate the new power sources and guarantee power quality, efficiency and reliability. Our paper describes a reliable and precise power grid impedance estimation method using an innovative scheme to control the Pulse Width Modulator’s pulse pattern on the inverters, in order to inject broad spectrum identification patterns. The generated harmonics and inter-harmonics will allow the online computation of the complete spectrum of the grid impedance at the Point of Common Coupling during normal operation. Simulations in typical grid situations verify that the proposed algorithm is robust to a realistic environment and can be used for automated feedback control