Thévenin Equivalent Impedance Estimation for Power Electronic Devices in Smart Grids

Distributed generation (DG) based on renewable energy sources (RESs) as well as electric mobility and battery storage are currently penetrating electrical energy networks, especially at medium voltage (MV) and low voltage (LV) levels. The energy conversion is mostly based on power electronic devices. The control stability of these power converters is becoming increasingly important as more and more converters are being established in the grids, transforming the grid dynamic response. The Thévenin equivalent (TE) impedance at the point where a converter is connected can be used to represent the grid response seen from the converter. Therefore, an accurate TE parameter estimation is a key enabling feature for high control stability and performance enhancement in smart grids. An analysis of the main sources of TE estimation errors is given in this paper. Focusing on its core mathematical calculation, a new TE estimation algorithm based on least squares fitting for non-linear systems is presented. Simulation results show higher accuracy than a classical linear calculation method, especially at a high degree of measurement errors and reference frame shifts. More accurate TE impedance results can be beneficial for controller optimization of power converters, which will subsequently contribute to the stability of the future power supply systems with high integration of RESs as a whole.