Minimal Invasive Equivalent Grid Impedance Estimation in Inductive-Resistive Power Networks Using Extended Kalman Filter

Real-time estimation of the equivalent grid impedance and the equivalent grid voltage seen from a power converter connected to the public electric distribution network by means of extended Kalman filter is addressed. The theoretical background of the extended Kalman filter used for equivalent grid impedance estimation is introduced. Practical aspects like the use of the filter in an environment with highly distorted voltage waveforms, the tuning of the noise covariance matrices, and the implementation on a laboratory system are discussed. The theoretical analysis is verified on a 22-kW test-bench where a grid impedance emulator is used to simulate grid impedance steps in the laboratory environment. The proposed extended Kalman filter is designed to utilize the noise that is already present at the connection point of the power converter to overcome the need of active disturbance injection to estimate the equivalent grid impedance. Thus, electrical equipment connected close to the grid-connected converter is only affected marginally by the equivalent grid impedance estimation technique.