Development Of A Two-Level Vsc Based Dc Impedance Measurement Unit

To analyze the small- signal stability of a power-electronics-based dc distribution system, it is important to know the converter input and output impedances. In a physical system, the converter impedances are measured for stability analysis in different ways. Many impedance measurement methods require dedicated frequency analysis equipment and/or are not suitable for high-power applications. This paper proposes one practical and easy-to-use solution for dc impedance measurement, which does not need any dedicated equipment or any extra power supply. Instead, it uses a two-level voltage source converter, which is usually available in a hybrid dc grid, to inject small perturbations into the system under test. Then the dc terminal voltage and current waveforms are measured by oscilloscopes and imported to MATLAB for further handling. Fast Fourier transform and system identification techniques are conducted to get the non-parametric impedance transfer functions. Simulation and experimental results are also given to validate the effectiveness of this approach.