Output Impedance Measurement of Digitally Controlled Power Converters in LVDC-Grids

Due to the increase in possible sector couplings to local low voltage DC grids, the amount of controlled infeed converters connected to the grids increases. For these grids to remain stable, proper system analysis is required. While simulation of these systems is possible, the final setup requires measurements. In this paper, the problem of output impedance measurement of digitally controlled power converters, which make up the majority of infeed converters in medium to high power LVDC grids, is discussed. Digital control leads to several requirements regarding the test signals used to measure the converters. Due to the nonlinearity of certain power converter types, the measurements required for a full description of the power converter typically need to be taken for a variety of loads and grid voltages. Wide bandwidth measurements can be used to reduce the overall measurement time. These wide bandwidth measurements require further investigation regarding signal amplitude, which is presented in this paper.