Design of a wide-band low-voltage grid impedance analyzer

In this paper the design and measurement results of a grid analysis and grid impedance measurement system are presented. The system is provided to measüre the freqüency dependent grid impedance in different PoCs to detect resonances and improve the power quality especially of grids with high amount of DERs. Moreover Active Filtering (AF) and reactive power feed-in are possible. It comprises also measurement of the negative and zero sequence as well as of subharmonics. The design of the converter is discussed in detail, the chosen method of impedance measurement is explained briefly, calculations for the selection of the converter topology and the selection of power semiconductor devices are made. A special hysteresis current control for 3-level Active Neutral Point Clamped (ANPC) converters is presented. Finally different measurement results are shown. These measurements of the grid impedance include subsynchronous frequencies in the range of 0.1 Hz to 30 Hz and frequencies in the range of 70 Hz to 10 kHz as well as measurements of the negative sequence and the zero sequence impedance of different low voltage grids.