ENS Implementation - Part of the PSO Eltra contract 4524/2003

with PowerLynx A/S for the development of the ENS function for the PowerLynx PV inverters. The work started 01.01.03 and ended 29.02.04 and involved Frede Blaabjerg, Remus Teodorescu, Lucian Asiminoaei and Adrian Timbus from Aalborg University and Uffe Borup from PowerLynx A/S. The objective was to make the PowerLynx PV inverters compatible with the germans ENS standard which mainly consist in the requirement to disconnect from the grid in max. 2 seconds if the grid impedance is changed with 0.5 ohms resistive. During 01.07 ? 31.08 2003, an algorithm based on the injection of a voltage of 75 Hz and the on-line measurement the 75 Hz component from the grid current and voltage using simplified DFT was developed by Uffe Borup, Remus Teodorescu and Lucian Asiminoaei. The algorithm is described in detail in the report ?ENS design? enclosed in Appendix A and in the two published paper (final paper for APEC ?04 and approved digest for PESC ?04). Then the algorithm was finally implemented and the experimental test carried out proved to be satisfactory as shown in chapter 2 ?ENS implementation?. Very few missed tests were recorded on very high inductive grid (0.6 + 1.1i) when the reactance is higher than the resistance. In the period 03.02.04 ? 13.02.04 some attempts was done in order to improve the detection by compensating the delay in the voltage measurement but no improvement was noticed. Thus, these last minute changes was not included in the final version of the software. Finally, the detection mechanism of another PV running in parallel that injects t5Hz for ENS grid measurements has been done. The code for parallel ENS is also enclosed.