Uncertain Harmonic Power Flow Calculation For Distribution System With DGs

Harmonic power flow calculation is an important tool for grid harmonic analysis, which can provide basis for harmonic suppression through calculation of harmonic distribution. However, current algorithms are mostly applied to certain cases, and cannot consider uncertain factors. The loads in distribution system are of great variety and variation, and the output of distributed generations(DGs) is also random and intermittent as to the impact of weather. This directly leads to the uncertainty of harmonic injection and then the harmonic distribution in distribution network.Complex affine based constant current source model of harmonic source is proposed, where the uncertainty is expressed as an interval. As backward/forward sweep algorithm is efficient in dealing with the radical distribution system, and affine arithmetic overcomes the conservative problem of interval arithmetic, the complex affine based backward/forward sweep harmonic power flow algorithm is proposed. The validity of the algorithm is tested via a typical test system of distribution network. The results are compared with that of Monte Carlo method, and evaluation is made covering completeness, conservatism, convergence and computation speed.Harmonic power flow algorithm for distribution system with DGs is proposed. Since DGs are mostly connected to grid via inverters which may cause harmonic interactions, the output-impedance model of DG inverter is introduced and used in harmonic power flow calculation, so factors like grid structure and background harmonic can be considered. To test the effectiveness when output-impedance model is used in harmonic power flow calculation, the results obtained from the case in which DG is modeled as constant current source are provided for comparison purpose, and influence factors like DG location and background harmonic are evaluated.As to the uncertainty of DG output, a complex affine based output-impedance model for DG inverter is built, and then the uncertain harmonic power flow algorithm for distribution system with DGs is proposed. The performance of the algorithm is also evaluated through comparison with Monte Carlo method.