Microgrids harmonic assesment based on an acceleration procedure to the limit cycle

A harmonic-oriented analysis of a Microgrid based on an acceleration procedure to the limit cycle is presented in this paper. The computation of the periodic steady-state solution of the microgrid relies on the application of the Poincaré map to discretize the state variables at the vicinity of the limit cycle and a Newton-Raphson method to extrapolate the state variables to the steady-state. The microgrid model comprises a distributed generator, a storage energy system, non-linear loads and a control system. The distributed generator consists of a Proton Exchange Membrane Fuel Cell stack, while the energy storage system is based on an ultracapacitor. Furthermore, three-phase transformers involved in the power electronic converters are modeled with three single-phase transformers considering saturation and core losses. The control system provides power exchange with the main grid and voltage support for short term and momentary voltage fluctuations. Simulation results are reported for a 0.1 MW microgrid operated in stand-alone and grid connected modes. The application of the acceleration procedure to the limit cycle allows the efficient computation of the periodic steady-state of microgrids where the presence of a large number of VSC converters may lead to high harmonic distortion levels and prolonged transients.