Active damping based on the capacitor voltage positive-feedback for grid-connected power converters with LCL filter

The capacitor voltage positive-feedback is a widely extended active damping strategy. It can effectively damp the LCL output filter resonant poles for low ratios of resonance to sampling frequencies. However, the existing delays in the control loop limit the applicability of the capacitor-voltage positive-feedback. For high ratios of resonance to sampling frequencies, it becomes ineffective and can even destabilize the system. This limitation is overcome in this paper by adjusting the delay in the feedback path. With the delay adjustment, a robust damping can be achieved if the delays are properly considered, including the filters, and the grid impedance variations are taken into account. Simulation results validate the proposed active damping strategy.This work has been supported by the Spanish State Research Agency (AEI) and FEDER-UE under grant DPI2016-80641-R

Modeling solar cavity receivers: a review and comparison of natural convection heat loss correlations

Trabajo presentado al International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2014. Beijing (China), 2014As the main difficulty of modeling cavity receivers is determining natural convection heat losses, this paper presents a survey of the different natural convection correlations developed by several authors to model natural convective heat losses from cavity receivers of solar thermal power tower plants. The different correlations studied for modeling convective heat losses are later compared by performing simulations on an implemented cavity receiver. For this work a model of a PS10-like cavity receiver, using Solar Salt as the heat transfer fluid, is implemented in Modelica. The simulations have shown how the results of four out of the five studied correlations do agree, while one of the analyzed correlations clearly overestimates convective heat losses for the simulations performed