Power Quality Improvements for Integration of Hybrid AC/DC Nanogrids to Power Systems

The coexistence of a hybrid ac/dc infrastructure for residential homes (Hybrid Nanogrid) is in the foreseeable future. This paper presents a hybrid ac/dc home infrastructure which involves DC distribution network connected to the current AC infrastructure through an efficient ac/dc controlled converter. DC network in the home allows for efficient integration of renewable sources and electric vehicles supplying all the native DC loads (DC appliances), while the AC loads (AC appliances) will continue to be connected to an existing AC infrastructure. In this paper, a control scheme for the ac/dc converter is proposed based on a modified synchronous reference frame for Active Power Filter control (APF) to mitigate harmonics, providing a power factor correction and compensating for unbalances resulting from nonlinear loads. The objective of the controller is to force the AC grid currents at the point of common coupling (PCC) to be balanced three-phase currents with minor harmonics while maintaining a controllability of power flow regardless of the characteristics of the local AC load. The results show that the developed controller succeeds to maintain bi-directional power flow controllability, while simultaneously acting as an active power filter to assure improved power quality at the PCC under various loading conditions.