Adjusting the Low Order Harmonics in the Battery Currents for the Microgrid Power Converters with the Instant Islanding Capabilities

The instant islanding of a microgrid with the minimal voltage sag requires the instant outage detection, grid disconnection and switching of the inverters operating modes. This paper deals with the inverter (AC/DC) supplied by the DC/DC converter connecting the energy storage devices. The P/Q and V/F controls are used in the grid-tied and the islanding modes, respectively. The seamless islanding transition can be achieved if the DC/DC regulates the dc-link voltage for both modes. However, the stability requirements of the battery charging and discharging currents are not satisfied in this scenario. The paper introduces the low order harmonic (LOH) powers distribution mechanism in between different stages in the system, so that the LOH powers due to the non-sinusoidal grid voltages will not pass through to the battery side. The proposed adjusting mechanism are verified by the simulation. The experiment on a battery storage system (AC/DC and DC/DC) prototype is being carried out within a microgrid and the partial lab results are shown.