Distributed generators as reactive power providers and their impacts on standalone micro-grid performance during both symmetrical and unsymmetrical faults

摘要

This paper investigates the capability of providing reactive power by Distributed Generators (DGs) interfacing inverters to the standalone Micro-Grid (MG). To enable the DG interfacing inverter to supply reactive power to the hosted MG, the inverter rating must be modified to be suitable for power factor less than unity. Effect of the modified rating of the inverter on the standalone MG symmetrical and unsymmetrical fault performances are investigated in detail. It is shown that, the modified DG interfacing inverter increases the short circuit current by 15% for symmetrical fault, and by 12.5% for unsymmetrical fault. The increase in the short circuit current results from modifying the inverter size. This increase in fault current must be considered while setting the MG protection relays. The injected fault current by each DG interfacing inverter is not affected by the fault location or MG feeding cable lines' impedances. The injected fault current by each DG inverter is only dependent on the inverter designed current and the maximum allowable inverter short circuit current. For unsymmetrical fault, touch voltages are increased with increasing the inverter size. For symmetrical fault, touch voltages is not affected by the inverter size nor the designed power factor.