Inverter Control for Power Injection from PV Sources in Microgrids Under Unbalanced Power Grid and Load Conditions

The increase in solar power penetration during the last years has prompted development of control techniques to inject power into grids with wide and sometimes varying characteristics. Among them, microgrids represent small versatile networks with different load types. Some microgrids require power injection at the three phase level, with stringent tolerance levels, as dictated by IEEE Standard 1547. This work presents the results of using two type of strategies, the first using direct power control DPC, and the second using d/q control. The connection to the power grid uses an L-filter with (DPC) and an LCL-filter with a PI controller in d/q coordinates. Simulations show that the DPC controller behaves well under wide varying conditions, but requires large filter inductance, while the d/q controller with LCL-filter needs special compensation to reduced inherent oscillations due to the LCL-filter.