Analysis of Hybrid Reference Frame Limiting Strategy Performance in the Presence of Secondary Control of Inverter Based Islanded Microgrids

With increasing the capacity and number of distributed energy resources (DERs), it is necessary to keep them connected to the microgrid during the disturbances. Two of the most important measures for satisfying this requirement are to provide the high quality voltage for feeding the critical loads and to limit the electronically-coupled DERs current and voltage. This paper investigates the performance of hierarchical control structure of islanded microgrids during and after the fault conditions. The primary control level of this control structure is equipped with the hybrid reference frame limiting strategy to limit the voltage-sourced converter (VSC) current and voltage. The effect of employing the concept of independent control of natural reference frame in both primary and secondary control levels and the influence of using the conditional integration method in the voltage controller of secondary control level on the microgrid performance during and after fault condition are investigated. The study results are demonstrated through several time-domain simulations of symmetrical and asymmetrical faults.