Biblio

The continuous integration of intermittent low-carbon energy resources makes islanded microgrids vulnerable to voltage fluctuations. Besides, different dynamic response of synchronous-based and inverter-based distributed generation (DG) units can result in an instantaneous power imbalance between supply and demand during transients. As a result, the ac-bus voltage of microgrid starts oscillating which might have severe consequences such as blackouts. This paper modifies the conventional control scheme of battery energy storage systems (BESSs) to participate in improving the dynamic behavior of islanded microgrids by mitigating the voltage fluctuations. A piecewise linear-elliptic (PLE) droop is proposed and employed in BESS to achieve an enhanced voltage profile by injecting/absorbing reactive power during transients. In this way, the conventional inverter implemented in BESS turns into a smart inverter to cope with fast transients. Using the proposed approach in this paper, any linear droop curve with a specified coefficient can be replaced by a PLE droop curve. Compared with linear droop, an enhanced dynamic response is achieved by utilizing the proposed PLE droop. Case study results are presented using PSCAD/EMTDC to demonstrate the superiority of the proposed approach in improving the dynamic behavior of islanded microgrids.

The vulnerability of islanded microgrids to voltage and frequency variations is due to the presence of low-inertia distributed generation (DG) units. Besides, the considerable difference between the inertia of synchronous-based and inverter-based DGs results in a power mismatch between generation and consumption during abnormal conditions. As a result, both voltage and frequency of microgrid ac-bus start oscillating which might lead to blackouts. This paper deploys the traditional controller of photovoltaic (PV) units to improve the dynamics of islanded microgrids by reducing the voltage and frequency deviations. To this end, an adaptive piecewise droop (APD) curve is presented and implemented in PV units to attain a faster balance between supply and demand during transients, leading to an enhanced frequency response. Besides, the reactive-power control loop is equipped with a droop characteristic which enables the PV units to inject/absorb reactive power during transients and participate in voltage-profile enhancement of the system. Case study results are presented using PSCAD/EMTDC to confirm the validity of proposed method in improving the dynamic behavior of islanded microgrids.