Designing robust controller to improve current-sharing for parallel-connected inverter-based DGs considering line impedance impact in microgrid networks

چکیده مقاله

Microgrids are designed to supply electrical and heat loads for small communities. An important research area related to microgrids is proper controller strategy for ensuring the current and power sharing of each generating unit under different load and system conditions. In this paper, considering effect of line impedance, a new approach based on robust control design method, H1 loop-shaping design (HLSD) procedure, was presented for parallel-connected inverters of DGs in an islanded microgrid. Changes in the parameters of lines were considered uncertainties, based on which the system model was built. The designed controller adjusted the output voltage of each inverter by controlling duty cycles in order to change the output current delivered by each inverter. So, the controller controlled the duty cycles as control inputs to the system so that the system robustness to uncertainties was maximized and the voltage error was minimized, which in turn would cause reduction of the circulating current. For resistive, inductive, and non-linear loads, time responses of the system were achieved. Results of simulations indicated that the designed robust controller, in comparison with gain scheduling controller, was capable of guaranteeing robust stability and performance under parameter uncertainty and different loads. Also, effectiveness of the proposed controller in minimizing the circulating current among parallel-connected inverters was demonstrated.