An Adaptive Virtual Impedance Based Droop Control Scheme for Parallel Inverter Operation in Low Voltage Microgrid

This paper presents an adaptive virtual impedance based droop control scheme for parallel inverter operation in low voltage microgrid. Because it is essential to achieve power sharing between inverters in microgrid , various droop control scheme s ha ve been proposed . In practice, the line impedance between inverters and the point of common coupling (PCC) in microgrid are not always equal. This im balance in line impedance often results in a reactive power mismatch among inverters. This problem has been solved by introducing a virtual impedance loop in the conventional droop control scheme. However, the reactive power sharing performance of this method is still deteriorate d when the line impedances change during operation. To overcome such a problem , a new control scheme that is based on a virtual impedance loop and an impedance estimation scheme is proposed. To monitor the changes in line impedances , t he impedance estimator is implemented by using the output voltages and currents of inverters as well as the voltages at the PCC. To compensate for the reactive power mismatch due to the line impedance changes , t h e estimated line impedance is fed to the virtual impedance loop in which it adjusts the virtual impedance value . Comparative s imulation results with the conventional ones verify the effectiveness of the proposed adaptive virtual impedance based droop control scheme .