Reactive Power Sharing using modified Virtual Impedance and Local load measurement for Islanded Microgrid

Abstract:
The reactive power sharing is a big issue in the microgrid especially in islanded mode which has local load connected and there is no power reference available from grid. The reactive power sharing error is usually caused by the mismatch of impedances in connecting circuit. Different connecting circuits may have different impedance which results in different voltage drop across these impedances in connecting circuit and hence mismatch of active and reactive power. The P-ω droop normally results in good active power sharing. However, reactive power sharing by Q-V droop is not so accurate and results in unequal reactive power sharing. This mismatch problem becomes worse when microgrid has local load connected. To solve the problem of reactive power sharing in microgrid, this paper presents a modified virtual impedance based reactive power sharing technique which takes into account the mismatch of impedance in connecting circuits for parallel DG’s. This paper also considers of mismatch caused by local load connected with microgrid before point of common coupling PCC. By adjusting virtual impedance in a particular way presented in this paper, the mismatch of impedances can be compensated. This way virtual impedance can be regulated so that all DG’s have similar overall connecting circuit impedance which will result in equal reactive power sharing. The calculation method of virtual impedance method is given and validated by both MATLAB SIMULINK simulation and experimental platform. The result are shown in results section below.