Analysis, design and implementation of droop-controlled parallel-inverters using dynamic phasor model and SOGI-FLL in microgrid applications

Abstract

The droop control strategy is widely used in islanded microgrids to control power flows according to the load condition, with the absence of a critical communication line, interfacing distributed energy sources to provide for the active and reactive power demand of loads. In this case, the system modeling for both steady-state and transient time is one of the key issues of a droop-controlled system for an inverter-based microgrid (MG). With the rapid development of microgrids, it is essential to identify the system stability and optimize the control parameters, taking into account the network and control dynamics caused by multiple tasks such as electric signal filtering, network synchronization, and so on. Therefore, in order to improve model accuracy and determine control coefficients, this paper analyzes and extends a dynamic phasor-based model to the droop-controlled parallel-inverters, considering network and control dynamics such as a low-pass filter, a second-order generalized integrator frequency-locked-loop (SOGI-FLL), and a system operating sequence. Moreover, discussed in this paper are both the design approaches for and the implementation of a droop-controlled parallel-inverter, which enables the system to be stable and reliable. To demonstrate the effectiveness and validity of this paper, PSIM simulation was performed and two parallel-inverters were combined as the proposed design procedure for the 4-kVA prototypes.