This paper proposes a new active method for low frequency (LF) current/power oscillations damping in droop-controlled dc microgrids. Since, LF oscillations are mainly affected by droop controllers of voltage controlled (VC) DGs, detailed small-signal analysis of VC-DGs is provided. Analysis shows that each droop-controlled VC-DG creates a pair of LF complex conjugate zeros. In the proposed method, these zeros are damped by a negative feedforward of the disturbance variables (output currents) of VC-DGs. Stability analysis of the overall dc microgrid reveals that the LF zeros of VC-DGs can affect the LF modes of the system. Therefore, in the proposed method, the effective tuning of feedforward gain of each VC-DG can increase the damping factor of microgrid LF modes and consequenctly improve the dynamic response of the whole system. Moreovere, to gurantee the plug-and-play performance of DGs, a coordinanted tuning criterion for adjusting the proper feedforward gains is presented. It is shown that the proposed method is also robust against structural changes in dc microgrids. A complete set of simulation studies using MATLAB/Simulink is provided which further supports the effectiveness of the proposed active damping method.
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Rashidirad et al. (2017) studied this question.
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