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In this paper an analytical approach is conducted to evaluate the droop control method in an islanding microgrid. Droop control is the key solution for sharing the demand power between generators in autonomous microgrids where there is no support from the electricity distribution grid. In the paper, three important load types are investigated to verify the droop control performance. First, coupling of active power and reactive power is considered in the microgrid and a new method is proposed to facilitate separate control of powers. In the proposed method the effects of droop gains on decoupling of active power and reactive power control, voltage regulation, power oscillation and system stability are studied. In the second load type study, by applying the different types of faults, induction motor characteristics are observed. By simulation results it is shown that the fault intensity and duration will determine how the microgrid attains to fast frequency convergence and how fast protection system operation can improve system stability. In the third case, imbalanced nonlinear load is studied in the microgrid and the influences of embedded controllers on harmonic distortion, system balance and voltage regulation are observed.

To cite this article: A. Khaledian & M. Aliakbar Golkar (2018) A new power sharing control method for an autonomous microgrid with regard to the system stability, Automatika, 59:1, 87-93, ABSTRACTDroop control is the conventional way to share the demand power among the generators in a microgrid. Analyzing this control method shows that it has poor performance in reactive power sharing. Generated reactive power of each microsource depends on the active load demand. In this paper, a control method is proposed to improve the reactive power sharing performance. It is indicated that higher reactive power droop gains make the generated reactive power to be less influenced from the changes in active load. However, high droop gains can lead the system to instability. Hence considering eigenvalue analysis of the microgrid, a new auxiliary controller is proposed to damp the oscillations caused by high droop gains. In the new method, there is not the need for monitoring the grid impedance to tune the controllers. To verify the proposed method, load step is applied to a test microgrid and the results are shown. In the new method, total generated reactive power is reduced in comparison to the conventional droop controller and the system stability is maintained. ARTICLE HISTORY

In this paper the response of a microgrid to the interfaced harmonic distorted load is analyzed. A new control algorithm to mitigate harmonic distortion is considered for distributed generators (DGs) and the effect of this control scheme is shown in the currents of DGs and other loads.The proposed control algorithm is compared with the conventional control strategy for harmonic distorted loads that is sinusoidal source current strategy based on the instantaneous reactive power (IRP) theory. PSCAD simulation results for IRP theory control show high total harmonic distortion (THD) and 3rd harmonic percent. In comparison inner voltage and current controllers of the proposed control scheme with their disturbance rejection capability, mitigate THD and 3rd harmonic percent. For this control system MATLAB simulation results are shown.By demonstrating the traditional sinusoidal source current control strategy based on IRP theory, it is concluded that ignoring the distortion power (D) in compensating process and also sub-harmonics of Pαβ crossing from the controller interior high pass filter cause the presence of some harmonic components and high THD.