Triple droop control method for ac microgrids

Abstract

In this study, a novel droop control method for ac microgrids is proposed to enhance the performance of power regulation, which is composed of three parts. The angle droop and the frequency droop are adopted to control the active power in coordination, while the modified voltage droop is used to control the reactive power. There are several improvements in this proposed triple droop control method compared with the conventional droop control. First, the dynamics of active power regulation are enhanced because of the angle droop. Second, the stability of the system is upgraded and the droop coefficients can vary in greater range. Third, the accuracy of reactive power regulation is improved, especially in the grid-connected mode, the DGs can output the specified reactive power with the modified voltage droop, which benefits the economic dispatch of the microgrid. Through these three combined droop control strategies, the performance of the whole system can be improved a lot whether in the grid-connected mode or the islanded mode. Furthermore, the stability of the proposed triple droop control is analysed, which shows that the stability of the system is upgraded. The effectiveness of the proposed control method is verified by the hardware-in-loop tests.

A Quasi-Average Estimation Aided Hierarchical Control Scheme for Power Electronics-Based Islanded Microgrids

“…Assume that we apply a constant input to each node, the steady state output can be obtained by final value theorem (19),…”

“…As such there are several variations of basic droop methodologies for different inductive and resistive nature of microgrids considered [10][11][12]. A secondary control layer is however required to observe and correct such deviations in frequency and voltage to keep these parameters within a nominal range [10,[13][14][15][16][17][18][19].…”

Improved Droop Control with Washout Filter

“…It should be noted that there is no size relationship between ω l1 and ω h . When ω h = ω l1 and ω l2 ω l1 , the DWC degenerates to a PD (proportional-differential) control method [6,9], where the differential coefficient is control loop aims to compensate the APDP caused by the small droop coefficient. Thus, the control scheme of the DWC can be derived as:…”

“…To improve the active power dynamic performance (APDP) of a DG embedded with the droop strategy, various control strategies have been put forward [5][6][7][8][9]. Another DOF (degree of freedom) is added in [5], in which the derivative term is introduced to achieve a better APDP [7].…”

“…The APDP is improved by introducing derivative control with an adaptive coefficient which is small [8]. In [9], the angle and frequency droop control strategies are combined to improve the performance of active power output. A washout, i.e., the lack of low-frequency component of output power, filter control strategy is proposed in [10].…”