# Modeling and Simulation of Autonomous DC Microgrid with Variable Droop Controller
## 2 Literature Review
Additionally, inaccurate load sharing due to variations in line impedance remains a significant limitation of fixed droop control. A performance comparison between P and PI controllers for voltage droop control is discussed in [15], revealing that while these methods can regulate voltage, they often suffer from poor current sharing and deviations in the bus voltage under varying load dynamics [16; 17]. Ref. [18] proposes a modified droop control method that adaptively adjusts droop coefficients to reduce circulating currents and improve load-sharing accuracy. This approach enhances both voltage regulation and system stability, while mitigating the adverse effects of mismatched line impedances. The effectiveness of this adaptive droop method is validated through simulations and experiments under dynamic operating conditions, as demonstrated in [19]. Communication-based techniques for voltage regulation are explored in [20], where a low-bandwidth secondary control system dynamically adjusts droop coefficients to optimize microgrid performance. Ref. [21] implements a feed-forward compensation-based droop control for improved load sharing and bus voltage stability. In [22], an adaptive approach to tune the droop coefficient based on real-time system feedback is proposed to further enhance system performance. Moreover, communication-enabled coordination techniques for improving stability in decentralized microgrids are discussed in [23]. In ref. [24] a disturbance observer-based droop control strategy is proposed to address uncertainties arising from renewable energy sources, while in [25] non-linear droop characteristics are used to improve microgrid performance under varying load conditions. This approach improves stability, especially in the presence of large load variations. However, challenges such as design complexity and the need for precise tuning persist. Coordinated control of multiple sources for enhanced voltage regulation is explored in [26], where a combination of primary droop control with secondary and tertiary control layers leads to improved system performance. However, the need for a communication infrastructure increases the complexity of the system. The performance comparison of various droop control strategies used in DC microgrids and the operating conditions is also reviewed and summarized as follows. Ref. [27] implemented an adaptive droop control strategy based on the virtual impedance method to improve voltage stability, regulation, and power flow management. This method is more suitable for microgrids with considerable variation in line impedance. In [28] a hybrid droop control strategy is utilized to reduce total generation cost and transmission power loss using suitable weighting factors which makes it more suitable for economical and efficient operating conditions. In [29], a complex droop-based method is used to tune the droop functions mainly to achieve the desired power management in hybrid DC microgrids. This type of droop control is more suitable for microgrids with high source and load dynamics. Ref. [30] proposes a variable droop control strategy for a hybrid energy storage system, with supercapacitors and batteries, to address power fluctuations in ship DC microgrids. This method is suitable for ship-board type applications where load dynamics is very high. Ref. [31] proposes a novel mixed integer-based optimization technique to design the optimal converter size and location in the microgrid network. This method is suitable for microgrids where optimal resource allocation is of high priority. From the existing literature, the main research gap in the area of conventional fixed droop control strategy is that it cannot change dynamically to the load transients. The sharp voltage bus fluctuations due to the fixed droop resistor deteriorate the power quality. The variation in the droop coefficient with respect to the load in the proposed strategy successfully eliminates the sharp fluctuations in the DC bus voltage, thereby enhancing the transient performance subject to load dynamics.