Enhanced Distributed Non-Linear Voltage Regulation and Power Proportion Technique for an Islanded DC Microgrid  
[PERSON]  
1 Discipline of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal,  
Durban 4041, South Africa; [EMAIL_ADDRESS] (A.S.); [EMAIL_ADDRESS] (I.J. );  
[EMAIL_ADDRESS] (M.B.) [PERSON]  
1 Discipline of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal,  
Durban 4041, South Africa; [EMAIL_ADDRESS] (A.S.); [EMAIL_ADDRESS] (I.J. );  
[EMAIL_ADDRESS] (M.B.) [PERSON]  
1 Discipline of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal,  
Durban 4041, South Africa; [EMAIL_ADDRESS] (A.S.); [EMAIL_ADDRESS] (I.J. );  
[EMAIL_ADDRESS] (M.B.) [PERSON]  
2 Power Research Laboratory, Department of Electrical and Software Engineering, University of Calgary,  
Calgary, AB 72N 1N4, Canada; [EMAIL_ADDRESS] (Correspondence: [EMAIL_ADDRESS]. of DC-based resources. In contrast to traditional AC microgrids, direct current microgrids operate in a more streamlined way due to the absence of certain concerns: controlling reactive power and frequency, power factor losses, and harmonics disturbances [5; 6; 7]. As a result, DC microgrids offer several advantages, such as enhanced stability, improved efficiency, lower control complexity, and higher power quality [7; 8]. These advantages have gained significant attention for DC microgrids in recent times. Research studies in [9] demonstrated that DC microgrids exhibit a 15% enhancement in voltage stability compared to AC microgrids. An islanded DC microgrid setup features multiple distributed energy resources, storage systems, and loads that connect in parallel to a shared DC bus via controllable DC-DC power electronic converter interfaces. The control of the converter at each DER interface plays a pivotal role in ensuring the operational stability of the MG. Therefore, the control system of a DC microgrid involves various control operations, including power distribution, cost optimization, balanced current sharing, power management, energy storage management, and voltage regulation [5; 9]. A hierarchical control framework comprising primary, secondary, and tertiary controls can be employed to attain the diverse control objectives in a DC microgrid [10]. Using this control approach allows microgrid operations to be effectively coordinated and managed. The primary control level focuses on instantaneous control tasks, such as current sharing and voltage regulation. It involves implementing conventional internal proportional-integral (PI)-based voltage and current controls within the DER converters. The primary control loop is augmented with droop control to facilitate power sharing among the DERs [8; 11]. Droop control implementation involves incorporating a virtual resistance (droop gain) into the primary control loop of the converter [12]. As droop control, a traditional integral controller is proposed in [13] to enhance the transient capabilities of converters in DC microgrids. Reference [14] presented a modified droop control approach to effectively tackle the adverse influence of circulating current resulting from voltage deviations in direct current microgrids. In [15], researchers put forth a non-linear droop control approach to enhance the operational capabilities of the traditional droop control, which is susceptible to degradation caused by the line impedance of the MG. A notable advantage of the droop control method is its fully decentralized implementation, eliminating the need for communication between DERs. As highlighted in [7; 16], the application of droop control entails a trade-off between direct current-sharing precision and voltage regulation at the DC bus. A high droop gain results in accurate current sharing but poor voltage regulation, leading to significant deviations in the direct current bus voltage. In addition, maintaining the desired reference value of the bus voltage becomes challenging as a result of its tendency to vary under different load conditions [16].