DC microgrids look attractive in distribution systems due to their high reliability, high efficiency, and easy integration with renewable energy sources. The key objectives of the DC microgrid include proportional load sharing and precise voltage regulation. Droop controllers are based on decentralized control architectures which are not effective in achieving these objectives simultaneously due to the voltage error and load power variation. A centralized controller can achieve these objectives using a high speed communication link. However, it loses reliability due to the single point failure. Additionally, these controllers are realized through proportional integral (PI) controllers which cannot ensure load sharing and stability in all operating conditions. To address limitations, a distributed architecture using sliding mode (SM) controller utilizing low bandwidth communication is proposed for DC microgrids in this paper. The main advantages are high reliability, load power sharing, and precise voltage regulation. Further, the SM controller shows high robustness, fast dynamic response, and good stability for large load variations. To analyze the stability and dynamic performance, a system model is developed and its transversality, reachability, and equivalent control conditions are verified. Furthermore, the dynamic behavior of the modeled system is investigated for underdamped and critically damped responses. Detailed simulations are carried out to show the effectiveness of the proposed controller.

DC microgrids are localized and independent power distribution networks which show high efficiency when batteries and renewable sources are interconnected with the system. This paper addresses the stability of the dc microgrid through a decentralized control scheme. A centralized control architecture can improve the stability but reliability is compromised if the central controller fails. Droop control is commonly used to address the stability problem based on techniques through linear controllers. However, the Droop controller requires a tradeoff between voltage regulation and droop gain. Further, the global stability of the systems cannot be ensured through linear control techniques. Additionally, for different operating requirements and load conditions, it is difficult to optimize the parameters of these controllers. To address limitations, a PWM Based fixed frequency equivalent sliding mode (SM) control technique is proposed for dc microgrid stability. SM controllers show high robust performance. To formulate the problem, system equations are modeled and the operation of the system under SM is verified for existence and stability conditions. To examine the transient performance, the responses for critically damped and underdamped are investigated and presented. The results of detailed experiments simulations are presented which show the efficiency of the proposed control method.

In a standalone DC microgrid, sources are interconnected in a parallel configuration. When sources of different power ratings are parallel connected, there arises a major issue of circulating currents which disturb current sharing by sources as per their capacity. Consequently, the voltage regulation becomes poorer. Additionally, connecting line resistances also play their part to contribute to abnormal current sharing. Droop controllers are normally preferred for the mitigation of circulating currents among parallel-connected sources. However, droop controllers cannot eliminate circulating currents for different rating sources. Hence, current sharing and voltage regulation cannot be ensured simultaneously. To address the issues, a distributed architecture-based Sliding Mode Control (SMC) technique is proposed in this paper. An analysis of the circulating currents for a two-source system is presented. Simulation results are presented to show the effectiveness and fail-safe operation of the proposed technique in a steady-state condition.

DC microgrids are gaining popularity due to their lack of reactive power compensation, frequency synchronization, and skin effect problems. However, DC microgrids are not exempted from stability issues. The stability of DC microgrids based on decentralized architecture is presented in this paper. Centralized architecture can degrade system performance and reliability due to the failure of a single central controller. Droop with proportional integral (PI) controller based on decentralized architecture is being used for DC microgrid stability. However, droop control requires a tradeoff between voltage regulation and droop gain. Further, global stability through PI controller cannot be verified and controller parameters cannot be optimized with different operating conditions. To address limitations, an equivalent sliding mode (SM) controller is proposed for a DC microgrid system in this paper. Detailed simulations are carried out, and results are presented, which show the effectiveness of an equivalent SM controller.

Load-sharing and voltage regulation are key challenges in low voltage dc microgrid systems. Droop-based decentralized control methods are used to control dc grids which cannot achieve these challenges simultaneously due to unequal voltages and load power variations. Centralized control schemes can achieve these challenges using high bandwidth communication. However, the failure of a single central controller can degrade performance and reliability. In addition, cascaded proportional-integral (PI) type controllers are used to control the voltage and current loop of each power electronic converter. These controllers suffer stability and show slower dynamic responses. Furthermore, control parameters cannot be optimized for different operating conditions. To address these challenges, a distributive control method using an equivalent sliding mode (SM) controller utilizing low bandwidth communication is proposed in this paper. The distributive method improves reliability and achieves load sharing and voltage regulation simultaneously. Furthermore, in SM, both voltage and current loop operate in the parallel configuration which improves the dynamic response and shows stability in all operating conditions. To analyze, a system model is developed, and existence and stability conditions are verified. Detailed simulations are carried out to show the steady-state and transient performance. The presented results show the effectiveness of the proposed scheme.