This article proposes an improved distributed cooperative control strategy for the energy storage system (ESS) in islanded dc microgrid. To meet the requirements of state of charge (SoC) balance, accurate current sharing, and voltage regulation, a hierarchical control structure is established. In the primary control layer, the droop coefficient is adaptively adjusted through the SoC dynamic changes in each energy storage unit (ESU) to achieve SoC balance, and two balance adjustment factors are introduced to improve SoC convergence speed and accuracy. In the secondary control layer, an information state factor $\zeta $ is designed to eliminate the influence of the inconsistent line resistance on the SoC balance and realize the dc bus voltage recovery. In the communication layer, each ESU only exchanges information with neighboring nodes through a sparse communication network, in which a dynamic consensus algorithm is used to achieve stable convergence of global average information. Finally, a dc microgrid simulation model and StarSim HIL experimental platform are built. The results show that the proposed control strategy can achieve SoC balance and accurate load current sharing under a variety of complex operating conditions and have excellent plug-and-play performance.

The control performance of traditional model predictive control (MPC) usually deteriorates dramatically with the permanent magnet synchronous motor (PMSM) parameter changes in operation, leading to current harmonics and torque ripple. This paper proposes a robust model predictive current control (MPCC) method based on a nonlinear extended state observer (NESO) to resolve this problem. The NESO is used to observe the current disturbance part to avoid the influence of motor parameters on the current model. Because this method is not sensitive to changes in motor parameters, the system is robust and has a low current harmonic. Second, the ESO designed in this paper based on the nonlinear function has a lower observation error. In addition, this paper uses the fixed coefficient method to simplify the design process. A more accurate parameter design method is proposed based on the bounded analysis of observation error. At the same time, the root locus diagram proves that NESO contributes to the stability of the current loop. Finally, hardware and simulation experiments proved that the robust MPCC based on NESO has lower harmonic content and better dynamic performance.

This paper presents a novel hierarchical cooperative control strategy to solve the problems of unbalanced State of Charge (SoC), unreasonable load current sharing, and unstable bus voltage for battery storage system (BSS) in islanded DC microgrid. In the communication layer, a neighbor-to-neighbor communication network architecture is constructed in which each battery storage unit (BSU) only communicates information with neighboring nodes, and a multi-agent consensus algorithm is used to iteratively estimate the relevant average global variables. In the main control layer, the droop coefficient is dynamically adjusted by constructing a fast SoC convergence function to ensure that the load current is reasonably distributed based on the rated capacity of each BSU. In the secondary control layer, a virtual voltage drop equalization controller and an average bus voltage compensation controller are designed to eliminate the impact of line impedance mismatch and compensate the average bus voltage. Furthermore, an optimized factor is designed to accelerate the later stage of SoC convergence. Finally, a DC microgrid experimental platform based on StarSim HIL is built, and the results demonstrate that the proposed strategy can achieve the control objectives of fast SoC balance, proportional load current sharing, and bus voltage stability.

In this paper, a novel distributed unified controller is designed to solve the problems of unbalanced State of Charge (SoC), unreasonable load current sharing, and unstable DC bus voltage for parallel battery storage systems (BSSs) in DC shipboard microgrid (DC-SMG). Different from the droop-based secondary controller, the designed distributed unified controller is a droop-free primary controller, which can incorporate SoC balancing, current sharing, and voltage regulation functions in the primary control layer. On this basis, each BSS uses an improved dynamic diffusion algorithm (DDA) to iteratively estimate the average information, and completes information exchange by a neighbor-to-neighbor communication network. Furthermore, the small-signal stability, large-signal stability, and global steady-state performance of the system is investigated using eigenvalue analysis, mixed potential theory (MPT), and matrix theory, respectively. Finally, the Matlab/Simulink simulation model and the StarSim HIL experimental platform for DC-SMG are built. The results show that the designed distributed unified controller can simultaneously achieve dynamic SoC balancing, proportional load current sharing, and smooth average bus voltage regulation, and has a faster SoC convergence speed and more stable control effect than the state-of-the-art methods.

Typically, the secondary controllers for distributed battery storage units (BSUs) have been designed using asymptotic or finite-time consensus protocols, which may not be suitable for DC microgrids with intermittent renewable energy operations and frequent load power fluctuations. This article presents a novel fixed-time secondary controller, which designed to achieve both rapid State-of-Charge (SoC) balancing and flexible bus voltage regulation for parallel BSUs in DC microgrids. The proposed fixed-time secondary controller provides a bounded settling time independent of initial conditions, whereas also offering a rapid SoC balancing speed. Pinning control is combined with the proposed fixed-time secondary controller to achieve flexible regulation and accurate restoration of the average bus voltage. This scheme saves computing resources and releases communication pressures. Rigorous Lyapunov stability proofs, along with experimental results using StarSim, demonstrate the effectiveness and superiority of the proposed fixed-time secondary controller under various testing scenarios.

Conventionally, voltage regulation and economic dispatch in DC microgrid are performed at different time scales, which cannot keep the distributed generators (DGs) at the optimal operating point in real time. In this article, a novel distributed cooperative control strategy is proposed to synchronously achieve stable bus voltage restoration and optimal power sharing in islanded DC microgrids. The proposed strategy breaks the constraints of hierarchical control strategies, and incorporates the objectives of voltage regulation and economic dispatch into a distributed cooperative control framework to eliminate average bus voltage deviation and minimize total power generation costs in real time. The stability of the proposed strategy is verified by eigenvalue analysis and steady-state analysis. Furthermore, the concept of “incremental cost (IC) margin” is introduced in cooperative control considering capacity constraints to avoid the converter output power violation and performance degradation. Finally, the MATLAB/Simulink simulation and StarSim HIL experimental results verify the effectiveness and robustness of the proposed strategy in an islanded DC microgrid under various testing scenarios.