This paper addresses the stability analysis of DC distribution networks with voltage source rectifiers (VSRs) and constant power loads (CPLs). Existing stability criteria for DC networks often rely on simplified models neglecting source converter controller dynamics, limiting their applicability in practical controller design. To overcome this, a singular perturbation-based framework is proposed to derive analytical stability conditions for closed-loop DC distribution network systems. By decomposing the high-dimensional Jacobian matrix into two structured low-dimensional matrices, tractable stability criteria are established using properties of Karush-Kuhn-Tucker (KKT) matrices. Sufficient stability conditions for local stability of a VSR-based DC distribution network are derived without requiring global VSR information, while a robust stability criterion dependent solely on maximum load data is developed to handle uncertainties. These results provide explicit design guidelines to enhance robustness and reduce computational complexity in stability analysis. Simulations validate the effectiveness of the proposed approach.

In this paper, we find that multiple attractors may coexist with the stable equilibrium point in an islanded microgrid containing identical grid-forming converters and a ring power network, which was once believed to be impossible in previous study. The existence of such an attractor separates the microgrid into several clusters, each of which is internally synchronized, but desynchronized with each other. We define a cluster coherence metric to measure the internal coherence of each cluster. Finally, full-circuit cycle-to-cycle simulation is provided for verification.

In conventional power systems dominated by synchronous generators, transient stability was found to be less influenced by the secondary control (e.g., automatic generation control). However, due to the flexibility of control and communication of grid-connected converters, more advanced control schemes such as the virtual-impedance-based distributed secondary control can be applied to multi-converter islanded microgrids, which may have a significant impact on the microgrid’s transient stability. In this paper, a simplified model considering the essential synchronization dynamics is established, and the metric named microgrid stable basin is proposed to measure the impact of critical secondary control parameters on the transient stability. Finally, laboratory measurement is provided to verify the theoretical findings.

Frequency damping control is a crucial aspect of islanded microgrids utilizing multiple virtual synchronous generators (VSGs). This paper studies the effects of line impedance mismatches and transient frequency out-of-sync leading to frequency interactive oscillation in VSGs. To address this issue, we propose a distributed interactive damping and zero-error control method that utilizes sparse communications. The objective of this method is to effectively suppress frequency oscillation by minimizing the differences in frequency dynamics among all VSGs. By implementing this approach, a low rate of change of frequency (RoCoF), accurate active power sharing, and zero frequency deviation are ensured. Through dynamic performance analysis, frequency characteristic analysis, and stability analysis based on LaSalle’s invariance principle, we demonstrate significant improvements in system stability, as well as dynamic and steady state performances. Finally, simulation and experimental results obtained under load changes, short-circuits, and communication faults validate the effectiveness of the proposed control method.

The continuous conduction mode (CCM) totem-pole bridgeless power factor correction (TPBPFC) converters are feasible because of the better reverse-recovery performance of the wide band gap (WBG) devices. However, practical applications encounter challenges such as low power density, high cost, and high-power loss. This paper proposes an improved hybrid Si/SiC CCM TPBPFC rectifier. A buck-type active power decoupling (APD) circuit is used to remove the bulky capacitor and increase the power density. A SiC-based bidirectional switch is connected between the Si-based PFC and APD bridges to achieve the soft switching of Si-based switches and decrease the power losses. The operation principle is given and then the analysis of soft switching conditions and power loss are provided. Finally, the verification of proposed circuit is experimented on a 500 W prototype and a 2% efficiency improvement is demonstrated.

A hierarchical fault detection and fault location framework consisting of two levels is proposed for DC ring bus microgrids. In the primary level, a decentralized fault detection scheme based on back propagation (BP) artificial neural network (ANN) and discrete wavelet transform (DWT) is proposed to classify the pole-to-pole (P-P) and pole-to-ground (P-G) faults under measuring noises and load disturbances only relying on the information needed by the local double closed-loop controller, and the diagnosis speed and reliability of system are guaranteed. In the secondary level, a distributed line fault location method is presented by synthesizing the detection results of local and neighbor DG units with low bandwidth communication, and the accuracy of line faults is improved greatly without the central controller and additional sensors. Several simulation cases are analyzed under various fault configurations such as load mutations, different fault types, fault locations and fault impedance. The effectiveness and feasibility of the proposed method are verified.

This paper proposes a novel universal control for multi-bus AC microgrid with the capability to operate in both grid-connected (GC) and islanded (IS) modes. The control scheme is based on distributed manner, and the leader-follower consensus protocol is designed. Only few leader distributed generators (DGs) receive the correction signals from the unified mode controller, which is installed at the point of common coupling (PCC). The rest follower DGs would track the leader DGs, and exchange information with their neighbors. Under this control framework, the active and reactive power can be flexibly controlled to inject into the grid in GC mode. Meanwhile, the voltage/frequency support and active/reactive power sharing are guaranteed in IS mode. Moreover, the proposed method is able to offer seamless transition between GC and IS modes. Finally, simulations are presented to verify the satisfied transition process of different modes.

Cascaded H-bridge converters based islanded microgrids are applied to integrate the distributed generators (DGs). The accurate load sharing is an important task for the research of microgrids. Due to the characteristics of series connection, all DGs share a single common current. In this paper, the power factor of each DG is assigned to be consistent via regulating both the frequency and voltage. The real power and reactive power are shared accurately through the power sharing coefficients under the resistance-inductance and resistance-capacitance load. Meanwhile, an excellent load voltage quality is retained. The implementation of the proposed scheme only needs the local information in decentralized manners. The AC microgrid model is developed through simulations to verify the effectiveness of the proposed scheme.

This paper proposes a novel distributed control scheme for DC microgrids to acquire minimum generation cost and recover the global average voltage with consideration of capacity constraints. Our main focus is on constrained problems where the power of each distributed generator (DG) is restricted to lie in the feasible region. In this paper, a global load observer (GLO) is introduced that uses neighbor's data to estimate the total load across the microgird. To achieve minimizing generation cost, an alternative control strategy is proposed based on the specific characteristics of the optimum solution. When the total load which can be obtained by the GLO is less than the critical point, it generates power according to equal incremental cost rate (ICR) criteria; otherwise, it generates power maintain the maximum output point. To achieve voltage recovery, a voltage regulator is designed. The proposed controller on each DG communicates with its neighbor DGs on a sparse communication graph. The performance of the proposed scheme is validated and tested through MATLAB simulation.

A predictive control scheme for the third-harmonic injection two-stage matrix converter (3TSMC) under unbalanced input voltages is presented. The proposed scheme is designed to predict the future behavior of the third-harmonic injection current and load currents respectively for each valid switching state. The control scheme selects the state that minimizes the error between the predicted currents and references. For the 3TSMC, the input currents are synthetized by the injection current. In order to keep sinusoidal input currents under unbalanced input voltages, the reference of the third-harmonic injection current is obtained by symmetrical component extraction. Firstly, this paper introduces the proposed control method, including establishing the discrete-time model and selecting cost functions. Then, the extraction for the reference of injection current is presented. Finally, this paper shows the simulation results to demonstrate that the proposed control method can generate good tracking of input and output currents under unbalanced input voltages.

In cascaded-type microgrid, the synchronization and power sharing of distributed generators (DGs) become two new issues that needs to be addressed urgently. In this paper, a unified droop control is proposed and its stability is analyzed in the islanded mode. The proposed scheme can ensure the system stability and accurate power sharing without communication in four-quadrant operations. Finally, simulation and experimental results are presented to verify the system effectiveness. Furthermore, the application of droop control in grid-connected mode would be researched in our future work. The preliminary simulation results are presented in this paper.