A distributed control strategy (DCS) is an efficient way to realize power sharing among distributed generators (DGs) and restore the voltage deviation caused by droop control. However, there are several limitations in the traditional strategy of hybrid ac/dc microgrid (MG), such as the heavy communication burden and sensitivity to the working conditions. In this article, a distributed model-free adaptive control strategy (DMFAC) is proposed with an event-triggered (ET) mechanism. A unified control framework of hybrid MG is established and the ET-DMFAC can operate within it to realize multiple control strategies simultaneously. The dynamic linearization parameters of hybrid MG are estimated online to reflect the working condition, and an ET mechanism is designed to reduce the communication burden. The stability of ET-DMFAC is analyzed with the discrete Lyapunov theory and experiments are carried out to verify the effectiveness of the proposed ET-DMFAC strategy under different operating conditions. The outperformance of ET-DMFAC is demonstrated by comparing it with many existing DCS of hybrid AC/DC MG.

Traveling wave (TW)-based fault-location methods have been used to determine single-phase-to-ground fault distance in power-distribution networks. The previous approaches detected the arrival time of the initial traveling wave via single ended or multi-terminal measurements. Regarding the multi-branch effect, this paper utilized the reflected waves to obtain multiple arriving times through single ended measurement. Potential fault sections were estimated by searching for the possible traveling wave propagation paths in accordance with the structure of the distribution network. This approach used the entire propagation of a traveling wave measured at a single end without any prerequisite of synchronization, which is a must in multi-terminal measurements. The uniqueness of the fault section was guaranteed by several independent single-ended measurements. Traveling waves obtained in a real 10 kV distribution network were used to determine the fault section, and the results demonstrate the significant effectiveness of the proposed method.

In a hybrid AC/DC microgrid (MG), power quality issues arise when an unbalanced load connects to the AC subgrid, which are not confined to the AC subsystem but extend to affect the DC subsystem as well. This paper investigates the potential power quality issues caused by AC imbalance, including DC voltage fluctuation and AC current harmonics. Multiple control objectives are developed, aiming to eliminate DC fluctuation, reduce AC distortion and imbalance, and achieve negative sequence current sharing among distributed generations in the AC subgrid. To realize these control objectives, a two-layer coordinated control strategy is proposed. The first layer involves local interlinking converter (IC) control to improve the power quality of the DC subgrid, while the second layer focuses on distributed unbalance compensation control to improve the power quality of the AC subgrid. Finally, several experiments are conducted to verify the effectiveness of the proposed control strategy.

This paper presents a multi-terminal traveling-wave-based fault location method for phase-to-ground fault in non-effectively earthed distribution systems. To improve the accuracy of fault location, a two-terminal approach is used to identify the faulty branch and a single-ended approach is followed to determine the fault distance based on the arrival time of reflected traveling waves. Wavelet decomposition is employed to extract the time-frequency component of the aerial-mode traveling waves. Magnitude and polarity of the wavelet coefficients are used to estimate the fault distance starting from the propagation fault point to the branch terminal. In addition, the network is divided into several sub-networks in order to reduce the number of measurement units. The effectiveness of this approach is demonstrated by simulations considering the phase-to-ground fault that happens at different positions in the distribution network.

A solid state transformer (SST), as a kind of energy router in the Energy Internet, provides a unified access point for AC or DC distributed power subjects. However, the DC-link capacitors inside the SST will suffer huge voltage fluctuations when the output power of the microgrid changes dramatically. With respect to this problem, caused by the random and intermittent characteristics of distributed generation (DG), a hierarchical coordinative control strategy is proposed. Compared with the common independent control, the proposed method not only makes full use of the regulation capacity of super capacitors, but also enhances the dynamic power tracking speed and reduces the speed difference between different stages of an SST. The dynamic voltage response under the proposed method is analyzed in frequency domain and compared with the independent control. To validate the effectiveness of the coordinative control strategy, a simulation model of an SST-based grid-connected DC microgrid system is established, and the topology of the SST is improved. The voltage stability of the DC bus is compared under different control strategies, and the coordinative control strategy is also verified, effectively under transition conditions.