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.

Non-destructive inspection methods that use broadband reflecting signals to identify microscopic flaws and aging characteristics in power cables are often employed, however they suffer from limited detection distances and a single detection target. This study proposes a scheme for harnessing power line communication (PLC) devices to accomplish the detection and identification of multiple cable aging. A model of the propagation of a high-frequency carrier signal through a cable is first combined with mathematical models of various types of aging, such as water-tree aging, electric-tree aging, and thermal aging, to simulate the network channel state in the process of different insulation degradation of the cable. The channel frequency domain response (CFR) at the receiver can then reflect the incidence of cable aging, and the proposed approach, in conjunction with machine learning algorithms, can recognize different types and severity of aging under interference. Computer simulations and field experiments were conducted to validate the viability of the suggested approach, and the results shown that 98% correctness could be attained in on-line monitoring despite interference considerations. In theory, the range is doubled when compared to the reflected signal approach with the same bandwidth and power.

Power transformer rupture and fire resulting from an arcing fault inside the tank usually leads to significant security risks and serious economic loss. In order to reveal the essence of tank deformation or explosion, this paper presents a 3-D numerical computational tool to simulate the structural dynamic behavior due to overpressure inside transformer tank. To illustrate the effectiveness of the proposed method, a 17.3MJ and a 6.3MJ arcing fault were simulated on a real full-scale 360MVA/220kV oil-immersed transformer model, respectively. By employing the finite element method, the transformer internal overpressure distribution, wave propagation and von-Mises stress were solved. The numerical results indicate that the increase of pressure and mechanical stress distribution are non-uniform and the stress tends to concentrate on connecting parts of the tank as the fault time evolves. Given this feature, it becomes possible to reduce the risk of transformer tank rupture through limiting the fault energy and enhancing the mechanical strength of the local stress concentrative areas. The theoretical model and numerical simulation method proposed in this paper can be used as a substitute for risky and costly field tests in fault overpressure analysis and tank mitigation design of transformers.