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• By the characteristic analysis of VSG, the causes and influencing factors of TPAI and FOC are revealed, and the inherent relationship between TPAI and FOC is found. • Based on the phase portrait theory, the stability analysis of different influencing factors is carried out. It is found that the proposed method can significantly enhance the TPAS of VSG under serious grid faults. • According to the verification results, the proposed method can simultaneously realize the TPAS and FCS of VSG during the fault, and the virtual inductance based on QSA can effectively suppress IIC. In addition, this method has the advantages of simple operation, no need to freeze the reactive power loop, and strong adaptability to engineering application problems such as considering the change of fault impedance and the difficulty of grid fault voltage measurement. When a serious grid fault occurs, a virtual synchronous generator (VSG) tends to lose transient power angle stability (TPAS) and cause the fault current to exceed the limit. Most existing research usually neglects the inherent relationship between transient power angle instability (TPAI) and fault over-current (FOC), which leads to the two problems being solved separately rather than simultaneously. In this paper, the transient power angle and fault current characteristics of VSG are first studied, and the causes and influencing factors of TPAI and FOC are explored. Then, the TPAS analysis is carried out based on the phase portrait theory. A TPAS control method for VSG considering fault current suppression (FCS) is proposed. This method is fulfilled by the combined regulation of active power reference and reactive voltage regulation coefficient, in which the reference and coefficient can be adjusted adaptively according to different fault degrees and application scenarios. In addition, a quasi-static approximate (QSA)virtual inductance is introduced to limit the instantaneous inrush current (IIC). The proposed method achieves both the TPAS and FCS at the same time during the fault. Finally, simulations and experiments verify the correctness of the theoretical analysis and the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel bridge-type solid-state fault current limiter based on dynamic voltage restorer (BFCL-DVR). The new topology uses a DC-link in the back-to-back converter of DVR. The proposed BFCL-DVR is equivalent to the conventional DVR during normal operation mode. At fault inception, the controller deactivates the series converter IGBTs in faulty phase and activates the DC-link semiconductor switches, thus establishing an equivalent bridge-type current limiter to restrict the fault current. The magnitude of the fault current is adjustable by controlling the frequency and duty ratio of the semiconductor switch that is in parallel with the discharging resistance. Moreover, the device is able to quickly recover from the current limiting mode to the normal operation mode. In this study, the operation sequence, optimal value of discharging resistance, duty cycle, and frequency of semiconductor switches are obtained. The design methodology of the proposed BFCL-DVR is fully verified using PSCAD/EMTDC software. Experimental results validate the proposed topology and theoretical analysis. [ABSTRACT FROM AUTHOR]

There are both economic and environmental urges for transition from the current outdated power grid to a sensor-embedded smart grid that monitors system stability, integrates distributed energy and schedules energy consumption for household users. Especially with the proliferation of intelligent measurement devices, exponential growth of data empowers this transition and brings new tools for the development of different applications in power system. Under this context, this paper presents a holistically overview on the state-of-the-art of big data technology in smart grid integration. First, the features of smart grid and the multisource of energy data are discussed. Then, this paper comprehensive summarizes the applications leveraged by big data in smart grid, which also contains some brand new applications with the latest big data technologies. Furthermore, some mainstream platforms and knowledge extraction techniques are looked to promote the big data insights. Finally, challenges and opportunities are pointed out in this paper as well. [ABSTRACT FROM AUTHOR]

• A coordinated voltage controller based on the improved droop control strategy which is proposed improves the voltage of each node of the feeder. • In order to simplify the calculation method of each slope of BESS group, a simple calculation method of BESS slope considering line impedance and capacity is proposed; • frequency deviation controller based on double hysteresis loop which is proposed in this paper activates the frequency control loop to control the frequency and voltage of the island together with the coordinated voltage controller, so as to realize the self-healing of the island, and then realize the grid re-connection of the island through reclosing. • In addition, a real-time closed-loop simulation platform Composed of RTDS and line protection device is built. The correctness of the proposed method is proved by simulation results. In order to solve the problem of voltage fluctuation caused by distributed generation connected to feeder and the failure of reclosing caused by disordered operation after isolated island, a comprehensive control method including coordinated voltage controller and frequency deviation controller is proposed in this paper, which is applied to distributed energy storage group. When the feeder is connected normally, the frequency deviation controller is invalid, and the coordinated voltage controller based on the improved droop control strategy improves the voltage of each node of the feeder.The improved droop control strategy adjusts the voltage control behavior of BESS through the slope to ensure that multiple BESS jointly undertake the voltage control task, and effectively suppress the voltage fluctuation of feeders. In order to simplify the calculation method of each slope of BESS group, a simple calculation method of BESS slope considering line impedance and capacity is proposed; When the feeder is isolated due to fault, the frequency deviation controller based on double hysteresis loop activates the frequency control loop to control the frequency and voltage of the island together with the coordinated voltage controller, so as to realize the self-healing of the island, and then realize the grid re-connection of the island through reclosing. In addition, a real-time closed-loop simulation platform Composed of RTDS and line protection device is built.The voltage control effect is verified by simulating the power fluctuation of feeders, and the effect of islanding self-healing is verified by simulating the whole process from feeder fault, fault isolation, island self-healing to grid-re-connection. Index Terms: BESS group; Improved droop control; Slope setting; Coordinated voltage control; Frequency deviation control; Island self-healing. [ABSTRACT FROM AUTHOR]

Improving the operational reliability of distribution networks is an important goal in many countries and regions. The increase in the total length of feeders and the proportion of cable lines creates a larger single-phase-to-ground fault current, which makes the grounding arc difficult to self-extinguish, and then it may easily cause permanent fault events in the distribution network. The ground fault regulation device, also known as an arc-suppression device, is regarded as an important piece of equipment for the reliable and safe operation of ineffective grounding distribution networks. However, owing to the extensive access of cable lines and power electronic devices in the distribution network, the proportion of harmonic and active power contents in the ground fault current has increased, resulting in higher requirements for arc-suppression device performance. Based on the aforementioned, this study systematically summarizes the research work regarding arc-suppression devices from three aspects, namely, the topology of the arc-suppression device with its evolution trend, the control strategy of the arc-suppression device with its optimization method, and the functional integration method of the arc-suppression and electrical power regulation devices. Furthermore, the most representative topologies and control methods in each category are thoroughly described and briefly compared. The main challenges and critical problems of arc-suppression devices in the new distribution network are analyzed and summarized. [Display omitted] • The present situation of the topologies and control methods for the arc suppression devices is systematically studied. • The active and passive hybrid arc suppression devices can effectively integrate the high performance and low cost. • The functional integration of arc suppression and power control is the future development trend of arc suppression device. [ABSTRACT FROM AUTHOR]

• A two-stage optimal strategy for flexible interconnection distribution network based on SOP. • Considering the loss characteristic of key equipment in distribution networks. • Economical operation area of distribution transformers. • Improve the economy and reliability of the flexible interconnection distribution network. The flexible interconnection distribution networks (FIDN) based on soft open points (SOP) provides an opportunity to improve the economy and reliability of distribution networks. However, the existing optimal strategies have mainly focused on line power loss reduction, and the loss characteristic of SOPs and distribution transformers is ignored. Therefore, the capability of reducing total power loss for the existing optimization strategy needs further improvement. Thus, based on SOP's locating, sizing and optimal operation, a two-stage optimal strategy for FIND is proposed considering the loss characteristic of key equipment including SOPs and distribution transformers. Firstly, considering the transformer equivalent loss model and different load states, an improved loss sensitivity model is proposed to determine the optimal access location of SOP. Further, the SOP's capacity is designed by the total cost optimization model. Secondly, based on the loss characteristic of key equipment, the optimal operation strategy is proposed to reduce the total power loss of FIND while realizing optimal economic area operation of transformers. Finally, the case studies were performed on a FIND test system with 22-bus and 15-bus to validate the proposed two-stage optimal strategy, and the results of the case studies show that the economy of FIND is greatly improved. [ABSTRACT FROM AUTHOR]

• MF-ASD can realize reactive power compensation and arc suppression. • The variation law of the DC-link voltage of the MF-ASD under different conditions is analyzed. • The proposed alternate arc suppression method does not need additional DC power supply devices. • The MF-ASD can also realize the DC-link voltage stability when the active component of the fault current is large. To fully compensate reactive and active components of the single line-to-ground (SLG) fault current, additional DC power supply devices are usually used for arc suppression devices. Therefore, the alternate arc suppression method is proposed for the non-neutral multi-function arc suppression device (MF-ASD) in this paper, which can achieve energy self-balance in the MF-ASD during the SLG fault without additional DC power supply devices. Firstly, the DC-link charge–discharge characteristic of the MF-ASD is analyzed under different SLG fault conditions. Then, the alternate arc suppression principle and energy flow law between two non-faulty phases of the MF-ASD are described in detail. Further, the relationship between the alternate period, switching time, and the DC-link voltage are deduced as well. Then, the control parameters are reasonably designed for the DC-link voltage stability of two non-faulty phases of the MF-ASD. Finally, the correctness and feasibility of the proposed method are verified by simulation and experiment results. [ABSTRACT FROM AUTHOR]

Series-connected voltage sources converters (SVSCs), (i.e., dynamic voltage restorer, fault current limiter, electrical spring, etc.), have been widely used in the electricity grid to improve the electricity grid performances in terms of voltage fluctuation compensation, flexible power flow regulation, fault overcurrent limitation, flexible access of renewable energy, etc. However, SVSCs have a relatively short effective operating time and a low utilization rate, because they are generally operated during abnormal grid conditions. The new trend is to increase the utilization by extending the functions of SVSC, e.g., integrating the voltage compensation and overcurrent limiting in a single SVSC. On the other hand, the series connection architecture results in the SVSCs experiencing overvoltage and overcurrent from the main grid, and consequently the reliability of SVSC is challenged. Based on these details, this paper systematically studies the state of the art multifunctional techniques and the corresponding strategies of SVSCs, which can be mainly divided into three categories as follows: function integration between different SVSC; function coordination between SVSC and parallel-connected VSC(PVSC); function integration between SVSC and PVSC. The most representative topology and control optimization method in each category is elaborated, and a brief comparison of them is conducted as well. On this basis, the key problems and challenges in the research and engineering application of multifunctional SVSC system are summarized. • The state of the art multifunctional techniques of SVSCs is systematically studied. • The function coordination between SVSC and parallel-connected devices improves the output performance of the parallel part. • The multifunctional SVSC with fault current limiting capability can protect itself and the power grid actively. • The function integration between SVSC and PVSC open a new way to improve the utilization rate of power electronic devices. • The multifunctional SVSC with minimized additional physical switches and topology complexity needs further studied. [ABSTRACT FROM AUTHOR]

A novel space vector modulation (SVM) strategy called maximum-boost discontinuous SVM (MBDSV) is proposed in this paper to reduce the thermal stress of three phase impedance source inverters (ISI). By exploiting the switch clamping mechanism and arranging the shoot-through (ST) states properly, the proposed strategy obtains the flowing merits: further optimize the thermal performance, improve the reliability, reduce the current stress and maximize the dc-link utilization of ISI. The proposed MBDSV was compared to the existing modulation strategies and the feasibility of the MBDSV had been benchmarked by simulation and experiments. • Thermal optimized space vector modulation strategy for impedance source inverter. • Discontinuous SVM is developed to reduce the thermal stress of inverters. • Suitable for medium or high output frequency applications • Simulation and experimental tests are carried out with three-phase qZSI. [ABSTRACT FROM AUTHOR]

Microgrid is becoming an attractive concept to meet the increasing demands for energy and deal with air pollutions. Distributed energy sources (DERs) in Microgrid are usually interfaced with the utility grid by inverters, so the characteristics of Microgrid stability are much different from that of a traditional grid. However, the classifications, guidelines, and analysis method of Microgrid stability are well behind of the Microgrid development. In this paper, a Microgrid stability classification methodology is proposed on the basis of the of Microgrid characteristics investigation, which considers the Microgrid operation mode, types of disturbance and time frame. Then a comprehensive review of the body of research on Microgrid stability is presented in order to identify and advance the field. Finally, some challenges and suggestions of Microgrid stability for further researches are discussed. [ABSTRACT FROM AUTHOR]

Reliability of bond wires in power modules has been a main subject of interest in both industry and academia. Until now, analytical modeling of thermo-mechanical stress mainly focuses on the loop height variation of bond wires instead of plastic strain, which is the key factor causing the fatigue failure. In this paper, an analytical model for analyzing plastic strain of bond wires in IGBT modules is proposed. Using a laser displacement sensor, the dynamic loop height variations of bond wires under different heating currents are experimentally measured, based on which the finite element analysis (FEA) simulation is calibrated and verified to reveal the actual thermo-mechanical stress. In this way, the usefulness of our proposed method is verified by comparing its simulation results with those from the multi-physics fields FEA method. Finally, the relationship between the bonding angle and the plastic strain at the heel of bond wires is established. This study would provide new perspectives into further research on thermo-mechanical fatigue analysis and optimal design of bond wires in power modules. • An analytical model for analyzing plastic strain of bond wires in IGBT modules is proposed. • The FEA simulation is calibrated based on the experimental results of loop top displacement. • The relationship between the bonding angle and the plastic strain at the heel of bond wires is established. • The models have been compared with FEA simulation results with good agreements. [ABSTRACT FROM AUTHOR]

Physical lifetime prediction methods based on inelastic strain energy density (energy-based lifetime prediction) have been proven to be effective in producing reliable results on small solder joints (ball-grid arrays or chip-scale package) due to their capabilities to represent physical characteristics of soldering materials and loading history. However, in the existing energy-based lifetime models for solder layer failure the inelastic strain energy density is usually assumed to unchanged during aging, which is untrue particularly for large-area solder joints when crack propagation is considered. In this paper, an energy-based lifetime prediction method is proposed for failure of IGBT modules by explicit emulation of solder layer degradation. Inelastic strain energy density variances with respect to aging are meticulously modeled. The large-area solder layer is evenly divided into meshed elements, birth and death technique in finite element analysis (FEA) is used to successively emulate crack propagation. In this way, the increment of thermal resistance due to the solder layer degradation can be predicted. The lifetime prediction results by our proposed method show nice agreement with the experiment under different aging conditions. • An energy-based lifetime prediction method is proposed for failure of IGBT modules • Birth and death technique in FEA is used to successively emulate crack propagation • The increment of thermal resistance due to the solder layer degradation can be predicted • ΔW will change with different aging stage [ABSTRACT FROM AUTHOR]