This paper presents a framework for cyber attack impact analysis of a smart grid. We focus on the model synthesis stage in which both cyber and physical grid entity relationships are modeled as directed graphs. Each node of the graph has associated state information that is governed by dynamical system equations that model the physics of the interaction (for electrical grid components) or functionality (for cyber grid elements). We illustrate how cause-effect relationships can be conveniently expressed for both analysis and extension to large-scale smart grid systems.

Microgrid technology has found its applications in various areas including the institutional campus, military base, and remote island. Many research efforts focus on the development of the microgrid steady-state energy management system (EMS) that can provide the day-ahead schedule or the multi-interval economic dispatch (ED) for distributed energy resources (DERs). This work advances the state-of-the-art microgrid EMS technique by developing a novel EMS approach to achieve a flexible time frame (FTF) DER schedule combined with a single time interval optimal power flow (OPF)-based ED. The FTF DER schedule enables the microgrid fully utilize the latest updated renewable and load forecasts, and OPF-based ED integrates realistic microgrid operating constraints in the real-time control. In addition, a mode switching control function is included to re-dispatch DERs in the microgrid for the planned microgrid switching from grid-connected mode to island mode. The feasibility and effectiveness of the proposed microgrid EMS technology are tested and demonstrated using modified IEEE 34-node and 123-node systems.

DC fault current is contributed by various distributed energy resources in DC distribution systems. The tightly coupled DC distribution systems have relatively low line impedance values. The fault current increases fast because of the low impedance. Some converters in DC distribution systems include fault current limiting (FCL) function. The controlled fault currents at different locations are very close. Thus, it is important to design a reliable and fast fault detection and location method for DC distribution systems. This paper proposes a novel local measurement-based fault location algorithm for tightly coupled DC distribution systems. The proposed fault location algorithm can estimate the equivalent inductance between a protective device and a fault in less than one millisecond. The performance of the developed protection algorithm was validated by numerical simulation and hardware tests.

This article presents a design and optimization methodology for a 200-kW medium-frequency transformer (MFT) based on low-loss magnetic core (FINEMET FT-3TL). The proposed optimal design methodology consists of predesign, preliminary design, and optimal design. In the preliminary design, the parallel-concentric winding structure is selected to increase the current carrying capability and reduce the leakage inductance. Based on the parallel-concentric winding concept, a novel cooing and insulation structure with 3-D printed bobbins are proposed. The optimal designed MFT prototype achieves a power density higher than 19.23 kW/L. The electrical insulation system is tested at 12 kV ac peak voltage. In addition, the partial discharge (PD) test is conducted at 7.5 kV ac peak voltage to ensure the PD-free design. The high-frequency bipolar pulsewidth modulation voltage insulation (PD) test is the first time applied in MFT design and test process. Finally, the transformer is applied in a dual-active-bridge (DAB) converter with 200 kW rated power. The peak efficiency of the DAB converter is 99.53%, and the efficiency at 200 kW is 98.85%. The peak efficiency of MFT is 99.844%, and the efficiency at 200 kW is 99.842%.

Series arc faults can cause fire hazards in dc distribution systems. During a series arc fault, the line impedance usually increases rapidly and the arc current includes high-frequency components. To capture the arc-induced high-frequency signals, parallel capacitors are added to the circuit. The characteristics of the currents through these capacitors permit fault detection and localization. This paper determined that a Rogowski coil could be constructed with adequate bandwidth to cover the relevant frequency band of 1 kHz-1 MHz, found that the amplitude of the pulse and the difference in the integrated fast Fourier transform of the current signal are well correlated with the series fault, described experiments to demonstrate that, over the range tested, the two parameters are robust with respect to the pressure of the atmosphere in which the arc forms, the electrode material, the speed at which the electrodes separate to initiate the arc, the switch operation, the load-type and the load change, and demonstrated that within the well-known limits of traveling wave localization, such localization can be used based on the capacitor current pulse information after it has been validated by the spectrum analysis as a fault and not a spurious signal. The proposed approach was demonstrated in two low-voltage dc cable circuits.

Microgrid concept has been widely adopted by power and energy community to boost the resilience and enhance the economics of the energy system. Stability control and economic control are two main factors to enable the reliable and efficient operation of microgrids. This paper presents two different control approaches for microgrids. The first control method adopts hierarchical structure. Each controllable resource is complied with a local controller and the microgrid is managed and optimized by a central supervisor controller. The second control method adopts the distributed structure. Distributed controller of each energy resource can communicate with each other to achieve global goals. This paper discusses the main features of these two methods and provides recommendations on how to choose appropriate control for different types of microgrids. A case study illustrates the performance difference of the two methods from economic point of view.