Power electronic-interfaced renewable energy sources (RES) exhibit lower inertia compared to traditional synchronous generators. The large-scale integration of RES has led to a significant reduction in system inertia, posing significant challenges for maintaining frequency stability in future power systems. This issue has garnered considerable attention in recent years. However, the existing research has not yet achieved a comprehensive understanding of system inertia and frequency stability in the context of low-inertia systems. To this end, this paper provides a comprehensive review of the definition, modeling, analysis, evaluation, and control for frequency stability. It commences with an exploration of inertia and frequency characteristics in low-inertia systems, followed by a novel definition of frequency stability. A summary of frequency stability modeling, analysis, and evaluation methods is then provided, along with their respective applicability in various scenarios. Additionally, the two critical factors of frequency control—energy sources at the system level and control strategies at the device level—are examined. Finally, an outlook on future research in low-inertia power systems is discussed.

Flying cars and electric vertical takeoff and landing (eVTOL) aircraft could become the future of personal transportation and taxis, which would significantly reduce greenhouse gas emissions. Presently, over 250 companies are developing flying cars and eVTOLs, and at least a few vehicles are expected to be commercialized soon. This article presents the current trends and technology of VTOL flight mechanisms and identifies the vehicles in each category to evaluate their advantages and limitations. Most of the flying cars that are being developed do not have VTOL capability because of the requirement for high power during takeoff/landing for a roadworthy vehicle. This article proposes the powertrain architectures for incorporating VTOL capability for flying cars based on dual power sources, such as fuel cells and batteries. Besides, possibilities of using a single propulsion system for both drive and flight modes are explored. General design guidelines are presented for the proposed powertrain architecture to estimate the maximum takeoff weight (MTOW), power/energy demands, and source capacities. Furthermore, the technologies of the powertrain components, such as electric motors and power converters, are also discussed in this article.

This paper proposes a novel bidirectional single-phase single-stage ac-dc converter for Electric Vehicle (EV) charging application. AC side of the proposed converter has current-fed half-bridge converter that is connected to the full-bridge converter on secondary side of a high-frequency transformer. Current at the input of the ac side can be regulated to realize power factor correction. The proposed converter achieves Zero Current Switching of primary side switches and zero current turn-ON for secondary side devices throughout the operation without any additional components. This paper also presents novel modulation technique and control algorithm to ensure soft switching throughout the operation range of the converter in both directions of power flow. Design equations are derived to help suitable selection of components for a given specification. Design of the converter, control strategy, and the results are presented for a 1.5-kVA converter for EV charger.

This paper proposes a coupled inductor based hybrid DC circuit breaker topology with zero current switching (ZCS) for fast fault interruption in DC systems. A series resonant circuit comprising of the secondary winding of a two-winding coupled inductor and a charged capacitor (commutation capacitor) is switched on during fault to inject a counter-current pulse, and, consequently, force a zero crossing of fault current. Proposed solution facilitates arcless breaking for a mechanical circuit breaker due to zero current turn-off. The proposed circuit breaker exhibits fast fault response (~30 μs), and the response time is programmable based on the design of the coupled inductor and commutation capacitor. Furthermore, presented solution mitigates the requirement of energy-absorbing elements for demagnetizing the DC network following fault interruption, in contrast to conventional DC breakers. The paper also presents two modified circuit breaker topologies to achieve unipolar voltage profile on the capacitor, which will enable the use of electrolytic capacitors for commutation so that the capacitor stack size is reduced in high voltage applications. Detailed Analysis and design equations are presented to explain the operation of the proposed topologies. Functionality of the proposed circuit breakers is verified through simulation, and experimental results based on two laboratory prototypes.

Electric vehicles (EV) that are connected to the charging station of a parking lot in a workplace can be considered as potential power sources. These EVs can be operated in both grid-to-vehicle (G2V) and vehicle-to-grid (V2G) modes of power transfer. However, an intelligent energy management (EM) controller is required for providing optimal schedule for V2G and G2V modes of operation. This paper proposes a real-time optimal EM controller for EV to grid integration for workplace microgrid system. In this proposed EM scheme, charging and discharging of EV battery is scheduled by forecasting the EV travel pattern using Random Forest methodology. In addition, the EM scheme is designed as optimization problem that utilizes this predicted EV travel data to minimize the cost energy consumption at the workplace. The EM scheme is developed by considering economic benefits to both the EV owner and the workplace. The EM controller is developed using Java Agent Development framework (JADE) and it is tested with real-world data in real-time simulation testbed. The real-time testbed is developed by interfacing two Typhoon HIL units emulating two electric vehicle batteries, and RTDS emulating the grid side power network.