This paper presents a decentralized fault detection technique for power distribution systems with resonant grounding. The aim of this paper is to detect single phase to ground faults and identify the faulty feeder within three cycles of the fault occurrence. In the proposed technique, faults are first detected based on the neutral voltage displacement. The pre-fault and post-fault voltages (phase to ground) are then used to identify the faulty phase. Finally, the faulty feeder (as well as the faulty area of a long feeder) is identified from the relationship between the initial transient of the zero-sequence current and the faulty phase voltage just after the occurrence of faults. A signal processing tool called mathematical morphology is utilized to identify the faulty feeder. To identify the faulty feeder, it is also required to know the fault occurrence time that is estimated using the slope of the neutral voltage. The main feature of the proposed scheme is that this technique only uses voltage and current signals from the corresponding voltage transformers and current transformers. Therefore, it does not require communication among protection devices in the same or different feeders to identify the faulty feeder. The proposed technique also has the ability to distinguish the nature of faults, i.e., whether the faults are permanent or temporary. The effectiveness of the proposed scheme is tested, on an IEEE test system as well as on a practical test system, using MATLAB/SimPowerSystems. Simulation results show that the proposed technique can quickly detect the single phase to ground faults in a resonant grounding power distribution system and identify the faulty feeder. It is also capable of distinguishing faults from other disturbances. Moreover, it works under different compensation levels as well as for different fault inception angles.

The main purpose of developing microgrids (MGs) is to facilitate the integration of renewable energy sources (RESs) into the power grid. RESs are normally connected to the grid via power electronic inverters. As various types of RESs are increasingly being connected to the electrical power grid, power systems of the near future will have more inverter-based generators (IBGs) instead of synchronous machines. Since IBGs have significant differences in their characteristics compared to synchronous generators (SGs), particularly concerning their inertia and capability to provide reactive power, their impacts on the system dynamics are different compared to SGs. In particular, system stability analysis will require new approaches. As such, research is currently being conducted on the stability of power systems with the inclusion of IBGs. This review article is intended to be a preface to the Special Issue on Voltage Stability of Microgrids in Power Systems. It presents a comprehensive review of the literature on voltage stability of power systems with a relatively high percentage of IBGs in the generation mix of the system. As the research is developing rapidly in this field, it is understood that by the time that this article is published, and further in the future, there will be many more new developments in this area. Certainly, other articles in this special issue will highlight some other important aspects of the voltage stability of microgrids.

This paper designs three coordinated control schemes for a grid-connected wind energy conversion system based on a permanent magnet synchronous generator. The system includes a static synchronous compensator (STATCOM) and a supercapacitor energy storage (SCES) to maintain stable operation during different operating conditions. Coordinated control scheme-I (CCS-I) integrates the SCES into the DC-link via a bidirectional DC/DC converter to stabilize the voltage under varying wind speeds and grid disturbances. Coordinated control scheme-II (CCS-II) uses a STATCOM at the point of common coupling (PCC) to enhance the grid voltage stability during voltage sag or swell, where the SCES balances active power, and the grid side converter (GSC) provides reactive power support. The STATCOM is only activated when the PCC's reactive power requirement exceeds the GSC's support capacity. Coordinated control scheme-III (CCS-III) considers simultaneous disturbances on both the wind turbine and grid side to stabilize the DC-link and grid voltage. The proposed control schemes have been experimentally implemented with a dSpace MicroLabBox. Additionally a Lyapunov function based stability analysis of the system including the SCES is presented in the paper.