A multiple stage gate driver for SiC MOSFETs based on a switched resistor topology is introduced and a hardware realization is presented. The measurement setup is shown in detail to highlight the quality of the shown measurement results. The evaluation of the stage-wise driver is conducted by comparing the switch and diode peak voltages as well as peak currents with regard to the switching losses to a reference driver. The switching transients are generated using a double pulse test bench. A detailed investigation on two- and three-stage operation for both, the turn-on and turn-off events are presented. A variation of gate resistors and different timings is conducted for each stage and evaluated using the resulting measurements. It is shown that the drain-source peak voltage is reduced by 45% while maintaining equal turn-off losses. Analogously, a reduction of 51% of the diode peak voltage and a reduction of 50% of the peak reverse recovery current at the same time is feasible for equal turn-on losses.

The increase in the popularity of the medium voltage dc (MVDC) electrical distribution, as a possible evolution of the medium voltage ac (MVAC) electrical distribution for the ship onboard power systems, arises a need for a comparative evaluation and demonstration of feasible technologies for the MVDC supplies. For designing the MVDC supplies in the range from 5-35 kV, different available technologies can be considered for the designs and have a direct influence on the overall system performance. In this paper, different technologies for prime movers, electrical generators and rectifiers are discussed in terms of feasibility for the MVDC supplies. Different supply configurations can be envisioned from these based on the commercial availability, quality of supply, efficiency, dynamic performance and volume. Multi-phase multipulse supply configurations are identified and proposed for the marine MVDC systems. Combination of multi-phase generators and multi-pulse rectifiers offer reliable, simple and fault tolerant solution with acceptable dynamics. To explore and highlight these benefits, a six-pulse rectifier sub-module is designed and analysed in two arrangements for multi-pulse configurations, namely parallel and series. It has been shown that with appropriate selection of semiconductor devices, coupled with properly selected fast fuses, excellent fault current (thermal) withstand capabilities can be achieved. 

SPICE modeling of silicon carbide (SiC) MOSFET considering the influence of interface traps has been carried out, which is able to describe the characteristics of the MOS transistors in all operation modes at different interface trap densities and measurement temperatures. This modeling employs the SPICE level-1 model of MOSFET, but the constant mobility in the piece-wise current equations has been replaced by the advanced mobility expression, which can exactly reflect the effect of SiC/SiO2 interface traps on the electrical characteristics of SiC MOSFET. Key parameters in the advanced mobility model are obtained according to charge-sheet model (CSM) of MOS system. The static characteristics of the developed SiC MOSFET model have been validated with the production Datasheet, and the dynamic characteristics have been experimentally verified in Boost converter. Based on the developed model, the effect of SiC/SiO2 interface-trap densities on the switching performances of SiC MOSFET has been quantitatively discussed, and reasonable gate driving voltage of SiC MOSFET with different interface-trap densities has been revealed.

The main focus of this paper is to propose a reconfiguration method to mitigate short circuit faults in a neutral point clamped multilevel inverter which is widely used as a power conversion system with distributed energy resources. Existing reconfiguration methods use either a redundant strategy or need a large number of additional devices pre-installed in the circuit; these will increase the bulk and complexity of the system. Most existing control-strategy-based methods distort the phase-to-neutral voltage, which results in degradation of power quality. To maintain control-strategy-based reconfiguration, avoid significant change to the circuit topology, and avoid phase voltage distortion, a new and practical reconfiguration method is proposed in this paper. The proposed method is applicable to neutral point clamped (NPC) multilevel inverters at any voltage level and can mitigate short circuit faults in any device. A technique of switching series-connected switches is selected to combine with the proposed reconfiguration method since it’s a practical design consideration for realistic implementation. MATLAB/Simulink is used to simulate a five-level NPC inverter with non-idealities to verify the proposed reconfiguration method. A five-level NPC is also built and tested to experimentally verify the proposed method. Short circuit faults are injected to different devices and the proposed method is verified to quickly and effectively recover the NPC inverter from these faulty conditions.

Renewable energy is seen as a viable alternative to traditional energy sources, and distributed generation (DG) based on renewable energy sources has experienced rapid growth worldwide. High penetration of renewable energy based DG systems makes the grid more vulnerable, and stricter standards have been issued for grid interconnection of DG systems. DG systems are expected to be controllable with high flexibility and reliability. Provision of grid support functions and ancillary services, such as reactive power control, fault ride-through and harmonic compensation, is the key to attaining higher utilization of DG. Such functionalities are implemented in new generation smart inverters, which can contribute to the reduced cost of energy and need for additional system resources. The state-of-the-art power system support functions are summarized in this paper for the purpose of enhancing operation in low-voltage networks. Experimental results are given to better understand the implementation of the functions.

Virtual synchronous generator (VSG) technology for integration of distributed energy resources attracts increasing attentions for its enabling inverters to simulate the inertia and damping characteristics of synchronous generators and improve the stability of the system. In this paper, a decentralized VSG-based adaptive coordinated control strategy is proposed for islanding microgrids consisting of photovoltaic generators combined with battery energy storages in DC side (PV/BES-VSG). By the proposed method, the droop characteristics of VSGs can be adaptively adjusted according to the DC bus voltage. In this way, the local controllers of PV/BES-VSG units can switch operating modes automatically without the need of a central controller, so that the power sharing among PV/BES-VSG units is allocated according to the maximum output power of PVs and the limit of charging/discharging power of BES instead of merely rated capacity of the inverters. To test the proposed method, an islanding model of microgrid with two PV/BES-VSG units in parallel is built in Matlab/Simulink. The simulation results show that by the proposed control strategy, the coordination control between PV and BES, and between PV/BES-VSG units can be effectively realized with maximum use of PV power under the premise of the rational distribution of power.

High operational costs, environmental concerns and fuel handling challenges in diesel-based remote off-grid systems have prompted the application of alternative sources of energy and energy storage systems. Based on these drives, operators of isolated microgrids have been seeking out these alternatives. In response, a Canadian utility is investigating the application of utility scale photovoltaic (PV) generation and Battery Energy Storage Systems (BESS) to supplement existing Diesel Generators (DiGs) in an off-grid community. This paper presents the design, operation, and dispatch strategy for this hybrid PV/BESS/DiG isolated microgrid. A Northern remote off-grid community in Canada is used as a case study. Custom models to accurately represent all components of the hybrid microgrid in the Northern climate are developed first. Then, optimization algorithm that minimizes the Annual System Cost (ASC) are developed to size the PV and BESS. The algorithm incorporates the cost of the BESS, the rated power limits of PV and BESS, and the prime rating capability of DiGs. Finally, the paper proposes to optimally site the BESS by minimizing the total system loss and optimizing the voltage profile along the feeders. The study reports both cost saving and power quality improvement with the installation of PV and BESS, and presents guidelines on how to generalize these results to other hybrid isolated microgrids.

Transformation of the existing electric power systems into modern smart grids is gaining momentum as most jurisdictions are seeking ways to lower their energy consumptions, life cycle costs and greenhouse gas (GHG) emissions. The transformation requires the integration of significant renewable energy into the existing power systems, which has posed tremendous technical and operational challenges involving the issues of voltage and frequency stability, insufficient energy storage, resources for system balancing and dispatch, renewable energy intermittency, and much more. During a recent research trip of mine to an island country, I got the first-hand experience in how the fast down-ramping events of a large central photovoltaic (PV) plant could cause load shedding and PV generation curtailment. Innovative solutions are needed to support this power system transformation, as the need for additional system resources can no longer be met by building more central generation plants. As an integral part of modern power systems, distributed energy resources (DER) have been rapidly deployed throughout the world, initially as an effective means of clean generation to displace fossil fuels and subsequently as resources to provide power system functions such as ancillary services and peak load reduction. DERs include distributed generation systems such as wind, solar and CHP systems, energy storage units including electric vehicles, controllable loads, and associated power conversion and control systems, all in power distribution networks. The innovative solutions to facilitate the seamless integration of DERs into electric grids and the creation of new power systems resources have never been more important than today. These solutions are critical to enabling maximum penetration of renewable energy, while allowing utilities to maintain high standards of grid stability, reliability, flexibility, and economy. The purpose of this Special Issue is to review the state-of-the-arts in the DER fields and to disseminate the recent technological advancement in DERs, pertinent to analysis, design, conversion, control, performance, and application. The Special Issue on Distributed Energy Resources collected 5 papers on diverse topics, ranging from the state-of-the-art reviews to the focused new discoveries. The first paper entitled “Optimal Design and Operation of a Remote Hybrid Microgrid” as written by Dr. Farzam Nejabatkhah and his colleagues at the University of Alberta (Canada) presented the design, operation, and dispatch strategies for an isolated hybrid microgrid containing photovoltaic (PV) systems, battery energy storage systems (BESS) and diesel generators. A Northern remote off-grid community in Canada was used for the case study. Custom models to accurately represent all components of the hybrid microgrid in the Northern climate were developed. Optimization algorithm that minimizes the annual system cost were developed to size the PV and BESS. The paper demonstrated both cost saving and power quality improvement with the installation of PV and BESS systems, which may present guidelines for achieving similar benefits in other isolated hybrid microgrids. The second paper contributed by Dr. Meiqin Mao and her colleagues at Hefei University of Technology (China) has a title of “Decentralized Coordination Power Control for Islanding Microgrid Based on PV/BES-VSG”. The paper proposed a decentralized virtual synchronous generator (VSG)-based adaptive coordinated control strategy for islanded microgrids consisting of photovoltaic generators combined with battery energy storage (BES) on the DC side (PV/BES-VSG). With the proposed method, the droop characteristics of VSGs could be adaptively adjusted according to the DC bus voltage. The local controllers of PV/BES-VSG units could switch between the operating modes automatically without the need of a central controller. In this way, the power sharing among PV/BES-VSG units was achieved according to the maximum output power of PVs and the limit of charging/discharging power of BES, leading to the maximum utilization of renewable energy resources. The third paper on “Power System Support Functions Provided by Smart Inverters—A Review” was contributed by Dr. Xin Zhao and his colleagues at the University of New Brunswick (Canada). The paper reviewed the new development in international standards relevant to “smart inverters” for distributed energy resources, particularly for the provision of grid support functions, such as reactive power control, harmonic compensation, voltage and frequency fault ride-through, which is key to achieving higher utilization of renewable energy based distribution generation systems in the distribution power networks. Experimental results from smart inverters were given in the paper to demonstrate the implementation of these power system support functions in contributing to reduced cost of energy and additional system resources. The fourth paper is on an interesting topic of “Integration of Distributed Energy Resources into Offshore and Subsea Grids”, and was submitted by Ms. Razieh Nejati Fard and Dr. Elisabetta Tedeschi of the Norwegian University of Science and Technology (Norway). This paper reviewed the recent developments in offshore and subsea electric distribution grids, particularly in case of high penetration of distributed and intermittent renewable energy sources. The paper provided an overview of electric loads operating in the ocean environment, their power and energy demands, and their main operational characteristics and corresponding maturity of technologies. This paper presented the emerging trends in the electrification of the ocean space through the development of “offshore smart grids”, a fascinating area where most of us would have not been exposed to yet. The fifth paper entitled “Reconfiguration of NPC Multilevel Inverters to Mitigate Short Circuit Faults Using Back-to-Back Switches” was composed by Mr. Weiqiang Chen and his colleagues at University of Connecticut. This paper proposed a new reconfiguration method to mitigate short circuit faults in any devices and at any voltage levels in neutral point clamped (NPC) multilevel inverters which have been widely used as power conversion apparatuses for distributed energy resources. Simulation was conducted on a five-level NPC inverter with non-idealities to verify the proposed reconfiguration method. A five-level NPC inverter was built and tested to experimentally demonstrate that the proposed method could lead to a quick and effective recovery of the NPC inverter from faulty conditions.

The transformation of the existing electric power systems into modern smart grids is gaining momentum as more countries seek to lower their energy consumption and greenhouse gas (GHG) emissions. The transformation requires the integration of significant renewable energy and other transmission and distribution assets, which raises tremendous technical challenges involving voltage and frequency stability, energy storage, system balancing, intermittency of renewable energy, and more. As an integral part of modern power systems, distributed energy resources (DER) have been rapidly deployed throughout the world, initially as an effective means of clean generation to displace fossil fuels and subsequently as resources to provide power system functions. DERs include distributed generation systems such as wind, solar and CHP systems, energy storage units including electric vehicles, controllable loads, and associated conversion and control systems in power distribution networks. The innovative solutions to facilitate the seamless integration of DERs into electrical grids have never been so important. These solutions are critical to enabling maximum penetration of renewable energy, while allowing utilities to maintain high standards of grid stability, reliability, and energy costs. The purpose of this Special Issue is to disseminate the recent technological advancement in distributed energy resources, pertinent to analysis, design, conversion, control, performance, and application.