Z. John Shen

Bio: Z. John Shen is an academic researcher from Illinois Institute of Technology. The author has contributed to research in topics: Microgrid & Fault (power engineering). The author has an hindex of 1, co-authored 2 publications receiving 19 citations.

System specification for a DC community microgrid and living laboratory embedded in an urban environment

Abstract: A community DC microgrid is proposed that is embedded within an urban neighborhood in an underserved community in Milwaukee, Wisconsin. This community microgrid will be a proving ground for residential DC power distribution and sharing of renewable energy resources between homes. The system will be built into existing homes that have been vacated as a result of a long period of economic recession in the area in such a way that homes can be occupied while their energy usage is being monitored and managed with in a non-invasive way. Renovated homes will either operate off of the 380Vdc or from the utility. The detached home garage for each home will be equipped with solar PV and battery energy storage with a lead home acting as substation that connects the microgrid into the larger utility through a 240Vac gateway connection. The homes will also be outfitted with readily available DC appliances so that a large portion of the home load can be directly fed from DC. In this environment living laboratories will be created that will enable participation of community members and students from a local STEM high school to become stakeholders in the operation of the community microgrid. The community microgrid will also demonstrate safe power distribution between homes using both wide band gap solid state circuit breakers. This aspect of the community microgrid will be a developmental environment for a protective system design that undergirds the entire system.

Short-Circuit Fault Discrimination Using SiC JFET-Based Self-Powered Solid-State Circuit Breakers in a Residential DC Community Microgrid

Abstract: This article identifies and validates the use of ultrafast silicon carbide (SiC) junction field effect transistor (JFET)-based self-powered solid-state circuit breakers (SSCBs) as the enabling protective device for a 340 Vdc residential dc community microgrid. These SSCBs will be incorporated into a radial distribution system in order to enhance fault discrimination through autonomous operation. Because of the nature and characteristics of short-circuit fault inception in dc microgrids, the time–current trip characteristics of protective devices must be several orders of magnitude faster than conventional circuit breakers. The proposed SSCBs detect short-circuit faults by sensing the sudden voltage rise between its two power terminals and draw power from the fault condition itself to turn off SiC JFETs and then, coordinate with no-load contacts that can isolate the fault. Depending upon the location of the SSCBs in the microgrid, either unidirectional or bidirectional implementations are incorporated. Cascaded SSCBs are tuned using a simple resistor change to enable fault discrimination between upstream high-current feeds and downstream lower current branches. Operation of one of the SSCBs and three in cascaded arrangements are validated both in simulation and with a hardware test platform. Thermal impact on the SSCB is discussed as well. The target application is a residential dc microgrid that will be installed as part of a revitalization effort of an inner city Milwaukee neighborhood.

Assessment of the feasibility of interconnected smart DC homes in a DC microgrid to reduce utility costs of low income households

Abstract: DC Microgrids (DC MG) present themselves as an obvious choice enabling integration of multiple renewable energy sources and distributed energy storage. This concept of DC electrification of homes in small communities is being explored in many parts of the world. Furthermore, typical household loads are increasingly becoming natively DC. In this paper, a community DC MG in an urban environment is analyzed. In combination with a community revitalization effort, up to 9 renovated dwellings (a mixture of apartments in a commercial property and houses) will be equipped with a smart DC power panel for loads such as LED lights, fans and air conditioning while a portion of loads will remain AC with an AC/DC converter interface between the loads. The smart DC power panel interfaces to the community DC MG. The effectiveness of driving down utility costs in a low-income household using this concept is compared to a home with conventional AC loads and AC loads with smart technologies. The efficacy of the DC MG to optimal installation and usage of solar energy and battery energy storage is determined and a notional smart energy management approach is presented.

Fault characterization and protective system design for a residential DC microgrid

Abstract: A residential DC microgrid is being built in an underserved community in Milwaukee, Wisconsin. The short circuit protection for this DC system and discrimination of faults along the interconnecting cables is a significant challenge. This paper addresses discrimination of sudden short circuit faults using an ultra-fast normally-on Silicon Carbide (SiC) Junction Field Effect Transistor (JFET)-SiC based solid state circuit breaker (SSCB). JFET gating for turn-off is self-powered from the drain to source voltage that occurs during a high current fault. Fault characterization of the system is performed using PLECS — a high resolution power electronics systems simulation platform. Fault discrimination of series connected SiC JFETs, with settings adjusted by a simple resistor change, is a validated both using an LTSPice model and a laboratory test fixture.

Fault discrimination using SiC JFET based self-powered solid state circuit breakers in a residential DC community microgrid

Abstract: This paper identifies validates the use of ultra-fast SiC JFET based self-powered solid state circuit breakers (SSCBs) as the enabling protective device for a 340Vdc residential DC community microgrid. These SSCBs will be incorporated into a radial distribution system in order to enhance fault discrimination through autonomous operation. Because of the nature and characteristics of short circuit fault inception in DC microgrids, the time-current trip characteristics of protective devices must be several orders of magnitude of faster than conventional circuit breakers. The proposed SSCBs detect short circuit faults by sensing the sudden voltage rise between its two power terminals and draw power from the fault condition itself to turn off SiC JFETs and then coordinate with no load contacts can isolate the fault. Depending upon the location of the SSCBs in the microgrid either unidirectional or bidirectional implementations are incorporated. Cascaded SSCBs are tuned using a simple resistor change to enable fault discrimination between upstream high current feeds and downstream lower current branches. Operation of the SSCBs in these cascaded arrangements are validated both in simulation and with a hardware test platform. The target application is a residential DC microgrid that will be installed as part of a revitalization effort of an inner city Milwaukee neighborhood.

Single ground fault location algorithm in DC microgrid based on wavelet transform

Abstract: As the proliferation of distributed generation and power electronic equipment in power systems, direct current (DC) microgrid has emerged and attracted more research attention. Protection of DC microgrid is a significant challenge and to build a well-functioning protection system, locating faults accurately is important. This is especially the case with the location of ground faults in DC microgrid because of the high likelihood of capacitors connected to ground associated with the connected distributed resources. The focus of this paper is to apply Wavelet Transform to decompose the common mode currents which are collected at different sensor points in a community DC microgrid and methodologies for the capture and characterization of single ground faults at different locations within the microgrid. Based upon these characterizations, a single ground fault location algorithm in DC microgrid is proposed. MATLAB/Simulink and PLECS are used to assist in the process. A community DC microgrid model is built based upon the sharing of energy resources among interconnected homes and single ground faults at different locations are applied.

A comparison between silicon carbide based current source rectifier and voltage source rectifier for applications in community DC microgrid

Abstract: Community DC microgrid is considered as an efficient solution for providing clean energy for residential areas. Connection of the DC microgrid to the AC utility grid would need a power electronic based rectifier. Voltage Source Rectifier (VSR) and Current Source Rectifier (CSR) are considered as the two options for such application. This study compares the two topologies based on their power density and efficiency. Silicon Carbide (SiC) switches are used for designing the rectifiers to get better power density and efficiency. The close proximity of the rectifier to the residential area requires electromagnetic compatibility (EMC) of the rectifier with established standards such as IEC 61000-3-4 and FCC B. This analysis shows that CSR has higher efficiency and higher power density compared to VSR.