System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration

Experimental Test bed to De-Risk the Navy Advanced Development Model

This paper presents a reduced scale demonstration test-bed at the University of Texas’ Center for Electromechanics (UT-CEM) which is well equipped to support the development and assessment of the anticipated Navy Advanced Development Model (ADM). The subscale ADM test bed builds on collaborative power management experiments conducted as part of the Swampworks Program under the US/UK Project Arrangement as well as non-military applications. The system includes the required variety of sources, loads, and controllers as well as an Opal-RT digital simulator. The test bed architecture is described and the range of investigations that can be carried out on it is highlighted; results of preliminary system simulations and some initial tests are also provided. Subscale ADM experiments conducted on the UT-CEM microgrid can be an important step in the realization of a full-voltage, full-power ADM three-zone demonstrator, providing a test-bed for components, subsystems, controls, and the overall performance of the Medium Voltage Direct Current (MVDC) ship architecture.Center for Electromechanic

Specification, Control, and Applications of Z-Source Circuit Breakers for the Protection of DC Power Networks

There is a highly-increasing demand for the DC power transmission and distribution in modern power systems for the integration of newly-installed renewable energy resources and storage systems to the existing utilities. Application of DC power systems in electric ships, battery energy devices, high-voltage DC networks, smart grids, electric vehicles, microgrids, and wind farms is a recent trend that is being highly investigated. The fault protection of DC systems is an essential but challenging issue that needs careful attention to maintain system operation reliability and device safety. In this research, the specification, control, and application of Z-source breakers (ZCBs) are investigated for DC network protection. Initially, the power loss associated with the topology of ZCBs is a key consideration in the design, and thus, the most efficient ZCB topology is identified. In this study, the topology of inter-cross-connected bi-directional ZCB (ICC-BZCB) was selected due to its least power loss when operating in a steady-state condition. Based on ICC-BZCB, a new approach of parameter specification is proposed by considering the reverse-recovery time of thyristors. The proposed approach ensures the turnoff action of ZCB in practical application. Its effectiveness was verified by experimental tests on a hardware testbed in the laboratory. Secondly, a new method of specifying the Z-source capacitances is proposed to identify the high-impedance faults in DC power networks. The method defines the principle of HIF detection and interruption by monitoring the status of Z-source capacitances. Finally, the assessment of cable length limit for ZCB application is analyzed for the DC system applications

Assessment of Cable Length Limit for Effective Protection by Z-Source Circuit Breakers in DC Power Networks

This paper introduces groundbreaking research on how to assess the Cable Length Limit (CLL) to ensure effective protection by Z-source Circuit Breakers (ZCBs) in DC power networks. It has been revealed that the line parameters of power cables have a significant impact on the cutoff performance of ZCBs. The question of assessing the CLL has been raised as an unsolved problem. In this paper, a method of CLL assessment is proposed based on physical models and simulation tests. To verify the proposed method, two studies were performed to assess the Cable Length Limits depending on fault levels and power delivery levels, respectively. The ZCB parameters were specified for a simulation testing system for a 5 MW distribution line feeder. The effectiveness of ZCB protection was tested in groups of simulation tests with various impacting quantities, i.e., cable lengths, fault current levels, and power delivery levels. The effective cable lengths for the ZCB to detect and successfully interrupt a faulty branch in the DC network were assessed and analyzed. The testing results prove that the CLL decreases along with a decreasing fault current level, as well as an increasing power delivery level. Based on data analysis, an equation was derived to calculate the effective length of the ZCB for DC lines, and the equation can be used to generate new CLL curves for various load-power requirements. This study could increase the reliability of a ZCB’s response to a fault in DC transmission and distribution lines. It could also help power system designers/operators to maintain reliable protection with ZCBs in DC power system networks

Solid State Protective Device Topological Trade-offs for Mvdc Systems

Presently accepted approaches to protection are “Unit-Based” which means the power converter(s) feeding the bus coordinate with no-load electromechanical switches to isolate faulted portions of the bus. However, “Breaker-Based” approaches, which rely upon solid state circuit breakers for fault mitigation can result in higher reliability of power and potentially higher survivability. The inherent speed of operation of solid state protective devices will also play a role in fault isolation, hence reducing stress level on all system components. A comparison study is performed of protective device topologies that are suitable for shipboard distribution systems rated between 4kVdc and 20kVdc from the perspectives of size and number of passive components required to manage the commutation energy during sudden fault events and packaging scalability to higher current and voltage systems. The implementation assumes a multi-chip Silicon Carbide 10kV, 240A MOSFET/JBS diode module. A static fault simulator device is proposed to characterize DC faults

Monolithic Bidirectional Switch Based on GaN Gate Injection Transistors

The paper deals with a bi-directional switch based on N-channel enhancement-mode GaN FET. The proposed device is a Gate Injection Transistor monolithic solution to reduce the volume of the switch with high current density and blocking voltage of 600V. It features a dual-gate control pin and two power terminal. In the paper, the main characteristics of the bi-directional switch and the performance in the four-quadrant of operation are examined and discussed. The device characteristics are compared with the traditional MOSFET and IGBT solutions. The gate driver design issues are considered to optimize the switching transient of the GaN-based switch. Finally, an experimental evaluation of the GaN FET as the bidirectional circuit breaker is carried out in an AC power supply system to validate the effectiveness of the proposed monolithic new device

Bidirectional Hybrid DC Circuit Breaker with Zero Voltage and Current Switching for Radar Power System

This paper proposes a novel zero-voltage switching (ZVS) and zero-current switching (ZCS) based hybrid DC circuit breaker for a radar power system. Long-range radars demand huge power, in the order of hundreds of kW. Radar's phased array antenna houses a large number of electronic devices and works primarily on a DC power supply. Typically, military systems are required to have the highest operational reliability, as a result, electrical system protection plays a crucial role. A high power 310 V DC electrical power grid in radar carries hundreds of amperes of current under nominal operating conditions, results in significant fault current due to very low impedance, and demands a very fast fault interruption device. This paper proposes and demonstrates the complete operation of a hybrid DC circuit breaker topology for radar applications. The proposed DC circuit breaker employs a mechanical switch that carries the entire current during the nominal operating conditions, and a Power Electronic Module (PEM) connected in parallel helps in diverting the fault current from the main path. Fault current transfers to the PEM branch in a fraction of a second (5μs), which ensures faster load-side isolation. During the fault interruption process, mechanical switch contact opening experiences both ZVS and ZCS features, resulting in arcless operation, and also helps in faster contact separation. The ZVS and ZCS feature greatly improve the reliability of the mechanical switch. The proposed concept does not involve any capacitors and corresponding pre-charging circuits for the ZVS/ZCS features. The proposed DC circuit breaker is analyzed theoretically, and also by simulations in LTspice. Additionally, an experimental prototype with a DC system rating of 310 V - 10 A is developed to experimentally validate the performance of the proposed breaker topology. The paper also presents a detailed design and comparative analysis, along with a discussion on the limitations of the proposed DC circuit breaker, and the scope for improvements

Semiconductor devices in solid-state/hybrid circuit breakers: current status and future trends

Circuit breakers (CBs) are the main protection devices for both alternating current (AC) and direct current (DC) power systems, ranging from tens of watts up to megawatts. This paper reviews the current status for solid-state circuit breakers (SSCBs) as well as hybrid circuit breakers (HCBs) with semiconductor power devices. A few novel SSCB and HCB concepts are described in this paper, including advantage and limitation discussions of wide-band-gap (WBG) devices in basic SSCB/HCB configuration by simulation and 360 V/150 A experimental verifications. Novel SSCB/HCB configurations combining ultra-fast switching and high efficiency at normal operation are proposed. Different types of power devices are installed in these circuit breakers to achieve adequate performance. Challenges and future trends of semiconductor power devices in SSCB/HCB with different voltage/power levels and special performance requirements are clarified