Development of reliability methodology for systems engineering. Volume II - Application - Design reliability analysis of a 250 volt-ampere static inverter Final report

Design stage reliability analysis application to static inverte

An experimental model of a 2kw, 2500 volt power converter for ion thrustors using gate controlled switches in two phase-shifted parallel inverters summary report

Power converter for ion thrustors using electronic gate controlled switches in two phase-shifted parallel inverter

Protection and Disturbance Mitigation of Next Generation Shipboard Power Systems

Today, thanks to modern advances mainly in the power electronics field, megawatt-level electric drives and magnetic levitation are being integrated into the marine power grids. These technologies operate based on Direct Current (DC) power which require Alternating Current (AC) to DC conversion within the current grid. Medium-voltage Direct Current (MVDC) and Flywheel Energy Storage Systems (FESS) are the next state-of-the-art technologies that researchers are leaning on to produce, convert, store, and distribute power with improved power quality, reliability, and flexibility. On the other hand, with the extensive integration of high-frequency power electronic converters, system stability analysis and the true system dynamic behaviors assessment following grid disturbances have become a serious concern for system control designs and protection. This dissertation first explores emerging shipboard power distribution topologies such as MVDC networks and FESS operation with charge and discharge dynamics. Furthermore, the important topic of how these systems perform in dynamic conditions with pulsed power load, faults, arc fault and system protection are studied. Secondly, a communication-based fault detection and isolation system controller that improves upon a directional AC overcurrent relay protection system is proposed offering additional protection discrimination between faults and pulsed-power Load (PPL) in MVDC systems. The controller is designed to segregate between system dynamic short-circuit fault and bus current disturbances due to a PPL. Finally, to validate the effectiveness of the proposed protection controller, different bus current disturbances are simulated within a time-domain electromagnetic transient simulation of a shipboard power system including a PPL system operating with different ramp rate profiles, pulse widths, peak powers, and fault locations. This overarching goal of this work is to address some of the critical issues facing the US Navy as warfighter mission requirements increase exponentially and move towards advanced and sophisticated pulsed power load devices such as high energy weapon systems, high energy sensor and radar systems. The analyses and proposed solutions in this dissertation support current shipbuilding industry priorities to improve shipboard power system reliability and de-risk the integration of new power system technologies for next generation naval vessels

Solar electric propulsion system tests

Design and performance of solar-powered electric propulsion system for interplanetary space exploratio

Wide-Area Time-Synchronized Closed-Loop Control of Power Systems And Decentralized Active Distribution Networks

The rapidly expanding power system grid infrastructure and the need to reduce the occurrence of major blackouts and prevention or hardening of systems against cyber-attacks, have led to increased interest in the improved resilience of the electrical grid. Distributed and decentralized control have been widely applied to computer science research. However, for power system applications, the real-time application of decentralized and distributed control algorithms introduce several challenges. In this dissertation, new algorithms and methods for decentralized control, protection and energy management of Wide Area Monitoring, Protection and Control (WAMPAC) and the Active Distribution Network (ADN) are developed to improve the resiliency of the power system. To evaluate the findings of this dissertation, a laboratory-scale integrated Wide WAMPAC and ADN control platform was designed and implemented. The developed platform consists of phasor measurement units (PMU), intelligent electronic devices (IED) and programmable logic controllers (PLC). On top of the designed hardware control platform, a multi-agent cyber-physical interoperability viii framework was developed for real-time verification of the developed decentralized and distributed algorithms using local wireless and Internet-based cloud communication. A novel real-time multiagent system interoperability testbed was developed to enable utility independent private microgrids standardized interoperability framework and define behavioral models for expandability and plug-and-play operation. The state-of-theart power system multiagent framework is improved by providing specific attributes and a deliberative behavior modeling capability. The proposed multi-agent framework is validated in a laboratory based testbed involving developed intelligent electronic device prototypes and actual microgrid setups. Experimental results are demonstrated for both decentralized and distributed control approaches. A new adaptive real-time protection and remedial action scheme (RAS) method using agent-based distributed communication was developed for autonomous hybrid AC/DC microgrids to increase resiliency and continuous operability after fault conditions. Unlike the conventional consecutive time delay-based overcurrent protection schemes, the developed technique defines a selectivity mechanism considering the RAS of the microgrid after fault instant based on feeder characteristics and the location of the IEDs. The experimental results showed a significant improvement in terms of resiliency of microgrids through protection using agent-based distributed communication

Adaptive overcurrent protection application for a micro-grid system in South Africa

Abstract: The non-directional overcurrent protection (International Electrotechnical Commission standard IEC 617 or American National Standards Institute ANSI/Institute of Electrical and Electronic Engineers IEEE C37.2 standard device number 51) is one protection type/relay function that has stood the test of time. The latest generation of relays has brought about enhanced capabilities. The most popular overcurrent protection, which is the Inverse Definite Minimum Time (IDMT) function, has proven to provide coordination of electrical nodes with ease. This is one of the oldest but extremely reliable relay characteristic. A number of new protection functions and enhancements to existing functions are commensurate to the advanced technical capabilities of the newer generation protective devices. The new development techniques include “acceleration”, which is a technique of sending the circuit breaker status of the near end of a line or feeder to the far end to influence the relay decision at the far end. Impedance protection, unit line protection, etc. have come with many advanced characteristics and properties. The enhancements to protection devices bear special features but cannot substitute inverse time overcurrent protection, which, up to now, is a reliable backup in feeder protection schemes in South Africa. The superior feature is the capability to achieve coordination between a series of protective devices. This is achievable without excessive damage to the electrical components of the circuit...M.Ing. (Electrical Engineering

A universal grid-forming VSC control for future power system

To decarbonise the electricity sector, power systems are facing a significant transition to converter-dominated systems with higher penetration of renewable energy generations to replace conventional power generations using synchronous generators (SGs), changing the characteristics of power grid. Unlike SGs, power electronic converters do not contain rotating mechanical components. Accordingly, the mechanical properties owned by SGs will not be exhibited in the future power system, which can result in various issues in term of power system stability and the ability of faults and disturbances ride through. As power electronic converters are used to interface renewable resources with the power grid, they rely on the control dynamics and algorithms to maintain the entire system power balance and stability. However, there are lots of different control requirements considering the various grid conditions, including weak and strong grid connection, islanding, symmetrical and asymmetrical AC faults, which brings a big challenge for the control design of the power electronic converters. This thesis proposes a universal grid-forming (GFM) VSC (Voltage source converter) control for future power system with consideration to the corresponding various grid conditions. In this thesis, the control of grid-following (GFL) and GFM converters are reviewed firstly. The GFL control usually contributes to the regulation of active and reactive power output by injecting current through a vector current controller at a given phase. The grid phase is tracked by using a phase-locked loop (PLL) at all times. Different outer controller can be applied for different control purposes such as active power and voltage control. The GFL converters are predominantly applied in present renewable power generations, due to the capability in handing transient current during large transient events, precise control of current and good control dynamics, etc. However, as the GFL converters cannot regulate the system voltage and frequency directly, which makes them lack the capability of islanded operation. In addition, another constraint comes along with the use of vector current controller that causes the risk of instability on a weak grid. Intrinsically different from the GFL converters, the GFM converters use voltage regulation as the inner loop combined with power droop controller as the outer loop, to actively control their voltage and frequency outputs for the aim of voltage support. Hence, the GFM converters have the ability to work stably on islanding network, as well as weak grid connection network. However, the most common issue for GFM converters is the absence of effective current control loop, which limits their overcurrent capability. To synthesise the advantages of both GFM and GFL converters, a universal GFM VSC control is proposed. A direct voltage control in the dq reference frame is combined with a frequency droop control to regulate the AC voltage and frequency. Hence, the VSC has the capability of handling islanded operation. To ensure a stable grid connected operation, an adaptive power droop control is added as the outer loop to regulate the power exchanged between the converter and grid. A universal current limit control is also developed to limit the overcurrent and share the active and reactive current on both grid connection and islanding networks. In order to enable the ability of asymmetrical faults ride-through, the GFM VSC control is built in double synchronous frames to enable independent control of positive- and negative sequence components. An enhanced AC fault current control that employs both positive and negative-sequence current control is proposed. An additional voltage balancing control is also developed to retain the AC voltage controller for fault current limiting. By applying this controller, the general fault current limiting, dq current distribution and negative sequence current control when required can be achieved on a weak grid connection. Finally, small signal analysis is carried out to compare the stability of the GFM and GFL VSCs on weak networks. The impedance-based method is adopted to derive the admittances of the VSCs and connected grid in the positive- and negative-sequence (pn) reference frame. Time-domain simulations are also performed to verify the accuracy of the small signal admittances. Stability improvement with the GFM VSC on a very weak grid is validated.To decarbonise the electricity sector, power systems are facing a significant transition to converter-dominated systems with higher penetration of renewable energy generations to replace conventional power generations using synchronous generators (SGs), changing the characteristics of power grid. Unlike SGs, power electronic converters do not contain rotating mechanical components. Accordingly, the mechanical properties owned by SGs will not be exhibited in the future power system, which can result in various issues in term of power system stability and the ability of faults and disturbances ride through. As power electronic converters are used to interface renewable resources with the power grid, they rely on the control dynamics and algorithms to maintain the entire system power balance and stability. However, there are lots of different control requirements considering the various grid conditions, including weak and strong grid connection, islanding, symmetrical and asymmetrical AC faults, which brings a big challenge for the control design of the power electronic converters. This thesis proposes a universal grid-forming (GFM) VSC (Voltage source converter) control for future power system with consideration to the corresponding various grid conditions. In this thesis, the control of grid-following (GFL) and GFM converters are reviewed firstly. The GFL control usually contributes to the regulation of active and reactive power output by injecting current through a vector current controller at a given phase. The grid phase is tracked by using a phase-locked loop (PLL) at all times. Different outer controller can be applied for different control purposes such as active power and voltage control. The GFL converters are predominantly applied in present renewable power generations, due to the capability in handing transient current during large transient events, precise control of current and good control dynamics, etc. However, as the GFL converters cannot regulate the system voltage and frequency directly, which makes them lack the capability of islanded operation. In addition, another constraint comes along with the use of vector current controller that causes the risk of instability on a weak grid. Intrinsically different from the GFL converters, the GFM converters use voltage regulation as the inner loop combined with power droop controller as the outer loop, to actively control their voltage and frequency outputs for the aim of voltage support. Hence, the GFM converters have the ability to work stably on islanding network, as well as weak grid connection network. However, the most common issue for GFM converters is the absence of effective current control loop, which limits their overcurrent capability. To synthesise the advantages of both GFM and GFL converters, a universal GFM VSC control is proposed. A direct voltage control in the dq reference frame is combined with a frequency droop control to regulate the AC voltage and frequency. Hence, the VSC has the capability of handling islanded operation. To ensure a stable grid connected operation, an adaptive power droop control is added as the outer loop to regulate the power exchanged between the converter and grid. A universal current limit control is also developed to limit the overcurrent and share the active and reactive current on both grid connection and islanding networks. In order to enable the ability of asymmetrical faults ride-through, the GFM VSC control is built in double synchronous frames to enable independent control of positive- and negative sequence components. An enhanced AC fault current control that employs both positive and negative-sequence current control is proposed. An additional voltage balancing control is also developed to retain the AC voltage controller for fault current limiting. By applying this controller, the general fault current limiting, dq current distribution and negative sequence current control when required can be achieved on a weak grid connection. Finally, small signal analysis is carried out to compare the stability of the GFM and GFL VSCs on weak networks. The impedance-based method is adopted to derive the admittances of the VSCs and connected grid in the positive- and negative-sequence (pn) reference frame. Time-domain simulations are also performed to verify the accuracy of the small signal admittances. Stability improvement with the GFM VSC on a very weak grid is validated

A high power CMOS class-D amplifier for inductive-link medical transmitters

Powering of medical implants by inductive coupling is an effective technique, which avoids the use of bulky implanted batteries or transcutaneous wires. On the external unit side, class-D and class-E power amplifiers (PAs) are conventionally used thanks to their high efficiency at high frequencies. The initial specifications driving this work require the use of multiple independent stimulators, which imposes serious constraints on the area and functionality of the external unit. An integrated circuit class-D PA has been designed to provide both small area and enhanced functionality, the latter achieved by the addition of an on-chip phased-locked loop (PLL), a dead-time generator and a phase detector. The PA has been designed in a 0.18μm CMOS high-voltage process technology and occupies an area of 9.86 mm2. It works at frequencies up to 14 MHz and 30 V supply and efficiencies higher than 80% are obtained at 14 MHz. The PA is intended for a closed-loop transmitter system that optimises power delivery to medical implants

Characterization Methodology, Modeling, and Converter Design for 600 V Enhancement-Mode GaN FETs

Gallium Nitride (GaN) power devices are an emerging technology that have only become available commercially in the past few years. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This dissertation reviews the unique characteristics, commercial status, and design challenges that surround GaN FETs, in order to provide sufficient background to potential GaN-based converter designers.Methodology for experimentally characterizing a GaN FET was also presented, including static characterization with a curve tracer and impedance analyzer, as well as dynamic characterization in a double pulse test setup. This methodology was supplemented by additional tests to determine losses caused by Miller-induced cross talk, and the tradeoff between these losses and overlap losses was studied for one example device.Based on analysis of characterization results, a simplified model was developed to describe the overall switching behavior and some unique features of the device. The impact of the Miller effect during the turn-on transient was studied, as well as the dynamic performance of GaN at elevated temperature.Furthermore, solutions were proposed for several key design challenges in GaN-based converters. First, a driver-integrated overcurrent and short-circuit protection scheme was developed, based on the relationship between gate voltage and drain current in GaN gate injection transistors. Second, the limitations on maximum utilization of current and voltage in a GaN FET were studied, particularly the voltage overshoots following turn-on and turn-off switching transients, and the effective cooling of GaN FETs in higher power operation. A thermal design was developed for heat extraction from bottom-cooled surface-mount devices. These solutions were verified in a GaN-based full-bridge single-phase inverter