A Fault-Tolerant T-Type Multilevel Inverter Topology with Soft-Switching Capability Based on Si and SiC Hybrid Phase Legs

The performance of a novel three-phase four-leg fault-tolerant T-Type inverter topology is presented in this paper, which significantly improves the inverter\u27s fault-tolerant capability regarding device switch faults. In this new modular inverter topology, only the redundant leg is composed of Silicon Carbide (SiC) power devices and all other phase legs are constituted by Silicon (Si) devices. The addition of the redundant leg, not only provides fault-tolerant solution to switch faults that could occur in the T-Type inverter, but also can share load current with other phase legs. Moreover, quasi zero-voltage switching (ZVS) and zero-current switching (ZCS) in the Si Insulated-Gate Bipolar Transistors (IGBTs) of the main phase legs can be achieved with the assistance of SiC Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs) in the redundant leg. Simulation and experimental results are given to verify the efficacy and merits of this high-performance fault-tolerant inverter topology

An Advanced Three-Level Active Neutral-Point-Clamped Converter With Improved Fault-Tolerant Capabilities

A resilient fault-tolerant silicon carbide (SiC) three-level power converter topology is introduced based on the traditional active neutral-point-clamped converter. This novel converter topology incorporates a redundant leg to provide fault tolerance during switch open-circuit faults and short-circuit faults. Additionally, the topology is capable of maintaining full output voltage and maximum modulation index in the presence of switch open and short-circuit faults. Moreover, the redundant leg can be employed to share load current with other phase legs to balance thermal stress among semiconductor switches during normal operation. A 25-kW prototype of the novel topology was designed and constructed utilizing 1.2-kV SiC metal-oxide-semiconductor field-effect transistors. Experimental results confirm the anticipated theoretical capabilities of this new three-level converter topology

A Fault-Tolerant T-Type Multilevel Inverter Topology With Increased Overload Capability and Soft-Switching Characteristics

he performance of a novel three-phase four-leg fault-tolerant T-type inverter topology is introduced in this paper. This inverter topology provides a fault-tolerant solution to any open-circuit and certain short-circuit switching faults in the power devices. During any of the fault-tolerant operation modes for these device faults, there is no derating required in the inverter output voltage or output power. In addition, overload capability is increased in this new T-type inverter compared to that in the conventional three-level T-type inverter. Such increase in inverter overload capability is due to the utilization of the redundant leg for overload current sharing with other main phase legs under healthy condition. Moreover, if the redundant phase leg is composed of silicon carbide metal-oxide-semiconductor field-effect transistors, quasi-zero-voltage switching, and zero-current switching of the silicon insulated-gate bipolar transistors (IGBTs) in the conventional main phase legs can be achieved at certain switching states, which can significantly relieve the thermal stress on the outer IGBTs and improve the whole inverter efficiency. Simulation and experimental results are given to verify the efficacy and merits of this high-performance fault-tolerant T-type inverter topology

Investigation of Fault-Tolerant Capabilities in an Advanced Three-Level Active T-Type Converter

A novel fault-tolerant three-level power converter topology, named advanced three-level active T-Type (A3L-ATT) converter, is introduced to increase the reliability of multilevel power converters used in safety-critical applications. This new fault-tolerant multilevel power converter is derived from the conventional T-Type converter topology. The topology has significantly improved the fault-tolerant capability under any open circuit or certain short-circuit faults in the semiconductor devices. In addition, under healthy condition, the redundant phase leg can be utilized to share overload current with other main legs, which enhances the overload capability of the converter. The conduction losses in the original outer devices can be reduced by sharing the load current with the redundant leg. Moreover, unlike other existing fault-tolerant power converters in the literature, full output voltages can be always obtained in this proposed A3L-ATT converter during fault-tolerant operation. A 13.5-kW ATT-A3L converter prototype was developed and constructed using silicon carbide MOSFETs. Simulation and experimental results were obtained to substantiate the theoretical claims of this new fault-tolerant power converter

On the false positives and false negatives of the Jacobian Matrix in kinematically redundant parallel mechanisms

The Jacobian matrix is a highly popular tool for the control and performance analysis of closed-loop robots. Its usefulness in parallel mechanisms is certainly apparent, and its application to solve motion planning problems, or other higher level questions, has been seldom queried, or limited to non-redundant systems. In this paper, we discuss the shortcomings of the use of the Jacobian matrix under redundancy, in particular when applied to kinematically redundant parallel architectures with non-serially connected actuators. These architectures have become fairly popular recently as they allow the end-effector to achieve full rotations, which is an impossible task with traditional topologies. The problems with the Jacobian matrix in these novel systems arise from the need to eliminate redundant variables when forming it, resulting in both situations where the Jacobian incorrectly identifies singularities (false positive), and where it fails to identify singularities (false negative). These issues have thus far remained unaddressed in the literature. We highlight these limitations herein by demonstrating several cases using numerical examples of both planar and spatial architectures

Kinematically Redundant Octahedral Motion Platform for Virtual Reality Simulations

We propose a novel design of a parallel manipulator of Stewart Gough type for virtual reality application of single individuals; i.e. an omni-directional treadmill is mounted on the motion platform in order to improve VR immersion by giving feedback to the human body. For this purpose we modify the well-known octahedral manipulator in a way that it has one degree of kinematical redundancy; namely an equiform reconfigurability of the base. The instantaneous kinematics and singularities of this mechanism are studied, where especially "unavoidable singularities" are characterized. These are poses of the motion platform, which can only be realized by singular configurations of the mechanism despite its kinematic redundancy.Comment: 13 pages, 6 figure

Efficiency Improvement of Fault-Tolerant Three-Level Power Converters

Fault-tolerant power converters play a critical role in the transportation electrification. However, fault-tolerant operation, high efficiency, and low cost usually result in design criteria that have conflicting constraints and goals. The majority of the fault-tolerant power converter topologies presented in the literature confirm these conflicts. In this paper, three types of fault-tolerant neutral-point clamped (NPC) converters are investigated. Various modulation strategies are explored to reduce the losses of the redundant phase leg. The simulation and experimental results show that the Switching Frequency Optimal Phase opposition Disposition modulation strategy is the most effective approach in minimizing the losses in the redundant phase leg

Independent Orbiter Assessment (IOA): Analysis of the atmospheric revitalization pressure control subsystem

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis/Critical Items List (FMEA/CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The independent analysis results corresponding to the Orbiter Atmospheric Revitalization and Pressure Control Subsystem (ARPCS) are documented. The ARPCS hardware was categorized into the following subdivisions: (1) Atmospheric Make-up and Control (including the Auxiliary Oxygen Assembly, Oxygen Assembly, and Nitrogen Assembly); and (2) Atmospheric Vent and Control (including the Positive Relief Vent Assembly, Negative Relief Vent Assembly, and Cabin Vent Assembly). The IOA analysis process utilized available ARPCS hardware drawings and schematics for defining hardware assemblies, components, and hardware items. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode

Advanced Silicon Carbide Based Fault-Tolerant Multilevel Converters

The number of safety-critical loads in electric power areas have been increasing drastically in the last two decades. These loads include the emerging more-electric aircraft (MEA), uninterruptible power supplies (UPS), high-power medical instruments, electric and hybrid electric vehicles (EV/HEV) and ships for military use, electric space rovers for space exploration and the like. This dissertation introduces two novel fault-tolerant three-level power converter topologies, named advanced three-level active neutral point clamped converter (A3L-ANPC) and advanced three-level active T-Type (A3L-ATT) converter. The goal of these converters is to increase the reliability of multilevel power converters used in safety-critical applications.These new fault-tolerant multilevel power converters are derived from the conventional ANPC and T-Type converter topologies. The topologies has significantly improved the fault-tolerant capability under any open circuit or certain short-circuit faults in the power semiconductor devices. In addition, under healthy conditions, the redundant phase leg can be utilized to share overload current with other main legs, which enhances the overload capability of the converter. The conduction losses in the power devices can be reduced by sharing the load current with the redundant leg. Moreover, unlike other existing fault-tolerant power converters in the literature, full output voltages can be always obtained during fault-tolerant operation. Experimental prototypes of both the A3L-ANPC and A3L-ATT converters were built based on Silicon Carbide (SiC) MOSFETs. Experimental results confirmed the anticipated performance of the novel three-level converter topologies.SiC MOSFET technology is at the forefront of significant advances in electric power conversion. SiC MOSFETs switch significantly faster than the conventional Silicon counterparts resulting in power converters with higher efficiency and increased switching frequencies. Low switching losses are one of the key characteristics of SiC technology. In this dissertation, hard and soft switching losses of a high power SiC MOSFET module are measured and characterized at different voltage and current operating points to determine the maximum operating frequency of the module. The purpose of characterizing the SiC MOSFET module is to determine the feasibility of very high frequency (200kHz-1MHz) power conversion which may not be possible to be implemented in the conventional Silicon based high power conversion. The results show that higher switching frequencies are achievable with soft switching techniques in high power converters