Redundant Leg Research Articles

Transition and Post-fault Correction Strategy for a Single-Phase Inverter With Improved Redundant Leg Utilization

Transition and Post-fault Correction Strategy for a Single-Phase Inverter With Improved Redundant Leg Utilization

Kinematically redundant (6＋2)-dof HEXA robot for singularity avoidance and workspace augmentation

This paper introduces a novel (6＋2)-degree-of-freedom (dof) kinematically redundant parallel robot. The proposed architecture is based on the 6-dof HEXA parallel robot. The paper applies methodologies for avoiding type II singularities using kinematic redundancy that were originally proposed for robots with prismatic actuators to a new architecture with revolute actuators. The singularities of the HEXA robot are first examined based on previous work, and new instances of singularities are discovered. The singularity locus in the orientational workspace is identified using the Power Inspired Measure. Then, a novel kinematically redundant leg architecture is proposed to allow for the avoidance of these type II singularities. It is shown that the singularities present within the orientational workspace can successfully be avoided if two kinematically redundant legs are included in the robot architecture. The performance of the new architecture is then examined in various trajectories within the orientational workspace. Results show that the attainable orientational workspace is significantly increased with the proposed architecture.

Fault-tolerant control for three-phase three-level T-type inverters with a redundant leg

Fault-tolerant control for three-phase three-level T-type inverters with a redundant leg

Fault-Tolerant Operation of Bidirectional ZSI-Fed Induction Motor Drive for Vehicular Applications

This paper presents an efficient and fast fault-tolerant control scheme for a bidirectional Z-source inverter (BiZSI)-fed induction-motor drive system for vehicular applications. The proposed strategy aims for the fault detection, localization and diagnosis of the proposed system during switch failures in the inverter module. Generally, power–semiconductor switch failures in inverter modules occur due to open- and short-circuit faults. An efficient modulation scheme is proposed and design specifications are thoroughly derived to obtain high voltage gains across the BiZSI network. A suitably fast detection and diagnosis scheme to isolate the faulty leg and resume the normal operation is discussed in this paper. The control scheme is provided such that the faulty leg is isolated and the motor phase is fed from a redundant leg to resume the operation. A feasible localization algorithm based on experimentally derived values and switching vectors is implemented. In addition, a fast fault diagnosis method based on current estimation and motor speed variation is designed and implemented. Moreover, the most important advantages of the proposed strategy include lower hardware requirements and less harmonic distortion in the output currents. Finally, the simulation and experimental results are presented to validate the feasibility of the theoretical analysis. An extensive performance evaluation of the proposed system with fault ride-through capabilities is performed to prove its suitability for vehicular applications. To validate its merits, the proposed strategy is compared with similar fault-tolerant schemes currently used in the industry.

A fault-tolerant photovoltaic integrated shunt active power filter with a 27-level inverter

This paper introduces a fault-tolerant shunt active power filter (SAPF). The novility in of this work is that it poposes a solutions to increase the reliability of shunt active power filter to maintain its operation under a single-phase open-circuit fault in the SAPF. This will increase the reliability of the whole power system. The SAPF is composed of a 4-leg 27-level inverter based on asymmetric cascaded H-bridge topology. If an open-circuit fault is introduced to the operation of the SAPF, a special control technique will be implemented and the redundant leg of the SAPF will be activated. The fault-tolerant SAPF can do many tasks under healthy operating conditions and post and open circuit fault depending on the state of charge (SOC) of the batteries. It can mitigate harmonics in the power system, improve power factor in the system by injecting reactive power, and inject real power to the system. The proposed SAPF is tested and simulated in MATLAB/Simulink and the results have shown a significant improvement in total harmonics distortion (THD) of the source current from 13.9% to 3.9% under the normal operating condition and from 42% to 8.4% post and open circuit fault.

SSTPI-IM Reconfiguration and Diagnostic under OCF Appearance Used in PV System

In order to the increase of the conventional inverter reliability used in PV systems, many diagnostic methods have been investigated to these converters reliability. These diagnostic methods are applied in order to detect and identify the IGBT's OCF. In this paper, the proposed diagnostic method is based on the normalized currents and current's slope information's. Due to the continuity importance in PV systems after the appearance of IGBT's OCF, this paper presents a SSTPI-IM diagnostic method and reconfiguration strategy controlled by the direct RFOC used in PV system. The fault reconfiguration is based on the change of the SSTPI topology to the FSTPI topology using relays and a redundant leg. The redundant leg is only used in the cases of IGBT’s fault’s appearance in more than one SSTPI leg. The effectiveness and performance of the proposed SSTPI-IM diagnostic method and reconfiguration strategy in terms of systems continuity and fast detection and reconfiguration are validated by the simulation results.

Reliability Assessment of a Fault-Tolerant PV Multistring Inverter

In photovoltaic (PV) systems, the reliability of the system components, especially the power converters, is a major concern in obtaining cost effective solutions. In order to guarantee service continuity in the case of failure of elements of the PV converter, in particular, semiconductor switching devices, a solution is to design power converter with fault-tolerance capability. This can be realized by aggregating hardware redundancy on an existing converter, providing the possibility of replacement of faulty elements. This paper evaluates the reliability of a fault-tolerant power electronics converter for PV multistring application. The considered fault-tolerant design includes a single redundant switching leg, which is used in order to reconfigure the structure in case of a switch failure either on DC-AC or DC-DC stages. This paper details the reliability estimation of the considered PV multistring fault-tolerant converter. Furthermore, a comparison with a conventional structure without fault-tolerant capability is provided. The results show that the introduction of a single redundant leg allows for improving the converter mean time to failure by a factor of almost two and it reduces, by half, the power loss due to system-failure shutdowns in PV applications, while only increasing the converter cost by 2–3%.

A Photovoltaic-Fed Z-Source Inverter Motor Drive with Fault-Tolerant Capability for Rural Irrigation

In recent years, photovoltaic (PV) systems have emerged as economical solutions for irrigation systems in rural areas. However, they are characterized by low voltage output and less reliable configurations. To address this issue in this paper, a promising inverter configuration called Impedance (Z)-source inverter (ZSI) is designed and implemented to obtain high voltage output with single-stage power conversion, particularly suitable for irrigation application. An improved and efficient modulation scheme and design specifications of the network parameters are derived. Additionally, a suitable fault-tolerant strategy is developed and implemented to improve reliability and efficiency. It incorporates an additional redundant leg with an improved control strategy to facilitate the fault-tolerant operation. The proposed fault-tolerant circuit is designed to handle switch failures of the inverter modules due to the open-circuit and short-circuit faults. The relevant simulation and experimental results under normal, faulty and post-fault operation are presented. The post-fault operation characteristics are identical to the normal operation. The motor performance characteristics such as load current, torque, harmonic spectrum, and efficiency are thoroughly analysed to prove the suitability of the proposed system for irrigation applications. This study provides an efficient and economical solution for rural irrigation utilized in developing countries, for example, India.

Open circuit fault detection and FTC for sensorless PMS motor control based on the back-EMF SMO

ABSTRACT The detection of the electrical fault in speed controller under a Motor Control Unit System (MCUS) has been amply viewed in the research paper. Nevertheless, the research work in this domain have been constantly followed on sensor-based vector control of synchronous motor. This paper combines the Power Inverter Voltage (PIV) faults detection (signal-based approach) with sliding mode technique (model-based) to provide Fault Tolerant Control (FTC) for sensorless speed Permanent Magnet Synchronous (PMS) motor drive. Back-EMF sliding mode observer (Back-EMF-SMO) is used for rotor position and stator currents estimation and simultaneously MCUS fault diagnosis. The fault diagnosis for MCUS faults of PMS motor drives using a Hilbert Transform. The motor phase currents signals shapes for various modes of MCUS faults are examined. A PIV Faults Detection and Isolation (FDI) algorithm is used to allow the switchover to a redundant leg. The obtained findings exhibit the effectiveness of the suggested FDI process particularly to detect and to isolate a PIV faults for sensorless PMS motor drives.

Single and multiple switch fault‐tolerance capabilities in a hybrid five‐level inverter topology

The redundancy in switching states to generate different voltage levels is of great importance to incorporate fault-tolerant features in multilevel inverters. However, this redundancy comes at the expense of high device count, which is paralleled with vulnerable characteristics of semiconductor devices, resulting in low reliability. About this concern, the present study introduces a novel fault-tolerant topology to generate the five-level output voltage. The proposed topology can tolerate open-circuit failure, for single and multiple switches with the help of novel redundant leg architecture and short-circuit condition is dealt with the fast fuses. The comparative study with recent literature is discussed, which reveals the superiority of the proposed topology, in terms of qualitative as well as quantitative parameters. Switching strategies are proposed under different single and multiple switch fault cases, which achieves self-balancing of capacitor voltage. Thus, no complex control scheme is required. The simulation is performed in MATLAB/Simulink, and the feasibility of the proposed topology is validated using experimental results.

Fault tolerant architecture of an efficient five‐level multilevel inverter with overload capability characteristics

Multilevel inverters (MLIs) are gaining the widespread attention in various industrial applications. However, the advantages offered by MLIs are only met with the employment of a high number of semiconductor switches and capacitors, which are most vulnerable amongst all the power electronic components. Thus, designing of a reliable MLI topology is a need of the present hour. In this regard, a five-level fault tolerant MLI topology has been proposed here. The proposed MLI topology comprises the main inverter topology and a redundant leg. The main inverter topology comprises bidirectional switches which result in high power losses under both healthy and faulty conditions. Eighteen different cases arising from the inherent redundancy available in the main inverter topology have been analysed to achieve the optimum solution for obtaining high efficiency. A novel redundant leg architecture has been designed, which achieves significantly improved efficiency under all faulty conditions. Under overload conditions, the proposed redundant leg architecture is capable of reducing the current stress on the main inverter switches. An effective qualitative and quantitative comparison of the proposed topology with the recent literature has been presented. The feasibility of the proposed concepts has been verified by the obtained simulation and hardware results.

L- and LCL-Filtered Grid-Tied Single-Phase Inverter Transistor Open-Circuit Fault Diagnosis Based on Post-Fault Reconfiguration Algorithms

This paper presents a transistor open-circuit fault diagnosis method based on an average model and post-fault reconfiguration algorithms for a grid-tied single-phase inverter that transfers power bi-directionally. The transistor open-circuit fault occurrence is detected by comparing the average bridge arm pole-to-pole voltage deviation and threshold first. Then, the exact faulty transistor is identified by developed algorithms based on post-fault reconfiguration of control (PFRC) and of utilizing redundant leg (PFRUR). These two fault identification algorithms are suitable for different situations. Compared with the PFRUR, the PFRC can identify the faulty transistor without the help of redundant leg, but the identification time is longer. For inverters equipped with redundant leg already, the PFRUR can achieve faster identification speed so that inverters in reliability-oriented applications can return to normal operation after fault with short interruption. With average model, this method only requires existing signals sampled for control, thus it can be embedded in system easily without adding extra sensors and diagnosis circuits. The sampling frequency can be as low as switching frequency. Furthermore, this method is suitable for both inverters with L or LCL filters. Finally, experiments are carried out on a 550-W/10-kHz grid-tied single-phase inverter to verify the effectiveness.

IGBT Open-Circuit Fault Diagnosis in a Quasi-Z-Source Inverter

In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared with the existing fast OC FD techniques in three-phase voltage source inverters, this method is more cost-effective since no ultrafast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification. When both stages of the OC FD algorithm are done, a redundant leg is activated and utilized instead of the failed leg. The accuracy of the proposed method is confirmed by the experimental results from a low-voltage q-ZSI prototype.

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.

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.

Sensorless Speed Control and High-Performance Fault Diagnosis in VSI-Fed PMSM Motor Drive Under Open-Phase Fault: Analysis and Experiments

This paper aims to provide a high-performance sensorless fault-tolerant direct torque control of permanent magnet synchronous motor based on nonlinear position and speed observer. The nonlinear observer is based on a trigonometric function to estimate the rotor position, and a proportional–integral controller is used to estimate the speed from estimated position. A faulty leg (open phase) in the PWM VSI changes the corresponding terminal voltage and introduces the voltage distortions to each phase voltage. The ordinary two-level inverter is composed of three legs. In the proposed fault-tolerant inverter, a redundant leg is added that replaces the faulted leg. The detection of the open-phase fault is based only on the current signals and the maximum threshold they exceed that in case of fault.

Fault-tolerant VSI for stand-alone DFIG feeding an isolated DC load

ABSTRACTIn this article, a fault-tolerant voltage source inverter (VSI) is proposed for a novel topology of stand-alone doubly fed induction generator (DFIG) feeding an isolated DC load. In this topology, stator and rotor sides of DFIG are connected to DC-bus through a diode rectifier and VSI, respectively. The fault-tolerant VSI includes a redundant leg connected by bidirectional switches in order to replace the faulted leg and improve the reliability of the proposed system. The field oriented control strategy is adopted to control the d and q-axis rotor currents in order to maintain the voltage and the frequency at the output of the generator constant. A novel, easy and fast approach for fault detection and isolation (FDI) of open-switch damage in insulated gate bipolar transistor-based VSI is proposed in this study. This approach is developed using mathematical transformations such as a hysteresis detector, an integrator and a trigger. The FDI algorithm proposed here does not require the knowledge of the system model and is independent from its complexity. Simulations results are illustrated for a 3.7 kW DFIG feeding a DC load with open-switch fault in VSI that confirm the concepts proposed in this study.

Extended Kalman Filter for Sensorless Fault Tolerant Control of PMSM with Stator Resistance Estimation

<p><span>This paper aims to provide a high performance sensorless control based on an Extended Kalman Filter (EKF) applied to fault-tolerant PMSM drive system with stator-resistance estimation. It proposes a fast method of fault switches detection in the power converters. The considered drive is composed of three phases PMSM and a four leg three phase’s inverter when the fourth is the redundant leg. After a short-switch fault occurrence, the redundant leg replaces the faulty leg. The simulation results verify that the proposed control method and the fault tolerant inverter ensure the high reliability and continuously operation of the sensorless vector control PMSM system under inverter fault.</span></p>

A Fault-Tolerant Single-Phase Grid-Connected Inverter Topology With Enhanced Reliability for Solar PV Applications

Reliability is an essential requirement for a grid-connected Photovoltaic (PV) system, especially in remote military secured areas, which are difficult to access for the purpose of maintenance. However, the reliability of inverters used in the PV system is mainly affected due to the vulnerability of power semiconductor devices to failure. To improve the reliability of inverters, several fault-tolerant topologies are proposed in the literature. A redundant leg is used in most of these topologies to incorporate redundancy in the inverter operation. However, these topologies require an additional leg and four TRIACs, which increase the device count, and hence are not cost-effective. In this paper, a single-phase fault-tolerant inverter topology is proposed, which does not use the redundant leg and achieves the fault-tolerant feature with minimal device count. Moreover, the reliability of the proposed topology is calculated to be more than that of the redundant leg-based topologies. The operation of the proposed topology is explained under various device fault conditions, and validated through simulation and experimental studies. Finally, the reliability of the proposed topology is evaluated using the Markov reliability model.

Joint torque and velocity optimization for a redundant leg of quadruped robot

Hydraulic actuated quadruped robot similar to BigDog has two primary performance requirements, load capacity and walking speed, so that it is necessary to balance joint torque and joint velocity when designing the dimension of single leg and controlling its motion. On the one hand, because there are three joints per leg on sagittal plane, it is necessary to firstly optimize the distribution of torque and angular velocity of every joint on the basis of their different requirements. On the other hand, because the performance of hydraulic actuator is limited, it is significant to keep the joint torque and angular velocity in actuator physical limitations. Therefore, it is essential to balance the joint torque and angular velocity which have negative correlation under the condition of constant power of the hydraulic actuator. The main purpose of this article is to optimize the distribution of joint torques and velocity of a redundant single leg with joint physical limitations. Firstly, a modified optimization criterion combining joint torques with angular velocity that takes both support phase and flight phase into account is proposed, and then the modified optimization criterion is converted into a normal quadratic programming problem. A kind of recurrent neural network is used to solve the quadratic program problem. This method avoids tremendous matrix inversion and fits for time-varying system. The achieved optimized distribution of joint torques and velocity is useful for aiding mechanical design and the following motion control. Simulation results presented in this article confirm the efficiency of this optimization algorithm.