Fault-tolerant Mode Research Articles

Sequence extraction-based low voltage ride-through control of grid-connected renewable energy systems

Various faults can cause voltage sag in the power grid at different voltage levels across the network. Balanced or unbalanced voltage sags lead to grid instability by tripping off a large number of wind or solar power plants from the electric power network. This is particularly problematic to maintain the stability of renewable energy-rich converter-dominated modern power systems. To mitigate the adverse effects of voltage sag, grid-connected converters (GCCs) need to be capable of operating in self-healing and fault-tolerant mode by embedding low voltage ride-through (LVRT) capability into the control system of GCCs. In order to facilitate the implementation of LVRT capabilities for unbalanced faults, fast and accurate frequency-adaptive sequence extraction of grid voltages and currents is essential. This motivated the present work of making a systematic comparison of adaptive observer-based sequence extraction techniques to provide LVRT capabilities into the control system of GCCs. In order to show the effectiveness of each observer, various comparative analyses were performed through Matlab-based numerical simulation. Different observers were benchmarked by the dynamic performance improvement during the low-voltage fault period. Experimental results using a laboratory-scale prototype GCC show that adaptive observers are a suitable choice of sequence extractors for LVRT operation of grid-connected converters in unbalanced and distorted grids. The results obtained in this work will contribute to enhancing the stability of modern power systems that are getting more and more converter-dominated.

Temperature Analysis for the Asymmetric Six-Phase Permanent Magnet Synchronous Motor in Healthy and Fault-Tolerant Modes

The asymmetric six-phase permanent magnet synchronous motor (AS-PMSM) can switch to five- or three-phase operation in the case of winding and drive leg fault. This paper analyses the temperature distribution of the AS-PMSM with different fault-tolerant modes and provides theoretical support to improve the reliability of the machine and its drive system. A 22-pole 24-slot AS-PMSM with physical, magnetic, and thermal isolation is designed first. Then, the systematic analysis method, considering the inverter, the machine and the control algorithm, is proposed. The magnetic field and losses of the AS-PMSM are addressed in multiple modes, including the six-phase, the five-phase (minimum loss / maximum torque) and the three-phase operation. Furthermore, a three-dimensional model, bi-directionally coupling electromagnetic field and temperature, is established based on the theory of transient temperature field and fluid dynamics. The model reveals the temperature propagation law and the temperature variation of the AS-PMSM in four modes. The proposed theoretical analysis is finally proved effective by experiments.

Fault-Tolerant Predictive Current Control of Six-Phase PMSMs With Minimal Reconfiguration Requirements

By manipulating the additional degrees of freedom of multiphase machines, inherent to this type of machine, fault-tolerant control strategies are able to keep multiphase drives in service after one or more open-phase faults (OPFs). Therefore, multiphase machines controlled by finite control set model predictive control (FCS-MPC) strategies are an excellent fit for critical systems, where reliability and excellent dynamic performance are necessary. However, the existing fault-tolerant FCS-MPC strategies typically require considerable changes to the structure of the control algorithm when transitioning between healthy and fault-tolerant modes of operation. Therefore, this article proposes a novel fault-tolerant predictive current control (FT-PCC) strategy with minimal reconfiguration requirements for the six-phase permanent magnet synchronous machine (PMSM) drives. The proposed method only requires the adjustment of current references during fault-tolerant operation and keeps the structure of the control algorithm unchanged. To validate this FT-PCC strategy, several simulation and experimental results are presented for different OPF scenarios, in which the excellent performance obtained with the proposed method is demonstrated.

Proposal of Hybrid Discontinuous PWM Technique for Five-Phase Inverters under Open-Phase Fault Operation

One of the most common issues in inverters are open-circuit faults (OPF). In this scenario, a proper fault-tolerant technique must be used to improve the motor performance. Although basic fault-tolerant modulation techniques are normally preferred, this paper proposes a discontinuous pulse-width modulation algorithm (HD-PWM) to operate five-phase inverters under a single OPF. In particular, loss equalization between the remaining switches after a fault occurs is the main objective of the HD-PWM algorithm, thus preventing future faults from occurring. The efficiency and harmonic distortion of the proposed technique are compared to the well-known sinusoidal PWM by simulation and experimentation under OPF conditions. The results obtained show a great performance of the proposed modulation technique, obtaining a relevant efficiency improvement.

A new multi-mode fault-tolerant operation control strategy of multiphase stacked interleaved Buck converter for green hydrogen production

This paper presents a new fault-tolerant operation method of multiphase stacked interleaved Buck converter for green hydrogen production. An improved topology and new fault-tolerant control strategy is proposed. Multi-mode fault-tolerant operation of multiphase stacked interleaved Buck converter for different performance requirements of electrolyzer in hydrogen production system is realized. The multiphase stacked interleaved Buck converter can not only achieve elimination of output current ripple in normal operation mode, but also adopt different fault-tolerant modes according to different demands of electrolyzers in case of failure of any phase of converter. The proposed method is able to improve the availability of multiphase stacked interleaved Buck converter, reduce the times of equipment shutdown, and ensure the continuous operation of hydrogen production system from renewable energy sources. The effectiveness of the proposed method has been verified by experimental results.

Computer User Behavior Anomaly Detection Based on K-Means Algorithm

As an effective network protection method, computer user behavior anomaly detection can detect unknown attack behaviors. In order to detect user behavior anomalies more efficiently, the authors propose a computer user behavior anomaly detection model based on the K-means algorithm. According to the actual characteristics of single-user behavior, the algorithm uses sliding time window to define transactions and uses the first location strategy to mine behavior patterns. On this basis, the fault-tolerant mode is adopted to compare the current behavior mode with the normal behavior mode, and the anomaly detection results are obtained. Experiments show that using data mining technology, the association rules of user commands, and the mining of sequence patterns, it can effectively discover the user’s behavior pattern, and using sequence matching algorithms such as recursive correlation functions and calculating the similarity between the user’s historical pattern and the current pattern, it provides the possibility to accurately judge user behavior. The following conclusions are obtained through experiments: the model training time is short, the accuracy is high, and it has certain robustness.

A fault-tolerant reconfiguration system based on pilot switch for grid-connected inverters

The multi-level inverter has been widely applied in high-power applications, especially in grid-connected systems. In addition to some of the benefits provided by the multi-level inverter, it has the disadvantage to be more prone to failure because of the large number of components used. Therefore, fault-tolerant control of multi-level inverters is critical to ensure the stability and reliability of the system. This paper introduces a fault-tolerant reconfiguration system (FTRS) based on pilot switch for grid-connected inverters. FTRS includes the grid-connected inverter using pilot switches and a fault-tolerant modulation algorithm. FTRS aims to reduce the damage of insulated gate bipolar transistor (IGBT) failure of cascaded H-bridge (CHB) inverter and meet such application requirements as grid-connected systems. The grid-connected inverter using pilot switches and its modulation algorithm can complete fault isolation without the redundant backup H-bridge and can make H-bridge reconfiguration after the system receives the fault signal so that the healthy H-bridge will keep working with voltage peak. Reliability evaluation and comparison of the FTRS and other inverters are presented. The validation of the proposed method is confirmed by simulation and experiment results on the five-level grid-connecter inverter.

A Low-Overhead Reconfigurable RISC-V Quad-Core Processor Architecture for Fault-Tolerant Applications

Radiation can affect the correct behavior of an electronic device. Hence, the microprocessors used for space missions need to be protected against fault. TMR (Triple modular redundancy) is used for mitigating various kinds of faults in an electronic circuit. Although TMR provides an excellent level of reliability, it takes a large area and suffers from high power consumption. To reduce the area and power overheads DMR (double modular redundancy) is used. The DMR approach significantly reduces the resource overhead but it also reduces the performance by imposing timing penalty. Various methods have been proposed since the incarnation of TMR and DMR, but the resource overhead is still a challenging issue. Hence, in this work, a new DMR based reconfigurable quad-core RV32IM processor architecture is proposed for fault-tolerant applications. Depending upon the environment of operation and application sensitivity, the designed processor can be reconfigured to work either in normal mode or fault-tolerant mode. The novelty of the proposed architecture is that the reconfigurable feature reduces the resource overhead and makes the processor energy-efficient by optimally using all four processor cores to provide fault-tolerant results. The proposed computing architecture is designed using Verilog HDL(Hardware Description Language) and synthesized on 32nm CMOS (Complementary Metal-Oxide Semiconductor) process technology node using Synopsys Design Compiler EDA (Electronic Design Automation) tool. Compared to unprotected design, the synthesis tool reports -21.75% reduction in power with a time penalty of +9.96% and area overhead of +17.89% for the proposed fault-tolerant approach. Compared to the state-of-the-art fault-tolerant computing system, the proposed design achieves -2.26% low area overhead with its reliability intact as DMR. Further, the proposed processor is prototyped and tested on FPGA (field-programmable gate array) with fault-injection using SEM (soft error mitigation) IP core.

Fault Tolerant Sliding Mode Controller Design Subject to Sensor Faults for Output Voltage Regulation of a Self-Excited Induction Generator

This paper aims to improve the performance of the output voltage regulation of the Self-Excited Induction Generator (SEIG) with fixed capacitor-thyristor controlled reactor (FC-TCR) structure in case of sensor faults. A sliding mode controller (SMC) is designed to generate the triggering angle of the FC-TCR to regulate the output voltage. The performance of proposed SMC is firstly tested without sensor faults and high success in tracking the reference is obtained. Since an additive fault occurs on the sensor, SMC performs well tracking dynamic but is on the incorrect reference. Therefore, Radial Basis Function Neural Network (RBFNN) is trained accurately with the 2% mean squared error (MSE) by taking the stator currents, triggering angle and generator speed as inputs, whereas the output voltages of the SEIG are outputs. Further, fault detection architecture is well designed with a voltage error index calculated by subtracting the sensor output from the estimated output. The threshold based selector reconfigures the controller well. The simulation results show that in case of sensor faults and various loading conditions, proposed fault tolerant SMC remains the actual output voltage of the SEIG at real reference with maximum 2.2% steady state error in a finite time.

Design and Validation of a Sensor Fault-Tolerant Module for Real-Time High-Density EMG Pattern Recognition.

With the advancements in electronics technology, high-density (HD) EMG sensing systems have become available and have been investigated for their feasibility and performance in neural-machine interface (NMI) applications. Comparing to the traditional single channel-based targeted muscle sensing method, HD EMG sensing performs a sampling of the electrical activity over a larger surface area and has the promise of 1) providing richer neural information from one temporal and two spatial dimensions and 2) ease of wear in real life without the need of anatomically targeted electrode placement. To use HD EMG in real-time NMI applications, challenges including high computational burden and unreliability of EMG recordings over time need to be addressed. This paper presented an HD EMG PR based NMI which seamlessly integrates HD EMG PR with a Sensor Fault-Tolerant Module (SFTM) which aimed to provide robust PR in real time. Experimental results showed that the SFTM was able to recover the PR accuracies by 6%-22% from disturbances including contact artifacts and loose contacts. A Python-based implementation of the proposed HD EMG SFTM was developed and was demonstrated to be computationally efficient for real-time performance. These results have demonstrated the feasibility of a robust real-time HD EMG PR-based NMI.

Fuzzy logic based dynamic performance enhancement of five phase induction motor under arbitrary open phase fault for electric vehicle

Abstract The multiphase induction motor can be a highly preferable choice for the EV application, where the reliability and safety of passengers are one of the major concerns. The main objective of this article is to design high performance fault tolerant control of five phase induction motor (FPIM) drive to enhance the dynamic performance under healthy, faulty and fault tolerant modes of operation under arbitrary open phase fault condition. First, a simple method of modeling open phase fault in any phase of the FPIM drive is proposed. The most frequently occurring open phase faults due to the power electronics switch failure in the inverters are considered for the analysis. A generalized method of modeling arbitrary open phase fault in FPIM drive using back EMF calculations in faulty phase is suggested. The developed method utilizes the same transformation matrix for any open phase fault such that the minimum modification in control strategy is required under fault condition. Thereafter, the control technique is detailed. The rotor field oriented control (RFOC) of FPIM with fuzzy logic speed controller is developed to generate optimal torque reference. The design of FLC is detailed with fine-tuned scaling factor, rule base and membership function to obtain robust performance of the drive under healthy and fault tolerant modes of operation. The complete RFOC scheme for 2 HP FPIM drive is built in MATLAB/SIMULINK incorporating fuzzy logic based controller to verify its performance. The comparison of transient and steady state response and robustness (to the load disturbance as well as fault) obtained using developed fuzzy logic based controller with those using conventional PI controller is presented to prove the efficiency of the suggested controller under various speed torque profiles. The effectiveness of the proposed fuzzy based fault tolerant controller for FPIM drive is validated using OP4510 controller based real time HIL simulator.

Innovative Fault-Tolerant Three-Phase SPMSM Drive Without Split Capacitors, Auxiliary Legs, or TRIACs

The existing fault-tolerant three-phase ac drives need split capacitors, auxiliary legs, and triode for alternating current (TRIACs) upon a standard three-phase two-level voltage source inverter (VSI) to obtain the self-healing ability toward open-phase faults (OPFs). In order to reduce the cost, volume, and weight, this article proposes a novel fault-tolerant three-phase surfacemounted permanent magnet synchronous machine (SPMSM) drive without split capacitors, auxiliary legs, or TRIACs. The proposed drive is still built upon a three-phase two-level VSI, whereas its dc-source is directly connected to the neutral point of the motor. First, mathematical model and equivalent circuit are established to reveal the existence of an equivalent dc/dc boost converter in the drive system. Second, the brand-new d-0 axes current references are proposed in order to preserve the motor's performance when an OPF occurs. In this case, both id and i0 are nonconstant. Third, an overall control strategy including the healthy and fault-tolerant modes is presented. In the fault-tolerant mode, a deadbeat current controller is developed to track the nonconstant current references. Finally, experiments are carried out on an SPMSM test-bench to verify the effectiveness of the proposed scheme.

Open Transistors Fault-Tolerant Schemes of Three-Phase Dual Active Bridge DC-DC Converters

This work proposes fault-tolerant schemes for open-transistor faults applied to three-phase dual active bridge converters (TPDABC), using different transformers: star-star, delta-delta, and delta-star. The proposal consists of operating the TPDABC as a single-phase dual active bridge converter, modifying the modulation strategy. This strategy avoids the need for additional components, which allows the converter to continue operating after an event of open transistor failure. The expressions of the average power when the converter operates in the fault-tolerant modes are determined. The analysis determines that the maximum power that can be transferred using the transformer delta-star is larger than the power obtained for star-star and delta-delta connections. Simulation results allow the proposed schemes to be validated.

Design and Analysis of a Five-Phase Permanent-Magnet Synchronous Motor for Fault-Tolerant Drive

Reliability is a fundamental requirement in electric propulsion systems, involving a particular approach in studies on system failure probabilities. An intrinsic improvement to the propulsion system involves introducing robust architectures such as fault-tolerant motor drives to these systems. Considering the potential for hardware failures, a fault-tolerant design approach will achieve reliability objectives without recourse to optimized redundancy or over-sizing the system. Provisions for planned degraded modes of operation are designed to operate the motor in fault-tolerant mode, which makes them different from the pure design redundancy approach. This article presents how a five-phase permanent-magnet synchronous motor operates under one- or two-phase faults, and how the system reconfigures post-fault motor currents to meet the torque and speed requirement of reliable operation that meets the requirements of an electric propulsion system.

Switching Sequence Model Predictive Direct Torque Control of IPMSMs for EVs in Switch Open-Circuit Fault-Tolerant Mode

A switching sequence model predictive direct torque control (MPDTC) of IPMSMs for EVs in switch open-circuit fault-tolerant mode is studied in this paper. Instead of selecting one space vector from the possible four space vectors, the proposed MPDTC method selects an optimized switching sequence from two well-designed switching sequences, including three space vectors, according to a new designed cost function of which the control objectives have been transferred to the dq-axes components of the stator flux-linkage under the maximum-torque-per-ampere control. The calculation method of the durations of the adopted space vectors in the optimized switching sequence is studied to realize the stator flux-linkage reference tracking. In addition, the capacitor voltage balance method, by injecting a dc offset to the current of fault phase, is given. Compared with the conventional MPDTC method, the complicated weighting factors designing process is avoided and the electromagnetic torque ripples can be greatly suppressed. The experimental results prove the effectiveness and advantages of the proposed scheme.

A Category-Based Calibration Approach With Fault Tolerance for Air Monitoring Sensors

Air pollution monitoring has attracted much attention in recent years because of the deterioration of the environment. Standard stations, installed by governments with a high cost, can provide reliable air quality information; whereas a large number of portable air monitoring sensors with low cost are widely used and output less precise results. In this paper, we propose a category-based calibration approach (CCA) using machine learning algorithms for such portable sensors. Compared with traditional methods that often learn a single regression model, CCA includes multiple regression models according to pollutant concentration categories, and builds a more accurate mapping from sensor readings to reference. Furthermore, CCA introduces two fault-tolerance modules: classification tolerance and sample tolerance. The former mitigates the impact of misclassification for concentration category, and the latter improves the robustness of individual regression model. Our approach is evaluated on carbon monoxide (CO) and ozone (O3) from two cities of China. The experiment results show that CCA has a better performance than traditional calibration models in both accuracy and robustness.

Control strategy with multivariable fault tolerance module for automatic intravenous anesthesia.

In the anesthesia automation, an automatic propofol infusion system uses Bi-spectral Index Signal (BIS) as a primary feedback signal to manipulate propofol dose. However, the BIS signal may be suspended for some time due to poor EEG signal quality, noise, and many other factors. Therefore, BIS signal failure may be the main cause of inadequate propofol infusion. This fact motivates the need for integration of multivariable fault tolerance module (MFTM) and fractional-order Smith predictor controller to avoid adverse reactions of inadequate propofol dosing during BIS failure. Smith Predictor control strategy is sufficiently robust to predict feedback BIS during BIS failure via patient pharmacological modeled BIS. However, modeled BIS may not provide a guarantee of adequate propofol infusion during BIS failure and especially in the presence of hypotension and hypertension. Thus, the proposed control strategy is designed with MFTM to detect BIS sensor fault and to estimate feedback BIS during BIS failure. Further, the proposed control strategy is designed with a multivariable pharmacological patient model to analyze the cross effect of propofol infusion on BIS and hemodynamic variables. The robustness of the proposed control strategy is tested in the presence of noxious surgical stimulation, BIS sensor fault and heavy hemodynamic disturbance. The pharmacological parameters and recorded signals of 30 patients during various surgeries have been used to validate simulated results. The performance of the proposed control strategy assures optimization and smooth propofol infusion during BIS failure. The proposed system provides stability for a wide range of physiological parameters range. The proposed scheme maintains smooth BIS and MAP signal despite the delay, BIS sensor fault, and surgical disturbances.

Open-Phase Fault-Tolerant Operation of the Three-Phase Dual Active Bridge Converter

The three-phase dual active bridge (3p-DAB) converter is widely considered in dc-grid applications. Because of the higher number of switches in the 3p-DAB, it can be argued that the reliability of the 3p-DAB is reduced when compared to other isolated-bidirectional dc-dc converter topologies. The previous work has shown that the 3p-DAB can be operated in a frozen leg fault-tolerant mode, i.e., with the two transistors of the same phase being opened by their gate driver internal protections. Because the free-wheeling diodes are left self-commutated, the analytical characterization of the converter for all voltage and loading conditions is not trivial. In this article, it is proposed to open the faulty phase such as it eliminates the interaction with the faulty-phase free-wheeling diodes. This allows the converter to fall in a characterizable operating mode for all voltage and loading conditions. The results further show that the open-phase operation provides advantages over the frozen leg operation in terms of current stress and power transfer capability. Experimental results on a small-scale closed-loop gallium nitride-based prototype as well as time-domain simulation results are provided to support the theoretical analyses.

Fault-Tolerant Operation of a TLC-MMC Hybrid DC-DC Converter for Interconnection of MVDC and HVdc Grids

An isolated bidirectional dc-dc converter, which combines multiple two-level converters (TLCs) in parallel on the medium-voltage side and a modular multilevel converter (MMC) on the high-voltage side, namely the TLC-MMC converter, is a promising candidate for the interconnection of MVdc and HVdc grids. In utility applications, the availability of power converters is of great importance, which makes the fault-tolerant operation (FTO) capability a required feature. In this paper, an FTO scheme of the TLC-MMC converter in case of a TLC failure is addressed. The FTO capability is enabled by employing only mechanical disconnectors. The faulty TLC can be bypassed and isolated for maintenance, and the TLC-MMC converter can continuously operate with a reduced power capacity. A dedicated mode-transition strategy is developed, whereby the TLC-MMC converter can transit to the fault-tolerant mode seamlessly without resulting in overvoltage or overcurrent despite the involvement of low-speed mechanical disconnectors. Thus, the proposed approach can effectively enhance the availability of the TLC-MMC converter. The validity of the proposed approach is verified by both simulation and experimental test with a down-scale prototype.

Fault-Tolerant Control Strategy of the Open-Winding Inverter for DC-Biased Vernier Reluctance Machines

This paper proposes a fault-tolerant control strategy of the open-winding inverter for dc-biased vernier reluctance machines (dc-biased VRMs), aiming to maintain the output capability after the open-circuit fault occurs in the inverter switches. DC-biased VRMs are with integrated winding current for both dc component for field excitation and ac component for torque generation. The torque generation is not associated with the current direction, making the full-bridge inverter be divided into two groups of devices. The proposed fault-tolerant control strategy is based on the regular full-bridge inverter for each open winding and can control the motor in the fault-tolerant mode with one group of devices. When an open-circuit fault of a device appears in the normal mode, the controller will switch to the fault-tolerant mode. After a short transient period, the motor will be able to work. Moreover, in the fault-tolerant mode, a pulsewidth modulation driving method is proposed to reduce the current ripple. The proposed method does not require any additional components, and the reliability of the drive control system with the open-winding inverter is improved. Experimental results verify the validity and feasibility of the proposed fault-tolerant control strategy.