Post-fault Operation Research Articles

Short-Circuit Fault-Tolerant Control Without Constraint on the D-Axis Armature Magnetomotive Force for Five-Phase PMSM

In this article, we investigate the short-circuit (SC) fault-tolerant control (FTC) method for a five-phase permanent-magnet synchronous machine (PMSM) with surface-mounted permanent magnets. By relieving the constraint of zero <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis armature magnetomotive force (MMF) and restraining the backward-rotating MMF components to be zero, round-rotating armature MMF with maximum <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis armature MMF is achieved, which enables five-phase PMSM to output maximum smooth torque with lower losses and higher efficiency under SC fault condition. To ensure smooth postfault operation in full-speed range, the influence of winding resistance on SC current is further considered, which improves low-speed operation performance. The proposed FTC method features sinusoidal currents with equal amplitude, which ensures better control simplicity and postfault thermal uniformity between phases. The finite-element analysis and experiments are carried out to verify the proposed method.

A Robust Exciter Controller Design for Synchronous Condensers in Weak Grids

Weak grid scenarios and low-inertia systems are emerging issues in power systems, which could lead to voltage and frequency instabilities. Synchronous Condensers (SynCons) have recently drawn renewed attention as a promising solution to provide system strength and inertia support. Even though the exciter control of SynCons is a well-established technology, further developments are required to guarantee the stability of post-fault operations, in particular, in weak grids. This paper proposes a data-driven approach for designing higher-order optimized exciter controllers to meet this requirement. A pseudo-random binary sequence (PRBS)-based system identification method is used to obtain frequency response data of the power system, from the exciter point of view, which is then fed into the proposed optimal control design procedure. The proposed exciter controller is tested for voltage ride-through and fault scenarios in a single machine infinite bus (SMIB) case and the IEEE 39-bus test system to assess its performance compared to the conventional AC1A exciter controller. The results obtained through simulation tests carried out using the PSCAD/EMTDC software verify that the proposed exciter controller guarantees the post-fault stability in both strong and weak grids.

Post‐fault operation strategy for single open‐phase fault in three‐phase induction motor drives

Single open-phase fault (SOPF) in three-phase induction motor (TPIM) drives leads to undesired performances and in some cases shutdown of the drive system. This research proposes a post-fault operation strategy based on direct rotor field-oriented control (RFOC) technique for wye-connected TPIM drives during SOPF. In the proposed control system, symmetrical and asymmetrical transformation matrices are utilized for stator voltage and current variables, respectively. In addition, an extended Kalman filter (EKF) is used for the rotor flux estimation, filtration of stator currents, and obtaining their time derivatives. The performance of the introduced technique including steady and transient states during different reference speeds is experimentally validated for a wye-connected TPIM drive considering SOPF. Additionally, the performance of the proposed strategy is experimentally compared with conventional RFOC strategies.

Throughput Estimation of K-zone Gbps Radio Links Operating in the E-band

This paper presents a method for post-fault operation with reduced performance of a permanent magnet synchronous motor following a battery supply open circuit fault. The approach upgrades the previously developed fast model-oriented supply fault detection algorithm based on comparing actual and estimated values of a DC-link voltage. The latter is determined by the model of supply circuit and observer of battery open-circuit voltage. Implementing a post-fault concept does not require additional hardware, as it uses quantities from an already existent vector control algorithm. After the fault is detected, the algorithm is upgraded by a DC-link voltage cascade control loop. An analytical approach to parametrization of the controller, based on the linearization and the reduction of the system's transfer function, is also proposed. Simulations and experimental results have validated the performance of the post-fault algorithm.

Cascaded H-bridge Based STATCOM With Improved Ride Through Capability of Submodule Failures

This article investigates the operation of cascaded H-bridge (CHB) based static synchronous compensator (STATCOM) after failure in its submodules (SMs). Once a switch fails, the corresponding faulty SM is bypassed. In the post-fault operation, a zero-sequence voltage (ZSV) is injected to the converter phases to generate the maximum possible line-to-line voltage. Using a clamping technique, the fundamental component of injected ZSV (FZSV) is minimized according to the operating point of CHB STATCOM. But, FZSV leads to unequal flow of active power into the converter phases. In the proposed method, negative-sequence current is controlled to manage the active power flow within CHB phases. By doing this, the effect of FZSV on active power of CHB phases is compensated and the voltages of capacitors are kept balanced. This method ensures the continuous operation of CHB STATCOM with the minimum over-design and guarantees the voltage balance of capacitors after a failure. The presented simulation and experimental results validate the feasibility and effectiveness of the proposed method.

Asymmetrical six-phase induction motor drives based on Z-source inverters: Modulation, design, fault detection and tolerance

Multiphase machines are becoming one of the mainstream research topics during the last decade, especially in high-reliability based systems. Among the different configurations of the multiphase machines, Asymmetrical Six-Phase Induction Motor (ASPIM) with a spatial displacement of 30° is popular as it has a better magnetomotive force (MMF) distribution. This paper therefore concerns with detecting and mitigating the operation of ASPIM during healthy and faulty modes. Recently, the Z-source Inverter (ZSI) technology has attracted great concerns of the researchers. The key idea of this paper is to combine together the technologies of ASPIM and ZSI. This combination produces a very high reliable drive system. Traditional modulation methods associated with the ZSI are modified in this paper to be convenient for ASPIM drives. Besides, the impedance network design procedures are introduced. Moreover, the Vector Space Decomposition Fault Detection (VSDFD) method has been applied to detect open-circuit faults and used to select the proper post-fault operation. An experimental setup has been established in the laboratory to validate the proposed ideas. Finally, the actual machine parameters are measured and used to investigate the system performance via simulation and experimental results in both healthy and faulty conditions.

A Mission Profile-Based Reliability Modeling Framework for Fault-Tolerant Electric Propulsion

This article proposes a thermally enhanced reliability modeling framework which works from the mission profile of an electrified aviation propulsion system, incorporating known fault-tolerant power electronics, motor drives, control, and their pre and postfault behaviors. The reliability framework is presented in a hierarchical fashion. Multiphysics modeling is used, incorporating electromechanical states, power losses, and thermal behaviors. The approach includes the device thermal stress in healthy and postfault operating states in the failure rate calculations. Markov chain models are then used with the calculated failure rates to form system level reliability models. A case study of an electric vertical takeoff and landing urban aerial vehicle (eVTOL UAV) walks through the proposed method, modeling multiple versions of the propulsion system, with various levels of fault tolerance and redundancy. The proposed reliability modeling framework captures the operating temperatures and thermal swings seen by the components due to the flight mission, enhancing the failure rate calculation. Further, since the postfault operating mode of the fault tolerant system causes higher component currents and temperatures, different component failure rates are calculated for postfault operation. Finally, the Markov chain modeling allows for a reliability comparison between various UAV propulsion systems, including the effect of combining fault tolerance at the subsystem level, with redundancy at the system level.

Power Distribution Grid Reliability Assessment Considering Protection and Control Devices’ Optimal Post-Fault Operation

The reliability level of the distribution network is a judgment tool of the grid and protection design quality, the effectiveness of the fault management unit, and customers’ satisfaction. In this paper, a new approach is presented to evaluate common reliability indices namely ENS, SAIDI, SAIFI, MAIFIe, etc., while reliability improvement via optimal post-fault restoration describes the coordinated operation of various protection and control devices in temporary and permanent fault event conditions. Customers’ outage times are calculated considering different switching operation times to capture manual operation issues, e.g., traffic level, geographical issues, fuse replacements, etc. The optimal service restoration scheme being formulated in a mixed-integer linear programming (MILP) fashion is constrained to network technical limitations, e.g., line thermal capacity, load points voltage level, DG units’ parameters, and island operation. Performance of the proposed framework is verified in IEEE 33-bus test system.

Online Fault Diagnosis Method for Grid-Connected Inverters Based on Finite-Set Mixed Logical Dynamical Model Prediction

The grid-connected inverter is a key device in the renewable energy power generation system and large-scale energy storage system, which the operational stability and reliability are the basis for the efficient and safe application of electrical energy. A real-time fault diagnosis method of a three-phase for grid-connected application combining a mixed logic dynamic (MLD) model and finite control set model predictive control (FCS-MPC) is proposed. This paper not only realizes the open circuit fault diagnosis and location of the switching devices in the main power circuit, but also discusses the threshold issues and post-fault operations. The advantage of the proposed method is that it directly uses the control data and measurement signals of the controller without extra sensors and calculation, which will shorter the fault diagnosis time and occupy less calculation resource of the main processor. Simulation results illustrate the quickness of the fault identification and accurate position with robustness to the interference of the diagnosis method. Finally, the effectiveness of the diagnosis method was verified by a 1500W experimental prototype in a laboratory.

Connections Between System of System Sustainability and Resilience in an Electric Motor Manufacturing Supply Chain

Systems of Systems combine constituent systems (such as financial, transportation, energy, food, and water) to improve performance. System of Systems employment, however, often requires additional material and infrastructure investment. Due to their widespread use, it is essential that Systems of Systems are sustainable. One approach to increasing Systems of Systems sustainability is to increase its resilience (e.g. a less-resilient System of Systems would require additional resources to recover from a fault). The need for increased Systems of Systems resilience inspired our research question: How does SoS resilience change environmental impact during post-fault operation? To examine this research question, a model of an electric motor supply chain is examined. The supply chain architecture is divided into two parallel supply chains servicing four distribution centers. If supply to a distribution center is disrupted, the non-impacted supply chain can provide motors, but at a changed use-phase impact due to new shipping routes (e.g. further geographic distance). To answer our research question, each of the 14 constituents were disrupted one at a time, supply rerouting occurred as necessary, and the change in operational impact is reported (additional km of supply chain travel per week. This study provides key evidence that even if System of System infrastructure repair could occur without impact, changes in operational impact is an important factor for decision makers. Additionally, this paper provides case study evidence supporting the claim that improved resilience can improve System of Systems sustainability.

Open circuit fault-tolerant operation of 3-Φ multilevel inverter

A modified Fault-Tolerant (FT) structure is presented for the five-level Multi-Level Inverter (MLI) in this research work. A self capacitor voltage balancing control regulates the voltage across the capacitor by a half magnitude of the DC source value to produce a five-level output voltage waveform. Furthermore, the self capacitor voltage balancing control reduces complexity and enhances system reliability. A possible Open Circuit (OC) fault in the switches of the proposed structure is further analyzed. On the basis of a comparative analysis between the five-level MLI and the proposed faulttolerant structure, this structure is presented. When compared with the most recent FT topologies, it contains fewer devices. MATLAB/Simulink are used to study the proposed single-phase and three-phase FT structures under pre-fault, fault and post-fault operation.

Influence of the stator current reconstruction method on direct torque control of induction motor drive in current sensor postfault operation

Influence of the stator current reconstruction method on direct torque control of induction motor drive in current sensor postfault operation

Performance Analysis of Direct Torque Controllers in Five-Phase Electrical Drives

The industrial application of electric machines has grown in the last decades, thanks to the development of microprocessors and power converters, which have permitted their use as variable-speed drives. Although three-phase machines are the common trend, the interest of the research community has recently focused on machines with more than three phases, known as multiphase machines. The principal reason lies in the exploitation of their advantages in terms of reliability, i.e., post-fault operating capability. Additionally, multiphase machines provide a better current distribution among phases, and lower current harmonic production in the power converter, than conventional three-phase machines. However, multiphase drive applications require the development of complex controllers to regulate the torque (or speed) and flux of the machine. In this regard, direct torque controllers have appeared as a viable alternative due to their easy formulation and high flexibility to incorporate control objectives. However, these controllers face some peculiarities and limitations in their use that require attention. This work aims to tackle direct torque control as a viable alternative for the regulation of multiphase drives. Special attention will be paid to the development of the control technique and the expected benefits and limitations in the obtained results. Case examples based on symmetrical five-phase induction machines with distributed windings in the motoring mode of operation will be used to this end.

Real-Time Fault Detection to Ensure the Safe Operation of the Single-Phase Five-Level VIENNA Rectifier

This work aims to explore and evaluate the nonreversible AC/DC five-level structure from the point of view of its operational safety: high electrical security on internal destruction and continuity in operation. It only has low-voltage monotransistor cells (Si and SiC 600 V max) and is intrinsically tolerant to imperfection control and parasites, therefore naturally secure. The design and lab-test of fault monitoring and fault diagnosis with just one voltage sensor of a single-phase five-level VIENNA rectifier were proposed. This real-time diagnostic method allows for a safe stop or corrective control strategy based on the reconfiguration of the modulation. The reconstruction strategy allows for optimization of the current and voltage signals as well as power factor. A continuous post-fault operation can be achieved for critical applications. An experimental prototype 3 kW/230 VAC/800 VDC/32 kHz was created to validate the proposed fault diagnosis method and reconfiguration control method.

Operational strategy of nine‐phase induction machine under the open‐switch fault condition

Multiphase induction machines are getting more attention in industry and academia because of their advantages and need for electric vehicles as well as ship propulsion. In this case, more number of power electronics devices are required due to higher number of phases. Moreover, in comparison with electromechanical systems, the probability of failure in power electronic inverter switches will be high. A fault in a semiconductor switch, without any proper alleviating methods, may result in the failure of the entire drive. To improve the reliability of induction motor drives (IMD), there is a necessity to enhance the postfault operation of the inverters. In this article, the proposed nine-phase IMD incorporates simple mathematical equations and less circuit reconfigurations to work under conditions of open-switch fault in either a single switch or the inverter's entire leg. This enables the drive to achieve balanced steady-state operation with minimal deration in output power/torque under the fault conditions. In addition, alternative operational technique, which modulates the healthy phases of fault phase group with 50% duty ratio and minimal circuit reconfiguration, is discussed in this article. Moreover, all possible fault conditions and associated reconfiguration details of the drive are described in detail. To validate the proposed concepts, finite element method analysis is performed using ANSYS Maxwell, and experimentation is performed in the laboratory for both normal and fault conditions on nine-phase IMD.

Performance Analysis of Permanent Magnet Synchronous Machine due to Winding Failures

The paper describes winding failures in Permanent Magnet Synchronous Motor (PMSM) which are preferred in Electric Vehicles. Drive can be designed with fault tolerance to continue to operate under occurrence of faults. Winding insulation failure is responsible for some of the most serious faults. A method for detecting open circuit of winding, short circuit of winding or turn to turn short circuit in winding may result as a failure of winding insulation is presented. Further a technique for continued post-fault operation of the drive is discussed based upon mathematical model. The detection method operates in real time without the use of additional sensors and is sensitive enough to detect the presence of an air-gap between turns.

Applicability Analysis of Indices-Based Fault Detection Technique of Six-Phase Induction Motor

The multiphase induction motor is considered to be the promising alternative to the conventional three-phase induction motor, especially in safety-critical applications because of its inherent fault-tolerant feature. Therefore, the attention of many researchers has been paid to develop different techniques for detecting various fault types of multiphase induction motors, to securely switch the control mode of the multiphase drive system to its post-fault operation mode. Therefore, several fault detection methods have been researched and adapted; one of these methods is the indices-based fault detection technique. This technique was firstly introduced to detect open-phase fault of multiphase induction motors. The main advantage of this technique is that its mathematical formulation is straightforward and can easily be understood and implemented. In this paper, the study of the indices-based fault detection technique has been extended to test its applicability in detecting some other stator and rotor fault types of multiphase induction motors, namely, open-phase, open-switch, bad connection and broken rotor bar faults. Experimental and simulation validations of this technique are also introduced using a 1 kW prototype symmetrical six-phase induction motor.

Predictive current control of asymmetrical six-phase induction motor without weighting factors

Control of multi-phase machine in both healthy and post-fault operations has recently gained considerable interest. Finite control set model predictive control (FCS-MPC), in particular, has been proposed to drive multi-phase machines to avoid sophisticated pulse width modulation (PWM) methods. Nevertheless, FCS-MPC generally experiences some technical limitations. One of the widely reported challenges related to FCS-MPC is the weighting factor (WF) design, which is empirically designed and found to be an operating point dependent factor. Thus, assuming a constant WF can result in poor performance. In this paper, the prediction stage of FCS-MPC for asymmetrical six-phase (A6P) induction motor (IM) has been reformulated based on double dq (2dq) modeling approach. Unlike the reported vector space decomposing (VSD)-based FCS-MPC algorithms, the proposed approach results in four control variables (the stator sequence currents isα1,isβ1,isα2, and isβ2) which have the same priority. Thus, equal weighting factors could be used in the cost function, which will inherently minimize the effect of the circulating x-y current components. Performance comparison of the proposed method against VSD-based FCS-MPC is investigated. The theoretical findings are experimentally validated using a 1 kW prototype six-phase IM.

Space Harmonics and Saturation Interaction in Fault-Tolerant Induction Machine Drives Due to a Zero-Sequence Stator Current

Postfault operation strategies for three-phase squirrel cage induction machine drives enable increased fault-tolerance in the case of inverter faults. However, in strategies that apply a zero-sequence stator current, additional space harmonics interact with the fundamental wave. This article studies these space harmonics and the occurring saturation interaction with the main system based on two different induction machines. For illustration, and to support the analysis with quantitative results, it exemplarily investigates the effects of this saturation interaction on the flux linkages and the torque during the postfault operation of a rotor flux-oriented drive.

A Circuit Topology of Cascaded H-Bridge STATCOM to Operate With Multiple Faulty Bypassed Cells

In the present work, a circuit topology of cascaded H-bridge (CHB) converter for static synchronous compensator (STATCOM) application is proposed, which can operate with multiple faulty bypassed cells. The topology uses one redundant three-phase cell connected in series with the CHB converter. After the faulty cells are bypassed in CHB, the redundant cell is inserted into the power circuit of the CHB. The aim of the proposed topology is to tolerate multiple faulty bypassed cells in a single leg or multiple legs of the CHB converter and maintain prefault rated line voltage and reactive power capability of the converter during postfault conditions. A novel geometrical approach is proposed for output voltage generation for the healthy cells and the redundant cell during postfault operation, which ensures that the capacitor voltages are balanced for all the remaining healthy cells in CHB and the redundant cell. Additionally, the voltage stress on the remaining healthy cells does not increase during postfault condition. The proposed fault tolerant topology of CHB STATCOM is verified for single and multiple faulty bypassed cells using simulation and a downscaled experimental prototype.