Open-phase Fault Research Articles

General Online Current-Harmonic Generation for Increased Torque Capability With Minimum Stator Copper Loss in Fault-Tolerant Multiphase Induction Motor Drives

This paper proposes a current-reference generation method including current harmonic injection (CHI) for enhancing the torque capability of multiphase induction machines (IMs) with negligible space-harmonic effects, which is useful, e.g., during transient overload in electric vehicles. The admissible torque is increased because the harmonics reduce the phase-current peaks, so that the instantaneous peak-current constraint of the drive, usually associated with the converter ratings, is respected. The harmonics are injected in the so-called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x-y</i> subspaces of the IM, which do not produce torque, so that no torque ripple is introduced. The optimum harmonics are found online for each load, making it possible to minimize the stator copper loss (SCL) per torque in the entire torque range, ensuring full-range minimum loss (FRML). The method is suitable for healthy operation or open-phase faults, and for multiphase machines of any phase number and with either symmetrical or asymmetrical windings. Compared with FRML methods without CHI, higher torque is achieved. Although some techniques were available for increasing the torque capability by CHI, FRML was not attained, laborious offline optimization was needed, or they were only suitable for specific drives or for healthy conditions, unlike the proposal. Experimental results with a symmetrical six-phase IM are provided.

Design and Analysis of Universal Natural Fault-Tolerant SVPWM Strategy With Simplified Fault Diagnosis for Multiphase Motor Drives

Conventional space vector pulse width modulation (SVPWM) would degrade the operating performance of the multiphase motor drives under open-phase fault. To resolve this issue, existing solutions require the reconfiguration of transformation matrices. However, for the variable positions of faulty phases, the structure of matrices needs to be redefined, which is a restraint to the industrial implementation of such technologies. This study examined the offset of the voltage vectors after fault occurrence. Accordingly, a universal fault-tolerant SVPWM strategy is proposed for the purpose of natural fault-tolerance, as well as a simplified fault detection scheme. Compared with conventional fault-tolerant SVPWM, it is highlighted with the characteristics of minimum reconfiguration, torque-ripple free operation, and applicability to handle various types of open-phase faults using a single transformation matrix. Besides, proposed strategy eliminates the redundant controllers and also reduces the degree of difficulty for fault diagnosis. Finally, the effectiveness of proposed approach is evaluated experimentally with a seven-phase induction machine, which shows that the torque ripple could be reduced by about 40% in the presence of multiple faults compared to the conventional SVPWM strategy.

Open-Phase Fault Research on the Parallel-Connected 40-Pulse Rectifier With Multioutput Auto-Connected Phase-Shifting Transformer

In order to improve the normal operation power quality, the DC side harmonic reduction circuit (HRC) has been extended to the multi-pulse rectifiers (MPRs) based on five-phase bridge rectifier. The power quality under fault conditions is also an important aspect that affects the overall reliability of the rectifier system. This paper is focused on the open-phase fault research on the passive MPRs with auto-connected phase-shifting transformer. The parallel-connected 40-pulse rectifier based on the five-phase bridge rectifier is selected as the main research circuit. Under the primary or secondary side open-phase faults, the operation modes of the main circuit and the HRC are discussed. Based on the waveform information, the relations between the fault characteristics and the fault types are established, which is useful for fault detection. Under the primary side open-phase fault, the current proportions of the two parallel-connected bridge rectifiers are calculated. In comparisons with the 24-pulse rectifier, the quantitative relationship between the increase of phase number and the improvement of fault power quality is clarified. Based on the research methods and conclusions presented in this paper, the structure of the MPR can be designed that fulfills the specific power quality standard under fault cases or reserves a certain safety margin to reduce the damage to the rectifier system and the AC grid.

A New Post-Fault Reconfiguration Strategy under Open-Phase Operation Conditions of Asymmetrical Double-Star Induction Machines

The fault tolerance proprieties of multiphase induction machines make them candidate technologies for future electrified transport systems. Indeed, the use of multiphase drives is primarily recommended for their redundancy, which allows them to handle increasing power demands as well as provide fault-tolerant operation. One of the most common failures in polyphase induction machines is open-phase fault (OPF). Under this degraded mode, machine performance deteriorates with increased torque ripples and copper losses. This work investigates the fault-tolerant operation of dual star induction machines (DSIM) with two connected neutral points in which a new post-fault operation technique is introduced to manage the OPFs. The machine was modeled on the natural reference frame, and no transformations were used. The phase opening is caused by inserting a high-value resistor in series with the faulty phase, which cancels the current flowing in the latter. A post-fault reconfiguration strategy that reorganizes the power converter in order to cancel torque ripples by exploiting the principle of multi-biphase modeling of the DSIM is proposed. The performance of the proposed reconfiguration strategy was verified through detailed simulation results.

Experimental Validation of Different Control Techniques Applied to a Five-Phase Open-End Winding Induction Motor

Open-end winding five-phase induction motor (OeW-5PIM) configuration is used in industrial applications, where minimization in the total harmonic currents and high reliability are needed. The majority of the literature on OeW-5PIM topology discusses field-oriented control and direct torque control in addition to other robust control techniques such as the backstepping approach. This paper focuses on the mathematical and experimental approaches of backstepping control (BSC) and rotor-flux-oriented control (RFOC) for an OeW-5PIM topology. The space vector pulse width modulation (SVPWM) strategy is associated with the suggested control techniques to improve the dynamic performance (i.e., reducing ripple, fixed switching frequency, etc.) of the studied motor. Furthermore, the RFOC-SVPWM and BSC-SVPWM are comprehensively compared using experimental implementation under various situations such as load torque, open-phase fault, and high/low-speed operation.

Modulated Model Predictive Torque Control for Fault-Tolerant Inverter-Fed Induction Motor Drives With Single DC-Link Voltage Sensor

Four-switch three-phase inverter (FSTPI) is widely used as a cost-effective fault-tolerant topology of six-switch three-phase inverter with an open-phase fault. To solve the inherent dc-link capacitor voltage offset (CVO) issue of FSTPI, two dc-link capacitor voltage sensors are required in conventional model predictive torque control (MPTC) strategies. To improve the reliability and reduce the cost of induction motor (IM) drives, a modulated MPTC (M-MPTC) for FSTPI-fed IM with single dc-link voltage sensor is proposed in this article. Therein, the relationship of the CVO and the load current is established to obtain the fundamental component of CVO. The two capacitor voltages are reconstructed by single dc-link voltage sensor and the fundamental component of CVO. To suppress the CVO, a cost function that only contains the output voltage vector is designed. The inner relationship between the proposed M-MPTC with single dc-link voltage sensor and the conventional M-MPTC with two dc-link voltage sensors is derived. To retain the load current within the allowed range, a current constraint scheme is proposed and integrated into the M-MPTC. Various simulation and experimental studies are carried out to verify the effectiveness of the proposed strategy.

A Novel Two-Mode Inverter-Based Open-Winding PMSM Drive and Its Modulation Strategies

A novel two-mode inverter based open-winding permanent magnet synchronous motor (OW-PMSM) drive is proposed in this article. The proposed drive operates in hybrid-inverter mode at low and medium speed to achieve high power quality. The common-DC-bus mode is adopted at high speed to fulfill a wider speed range than hybrid-inverter mode. Based on the proposed drive, a modulation strategy for any voltage ratio is proposed, which integrates the instantaneous floating capacitor (FC) voltage into modulation to synthesize the reference voltage vector. The proposed modulation strategy can not only guarantee the FC voltage regulation but also start the drive when the FC voltage is zero and switch the mode of the drive smoothly. Besides, the excellent fault-tolerant capability of the proposed drive is studied under open-phase and switch faults. In the proposed fault-tolerant control, a sinusoidal zero-sequence current is injected to tolerate the open-phase fault in the common-DC-bus mode and redundant switching combinations are used to tolerate switch faults in the hybrid-inverter mode. All the claimed advantages have been validated by experimental results.

DC-Signal Injection for Stator-Resistance Estimation in Symmetrical Six-Phase Induction Motors Under Open-Phase Fault

Multiphase machines are often chosen due to their enhanced fault tolerance. Six-phase ones are especially convenient because they may be fed by off-the-shelf three-phase converters. In particular, those with symmetrical windings offer superior postfault capabilities. On the other hand, estimation of the stator resistance is important for purposes such as thermal monitoring and preserving control performance. Resistance estimation by dc-signal injection provides low sensitivity to parameter deviations compared with other techniques. It has previously been shown that the dc signal can be added in the non-torque-producing (<inline-formula><tex-math notation="LaTeX">$x$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$y$</tex-math></inline-formula>) plane of a six-phase machine to avoid the torque disturbances that typically arise in three-phase machines. However, extending this method to the case of an open-phase fault (OPF) is not straightforward, because of the associated current restrictions. This paper addresses dc-signal injection in a symmetrical six-phase induction motor with an OPF. It is shown that, in contrast to healthy operation, the postfault dc injection should be carefully performed so that minimum copper loss, peak phase current and zero-sequence braking torque are achieved. A solution that attains optimum performance in all these aspects simultaneously is proposed. Adapted controller and resistance estimation are also presented. Experimental results confirm the theory.

Fault-tolerant switched reluctance motor propulsion system for eVTOLs

eVTOLs are receiving a lot of attention as a potential solution to urban air mobility challenges. Many configurations are multirotors, which are open loop unstable, therefore very susceptible to actuator failures. Due to their usually short mission duration (20-30 min), fault-tolerance of the propulsion system is of greater importance then reliability. Thus, novel approaches to enhance this capability are required. This study proposes a new fault-tolerant propulsion system using 4-phase switched reluctance motors. It is designed for an 8-10 kg scale multirotor eVTOL, to replace redundant coaxial brushless DC motors with a single fault-tolerant drive. Acknowledging the role of fault-tolerant control algorithms, the propulsion system is validated in terms of the loss of effectiveness metric, typically used in the evaluation of control solutions. The switched reluctance motor propulsion system was found to be highly resilient to open phase and current sensor faults, but susceptible to position sensor faults. This can, however, be mitigated with sensorless control solution. Extending the findings to full-scale eVTOLs is also discussed.

A Novel Square-Wave Voltage Injection Based Sensorless Control Method Robust to Single Open-Phase Fault for Dual Three-Phase IPM

The sensorless control for dual three-phase motors (DTMs) under faulty conditions are insufficiently studied in previous research. This research aims to investigate the effects of single open-phase faults (SOFs) on the high-frequency (HF) injection (HFI)-based sensorless control for a DTM and present a new sensorless control method robust to the SOFs. Firstly, the HFI-based sensorless control is introduced into the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">αβ</i> -subspace, where responded HF currents can reflect changes of two sets of three-phase windings simultaneously. Next, an HF fault analysis method is given to simplify the analysis process by making the inductance matrixes in the HF models unchanged under healthy and faulty conditions. Besides, an equivalent coordination method is proposed to extend the result under the phase-A SOF to an arbitrary SOF, avoiding repetitive derivation and obtaining a generalized conclusion directly. The SOFs cause the negative sequence components and varying amplitudes in the HF currents, resulting in large rotor position estimation errors. Then, a new rotor position estimation method based on a modified adaptive filter is presented to suppress these effects, which is robust to the SOFs without any fault diagnosis. The validity of the proposed analysis methods and sensorless control methods are all verified on a prototyped DTM.

A simple fault-tolerant control method for open-phase three-phase induction motor drives

Fault-Tolerant Control (FTC) strategies for Three-Phase Induction Motors (TPIMs) against an open-phase fault have attracted considerable interest in safety-critical applications. In the available literature, open-phase FTC methods for TPIMs are typically implemented using suitable Current Transformation (CT) and Voltage Transformation (VT) matrices. However, the controller design becomes complicated due to different transformations. In addition, the model based on CT and VT suffers from slow dynamics due to several Proportional–Integral (PI) controllers. This paper proposes an open-phase FTC technique for TPIM drives with proof of its asymptotic stability. It is designed based on a new CT for stator current components. Using this CT, the traditional vector control method can be used for Open-Phase TPIMs (OPTPIMs). Furthermore, considering that parameters of the PI controller have an important effect on the OPTPIM drive performance, a design technique is presented to achieve the best values of PI controller parameters. Additionally, an open-phase fault detection technique is presented based on the third-difference operator. The proposed FTC has a simple structure and fast dynamic responses. Matlab simulation and experimental results using DSP/TMS320F28335 approve the ability and good performance of the introduced FTC technique for TPIM drive systems under different conditions.

Open-Phase Fault-Tolerant DTC Technique for Three-Level NPC VSI-Fed Five-Phase Induction Motor Drives

The demand for motor drives based on multiphase machines (MMs) is increasing due to their inherent fault-tolerant capabilities. To achieve satisfactory post-fault operation, a proper fault-tolerant controller is needed. Some direct-torque-control (DTC) techniques have been reported for five-phase induction motor (FPIM) drives under an open-phase fault (OPF). DTC offers simplicity, fast response, and less parameter sensitivity. However, the existing fault-tolerant DTC methods were designed for two-level voltage-source inverters (VSIs). A three-level neutral-point-clamped (NPC) VSI allows greater flexibility in the switching states, lower current and torque ripple, and reduced common-mode voltage (CMV). However, the increased number of switching states requires the design of new DTC methods, able to tolerate OPFs while providing satisfactory performance in various aspects. In this article, two fault-tolerant DTC techniques are developed for three-level NPC VSI-fed FPIM drives under an OPF. The possible switching states are synthesized with suitable virtual vectors (VVs), addressing the dc-link voltage balance, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {d}v/\text {d}t}$ </tex-math></inline-formula> , CMV, and dc-link utilization. The two methods are compared under an OPF in these terms, as well as regarding the average switching frequency. Comparative experimental results are provided to assess the viability of the developed DTC schemes at steady-state and dynamic conditions.

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.

Optimization-Based Maximum-Torque Fault-Tolerant Control of Dual Three-Phase PMSM Drives Under Open-Phase Fault

In this article, a novel optimization-based maximum-torque fault-tolerant control scheme is proposed for the open-phase fault of dual three-phase permanent-magnet synchronous motor drive. First, the relationship between torque output capability and single-phase copper losses under open-phase fault is derived with the consideration of overheating problems. Since the derived expression has multiple optimization goals, a new objective function is designed to simplify the current optimization. Second, particle swarm optimization (PSO) is utilized to obtain the maximum-torque current references based on the designed objective function. Different from the conventional maximum-torque fault-tolerant schemes which limit the current patterns, the proposed fault-tolerant control scheme employs PSO to search for the global optimal result without adding any unnecessary restrictions, such as sinusoidal current patterns. In this way, the proposed fault-tolerant control scheme can achieve the theoretical highest torque output capability of 73.3% with lower total copper loss. Both the theoretical and experimental results are presented to prove the effectiveness and superiority of the proposed optimization-based maximum-torque fault-tolerant control scheme.

A Three-Phase Nonisolated Pseudo-Six-Phase-Based Integrated Onboard Battery Charger for Electric Vehicles

The trending modern designs of electric vehicle (EV) motors are concerned with maximizing the machine torque density while offering a fault tolerance capability. Among different available stator winding layouts, the so-called pseudo-six-phase (P6P) winding has recently been proposed, which offers an improved torque density and fault tolerance over conventional six-phase distributed winding. An integrated onboard battery charger (IOBC) has also been proposed as a new leading technology that employs the propulsion components of the EV in the charging process to achieve the highest possible charging current with zero machine torque production. In this context, this article proposes a new P6P-based IOBC system. Two different controllers have been investigated, namely, conventional proportional–resonant (PR)-based current control and predictive current control (PCC) techniques. Under the charging mode, the control objectives aim at achieving a balanced three-phase grid current while nullifying machine torque production. To this end, the sequence stator currents are regulated to ensure a balanced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${xy}$ </tex-math></inline-formula> current, while both the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\alpha \beta }$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${ {0}}^{ {+}}{ {0}}^{ {-}}$ </tex-math></inline-formula> current components are controlled to zero. Furthermore, a novel postfault controller using a PR-based current controller has been proposed, which ensures balanced grid line currents under one open-phase fault. A comparative experimental study has been carried out under different controllers for both vehicle-to-grid (V2G) and grid-to-vehicle (G2V) modes using a 2-hp prototype machine.

Encoderless Five-phase PMa-SynRM Drive System Based on Robust Torque-speed Estimator with Super-twisting Sliding Mode Control

In this paper, a robust torque speed estimator (RTSE) for linear parameter changing (LPC) system is proposed and designed for an encoderless five-phase permanent magnet assisted synchronous reluctance motor (5-phase PMa-SynRM). This estimator is utilized for estimating the rotor speed and the load torque as well as can solve the speed sensor fault problem, as the feedback speed information is obtained directly from the virtual sensor. In addition, this technique is able to enhance the 5-phase PMa-SynRM performance by estimating the load torque for the real time compensation. The stability analysis of the proposed estimator is performed via Schur complement along with Lyapunov analysis. Furthermore, for improving the 5-phase PMa-SynRM performance, five super-twisting sliding mode controllers (ST-SMCs) are employed with providing a robust response without the impacts of high chattering problem. A super-twisting sliding mode speed controller (ST-SMSC) is employed for controlling the PMa-SynRM rotor speed, and four super-twisting sliding mode current controllers (ST-SMCCs) are employed for controlling the 5-phase PMa-SynRM currents. The stability analysis and the experimental results indicate the effectiveness along with feasibility of the proposed RTSE and the ST-SMSC with ST-SMCCs approach for a 750-W 5-phase PMa-SynRM under load disturbance, parameters variations, single open-phase fault, and adjacent two-phase open circuit fault conditions.

A Method Based on Phase-shifting Carrier for Reducing DC-link Current Harmonics in Dual Three-phase PMSM Drive under Open-phase Conditions

The All-Electric of modern military equipment has become an important trend, in the field of aircraft the traditional servo control focus on the exact control of the motor. With the development of power electronics technology, a high-power motor has expanded into a multiphase kind which cast off the limitation of traditional three-phase motors. The multiphase motor has more control resources and fault-tolerant control ability under the fault condition, which has practical meaning for high safety and high-reliability applications in an airborne environment. The multiphase motor can be controlled by a series of phase-shift carriers, which can reduce DC current ripple more effectively than the traditional carrier-based pulse width modulation, but it needs to find the optimal phase shift angle. In this paper, the optimal carrier phase shift angle is analyzed mathematically which can be used for both under health and single open-phase fault of a dual three-phase motor, and the simulation result illustrates that the carrier phase shift method used in this paper has the DC current ripple optimization effect.

Adaptive Fault-Tolerant Control for Open-Circuit Faults in Dual Three-Phase PMSM Drives

The traditional fault-tolerant procedure usually comprises fault detection and fault tolerance. Fault detection is adopted to locate the specific fault, which increases the complexity and misdiagnosis risk of fault-tolerant systems. This article introduced an adaptive fault-tolerant control for open-phase faults and open-switch faults in dual three-phase permanent magnetic synchronous machine (PMSM) drives. The proposed fault-tolerant scheme is fulfilled by going through three operation states: healthy operation, transient <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> open-loop faulty operation, and fault-tolerant operation. The angle of fault-tolerant reference currents on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> plane is obtained from the transient <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> open-loop faulty operation. Unified fault-tolerant reference currents of open-circuit faults are built up by using the above reference angle. After the open-circuit faults occur, the unified fault-tolerant reference currents are directly applied to the drive system without fault localization. Experimental results demonstrate a very smooth switching capability of the developed adaptive fault-tolerant control from the faulty operation to the fault-tolerant operation without extra hardware.

Application of a Model-Based Method to the Online Detection of Rotating Rectifier Faults in Brushless Synchronous Machines

Converters are one of the most sensible components of any power conversion system when it comes to electrical faults. Moreover, if these converters are used in a rotating system, as is the case with rotating rectifiers used in brushless synchronous machines, apart from also being exposed to mechanical effects and thus having a greater likelihood of failure, no access is available directly, causing a lack of available measurements for condition monitoring. This paper applies a model-based method to the online detection of open-diode faults, shorted-diode faults and exciter open-phase faults in the rotating rectifiers of brushless synchronous machines. The applied method relies on the comparison between the measured and the theoretical exciter field currents, the latter computed through a healthy machine model from the machine actual output values. The proposed protection strategy stands out for its computational simplicity and its non-invasiveness, which makes its industrial application straightforward without the need of any further equipment or adaptation. Its applicability has been verified through a double approach, on the one hand, through computer simulations, and, on the other hand, through experimental tests, achieving satisfactory results. The research conducted proves that with the proposed method, given reasonable measurement and model estimation typical errors of less than 5%, positive differences between the measured and the theoretical exciter field currents of more than 13%, 200% and 30% for open-diode faults, shorted-diode faults and exciter open-phase faults, respectively, are detectable with at least a 95% confidence interval.