Fault Tolerance in Direct Torque Control with Virtual Voltage Vectors

[EN] Reliability is considered a fundamental requirement of some variable-speed electric drives. Therefore, multiphase systems, which introduce a higher fault tolerance than conventional three-phase ones, turn out to be an interesting alternative for these applications. This high fault-tolerant capability is obtained thanks to the higher number of freedom degrees. This paper presents a direct torque control strategy based on virtual voltage vectors when an open phase fault appears in a six-phase induction machine. These virtual voltage vectors reduce the copper losses due to x-y current components. Experimental tests have been provided to validate the control strategy.[ES] La fiabilidad es considerada una característica fundamental en algunos accionamientos eléctricos de velocidad variable. Es por ello que los sistemas multifásicos, que presentan una mayor tolerancia al fallo que los sistemas trifásicos convencionales, resultan una alternativa interesante para este tipo de aplicaciones. Esta mayor tolerancia al fallo es debida a su mayor número de grados de libertad, lo que se traduce en un aumento de su fiabilidad. En este artículo se presenta la aplicación de un control directo de par basado en vectores virtuales de tensión para una máquina de inducción de seis fases, considerando un fallo de fase abierta. La introducción de estos vectores virtuales permite reducir las pérdidas en el cobre debido a la reducción de las componentes x-y de corriente propias de los sistemas multifásicos. La implementación de la estrategia de control propuesta va a permitir tanto un incremento de la fiabilidad del accionamiento eléctrico como la disminución de las pérdidas debidas a las citadas componentes x-y. La bondad del método propuesto ha sido validada mediante resultados experimentales.García Entrambasaguas, P.; González-Prieto, I.; Durán, M.; Bermúdez, M.; Barrero, F. (2018). Tolerancia al Fallo en Control Directo de Par con Vectores Virtuales de Tensión. Revista Iberoamericana de Automática e Informática. 16(1):56-65. doi:10.4995/riai.2018.9288SWORD566516

Analysis and Fault-Tolerant Control for Dual-Three-Phase PMSM Based on Virtual Healthy Model

Dual-three-phase permanent magnet synchronous machines (DTP-PMSMs) are famous for their fault-tolerant capability. However, the complex modeling, high copper loss, and torque ripple under postfault operation limit their further application. In this article, a fault-tolerant control (FTC) strategy is developed for DTP-PMSMs under the open-phase fault (OPF) with straightforward modeling and smooth output torque. The virtual healthy DTP-PMSM model, where the coordinate transformation, the modulation strategy, and the controller structure remain unchanged under OPF, is adopted in the proposed FTC scheme. And the current references are derived in sinusoidal waves with minimum copper loss. The inaccurate transmission of control signals under OPF is also focused on. Comprehensive theoretical analysis shows the relationship between the controller output voltage and the actual stator voltage should be considered in the proposed FTC strategy; otherwise, distortion in torque and current will be introduced. The voltage compensation is utilized to compensate for the voltage difference and ensure the smooth torque output. Besides, a quasi proportional resonance controller is designed to further suppress the residual torque ripple. The proposed strategy will not induce complex implementation and heavy computation burden. The simulation and experimental results prove the analysis and the effectiveness of the proposed strategy

Comprehensive Diagnosis and Tolerance Strategies for Electrical Faults and Sensor Faults in Dual Three-Phase PMSM Drives

IEEE In this paper, fault diagnosis and tolerant control strategies have been studied comprehensively for dual-three phase PMSM drives to improve the reliability. Based on direct torque control (DTC) with space vector modulation (SVM), a series of diagnostic and tolerant control methods have been proposed for five types of faults, namely speed-sensor fault, DC-link voltage-sensor fault, current-sensor fault, open-phase fault and open-switch fault. Firstly, diagnosis and tolerant schemes are proposed for speed-sensor fault by estimating the rotor angle speed with the rotating speed of stator flux. Secondly, diagnosis and tolerant schemes are proposed for DC-link voltage-sensor fault by combining the current model based stator flux observer with the voltage model based stator flux observer. Thirdly, a three-step method is designed to diagnose three types of faults related to current signals, namely current-sensor fault, open-phase fault and open-switch fault simultaneously. A vector space decomposition (VSD) based current estimation method is proposed to achieve fault-tolerant control for the current-sensor fault, and the voltage compensation based fault-tolerant control is presented for both open-phase fault and open-switch fault. The experiments have been taken on a laboratory prototype to verify the effectiveness of the proposed fault diagnosis and tolerance schemes

Extended Kalman filter based sliding mode control of parallel-connected two five-phase PMSM drive system

This paper presents sliding mode control of sensor-less parallel-connected two five-phase permanent magnet synchronous machines (PMSMs) fed by a single five-leg inverter. For both machines, the rotor speeds and rotor positions as well as load torques are estimated by using Extended Kalman Filter (EKF) scheme. Fully decoupled control of both machines is possible via an appropriate phase transposition while connecting the stator windings parallel and employing proposed speed sensor-less method. In the resulting parallel-connected two-machine drive, the independent control of each machine in the group is achieved by controlling the stator currents and speed of each machine under vector control consideration. The effectiveness of the proposed Extended Kalman Filter in conjunction with the sliding mode control is confirmed through application of different load torques for wide speed range operation. Comparison between sliding mode control and PI control of the proposed two-motor drive is provided. The speed response shows a short rise time, an overshoot during reverse operation and settling times is 0.075 s when PI control is used. The speed response obtained by SMC is without overshoot and follows its reference and settling time is 0.028 s. Simulation results confirm that, in transient periods, sliding mode controller remarkably outperforms its counterpart PI controller

Analysis and Reduction of Current and Voltage Ripple in DC-Link for Three-Level NPC Inverter-Fed Dual Three-Phase Motor Drives

In this paper, switching strategies for DC-link current and voltage ripple reduction have been studied. Considered topology is a neutral-point clamped three-level (NPC-3L) inverter feeding a dual three-phase permanent-magnet synchronous motor (PMSM). The mechanisms of DC-link current and voltage ripple generation in NPC-3L inverter-fed PMSM drive are analysed in detail. Then, a two-step collaborative switching strategy is proposed, where the optimum switching sequences, including opposite small vectors, are applied in the two inverters collaboratively. Furthermore, the switching vectors of two inverters are rearranged in the sequence of their corresponding DC-link capacitor currents so that the overlapping of their peaks is avoided. Consequently, both the voltage ripple and current ripple in the DC-link capacitors are mitigated with the proposed two-step collaborative switching strategy. For the mid-point voltage of the NPC-3L inverter, the amplitude of fluctuation is reduced under low modulation index operation, while the high-frequency harmonic components are mitigated under high modulation index operation. The experimental results are given to verify the validity of the theoretical analysis and the proposed switching strategy

Modelling, Diagnosis, and Fault-Tolerant Control of Open-Circuit Faults in Three-Phase Two-Level PMSM Drives

Attributing to the high efficiency, compact structure, and rapid dynamics, powertrains utilizing Permanent Magnet Synchronous Motors (PMSM) have emerged as a promising alternative and have seen extensive deployment in various industrial and transportation sectors, including electric vehicles (EVs), more-electric aircraft, and robotics. Despite ongoing interest in advanced redundant topologies for PMSM drives from both academia and industry, the three-phase two-level (3P2L) PMSM drive continues to dominate the majority of the electric drive market. However, when compared to its multi-phase counterparts, the most-commonly used 3P2L PMSM drive exhibits limited reliability and fault tolerance capabilities, particularly in safety-critical or cost-sensitive scenarios. Therefore, the development of embedded reliability-enhancing techniques holds great significance in enhancing the safety and maintenance of on-site powertrains based on the 3P2L PMSM drive. The purposes of this study are to investigate post-fault system models and develop hardwarefree fault diagnostic and fault-tolerant methods that can be conveniently integrated into existing 3P2L PMSM drives. Special attention is dedicated to the open-circuit fault, as it represents one of the ultimate consequences of fault propagation in PMSM drives. In the first place, the fault propagation from component failures to open-circuit faults is analyzed, and the existing literature on the modelling, diagnosis, and fault-tolerant control of PMSM drives is comprehensively reviewed. Subsequently, the study delves into the postfault system model under the open-phase (OP) fault, which includes the examination of postfault phase voltages and current prediction. Based on the phase voltages observed under the OP fault, a phenomenon of particular interest is modelled: the remaining current that flows through the free-wheeling diodes of the faulty phase under the open-switch (OS) fault. The conduction mechanism is elucidated, and a real-time estimation model is established. Furthermore, a sampling method is designed to enable the motor drive to detect the remaining current in the OS phase, along with a set of diagnostic rules to distinguish between OS and OP faults. Finally, an embedded fault-tolerant control method is introduced to enhance the post-fault speed and torque outputs of 3P2L PMSM drives