Multiphase Machines and Drives-Revisited

Although the concept of a multiphase drive system dates back to the middle of the 20th century, the initial pace of development was rather slow, as witnessed by the first two surveys of the area published in the beginning of this century. However, considerably new developments have resulted in the last decade of the 20th century and the beginning of this century, leading to an authoritative survey of the asymmetrical six-phase drive control and subsequently of the review of the complete area. This also initiated the organization and subsequent publication of the first IEEE Transactions on Industrial Electronics "Special Section on Multiphase Machines and Drives" in May 2008, which commenced with another survey paper, and that contained 12 original research papers. Since the publication of this Special Section in May 2008, the level of interest and pace of developments in the area have further accelerated and substantial new knowledge has been generatedwith an ever-increasing number of published research papers and reported new industrial applications. Such a trend has been emphasized in a recent paper. It therefore seemed appropriate to revisit the area and organize this Special Section as a sequel to the first one. The call for the Special Section papers resulted in 51 submissions, almost twice as many as the total back in 2008, thus confirming a substantial growth of the area. Indeed, the amount of new knowledge acquired since the publication of the first Special Section in 2008 has meant that it was not possible to provide a complete and thorough survey of the field in a single review paper

Assessment of a Universal Reconfiguration-less Control Approach in Open-Phase Fault Operation for Multiphase Drives

Multiphase drives have been important in particular industry applications where reliability is a desired goal. The main reason for this is their inherent fault tolerance. Di erent nonlinear controllers that do not include modulation stages, like direct torque control (DTC) or model-based predictive control (MPC), have been used in recent times to govern these complex systems, including mandatory control reconfiguration to guarantee the fault tolerance characteristic. A new reconfiguration-less approach based on virtual voltage vectors (VVs) was recently proposed for MPC, providing a natural healthy and faulty closed-loop regulation of a particular asymmetrical six-phase drive. This work validates the interest in the reconfiguration-less approach for direct controllers and multiphase drives

Multiphase Current Imbalance Localization Method Applied to Natural Fault- Tolerant Strategies

Multiphase machines are interesting options for high-reliability applications due to their inherent fault tolerance against open-circuit faults (OCFs). Moreover, if the regulation of the x-y currents is realized in open-loop mode using virtual voltage vectors (VVs), the mandatory post-fault control reconfiguration is avoided. The new reconfiguration-less approach was recently defined as a natural/passive fault-tolerant strategy, offering good prospects for industry applications. This work extends the idea to the fault detection (FD) procedure and suggests new settings for the current imbalance localization (CIL) method. The proposal is based on the vector space decomposition (VSD) approach that allows the joint detection of OCFs and stator resistances dissymmetry (RDs). Experimental results in a five-phase induction motor (IM) drive using VVs confirm the viability of the technique

Current Imbalance Detection Method based on Vector Space Decomposition Approach for Five-Phase Induction Motor Drives

The inherent fault-tolerant capability against open-phase faults (OPFs) of multiphase machines is an appreciated advantage in applications where high-reliability is a main concern. This desirable feature has usually required fault localization and post-fault control reconfiguration to provide a suitable performance in this anomaly situation. However, recent model predictive control (MPC) based on virtual voltage vectors (VVs) has validated the multiphase machine fault-tolerant capability without post-fault control reconfiguration. This fact allows to relax some of the OPF detection methods requirements. On the other hand, incipient faults or damaged connections can generate resistance dissymmetry (RD) situations that produces overheating and control degradation. Although the origin of OPFs and RDs can be of a different nature, the symptoms of both anomalies are common: a current imbalance that generates non-null x-y currents appears. Focusing on this approach, this work suggests new settings for an OPF detection method based on the vector space decomposition (VSD) in order to make it universally valid both in OPF and RD situations. The proposed current imbalance detection (CID) method is implemented together with a natural fault-tolerant direct torque control (DTC) for five-phase induction motor drives. Experimental results are employed to verify the goodness of the proposed method.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Model predictive control of six-phase induction motor drives using virtual voltage vectors

The most serious and recent competitor to the standard field oriented control for induction motors (IM) is the finite control set model predictive control (FCS-MPC). Nevertheless, the extension to multiphase drives faces the impossibility to simultaneously regulate the flux/torque and the secondary current components (typically termed x − y in the literature). The application of a single switching state during the whole sampling period inevitably implies the appearance of x − y voltage/currents that increase the system losses and deteriorate the power quality. These circulating currents become intolerably high as per the unit x − y impedance and the switching frequency diminish. Aiming to overcome this limitation, this work suggests the integration of virtual voltage vectors (VVs) into the FCS-MPC structure. The VVs ensure null x − y voltages on average during the sampling period and the MPC approach selects the most suitable VV to fulfill the flux/torque requirements. The experimental results for a six-phase case study compare the standard FCS-MPC with the suggested method, confirming that the VV-based MPC maintains the flux/torque regulation and successfully improves the power quality and efficiency

Fault-tolerant control of six-phase induction motor drives with variable current injection

Three-phase machines are the industry standard for electrical drives, but the inherent fault tolerance of multiphase machines makes them an attractive alternative in applications requiring high reliability. For this reason, different fault-tolerant control schemes for multiphase drives have been recently suggested, proving their capability to perform a ripple-free operation after an open-circuit fault occurrence. Nevertheless, the postfault strategies proposed so far consider a single mode of operation and do not allow a high-performance braking process in drives with unidirectional power flow where regenerative braking is not possible. This paper first explores the possibility of enhancing the braking process by using a proper injection of circulating currents that prevent the active power to reach the dc-link capacitor. This novel strategy is then combined with minimum losses and maximum torque criteria to obtain a variable current injection method that minimizes the drive derating, reduces the copper losses, and improves the braking transients. Experimental results confirm the successful performance in the different zones for the case of a six-phase induction motor drive

Model Predictive Control based on Dynamic Voltage Vectors for Six-phase Induction Machines

Model predictive control (MPC) has been recently suggested as an interesting alternative for the regulation of multiphase electric drives because it easily exploits the inherent advantages of multiphase machines. However, the standard MPC applies a single switching state during the whole sampling period, inevitably leading to an undesired x y voltage production. Consequently, its performance can be highly degraded when the stator leakage inductance is low. This shortcoming has been, however, mitigated in recent work with the implementation of virtual/synthetic voltage vectors (VVs) in MPC strategies. Their implementation reduces the phase current harmonic distortion since the average x y voltage production becomes null. Nevertheless, VVs have a static nature because they are generally estimated offline, and this implies that the flux/torque regulation is suboptimal. Moreover, these static VVs also present some limitations from the point of view of the dc-link voltage exploitation. Based on these previous limitations, this article proposes the implementation of dynamic virtual voltage vectors (DVVs), where VVs are created online within the MPC strategy. This new concept provides an online optimization of the output voltage production depending on the operating point, resulting in an enhanced flux/torque regulation and a better use of the dc-link voltage. Experimental results have been employed to assess the goodness of the proposed MPC based on DVVs.Ministerio de Ciencia, Innovación y Universidades RTI2018-096151-B-100

Field Oriented Control of Multiphase Drives with Passive Fault-Tolerance

Multiphase machines provide continuous operation of the drive with no additional hardware in the event of one or more open-phase faults. This faulttolerant capability is highly appreciated by industry for security and economic reasons. However, the steadystate post-fault operation has only been feasible in previous works after the fault localization and control reconfiguration. Even though this is done at the software stage, the obligation to identify the faulty phases and store the modifications for every fault scenario adds further complexity. This work reveals that this software reconfiguration can be avoided if the field-oriented control (FOC) strategy is designed to satisfactorily handle pre- and post-fault situations. Experimental results confirm the capability to obtain suitable postfault operation without fault localization and control reconfiguration, thus achieving a passive/natural fault tolerance.Ministerio de Ciencia, Innovación y Universidades RTI2018-096151-B-I0

Optimal Third-Harmonic Current Injection for an Asymmetrical Nine-phase PMSM with Non-Sinusoidal back-EMF

The paper investigates an optimal strategy to exploit the third harmonic current injection for the torque enhancement in a nine-phase permanent magnet synchronous machine (PMSM). The machine is with asymmetrical winding configuration and has a single isolated neutral point. The optimization follows the minimization of the average power losses for a given reference torque or, equivalently, the maximization of the developed torque for a given current RMS. It is shown that, in contrast to the situation for a symmetrical configuration, the optimal ratio between the fundamental and the third harmonic components does not correspond to the ratio between the corresponding back-EMF components. It is demonstrated that this is due to the fact that the phase currents have to sum to zero; consequently, the third harmonic current injection in different three-phase sets has to be different with regard to the magnitude and phase shift. The strategy is introduced using an entirely analytical approach and its effectiveness has been successfully validated through numerical simulations

Evaluation of harmonic and THD using LC filter for five phase induction motor drive at low speed

Distortion in the power system plight cause many problems, periodic distortions cause unwanted harmonics, these harmonics does not contribute additional energy for load, instead it is dissipated as heat in the load. It is also effective in voltage and current waveforms distortion, leading to many problems within the power systems and also to other peripherals. Minimization of THD is critical task, in order to maintain the good efficiency of the power systems. Power conversion is globally necessary according to the user requirement, inverters are commonly used in the power conversion systems, which produce harmonics. The various filters are used to eliminate these harmonics. In this work an LC filter is proposed and studied experimentally coupling to the Five Phase Induction motor load, experimental results are obtained and compared the results with normal five phase inverter drive. © 2017 IEEE