A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 2: Phase and Switch Open-Circuit Faults

Abstract

Multiphase machines are very convenient for applications that require high reliability. In this two-part survey, the state of the art about fault tolerance in multiphase drives is reviewed. In Part 1, an overview including numerous fault types was presented, along with fundamental notions about multiphase drives. Here, in Part 2, the focus is placed on phase/switch open-circuit (OC) faults in particular, which have received the most attention in the literature. Phase OC failures involve OCs in stator phases or in converter-machine connections, and switch/diode OCs are frequently dealt with similarly or identically. Thanks to the phase redundancy of multiphase drives, their operation can be satisfactorily continued under a certain number of OCs. Nonetheless, the procedure to follow for this purpose is far from unique. For given OC fault conditions, numerous fault-tolerant possibilities can be found in the literature, each of them with different advantages and disadvantages. Moreover, a great variety of methods have also been devised to detect and diagnose phase/switch OC failures so that, as soon as possible, the most appropriate fault-tolerance measures are applied. Thus, given the broad literature about tolerance to phase/switch OC faults in multiphase drives, the survey presented here is expected to be of great interest for the research community and industry.

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

“…The proposed technique is implemented in a Texas Instruments F28379D LaunchPad. The ac current references are computed based on the popular ML strategy [1], [5], [8], [28], with the αβ references set by conventional indirect field-oriented control. In a synchronous d-q frame within the α-β plane, the dand q-axis currents i ds and i qs are set for rated rotor flux and the required torque, respectively, with the latter being adjusted by a PI speed controller.…”

“…If the stator is supplied by a balanced fundamental current, complying with the machine SCL rating also means that the peak-current limit of the inverter devices is respected, provided the drive is properly designed. However, if the phase currents are unbalanced or with more frequency components (e.g., dc), the relation between SCL and peak current becomes more complicated and special care should be paid in this regard [2], [5], [30]. This is aggravated in the presence of OPFs, because of the associated current imbalance.…”

“…The ac current references ĩvsd * s may be set based on the αβ ones ĩ * αβs according to the ML, maximum-torque (MT) or full-range-minimum-loss (FRML) strategies [5], [10]. These references can be tracked by using PR (or equivalent dual synchronous PI) controllers in the α-β and x-y planes [see Fig.…”

“…Some of the typical applications where this property is exploited are those with safety-critical requirements such as aerospace systems [1], [2], as well as those where unscheduled maintenance is highly undesired and difficult such as wind [1] and marine-current turbines [3]. Specifically, the operation of multiphase drives under open-phase faults (OPFs) has received considerable attention [1], [4], [5]. Although a short-circuit fault may also occur, it is commonly transformed into an OPF by applying a remedial action [4]- [8].…”

“…Most importantly, only healthy operation was considered in [13], [18], but obtaining the resistance value is equally important in case of OPFs [24]- [26]. Applying these estimation methods to a faulty drive is not straightforward, since OPFs cause coupling between machine subspaces [1], [5], [9], [10], [27], [28]. Some current injection methods have been devised for estimating the stator resistance in six-phase machines with OPFs [24]- [26].…”