Abstract One of the most attractive features of multiphase machines is the fault-tolerant capability due to the higher number of phases. Different post-fault control strategies based on hysteresis, PI-resonant and predictive techniques have been recently proposed. They all proved their capabilities to withstand fault situations and to preserve the fundamental component of the air-gap field, while achieving minimum losses, maximum torque per-ampere and reducing torque vibrations. Nonetheless, due to their recent introduction, no thorough study has yet appeared comparing the performance of these controllers. In this paper two open-phase fault-tolerant control schemes are experimentally compared in a real five-phase induction machine. The controllers being compared are based on PI-resonant and predictive control techniques, respectively. The experiments include pre-and postfault situations. Obtained results show that both control methods offer nearly the same performance. When compared, predictive control provides faster control response and superior performance at low speed operation but is found to be less resilient to fault detection delays and to have higher current ripple. Regarding the controller implementation, it is shown that the transition from preto post-fault operation involves modelling the non-linear effects observed when an open-phase fault occurs for the predictive controller, and the proper retuning of the PI trackers for the PIresonant controller, in order to ensure post-fault operation.

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an alternative to traditional field-oriented control (FOC) methods for three-phase drives. The conventional DTC scheme has been successfully extended to multiphase drives in recent times, using hysteresis regulators to independently track the desired torque and flux in symmetrical five-phase induction machines (IM). The fault-tolerant capability of multiphase drives is an interesting intrinsic advantage for safety-critical applications, where recent research has demonstrated the effectiveness of FOC schemes to perform ripple-free post-fault operation. In spite of the utility of DTC methods in normal operation of the multiphase machine, no extension to manage the post-fault operation of the drive is found in the literature. In this paper, a novel fault-tolerant DTC scheme is presented. The performance of the proposed method is experimentally validated in a five-phase IM drive considering an open-phase fault condition. Provided tests analyze steady and transient states, including the transition from pre-to post-fault operation. Obtained results prove the interest of the proposal, which ensures the open-phase fault-tolerant capability of DTC controlled five-phase IM drives. Index Terms-Direct torque control (DTC), fault-tolerant capability, multiphase induction motor (IM) drives, open-phase fault operation.

Direct torque control (DTC) has been recently used for the development of high performance five-phase induction motor (IM) drives, where normal operation of the system has been usually considered and the ability of DTC to manage the situation has been analyzed in comparison with different rotor field-oriented control (RFOC) strategies. The exploitation of fault-tolerant capabilities is also an interesting issue in multiphase machines, where the utility of RFOC controllers has been stated when the open-phase fault operation is considered. In this paper, the performance of DTC and RFOC controllers based on proportional resonant regulators and predictive control techniques is compared when an open-phase fault appears in a five-phase IM drive. Experimental tests are provided to compare the performance of the system using these control alternatives. Index Terms-Direct torque control, multiphase induction motor drives, rotor field-oriented control, open-phase fault operation. NOMENCLATURE DSP Digital Signal Processor. DTC Direct torque control. EMF Electromotive force. IM Induction machine. MCL Minimum copper loss. MMF Magnetomotive force. PCC Predictive current control. PI Proportional integral. PR Proportional resonant. PWM Pulse width modulation. RFOC Rotor field-oriented control. THD Total harmonic distortion. VSD Vector space decomposition. VSI Voltage source inverter. VV-DTC Virtual vector based DTC ed,q Direct and quadrature feedforward terms. In Nominal stator current value. iα,βr Rotor currents in the α-β subspace. ia,b,c,d,es Stator phase currents. id,qs Direct and quadrature stator currents. iα,βs Stator currents in the α-β subspace. ix,ys Stator currents in the x-y subspace. izs Stator current in the z subspace. i * α,βs,max Maximum reference currents in the α-β subspace. J Cost function for PCC. Llr Rotor leakage inductance. Lls Stator leakage inductance. Lm Magnetizing inductance. Lr Rotor inductance. Ls Stator inductance. p Number of pole pairs. Rr Rotor resistance. Rs Stator resistance. Si Switching signals of every VSI leg. Te Electrical torque. TL Load torque. Tn Nominal torque. T0 Generalized Clarke transformation matrix. TPOST Modified VSD transformation matrix. Vdc DC-link voltage. VVi Virtual voltage vectors. va,b,c,d,es Stator phase voltages. vd,qs Direct and quadrature stator voltages. vα,βs Stator voltages in the α-β subspace. vx,ys Stator voltages in the x-y subspace. ϑ Fixed spatial displacement between windings. λα,βs Stator fluxes in the α-β subspace. ωe Electrical speed. ωm Mechanical speed. ωr Rotor electrical speed (defined as p•ωm). * (superscript) Reference variables. ^ (superscript) Estimated variables.

Multiphase machine drives are gaining importance in high reliability applications due to their fault-tolerance capability and their ability to cope with the post-fault operation without any extra electronic components. Predictive current controllers have been recently proposed for managing post-fault operation of these drives when an open phase fault is considered. However, the faulty situation assumes zero stator current while free-wheeling diodes can continue conducting in a non-controlled mode. This work analyses the post-fault operation of the fivephase drive when the free-wheeling diodes of the faulty phase are still conducting. Experimental results are provided using a conventional IGBT-based multiphase power converter to quantify the effect of the free-wheeling diodes, when an IGBTgating fault occurs, on the model-based predictive current controlled drive.