Multi three-phase drives are a particular case of multiphase systems, which are often used in high-power applications, such as wind-energy generation, naval and railway propulsion. In a multi three-phase system the electric machine is fed by more than one three-phase converter. A current sharing algorithm for multi three-phase drives allows setting unequal current references among the converters so that each of them differently contributes to the generation of the magnetic torque and flux. Suitable current sharing control systems already exist and have been presented for multi three-phase machines. This paper illustrates a current sharing technique where the contributions to the rotor flux for the three-phase inverters, related to the d-axis current, is decoupled from the contributions to the electromagnetic torque, which depends on the q-axis current. Also, the presented algorithm minimizes the Joule losses in the stator winding. Finally, the advantages of the proposed method are analyzed and confirmed by experimental tests. The effectiveness of the control strategy is validated on a scaled prototype of a quadruple three-phase starter/generator for more-electric-aircraft applications.

In three-phase electric drives, overmodulation is commonly used to fully exploit the dc-bus voltage, increase the dynamic performance of the motor, and reduce the inverter switching frequency. The same advantages can be found in multiphase converters, where a higher number of degrees of freedom allows defining new operating modes. In this paper, the extension of the overmodulation strategies of three-phase inverters to five-phase systems is investigated. Experimental tests on a five-phase induction motor drive are carried out to verify the feasibility of the developed techniques, the quality of the current waveforms, and the improvement in the dynamic performance of the drive.

The partial demagnetization process in surface-mounted permanent-magnet synchronous motors (SMPMSMs) negatively affects the performance of an electric drive, reducing the rated torque and the efficiency of the machine. This article presents a comprehensive analysis of the rotor demagnetization caused by an overcurrent event for a six-phase SMPMSM. Multiphase drives may become a key solution for safety-critical applications because they allow one to increase the intrinsic reliability of electric systems and monitor the health state of electric motors and power converters. This article proposes a diagnostic algorithm for the online detection of rotor demagnetization faults that also considers the magnetization direction of the magnets. The effects of the parallel or radial magnetization of the rotor magnets are analyzed for multiphase machines. The technique quantifies the demagnetization degree to estimate the fault severity and corrects the angular position of the encoder to ensure maximum motor performance under postfault conditions. Experimental tests have been carried out on two identical six-phase PMSMs differing only in the size of the rotor magnets to emulate the effect of trailing-edge demagnetization. The experimental results confirm the effectiveness and robustness of the proposed solution.

Over the past few years, Artificial Intelligence (AI) techniques have become one of the most exciting technologies of our age. This fascinating field paves the way for new possibilities and extends to almost all areas of industry and research. This paper illustrates a Short-Circuit (SC) diagnosis strategy for a multi-three-phase brushless AC motor drive based on Machine Learning (ML). A thorough model of the electrical machine is obtained through specific finite-element simulations and used to replicate various fault scenarios. This model quickly yields a large amount of data, which is then employed for training the ML algorithms. Once trained, the ML models are tested, with experimental data directly obtained from a prototype of multiphase drive, to verify the effectiveness of the diagnostic algorithms. The ML algorithms allow monitoring the health condition of the machine, distinguishing and localizing two types of faults, i.e., inter-turn SCs and Extra Turns (ETs), placed in different coils of the machine.

This paper presents a post-fault control algorithm that minimizes the stator Joule losses in multiphase induction machines under an open-phase fault and for different star connection layouts. The key novelty is that the algorithm can be applied to any configuration of a multi n-phase machine, independently of the connection of the neutral points. The latter is analytically derived and is based on the space vector representation of the machine model. Also, it is shown that a low number of neutral points helps to reduce the winding losses in case of an open-phase fault but requires additional control regulators and computational efforts. The theory is applied to an asymmetrical quadruple three-phase induction machine, which is configured to represent five different motor layouts. Finally, experimental results are presented to validate the control algorithm. The optimal solution that is given in the paper can be employed for the control of symmetrical or asymmetrical multiphase machines with different star connection layouts and in any open-phase post-fault operation.

This article illustrates an algorithm to balance the voltages across the dc-link capacitors of a three-level multiphase inverter feeding a star-connected load with an odd number of phases. The proposed strategy keeps the dc-link capacitors balanced in any operating condition and minimizes the low-frequency voltage oscillations, even during open-phase faults and with non-sinusoidal output currents. Finally, the article identifies the operating region where the voltage oscillations of the dc-link capacitors can be canceled. The developed algorithm can maintain constant voltages even if the capacitors are unbalanced, and its performance is compared to that of other carrier-based algorithms. Experimental tests are carried out on a five-phase induction motor in healthy and faulty conditions.