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 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.

This article considers a three-phase induction motor with open-end windings fed by a primary bridge connected to the main power source and a floating bridge. The floating bridge supplies the motor with the required reactive power, while the primary inverter only exchanges active power with the main power source. This greatly extends the speed range over which the drive can operate at rated power. To further utilize the input power source, the primary inverter can work in the overmodulation region, and the floating bridge, acting as a harmonic compensator, improves the quality of the current flowing through the motor phases. Also, the article includes some considerations on the sizing of the floating capacitor. Three different overmodulation techniques are evaluated and compared in terms of peak torque/power and efficiency. The highest performance is obtained when the main inverter generates a six-step voltage waveform, which increases motor power by almost 20% and ensures a broader speed range at maximum efficiency.

The torque density of a multiphase motor can be increased without exceeding the admissible current of the drive if the high-order spatial harmonics of the magnetic field in the air gap are appropriately synchronized with the fundamental one. Notably, due to the converter voltage limitation, this method is feasible only if the speed of the rotor is below its base speed. As the speed of the rotor increases, the voltage must correspondingly increase to sustain the field harmonics in the air gap. Above the base speed, the prevalent strategy in motor control focuses on regulating only the fundamental component of the magnetic field in the air gap. Nevertheless, this paper presents a new method that employs the injection of voltage harmonics to extend the linear modulation range of the fundamental voltage vector, thereby improving motor performance. In the field weakening region, an increase in the magnitude of the stator voltage vector improves the motor power and torque by over 40%. Experimental tests on a fivephase induction motor drive confirm the feasibility and the effectiveness of the developed control scheme. Overall, this approach shows great potential for improving motor performance and has applications in various sectors of motor control