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Multiphase drives exhibit remarkable advantages (e.g., fault tolerance) over three-phase ones. Six-phase drives are particularly attractive, given their moderate complexity and suitability for off-the-shelf three-phase converters. Regarding the stator winding arrangement, the symmetrical one offers superior postfault capabilities in most scenarios. On the other hand, resistance asymmetry in the stator phases or connections may arise due to different causes. The conventional full-range minimum-loss strategy (FRMLS) generates stator-current references under open-phase (infinite resistance) faults so that torque ripple is prevented while minimizing the losses for each torque ($\boldsymbol{d}$ - $\boldsymbol{q}$ current) value and maximizing the torque range; however, this method is unsuitable for unequal resistances of finite value. This article proposes an FRMLS for setting the current references to reach these goals in symmetrical six-phase drives with any resistance asymmetry. The optimum references are found online depending on the resistances, without lookup tables. The phase currents are individually limited by an iterative algorithm, so that minimum stator copper loss (SCL) is achieved over the maximum admissible torque range. In this manner, unlike the conventional FRMLS, minimum SCL and maximum torque range are attained even for finite resistance imbalance. The currents in phases affected by high resistances are suitably reduced. Experimental results are provided. [ABSTRACT FROM AUTHOR]

This paper studies the postfault control of a nine-phase six-terminal induction machine (IM) during single open-line fault, which was recently proposed for high-power medium-voltage applications as a promising alternative to conventional six-phase IMs. The required optimal reference currents to provide prefault loading conditions under one-line open are derived using the two most common optimization criteria employed in multiphase drives, namely, maximum torque and minimum loss modes. A postfault controller, based on conventional decoupling Clarke's transformation, is then used to ensure the same controller structure under all conditions. Consequently, the machine characteristic curves, achievable torque, and stator copper losses under these different modes are compared. A comparison with a conventional asymmetrical six-phase winding is also given. A 1.5-Hp prototype IM is used for experimental verification. [ABSTRACT FROM PUBLISHER]

In multiphase machine drives, accuracy of the estimated machine parameters is crucial for effective performance prediction and/or control. While a great amount of work has been done on parameter estimation for three-phase machines, corresponding discussions for six-phase machine remain scarce. It has been proven in the literature that the effect of mutual leakage inductance between different winding layers has a significant impact on the equivalent machine reactance, which challenges the standard separation method of stator and rotor leakage inductances from the measured locked-rotor impedance. In this paper, parameter identification of an asymmetrical six-phase induction machine using six-phase no-load and locked-rotor tests is discussed. A zero-sequence test using an improved equivalent circuit is proposed to improve the accuracy of the estimated parameters. The concept is verified using experimental results obtained from a low-power prototype asymmetrical six-phase machine. [ABSTRACT FROM AUTHOR]

The steady-state modeling of multiphase induction machines (IMs) with m phases under open-line fault conditions is usually carried out based on symmetrical component theory. Hence, the estimation of the machine characteristic curves usually involves complex mathematical calculations and inversion of high-order matrices, which complicates the analysis. Moreover, the effect of the different subspaces’ impedances on the machine performance cannot be easily recognized using this modeling technique. Instead, this paper presents the first attempt to derive a simple equivalent circuit for a five-phase IM under open-line conditions that includes the effect of all subspaces in a single circuit. The derivation is carried out for both star and pentagon connections. The equivalent circuit can be a simple technique to explain the advantages obtained from a pentagon connection compared to the star connection under open-circuit faults. It can also be used to derive a simple expression for torque gain and torque ripple magnitude for different stator connections based on the circuit parameters. The derived equivalent circuits are verified using a 1-kW five-phase prototype machine. [ABSTRACT FROM PUBLISHER]

One of the main drawbacks of nonoverlapped coils in fractional slot concentrated winding permanent magnet (PM) machines are the high eddy current losses in both rotor core and permanent magnets induced by the asynchronous harmonics of the armature reaction field. It has been shown in the literature that the reduction of low space harmonics can effectively reduce the rotor eddy current losses. This paper shows that employing a combined star-delta winding to a three-phase PM machine with fractional slot windings and with a number of slots equal to 12, or its multiples, yields a complete cancellation to the fundamental magneto-motive force (MMF) component, which significantly reduces the induced rotor eddy current. Besides, it offers a slight increase in machine torque density. A case study on the well-known 12-slot/10-pole PM machine is conducted to explore the proposed approach. With the same concept, the general $n$ -phase PM machine occupying $4n$ slots and with a dual $n$ -phase winding is then proposed. This configuration offers a complete cancelation of all harmonics below the torque producing MMF component. Hence, the induced eddy currents in both rotor core and magnets are significantly reduced. The winding connection and the required number of turns for both winding groups are also given. The concept is applied to a 20-slot/18-pole stator with a dual five-phase winding, where the stator winding is connected as a combined star/pentagon connection. The proposed concept is assessed through a simulation study based on 2-D finite element analysis. [ABSTRACT FROM AUTHOR]

This paper investigates a nontriplen multiphase induction machine when fed with harmonic current injection with different sequences for an open loop optimized flux distribution that produce a quasi-square wave in the machine air gap. This maximizes iron utilization, giving more torque per ampere. The relation between the fundamental and other harmonic components can be determined for the best iron utilization using genetic algorithms where optimum flux distribution with different injected harmonic order can be obtained. This means, the target is to optimize the flux distribution during no-load to determine the optimum constants that guarantee approximate square wave air-gap flux. The paper focuses on an 11-phase machine that can be excited with harmonics up to the ninth. The technique is assessed using both winding function and finite element analysis methods. The prototype machine is fed from an 11-phase inverter. The system DSP control using genetic algorithm produces an optimum flux distribution by using winding sequence and harmonic current injection. Simulation results for the 11-phase dq model and prototype drive experimental results are presented. [ABSTRACT FROM AUTHOR]