Multiphase Machines Research Articles

Performance analysis of packed U-cell based inverter-fed five-phase induction motor drive using SINPWM technique

Induction motor is the backbone of current industrial applications. Multiphase machines can handle high power application easily. With the use of five-phase induction motor, advantage of both multi-phase and induction motor can be achieved. This paper presents analysis of five-phase seven level-based Induction motor system fed by packed U-cell based inverter. Modelling of five-phase induction motor is done with the help of mathematical equations using d-q axis transformation. Inverter voltage output comes to be approximately sinusoidal with 18.07% Total Harmonic Distortion (THD). Induction motor with specified parameters is simulated under no-load condition and attains steady state conditions after transient state.

Research on torque ripple under healthy and open-circuit fault-tolerant conditions in a PM multiphase machine

In this paper, research into torque ripple production has been undertaken for both the healthy and open-circuit fault- tolerant conditions of a five-phase permanent magnet (PM) machine by using the instantaneous power (I-Power) approach. When only the fundamental component of the phase currents is applied to the phase windings, it has been shown that the 9th and 11th harmonics of the back-electromotive force (back-EMF) causes torque ripples in a five-phase PM machine and its frequency is ten times the frequency of the fundamental phase currents. When the combined fundamental and third harmonic components of the phase currents are applied to the phase windings, it has been shown that the 7th and 13th harmonic of the back-electromotive force (back-EMF) causes additional torque ripples in a five-phase PM machine .These torque ripples under fault-tolerant conditions have been analyzed analytically, as well. It has been proven that there are interactions between the fundamental component of current and the third harmonic component of the back-EMF and vice versa. These interactions cause torque ripples. A finite element analysis (FEA) model of the five-phase PM machine has been done to validate the analytical results.

Saturated VSD model of a six‐phase induction machine

In this study, a saturated model of an asymmetrical six-phase induction machine is presented. The model is based on the vector space decomposition approach, and it includes main and leakage flux saturation, as well as the mutual coupling between orthogonal planes while using the Gamma equivalent circuit approach. The accuracy of the proposed model in unbalanced operating modes that are characteristic for multiphase machines, such as post-fault and power-sharing operation, makes it advantageous compared to existing models. The model is developed assuming that the machine operates in asymmetrical conditions and that, therefore, there is fundamental frequency excitation in both planes. The inter-plane coupling effect is examined using finite element analysis and an experimental procedure for its quantification is developed. The model is verified by comparison with the experimental results obtained from a prototype asymmetrical six-phase induction machine, and its advantages compared to existing models are emphasised.

Impact of Current Harmonic Injection on Performance of Multi-Phase Synchronous Reluctance Machines

This paper combines the use of multi-phase configurations and current harmonic injection methods to achieve significantly improved performance for doubly salient synchronous reluctance machines (DS-SRMs). In order to understand the torque production mechanism of multi-phase DS-SRMs with current harmonic injection, some general analytical torque models have been developed. The models are based on Fourier Series analysis of self- and mutual-inductances. It has been established that with current harmonic injection, the torque ripple of both 5-phase and 6-phase DS-SRMs can be significantly reduced and the average torque can be enhanced. It contrast, harmonic injection always has a detrimental impact on 4-phase machines. The investigations of losses and dynamic performance with current harmonic injection for multi-phase machine have also been carried out and demonstrated that the proposed method can improve the efficiency in constant torque region and maintain comparable performance to fundamental current supply in the flux weakening region. Experimental validation based on single layer, 6-phase, DS-SRM has been performed.

Development of a vector control system of the semiconductor converter, which will provide a polyharmonic operating mode of a polyphase electric machine

A system for vector control of current in the circuit of a polyphase electric machine has been developed. For this, on the basis of the analysis of electromagnetic processes in a multiphase semiconductor converter of electrical energy, its discrete mathematical model was created, which takes into account the redistribution of electromagnetic energy by individual spatial harmonic components depending on the number of phases. Using this mathematical model and the scheme of injection of higher current harmonics, which provides a polyharmonic mode of operation of a semiconductor converter, a method for independent control of the spatial harmonic components of the input current of the converter has been developed. The formation in each of the phases of polyharmonic currents, conjugated in shape and phase with the voltage supplying the converter, is carried out by means of control actions in the form of voltage vectors of a semiconductor switch, the implementation of which is carried out by the method of multiphase space-vector modulation. To check the developed provisions, a simulation model of a nine-phase semiconductor converter of electrical energy with a vector control system was created. The results of the study of the model confirmed the adequacy of the developed technical solutions, the use of which will ensure the most complete realization of the own advantages of a multiphase electric machine in order to generally improve the weight, size and energy indicators of the autonomous power supply system.

A General Investigation on the Differential Leakage Factor for Symmetrical and Asymmetrical Multiphase Winding Design

This work provides an investigation based on a fast estimation of the degree of unbalance (D.U.%) and the differential leakage factor (σ0) of multiphase electrical machine windings. This analysis is carried out by exploring almost 5000 combinations in terms of number of slots, pole pairs, phases and layers. The variability of the leakage factor is examined for each condition, defining an optimal region for its minimization. As a result, an extended mapping is carried out for both the degree of unbalance and the leakage factor, providing a useful tool during the early design stage of winding configurations for multiphase electric machines, even with slight asymmetries. The results obtained from this investigation are validated through finite element analysis and demonstrate that the differential leakage factor can be significantly reduced by adopting winding configurations with slight asymmetries, which also represent a valuable alternative in the electrical machine design.

Design, Analysis and Validation of a Six-Phase Induction Machine from a Commercial Three-Phase for Academic Research

Multiphase machines have been reemerged for high-power as well as fault-tolerant applications such as electric vehicles and wind turbines. Nevertheless, these types of machines are typically built only for industries for specific purposes. Therefore, the availability of multiphase machines in the market for academic research work, for instance at universities, is limited due to they require special construction processes and involve high initial costs for the companies. For that reason, the aim of this paper is to present a step-by-step design of a multiphase winding of an induction machine (IM) from a commercial three-phase IM for academic research use. The obtained results will be first analyzed by using the ANSYS Maxwell simulation environment. Then, a model-based current controller will be performed to validate the proposed design and the electric parameters of the six-phase IM.

Smart Voltage Vectors for Model Predictive Control of Six-Phase Electric Drives

Model predictive control (MPC) has been recently in the limelight within the field of multiphase machines and drives because it can naturally exploit some of their inherent advantages. Unfortunately, the phase current quality provided by standard MPC is unacceptable when the values of the stator resistance and leakage inductance are low. Aiming to overcome this disadvantage, different MPC strategies using synthetic/virtual voltage vectors (VVs) have been developed. Nevertheless, static VVs are created offline, and consequently, they cannot be adapted to the operating point. This limitation has been recently mitigated with the creation of dynamic virtual voltage vectors (DVVs), where VVs are generated online combining two different switching states per sampling time. Despite the current quality improvement using DVVs, the refinement of the voltage output is still limited, and consequently, the solution is suboptimal. This article suggests the use of smart voltage vectors (SVVs) that are obtained by composing the three best voltage vectors in a smart proportion during the sampling period. The calculation of the duties is performed with an online smart search that allows the real-time implementation of this MPC version. The capability of the proposed SVV-MPC to enhance the current quality indices is validated with experimental results.

Field oriented control based on a 24-sector vector space decomposition for dual three-phase PMSM applied on electric ship propulsion

<p><span lang="EN-US">A Field Oriented Control (FOC) strategy based on a 24-Sector Vector Space Decomposition (24SVSD) technique used to control a Dual Three-Phase Permanent Magnet Synchronous Motor (DTP-PMSM) applied on electric ship propulsion prototype is presented in this paper. This machine is supplied by Dual Three-Phase Voltage Source Inverter (DTP-VSI). This study carried out on these multiphase machines has revealed that the large zero sequence harmonic current components on (z<sub>1</sub>, z<sub>2</sub>) subspace, constitutes major drawbacks; despite their advantages. The machine’s dynamic model is accomplished in three two-dimensional and orthogonal subspaces. In order to reduce more extra stator harmonic currents that produces losses, the current work is also concering of to consider the three different approaches for the sake of boosting the machine’s efficiency. Thus, the principle selection of the reference voltage vector and the time calculation method are presented in details. The proposed strategy effectiveness is validated by simulation results.</span></p>

Design of a Bi-Harmonic 7-Phase PM Machine With Tooth-Concentrated Winding

If multi-phase machines equipped with tooth-concentrated winding with half a slot per pole and per phase offer interesting characteristics (simplified manufacturing, no space subharmonic, fault-tolerant ability), their low fundamental winding factors make their designs and controls challenging. The paper addresses the case of a seven-phase Surface-mounted Permanent Magnet (SPM) machine which has a fundamental winding factor lower than the third. This so-called bi-harmonic specificity is considered in order to achieve good torque quality (average value and ripples). Regarding the design, the magnet layer is segmented into two identical radially magnetized tiles that cover about three-quarters the pole arc. Regarding the control, the rated Maximum Torque Per Ampere (MTPA) supply strategy (h1h3 control) aims at generating a third harmonic current component greater than the fundamental. A prototype has been manufactured: the ability of the machine to provide smooth torque is experimentally confirmed through the implementation of a simple MTPA control which copes with high distortion in no-load voltage.

Multiple Open-Switch Fault Diagnosis for Five-Phase Permanent Magnet Machine Utilizing Currents in Stationary Reference Frame

Apart from the passive fault-tolerant control strategies, any active fault-tolerant strategy requires a timely fault diagnosis signal to trigger the control reconfiguration under asymmetric condition. This article proposes a fault diagnosis method where the inherent relationship between fundamental and third harmonic stationary reference currents is established by declaring two new groups of current-based variables. Then two distinct fault characteristics of current performance in the transient conversion from healthy to faulty operation are derived. Based on the fault characteristics, a fast, robust and easy-implemented diagnosis algorithm is proposed based on currents in stationary reference frame to address the multiple open-switch fault diagnosis in five-phase permanent magnet machines. In order to verify the effectiveness of the proposed algorithm, a series of experiments have been conducted and the results indicate the strong robustness even under load variation and the valid diagnosis to each type of faults are performed. Moreover, the proposed method possesses favorable generality and can be extended to other multiphase machines.

Refurbishing three-phase synchronous reluctance machines to multiphase machines

Refurbishing electrical machines to have a higher performance and/or reliability is a clear trend in the circular economy. This paper investigates the gain in efficiency, torque density and reliability with replacing the windings and the iron of the stator of existing three-phase synchronous reluctance machines (SynRMs), resulting in a multiphase machine. The stator housing, shaft, bearings and the rotor are not changed, to keep the cost of refurbishing low. As the housing and rotor are kept, logical constraints are to have the same inner and/or outer stator diameters, air gap length and axial length. In the new windings, an identical copper volume is considered as a constraint. An optimization technique is coupled to 2D finite element method to select the optimal slot dimensions. Case studies showed that it is possible to replace the stator of existing three-phase SynRMs with a better performance multiphase one. It is found that the average torque, efficiency and power factor of the five-phase SynRM are increased by 11.78%, 0.72% and 5.54%, respectively, compared to a three-phase SynRM at rated conditions. At higher speeds (three times rated value), the efficiency and average torque are greatly improved by about 3.64% and 33.67%, respectively, compared to the three-phase SynRM. Moreover, a faulty case of one phase opened is also investigated. The five-phase SynRM works at 75.45% of the healthy rated torque of the three-phase SynRM, whereas the three-phase SynRM works at only 43%. Measurements on an existing 5.5-kW, three-phase SynRM confirm the observed results.

Multiphase Open-End Winding Induction Machine Drive With the Floating Capacitor

A comprehensive control scheme is presented for the multiphase open-end winding induction machine drive topology, where the main inverter (MI) and floating inverter (FI) are supplied by a dc power source and a capacitor, respectively. Under the proposed method, the MI can work with the unity power factor, while the FI provides all the reactive power. Besides, the current waveform quality is improved by the harmonic suppression and current balance control. Moreover, the voltage of the floating capacitor is adjusted to keep the modulation ratio of the FI near one during the operation, which helps to reduce the switching losses of the system. Experimental results are presented to verify that the proposed control scheme is practical in controlling this open-end drive topology and suitable for expansion to high-phase-number occasions.

Predictive current control in electrical drives: an illustrated review with case examples using a five‐phase induction motor drive with distributed windings

The industrial application of electric machines in variable-speed drives has recently grown thanks to the development of microprocessors and power converters. Although three-phase machines constitute the most common case, the interest of the research community is also focused on multiphase machines with more than three phases. The principal reason lies in the exploitation of their advantages such as reliability, better current distribution among phases or lower current harmonic in the converter, to name a few. Nevertheless, multiphase drive applications require the development of complex controllers to regulate the torque (or speed) and flux of the machine. In this regard, predictive current controllers have appeared as a viable alternative due to an easy formulation and high flexibility to incorporate different control objectives. It is found, however, that these controllers face some peculiarities and limitations in their use that require attention. This work attempts to tackle the predictive current control technique as a viable alternative for the regulation of multiphase drives, paying special attention to the development of the control technique and the discussion of the benefits and limitations. Case examples with experimental results using a symmetrical five-phase induction machine with distributed windings are included to this end.

High Resistance Fault-Detection and Fault-Tolerance for Asymmetrical Six-Phase Surface-Mounted AC Permanent Magnet Synchronous Motor Drives

In the last decade, the interest for higher reliability in several industrial applications has boosted the research activities in multiphase permanent magnet synchronous motors realized by multiple three-phase winding sets. In this study, a mathematical model of an asymmetric surface-mounted six-phase permanent magnet synchronous motor under high resistance connections was developed. By exploiting the intrinsic properties of multiphase machines in terms of degrees of freedom, an improved field-oriented control scheme is presented that allows online fault detection and a quite undisturbed operating condition of the machine under high resistance connections. More specifically, the proposed strategies for online fault-detection and fault-tolerance are based on the use of multi-reference frame current regulators. The feasibility of the proposed approach was theoretically analyzed, then confirmed by numerical simulations. In order to validate experimentally the proposed strategies, the entire control system was implemented using TMS-320F2812 based platform.

Computationally efficient steady‐state finite element simulation of multiphase PM AC machines

In this study the authors propose a generalised procedure for computationally efficient steady-state finite element (FE) simulation of symmetrical multiphase permanent magnet (PM) AC machines with an arbitrary number of phases. The procedure is based on newly derived general equations for phase waveform reconstruction that fully exploit the phase symmetry of multiphase electrical machines. This result can be used to reconstruct the full electrical period of any phase waveform from the smallest possible number of magnetostatic FE simulations executed within the minimum angular displacement of the rotor. Reconstruction of phase waveforms is done during post-processing and does not contribute to the execution time of FE simulations. The applicability of the proposed method is demonstrated by deriving specific equations for two-phase, three-phase, five-phase and six-phase machines. Results of classical time-stepping and newly proposed computationally efficient FE simulation are presented for four rotor PM flux switching machines with the different number of phases. Obtained results show that the relative reduction of simulation time increases with the number of machine phases.

Multiphase current imbalance localisation method applied to natural fault‐tolerant strategies

Multiphase machines are interesting options for high-reliability applications due to their inherent fault tolerance against open-circuit faults (OCFs). Moreover, if the regulation of the x–y currents is realised in open-loop mode using virtual voltage vectors (VVs), the mandatory post-fault control reconfiguration is avoided. The new reconfigurationless approach was recently defined as a natural/passive fault-tolerant strategy, offering good prospects for industry applications. This work extends the idea to the fault detection procedure and suggests new settings for the current imbalance localisation method. The proposal is based on the vector space decomposition approach that allows the joint detection of OCFs and stator resistances dissymmetry. Experimental results in a five-phase induction motor drive using VVs confirm the viability of the technique.

An Improved Open-Phase Fault-Tolerant DTC Technique for Five-Phase Induction Motor Drive Based on Virtual Vectors Assessment

The multiphase machine (MM) drives are best suitable for safety-critical applications due to its inherent fault-tolerant capability. The fault-tolerant operation of MM drives is challenging and necessary for applications such as off-shore ship propulsion, highway electric vehicles, and more electric aircraft. A two-level voltage source inverter fed five-phase induction motor (FPIM) drive has been considered for the postfault performance assessment. In this article, an improved fault-tolerant direct torque control (DTC) technique is proposed for the FPIM drive based on virtual vector (VV)s assessment under the open-phase fault condition. The theoretical analysis is carried out to investigate the impact of VVs on the change in torque as well as flux response at different speeds and loading conditions. Based on this analysis, a modified lookup table, flux, and torque hysteresis bands are designed to improve the functioning of the fault-tolerant DTC of FPIM drive. The FPIM drive performance is analyzed and tested experimentally with an open-phase fault. Studies have confirmed the reliability and superiority of the proposed DTC controller over existing postfault solutions. In addition, the robustness of the FPIM drive at steady-state and dynamic operating conditions is evaluated from the given results, including the transition from pre-to-post fault operation.

A Novel Sensorless Control for Multiphase Induction Motor Drives Based on Singularly Perturbed Sliding Mode Observer-Experimental Validation

This paper aims to develop an innovative sensorless control approach for a five-phase induction motor (IM) drive. The operation principle of the sensorless scheme is based on the sliding mode theory, within which a sliding mode observer (SMO) estimates the speed and rotor resistance simultaneously. The operation methodology of the proposed control technique is formulated using the mathematical model of the machine and the two-time-scale approach. The observation technique offers a simple and robust solution of speed and rotor resistance estimation for the sensorless control approach of the multiphase drive. The paper considers the five-phase induction motor (IM) as a case study; however, the proposed control algorithm can be employed by different types of multiphase machines. To test the applicability of the proposed sensorless control approach, the drive performance is firstly validated using MATLAB/Simulink-based simulation. Then, the simulation results are verified using real-time simulation and experimentally using TMS320C32 DSP-based control board. The obtained results confirm and validate the ability of the proposed control procedure in achieving a robust dynamic performance of the drive against the system uncertainties such as parameter variation.

Overload Capability of Multiphase Machines Under Normal and Open-Phase Fault Conditions: A Thermal Analysis Approach

Multiphase drives are convenient for high-power/high-current applications as they allow the reduction of the phase current for given rated power and phase voltage. Due to their redundant structure, the multiphase drives have intrinsic open-phase fault-tolerant operation capability. This situation may happen when one or more power electronic units are turned off after a fault event, and the drive configuration allows phase disconnection. In this case, the healthy machine phases can be overloaded to keep the torque constant and without any pulsations. The goal of the work is the evaluation of the thermal parameters of the stator windings of multiphase machines to be used in the analysis of both short thermal transients and steady-state operation, during normal and open-phase faults. The approach has general validity and can be applied to any ac multiphase machine having a distributed winding configuration. The prototype used for the experimental tests is an asymmetrical 12-phase induction machine, having four 3-phase stator sets with isolated neutral points. The stator windings thermal model is obtained experimentally, by considering the mutual heat exchange phenomena among the windings when one or more winding sets are disconnected. This thermal model allows at evaluating the proper machine overloading for short thermal transients and steady-state operation in case of open-phase faults.