Three-phase Stator Windings Research Articles

Effects Generated by the Magnetic Core Anisotropy of an Induction Motor

A theoretical analysis enables effects generated by the magnetic core anisotropy of an induction motor to be determined qualitatively. Relationships formulated between currents and magnetic flux linkages that are associated with three-phase stator windings enable the qualitative determination of spectra of currents or voltages of a typical induction motor. These relationships account for nonlinear and anisotropic magnetization characteristics of the motor core, both during idle running and motor starting. Based on these relationships, components of the amplitude Fourier spectra of symmetrical components of currents or voltages, which are useful in the diagnostics of stator or rotor core anisotropy, were selected. Field calculations were performed for the core of a two-pole 5.5 kW motor supplied by three-phase sinusoidal currents. The components of the induced voltage Fourier spectra in both the idle running and short-circuit state were similar to analogous components predicted based on theoretical studies. The components occurring in the spectra, which were obtained based on field calculations, were distinguished in the measured spectra of the symmetrical components of the phase currents. These components were applied to estimate representative current signal levels in the diagnostics of motor core anisotropy. Relative values of these signals did not exceed 60 dB; however, they were significant for assessing the internal asymmetry level of the motor stator or rotor core. The results of laboratory measurements confirmed the results of the theoretical analysis.

Design Considerations for an Active–Reactive Induction Motor for Medium-Voltage Applications

The active–reactive induction motor (ARIM) has been introduced in the literature as a low-cost and high-efficiency alternative to the synchronous motor in load commutated inverter (LCI) fed drives. ARIM is a squirrel cage machine with two sets of dissimilar three-phase stator windings. While one winding is rated for high voltage and power, the other winding is rated for a lower voltage and power. The low-voltage winding fed from a voltage source inverter (VSI) supplies only reactive power to the machine such that a leading power factor appears at the high-voltage terminals, enabling LCI-fed operation at this winding. Since the ARIM is fundamentally an induction motor, the conventional induction machine design process is applicable. However, due to the nonconventional arrangement of stator windings and being intended specifically for an LCI-fed topology, this new class of induction machines requires some critical design considerations. It is shown in this article that the leakage inductances play a pivotal role in determining the ratings of the low-voltage windings and the VSI. Therefore, an iterative design procedure to obtain the correct ratings for the flux winding and the low-voltage components is proposed. It is also required to know the correct value of the leakage inductance in order to design the control loops for reliable operation. This article proposes experimental methods to determine these leakage inductances. The proposed methods are validated by designing a 3.3-kV, 75-kW prototype and experimental results are presented.

Investigation Study of Multi-Mode Multi-Speed Operation Method for Surface-Mounted Permanent Magnet Synchronous Machines

Typically, a surface-mounted permanent magnet synchronous machine (SPMSM) has a poor flux-weakening performance due to its low synchronous inductance; hence, its speed is proportional to the supply voltage. A relatively high DC-link voltage is required to operate an SPMSM at higher speeds. This paper proposes a multi-mode multi-speed operation method to overcome this issue. With this method, the total line-to-line back electromotive force (EMF) is modified using the winding switching. Each phase of the stator winding is divided into two equal coils. There are four modes of operation of the machine. In mode I, the three-phase stator winding is connected in a wye configuration. In modes II, III, and IV, the winding is reconfigured such that the sum of the individual back EMFs of the coils exhibits a difference in voltages between the line terminals. The back EMF in these modes decreased by 1.74, 3.67, and 6.49 times, respectively, compared with that in mode I. This resulted in a four-speed operation, with base speeds of 1, 1.97, 3.68, and 7.47 pu in modes I-IV, respectively. Herein, the analytical model of the machine and drive topology are explained and demonstrated. Simulation results obtained using the 2-D finite element method are presented along with the experimental measurements to verify the feasibility of the proposed method.

Decoupled and Modular Torque Control of Multi-Three-Phase Induction Motor Drives

In recent years, the development of multi-three-phase drives for both energy production and transportation electrification has gained growing attention. An essential feature of the multi-three-phase drives is their modularity since they can be configured as three-phase units operating in parallel and with a modular control scheme. The so-called multi-stator modeling approach represents a suitable solution for the implementation of modular control strategies able to deal with several three-phase units. Nevertheless, the use of the multi-stator approach leads to relevant coupling terms in the resulting set of equations. To solve this issue, a new decoupling transformation for the decoupled torque control of multi-three-phase induction motor drives is proposed. The experimental validation has been carried out with a modular power converter feeding a 12-phase induction machine prototype (10 kW, 6000 r/min) using a quadruple three-phase stator winding configuration.

Brushless Doubly Fed Machine Magnetic Field Distribution Characteristics and Their Impact on the Analysis and Design

This paper contributes to the characterisation of the brushless doubly fed induction machine (BDFIM), which is attractive as a variable speed generator in applications (off-shore wind turbine) with minimum maintenance requirements. The BDFIM has two three-phase stator windings of different pole numbers housed within the same stator slots and a short-circuited rotor winding capable of coupling fields of different pole numbers. The stator windings and rotor winding create a magnetic field distribution with a range of characteristics different to those of conventional induction machines. This paper presents an analysis to identify the field characteristics and discusses their impact on the analysis and design of the BDFIM. The characteristics are determined from an analysis of the sum of two rotating sinusoidal field waveforms and confirmed by comparison with time-stepping finite element results and measured magnetic flux density data.

Numerical-field evaluation of an efficiency of a shortening of a three-phase stator winding of a cylindrical magnetic field inductor

The efficiency of cylindrical magnetic field inductors is determined by the value of the field inside their working chamber. This field is driven by a three-phase stator winding. The electrical quantities and magnetic induction in the inductor depend on its shortening. The purpose of this work is to determine the rational shortening of the stator winding. The solution of the problem is achieved on the basis of numerical calculations of magnetic fields in the FEMM software package using the finite element method. The construction of physical and geometric design models of the stator, calculations of magnetic fields and electromagnetic parameters of the inductor are automated using the created Lua script built into the FEMM program. The pictures of the distribution of magnetic field lines with diametric and shortened stator windings are given. A comparison is made between the EMF and the winding voltage, as well as the distribution of the magnetic induction over the surface of the working chamber and along the center line of the teeth with different variants of shortening the winding pitch.

Numerical-field evaluation of an efficiency of a shortening of a three-phase stator winding of a cylindrical magnetic field inductor

The article proposes the implementation of the on-board battery system of energy accumulation of the DC rail - a reinforcing point that provides regulated parameters for the quality of electrical energy in the contact network. The expediency of using a matching converter, which provides the principle of separate commutation, in order to minimize the loss of switching of the power keys of the converter, is shown. The location of the reinforcement point in the immediate vicinity of the consumer - directly on the rolling stock - on a locomotive or in a special trailer car is substantiated. The energy and mass parameters of the system are estimated. The calculations are made to make the choice of specific power keys of the converter. The optimal frequency of switching of the power keys of the converter is determined, which provides a compromise between the overall properties of the magnetic elements and the losses in the magnetic material. The necessary value of transformer scattering inductance, mass of magnetic elements and batteries is estimated.

Modeling of sudden six-phase and three-phase short circuits of a six-phase turbogenerator

A demand for the highest possible power density in electrical machinery in some applications often requires a change in conventional and well-known three-phase stator winding solution. This paper discusses high-power turbogenerators with a six-phase winding. Mutual inductance between two three-phase windings requires updating of the equations for transient processes modelling. The equivalent circuits and equations for the dq0-reference frame are summarised, sudden six-phase and three-phase winding short circuit processes of the generator under load are modelled.

Modified steady‐state modelling of brushless doubly‐fed induction generator taking core loss components into account

Brushless doubly-fed induction machine (BDFIM) has recently gained considerable research interests due to its promising features when incorporated as wind generator or variable speed drive. The BDFIM has two three-phase stator windings with different pole-pair numbers and excitation frequencies. The performance of the machine is based on the magnetic cross-coupling of rotating fields produced by the stator windings through a special squirrel cage rotor. Contrary to the conventional induction machine (IM), the rotor slip and frequency are high throughout the operating speed range. Hence, the rotor core loss cannot be ignored in the steady-state analysis. Although the core loss components have much more study of BDFIM. In this study, analytical expressions are individually derived for a number of core loss components caused by the complicated nature than those of an IM, the precise calculation of these components is important especially on the efficiency each stator winding field. Then, the modified steady-state electric equivalent model is developed by considering the components. The experiments and finite element analysis based on a 3kW prototype BDFIM verify the accuracy of the proposed model.

An Improved Torque Density Pseudo Six-Phase Induction Machine Using a Quadruple Three-Phase Stator Winding

The nine-phase six-terminal induction machine has recently been proposed as a promising contender to the conventional six-phase asymmetrical winding machine in terms of torque density, phase current quality, stator winding simplicity, and fault-tolerant capability. However, the relatively lower dc-link voltage utilization of a single neutral arrangement in multiphase machines with multiple three-phase windings represents, in general, a technical challenge when compared to windings with isolated star points. Therefore, this paper proposes a new pseudo six-phase winding layout suitable for medium-voltage high-power induction machines, which employs quadruple three-phase stator winding sets, while providing the same terminal behavior of a nine-phase six-terminal winding. Additionally, like the traditional six-phase winding, two possible neutral arrangements can be configured. The proposed winding configuration provides the same dc-link voltage utilization as in conventional dual three-phase winding machines with isolated neutrals. The effect of the circulating zero-sequence current component experienced with a single neutral arrangement can also be avoided. A 1.5 Hp prototype induction machine is used to experimentally validate the proposed six-phase winding layout under both healthy and fault conditions.

A Novel Synthetic Loading Method for Multiple Three-Phase Winding Electric Machines

This paper develops a version of the synthetic loading method, suitable for the testing of multiphase machines with multiple three-phase distributed windings. The method is at first discussed in general terms for a structure with k three-phase stator windings (i.e., total number of phases is n = 3 k ). Subsequent detailed development is described for a dual three-phase (six-phase) stator winding configuration. With a control architecture that allows the use of half of the three-phase windings as a motor and the other half as a generator, the machine (and/or the converter) can be tested under full rated power without the need for any mechanical load. Moreover, the power consumed from the grid is in essence equal only to the total losses of the system. Modeling, based on the double d-q approach, and the control layout that includes full cross-coupling decoupling are described for a permanent magnet (PM) synchronous machine. An experimental test rig with a double three-phase PM machine of 150 kW rating is detailed and the samples of experimental results are provided to verity the theoretical considerations.

Multiple vertical axis wind turbines with passive rectification to a common DC-link

Abstract Wind turbines are commonly placed in wind farms, usually operating as separate units. Possible benefits could be found by allowing turbines to share a common DC-link. Diode rectifiers are a robust and cost effective way to rectify variable speed wind turbines, with loss of direct control of the generator. This paper studies the electromechanical interactions between four passively rectified vertical axis wind turbines connected to a common DC-link. Two different load approaches for the DC-link are compared using simulations in terms of performance and stability: a power source and a voltage source. The optimal torque (or optimal power) control is implemented for the two loads approaches. In addition, three-phase and dual stator winding (six-phase) generators are compared. The results show that all suggested solutions work with similar performance. However, the power load requires a large DC-link capacitance to achieve stability. More generatorphases improve the system with passive rectification in most cases. The simulations suggest that the common DC-link systems are expected to have a few percent lower energy capture due to the lack of individual turbine control. On the other hand, there is a significant reduction in peak power and a potential for smoother output power.

Design of a decoupling strategy and parameter calculation for six-phase PM machines with general angular displacement

A novel decoupling model for a six-phase permanent magnet machine is proposed in this paper. The model considers the machine as two independent three-phase stator windings that are spatially shifted by a generic angle [Formula: see text]. The proposed transformation considers the zero sequence and allows the coupling between phases to be eliminated. The parameters, which define the dynamic behaviour of the model, are calculated with simulations performed using the finite-element method. The decoupled model and the parameters are analyzed for two configurations of a traditional six-phase machine. Simulation results were validated by experimental results with a simple procedure.

Control of dual stator induction generator integrated in wind energy conversion system

This paper deals with the modeling and the control of a dual stator induction generator (DSIG) integrated into a wind energy conversion system with a variable speed wind turbine. DSIG is increasingly used because of its advantages in better reliability and supply division. It consists of two fixed three-phase stator windings displaced with an electrical angle 𝛼𝛼. To minimize the harmonic distortion (THD), the objective of this work is to study the influence of the angle between these two stator windings on the grid generated current quality. To improve the performance of the system, the proposed control is demonstrated through an illustrative simulation.

The dual three-phase open-end stator windings permanent magnet synchronous machine fed by four voltage source inverters

In this paper, the mathematical model in Park reference frame of the dual open-end stator winding salient-pole permanent magnet synchronous machine is described. The proposed machine is supplied by its four voltage source inverters based on PWM technique. Then, the feeding of this machine by four two-level cascaded inverters is presented. A multilevel PWM strategy is carried out to control the cascaded inverters. The simulation analyses using the THD voltage, THD stator current and the torque undulation are presented and show the benefits for the proposed machine.

The dual three-phase open-end stator windings permanent magnet synchronous machine fed by four voltage source inverters

In this paper, the mathematical model in Park reference frame of the dual open-end stator winding salient-pole permanent magnet synchronous machine is described. The proposed machine is supplied by its four voltage source inverters based on PWM technique. Then, the feeding of this machine by four two-level cascaded inverters is presented. A multilevel PWM strategy is carried out to control the cascaded inverters. The simulation analyses using the THD voltage, THD stator current and the torque undulation are presented and show the benefits for the proposed machine.

Modeling and analysis of a novel dual open-end stator windings wound rotor synchronous machine with dampers

This work presents a novel wound rotor synchronous machine with dampers with dual three-phase open-end stator windings. The aim of the proposed machine is to improve the power segmentation and the availability of the drive system. The mathematical model of this machine is presented in the Park reference frame. This machine is supplied by four 2-level inverters, where each inverter is dimensioned for quarter power of the machine. For comparison purposes, we use a double star synchronous machine fed by two 2-level inverters. Comparative simulation analysis using THD voltage, THD stator current, and torque undulation showed significant advantages of the proposed machine.

An Equivalent Carrier-based Implementation of a Modified 24-Sector SVPWM Strategy for Asymmetrical Dual Stator Induction Machines

A modified space vector pulse width modulation (SVPWM) strategy based on vector space decomposition and its equivalent carrier-based PWM realization are proposed in this paper, which is suitable for six-phase asymmetrical dual stator induction machines (DSIMs). A DSIM is composed of two sets of symmetrical three-phase stator windings spatially shifted by 30 electrical degrees and a squirrel-cage type rotor. The proposed SVPWM technique can reduce torque ripples and suppress the harmonic currents flowing in the stator windings. Above all, the equivalent relationship between the proposed SVPWM technique and the carrier-based PWM technique has been demonstrated, which allows for easy implementation by a digital signal processor (DSP). Simulation and experimental results, carried out separately on a simulation system and a 3.0 kW DSIM prototype test bench, are presented and discussed.

Optimization Design and Performance Analysis of a PM Brushless Rotor Claw Pole Motor with FEM

A new type of permanent magnet (PM) brushless claw pole motor (CPM) with soft magnetic composite (SMC) core is designed and analyzed in this paper. The PMs are mounted on the claw pole surface, and the three-phase stator windings are fed by variable-frequency three-phase AC currents. The advantages of the proposed CPM are that the slip rings on the rotor are cast off and it can achieve the efficiency improvement and higher power density. The effects of the claw-pole structure parameters, the air-gap length, and the PM thinner parameter of the proposed CPM on the output torque are investigated by using three-dimensional time-stepping finite element method (3D TS-FEM). The optimal rotor structure of the proposed CPM is obtained by using the response surface methodology (RSM) and the particle swarm optimization (PSO) method and the comparison of full-load performances of the proposed CPM with different material cores (SMC and silicon steel) is analyzed.

Sliding Mode Control of a New Wind-Based Isolated Three-Phase Induction Generator System with Constant Frequency and Adjustable Output Voltage

This paper presents a new stand-alone wind-based induction generator system with constant frequency and adjustable output voltage. The proposed generator consists of a six-phase cage-rotor induction machine with two separate three-phase balanced stator windings and a three-phase space vector pulse width modulation inverter that operates as a static synchronous compensator (STATCOM). The first stator winding is fed by the STATCOM and used to excite the machine while the second stator winding is connected to the generator external load. The main frequency of the STATCOM is determined to be constant and equal to the load-requested frequency. The generator output frequency is independent of the load power demand and its prime mover speed because the frequency of the induced emf in the second stator winding is the same as this constant frequency. A sliding mode control (SMC) is developed to regulate the generator output voltage. A second SMC is used to force the zero active power exchanged between the machine and the STATCOM. Some simulation and experimental results are presented to prove the validity and effectiveness of the proposed generator system.