Rotor Leakage Inductance Research Articles

Magneto-mechanical design of a high-speed machine for aeronautics

Electrical machines that can run at high speeds are more and more studied as they can respond to the increasing need of power onboard of aircrafts. However, to allow high-speed operability mechanical handling of the rotating parts need to be insured. In this paper an analytic design process of a novel high-speed induction machine is presented. The analytical magnetic and mechanical models developed are presented and validated with finite element simulations. The magnetic model is based on a classic equivalent electrical diagram of induction machine with a specific adaptation for the rotor leakage inductance as the squirrel cage is buried. The mechanical model is based on a field displacement approach leading to the stress tensor in all the rotating part. A four degrees of freedom vibration analysis model considering gyroscopic effects based on Euler–Lagrange equation allows to identify the critical speeds of the system. It is shown that some geometrical parameters will have opposed effects on the two physics. Thus, an optimization-based coupling between the different physics allows to design rapidly the desired machine regarding any technical specifications as analytical models are being used.

Experimental Parameter Estimation of Induction Motor Based on Transient and Steady-State Responses in Synchronous and Rotor Reference Frames

This paper presents a method for estimating the equivalent circuit parameters of three-phase induction motors by employing the extended Kalman filter. In this method, the stator currents and voltages, and rotor speed of the motor under an unspecified load and in unsaturated condition are considered. The rotor resistance, mutual inductance, and stator leakage inductance are estimated using the synchronous reference frame in the steady-state mode. Also, the rotor leakage inductance is estimated using the rotor reference frame in the transient mode. Experimental data are used to validate the analytical technique.

Design Method of Differential Cascading for Dual-Stator Brushless Doubly-Fed Induction Wind Generator With Staggered Dual Cage Rotor

This article proposes a new differential-cascading-based dual-stator brushless doubly-fed induction machine with a staggered dual cage rotor. Conventional differential mode of the brushless doubly-fed machine with cage rotor suffers from the low number of rotor bars because of the low equivalent synchronous pole pairs of |p1-p2|, and thus, severe rotor flux leakage, low capacity of magnetic field conversion of the rotor and low efficiency. To overcome the obstacle of the excessive harmonics of the rotor, a design method based on the differential cascading is proposed which enables the cage rotor with a high number of conductor bars even in the case of low pole pairs of |p1-p2|, hence the greatly reduced rotor leakage inductance and enhanced performance of the machine. The rotating magneto-motive force theory is applied to derive the interconnection rule of the staggered dual cage rotor, and meanwhile, the corresponding examples are illustrated. The performance comparisons between the differential cascading and the sum cascading based on the proposed machine are carried out. The results show that the proposed machine based on the differential cascading obtains higher power densities comparing to the sum cascading at the region of sub-natural synchronous speed, while its drawback is the increment of the loss due to the high rotor frequency, gaining lower efficiencies at the region of super-natural synchronous speed.

Standstill Identification of an Induction Motor Model Including Deep-Bar and Saturation Characteristics

This article deals with standstill identification of an induction motor drive for sensorless self-commissioning purposes. The proposed identification method is based on an advanced model of a squirrel-cage induction motor. The model includes the deep-bar effect and the magnetic saturation characteristics. The excitation signals are fed to the stator using a standard inverter without compensating for its nonlinearities. The saturable stator inductance is first identified by means of a robust flux-integration test, where unknown voltage disturbances are canceled with suitably selected current pulses. Then, the deep-bar characteristics are identified by means of a dc-biased sinusoidal excitation using different frequencies. Finally, the cross-saturation characteristics of the rotor leakage inductance are identified by altering the dc bias of the excitation signal. The identified characteristics are transformed to the parameters of the advanced motor model taking into account the interrelations of the aforementioned phenomena. Since the physical phenomena affecting the standstill identification process are properly included in the identified model, fewer approximations are needed and more accurate parameter estimates are obtained. The identification procedure is validated by means of experiments using two different induction motors (5.6 and 45 kW).

Parameter Identification Based Online Noninvasive Estimation of Rotor Temperature in Induction Motors

This article proposes a rotor temperature estimation method for in-service induction machine (IM) based on parameter identification, which combines the advantage of recursive least squares (RLS) and model reference adaptive system (MRAS). The RLS with forgetting factor is firstly adopted to identify the parameters of motor inductances. Then, the online identification of rotor resistance can be realized via the MRAS based on the instantaneous reactive power (IRP) and the proportional integral (PI) regulation adaptive law designed by the Popov hyper-stable theory. Thereby, the rotor temperature is computed by the resistance-temperature relationship of metals. To achieve a fast convergence of the parameter identification, rotor slot harmonics are extracted from the stator current and used to determine the rotor speed in real time. Furthermore, to obtain a more accurate initial value of the stator and rotor leakage inductances and resistances, the first 5–15 cycles of the IM starting process are used to mimic the locked-rotor test condition. A merit of the proposed method is that it requires significantly less time to estimate the rotor resistance than the traditional methods. With a novel test bench, experimental validation is performed on a 22-kW IM. In the test, the rotor temperature is measured in three different ways: 1) wireless sensors inserted in the rotating rotor core and rotor end rings, 2) infrared sensor for rotor end ring temperature, and 3) PT100 installed in stator end winding. With this test bench, the real rotor temperature was revealed, and the effectiveness of the presented method is also verified.

Calculation of magnetizing and leakage inductances of induction machine using finite element method

Distinguishing between the stator and rotor leakage inductances of induction machines is a challenge, and it becomes more difficult in the case of magnetic saturation that arises in some applications such as self-excited induction generators (SEIG). This paper presents a direct and simple procedure to determine the inductances of induction machines in magnetic saturation region, by combining the experimental tests and finite element modeling of the machine at a synchronous speed. The proposed method uses radial component of the magnetic flux density in air gap to calculate the magnetizing inductance. Also, the stator slot and end-winding leakage inductances are derived by calculating the linkage flux of the stator phases for the three-phase balanced induction machine. The effectiveness of the proposed method is verified by simulation and experimental investigation of SEIG.

Offline method for experimental identification of load‐dependentsaturation of induction motor taking into account variation of inverse rotortime constant

Accurate knowledge of induction machine parameters has a direct impact on the overall performance of field-oriented control strategies. In the case of rotor flux oriented control, parameter mismatch causes a discrepancy in the estimated rotor flux position and amplitude. Magnetising inductance is one of the parameters whose detuning has a direct impact on the setpoints of the control loops and estimation of hardly or non-measurable quantities. Conventional iron saturation, which can be obtained by a standard no-load test, is not the only type of saturation occurring in the machine. Depending on the rotor design, the magnetising inductance and the rotor leakage inductance may also strongly saturate as a function of load and, thus, rotor current. Based on the authors’ previous work, a new, improved experimental method for identifying the load-dependent saturation of induction motor, which takes into account variation of the inverse rotor time constant, is proposed. Experimental results conducted on 12 kW motor show improved static and dynamic behaviour of the drive compared to the constant parameter model.

Stray Loss Model for Induction Motors With Using Equivalent Circuit Parameters

This article presents new models to estimate the stray load losses (SLs) of an induction motor using equivalent circuit parameters(ECPs). The stator and rotor slot geometries influence the magnetic field distribution in a motor, and this has a direct impact on the stray load losses. In equivalent circuits, the influence of slots on the magnetic field is represented by stator and rotor leakage inductances and the magnetizing inductance. In this work, the SL is modeled as a function of these inductances for grid-connected induction motors. The validity and accuracy of the proposed models are shown using the test data of 18 premium efficiency motors. It is also shown that the proposed SL model is accurate enough to be used in the design phase. The applicability of the proposed model for the design of IMs is demonstrated by designing, prototyping and testing four different induction motors of the same power ratings.

Analysis of Equivalent Inductance of Three-Phase Induction Motors in the Switching Frequency Range

The equivalent inductance of three-phase induction motors is experimentally investigated in this paper, with particular reference to the frequency range from 1 kHz to 20 kHz, typical for the switching frequency in inverter-fed electrical drives. The equivalent inductance is a basic parameter when determining the inverter-motor current distortion introduced by switching modulation, such as rms of current ripple, peak-to-peak current ripple amplitude, total harmonic distortion (THD), and synthesis of the optimal PWM strategy to minimize the THD itself. In case of squirrel-cage rotors, the experimental evidence shows that the equivalent inductance cannot be considered constant in the frequency range up to 20 kHz, and it considerably differs from the value measured at 50 Hz. This frequency-dependent behaviour can be justified mainly by the skin effect in rotor bars affecting the rotor leakage inductance in the considered frequency range. Experimental results are presented for a set of squirrel-cage induction motors with different rated power and one wound-rotor motor in order to emphasize the aforesaid phenomenon. The measurements were carried out by a three-phase sinusoidal generator with the maximum operating frequency of 5 kHz and a voltage source inverter operating in the six-step mode with the frequency up to 20 kHz.

Parameter Estimation of Asymmetrical Six-Phase Induction Machines Using Modified Standard Tests

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.

Temperature influence analysis on parameter estimation of induction motors using differential evolution

Three-phase induction motors are widely used in industry due to their low cost and ruggedness compared with other electromechanical conversion machines, as the direct cur-rent motors, for example. Systems and control drives (DTC, FOC and V/f) are applied in industry, so it is important to know the electrical and mechanical parameters of the machine, such as, stator and rotor resistances, stator and rotor leakage inductance and magnetizing inductance, moment of inertia and friction coefficients. However, parameters like stator and rotor resistances suffer influences throughout its use due to external factors, such as temperature, which impairs the machine efficiency. In the search for a method to find these parameters, even with the changes provided by the temperature influence, this work proposes the use of differential evolution for the estimation of the parameters using as input the curve of a single phase stator current. Tests were realized using four different temperature values, and for each one it was assigned a corresponding input, in order to analyze the temperature influence on stator and rotor resistance. The results presented show that it is possible to estimate the motor electrical and mechanical parameters even with the changes provided by the temperature influences.

Inductance Saturation of the Induction Machine as a Function of Stator Voltage and Load with Steady State AC Magnetic Finite Element Solver

Magnetization inductance and the stator and rotor leakage inductances of an induction machine are studied as a function of magnetization state and load by the Finite Element Method. With a constant stator supply frequency, the stator voltage amplitude and the slip are varied. The current and flux linkage vectors used in the analysis are constructed based on the phase currents and the flux linkages seen by the conductors in every operating point. The magnetization inductance significantly varies as a function of the magnetization state and load of the machine. The saturation of the stator leakage inductance is dominated by the stator flux amplitude, and the rotor leakage inductance saturation is dominated by the load.

일정토크영역에서 유도전동기 고정자자속기준제어의 파라미터 비동조 영향 분석

It is well known that the stator-flux-oriented induction motor drives are not dependent on parameter detuning in constant torque region except low speed range. This paper presents parameter detuning effects of stator-flux-oriented induction motor drives in constant torque region. The detuning effects of stator resistance, rotor resistance and rotor leakage inductance are analyzed.

Edge optimisation for parameter identification of induction motors

In this work, a simple off-line identification algorithm for an induction motor (IM) is presented, which is based on an optimisation scheme without derivatives, called edge optimisation. The main idea of this identification scheme is to convert the problem of parameters characterisation to a finite-dimensional optimisation problem over a bounded set. The proposed approach relies on the information of a hard or soft startup of the motor, in order to identify all seven IM parameters: stator and rotor leakage inductances, stator and rotor resistances, mutual inductance, mechanical inertia and friction coefficient. Thus, the edge optimisation considers an iterative approximation in order to obtain a convergent sequence to the optimal parameters. This strategy is compared with an stochastic search algorithm and particle filter optimisation. Experimental results on a 1 and 3 HP IM test-rigs show an accurate characterisation with the proposed identification scheme, and validate the approach illustrated in this work.

약계자영역에서 유도전동기 고정자자속기준제어의 파라미터 비동조 영향 분석

The selection of flux level in the maximum torque control of stator flux-oriented induction motor drives in the field weakening region is dependent on stator resistance and inductances. This paper presents parameter detuning effects of stator flux-oriented control drives in the field weakening region. The detuning effects of stator resistance and rotor leakage inductance are analyzed. The decrease of torque and the flux control lost by the detuning of inductance are shown in the simulation results.

Calculation of load‐dependent equivalent circuit parameters of squirrel cage induction motors using time‐harmonic FEM

PurposeThe purpose of this paper is to define a time‐efficient numerical procedure for the extraction of load‐dependent equivalent circuit (EC) parameters of induction machines. The parameters are determined for every operating point, thus their variation due to skin effect and material saturation under arbitrary load condition is taken into consideration.Design/methodology/approachTwo methods are presented and compared. The first one is based on the numerical simulation of the standard measurement process, yielding an EC with constant parameters. A time‐harmonic finite element analysis is applied in the second method to calculate the load‐dependent EC parameters. Material linearization and the superposition principle for the magnetic flux are employed to define the leakage inductances.FindingsA distinct load dependence of all EC parameters has been proven as well as the clear disparity between stator and rotor leakage inductances. These effects can only be taken accurately into account by the EC obtained by the second numerical procedure proposed.Originality/valueThe presented method successfully overcomes typical problems of the measurement process and of the standard numerical procedure for EC parameter estimation, thus the obtained EC parameters are load‐dependent while the physical interpretation of the variables and parameters remains straightforward. Hence, the paper of the internal machine variables is enabled.

Use of the External Magnetic Field for Induction Machine Leakage Inductance Distinction

This paper is about the exploration and the analysis of the AC rotating machine external magnetic field. An experimental procedure is presented: it makes it possible to distinguish the stator and rotor leakage inductances which occur in the induction machine single phase equivalent circuit.

Induction Motor Rotor Temperature Estimation Based on a High-Frequency Model of a Rotor Bar

This paper analyzes a high-frequency (HF) voltage-injection-based rotor winding temperature estimation method for current-regulated squirrel-cage induction motors (IMs). We develop a theoretical HF model of the rotor bar and then first provide an analysis of relevant HF model-based estimation aspects, such as the dependence of the rotor leakage inductance on the temperature and the relationship between the rotor resistance and rotor leakage inductance. We also include an analysis of magnetic saturation to improve the estimation accuracy, as well as an analysis of the phase delay effect resulting from the drive that significantly affects the HF signal precision. Then, a specialized offline commissioning scheme is proposed to compensate for the effect of the phase delay and magnetic saturation. The estimation technique and sensitivity analysis are verified by means of experiments performed on an inverter-fed 1.5-kW IM.

Parameter determination of an induction machine for integrated starter alternator

This paper presents a study on parameter variations of an induction machine for integrated starter alternator (ISA) with respect to stator frequency, magnetisation and slip frequency. No-load and stand-still tests are conducted under variable-frequency and variable-voltage instead of conventional constant frequency tests, using a PWM inverter in order to obtain the variations of rotor resistance, rotor leakage inductance, magnetising inductance and core-loss. In addition to these tests, impressed stator voltage and impressed stator current tests are carried out. Theory, analysis and results of the above parameter determination methods are presented. The parameter variations obtained from the variable-frequency variable-voltage no-load and stand-still tests are compared with conventional tests parameters as well as the parameters obtained from impressed stator voltage and stator current tests. The parameter variations found in this study can be used to obtain a detailed model that predicts the behaviour of the induction machine over wide speed range and under dynamic loading conditions more precisely than the conventional constant parameter model.

MATLAB simulation of induction machine with saturable leakage and magnetizing inductances

At high stator phase currents, the effect of saturation of the stator and rotor leakage inductances becomes noticeable to the extent that the conventional machine model fails to represent the dynamic performances of induction machine. In this paper, a commercial software package, MATLAB is used to simulate the dynamic behaviour of induction machine with saturable inductances. The computer results presented in this paper show the errors resulting when the magnetizing, stator and rotor leakage inductances are assumed constant as in the case of conventional machine model. Key Words: Simulation, Saturation effect, Induction machine, Transient state, MATLAB. Botswana Journal of Technology Vol.13(2) 2004: 20-28