The influence of mistuned motor parameters on vector control performance and on line slip frequency correction strategy for induction machine operated under one‐pulse PWM mode

In high‐power, high‐speed traction drive systems, the traction motor usually operates under one‐pulse PWM (pulse width modulation) mode (square wave) during high‐speed operation. The constant output voltage in this condition makes the traditional vector control inoperative anymore. In this paper, a modified vector control strategy using open‐loop current control instead of closed‐loop current control is proposed. The modified control strategy is specially designed for an induction motor operating under one‐pulse PWM mode. As the field orientation is greatly affected by the deviation in the parameters, the influence of mistuned rotor time constant and mutual inductance (which are regarded as the most important parameters for field orientation) on the performance of modified vector control is studied comprehensively, including the influence on estimated angle and amplitude of rotor flux, d/q‐axis voltage, and output torque. Subsequently, based on the comparison between the different methods, a new slip frequency correction strategy is proposed to maintain proper field orientation for the modified vector control. The new correction strategy is based on the q‐axis current component error. It is independent of the motor parameters and can be easily realized through minor calculations. The simulation and experimental results show that the proposed slip frequency correction strategy can not only eliminate rotor flux angle error in steady state but also effect rapid torque response during the transient process under one‐pulse PWM mode. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Position and speed sensorless control system of permanent magnet synchronous motor with parameter identification

The model parameters of a permanent magnet synchronous motor (PMSM) are required for high‐performance control and a model‐based sensorless control. This paper proposes a sensorless control system of PMSM that does not need parametric information beforehand. The parameters of a PMSM drive system, including the inverter, are identified at standstill and under operating conditions. At first, the initial rotor position is estimated by a signal injection sensorless scheme in which the machine parameters are not required. After the initial position has been estimated, the resistance, including the on resistance of the IGBT, the voltage error caused by dead time in the inverter, and d‐axis and q‐axis inductances, are identified at standstill. After the motor starts by the signal injection sensorless control, the sensorless scheme changes to an extended EMF estimation scheme. The estimated parameters for the resistance, and daxis and q‐axis inductances are used in such sensorless control. The magnet flux‐linkage, which cannot be estimated at standstill, is identified under the sensorless operation at medium and high speeds. The effectiveness of the proposed method is verified by several experimental results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 68–76, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20548     

一种混合励磁同步发电机的气隙磁密分析及其电压谐波抑制

为改善混合励磁同步发电机的气隙磁密分布,采用三段式气隙长度对转子进行了优化,对比了优化前后的气隙磁密。为抑制电压谐波,在完成转子结构优化的基础上,进一步采用短距、分布电枢绕组以及定子斜槽等措施。最后对样机电压波形进行了实测和质量分析,结果表明:采用三段式气隙长度与定子斜槽相结合,可将电压波形的总谐波失真(THD)抑制在5%的范围内。此外,探讨了偏心距法在切向/径向混合励磁电机中应用的可行性,并对比了分别采用偏心距法和三段式气隙长度法时的气隙磁密。     

Novel voltage limiter for fast torque response of IPMSM in voltage saturation region

A new voltage limiter for fast torque response of IPMSM in the voltage saturation region is proposed, which we name the “maximum torque response voltage limiter.” In transient condition, the fastest response is vital while voltage saturation occurs. Thus, the problem is to divide the limited voltage into d‐ and q‐axis voltages so as to generate the fastest torque response. The nonlinear relation between the torque and the d‐q axis currents of the IPMSM makes the problem complicated. In our proposed method, both voltage equations and a torque equation of the IPMSM are considered and, based on the Lagrange optimization technique, explicit expressions for the d‐ and q‐axis voltages are derived. Compared with conventional voltage limiters such as the constant phase angle method, the constant back emf method, and the constant d‐axis voltage method, the proposed limiter yields faster torque response in the voltage saturation region, which is confirmed by computer simulation and experimental results. Furthermore, the proposed method uses simple software calculations, and it can be readily implemented without any modification of the hardware system. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 57–69, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21078     

Rotor position estimation method of IPMSM using HF signal injection and sliding‐mode controller

This paper presents a simplified algorithm for the estimation of rotor position. A high‐frequency (HF) sinusoidal voltage is injected into the stator of a motor. An interior permanent magnet synchronous motor (IPMSM) has spatial saliency because the d‐ and q‐axis inductances are different from each other. The injected HF voltage is influenced by this saliency. Therefore, the rotor position is included in the stator current of the motor. The proposed method uses different synchronous reference frame transformations (SFTs) to extract the rotor position error between the estimated value and actual value. Also, a sliding‐mode controller is used for robustness against parameter variation and external disturbance. The experimental results confirm the effectiveness of the proposed method by showing waveforms of the rotor speed and position with load conditions. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Speed estimation of induction motor drive using d‐axis slot harmonics and parameter identification method

This paper describes a rotor speed estimation technique of an induction motor, which utlizes slot harmonics on the d‐axis caused by permeance variation across the air gap. The frequency of the slot harmonics is a multiple of the actual rotor speed, and is proportional to the number of rotor slots. In order to extract the slot harmonics, a novel adaptive bandpass filter incorporating coordinate transformation is proposed, which is effective to estimate the rotor speed from 400 to 2000 rpm. This rotor speed estimation is applied to a field‐oriented controller as well as a speed controller. In addition, performance improvement is carried out by compensating a motor parameter mismatch. Feasibility of the proposed technique is confirmed through several tests, using a prototype experimental setup. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 50–58, 2010; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/eej.20901     

High‐efficiency,low‐torque ripple control of a permanent magnet synchronous motor based on current tracking vector of electromotive force

Since ordinary magnetic field poles of a PM (permanent magnet) motor generate higher harmonic flux, sinusoidal current will cause torque ripple. This is usually removed by short pitch winding, skew slot method, and so on. These methods have a drawback in terms of lower efficiency. Recently, new current control methods have been proposed to realize zero‐torque ripple and high‐efficiency drive at the same time. However, because the optimized reference current waveform obtained by these methods includes zero phase component, normal three‐phase full bridge inverter and d–q coordinate control method cannot be used. This paper proposes a new current control method that can achieve zero‐torque ripple and maximum efficiency by using a normal three‐phase inverter. The three‐phase optimum current can be derived by satisfying the following conditions: (1) the direction of the current resultant vector always agrees with that of the electromotive force resultant vector, and (2) the scalar product of the two vectors is held constant. By means of modifying the coordinate transformation angle, this method can also make it possible to compensate torque pulsation error with maximum efficiency using general d–q coordinate control method. The proposed method has been verified by experiments. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 57–64, 2001     

Modeling the dynamic and static operating conditions of a wind-driven electric plant with a double-supply asynchronous motor

The procedure for modeling a double-supply asynchronous motor during its operation in combination with a windmill is proposed. The advisability of presenting equations in axes d and q rotating at the speed of the rotor speed is given. Calculations are performed for transient processes in the given system during the regulation of both the amplitude and frequency of the rotor supply voltage.     

开关角对斜槽转子SRM稳态转矩的多目标优化

开关磁阻电机转子斜槽结构可有效减小电磁径向力,但会导致转矩特性变化。针对该问题,给出了线性模型下斜槽转子开关磁阻电机稳态转矩的解析方法,然后建立了四相8/6极开关磁阻电机模型,采用三维有限元仿真方法,计及端部漏磁,以电流开通角、关断角和转子斜槽角度为优化参数,以平均转矩变化量最小和转矩脉动最小为优化目标,基于正交试验法设计试验方案,通过极差和方差分析确定了相应参数的优组合,并将优化前后的转矩特性进行了比较,结果表明:小的斜槽角度对转矩特性的影响并不大,优化后电机的平均转矩相比优化前只变化了16.01%,但其转矩脉动下降了23.63%。     

Sensorless vector controlled converter for variable speed wind generation system using an induction generator

This paper proposed two types of speed sensorless converters that can control rotational speed and electric power. One is based on a slip frequency control system. The other is based on a vector control system. The rotational speed of the wind turbine is estimated with the phase voltage and phase current of the induction generator by the adaptive rotor flux observer. The estimated wind turbine rotational speed ω_r^est is used as the feedback of the speed control loop in the converter control system. Also, the estimated rotor flux ?_2d^est is used for the vector control. The simulation results confirm that both of them perform satisfactorily under the speed sensorless operation. The method based on the vector control system generates more electrical energy than does the method based on the slip frequency control system. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 62–75, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20323     

Determination of Synchronous Reactance and No‐Load Saturation Curve of Synchronous Machines by dc Test Considering Magnetic Saturation Effect

dc Tests can accurately determine the unsaturated synchronous machine‐equivalent circuit constants by a simple standstill test. This paper presents two improved dc tests that account for the magnetic saturation of the stator iron core by the main flux. These tests are tentatively named Step Response Test (I) and Step Response Test (II). The former can predict the incremental d‐axis synchronous reactance by performing a Fourier transform of the voltage and current measured when a small step voltage is applied to the two armature terminals as a field current flows. The latter can determine the incremental d‐ and q‐axes synchronous reactances by the same Fourier transform of the voltage and current measured when a small step voltage is applied to the two armature terminals as an armature current flows. In addition, this paper introduces a new method to calculate not only the static d‐ and q‐axes synchronous reactances but also the no‐load saturation and short‐circuit characteristic curves. This new method does not require the results from any additional tests including the rotational driving tests and dimensional information, which can only be obtained from the manufacturer. To demonstrate the validity of the proposed method, results of an experiment using 10‐kVA laminated synchronous machines with damper winding are presented.     

Extension of Mathematical Models Taking Temperature Variation in Permanent Magnet Synchronous Motors into Consideration

We have developed novel mathematical models of d‐axis and q‐axis magnetic fluxes ?_d and ?_q for permanent magnet synchronous motors (PMSMs). The models can be used to approximate magnetic characteristics using simple fractional equations with i_d and i_q as variables. They include eight constants, and some of them represent the degree of magnetic saturation and cross‐coupling. However, the magnetic characteristics are varied with the temperature rise in PMSMs, which are dependent on the load torque and motor speed. In this paper, the characteristics of the eight constants that vary with the motor temperature and the residual flux density B_r are shown. Further, we propose to extend the mathematical models by considering the temperature and B_r variation.     

A new approach for low voltage ride through capability in DFIG based wind farm

Protection against voltage dips is very important for transient stability in a Doubly Fed Induction Generator (DFIG). Conventional crowbar circuits have been used for protection of DFIGs; however, they may be insufficient in some transient situations. Therefore, the Low Voltage Ride Through (LVRT) capability was enhanced by a Demagnetization Current Controller (DCC) for the purpose of transient analysis. In addition, both stator and rotor circuit electromotive forces were modeled in a DFIG. The performances of the DFIG models with and without the DCC were compared. Modeling was carried out in a MATLAB/SIMULINK environment. A comparison of system behaviors was made between three-phase faults with and without a stator–rotor dynamic. Parameters for the DFIG including output voltage, speed, electrical torque variations and d–q axis rotor–stator current variations in addition to a 34.5 kV bus voltage were examined. It was found that in the DFIG model the system became stable in a short time when using the DCC.     

Magnetic field analysis of a squirrel cage induction motor considering rotor skew and higher harmonics in the secondary current

This paper describes a method to analyze harmonic magnetic fields of squirrel cage induction motors considering rotor skew and higher harmonics in the secondary current. The proposed method is based on a two‐dimensional finite element method. The rotor skew structure is expressed by multiple 2D finite element mesh models, produced in suitable axial positions, and the magnetic field in each mesh model is calculated by the revised secondary current taking into account the skew effect. The secondary currents, magnetic flux densities, and electromotive forces are calculated by the proposed method. Then the differences between a skewed rotor and a nonskewed rotor are discussed. From the comparison between the calculated and the experimental results, the proposed method is shown to be appropriate and useful for quantitative estimation of harmonic components of induction motors. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 98–109, 1999     

Experimental verification of stray losses in cage induction motors under no-load,full-load and reverse rotation test conditions

Contents The stray load losses of polyphase squirrel-cage induction motors have hitherto rarely been measured at rated voltage and full-load, owing to the great difficulties in achieving the required measuring accuracy; instead, mostly the reverse rotation test is used. This paper primarily deals with the question whether the reverse rotation test yields representative results. It is also examined to what extent it is possible to predetermine the stray losses by means of a series of new investigations on space harmonics of flux density and harmonics of rotor current. For this purpose the stray losses of a four-pole 11 kW polyphase induction machine with semi-closed and open stator slots as well as rotors with a varying number of unskewed and skewed slots are measured under no-load and full-load conditions and in the reverse rotation test and computed for machines with unskewed slots.

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Experimentelle Überprüfung der Zusatzverluste von Käfigläufermotoren im Leerlauf, unter Last und im Reverse Rotation Test

Übersicht Wegen der beträchtlichen meßtechnischen Schwierigkeiten sind die Zusatzverluste von Drehstromasynchronmotoren mit Käfigläufern bisher nur selten bei Nennspannung und Nennlast gemessen worden; statt dessen verwendet man weithin den Reverse Rotation Test. Die vorliegende Arbeit befaßt sich in erster Linie mit der Frage, inwieweit es möglich ist, die Zusatzverluste mit Hilfe einer Reihe neuer Untersuchungen der Oberfelder und Läuferoberströme vorauszuberechnen. Außerdem wird die Gültigkeit des Reverse Rotation Test untersucht. Zu diesem Zweck werden die Zusatzverluste einer vierpoligen 11 kW-Drehstromasynchronmaschine mit halbgeschlossenen und offenen Ständernuten sowie Läufern mit ungeschrägten und geschrägten Nuten unterschiedlicher Nutenzahl im Leerlauf, unter Nennlast und im Reverse Rotation Test gemessen und für Maschinen mit ungeschrägten Nuten berechnet.

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List of symbols B magnetic flux density - f frequency - g order of rotor slot harmonics - I, I ₀,I _n stator current, at no load, at rated load - I _vr harmonics of rotor current - N number of slots - P power - P _Cu fundamentalI ² R losses - P _Fe iron losses at no-load test - P _Fe50 iron losses due to 50 Hz flux density - P _f friction and windage losses - P _gap airgap power - P _m mechanical power output - P _rrt stray load losses at reverse rotation test - P _s electrical power input at stator - P _stray stray losses - P _strayn stray load losses at rated load - P _{stray 0} stray losses at no-load - p number of pairs of poles - q slots per pole and phase - s slip - T torque - U voltage - order of rotor harmonic pairs of poles - order of stator harmonic pairs of poles - supply angular frequency Principal subcripts n at rated load - r rotor - s stator     

Optimization of magnet arrangement in double‐layer interior permanent‐magnet motors

The arrangement of permanent magnets in double‐layer interior permanent‐magnet motors is optimized for variable‐speed applications. First, the arrangement of magnets is decided by automatic optimization. Next, the superiority of the optimized motor is discussed by considering d‐ and q‐axis equivalent circuits that take into account the magnetic saturation of the rotor core. Finally, experimental veri?cation is carried out with a prototype motor. It is con?rmed that the maximum torque of the optimized motor under both low‐speed and high‐speed conditions is higher than that of conventional motors because of the relatively large q‐axis inductance and small d‐axis inductance. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 54–63, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22348     

FLUX DISTRIBUTION AND REACTANCE IN ENCLOSED SLOT SOLID ROTOR INDUCTION MOTOR

ABSTRACT

In this paper flux distribution by finite element method in the solid rotor with enclosed slot induction motor compared with the flux distribution in the laminate core rotor with enclosed slot is examined.

This paper also presents a method of deriving the reactance from the magnetic energy stored at the portion of the rotor surface. The method of calculating the reactance of the slot tip of an induction motor with enclosed slots is examined. The starting performance calculation of this motor are also described.

Explanation is made here in the order as follows: Equivalent circuit of enclosed slot solid rotor induction motor, Flux distribution in the solid rotor with enclosed slots, Method of deriving the reactance from stored and accumulated magnetic energy, Calculation of the flux distribution, Examples of calculations on the reactance of the slot tip, Results of calculation and measurement on characteristics of the tested motor.

The method of deriving the reactance from the magnetic energy stored in the surface region of the core is considered to be utilizable widely in the technology of magnetic circuits involving non-linear magnetic characteristics     

A current sensorless drive system of a synchronous motor with a low‐resolution position sensor

High‐performance drive of synchronous motors such as a permanent magnet synchronous motor and a synchronous reluctance motor can be achieved by current vector control. In such drive systems, the armature current is controlled as a sinusoidal waveform based on rotor position information from a high‐resolution position sensor, and the current vector (d‐ and q‐axis currents) is suitably controlled by current feedback control. This paper proposes a current sensorless drive system with a low‐resolution position sensor in order to simplify the SM drive system. High‐performance current control is achieved in the proposed drive system, where the current sensors are eliminated and the simulated currents are used for current control. The low‐resolution position sensor is used instead of a conventional high‐resolution position sensor, and the higher position information is estimated. The steady‐state and transient characteristics are examined in several experiments with respect to the synchronous reluctance motor and the interior permanent magnet synchronous motor. It is confirmed that sinusoidal current drive, high‐performance current vector control, and speed control can be achieved by the proposed drive system. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 34–43, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10072     

A new modeling approach for circuit‐field‐coupled time‐stepping electromagnetic analysis of saturated interior permanent magnet synchronous motors

This paper proposes a new modeling approach for circuit‐field‐coupled time‐stepping electromagnetic analysis of a saturated interior permanent magnet synchronous motor (IPMSM). To predict the drive performance quickly, the proposed approach consists of a dynamic simulator based on a new analytical model of the d‐ and q‐axis magnetization characteristics (λ‐i_d‐i_q‐θ). The model can take into account not only cross‐saturation but also the harmonics of the inductance distributions and EMF waveforms. The validity of the model is verified from suitable simulation results for the instantaneous current and torque waveforms of the IPMSM. The proposed analysis leads to a dramatic reduction in the computation time compared to circuit‐field‐coupled time‐stepping FEA, while maintaining analytical accuracy. The effectiveness of the proposed method is experimentally verified using a 10‐kW, 15,000‐rpm concentrated‐winding IPM motor. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 49–58, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21024     

采用拼接式转子的内置永磁同步电动机的优化设计

针对传统内置永磁同步电动机漏磁系数较大,隔磁桥机械强度较差等特点,提出一种拼接式转子,这种转子具有若干个独立的铁心,用高强度非铁磁部件通过鸽尾形槽把这些铁心拼接起来,这种转子不需要隔磁桥,所以这种转子能够有效限制漏磁。拼接式转子的铁心具有一些磁障(空气槽),这些磁障可以影响气隙内的磁场分布从而实现近似正弦分布的气隙磁密波形。初步设计了一台基于拼接式转子的3 k W电动机,采用田口法对转子磁障的关键参数进行了优化,并对拼接式转子和传统内置永磁转子进行了对比分析,结果表明所提出的拼接式转子优于传统内置永磁转子。