Iron loss in rotor-flux-oriented induction machines:identification, assessment of detuning, and compensation

Iron loss, traditionally ignored in vector control schemes, has recently attracted more attention as a cause of detuned operation of rotor-flux-oriented induction machines. Appropriate mathematical tools, that enable evaluation of detuning due to iron loss, have become available, and these have been used so far only in assessment of detuning for rated speed operation in the constant flux region. The available studies are based on the measurement of iron losses with voltage supply of rated frequency. This paper attempts to provide a more detailed treatment of iron loss induced detuning in rotor-flux-oriented induction machines by presenting at first an experimental method of iron loss identification over the entire frequency (speed) range of interest. The experimental results enable calculation of the equivalent iron loss resistance that is subsequently used in evaluation of detuning. The regimes dealt with encompass motoring and braking operation in the base speed range and motoring in the field-weakening region up to the five times rated speed. It is shown that detuning in the base speed range will be the highest at rated speed operation and will exhibit opposite trends in motoring and braking regions. Detuning in the field-weakening region is found to be significantly in excess of the one at rated speed, provided that the machine operates at high speeds with relatively light loads. As compensation of iron loss seems to be necessary in this case, the concluding part of the paper presents a novel rotor flux estimator that utilizes experimentally identified equivalent iron loss resistance values and enables elimination of detuning that is otherwise present. The estimator is a modified version of the well-known scheme that operates on the basis of measurement of stator currents and rotor speed (position). Its ability to compensate for iron loss is verified by simulation     

Sensorless control of induction Machines at zero and low frequency using zero sequence currents

This paper considers both flux and rotor position estimations for sensorless control of delta-connected cage induction machines (IMs) at low and zero frequency operation. The variation of leakage inductance due to either saturation or rotor slotting is tracked by measuring the derivative of the zero sequence current in response to the application of appropriate voltage test vectors. The method requires only a single extra sensor. It requires access to machine phase windings and is appropriate for integrated-type induction motor drives. Both a closed-slot and an open-slot machine is used to demonstrate rotor flux and rotor position tracking, respectively. Experimental results are presented showing sensorless torque control and sensorless speed and position control at low and zero frequencies.     

On the Speed Limits of Permanent-Magnet Machines

Permanent-magnet (PM) machines are considered the most suitable machine type for very high speed applications. Still, due to the growing demand for the ever higher rotational speeds, PM machines are approaching their limits. The focus of this paper is the different factors that lie behind the inherent speed limitations of PM machines. The limits-thermal, elastic, and rotor dynamical-are defined, classified, and correlated to basic machine parameters.     

Vibration control of flexible rotor by inclination control magneticbearings with axial self-bearing motor

An inclination control method has been developed to stabilize a flexible rotor on magnetic bearings that operates over several critical bending speeds. It is desired to increase the rotating speed of the centrifuge which is supported by magnetic bearings on both ends of the rotor. Each magnetic bearing is composed of a pair of hybrid-type magnetic bearings and can control the inclination as well as the position of the rotor. The central position and the inclination of the rotor are calculated by the sum and difference of the measured displacements. These two quantities are supplied to the individual proportional and derivative controllers to obtain the actuating signals. The central position is controlled to provide sufficient stiffness to support the rotor while the inclination control capability is used to obtain adequate damping for the bending mode of the rotor. The control approach is tested on a rotor with three midspan disks to reduce the bending resonances with complete noncontact levitation. A high rotating speed of 6300 r/min was achieved, which is above the fifth bending critical speed     

Sensorless position measurement in synchronous reluctance motor

A new discrete position sensor elimination technique for a sinusoidally wound synchronous reluctance motor drive is presented. The proposed technique determines the rotor position at zero crossing of the phase currents. The rotor position between the zero crossings is determined by applying extrapolation. The proposed technique works well at all speeds, including zero speed. This technique can be used in both vector controlled and conventional constant volts/Hertz type of motor controllers     

Modular Three-Phase Permanent-Magnet Brushless Machines for In-Wheel Applications

This paper describes the merits of a recently developed form of a three-phase permanent-magnet (PM) brushless ac machine in which the concentrated coils of each stator phase are wound either on adjacent teeth or on alternate teeth. Such a machine is often referred to as modular and offers a number of significant advantages over conventional PM brushless machines. For example, it results in a smaller number of slots for a given number of poles, which is a distinct manufacturing advantage, and yields a fractional number of slots per pole, which is conducive to low cogging torque. It also enables a significant increase in the achievable machine inductance to facilitate constant power operation over a wide speed range by flux weakening. However, the torque in modular machines is developed by the interaction of a high-order stator space harmonic MMF with the PMs, since the fundamental stator MMF has fewer poles than the PM rotor. Hence, significant eddy currents may be induced in the rotor by the fundamental and low-order space harmonic MMFs. The eddy-current loss can, however, be reduced by segmenting the magnets. Given that modular machines combine the high specific power and efficiency of conventional PM brushless machines with a high machine inductance, to enable a wide speed range, constant power operation, their potential for low manufacturing cost, and the fact that they have inherently low cogging torque, they are eminently suitable for in-wheel traction applications.      

Anisotropy Comparison of Reluctance and PM Synchronous Machines for Position Sensorless Control Using HF Carrier Injection

Position sensorless control of reluctance and permanent magnet synchronous machines at zero and low speed is possible using HF voltage injection and proper demodulation. The so-called saliency position, which is tracked by the HF sensorless scheme, is different from the actual rotor position: the difference contains both offset and rotor-position-varying components, which may be explained by carefully considering the HF behavior of the machine and the effect that fundamental excitation and rotor position have upon it. This paper gives insight into the HF behavior of synchronous machines and serves as a practical guide for implementation of stable and robust position estimation at zero and low speed.      

Design and implementation of the extended Kalman filter for thespeed and rotor position estimation of brushless DC motor

A method for speed and rotor position estimation of a brushless DC motor (BLDCM) is presented in this paper. An extended Kalman filter (EKF) is employed to estimate the motor state variables by only using measurements of the stator fine voltages and currents. When applying the EKF, it was necessary to solve some specific problems related to the voltage and current waveforms of the BLDCM. During the estimation procedure, the voltage- and current-measuring signals are not filtered, which is otherwise usually done when applying similar methods. The voltage average value during the sampling interval is obtained by combining measurements and calculations, owing to the application of the predictive current controller which is based on the mathematical model of motor. Two variants of the estimation algorithm are considered: (1) speed and rotor position are estimated with constant motor parameters and (2) the stator resistance is estimated simultaneously with motor state variables. In order to verify the estimation results, the laboratory setup has been constructed using a motor with ratings of 1.5 kW, 2000 r/min, fed by an insulated gate bipolar transistor inverter. The speed and current controls, as well as the estimation algorithm, have been implemented by a digital signal processor (TMS320C50). The experimental results show that is possible to estimate the speed and rotor position of the BLDCM with sufficient accuracy in both steady-state and dynamic operation. Introducing the estimation of the stator resistance, the speed estimation accuracy is increased, particularly at low speeds. At the end of the paper, the characteristics of the sensorless drive are analyzed. A sensorless speed control system has been achieved with maximum steady-state error between reference and actual motor speed of ±1% at speeds above 5% of the rated value     

一种转子位置传感器无刷直流电机速度检测方法

本文提出了一种利用转子位置传感器发出的信号测量无刷直流电机（BLDC）转速的方法,并设计了相应的转动方向测定电路和数字PI速度控制器模块。通过利用比例积分控制器计算半个转动周期内的两次连续测量值,结合提出的转动方向测定电路和数字PI速度控制器,可以得出具有双倍测量频率的转子转动周期的准确值。最后将提出的方法在FPGA平台进行了实现,并与真实数据的对比表明,该算法在无换向器直流电机上可以获得具有高精度及高频率的速度测量值（每转动1周至少测量6次）。     

A high-performance sensorless indirect stator flux orientation control of induction motor drive

A new method for the implementation of a sensorless indirect stator-flux-oriented control (ISFOC) of induction motor drives with stator resistance tuning is proposed in this paper. The proposed method for the estimation of speed and stator resistance is based only on measurement of stator currents. The error of the measured q-axis current from its reference value feeds the proportional plus integral (PI) controller, the output of which is the estimated slip frequency. It is subtracted from the synchronous angular frequency, which is obtained from the output integral plus proportional (IP) rotor speed controller, to have the estimated rotor speed. For current regulation, this paper proposes a conventional PI controller with feedforward compensation terms in the synchronous frame. Owing to its advantages, an IP controller is used for rotor speed regulation. Stator resistance updating is based on the measured and reference d-axis stator current of an induction motor on d-q frame synchronously rotating with the stator flux vector. Experimental results for a 3-kW induction motor are presented and analyzed by using a dSpace system with DS1102 controller board based on the digital signal processor (DSP) TMS320C31. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method.     

Decoupling control of induction motor drives

The decoupling control of induction machines is investigated. Three different schemes for decoupling-control methods based on stator flux, airgap flux, and rotor flux field regulation are developed. The control dynamics of each scheme are outlined and studied. Simulation results are presented to verify that these schemes provide decoupling control with excellent dynamic behavior. The transient and steady-state relationships between slip frequency and torque, under constant stator flux, airgap flux, and rotor flux operations, are simulated and compared. The sensitivity characteristics of the three methods of flux-control, machine fed by impressed currents and voltages, are also compared and studied. A prototype torque-drive system is implemented to demonstrate the decoupling control of a squirrel-cage induction machine     

Sequences of field-oriented control for the detection of faultyrotor bars in induction machines-the Vienna Monitoring Method

Rotor cage asymmetries of induction machines cause disturbances of the air-gap flux pattern. These deviations affect torque and speed as well as stator terminal voltages and currents. The proposed fault detection technique senses the actual machine state with the help of real-time space-phasor models. The Vienna Monitoring Method compares online a voltage model output with a current model and observes the deviations in a rotor fixed reference frame. High accuracy and robustness allow the detection of a faulty rotor bar out of the switched voltage and current signals of an inverter-fed machine in an early state. The focus of this paper is the detection of a single rotor bar increase under transient speed conditions without the necessity of a clutched load. During an inverter-controlled acceleration, lasting only 200 ms, the Vienna Monitoring Method evaluates currents, voltages, and rotor position for the calculation of an indication quantity that allows for reliable detection. As only one acceleration task does not excite every rotor cage bar sufficiently, a set of acceleration and deceleration cycles has to be driven     

Magnetising method for speed sensorless controlled induction motordrives

In speed-sensorless controlled standard induction machine drives a start without torque is only possible if the rotor speed of the demagnetised machines is known. A new method is proposed, which allows a fast and accurate identification of the rotor speed of demagnetised machines without a speed or position sensor     

Optimization of a synchronous reluctance machine for a sensorless drive with a wide field-weakening range

For more than one century, electrical machines have been utilized for electrical drives. Nowadays, in most applications the electrical machine is fed by an inverter. Three types of machines are available for such purposes: the asynchronous induction machine, the permanent magnet excited synchronous machine and the synchronous reluctance machine. Reluctance machines represent an alternative to the other types when utilized in high-performance drives with a wide speed range. Due to the rotor saliency, these machines have an inherent suitability for a position-sensorless control. The parameters of a 5 kW machine with a maximum speed of 8000 rpm are evaluated by means of nonlinear finite element analyses. With regard to an application in a high-performance drive with a wide field-weakening range and a position-sensorless control scheme, the characteristics are calculated for the conventional reluctance machine as well as the reluctance machine with additional permanent magnets in the rotor. The comparison of the characteristics of the conventional reluctance machine and the permanent magnet assisted reluctance machine clearly shows the improved performance in terms of electromagnetic torque and power factor due to the interior permanent magnets. Thereby, the suitability for the application in position-sensorless drives due to the high effective saliency is preserved.     

PMSM无传感器初始位置检测及低速运行研究

目前,永磁同步电机(PMSM)无位置传感器运行研究受到广泛关注。文章采用一种基于高频方波信号注入的方法实现PMSM无位置传感器启动以及低速运行。首先详细分析了高频方波信号注入检测原理,然后对注入的高频方波信号以及电流采样模式进行了改进。在估计的两相旋转坐标系轴向注入频率等于逆变器开关频率的高频方波电压信号,通过巧妙的安排定子电流采样模式,根据检测到的定子电流并结合注入的方波电压信号即可获得转子位置信息;采用Luenberger观测器对转子位置信息进行观测,以获得较为平稳准确的电机转速和转子角度估计值;利用电机的磁路饱和特性,实现基于高频方波信号注入法的PMSM无位置传感器转子初始位置检测。所提出的改进方法不依赖于准确的电机参数,不需要使用任何滤波器,信号处理过程简单易实现。仿真结果验证了该方法的正确性。     

Hybrid rotor position observer for wide speed-range sensorless PM motor drives including zero speed

This paper addresses the problem of wide speed-range sensorless control of a surface-mount permanent-magnet (SMPM) machine including zero-speed operation. A hybrid structure integrating a flux observer and signal-injection techniques is proposed, which results in a rotor position signal independent of motor parameters at low and zero speed. Although the SMPM machine typically has a very low geometric saliency, the injection technique is effective in tracking the saturation-induced saliency produced by the stator flux. Experimental results are presented showing an excellent performance for both the sensorless speed and position control using an off-the-shelf SMPM machine.     

Development and testing of the torque control for the permanent-magnet synchronous motor

Hybrid electrical vehicles and electrical vehicles are being actively developed. A hybrid electric vehicle motor design requires high efficiency, high power/weight ratio, and reliability from low rotor speed to high rotor speed. The permanent-magnet synchronous motor is used in order to fulfill these requirements. The purpose of this paper is to develop a permanent-magnet synchronous motor control method for all rotor speeds. This method increases the torque and the efficiency at high speed when compared to the ordinary current error feedback method. A method composed of two compensators is proposed to achieve this objective. One of the compensators controls the torque using the voltage phases. The other one is the ordinary current error feedback. Several correcting methods for the voltage phase compensator have been proposed for the compensator for many control demands. The validity of the proposed method was confirmed using simulation and experimental evaluations.     

A fully digitized field-oriented controlled induction motor driveusing only current sensors

A field-oriented control method based on a predictive observer with digital current regulation of an induction motor, without speed and voltage sensors, is proposed. Measuring only stator currents and estimating motor speed and rotor fluxes by a predictive state observer with variable pole selection the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. The resulting speed and rotor fluxes are estimated with low sensitivity to parameter variation, and the torque ripples are reduced. The proposed method consists of four parts: identification of the rotor speed, derivation of a digital control law, construction of a state observer that predicts the rotor flux and the stator currents, and derivation of field-oriented control. A theoretical analysis of the method, computer simulations, and experimental results are described     

Sensorless speed control of nonsalient permanent-magnet synchronous motor using rotor-position-tracking PI controller

This paper presents a new velocity estimation strategy of a nonsalient permanent-magnet synchronous motor (PMSM) drive without a high-frequency signal injection or special pulsewidth-modulation (PWM) pattern. This approach is based on the d-axis current regulator output voltage of the drive system that has the information of rotor position error. Rotor velocity can be estimated through a rotor-position-tracking proportional-integral (PI) controller that controls the position error to zero. For zero and low-speed operation, the PI controller gains of rotor position tracking controller have a variable structure according to the estimated rotor velocity. In order to boost the bandwidth of the PI controller around zero speed, a loop recovery technique is applied to the control system. The proposed method only requires the flux linkage of the permanent magnet and is insensitive to parameter estimation error and variation. The designers can easily determine the possible operating range with a desired bandwidth and perform vector control even at low speeds. The experimental results show the satisfactory operation of the proposed sensorless algorithm under rated load conditions.