Sensorless position control of induction motors-an emergingtechnology

Concepts for the sensorless position control of induction motor drives rely on anisotropic properties of the machine rotor. Such anisotropies can be incorporated as periodic variations of magnetic saliencies in various ways. The built-in spatial anisotropy is detected by injecting a high-frequency flux wave into the stator. The resulting stator current harmonics contain frequency components that depend on the rotor position. Models of the rotor saliency serve to extract the rotor position signal using phase-locked loop techniques. A different approach makes use of the parasitic effects that originate from the discrete winding structure of a cage rotor. It has the merit of providing high spatial resolution for incremental positioning without sensor. The practical implementation of sensorless position identification and of a high-accuracy position control system are reported     

Implementation and experimental investigation of sensorless speed control with initial rotor position estimation for interior permanent magnet synchronous motor drive

In this paper, a new approach to sensorless speed control and initial rotor position estimation for interior permanent magnet synchronous motor (IPMSM) drive is presented. In rotating condition, speed and rotor position estimation of IPMSM drive are obtained through an extended Kalman filter (EKF) algorithm simply by measurement of the stator line voltages and currents. The main difficulty in developing an EKF for IPMSM is the complexity of the dynamic model expressed in the stationary coordinate system. This model is more complex than that of the surface PMSM, because of the asymmetry of the magnetic circuit. The starting procedure is a problem under sensorless drives, because no information is available before starting. The initial rotor position is estimated by a suitable sequence of voltage pulses intermittently applied to the stator windings at standstill and the measurement of the peak current values of the current leads to the rotor position. Magnetic saturation effect on the saliency is used to distinguish the north magnetic pole from the south. To illustrate our work, we present experimental results for an IPMSM obtained on a floating point digital signal processor (DSP) TMS320C31/40 MHz based control system.     

无速度传感器控制的外转子永磁同步电动机的优化设计

机车牵引、启动发电机和直接驱动等诸多应用场合都需要比较大的转矩。本文介绍了外转子永磁同步电动机和无速度传感器控制算法的优点，特别是使用INFORM方法时低速和零速时的性能。因此必须考虑饱和效应，并用于增强INFORM方法的性能。     

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.     

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.     

Sensorless torque control of salient-pole synchronous motor atzero-speed operation

A position and speed sensorless control using the counter electromotive force of a permanent-magnet motor (PM) debases the control performance at a low speed. We propose a controllable system at full speed, including a zero speed using saliency. At low speed, the sensorless control is made by observing a current ripple at a time when alternating voltage has been applied to a salient-pole motor. Also, for discriminating the S and N poles of the magnet, magnetic saturation is used. A device has been applied to the motor rotor to allow the magnetic saturation to come about easily. Furthermore, at a time of high speed, drive at a full-speed range has been accomplished by switching smoothly over to a sensorless driving system making use of counter electromotive force. All algorithms are implemented by software, and this system can operate successively from starting to high-speed operation. The paper discusses the operational principles at a low speed, analysis and experimental results, the control scheme, how to changeover the control mode at high speed, and the experimental results     

Initial rotor position estimation method of sensorless PMsynchronous motor with no sensitivity to armature resistance

This paper proposes a new initial rotor position estimation method of a sensorless permanent magnet (PM) synchronous motor at starting condition, which has no sensitivity to the armature resistance. The method is based on saliency of the rotor and employs the alternating magnetic field which is excited by a current controller. The phase differences between the magnetizing current references and the voltage references make it possible to estimate the rotor direction accurately without motor parameters, except the ratio of direct axis and quadrature axis inductance. Also, the magnetic pole is evidently identified by detecting the voltage reference oscillation phenomena caused by magnetic saturation, which can be performed without motor parameters. The experimental result has proven that the estimation error was within -4.5 to +2.5 mechanical degrees, even though the armature resistance varied to 125% of the nominal value     

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.      

A sensorless initial rotor position estimation scheme for a direct torque controlled interior permanent magnet synchronous motor drive

In direct torque control (DTC) scheme, the requirement of the continuous rotor position sensor and coordinate transformation is eliminated since all the calculation is done in stator reference frame. However, the DTC scheme requires the position sensor to determine the initial position of the rotor at starting. Elimination of the shaft-mounted position encoder is a very desirable objective in many applications since this sensor is often one of the most expensive and fragile components in the entire drive system. This paper presents a sensorless method of determining the initial rotor position of a direct torque controlled interior permanent magnet (IPM) synchronous motor drive. The method consists of injecting a high frequency voltage to the windings and examining the effects of the saliency on the amplitude of the corresponding stator current components. This method does not depend on the level of static load and on any motor parameters. The magnet polarity of the rotor at its initial position is also identified using the effect of saliency. Modeling and experimental results verify the effectiveness of the proposed method.     

Inductance model-based sensorless control of the switched reluctance motor drive at low speed

A sensorless control scheme for the switched reluctance motor (SRM) drive at low speed is presented in this paper. The incremental inductance of each active phase is estimated using the terminal measurement of this phase. The estimated phase incremental inductance is compared to an analytical model, which represents the functional relationships between the phase incremental inductance, phase current, and rotor position, to estimate the rotor position. The presented sensorless control scheme requires neither extra hardware nor huge memory space for implementation. It can provide accurate rotor position information even as the magnetic characteristics of the SRM change due to aging. Combined with other inductance model-based sensorless control techniques, the proposed method can be used to develop an inductance model-based sensorless control scheme to run the SRM from standstill to high-speed. Simulation and experimental results are presented to verify the proposed scheme.     

Performance of HF signal injection techniques for zero-low-frequency vector control of induction Machines under sensorless conditions

A number of HF signal injection techniques have been proposed for the sensorless zero-low-frequency control of induction machines (IMs). This paper reviews these methods and experimentally investigates their performance under true sensorless conditions for a standard cage IM with closed rotor slots. Implementation techniques covering hybrid methods, saliency decoupling, and saliency orientation are discussed. The paper concludes that, while HF techniques can outperform observer-based methods at low frequencies, the robust performance required for industrial application still presents a research challenge.     

Mechanical sensorless speed control of permanent-magnet AC motors driving an unknown load

A new sensorless scheme for high-performance speed control of permanent-magnet ac motors (PMACMs) driving an unknown load is proposed. This scheme uses an extended nonlinear reduced-order observer to estimate the induced electromotive force (EMF) and load torque. From the estimated variables, the rotor position, the rotor speed, and the position derivative of flux are calculated and are used to close the control loop. In order to improve the drive performance, the estimated load torque is incorporated as a feedforward signal in the closed control loop. In addition, the proposed sensorless PMACM drive allows the torque-ripple and copper-loss minimization for motors with an arbitrary EMF waveform. Simulation and experimental results to validate the proposal are presented in this paper.     

Sensorless PM brushless DC motor drives

To control PM brushless DC motors, position and speed sensors are indispensable because the current should be controlled depending on the rotor position. However, these sensors are undesirable from standpoints of size, cost, maintenance, and reliability. There are different ways of approaching this problem, depending on the flux distribution. The paper presents the speed and position sensorless control of PM brushless DC motors with a sinusoidal flux distribution. Two approaches are presented and compared with each other; one is based on the voltage model of the motor and another is based on the current model. The starting procedure is also a very difficult problem under sensorless drives, because the sensorless drive algorithm uses voltage and current for estimation of rotor position, but no information is available before starting. A novel starting method is presented by using a salient-pole machine. Experimental results based on DSP-TMS320C25 controller are shown for comparisons, which demonstrate desired characteristics both in steady-state and starting conditions     

Sensorlose INFORM-geregelte Permanentmagnet-Außenläufermotoren für Industrie, Automotive und Traktion

In this paper, the optimization of external rotor permanent magnet motors with respect to sensorless position detection using the INFORM method is presented. The external rotor type offers special advantages in drives with high torque demand, especially at low speed and standstill. Typical applications are elevators, starter-generators and traction drives. Furthermore, the paper shows the calculation of reluctance properties due to saturation and geometry using numerical field calculation. This is an important fact for high-performance position estimation using the INFORM method. The accuracy of position estimation reaches a few electrical degrees; therefore it is fully sufficient for practical application in the mentioned fields. At the Institute of Electrical Drives and Machines at Vienna University of Technology, such PM external rotor drives have been designed, built and tested. The sensorless operation has been verified successfully.     

Adaptive Spatiotemporal Feature Extraction and Dynamic Combining Methods for Selective Visual Attention System

This paper introduces a selective attention system that guides users to detect the regions of interest more effectively by adaptively selecting and using spatial and temporal features according to the input images. Although the proposed system is based on a typical bottom-up method, it achieved improvement in the method for extracting features and calculating the saliencies compared to existing studies. In the proposed system, spatial saliencies have dynamic information from which features are adaptively selected according to the input images. Also temporal saliencies in the proposed system have pieces of information for individual moving objects that are associated with each other obtained through multi-resolution feature analysis. In addition, when combining a spatial saliency and a temporal saliency, the activity of the input saliency is measured, and the weights that change dynamically according to the activity are calculated, and the spatial saliency and temporal saliency are combined according to the weights. In order to evaluate the performance of the proposed system, comparative experiments with the existing systems were conducted with diverse experimental images and as a result, it could be seen that the proposed system produces results closer to the results of humans’ visual recognition compared to previous systems.     

基于自适应状态观测器的异步电机无速度传感器矢量控制系统

异步电机无速度传感器矢量控制系统是目前研究的热点,本文采用一种闭环磁链观测器,即自适应状态观测器对转子磁链进行观测,与传统开环电压、电流模型相比,观测效果更好。在转子磁链观测的基础上,采用PI型自适应律,对转速进行了辨识。最后,通过Matlab仿真验证了本文给出的异步电机无速度传感器矢量控制系统的可行性,仿真结果表明该系统具有较好的动、静态性能,并具有一定的抗干扰能力。     

Sensorless vector control of synchronous reluctance motors withdisturbance torque observer

The elimination of the position sensor has been one important requirement in vector control systems because the position sensor spoils the reliability and simplicity of drive systems. Therefore, we present a sensorless vector control technique for synchronous reluctance motors. The rotor position is calculated easily from ds-qs-axes flux linkages which are estimated with a first-order lag compensator. Furthermore, utilizing estimated rotor position as the input of the full-order observer, the rotor speed and disturbance torque are estimated. The proposed sensorless vector control scheme is demonstrated with experimental results     

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     

Sensorless full-digital PMSM drive with EKF estimation of speed androtor position

This paper concerns the realization of a sensorless permanent magnet (PM) synchronous motor drive. Position and angular speed of the rotor are obtained through an extended Kalman filter. The estimation algorithm does not require either the knowledge of the mechanical parameters or the initial rotor position, overcoming two of the main drawbacks of other estimation techniques. The drive also incorporates a digital d-q current control, which can be easily tuned with locked rotor. The experimental setup includes a PM synchronous motor, a pulsewidth modulation voltage-source inverter, and floating-point digital-signal-processor-based control system     

A novel, robust DSP-based indirect rotor position estimation for permanent magnet AC motors without rotor saliency

This paper proposes and implements a novel rotor position sensorless technique for PM AC motor drives, which allows acceleration from standstill and can operate under various practical operating conditions including transient speed changes. The technique developed here relies on the measurement of the phase voltages and currents of the motor. It uses the incremental values of flux linkage, and the back-EMF functions to estimate incremental rotor position. Using a phase-locked loop (PLL) algorithm, an internal closed-loop correction algorithm can correct rotor position estimation drift, which may be due to the motor parameter variations or measurement inaccuracies. The method is implemented in closed-loop using a digital signal processor (DSP), and details of the implementation are provided in the paper. To demonstrate accuracy, robustness and reliability of the position estimation scheme, the paper presents a number of real-time experimental results, including dynamic operating conditions.