Comparative analysis of experimental performance and stability of sensorless induction motor drives

This paper compares the experimental performance of three flux and speed observers for speed-sensorless induction motor drives and discusses the cause of their differences. The small signal analysis using the linearized model is carried out to analyze stability. Three methods are generally accepted to be representative candidates for high sensorless performance, namely: 1) rotor-flux model reference adaptive system (MRAS); 2) torque-current MRAS; and 3) adaptive nonlinear flux observer. Many other sensorless methods improved these methods. The paper discusses baseline conditions for the experiments and the stability analysis, which include matched load inertia, specified speed estimator dynamics, and sensorless operation within a speed control loop. For the comparison tests in the paper, the speed estimation dynamics of the methods are the same; this is important for parameter sensitivity. The paper concentrates on the low-speed performance, and all results shown are under sensorless speed control.     

Comparative study of adaptive and inherently sensorless observers for variable-speed induction-motor drives

State observers are key components of modern ac drives. The paper presents a comparative analysis of two state observers for induction-motor (IM) drives: the speed-adaptive observer and the inherently sensorless observer. The adaptive observer employs the time-variable full-order motor model with the rotor speed as the adaptive quantity. Thus, the speed estimation accuracy significantly impacts on the flux observer. It is shown that the popular model reference adaptive system (MRAS) speed estimator displays reduced bandwidth, and does not deliver adequate performance for the flux estimation. The inherently sensorless observer employs a full-order dual reference-frame model in order to eliminate the speed adaptation. In this way, it becomes decoupled from the speed estimator and its performance is superior to that of its adaptive counterpart. Theoretical aspects and comparative simulation results are discussed for both observers. Comparative experimental results for both observers are presented. Very low-speed-operation (3 r/min) capability of the drive with the sensorless observer is demonstrated.     

Sliding-mode control of doubly-fed generator for optimum power curve tracking

Aiming to achieve superior tracking of a predefined optimum power curve, a simple standard sliding-mode controller (SMC) for the rotor-side converter feeding a doubly-fed induction generator (DFIG) is synthesised. Besides being robust against DFIG parameter variations, it is implementable on FPGA, and does not require PWM or SVM modulation. Results of real-time hardware-in-the-loop evaluation, obtained when running the proposed SMC together with an MRAS observer for sensorless control, are reported.     

Sensorless field orientation control of induction machines based ona mutual MRAS scheme

A mutual model reference adaptive system (MRAS) is proposed to implement a position sensorless field-orientation control (FOC) of an induction machine. The reference model and adjustable model used in the mutual MRAS scheme are interchangeable. Therefore, it can be used to identify both rotor speed and the stator resistance of an induction machine. For the rotor speed estimation, one model is used as a reference model and another is the adjustable model. Pure integration and stator leakage inductance are removed from the reference model, resulting in robust performance in low and high speed ranges. For the stator resistance identification, the two models switch their roles. To further improve estimation accuracy of the rotor speed and stator resistance, a simple on-line rotor time constant identification is included. Computer simulations and experimental results are given to show its effectiveness     

Sensorless Control of Induction Machines by a New Neural Algorithm: The TLS EXIN Neuron

This paper proposes two speed observers for high-performance induction machine drives, both adopting an online adaptation law based on a new total least-squares (TLS) technique: the TLS EXIN neuron. The first is a model reference adaptive system (MRAS) observer with a neural adaptive integrator in the reference model and a neural adaptive model trained online by the TLS EXIN neuron. This observer, presented in a previous article of the authors, has been improved here in two aspects: first, the neural adaptive integrator has been modified to make its learning factor vary according to the reference speed of the drive, second, a neural adaptive model based on the modified Euler integration has been proposed to solve the discretization instability problem in field-weakening. The second observer is a new full-order adaptive one based on the state equations of the induction machine, where the speed is estimated by means of a TLS EXIN adaptation technique. Both these observers have been provided with an inverter nonlinearity compensation algorithm and with techniques for the online estimation of the stator resistance of the machine. Moreover, a thorough theoretical stability analysis has been developed for them both, with particular reference to the field-weakening region behavior for the TLS MRAS observer and to the regenerating mode at low speeds for the TLS adaptive observer. Both speed observers have been verified in numerical simulation and experimentally on a test setup, and have also been compared experimentally with the BPN MRAS observer, the classic adaptive observer and with an open-loop estimator. Results show that both proposed observers outperform all other three observers in every working condition, with the TLS adaptive observer resulting in a better performance than the TLS MRAS observer     

基于MRAS的异步电机无速度传感器矢量控制

异步电机无速度传感器矢量控制系统中的速度辨识方法是目前研究的热点,其中MRAS由于其原理简单、实用性较强等优点,在交流调速系统中得到了广泛应用。本文采用改进的电压型转子磁链估算模型,避免了由纯积分环节造成的积分漂移等问题,采用可变PI型自适应律,结构简单且具有较好的辨识效果,最后给出了转子磁场定向的无速度传感器矢量控制系统的实现,仿真结果表明该系统具有良好的动静态性能,且具有一定的抗干扰能力。     

基于MRAS的异步电机无速度传感器的矢量控制

由于电机定转子参数的变化,利用一般的转子磁链对转速进行估算,将导致不能得到准确的结果。这里采用积分型转子磁链的参考和可调模型构建出一个基于MRAS的异步电机无速度传感器的矢量控制模型。该模型提高了矢量控制系统的动态性能并利用MATLAB,sIMULINK进行了异步电机无速度传感器矢量控制系统的仿真,验证了文中所采用的模型参考自适应的速度估算方法的可行性以及对参数误差的鲁棒性。     

Sliding-mode MRAS speed estimators for sensorless vector control of induction Machine

This paper presents two novel sliding mode (SM) model reference adaptive system (MRAS) observers for speed estimation in a sensorless-vector-controlled induction-machine drive. Both methods use the flux estimated by the voltage model observer as the reference and construct SM flux observers that allow speed estimation. Stability and dynamics of the two proposed SM flux observers are discussed. The observers are compared with the classical MRAS observer. The proposed estimators seem very robust and easy to tune. Unlike the classical MRAS, the speed-estimation process is based on algebraic calculations that do not exhibit underdamped poles or zeros on the right-hand plane. Simulations and experimental results on a 1/4-hp three-phase induction machine confirm the validity of the approaches.     

Observer using low-frequency injection for sensorless induction motor Control-parameter sensitivity analysis

The zero-frequency vector control of an induction motor without a speed sensor has proven to be a very difficult task. Uncertainty and variation in the electrical parameters of the motor deteriorate the performance of fundamental-wave flux observers as the frequency approaches zero, and observers based on high-frequency signal injection rely on motor-specific phenomena. A new method has recently been proposed, where a low-frequency current signal is injected in the estimated rotor flux direction. If there is an error in the orientation, the signal gives rise to a torque oscillation and affects the back electromotive force (EMF) through the mechanical system. The phenomenon makes it possible to reach sensorless zero-frequency operation. This paper shows that the method is insensitive to the variation of the motor parameters. Experiments confirm the result.     

变速恒频风力发电用双PWM变换器的协调控制

文章首先分析了双馈风力发电机的原理以及其数学模型,然后分析了变速恒频风力发电技术采用双PWM变换器常规控制策略,在此基础上提出了采用双PWM变换器的协调控制策略。最后利MATLAB/SIMULINK软件对整个风力发电系统进行仿真。结果表明此策略实现了风力发电机的变速恒频运行,另外在定子电流变化的同时,保持了恒定的功率因数,实现了对双馈感应电机的有功功率和无功功率的独立控制。     

风电系统中发电机励磁控制系统的研究

论文介绍了风电系统中双馈风力发电机（DFIG）的工作原理,论文中所提出的双馈风力发电系统主要采用了双PWM换流器结构的交流励磁系统。并运用矢量控制的控制策略对网侧变换器和励磁侧变换器进行控制。并通过Matlab软件构建了最大风能追踪的仿真模型对其进行仿真,仿真表明论文中所提出的控制策略能够实现现风力发电系统的最大风能追...     

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.     

变速恒频双馈风力发电机控制策略

本文基于对双馈感应发电机及其矢量控制的理论分析,采用基于速度外环的并网发电控制策略和基于变步长转速扰动的最大风能跟踪算法,构建了110kW变速恒频双馈风力发电模拟平台,实现了变速恒频双馈风力发电机的有功、无功功率的前馈解耦控制和最大功率点跟踪控制。     

基于MRAS的无速度传感器矢量控制的研究

利用异步电动机定子电压、电流易于检测的特点,运用模型参考自适应（MRAS）的算法对电动机的转速进行辨识,以MATLAB/Simulink里面的Simpower工具箱为基础,搭建了异步电机无速度传感器矢量控制系统的仿真模型。结果表明,本系统设计方法可行、具有良好的速度响应和动静态性能。     

A Secondary Voltage Control Strategy for Transmission Level Interconnection of Wind Generation

This paper addresses implementation issues associated with secondary voltage control in a doubly-fed induction generator based wind farm. The effects of different system parameters on the performance of the control are considered, namely the short circuit ratio of the interconnection and the inherent communication delay between the wind park and the remote bus. In addition, a strategy for allocation reactive power requirements to each of the generators within the wind park is proposed. The system is developed and simulated for a wind park consisting of six wind generators connected to a typical transmission system. The paper proposes an optimal tracking secondary voltage control method developed to achieve effective voltage regulation, enhance the network voltage profile and provide optimal reactive power compensation to the interconnected power system. The performance of the controller is compared with secondary voltage control at one selected bus, primary voltage control and the optimal voltage profile obtained from the optimal power flow analysis. The performance of the controllers is tested for steady state operation and in response to system contingencies, taking into account the impact of communication time delays and short circuit ratio (SCRs). Simulation results are presented to demonstrate the capability of the controllers to provide the desired reactive power compensation and voltage support to the electric power grid.     

Low-cost sensorless control of brushless DC motors using afrequency-independent phase shifter

This paper describes a sensorless control scheme for brushless DC motors (BLDCMs) using a phase shifter (FlPS) which can shift the zero-crossing point of the input signal with a specified amount of phase. The detection performance of the proposed FIPS is independent of the frequency of the input signal and quite robust with respect to the measurement noise. It is shown that the proposed sensorless control scheme using the FIPS is more effective in the respects of noise-robustness and cost than the previously known schemes. Moreover, a flux-weakening control scheme can be easily incorporated into the proposed sensorless control scheme. The generality and practicality of the proposed sensorless control scheme is demonstrated through performance analysis and experiments under various operating conditions     

Sensorless speed tracking of induction motor with unknown torque based on maximum power transfer

In this paper, the authors first derive the maximum power transfer theorem for an induction motor. Then, a nonlinear indirect adaptive sensorless speed tracking controller for the motor with the maximum power transfer is proposed. In this controller, only the stator currents are assumed to be measurable. The rotor flux and speed observers are designed to relax the need of flux and speed measurement. In addition, the rotor resistance estimator is also designed to cope with the problem of the fluctuation of rotor resistance with temperature. Stability analysis based on Lyapunov theory is also performed to guarantee that the controller design here is stable. Finally, the computer simulations and experiments are conducted to demonstrate the satisfactory tracking performance of the authors' design subject to maximum power transfer.     

Sliding-mode observer and improved integrator with DC-offset compensation for flux estimation in sensorless-controlled induction motors

Two flux observers for wide speed range direct torque control (DTC) of sensorless induction-motor drives are presented and compared. The first one is a full-order sliding-mode observer with proportional plus integral (PI) compensation, without rotor speed adaptation. The second one is based on a zero phase-delay-improved integrator of the voltage model, which uses only a PI flux amplitude control with stator-flux reference magnitude in the correction loop. In both cases, an estimated dc offset is built up and memorized by the PI integral component and this totally compensates for all dc offsets and drifts originated in the acquisition channels. Two feasible solutions for on-line stator-resistance identification are proposed. Simulation and experimental results prove the accuracy, robustness, and high-dynamic performance of both observers when employed in sensorless DTC drives. The effectiveness of state estimation is confirmed by a steady state and transient sensorless operation at very low speed with rated load torque and step-speed reversal.