Torque Observer Research Articles

Cost‐effective shaft torque observer for condition monitoring of wind turbines

AbstractImprovement of condition monitoring (CM) systems for wind turbines (WTs) and reduction of the cost of wind energy are possible if knowledge about the condition of different WT components is available. CM based on the WT drive train shaft torque signal can give a better understanding of the gearbox failure mechanisms as well as provide a method for detecting mass imbalance and aerodynamic asymmetry. The major obstacle preventing the industrial application of CM based on the shaft torque signal is the costly measurement equipment which is impractical for long‐term use on operating WTs. This paper suggests a novel approach for low‐cost, indirect monitoring of the shaft torque from standard WT measurements. The shaft torque is estimated recursively from measurements of generator torque, high speed shaft and low speed shaft angular speeds using the well‐known Kalman filter theory. The performance of the augmented Kalman filter with fading memory (AKFF) is compared with the augmented Kalman filter (AKF) using simulated data of the WT for different load conditions, measurement noise levels and WT fault scenarios. A multiple‐model algorithm, based on a set of different Kalman filters, is designed for practical implementation of the shaft torque estimator. Its performance is validated for a scenario where there are frequent changes of operating points. The proposed cost‐effective shaft torque estimator overcomes all major problems, which prevent the industrial application of CM systems based on shaft torque measurements. Future work will be focused on validating the method using experimental data and developing suitable signal processing algorithms for fault detection. Copyright © 2013 John Wiley & Sons, Ltd.

Sensorless Inverter‐Fed Compressor Drive System Using Back‐EMF Estimator with PIDNN Torque Observer

AbstractA saliency back‐EMF estimator with a proportional–integral–derivative neural network (PIDNN) torque observer is proposed in this study to improve the speed estimating performance of a sensorless interior permanent magnet synchronous motor (IPMSM) drive system for an inverter‐fed compressor. The PIDNN torque observer is proposed to replace the conventional proportional–integral–derivative (PID) torque observer in a saliency back‐EMF estimator to improve the estimating performance of the rotor flux angle and speed. The proposed sensorless control scheme use square‐wave type voltage injection method as the start‐up strategy to achieve sinusoidal starting. When the motor speed gradually increases to a preset speed, the sensorless drive will switch to the conventional saliency back‐EMF estimator using the PID observer or the proposed saliency back‐EMF estimator using the PIDNN observer for medium and high speed control. The theories of the proposed saliency back‐EMF rotor flux angle and speed estimation method are introduced in detail. Moreover, the network structure, the online learning algorithms and the convergence analyses of the PIDNN are discussed. Furthermore, a DSP‐based control system is developed to implement the sensorless inverter‐fed compressor drive system. Finally, some experimental results are given to verify the feasibility of the proposed estimator.

Low Speed Compound Direct-Drive Permanent Magnet Synchronous Motor Control Systemwith Load Torque Compensation

Effected by sensor measurement noise, system noise and load disturbance torque, dynamic performance of low speed compound direct-drive permanent magnet synchronous machine (PMSM) decreased and speed fluctuation increased, which result in creeping phenomenon and unstable working state of servo system directly driven by PMSM. A load torque observer based on extended kalman filter (EKF) is proposed here, which gives correct estimation of rotor position, rotor speed and load torque through electromagnetic torque and encoder signal. A control strategy using estimated load torque for forward feedback compensation is also discussed with no need of extra hardware equipment. Simulation results showed that PMSM can operate steadily at the speed of 2.5r/min with less speed fluctuation only using a low resolution encoder, which verified the effectiveness and practicability of the method mentioned in this paper.

A Novel Anti-Disturbance Control of PMSM Based on Reduced Torque Observer

A novel anti-disturbance control for permanent magnetic Synchronous Motor (PMSM) based on reduced order load torque observer is proposed to solve the speed ripple problem caused by the external uncertainties like load torque disturbance and parameter variation. Combined with the vector control, the estimation value of the reduced-order torque observer is used as compensation to the q-axis current to improve the dynamic response of the speed. The accuracy of the inertia estimation, the rationality of the reduced order load torque observer and the optimization of the system are verified by the simulation result.

New Simple Torque‐Sensorless Torque Control for Quasi‐perfect Compensation of Sixth‐Harmonic Torque Ripple Due to Nonsinusoidal Distribution of Back EMF of PMSM

SummaryThis paper proposes a new torque‐sensorless torque control method for permanent‐magnet synchronous motors (PMSMs). The proposed method can almost perfectly compensate the sixth harmonic torque ripple that is caused by nonsinusoidal distributions of the back electromagnetic force and the rotor magnetic flux of PMSMs. The torque control system is, in principle, constructed on the basis of vector control, but has two new, dedicated speed‐varying devices: a harmonic torque observer and a current controller. The speed‐varying harmonic torque observer can estimate the harmonic component over a wide range of speeds, even when the generated torque is constant, and produce a suitable compensation signal. The speed‐varying current controller shows stable control performance over a wide range of speeds; it can fully track the compensated current command containing the DC and sixth harmonic components. The effectiveness of the proposed method is examined and verified through extensive numerical experiments.

Internal model control of switched reluctance motor with torque observer for plant–model mismatches

As it is difficult to develop an accurate switched reluctance motor model for its highly nonlinear magnetization characteristics, the control system of switched reluctance motor ought to be robust to model inaccuracies. This article presents an internal model control scheme integrating with an internal model, feedback linearization technique, and filter technique such that the control system of switched reluctance motor is convergent and robust against parameter disturbances and plant–model mismatches. An internal model of switched reluctance motor is established based on the estimated derivative of speed and torque, so the speed ripple can be reduced. Furthermore, a torque observer is equipped with the model for compensating a disturbance torque. Simulation results demonstrate that internal model control in switched reluctance motor drive system can effectively reduce torque and speed ripple, and it is highly robust to plant–model mismatches. Experimental results further verify the effectiveness of internal model control as an alternative control technique for a flexible process of a mechanical press driven by switched reluctance motor.

Maximum power point tracking-based control algorithm for PMSG wind generation system without mechanical sensors

This paper presents maximum-power-point-tracking (MPPT) based control algorithms for optimal wind energy capture using radial basis function network (RBFN) and a proposed torque observer MPPT algorithm. The design of a high-performance on-line training RBFN using back-propagation learning algorithm with modified particle swarm optimization (MPSO) regulating controller for the sensorless control of a permanent magnet synchronous generator (PMSG). The MPSO is adopted in this study to adapt the learning rates in the back-propagation process of the RBFN to improve the learning capability. The PMSG is controlled by the loss-minimization control with MPPT below the base speed, which corresponds to low and high wind speed, and the maximum energy can be captured from the wind. Then the observed disturbance torque is feed-forward to increase the robustness of the PMSG system.

An Improved Torque Feed-forward Control with Observer-based Inertia Identification in PMSM Drives

This paper is concerned with speed tracking control problem for permanent-magnet synchronous drives (PMSM) in the presence of an variable load torque and unknown model parameters. The disturbance of speed control caused by inaccuracy of model parameters has been investigated. A load torque observer has been proposed to observe the load torque and estimate the disturbance caused by inaccuracy of model parameters. Both inertia and friction coefficient are identified in gradient descent approach. The stability condition of the observer has also been studied. Furthermore an improved feed-forward control has been introduced to reduce the speed track error. The proposed control strategy has been verified by both simulation and experimental results

Dynamics and control of gear upshift in automated manual transmissions

Automated Manual Transmission (AMT) is suitable for heavy-duty vehicles to offer an easy drive and good fuel efficiency. After the dynamics and control problems of gear upshift of AMT are described in detail, Model Predictive Control (MPC), together with a shaft torque observer, is adopted to address these challenging control problems. It is demonstrated through simulations that by using the proposed control scheme of gear shifting, a very short torque interruption time can be achieved, while the shift shock is kept small enough.

Assisted Control of Step Passage Motion and Its Comfort Evaluation in Two-Wheel Wheelchair Systems

SUMMARY Two-wheel wheelchair systems have been attracting attention because their mobility is better than that of conventional four-wheel wheelchair systems. However, two-wheel wheelchair systems must achieve stabilization control in the presence of disturbances caused by modeling error or the road situation, since these systems are underactuated systems similar to the inverted pendulum. In this investigation, step passage motion in two-wheel wheelchair systems is considered. A reaction torque observer was employed to estimate the pitch angular interaction torque and the pure external wheel disturbance. Repulsive compliance control was employed to determine the optimal pitch angle command to compensate for the center of gravity of the user and to assist the whole step passage motion. Experimental results are evaluated in terms of user comfort by utilizing the ISO 2631-1 generalized index.

Sensorless Position Control for Surface Permanent Magnet Synchronous Motors at Zero Speed and Acceleration

This paper proposes a position, speed and load torque observation technique for position control of a non-salient Permanent Magnet Synchronous Motor (PMSM). Unlike the speed control, the position control implies that the motor is often in low speed and standstill conditions. Observability analyze is done to show that the motor is not observable in standstill condition. A high-frequency signal injection is introduced to get round this unobservability. An Extended Kalman Filter is then used to observe the rotor position, speed and load torque by taking into account the injected signal into the observation model. Position tracking and load torque influence are studied on a test bench. Experimental results are provided to confirm the performance and efficiency of the proposed solution.

ADRC and Feedforward Hybrid Control System of PMSM

The permanent-magnet synchronous motor (PMSM) is a complex controlled object that is difficult to drive and control. In this study, the vector control strategy is adopted to drive the PMSM. The active disturbance rejection controller is used to achieve the closed-loop control of PMSM, which simplifies the computational complexity. A load torque observer and feedforward compensation component are designed to overcome the PMSM speed fluctuation of the load disturbance. An experimental system based on the DSP board is designed to test the controller performance. The results validate the control algorithm.

Improvement of boom control performance for hybrid hydraulic excavator with potential energy recovery

Potential energy recovery (ER) is an effective way to reduce energy consumption of hybrid hydraulic excavators; however, the ER system with a direct speed-control strategy is prone to oscillation of actuators due to the reduction of damping in comparison to the conventional throttle governing system. This paper aims to improve the boom control performance of a hybrid hydraulic excavator by properly designing the ER controller. Based on the dynamics of the system, mathematical modeling including hydraulic components and electrical components is carried out. A staged composite control strategy is proposed to achieve acceptable performance in the whole velocity range. Load torque observation is employed to increase the speed stiffness of the permanent magnet generator applied in the system as well as the stiffness of the boom motion. The leakage flow which affects the anti-disturbance capability and accuracy of the control system is compensated. Finally, the effectiveness of the proposed control scheme is verified by simulation and experimental results. ► Energy recovery system for hybrid excavator is modeled and analyzed. ► The boom performance is poor with conventional energy recovery controller. ► Composite strategy obtains acceptable boom performance in whole velocity range. ► Load observation and feedforward control increase system stiffness. ► Leakage flow compensation improves accuracy and anti-disturbance ability.

Direct design of a velocity controller and load disturbance estimation for a self-balancing industrial manual manipulator

Self-balancing manual manipulators are devices that countervail the weight of a load that must be manually handled and moved by a human operator. Standard manipulators are made of a framework with an electric motor on the top and a spool connected to the motor shaft through a transmission gear. The load is hung by a handling device connected to a metallic rope wound on the spool. The device considered in this paper, in its current layout, is endowed with a load cell that measures the load weight and is controlled in an open loop. A new layout has been designed, which is not including the weighting load cell and is feedback controlled. The load’s counterbalance and movement are obtained by a velocity closed loop control algorithm designed using a direct design method, the Virtual Reference Feedback Tuning (VRFT). VRFT provides controller parameters tuning in a completely automatic way based on a single I/O batch measurement on the plant. Moreover, the elimination of the load weight transducer causes issues to some handling devices that need weight measurements to attach and detach the load. So, a load mass observer has been designed using a gravitational torque estimator, which is an enhanced version of standard disturbance torque observer for electric motors.

SDRE-Based Near Optimal Control System Design for PM Synchronous Motor

This paper presents a nonlinear optimal speed controller based on a state-dependent Riccati equation (SDRE) for permanent magnet synchronous motor (PMSM). An SDRE-based near optimal load torque observer is also proposed to provide the load torque information for the controller. In both designs, the stability is analytically proven, and the Taylor series method is used to find an approximate solution because the SDRE cannot be directly solved. The SDRE-based optimal controller and the observer can ensure better control performance such as no overshoot and fast transient response in speed tracking than the linear conventional controllers such as linear quadratic regulator and proportional-integral controller even under the variations of the model parameters and load torque. The proposed SDRE-based control strategy is implemented on a PMSM testbed using TMS320F28335 DSP. The simulation and experimental results are given to prove the feasibility of the proposed control scheme.

An asymptotically stable sensorless speed controller for non‐salient permanent magnet synchronous motors

SUMMARYA solution to the longstanding problem of sensorless control of an electrical machine is provided in this paper. That is, the construction of an asymptotically stable controller that regulates the mechanical speed of the motor, measuring only the electrical coordinates. The result is presented for a non‐salient permanent magnet synchronous motor perturbed by an unknown constant load torque. The proposed scheme is a fourth order nonlinear observer‐based controller that does not rely on—intrinsically nonrobust—operations like open‐loop integration of the systems dynamical model nor signal differentiation and can be easily implemented in real time. The controller is easy to commission, with the tuning gains directly determining the convergence rates of the position, speed, and load torque observers. Simulation and experimental results are presented. In particular, a comparison with a sensorless field‐oriented controller, recently proposed in the drives literature, is carried out. Copyright © 2012 John Wiley & Sons, Ltd.

Design and Implementation of a Takagi–Sugeno Fuzzy Speed Regulator for a Permanent Magnet Synchronous Motor

In this paper, a fuzzy speed regulator, as well as a fuzzy load torque observer, for a permanent magnet synchronous motor (PMSM) is designed based on the Takagi-Sugeno fuzzy approach. In terms of linear matrix inequalities (LMIs), sufficient conditions for the existence of the regulator and the observer are derived. LMI parameterizations of the gain matrices are given. LMI conditions for the existence of the fuzzy speed regulator and the fuzzy load torque observer guaranteeing various performance criteria are also derived. The proposed load-torque-observer-based fuzzy speed regulator system is implemented by using a TMS320F28335 floating-point digital signal processor, and simulation and experimental results are given to verify that the proposed method can be successfully used to control a PMSM under model parameter and load torque variations.

Robust control for a direct-driven permanent magnetic synchronous generator without mechanical sensors based on model reference adaptive backstepping control method

This article is concerned with the robust control issues of direct-driven permanent magnetic synchronous generator without mechanical sensors. In this study, a novel nonlinear model reference adaptive backstepping control method is proposed. Extended electromotive force estimation-based rotor position and rotational velocity estimation methods are adopted, in which the stator parameters are identified online. Since the identified parameters are merely used in extended electromotive force estimator, the mathematically controlled plant cannot reflect the actual model, which decreases the robustness of the control. To provide a high-performance robust controller against uncertainties in stator parameters and mechanical torque fluctuation, a torque observer is adopted, and an adaptation law is derived with the identified parameters and estimated mechanical torque, in the sense of the Lyapunov theory. Meanwhile, the feasibility of the substitution of the actual stator parameters and state vector with estimated values is mathematically demonstrated based on the Lyapunov theory. Simulation experiments have been carried out both in surface permanent magnetic synchronous generator and interior permanent magnetic synchronous generator, and the results show that compared to the conventional process-interaction decoupling controller, the proposed controller has better disturbance rejection performance against wind speed perpetuation and parameter uncertainties.

Zero-Speed Operation of High-Power PWM Current-Source-Inverter-Fed Induction Motor Drive

Most research work in current-source inverter (CSI) fed motor drives has focused on general control strategies, pulsewidth modulation schemes, topologies, and efficiency evaluation. This paper, however, is dedicated to investigating zero-speed operation characteristics of CSI-fed induction motor drives (IMDs). Zero-speed operation can greatly increase the competitive value of the drive and expand its range of applications to include cranes, hoists, and draglines. The motor drive is controlled with rotor flux orientation, where stator currents and motor speed are employed for the rotor flux estimation. Unlike voltage-source-inverter-based drives, filter capacitors are required at the output of the CSI for current commutation and harmonics filtering. The influence of these capacitors on the system dynamic performance is comprehensively evaluated. Moreover, a classic load torque observer with feedforward control is employed to improve the speed dynamic response. Simulated and experimental results show that the CSI-fed IMD works well at zero speed with promising speed dynamic performance.

Sliding Mode Load torque Observer based effective disturbance rejection for a 3-Phase BLDC drive

controller (SMC) controller has been proposed for the outer loop speed control of the 3-Phase Brushless DC(BLDC) motor drive. The robust hysteresis controller is employed to control the inner loop current performance of the drive. The developed SMC control scheme is simulated on MATLAB/SIMULINK platform under varying load torque disturbances up to the rated torque capability and the variable speed performance of the drive is tested. A sliding mode based load torque observer has also been designed for implementation of the scheme on real time basis. The efficient load torque rejection capabilities of the developed control scheme using the sliding mode load torque observer is then compared with a Proportional Integral (PI) based controller.