Load Torque Compensation Research Articles

Load torque observation and compensation for permanent magnet synchronous motor based on sliding mode observer

Background Permanent magnet synchronous motors (PMSM) are widely used in various industries. However, in practical applications, the time-varying nature of load torque may lead to speed fluctuations, negatively impacting the motor's control performance and stability. To mitigate these issues, this paper proposes a load torque observation method for PMSMs based on a sliding mode observer. Methods The sliding mode observer is designed to estimate the load torque and convert it into a current, which is fed back as a feedforward compensation to the q-axis current in the current closed-loop control system. The observer's dynamic performance is optimized using a genetic algorithm to minimize the Integral of Time-weighted Absolute Error (ITAE) between the observer and the actual system state. Experimental tests are conducted on a motor torque testing platform. After stabilizing the motor at 800rpm, a sudden torque of 0.5Nm is applied. Results Compared to the situation without load torque compensation, the motor speed fluctuations are reduced by approximately 60% after adding load torque compensation. Conclusions This enhancement improves the system's speed control performance during torque variations and increases the system's robustness and disturbance rejection capability.

Inductance Estimation Based on Wavelet-GMDH for Sensorless Control of PMSM

In permanent magnet synchronous motor (PMSM) sensorless drive systems, the motor inductance is a crucial parameter for rotor position estimation. Variations in the motor current induce changes in the inductance, leading to core magnetic saturation and degradation in the accuracy of rotor position estimation. In systems with constant load torque, the saturated inductance remains constant. This inductance error causes a consistent error in rotor position estimation and some performance degradation, but it does not result in speed estimation errors. However, in systems with periodic load torque, the error in the saturated inductance varies, consequently causing fluctuations in both the estimated position and speed errors. Periodic speed errors complicate speed control and degrade the torque compensation performance. In this paper, we propose a wavelet denoising-group method of data handling (GMDH) based method for accurate inductance estimation in PMSM sensorless control systems with periodic load torque compensation. We present a method to analyze and filter the collected three-phase current signals of the PMSM using wavelet transformation and utilize the filtered results as inputs to GMDH for training. Additionally, a method for magnetic saturation compensation using the inductance parameter estimator is proposed to minimize periodic speed fluctuations and improve control accuracy. To replicate the load conditions and parameter variations equivalent to the actual system, experiments were conducted to measure the speed ripples, inductance variations, and torque component of the current. Finally, software simulation was performed to confirm the inductance estimation results and verify the proposed method by simulating load conditions equivalent to the experimental results.

ПОРІВНЯЛЬНИЙ АНАЛІЗ ПОКАЗНИКІВ ЯКОСТІ ВІДПРАЦЮВАННЯ КУТОВОЇ ШВИДКОСТІ В ОДНОКОНТУРНІЙ СИСТЕМІ ПРОГНОЗНОГО КЕРУВАННЯ ДВИГУНОМ ПОСТІЙНОГО СТРУМУ

The results of a comparative study of two speed control systems for a DC motor with permanent magnets are presented: a cascaded system based on PI controllers, and a single-loop system developed on the basis of model predictive control methods. The research was carried out by the simulations for the case of speed trajectory tracking task. It is shown that, under the conditions of known parameters, the controller based on predictive control, designed as a system with one input and one output, unlike the system with PI controllers and compensations of derivatives of the reference signal, does not provide asymptotic speed trajectory tracking. The transients during constant load torque compensation are similar, both control schemes provide asymptotical speed regulation with similar performances. In the case of introduc-ing variations of DC motor moment of inertia, the levels of dynamic trajectory tracking errors become commensurate for both control systems. Unlike the system based on PI regulators, the controller based on model predictive control does not need to measure the armature current and provides improved dynamics in voltage limiting modes. Ref. 17, fig. 7. Keywords: model predictive control, DC motor, speed trajectory tracking, PI-controller.

A Novel Sensitivity Analysis to Moment of Inertia and Load Variations for PMSM Drives

A high-performance electrical drive with a permanent magnet synchronous motor (PMSM) should ensure superior dynamic properties, reasonable load torque compensation, and robustness against parameter variations. The performance investigation related to the dynamic properties is usually made using the step response indicators and integral performance indexes. The robustness evaluation is more complex than performance analysis since there are no simple tools for this purpose, especially if it is done experimentally to consider nonlinearities and unmodeled dynamics of the plant. In this article, sensitivity functions suitable for investigating the closed-loop control systems in the time and the frequency domain are proposed, explained, and experimentally verified. Three control schemes designed for the speed control of PMSM are analyzed: a cascade control structure, robust two-degrees-of freedom speed controller, and a cascade-free constrained state feedback controller. Studies are conducted for experimental responses of the drive in the time and the frequency domain to investigate the sensitivity of the PMSM drive against the moment of inertia and load variations. Analysis of nonlinearities influence on the developed sensitivity functions is also presented.

Research on UDE control based on load torque compensation of PMSM

In order to solve the problem that the traditional uncertainty and disturbance estimator (UDE) control needs to increase the filter order to keep good performance when facing rapid disturbance changes, thus lead to cost increase in implementing the system, a speed control strategy of permanent magnet synchronous motor (PMSM) driver based on reduced order observer compensation is proposed. The designed control strategy is robust to the system with internal parameter variation and external torque disturbance. Through the compensation of load torque, the pressure of UDE controller is relieved, and then the tracking error of high-frequency component in load torque is eliminated, and the control performance of the system is improved more effectively. This paper proves the superiority of the new compound controller through comparison of simulation. results

Sensorless PMSM Drive Inductance Estimation Based on a Data-Driven Approach

In the permanent magnet synchronous motor (PMSM) sensorless drive method, motor inductance is a decisive parameter for rotor position estimation. Due to core magnetic saturation, the motor current easily invokes inductance variation and degrades rotor position estimation accuracy. For a constant load torque, saturated inductance and inductance error in the sensorless drive method are constant. Inductance error results in constant rotor position estimation error and minor degradations, such as less optimal torque current, but no speed estimation error. For a periodic load torque, the inductance parameter error periodically fluctuates and, as a result, the position estimation error and speed error also periodically fluctuate. Periodic speed error makes speed regulation and load torque compensation especially difficult. This paper presents an inductance parameter estimator based on polynomial neural network (PNN) machine learning for PMSM sensorless drive with a period load torque compensator. By applying an inductance estimator, we also proposed a magnetic saturation compensation method to minimize periodic speed fluctuation. Simulation and experiments were conducted to validate the proposed method by confirming improved position and speed estimation accuracy and reduced system vibration against periodic load torque.

Modeling and control of a 4-ADOF upper-body exoskeleton with mechanically decoupled 3-D compliant arm-supports for improved-pHRI

Safe physical human-robotic interaction is a crucial concern for worn exoskeletons where lower weight requirement limits the number and size of actuators to be used. A novel control strategy is suggested in this paper for the low degree of freedom exoskeletons, by combining proposed mechanically decoupled passive-compliant arm-supports with active compliance, to achieve an improved and safer physical-human-robotic-interaction performance, while considering the practical limitations of low-power actuators. The approach is further improved with a novel vectoral-form of disturbance observer-based dynamic load-torque compensator, proposed to linearize and decouple the nonlinear human-machine dynamics effectively. The design of a four-degree of freedom exoskeleton test-rig that can assure the implementation of the proposed strategy is also shortly presented. It is shown through simulation and experimentation, that the use of proposed strategy results in an improved and safer physical human-robotic interaction, for the exoskeletons using limited-power actuators. It is also shown both through simulation and experimentation, that the proposed vectoral-form of disturbance based dynamic load-toque compensator, effectively outperforms the other traditional compensators in compensating the load-torques at the joints of the exoskeleton.

Finite Control Set Model‐Predictive Speed Control with a Load Torque Compensation

This paper presents a gain tuning method of the load torque compensator for direct speed control based on finite control set model predictive control (FCS‐MPC). In this method, the transfer function between the error in predicted speed and the load torque is constructed and used for gain parameter tuning of a load torque observer‐based prediction error correction. By using the proposed method, the stability and the responsiveness of FCS‐MPC with a load torque compensation can be improved without a fully simulating the electric drive systems and experiments. The simulation and experimental results obtained with a permanent magnet synchronous motor, fed by a two‐level three‐phase voltage source inverter, show that the tracking performance of the direct speed control tuned by the proposed method was excellent under load torque conditions. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

On stability and performance of disturbance observer-based-dynamic load torque compensator for assistive exoskeleton: A hybrid approach

A disturbance observer-based-dynamic load-torque compensator for current-controlled DC-drives, as joint actuator of assistive exoskeletons, has been recently proposed. It has been shown that this compensator can effectively linearize and decouple the coupled nonlinear dynamics of the human-exoskeleton system, by more effectively compensating the associated nonlinear load-torques of the exoskeleton at the joint level. In this paper, a detailed analysis of the current controlled DC drive-servo system using the said compensator, with respect to performance and stability is presented, highlighting the key factors and considerations affecting both the stability and performance of the compensated servo system. It is shown both theoretically and through simulation results that the stability of the compensated servo system is compromised as performance is increased and vice-versa. Based on the saturation state of the servo system, a new hybrid switching control strategy is then proposed to select stability or performance-based compensator and controller optimally. The strategy is then experimentally verified both at the joint and task space level by using the developed four active-degree of freedom exoskeleton test rig.

자속 포화에 의한 PMSM 센서리스 위치 추정 오차 분석 및 보상 기법

For a pump or a compressor motor, a high periodic load torque variation is induced by the mechanical works, and it causes system vibration and noise. To minimize these problems, load torque compensation method, injecting periodic torque current, could be utilized. However, with the sensorless control method, which is usually utilized in the pump and compressor for low cost, the periodic torque current degrades the accuracy of the rotor position estimation owing to the inductance variation. This paper analyzes the rotor position and speed estimation error of sensorless control method with constant motor parameters under period loading. Assuming the constant speed by the accurate load torque compensation, the speed error equation is derived in frequency domain with inductance depending on the stator current. Further, it is also shown that the rotor position error could be minimized by compensating the inductance variation. The simulation and experimental results verify that the derived speed error model and the validity of the inductance compensation method.

Dynamic sliding mode position control of induction motors based load torque compensation using adaptive state observer

PurposeThe purpose of this paper is position control scheme for a servo induction motor (SIM) with uncertainty has been designed using a new observer issue and a dynamic sliding mode control (DSMC).Design/methodology/approachIn DSMC, the chattering is removed due to the integrator (or a low-pass filter) which is placed before the input control of the plant. However, in DSMC, the augmented system has one dimension bigger than the actual system (if integrator is used) and then, the plant model should be completely known. To solve this problem in SIM, the use of a new adaptive state observer (ASO) is proposed.FindingsThe advantage of the proposed approach is to maintain the system controlled under the external load torque variations. Then, the load variations do not affect the motor positioning. Moreover, it is demonstrated that the observer error converges to zero based on the Lyapunov stability theory.Originality/valueThe knowledge of the upper bound for the system uncertainty is not necessary in an adaptive state observer, which is important in practical implementation. Simulation results are presented to demonstrate the performance of the proposed approach.

Disturbance observer based dynamic load torque compensator for assistive exoskeletons

In assistive robotics applications, the human limb is attached intimately to the robotic exoskeleton. The coupled dynamics of the human-exoskeleton system are highly nonlinear and uncertain, and effectively appear as uncertain load-torques at the joint actuators of the exoskeleton. This uncertainty makes the application of standard computed torque techniques quite challenging. Furthermore, the need for safe human interaction severely limits the gear ratio of the actuators. With small gear ratios, the uncertain joint load-torques cannot be ignored and need to be effectively compensated. A novel disturbance observer based dynamic load-torque compensator is hereby proposed and analysed for the current controlled DC-drive actuators of the exoskeleton, to effectively compensate the said uncertain load-torques at the joint level. The feedforward dynamic load-torque compensator is proposed based on the higher order dynamic model of the current controlled DC-drive. The dynamic load-torque compensator based current controlled DC-drive is then combined with a tailored feedback disturbance observer to further improve the compensation performance in the presence of drive parametric uncertainty. The proposed compensator structure is shown both theoretically and practically to give significantly improved performance w.r.t disturbance observer compensator alone and classical static load-torque compensator, for rated load-torque frequencies up to 1.6 Hz, which is a typical joint frequency bound for normal daily activities for elderly. It is also shown theoretically that the proposed compensator achieves the improved performance with comparable reference current requirement for the current controlled DC-drive.

Tracking Problem for Induction Electric Drive under Influence of Unknown Perturbation

The tracking problem for induction motor drives is considered in the paper. The main attention is devoted to the problem of unknown load torque compensation not belonging to the control space. The model of induction motor is considered in the fixed reference frame concerned with the stator. A modification of vector control principle is designed on the base of new relay control law, which is used for generation of damping oscillating modes with unlimited growth in oscillation frequency. The theoretically infinite coefficient of relay linearization enabling asymptotic invariance of the output to a wide class of external perturbations. The simulation results show the efficiency of proposed approach.

Analysis and Design of a Speed Controller for Electric Load Simulators

Electric load simulator (ELS) is a resonant system and has a large coefficient caused by the stiffness of shaft. Its dynamic performance is always limited and stability is hard to be guaranteed. Besides, its external disturbance is the active motion of an actuator, and output is the load torque, which are both different from conventional servo systems. Therefore, the speed controller of ELS needs to be specially designed. In this paper, a speed controller for ELS is proposed to improve the dynamic performance and stability of ELS. The proposed controller consists of three control terms: a proportional (P) control term, a speed reference feedforward term, and a load torque compensation term. The tracking performance and surplus torque suppression performance of ELS with the proposed controller are analyzed in this paper. Stability analysis in discrete domain is carried out to guarantee the stability for digital applications. Robustness is also analyzed and an extended state observer is designed to compensate uncertainties and estimate speed. Furthermore, the proposed speed controller is compared with other three control methods. Experimental results on ELS are provided and validate the effectiveness of the proposed method.

Study on dynamic characteristic of wind turbine emulator based on PMSM

In this paper, a wind turbine emulator (WTE) based on the load torque dynamic compensation of PMSM is proposed to satisfy the further study of wind power system control technology in laboratory. The basic characteristic of wind turbine is analyzed to compare the wind turbine with its WTE. The dynamic compensation method based on the acceleration feedback is improved to propose the load torque dynamic compensation method to realize the dynamic characteristic simulation of wind turbine. Moreover, a low pass filter (LPF) is adopted at the load torque compensation module to suppress the torque ripple of the wind generator. An entire wind power system experimental platform is built to test the proposed torque compensation method. The results verify the proposed control method.

High-performance Load Torque Compensation of Industrial Robot using Kalman-filter-based Instantaneous State Observer

High-performance Load Torque Compensation of Industrial Robot using Kalman-filter-based Instantaneous State Observer

High Dynamic Performance of Interior Permanent Magnet Synchronous Motor Drives Based on Feed-forward Load Torque Compensator

This article presents an improvement in the dynamic performance of interior permanent magnet synchronous motor drives by using a feed-forward load torque compensator along with a proportional-integral speed controller. In such a case, the load torque estimator compensates the speed control by setting a feed-forward torque value through the q-axis current reference value, so that the machine speed can reach the reference speed very fast. The experimental and simulation results indicate that the proposed control technique improves the interior permanent magnet synchronous motor speed performance in terms of tracking precision and travel time. Moreover, the performance of an interior permanent magnet synchronous motor drive system using a conventional proportional-integral controller is compared with the proposed controller. The results show that the proposed proportional-integral controller with a feed-forward load torque compensator has achieved superior performance compared to those of the conventional one. An acceptable speed response under load torque variations and parameter uncertainty is found.

The Lower Extremity Exoskeleton Coordinated Control Method Based on Human Electromechanical Coupling

This paper has introduced electromechanical coupling characteristics in the lower extremity exoskeleton systems, considered model ,according to legs supporting gait when people walking, established the load torque compensation model , and a mathematical model of knee position control system which is made of the servo valve, hydraulic cylinders and other hydraulic components, designed hydraulic cylinder position control loop in case of existing load force interference compensation, and used the method of combining the PID and lead correction network for frequency domain design ,ensured system to meet a certain stability margin. The simulation results show that this position control method can servo on the knee angular displacement of normal human walking, reached a certain exoskeleton boost effect, at the same time, met the needs of human-machine coordinated motion.

Coordinated Control Method of the Portable Facility for Bearing Load Based on Human Electromechanical Coupling

This paper has introduced electromechanical coupling characteristics in portable facility for bearing load, considered model ,according to legs supporting gait when people walking, established the load torque compensation model , and a mathematical model of knee position control system which is made of the servo valve, hydraulic cylinders and other hydraulic components, designed hydraulic cylinder position control loop in case of existing load force interference compensation, and used the method of combining the PID and lead correction network for frequency domain design ,ensured system to meet a certain stability margin. The simulation results show that this position control method can servo on the knee angular displacement of normal human walking, reached a certain portable facility bearing load and assistant power effect, at the same time, met the needs of human-machine coordinated motion.

Adaptive Kalman Filter-Based Load Torque Compensator for Improved SI Engine Idle Speed Control

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents design of an SI engine load torque estimator based on an adaptive Kalman filter. The adaptive estimator is characterized by a fast response and good noise suppression ability. The estimator is used to establish a fast load torque compensation path within a proportiona-plus-integral (PI) controller-based idle speed control system. The proposed adaptive controller has been verified by means of experiments, and compared with PI, PID and polynomial controllers. The experimental results point out to favorable performance of the adaptive controller for a wide engine operating range. </para>