A novel adaptive PD-type iterative learning control of the PMSM servo system with the friction uncertainty in low speeds

High precision demands in a large number of emerging robotic applications strengthened the role of the modern control laws in the position control of the Permanent Magnet Synchronous Motor (PMSM) servo system. This paper proposes a learning-based adaptive control approach to improve the PMSM position tracking in the presence of the friction uncertainty. In contrast to most of the reported works considering the servos operating at high speeds, this paper focuses on low speeds in which the friction stemmed deteriorations become more obvious. In this paper firstly, a servo model involving the Stribeck friction dynamics is formulated, and the unknown friction parameters are identified by a genetic algorithm from the offline data. Then, a feedforward controller is designed to inject the friction information into the loop and eliminate it before causing performance degradations. Since the friction is a kind of disturbance and leads to uncertainties having time-varying characters, an Adaptive Proportional Derivative (APD) type Iterative Learning Controller (ILC) named as the APD-ILC is designed to mitigate the friction effects. Finally, the proposed control approach is simulated in MATLAB/Simulink environment and it is compared with the conventional Proportional Integral Derivative (PID) controller, Proportional ILC (P-ILC), and Proportional Derivative ILC (PD-ILC) algorithms. The results confirm that the proposed APD-ILC significantly lessens the effects of the friction and thus noticeably improves the control performance in the low speeds of the PMSM

Speed Ripple Reduction of Direct-Drive PMSM Servo System at Low-Speed Operation Using Virtual Cogging Torque Control Method

This paper presents a virtual cogging torque (VCT) control method to reduce the speed ripple of direct-drive permanent magnet synchronous machine (DD-PMSM) servo system under low-speed conditions. Compared with other factors, at low speeds, the cogging torque is the main factor that deteriorates the drive performance, even induces speed oscillations. Especially in this paper, due to volume limitation, the cogging torque is designed larger than normal one in order to remove the need of brake. Based on the model of PMSM, the cause and effect of the cogging torque are analyzed. Inspired by the characteristic of cogging torque, the VCT control method is proposed and investigated to significantly reduce the speed ripple at low speeds. The main idea of this proposed control method is to produce a proper virtual cogging torque and continuously move the corresponding virtual stable equilibrium point to drive the rotor smoothly. In addition to the principle of this control method, its analysis and implementation are studied as well. Simulation and experimental results from the prototype demonstrate that the proposed control method is correct and valid, and it is simple and effective to smooth the speed at low-speed operations

A New Position and Speed Estimation Scheme for Position Control of PMSM Drives Using Low-Resolution Position Sensors

A new position control method for permanent magnet synchronous motor (PMSM) drive with a low-resolution encoder is proposed in this paper. Three binary Hall position sensors are utilized to realize a moderate-performance position control system for the consideration of economy and simplicity in servo application. Compared with sensorless control, the usage of binary Hall position sensors is a guarantee of both control performance and low cost. However, the low resolution of the Hall sensor will heavily deteriorate the accuracy of the position and speed calculation. Such drawback can be effectively minimized by using appropriate position and speed estimation schemes. With the help of polynomial fitting and state observer techniques, a solution is provided to realize semi-closed loop control by treating the position and speed estimators as separate systems. The performance can be improved (1) by proposing a polynomial fitting scheme with least squares method, high-resolution rotor-position predictor can be derived by fitting the predefined position data from binary Hall position sensors in a linear or quadratic manner; (2) by adopting the dual-sampling-rate observer, instantaneous speed can be estimated at each control cycle and the estimation error is corrected once a new measurement form the Hall arrives. Furthermore, a nonlinear position control algorithm is introduced to increase standstill stability. Extensive experimental results are given to demonstrate the feasibility of the proposed method and its superiority over conventional methods

High performance disturbance observer based control system design for permanent magnet synchronous AC machine applications

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonAn electrical machine is one of the main workforces in different industries and serves them in various applications. Machine drive control design involves many technical issues for efficient and robust exploitation. Over several decades, Permanent Magnet Synchronous Motor (PMSM) is getting preferred for industrial applications over its counterpart Squirrel Cage Induction Motor (SCIM) drive, because of their higher efficiency, power density, and higher torque to inertia ratio. In the prospective that PMSM drives are considered the drives of the future, there are still technical challenges and issues related to PMSM control. Many studies have been devoted to PMSM control in the past, but there are still some open research areas that bring worldwide researchers’ interests back to PMSM drive control. One of the approaches that may facilitate better performance, higher efficiency, and robust and reliable work of the control system is the disturbance observer-based control (DOBC) with linear and nonlinear output feedback control for PM synchronous machine applications. DOBC is adopted due to its ability to reject external and internal disturbances with improving tracking performance in the variable speed wind energy conversion system (WECS) to maximize power extraction. The high order disturbance observer (HODO) is utilized to estimate the aerodynamic torque-based wind speed without the use of a traditional anemometer, which reduces the overall cost and improves the reliability of the whole system. Also, this method has been designed to improve the angular shaft speed tracking of the PMSM system under load torque disturbance and speed variations. The model-based linear and nonlinear feedback control are used in the proposed control systems. The sliding mode control (SMC) with switching output feedback control law and integral SMC with linear feedback and state-dependent Riccati equation (SDRE) based approaches have been designed for the systems. The SDRE control accounts for the nonlinear multivariable structure of the WECS and is approximated with Taylor series expansion terms. The chattering inherited from SMC is eliminated by the continuous approximation technique. The sliding mode is guaranteed by eliminating the reaching mode in the proposed integral SMC. The model-free cascaded linear feedback control system based on the proportional-integral (PI) controllers use a back-calculation algorithm anti-windup scheme. The proposed speed controllers are synthesized with HODO to compensate for the external disturbance, model uncertainty, noise, and modelling errors. Moreover, servomechanism-based SDRE control, a near-optimal control system is designed to suppress the model uncertainty and noise without the use of disturbance observers. The proposed control systems for PMSM speed regulation have demonstrated a significant improvement in the angular shaft speed-tracking performance at the transients. Their performances have been tested under speed, load torque variations, and model uncertainty. For example, HODO-based SMC with switching output feedback control law (SOFCL) has demonstrated improvement by more than 78% than the PI-PI control system of the PMSM. The performance of the HODOs-based Integral SMC with SDRE nonlinear feedback is improved by 80.5% under external disturbance, model uncertainty, and noise than Integral SMC with linear feedback in the WECS. The HODO-based SDRE control with servomechanism has shown an 80.2% improvement of mean absolute percentage error under disturbances than Integral SMC with linear feedback in the WECS. The PMSM speed tracking performance of the proposed HODO-based discrete-time PI-PI control system with back-calculation algorithm anti-windup scheme is improved by 87.29% and 90.2% in the speed commands and load torque disturbance variations scenarios respectively. The simulations for testing the proposed control system of the PMSM system and WECS have been implemented in Matlab/Simulink environment. The PMSM speed control experimental results have been obtained with Lucas-Nuelle DSP-based rapid control prototyping kit.Center for International Program “Bolashak” of the Ministry of Education and Science Republic of Kazakhsta

Electrohydraulic Drive with a Flow Valve Controlled by a Permanent Magnet Synchronous Motor

This article presents an electrohydraulic drive with a new electrohydraulic flow valve controlled by a Permanent Magnet Synchronous Motor (PMSM), designed and built by the authors. In comparison to a valve with a proportional electromagnet, the use of a PMSM has enabled significant improvements in the key characteristics of the valve. A theoretical framework and a model of a PMSM are presented; subsequently, a valve with this motor is proposed and tested. Step responses of the real valve and its static and frequency characteristics are measured. The characteristics obtained in the simulation are compared with those obtained in the laboratory investigations, showing their good compliance. The obtained characteristics of the new valve are better than those of a typical proportional valve. The new valve is applied in an electrohydraulic linear actuator. For positioning tasks, two types of controllers are applied and compared: a proportional-derivative controller and a fractional order proportional-derivative controller showing satisfactory parameters

Current and voltage shaping method via modified d–q transformation for the torque ripple compensation in PMSMs

This study deals with a novel control strategy for permanent magnet synchronous machines (PMSMs) to incorporate disturbance compensation features in the existing current controller maintaining at the same time the integrity of the reference tracking performances. The torque produced by a PMSM arises from the interaction of stator currents and rotor magnetic flux, therefore an intrinsic disturbance is propagated to the output, in case the flux is not perfectly sinusoidal. In particular, the authors focus is to propose the effective correction of undesired harmonic effects generated on the torque from the non-ideal machine rotor. With the knowledge of the back electromagnetic force waveform, it is possible to determine the current waveforms necessary to produce a smooth torque in normal operation and through model-base considerations, the required voltage harmonic waveforms are also computed. The method is also extended to the flux weakening operation of the machine. The analytical solutions found are used in place of the classical αβ/dq transformations, without modifying the field-oriented control performance of the main controller. The effectiveness of the proposed control scheme is verified by means of test-bench measurement

Rotor Position Tracking Control for Low Speed Operation of Direct-Drive PMSM Servo System

In this paper, a rotor position tracking control (RPTC) strategy is proposed to effectively reduce the speed fluctuation for a direct-drive permanent magnet synchronous motor (DD-PMSM) servo system operating at low speed with different torque disturbances. In this strategy, considering the derivative relationship between the rotor position and speed, a speed command is converted to a real-time rotor position trajectory, and then a position-current two-loop control with the RPTC controller is proposed based on the internal model method to smoothly track the rotor position. In addition, the parameter design of RPTC controller from the perspectives of robust stability and anti-disturbance capability is investigated as well. Comparative simulation and experimental results demonstrate that, at low speed, the proposed RPTC strategy has a good speed performance for both periodic and non-periodic torque disturbances. Moreover, it enjoys simple implementation for not requiring the precise speed feedback and specific torque disturbance information

Some Permanent Magnet Synchronous Motor (PMSM) Sensorless Control Methods based on Operation Speed Area

This paper compares some sensorless Permanent Magnet Synchronous Motor (PMSM) controls for driving an electric vehicle in terms of operating speed. Sensorless control is a type of control method in which sensors, such as speed and position sensors, are not used to measure controlled variables.  The controlled variable value is estimated from the stator current measurement. Sensorless control performance is not as good as a sensor-based system. This paper aims are to recommend a control method for the PMSM sensorless controls that would be used to drive an electric vehicle. The methods that we will discuss are divided into four categories based on the operation speed area.  They are a startup, low speed, high speed, and low and high-speed areas. The low and high-speed area will be divided into with and without switching.  If PMSM more work at high speed, the most speed area that is used, we prefer to choose the method that works at high speed, that is, the modification or combination of two or more conventional methods