Torque Undulations Research Articles

Enhanced direct torque control based on intelligent approach for doubly-fed induction machine fed by three-level inverter

This paper presents an adaptive neuro-fuzzy inference system (ANFIS) based on 24 sectors direct torque command (DTC) for a doubly-fed induction machine (DFIM) by using a 3-level neutral point clamped inverter. The DTC approach is used in this paper with 24 sectors based on the ANFIS regulator to minimize the torque fluctuations, flux fluctuations, and stator stream THD (Total Harmonic Distortion) of the DFIM drive. The composed technique is accomplished by replacing the hysteresis controllers of the flux and torque with the ANFIS controller. On the other hand, the results of the designed approach based on ANFIS controls were obtained compared to the traditional approach that uses usual controls, as MATLAB was used to realize these approaches in different working conditions. In all tests, the designed method shows improved performance in minimizing torque and flux undulations while reducing the THD of the stator stream. These results highlight the extent of efficiency, high competence, and effectiveness in improving machine features compared to the conventional approach, where the designed approach minimized the THD of current by ratios of approximately 77.50%, 48.34%, 75%, and 81.43% in all tests. Also, the torque undulation value was reduced by 30%, 39.24%, 31.94%, and 59.31% in all tests compared to the DTC. The designed approach minimized the speed overshoot compared to the DTC by percentages estimated at 98.83%, 97.11%, 96.75%, and 95.56% in all tests. These percentages demonstrate the high efficiency and effectiveness of the 24 sectors DTC-ANFIS compared to the conventional approach in improving the features of the control system, making it a promising solution in all electrical fields in the future.

IM Fed by Three-Level Inverter under DTC Strategy Combined with Sliding Mode Theory

The classical direct torque control (CDTC) of the induction motor (IM) drive is characterized by high ripples in the stator flux and the electromagnetic torque waveforms due to the use of hysteresis comparators. Furthermore, the motor speed in this control strategy is ensured through a proportional integral (PI) regulator, due to its simple structure. Nonetheless, this controller is sensitive to load disturbances. Hence, it is not robust against parameter variance, which can degrade the motor performance. To overcome this deficiency, many endeavors have been conducted in the literature to ensure a high dynamic response of the motor in all speed ranges, with minimum flux and torque undulations. Thus, the DTC of an IM associated with a three-level inverter based on sliding mode (SM) flux, torque and speed controllers was adopted to substitute the hysteresis comparators and the traditional PI regulator, since the SM speed controller is able to prevail against external disturbances. The second contribution of this manuscript is to develop the proposed DTC_SM approach using the Xilinx System Generator (XSG) in order to implement it on a field programmable gate array (FPGA) Virtex 5 on account of its ability to adopt parallel processing. The hardware co-simulation results verify clearly the merits of the suggested modified DTC strategy.

Improvement of torque undulation in BLDC using SEPIC and common end diode clamped three-level inverter

Improvement of torque undulation in BLDC using SEPIC and common end diode clamped three-level inverter

Vector Control Applied to Mitigate the Electromagnetic Torque Ripple in Doubly Fed Induction Generator

This paper proposes a novel Vector Control topology for stator current harmonic mitigation, due to the grid voltage harmonic content, focusing on mitigating the torque undulations in the Doubly Fed Induction Generator. The Proposed Controller referred here as to HVC - Harmonic Vector Control, is capable of mitigating any desired current harmonic. Voltage grid fifth, seventh, eleventh and thirteenth harmonic components causes current harmonic components of the same order (5th, 7th, 11th and 13th) in the generator but of higher relative amplitudes, due to the low stator series impedance. Therefore, the HVC has been tested for the control of such current harmonic components. As an advantage, the proposed control does not require a harmonic filter to estimate the harmonic content present in the stator current due to the power grid, which are the main disadvantages found in literature for the existing controllers. Firstly, the control topology is described and explained in detail. Next, simulation and experimental data are shown and compared to prove the suitability and efficacy of the proposed control. In the cases studied, the steady state error of the proposed controller is close to zero. Furthermore, the HVC can be used as a harmonic filter in DFIG and the harmonics can be chosen according to the application requirements.

Application of STA Methods and Modified SVM Strategy in Direct Vector Control System of ASG Integrated to Dual-Rotor Wind Power: Simulation Studies

This work presents the direct vector control (DVC) strategy of the asynchronous generator (ASG) with the application of super-twisting algorithms (STAs) and modified space vector modulation (MSVM). Two different strategies are designed to regulate the active and reactive powers of the asynchronous generator (ASG) driven by a variable speed dual-rotor wind power (DRWP). The main goal of the designed DVC method is to improve the quality of energy of the DRWP system by minimizing torque undulations, reactive and active power undulations in the ASG-DRWP systems. The mathematical model of the ASG has been described. The descriptions of the two-level MSVM technique and the STA method have been presented. The DVC-MSVM strategy with STA algorithms has been described. The simulation studies of the DVC-MSVM strategy with STA strategy have been performed, and the results of this study are presented and discussed.

Performance evaluation of PI and PI-fuzzy logic controller FPGA based permanent magnet synchronous motor drive

This paper depicts an experimental validation and simulation for speed control under load and no load conditions. It delineates the detail study of a closed loop vector controlled permanent magnet synchronous motor drive. This system consists of two loops for smooth speed tracking as well as reduced torque undulation. PMSM drives facilitate better dynamic responses during both steady state and dynamic conditions by monitoring the component of torque current. The resistive loads are varied and resultant speed and torque are studied. Experimental work has been performed on PMSM drives under different conditions and results are compared with conventional PI and Fuzzy logic controller. Â

Improved Finite Control-Set Model-Based Direct Power Control of BLDC Motor With Reduced Torque Ripple

This paper deals with active torque ripple compensation based on direct power control of permanent magnet brushless DC (BLDC) motor drive. The torque undulations caused by the mismatch between stator current and its nonsinusoidal back electromotive force (back EMF) waveforms is a well-known issue on BLDC motor drives. In this paper, to remedy this problem, a simple and comprehensive direct power control based approach is proposed. Instead of using conventional field-oriented control or direct torque control schemes, which are widely used in ac machines with sinusoidal flux distribution, an alternative approach is presented to control the mutual torque production through an active and reactive rotor power control loop. As a result, the proposed approach provides a simple way to reduce torque ripple of a permanent magnet synchronous motor with nonsinusoidal back EMF without requiring rotor orientation or back EMF harmonic content estimation method. In order to synthesize the proper input voltages in the context of torque ripple minimization, high bandwidth controllers are required to cope the torque ripple frequencies. In this sense, the power control loop is implemented based on two-vector finite control-set model-based predictive control approach, which provides fast torque response and good steady-state performance. The validity of the proposed control scheme for low torque ripple BLDC motor drive is verified through experimental results, achieving good steady-state performance while maintaining quick dynamic response.

Finite Control-Set Predictive Power Control of BLDC Drive for Torque Ripple Reduction

Due to advantages as high efficiency and high power density, brushless direct current (BLDC) motor has been used in a wide variety of applications. However, in conventional 120o conducting drive operation it develops significant torque ripple as a result of phase commutation. To reduce torque undulations, in this paper is proposed a power control based on Finite Control-Set Model based Predictive Control (FCS-MPC). The relationship between the control of the power delivered to rotor and torque ripple reduction is presented. The effectiveness of commutation torque ripple reduction of proposed method is presented in comparison with conventional torque control strategy. The results of proposed predictive control approach demonstrate fast torque response with no adjustable gains needed and operates with model variables on stationary reference frame.

Control of gliding in a flying snake-inspired n-chain model

Flying snakes of genus Chrysopelea possess a highly dynamic gliding behavior, which is dominated by an undulation in the form of lateral waves sent posteriorly down the body. The resulting high-amplitude periodic variations in the distribution of mass and aerodynamic forces have been hypothesized to contribute to the stability of the snake’s gliding trajectory. However, a previous 2D analysis in the longitudinal plane failed to reveal a significant effect of undulation on the stability in the pitch direction. In this study, a theoretical model was used to examine the dynamics and stability characteristics of flying snakes in three dimensions. The snake was modeled as an articulated chain of airfoils connected with revolute joints. Along the lines of vibrational control methods, which employ high-amplitude periodic inputs to produce desirable stable motions in nonlinear systems, undulation was considered as a periodic input to the system. This was implemented either by directly prescribing the joint angles as periodic functions of time (kinematic undulation), or by assuming periodic torques acting at the joints (torque undulation). The aerodynamic forces were modeled using blade element theory and previously determined force coefficients. The results show that torque undulation, along with linearization-based closed-loop control, could increase the size of the basin of stability. The effectiveness of the stabilization provided by torque undulation is a function of the amplitude and frequency of the input. In addition, kinematic undulation provides open-loop stability for sufficiently large frequencies. The results suggest that the snakes need some amount of closed-loop control despite the clear contribution of undulation to glide stability. However, as the closed-loop control system needs to work around a passively stable trajectory, undulation lowers the demand for a complex closed-loop control system. Overall, this study demonstrates the possibility of maintaining stability during gliding using a morphing body instead of symmetrically paired wings.

Control of a Uniform Step Asymmetrical 13-Level Inverter Using Particle Swarm Optimization

Harmonic Elimination Strategy (HES) has been a widely researched alternative to traditional PWM techniques. This paper presents the harmonic elimination strategy of a Uniform Step Asymmetrical Multilevel Inverter (USAMI) using Particle Swarm Optimization (PSO) which eliminates specified higher order harmonics while maintaining the required fundamental voltage. This method can be applied to USAMI with any number of levels. As an example, in this paper a 13-level USAMI is considered and the optimum switching angles are calculated to eliminate the 5th, 7th, 11th, 13th and 17th harmonics. The HES-PSO approach is compared to the well-known Sinusoidal Pulse-Width Modulation (SPWM) strategy. Simulation results demonstrate the better performances and technical advantages of the HES-PSO controller in feeding an asynchronous machine. Indeed, the harmonic distortions are efficiently cancelled providing thus an optimized control signal for the asynchronous machine. Moreover, the technique presented here substantially reduces the torque undulations.

The dual three-phase open-end stator windings permanent magnet synchronous machine fed by four voltage source inverters

In this paper, the mathematical model in Park reference frame of the dual open-end stator winding salient-pole permanent magnet synchronous machine is described. The proposed machine is supplied by its four voltage source inverters based on PWM technique. Then, the feeding of this machine by four two-level cascaded inverters is presented. A multilevel PWM strategy is carried out to control the cascaded inverters. The simulation analyses using the THD voltage, THD stator current and the torque undulation are presented and show the benefits for the proposed machine.

The dual three-phase open-end stator windings permanent magnet synchronous machine fed by four voltage source inverters

In this paper, the mathematical model in Park reference frame of the dual open-end stator winding salient-pole permanent magnet synchronous machine is described. The proposed machine is supplied by its four voltage source inverters based on PWM technique. Then, the feeding of this machine by four two-level cascaded inverters is presented. A multilevel PWM strategy is carried out to control the cascaded inverters. The simulation analyses using the THD voltage, THD stator current and the torque undulation are presented and show the benefits for the proposed machine.

Modeling and analysis of a novel dual open-end stator windings wound rotor synchronous machine with dampers

This work presents a novel wound rotor synchronous machine with dampers with dual three-phase open-end stator windings. The aim of the proposed machine is to improve the power segmentation and the availability of the drive system. The mathematical model of this machine is presented in the Park reference frame. This machine is supplied by four 2-level inverters, where each inverter is dimensioned for quarter power of the machine. For comparison purposes, we use a double star synchronous machine fed by two 2-level inverters. Comparative simulation analysis using THD voltage, THD stator current, and torque undulation showed significant advantages of the proposed machine.

Comparison between star winding and open-end winding induction machines

In this paper, the authors propose the mathematical model in Park reference frame of squirrel cage induction machine with dual open-end windings. A comparison between open-end stator winding induction machines and star winding induction machines is presented. In this comparison, the authors take into consideration the power segmentation, redundancy degrees in degraded mode, the THD current and the torque undulation.

A New DTC Scheme using Second Order Sliding Mode and Fuzzy Logic of a DFIG for Wind Turbine System

This article present a novel direct torque control (DTC) scheme using high order sliding mode (HOSM) and fuzzy logic of a doubly fed induction generator (DFIG) incorporated in a wind turbine system. Conventional direct torque control strategy (C-DTC) using hysteresis controllers presents considerable flux and torque undulations at steady state period. In order to ensure a robust DTC method for the DFIG-rotor side converter and reduce flux and torque ripples, a second order sliding mode (SOSM) technique based on super twisting algorithm and fuzzy logic is used in this paper. Simulation results show the efficiency of the proposed method of control especially on the quality of the provided power comparatively to a C-DTC.

An Artificial Neural Network Approach for Solving the Harmonic Distortions Elimination in Multilevel Converters

In this paper, a neural approach is applied to determine the switching angles for a uniform step asymmetrical multilevel inverter by eliminating specified higher-order harmonics while maintaining the required fundamental voltage. A Multi-Layer Perceptron (MLP) neural network is used to approximate the function between the modulation rate and the required switching angles. After learning, the artificial neural network is able to determine the appropriate switching angles for the inverter. This leads to a low-computational-cost neural controller which is therefore well suited for real-time applications. This technique can be applied to multilevel inverters with any number of levels. As an example, a nine-level inverter and an eleven-level inverter are considered and the optimum switching angles are calculated on-line. The neural approach is compared to the well-known sinusoidal Pulse-Width Modulation (PWM) strategy. Simulation results demonstrate the better performances and technical advantages of the neural controller in feeding an asynchronous machine. Indeed, the harmonic distortions are efficiently cancelled providing thus an optimized control signal for the asynchronous machine. Moreover, the technique presented here substantially reduces the torque undulations.

Elimination of System-Induced Torque Pulsations in Doubly-Fed Induction Generators Via Field Reconstruction Method

Effects of system unbalance and system harmonics on the operation of doubly-fed induction generator (DFIG) used in wind energy harvesting are of great concern. This is primarily due to the fact that system unbalance and harmonics can generate unwanted torque undulations that can potentially undermine the mechanical integrity of the tower, and reduce the lifetime of the moving components that are attached to the generator shaft. This paper focuses on the development of a solution for the above problem by judicious selection of the rotor currents to actively eliminate/mitigate these undesirable vibrations. The enabling technology for optimal calculation of the rotor currents is based on the field reconstruction method (FRM). FRM is an analytical tool for the approximation of the magnetic field distribution in the middle of the air gap. Once the FRM formulation is setup, it is capable to predict the tangential/normal components of the magnetic forces. In this paper, the FRM is applied to compute the rotor phase currents in lieu of the availability of the real-time stator currents such that the resultant field will generate a smooth torque.

Guest Editorial Optimal Design of Electric Machines

The papers in this special section cover the advances in multi-objective design and optimization based on genetic algorithms, surrogate, polynomial regression, and particle swarm optimization techniques. Design of novel trans-rotary magnetic gear, hybrid machines for dc generation, and two degrees of freedom split-stator induction machines highlight new magnetic configurations and their performance evaluations. Multiphysics analysis of magnetothermal and magnetostructural behavior of Switched Reluctance Machine (SRM) and brushless doubly fed machines shed light on analytical and practical aspects of design in electromechanical converters. Finally, control of torque undulation, loss minimization, low speed high torque operation, and advanced digital control of adjustable speed motor drives conclude this unique collection of papers.

An Analysis of the Impact of Rotor Winding Interturn Short Circuits on Turbine Generator Operating Variables

— In this article, the finite-element method is used to study the impact on a generator's electromagnetic torque by the position and level of a rotor winding interturn short circuit. The rules involving changes to the exciting current and the reactive power of generators are analyzed under the given adjustment patterns. The results of this study show that the saturability of ferromagnetic materials reduces the torque undulations that occur during the rotor winding interturn short circuit fault and that it improves the static stability of generators. Both the simulation experiment and the real case of a rotor winding interturn short circuit demonstrated that when a rotor winding interturn short circuit happens in a turbine generator, the generator can maintain its static stability by adjusting its state variables. This results in an increased exciting current and a decreased reactive power. The analytical method described herein allows accurate prediction of the change limits of the exciting current and the reactive power, enabling better diagnosis of the rotor winding interturn short circuit based on the two variables.

Control of a Uniform Step Asymmetrical 13-Level Inverter Using Particle Swarm Optimization

Harmonic Elimination Strategy (HES) has been a widely researched alternative to traditional PWM techniques. This paper presents the harmonic elimination strategy of a Uniform Step Asymmetrical Multilevel Inverter (USAMI) using Particle Swarm Optimization (PSO) which eliminates specified higher order harmonics while maintaining the required fundamental voltage. This method can be applied to USAMI with any number of levels. As an example, in this paper a 13-level USAMI is considered and the optimum switching angles are calculated to eliminate the 5th, 7th, 11th, 13th and 17th harmonics. The HES-PSO approach is compared to the well-known Sinusoidal Pulse-Width Modulation (SPWM) strategy. Simulation results demonstrate the better performances and technical advantages of the HES-PSO controller in feeding an asynchronous machine. Indeed, the harmonic distortions are efficiently cancelled providing thus an optimized control signal for the asynchronous machine. Moreover, the technique presented here substantially reduces the torque undulations.