Torque Flux Research Articles

Predictive direct torque control of a rotor-side matrix converter driven grid connected DFIG with torque and flux ripples minimisation criterion

The doubly fed induction generator (DFIG) is the most commonly used machine for variable speed wind power generation, and the single stage matrix converter (MC) can potentially replace the conventional back-to-back voltage source converters (VSCs) for rotor to grid inter connection. In this research work, the performance of grid connected DFIG with rotor side MC is analysed with predictive direct torque control (P-DTC) technique incorporating a criterion for minimising the torque and rotor flux ripples at a fixed switching frequency. Space vector modulation (SVM) is utilised for MC side control. The system exhibits better transient and steady-state behaviour over conventional configurations, for both sub and super-synchronous operating modes, as evaluated by simulation based on a 2 MW DFIG model in MATLAB-Simulink environment.

Novel ABC—Variable Based Closed-Form Analytical Model of Surface Mounted Permanent Magnet AC Machines With Sinusoidal and Non-Sinusoidal Back-EMF

This work presents a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> -based model applicable to surface-mounted permanent magnet AC (SM-PMAC) machines with sinusoidal and non-sinusoidal back-emf. It is capable of predicting the electromagnetic performance metrics such as torque waveforms, machine inductances, flux linkages and back-emf. The closed form expressions of the model, which can be evaluated with a high computational efficiency, are derived from basic geometric and winding parameters. Validation of the model is carried out numerically and experimentally with a very good match in results. Finally, the computational efficiency of the model is highlighted by considering a multi-objective evolutionary optimization design of SM-PMAC machine with a relatively large number of design parameters, where results are presented and discussed.

Optimization & control strategy for offshore wind turbine based on a dual fed induction generator

This work is motivated by the progression of wind farms installed in the world and by the will of researchers and specialists to develop techniques and solutions to solve the problem of their integration into the electrical grid. To have maximum converted power, the turbine velocity must be adapted to the wind speed. This is a challenge for manufacturers and researchers who face difficulties in designing powerful and reliable operating point control devices at maximum power. This paper has tried to find a solution that can extract the maximum power generated by the wind turbine and improve its efficiency. For this purpose, several control strategies have been implemented, such as the Maximum Power Point Tracking (MPPT) strategy with velocity control that extracts the maximum power from the wind turbine, the pitch control to limit the aerodynamic power, and the direct torque control of the generator to control the electromagnetic torque and rotor flux. The simulation results obtained in this work show the relevance of optimizing the energy transfer in the wind turbine system. They also show that the use of control strategies contributes greatly to the improvement of the overall energy efficiency of the wind power system used.

Investigation of Torque Performance and Flux Reversal Reduction of a Three-Phase 12/8 Switched Reluctance Motor Based on Winding Arrangement

The goal of this paper is to present a comparative analysis of two types of winding arrangements for a three-phase 12/8 switched reluctance motor (SRM), where short- and fully-pitched winding arrangements under unipolar operation are considered. From the analytical results, the short-pitched winding has the best torque per copper weight ratio. The core loss based on counting the number of flux reversals in the stator yoke for each winding arrangement is also proposed and mentioned. To reduce the magnetic flux reversals in the stator core, changing the direction of the magnetic flux path by modifying the winding polarities of the short-pitched winding could reduce 10–13% of core loss compared to the conventional winding. A 1 kW, 12/8 SRM prototype for the ventilation fan application is constructed and tested in order to verify the design consideration of winding configuration. At the rated condition, a maximum efficiency around 82.5% could be achieved.

An improved look-up table-based direct torque control for permanent magnet synchronous generator using Vienna rectifier

This paper presents an improved look-up table-based direct torque control of the permanent magnet synchronous generator using Vienna rectifier for a wind energy conversion system. A stator voltage model for the system was developed to allow an in-depth analysis of the effect of the switching vectors for the Vienna rectifier on the performance of direct torque control. The developed generator model is dedicated to reducing the complexity of look-up table development. Subsequently, an improved look-up table was designed to enhance the overall performance of the permanent magnet synchronous generator in both torque and stator flux ripples, along with the investigation of the computation delay compensation for the digital implementation. The performance was first investigated through Matlab / Simulink before being further validated using a small-scale prototype and a wind turbine emulator. Both simulation and experimental results obtained were compared with the existing direct torque control approach to verify the effectiveness of the proposed system for wind energy extraction. The results show that the enhanced look-up table generates lower ripples in torque and stator flux while improving their reference tracking, especially during unbalanced DC load scenarios. This achievement can be clearly seen by the lower discrepancy percentage between the reference and actual value in the generated torque and stator flux by 6.35% and 0.47%, respectively.

Multilevel Inverter fed Direct Torque and Flux Control‐Space Vector Modulation of Speed Sensorless Permanent Magnet Synchronous Motor drive with Improved Steady State and Dynamic Characteristics

AbstractIn this paper, multilevel inverter (MLI) fed direct torque and flux control with space vector modulation (DTFC‐SVM) of speed sensorless permanent‐magnet synchronous motor (PMSM) drive is proposed to improve the steady‐state and dynamic performance characteristics with less torque and flux ripples. In the DTFC‐SVM technique, the speed of PMSM drive is regulated by controlling stator flux and electromagnetic torque directly and independently. The MLIs further extend the performance characteristics of motor drive with reduced electromagnetic torque ripple and improved dynamics. Further, the robustness and reliability of drive system is improved by implementing the speed estimation control technique to eliminate the speed sensor usage. The model reference adaptive system (MRAS)‐based speed estimator is used to estimate the PMSM speed. The proposed method is simulated in MATLAB/SIMULINK environment using two‐level, three‐level, and five‐level inverter under different operating conditions, respectively. The proposed method with five‐level inverter gives very less ripples in electromagnetic torque and stator flux which consequences excellent steady‐state and dynamic performance of drive. The effectiveness and feasibility of the proposed method is validated by implementing hardware prototype and comparing simulation results with the experimental results.

Cascade Control of the Ground Station Module of an Airborne Wind Energy System

An airborne wind energy system (AWES) can harvest stronger wind streams at higher altitudes which are not accessible to conventional wind turbines. The operation of AWES requires a controller for the tethered aircraft/kite module (KM), as well as a controller for the ground station module (GSM). The literature regarding the control of AWES mostly focuses on the trajectory tracking of the KM. However, an advanced control of the GSM is also key to the successful operation of an AWES. In this paper we propose a cascaded control strategy for the GSM of an AWES during the traction or power generation phase. The GSM comprises a winch and a three-phase induction machine (IM), which acts as a generator. In the outer control-loop, an integral sliding mode control (SMC) algorithm is designed to keep the winch velocity at the prescribed level. A detailed stability analysis is also presented for the existence of the SMC for the perturbed winch system. The rotor flux-based field oriented control (RFOC) of the IM constitutes the inner control-loop. Due to the sophisticated RFOC, the decoupled and instantaneous control of torque and rotor flux is made possible using decentralized proportional integral (PI) controllers. The unknown states required to design RFOC are estimated using a discrete time Kalman filter (DKF), which is based on the quasi-linear model of the IM. The designed GSM controller is integrated with an already developed KM, and the AWES is simulated using MATLAB and Simulink. The simulation study shows that the GSM control system exhibits appropriate performance even in the presence of the wind gusts, which account for the external disturbance.

Design, 3D FEM Simulation and Prototyping of a Permanent Magnet Spherical Motor

In recent years, large tilt angles, uniform magnetic flux distributions, strong forces, and large torques for motors have increasingly become important for robotics, biomedical, and automotive applications that have multi-degrees of freedom (MDOFs) motion. Generally, one-degree of-freedom motors are applied in MDOF motion. These situations cause the systems to have very complex and large structures. In order to address these issues, a 2-DOF surface permanent magnet spherical motor with a new mechanical design for the movement of the rotor with a large tilt angle of ±45° was designed, simulated, produced and tested in this paper. The motor consisted of a 4-pole permanent magnet rotor and a 3-block stator with 18 coils. In this study, the mechanical structure of the proposed spherical permanent magnet motor surrounded the rotor with two moving parts to move at a large tilt angle of ±45° without using any mechanical components such as spherical bearings, joint bearings, and bearing covers. Thus, the tilt angle, force, and torque values of the proposed motor have been improved according to MDOF motion motors using spherical bearings, bearing covers, or joint bearings in their mechanical structures in the literature. Ansys Maxwell software was used for the design and simulation of the motor. Three-dimensional (3D) finite element method (FEM) analysis and experimental studies were carried out on the force, torque, and magnetic flux density distribution of the motor. Then, simulation results and experimental results were compared to validate the 3D FEM simulations results.

A Low-Complexity Three-Vector-Based Model Predictive Torque Control for SPMSM

In conventional model predictive torque control (MPTC), only one voltage vector (VV) is applied during a whole control period, thus causing a large torque ripple. To improve the steady-state performance, some two-vector-based control schemes have been proposed. However, the selection of the optimal VV pair is complex as well as has a large computational burden, and the improvement of performance is still limited by the direction and amplitude of the output VV. This article proposes a low-complexity three-vector-based MPTC for SPMSM drives, which can precisely determine the appropriate active voltage vectors (AVVs) with the predicted torque error. Then, a modified switching table is developed to directly select the AVVs, thus greatly reducing the complexity and computational burden of the algorithm. To obtain a better steady-state performance, a duty cycle calculation method based on torque and stator flux difference parameters is newly proposed to achieve the deadbeat control of torque and stator flux. And then, the experimental comparisons with the double-vector-based MPTC are conducted. The results show that the proposed MPTC can effectively reduce the steady-state torque ripple while maintaining a good dynamic performance as well as almost a fixed switching frequency for all speed ranges.

Levitation Performances Analysis of a Novel Bearingless Switched Reluctance Motor

To deal with the coupling between the levitation force and torque, a new bearingless switched reluctance motor (BSRM) is presented in the paper, in which the torque flux is separated with the levitation flux. In addition, due to the low cost and power of the three-phase power converter, the radial levitation of the proposed BSRM is driven by a three-phase power converter. The structure of the proposed BSRM is first introduced. The mathematical models of radial levitation force are second established by employing equivalent magnetic circuit approach. Finally, the electromagnetic characteristics of the BSRM, such as flux field distribution, transient levitation force and force-current relationship are investigated through the MagNet 3D. The research results indicate that the novel structure has good performances.

MRAS-Based Super-Twisting Sliding-Mode Estimator Combined With Block Control and DTC of Six-Phase Induction Motor for Ship Propulsion Application

This article presents the block control (BC) approach combined with the direct torque control (DTC) through employing a model reference adaptive system (MRAS) based on the super-twisting sliding-mode (STSM) speed estimator of a six-phase induction motor (6PIM) for ship propulsion application. The BC is a robust speed controller that is employed for regulating the 6PIM speed. The closed-loop approach is designed in an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">αβ</i> -reference frame as well as is based on the linearization BC approach. The flux estimator is based on the super-twisting technique that is a second-order sliding-mode approach. This observer is utilized as a reference model throughout the MRAS-based speed estimator for discarding the chattering problem of the conventional sliding-mode technique. Two STSM controllers are used for controlling the torque along with the stator flux and improving the drive system performance throughout external load disruptions. Furthermore, the STSM estimator estimates the torque and stator flux in a robust response with discarding the chattering problem. The proposed MRAS-based STSM speed estimator performance is investigated experimentally for the 750-W 6PIM as well as compared with the traditional DTC approach throughout various speed references, load disruptions, and low-speed command/low loading torque conditions.

Sensorless fuzzy direct torque control of induction motor with sliding mode speed controller

In this work, a fuzzy direct torque control (DTC) is developed for asynchronous motor drive powered by two-level inverter. The main objective is to enhance the system performance by reducing electromagnetic torque and stator flux ripples while improving stator current waveforms. The hysteresis comparators and voltage vector switching table of classic DTC are replaced by fuzzy logic block to ensure robust control against various disturbances. The outer speed loop is initially executed by PI regulator and secondly by sliding mode controller, for both systems stator flux MRAS estimator is adopted. A critical and comparative study between the DTC based on fuzzy logic and non-linear sliding mode DTC was done under MATLAB/SIMULINK. The performance analysis was carried out under different operating conditions such as steady and transient states, low , medium and high speeds, speed reversal and application of two different loads at various times.

Low-Complexity Multivector-Based Model Predictive Torque Control for PMSM With Voltage Preselection

In the double-vector-based model predictive torque control (MPTC), two voltage vectors are applied in one control period. Due to a large number of possible combinations among voltage vectors, the determination of optimal voltage vector pair is often complicated. This article proposes a new approach to reduce the number of candidate active voltage vectors. The concept is to preselect the active voltage vectors according to the stator flux vector error. The proposed MPTC is implemented in a stationary frame and avoids the complicated coordinate transformation as well as the tangent inverse calculations. Furthermore, a promising approach is conceived for calculating the duty cycle of active voltage vector, which can contribute to the less dependence on the system model, thus alleviating the sensitivity to motor parameter variations. To further improve the steady-state performance, a modified three-vector-based MPTC is newly put forward. Meanwhile, the proposed duty cycle calculation method is used to achieve the deadbeat control of torque and stator flux. Theoretical analyses and experimental results are given to verify the effectiveness of the proposed MPTC methods.

Improved dfig dftc by using a fractional-order super twisting algorithms in wind power application

Background: The direct flux and torque control are a robust, simple, and alternative approach control formulation that does not require decomposition into symmetrical components; the direct flux and torque control schemes have been proved to be preponderant for doubly-fed induction generators due to the simple implementation.&#x0D; Aim: This work presents the minimization of electromagnetic torque and rotor flux undulations of doubly-fed induction generators using fractional-order super twisting algorithms and modified space vector modulation techniques.&#x0D; Methods: The main role of direct flux and torque control is to regulate and control the electromagnetic torque and rotor flux of doubly-fed induction generators for wind turbine systems. The direct flux and torque control is a traditional control algorithm and robust technique. Fractional-order super twisting algorithms are a new and proposed nonlinear controller; characterized by a robust controller and a simpler algorithm, which gives a good harmonic distortion of current compared to other methods.&#x0D; Novelty: The A fractional-order super twisting algorithm is proposed. Proposed nonlinear controller construction is based on the traditional super twisting algorithm and fractional calculus to obtain a robust controller and reduces the electromagnetic torque and rotor flux undulations of doubly-fed induction generators. We use in our study a 1.5 MW doubly-fed induction generator integrated into a single-rotor wind turbine system to minimizes the electromagnetic torque, stator current, rotor flux undulations. As shown in the results figures using fractional-order super twisting algorithms ameliorate effectiveness especially minimizes the electromagnetic torque and rotor flux, and minimizes harmonic distortion of stator current (0.16 %) compared to the traditional control scheme.&#x0D; Results: As shown in the results figures using fractional-order super twisting algorithms ameliorate effectiveness especially minimizes the electromagnetic torque and rotor flux, and minimizes harmonic distortion of stator current (0.16 %) compared to the traditional control scheme.&#x0D; Conclusion: The direct flux and torque control are a robust, simple, and alternative approach control formulation that does not require decomposition into symmetrical components; the direct flux and torque control schemes have been proved to be preponderant for doubly-fed induction generators due to the simple implementation.

Squirrel cage induction motor predictive direct torque control based on multi-step delay compensation

The squirrel cage induction motor direct torque control main problems due to torque and large stator flux pulsation. In this an improved model predictive direct torque control algorithm considering multi-step delay compensation is proposed. At each sampling moment, predict the stator flux linkage and torque at the next moment under each voltage vector. The optimal voltage vector deviation from the stator flux linkage reference value and torque reference value are selected as the minimum objective function. Aiming at the problem of one-shot delay in digital control systems, a multi-step predictive delay compensation measure is studied. Simulation shows that the algorithm can effectively reduce torque and stator flux pulsation, reduce current harmonic distortion, and solve the delay problem in digital systems.

Direct Torque Control for a Bearingless Induction Motor Based on Model prediction

Purpose The purpose of this paper is to address the large stator flux linkage ripple and electromagnetic torque ripple caused by the hysteresis comparator in traditional direct torque control for a bearingless induction motor (BIM). Design/methodology/approach Model predictive direct torque control (MPDTC) strategy is adopted. On the basis of the mathematical model of BIM, the stator current and stator flux observational values are obtained, and the electromagnetic torque and stator flux at the next moment are predicted. Then, based on the relationship between the stator flux and the electromagnetic torque, the predicted stator flux can be transformed into an equivalent flux linkage vector, which eliminates the weighting coefficients problem among multiple variables in traditional objective functions. The objective function and torque PI controller will output the optimal stator flux linkage and the increments of the torque phase angle. Through the phase angle increments, the space voltage vector can be obtained by the reference flux linkage controller instead of the stator flux linkage and the torque hysteresis controller. Findings The proposed MPDTC method can effectively improve the stator flux linkage and the torque ripple. It can implement the stable suspension of the rotor and improve the dynamic performance and steady-state accuracy of the BIM system. Originality/value A MPDTC strategy is proposed to reduce the ripple of stator flux and electromagnetic torque. The phase angle increment angle of stator flux linkage and electromagnetic torque is optimized by model prediction, and the optimal space voltage vector is obtained by designing the reference flux controller.

Improved Performance of Direct Torque Control with PMSM compared to DTC with Induction Motor

For induction motor torque control, direct torque control is becoming the industry standard. This paper proposes a switching loss minimization technique for improved Direct Torque Control (DTC) of permanent magnet synchronous motors in order to increase the drive system's steady-state and dynamic results. Direct torque control (DTC) of a voltage source inverter-supplied PMSM is a simple scheme that requires little computation time, can be implemented without speed sensors, and is unaffected by parameter variations. In theory, the motor terminal voltages and currents are used to calculate the flux and torque of the motor. A voltage vector is chosen to restrict the flux and torque errors within their flux and torque hysteresis bands based on the instantaneous torque and stator flux magnitude errors, as well as estimates of the flux position. The electromagnetic torque, rotor speed, and stator current of DTC with PMSM and DTC with IM were successfully calculated using Total Harmonic Distortion (THD) in this article. As compared to DTC with IM, DTC with PMSM reduced THD by 12 percent in torque, speed, and stator current [21]. Switching Losses Minimization Technique by THD Minimization is used in this article. Since transistors are only switched when necessary to maintain torque and flux within their hysteresis limits, switching losses are minimised, resulting in increased efficiency and lower losses. Matlab SIMULINK has experimentally confirmed direct torque regulation with PMSM and IM.

A Parameter Independent Stator Current Space-Vector Reference Frame-Based Sensorless IPMSM Drive Using Sliding Mode Control

In this paper, a sliding mode control is presented for direct torque and stator flux control of interior permanent magnet synchronous motor in a rotor speed sensorless drive system. The control scheme is developed in a specific synchronous rotating reference frame (X-Y) in which the stator current space vector coincides with the direct (X) axis. For this control technique no need to have any knowledge of machine parameters such as stator two-axis inductances, rotor permanent magnets flux linkage, and even the rotor initial position. However, the on-line actual stator resistance value is required to estimate the stator flux components in the stator stationary two-axis reference frame. In this control strategy, two simple methods are described for estimating the rotor speed and stator resistance. Some simulation and experimental results are presented to support the validity and effectiveness of the proposed control scheme.

Novel fuzzy direct torque control based on constructed functional transformed grey model

To reduce the ripple of the magnetic flux and torque of motors and the reduce the hysteresis in motor speed control, an improved grey model predictive fuzzy direct torque control (DTC) method based on function transformation is proposed. First, a function transformation is used to transform the sampled sequences to nonnegative values. This overcomes the disadvantages caused by fluctuant and random sampling of the motor torque and stator flux linkage. Second, an equal dimensional new information model is used to keep the dimensions unchanged, which reduces the time to predict the motor parameters through the model. Moreover, the voltage space vector plane is divided into six sectors, which simplifies the fuzzy control system rules. Simulation results show that the proposed fuzzy direct torque control based on the improved grey model method reduces the influence of hysteresis on the control system, decreases the motor flux chain and torque ripple, improves the response speed of the torque and rotational speed, reduces overshoot, achieves good effects in terms of anti-interference capability and dynamic response, and improves the real-time performance and accuracy of the fuzzy control system.

Computationally efficient predictive torque control for induction motor drives based on flux positional errors and extended Kalman filter

This paper proposes an improved model based predictive torque control (MPTC) method based on positional error between reference and estimated stator flux vectors. The main advantages of the proposed method are: the improved computational efficiency which requires minimum hardware resources and weighting-factor-free cost function. Weighting factor is removed by using modified reference transformation, which converts torque reference into equivalent stator flux reference. Improvement in computational performance is achieved by using decreased number of voltage vectors for prediction. An admissibility criterion based on flux positional errors is introduced to reduce the number of voltage vectors. The computational time saved is utilised to incorporate extended Kalman filter for better estimation of flux and torque. The validity of the proposed method is tested on a two-level three-phase inverter fed induction motor drive with dSpace DS1104 as controller board. The dynamic response and computational cost of the proposed method is compared to other established MPTC methods. The superiority of the proposed technique is confirmed by experimental results, which show an average of 32% reduction in computational time when compared to conventional MPTC while comparable dynamic response in terms of torque ripple, flux ripple and load current harmonics, is also maintained.