Classical Direct Torque Control Research Articles

Experimental analysis of enhanced finite set model predictive control and direct torque control in SRM drives for torque ripple reduction

The magnet-less switched reluctance motor (SRM) speed-torque characteristics are ideally suited for traction motor drive characteristics and its advantage to minimize the overall cost of on-road EVs. The main drawbacks are torque and flux ripple, which have produced high in low-speed operation. However, the emerging direct torque control (DTC) operated magnitude flux and torque estimation with voltage vectors (VVs) gives high torque ripples due to the selection of effective switching states and sector partition accuracy. On the other hand, the existing model predictive control (MPC) with multiple objective and optimization weighting factors produces high torque ripples due to the system dynamics and constraints. Therefore, existing DTC and MPC can result in high torque ripples. This paper proposed a finite set (FS)-MPC with a single cost function objective without weighting factor: the predicted torque considered to evaluate VVs to minimize the ripples further. The selected optimal VV minimizes the SRM drive torque and flux ripples in steady and dynamic state behaviour. The classical DTC and proposed model were developed, and simulation results were verified using MATLAB/Simulink. The proposed model operated in SRM drives experimental results to prove the effective minimization of torque and flux ripples compared to the existing DTC.

Direct torque control for PMSM based on the RBFNN surrogate model of electromagnetic torque and stator flux linkage

Direct Torque Control (DTC) is widely used in motion control of motors. Classical DTC utilizes the Park transformation(dq-model) or observer to estimate the stator fluxlinkage and electromagnetic torque. However, the dq-model and observer lack descriptions of the cogging torque and magnetic saturation in permanent magnet synchronous motors (PMSM). This paper proposes a novel method based on the surrogate model to estimate stator fluxlinkage and torque for PMSM DTC. First, a finite element model (FEM) was established based on the parameters of PMSM. Using the FEM and Latin hypercube sampling (LHS), a surrogate model for estimating the stator fluxlinkage and torque of PMSM was constructed. The stator fluxlinkage and torque surrogate model, active flux observer, and dq current model under different control methods are constructed, respectively. The servo control parameters were tuned using the extended symmetric optimum algorithm, and simulation and experiments were conducted. Finally, electromechanical coupling models with a ball screw feed system were built based on various control and feedback methods. Simulation and experiment results indicate that the surrogate model reduces torque ripple, stator fluxlinkage offset, and feed system tracking error.

FPGA implementation of a robust DTC-SVM based Sliding Mode Flux Observer for a double star induction motor: Hardware in the loop validation

This paper presents an implementation of a robust Direct Torque Control (DTC)-Space Vector Modulation (SVM) strategy for a Double Star Induction Machine (DSIM) using a Field Programmable Gate Array (FPGA). The proposed control technique combines SVM and DTC strategies, incorporating the Sliding Mode Flux Observer (SMFO) to improve robustness and overcome the drawbacks of stator resistance variations. First, SVM is used to improve DTC performance by reducing torque and flux ripples generated with classical DTC strategies. Then, the SMFO is employed to estimate the mechanical speed and stator flux module, ensuring robustness in the face of stator resistance variations. A comparative study between conventional DTC, DTC-SVM, and DTC-SVM-SMFO is presented. Simulation tests of the three DTC strategies were conducted using Matlab/Simulink tools, demonstrating the robustness and high performance of the DSIM under DTC-SVM-SMFO. To further validate these results, the technique was implemented using Xilinx System Generator (XSG) on a parallel processing software environment, the FPGA Virtex 5. Hardware in the loop results confirms the effectiveness of the DSIM under the improved DTC-SVM-SMFO control strategy.

Improved twelve sectors DTC strategy of induction motor drive using Backstepping speed controller and P-MRAS stator resistance identification-design and validation

The Direct Torque Control (DTC) was previously designed to achieve high performance of induction motor (IM) by accurately and independently controlling its flux and torque. However, this classical DTC generates several disadvantages such as strong fluctuations in the torque and stator flux as well as quite significant switching losses. For these reasons, many modern techniques have been proposed in the literature to improve it. On the other hand, as the inadequacy of the parameters seriously affects the efficiency and stability of the induction motor, it is paramount to accurately estimate the stator resistance, for this, robust observers are necessary suggested to be employed. This paper proposes developed structure of DTC strategy using twelve sectors combined with Backstepping speed regulator for the external loop and robust model reference adaptive system based on active power principle to estimate the stator resistance. In addition, several simulations under Matlab/Simulink and experiment results using the dSPACE DS1104 board are discussed to confirm improvements in control and speed estimation.

Simulation of a direct torque control system in the presence of winding asymmetry in induction motor

The operation of a direct torque control (DTC) system for induction motors with the possible presence of unbalanced modes in the motor windings is studied. It is shown that in the presence of asymmetric modes in the motor windings, the classical DTC algorithm becomes unstable. It is proposed to improve the DTC by taking into account the unbalance of the active resistances of the motor stator windings when determining the DTC parameters. This will make it possible to study electrodynamic processes in DTC with the possible presence of asymmetric modes in the windings of induction motor.

Reducing torque ripple of induction motor control via direct torque control

<span lang="EN-US">The induction motor is extremely well known and used as an alternating current (AC) machine. Therefore, torque and speed regulations are very essential for this type of machine. This paper presents direct torque control (DTC) based on induction motors (IM). The mathematical model of IM is reported, and the machine is modeled in a synchronous coordinate farm. Classic DTC is applied to IM with two bandwidths of hysteresis controller for electromagnetic torque and stator flux. The system is simulated and investigated via MATLAB/Simulink and the results carry out a high ripple on the torque. There are numerous of improving torque response, one of them is adding a new loop for speed with proportional, integral, and derivative (PID) controllers. IM model with PID based on DTC is simulated through MATLAB. A contrast performance of IM is presented between traditional DTC and DTC with PID. As result, the new DTC with PID carries out improvement in the speed response as well reduces the ripples of torque.</span>

A Highly Effective Modified Direct Torque Control for Five Phase Induction Motor without AC Phase Current Sensors

The Direct Torque Control (DTC) technique requires stator currents and DC bus voltage, as well as inverter switch states, in order to estimate stator flux and electromagnetic torque values. Measurement of phase currents in real time with current sensors is a common method of gathering this data. To control a Five-Phase Induction Motor (FPIM), the DTC needs at least four alternating current (AC) sensors and one voltage sensor. When utilized in a global training system, this number has disadvantages due to cost, size, and non-linearity. The purpose of this article is to show how to remove the alternating current sensors from an FPIM's DTC. This is accomplished by reconstructing the phase currents using a simple DC current sensor placed at the voltage inverter's input and modifying the classical DTC control technique by using a good choice of certain allowable switching vectors of a five-phase voltage inverter, the 18° zone offset strategy of the stator flux, and developing a new commutation table for the stator currents construction. The proposed control approach is supported by simulation results.

Enhancement and Performance Analysis for Modified 12 Sector-Based Direct Torque Control of AC Motors: Experimental Validation

Direct torque control (DTC) is a promising control algorithm that is characterized by simplicity and effective performance for the AC motors drive systems. The design of the switching table is an important issue that directly affects the performance of the motor drive. The majority of the prior literature relies on the researcher’s knowledge when establishing the voltage vectors of the switching table to be applied to the inverter. Consequently, torque and flux ripples can still be large. In this paper, a modified twelve sector-based DTC is proposed to improve the AC motor drive. The proposed drive system offers several contributions, such as very low torque ripple reduction, faster dynamics, and reduced stator flux ripples compared to the classical DTC. Additionally, the proposed controller can provide high robustness at very low speed under parameter variation. The analytically developed switching table also contributes to reducing the switching frequency ratio between 40% to 50%. The aim of the aforementioned improvements is to obtain a quiet operation of the induction motor without vibration or audible noise. Simulation results of the proposed method were performed in MATLAB/Simulink environment. Furthermore, for the sake of validation and effectiveness of the method, experimental tests were conducted using dSPACE based platform. Finally, a fair comparison of both the proposed and classical methods was performed that revealed the superiority of the proposed strategy.

Modeling of energy-efficient direct torque control system for traction induction motor

A brief analysis of existing control systems for traction electric drives with induction motors has been carried out, as a result of which it has been established that vector control and direct torque control systems are the most promising. The comparative characteristic of these control systems according to different parameters of electric drive quality has shown that in energy-saving algorithms it is appropriate to use the systems of direct torque control. The work aims to simulate the electric drive with a direct torque control system, which provides the reduction of power losses in an asynchronous motor. The value of the stator winding power factor is chosen as a control action. The calculation and functional dependences between the main parameters of the control system and the induction motor are synthesized, the fulfillment of which allows reducing duce power losses. The functional diagram of the electric drive with an energy-efficient control system is given. The hardware of this control system does not differ from the currently used frequency converters. In the power channel of the frequency converter, a three-level autonomous voltage inverter with locking diodes is used. The results of modeling for electric drive with 11 kW motor, analysis of which showed the adequacy of the developed model and performance of the synthesized control system, the efficiency of the electric drive with energy-efficient control system increases to 18% compared with the classical direct torque control system.

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.

An enhanced control strategy based imaginary swapping instant for induction motor drives

<p>The main aim of this paper is to present a novel control approach of an induction machine (IM) using an improved space vector modulation based direct torque control (SVM-DTC) on the basis of imaginary swapping instant technique. The improved control strategy is presented to surmount the drawbacks of the classical direct torque control (DTC) and to enhance the dynamic performance of the induction motor. This method requires neither angle identification nor sector determination; the imaginary swapping instant vector is used to fix the effective period in which the power is transferred to the IM. Both the classical DTC method and the suggested adaptive DTC techniques have been carried out in MATLAB/SimulinkTM. Simulation results shows the effectiveness of the enhanced control strategy and demonstrate that torque and flux ripples are massively diminished compared to the conventional DTC (CDTC) which gives a better performance. Finally, the system will also be tested for its robustness against variations in the IM parameters.</p>

Performance enhancement of direct torque control induction motor drive using space vector modulation strategy

Purpose. The main objective of this work is to demonstrate the advantages brought by the use of space vector modulation technique in the direct torque control of the induction motor. To achieve this purpose, two different direct torque control approaches (with space vector modulation) are proposed and studied from a comparative aspect with each other and with the conventional direct torque control. The novelty of this work consists in the employment of an Integral-Proportional (IP) speed controller in the two proposed direct torque control approaches and a more in-depth evaluation for their performance mainly the switching frequency of inverter semiconductor components and motor torque ripples. Methods. Two different direct torque control approaches that use the space vector modulation strategy and/or fuzzy-logic control, are described in detail and simulated with IP speed controller. The simulation experiments are carried out using Matlab/Simulink software and/or fuzzy-logic tools. Results. Practical value. Comparison results show that the two proposed direct torque control structures (with space vector modulation) exhibit a large reduction in torque ripples and can also avoid random variation problem of switching frequency (over a wide range of speed or torque control). On the other hand, the use of IP speed regulator ensured good dynamic performance for the drive system as well as considerably minimized peak overshoot in the speed response. Practically all of these benefits are achieved while retaining the simplicity and the best dynamic characteristics of the classical direct torque control, especially with the modified direct torque control approach in which the design or implementation requires minimal computational effort.

Genetic and particle swarm optimization algorithms based direct torque control for torque ripple attenuation of induction motor

This paper introduces analysis, control, and comparison of two benchmarking optimization approaches called Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) for Direct Torque Control (DTC) of a three-phase Induction Motor (IM). This study aims to determine the most efficient and robust of the two different metaheuristic optimization techniques including PID-PSO and PID-GA for DTC of IM. The purpose of the proposed control technique that has been presented is to get over the most significant drawback of DTC, which is a high level of torque output. The issue of torque ripples needs to be reduced to a significant amount using the two proposed control methods PSO-DTC and GA-DTC. As a result, PSO-DTC is the most applicable scheme. The proposed PID-PSO of DTC provided an excellent work performance for IM system drive. The comparison results of the suggested control methods showed a significant improvement of the control system compared to the classical DTC. The result is a high fidelity estimate of electromagnetic torque and speed for computation of motor parameters. A high ripple suppression capability was achieved by the PSO-DTC, which was measured at 22.5 % out of 47.28 % for the traditional approach. Both proposed control schemes were implemented using MATLAB/Simulink platform.

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.

Neural network adaptive backstepping control via uncertainty compensation for PMSG-based variable-speed wind turbine: Controller design and stability analysis

This paper proposes a design scheme along with stability analysis of a new adaptive backstepping controller designed for permanent magnet synchronous generator-based wind turbine, by using artificial neural network-based uncertainty compensation. The idea is to control the rotor speed and the mechanical power generated under internal and external nonlinear parametric uncertainties. An uncertain model of permanent magnet synchronous generator is designed. Then, two artificial neural network compensators are built to compensate such uncertainties in the current loops. The stability of the closed-loop system is studied according to the Lyapunov function. Simulations of the dynamic model are performed under both variable step and random wind speeds by using the DEV-C++ software, and the results are plotted with MATLAB. Compared to the classical direct torque control technique, the obtained results show the robustness of the proposed controller despite the presence of different uncertainties.

A Novel Method of Electric Scooter Torque Estimation Using the Space Vector Modulation Control

In recent years, there are many studies have been conducted in the field of light electric vehicles, especially electric scooters. These are preferred in large urban areas that are crowded with cars and cause traffic congestion in the European and Asian continents. In this study, the three-wheel electric scooter contained two BLDC motors that drove the rear wheels and, each of these motors were controlled independently via an electronic differential. This paper aims to implement a Space Vector Modulation for the Direct Torque Control unit (SVM-DTC) of the BLDC wheel-motor of each driving wheel. The proposed system had been designed and simulated by using the MATLAB/SIMULINK environment. The performance of the overall system (scooter stability control system - energy storage system -power quality, etc.) with using SVM-DTC control was compared with the classical Direct Torque Control (DTC) algorithm by using the same electric scooter model. The obtained results showed clearly the improvement made by the proposed control loop system at different stages, where it could reduce the THD of the stator current from 30.99% to 6.16%,as well as it was able to achieve more than 0.2% of the charging state of the battery in 18 seconds only.

Vector Control of Induction Motor Using Neural Networks Based Lookup Table for Reduced CMV

This paper confers a vector control (VC) perspective for induction motor drives by combining the principles of vector and direct torque control (DTC) methods. In classical vector control, the switching states will be chosen dependent on current hysteresis regulators. Based on the instantaneous current waves, the hysteresis controllers generate the switching specimen. But, the classical DTC selects the pertinent voltage vector from lookup table extracted from the flux and torque error signals and sector information. The proposed perspective combines both VC and DTC techniques. In this paper d and q-axis current errors and sector information, the lookup table chooses an appropriate voltage vector. Moreover, to select the befitting voltage vector Neural Network (NN) based approach is presented in this paper. Also, to reduce the common mode voltage (CMV) variations, NN based lookup tables are proposed. To substantiate the proposed NN based vector control, simulation studies have been conveyed and results are collated.

DTC based on SVM for induction motor sensorless drive with fuzzy sliding mode speed controller

By using the direct torque control (DTC), robust response in ac drives can be produced. Ripples of currents, torque and flux are oberved in steady state. space vector modulation (SVM) applied in DTC and used for a sensorless induction motor (IM) with fuzzy sliding mode speed controller (FSMSC) is studied in this paper. This control can minimize the torque, flux, current and speed pulsations in steady state. To estimate the rotor speed and stator flux the model reference adaptive system (MRAS) is used that is designed from identified voltages and currents. The FSMSC is used to enhance the efficiency and the robustness of the presented system. The DTC transient advantage are maintained, while better quality steady-state performance is produced in sensorless implementation for a wide speed range. The drive system performances have been checked by using Matlab Simultaion, and successful results have been obtained. It is deduced that the proposed control system produces better results than the classical DTC.

Applying sliding mode technique for the nonlinear DTC-SPWM control strategy of sensorless squirrel cage asynchronous motor

The classical Direct Torque Control has been elaborated to achieve advanced performance of asynchronous motor, especially in speed behaviours. Due to its high level of ripples and variable frequency, several modifications have been proposed to improve it. In this paper, two modified strategies of the direct torque control dedicated to asynchronous motors are presented, the first method is based on the sinusoidal pulse width modulation and PI regulators for regulating torque, speed and stator flux. The second is based on sliding mode control where the principal purpose is to force the system’s trajectory to slide along the switching surface by a well-defined control law. Furthermore, this paper aims to design two observers; the first will be evaluated by the direct calculation method and the second will be formed by sliding mode. These observers can improve control performance while eliminating mechanical sensors and thereby increasing the overall system’s reliability.

Modified LUT-based DTC of NPC 3-Level Inverter fed Sensorless IPMSM Drive with DC Link Voltage Balance

In the proposed work, a modified look-up table-based direct torque control (DTC) scheme is reported for a neutral point-clamped three-level inverter-fed interior permanent magnet synchronous motor drive. In the classical DTC scheme, there are significant torque and flux ripples in the drive due to low number of available switching states. To reduce the oscillations in torque and flux, a three-level inverter-operated IPMSM drive is discussed. In a three-level inverter, the increased count of active voltage vectors is results in more sinusoidal output waveforms. Moreover, stator flux plane has 12 sectors in the proposed work unlike classical DTC. Besides, the higher level of flux and torque hysteresis comparators is implemented. DC link capacitor voltage balancing scheme is also instigated to minimize voltage stress on semiconductor devices, improve stator current THD and increased capacitor life. Based on the sector information, flux and torque hysteresis output and capacitor voltage balance logic, an improved LUT is established and explained for a three-level DTC scheme. Consequently, improved stator current (THD) and decrement in torque and flux ripples are observed. To make the system robust, model reference adaptive control (MRAC) based sensorless speed estimation algorithm is realized. The proposed DTC scheme is compared with a two-level inverter-fed and a three-level-inverter-fed DTC scheme without DC link voltage balance strategy. To carry out the analysis, MATLAB/Simulink environment is utilized. Moreover, to validate the simulation results, experimental analysis of the proposed technique is carried out using dSPACE1104.