Direct Torque Control Method Research Articles

Direct Torque Control Scheme for a Six-Phase Induction Motor With Reduced Torque Ripple

This paper presents an improved direct torque control (DTC) method for an asymmetrical six-phase induction motor using a two-level six-phase inverter. As is well known, a simple extension of three-phase DTC technique to an asymmetrical six-phase motor, using large vectors only, introduces significant current harmonics of the order 6 n ±1 ( n = 1, 3, 5,…), which are mapped into the nonflux/torque producing ( xy ) plane. These harmonics cause only losses in the motor winding as they do not take part in torque production. Hence, a number of different improved DTC techniques have been developed in the past for multiphase motor drives. The paper takes one such DTC method as the starting point and improves it further by using the concept of virtual voltage vectors. Developed vector selection algorithm, based on two virtual voltage vectors, requires the information on position of the flux in the auxiliary ( xy ) subspace and provides stator current quality commensurate with the currently available best DTC algorithm for six-phase drives. However, use of two virtual voltage vectors enables a substantial reduction of the torque ripple, which is achieved by means of a five-level torque comparator. Extensive experimentation is performed and it is shown that the reduction of the current harmonics is in essence almost the same as in another recently developed DTC scheme, based on the use of a single virtual voltage vector. However, the achieved torque ripple reduction, which is verified experimentally, makes the scheme superior when compared to the existing approaches. At the same time, developed scheme retains qualities of conventional DTC schemes, such as simple structure and fast response. Its additional beneficial feature is the easiness of implementation.

Study and comparison between two DTC strategies of induction machine fed by direct matrix converter

This work aims to study, analyze, and compare two direct torque control (DTC) methods of induction machine fed by [3 × 3] direct matrix converter (MC). The first method, DTC, uses the direct model of the matrix converter, whereas the second method, direct torque control indirect (DTCI), uses its indirect model, which describes MC as a combination of a four-quadrant rectifier with a two-level inverter. The two methods are simulated with the same parameters and references of speed and flux. An experimental validation is performed on a prototype of a [3 × 3] direct matrix converter realized in the laboratory, which feeds a three-phase induction machine coupled with a brake. These tests allowed us to demonstrate the practical feasibility of these control schemes. The algorithms are implemented on a dSPACE 1104 controller board. The input power factor is fixed to 1. A comparison between the two algorithms results based on several criteria (power quality, static and dynamic performance of the system, and maintenance of the unity power factor) is presented, and the results are discussed.

Rotary Switched Reluctance Actuator: A Review on Design Optimization and Its Control Methods

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 9pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; mso-bidi-font-style: italic;">A switched reluctance actuator (SRA) is a type of electromagnetic stepper actuator that is gaining popularity for its simple and rugged construction, ability of extremely high-speed operation and hazard-free operation. SRA gained supremacy over permanent magnet actuators due to the fact that its building material are relatively low cost compared to the expensive and rare permanent magnets. SRA is already making its debut in automotive, medical and high precision applications. However, many parties are still oblivious to this new age actuator. This paper reviews the latest literature in terms of journal articles and conference proceedings regarding the different design parameters and control method of SRA. The impact of the parameters on the performance of SRA are discussed in details to provide valuable insight. This paper also discussed the advantages of various novel SRA structure designs that prove to be a huge contribution to the future technology. It is found that several design parameters such as the air gap when kept minimum, increases torque value; while increasing number of phases in SRA minimizes torque ripples. Increased stator and rotor arc angles will increase torque, not to mention a larger excitation current can also achieve the same effect. Researches are often done through Finite Element Method (FEM) analysis to verify the optimized design parameters before fabrication, whilst experimental procedures are executed to verify the simulation results. To ensure smooth phase switching and improved torque output, intelligent controllers are employed in speed control and direct torque control (DTC) methods of SRA.</span>

Hardware Implementation of FTC of Induction Machine on FPGA

In this paper, a new design method of Direct Torque Control using Space Vector Modulation (DTC-SVM) of an Induction Machine (IM), which is based on Fault Tolerant Control (FTC) is proposed. Due to its complexity, the FTC implemented on a microcontroller and a Digital Signal Processor (DSP) is characterized by a calculating delay. To solve this problem, an alternative digital solution is used, based on the Field Programmable Gate Array (FPGA), which is characterized by a fast processing speed. However, as an FPGAs increase in size, there is a need for improved productivity, and this includes new design flows and tools. Xilinx System Generator (XSG) is a high-level block-based design tool that offers bit and cycle accurate simulation. This tool can automatically generate the Very High-Density Logic (VHDL) code without resorting to a tough programming, without being obliged to do approximations and more we can visualize the behavior of the machine before implementation which is very important for not damage our machine. Simulation and experimental results using Hardware In the Loop (HIL) of the FTC based DTC-SVM is compared with those of the conventional DTC. The comparison results illustrate the reduction in the torque and stator flux ripples. Our purpose is to reveal our algorithm efficiency and to show the Xilinx Virtex V FPGA performances in terms of execution time.

Torque Ripple and Harmonic Current Reduction in a Three-Level Inverter-Fed Direct-Torque-Controlled Five-Phase Induction Motor

In a switching-table-based direct torque control method (ST-DTC), the torque ripple reduces with increasing number of levels of the torque comparator. The number of levels is decided by the availability of the number of voltage vectors according to the topology of the inverter. This paper proposes the seven-level torque comparator to reduce the torque ripple in the DTC-controlled five-phase induction motor fed by the three-level five-phase inverter. In the five-phase induction motor, an elimination of x − y stator flux is inevitable otherwise the stator phase current will be distorted. In order to eliminate the x − y stator flux, the virtual voltage vectors are formed. Experimental results are presented to validate the proposed DTC method.

Five‐level torque controller‐based DTC method for a cascaded three‐level inverter fed induction motor drive

Two cascaded two-level inverters can synthesise three-level voltage space vector. For the cascaded three-level inverter controlled induction motor, this study proposes a five-level torque controller (FLTC)-based direct torque control (DTC) method especially for improving steady-state motor torque performance and retaining the high dynamic performance. The proposed FLTC method employs hysteresis controllers, uses look-up tables and ends up with variable switching frequency of the cascaded three-level inverter. Computationally, the envisaged FLTC method is quite comparable to that of the basic DTC method. The FLTC method ensures reduced switching commutations in the inverter switching devices during low speeds of operation and simultaneously achieves reduced d v /d t switching stresses. An inherent drawback of FLTC method at higher speeds of operation is identified, theoretically analysed and a pseudo error-based correction is also suggested in this study to overcome the drawback. The steady-state and transient motor torque performance of the induction motor with the use of the envisaged FLTC-based DTC method is thoroughly analysed, simulated using Matlab/Simulink and then experimentally validated on a laboratory prototype for starting, speed reversal and load change conditions with the use of the cascaded three-level inverter.

Design and simulation of electrical dynamometer using improved DTC induction motor driver

AC motors, especially the squirrel cage induction motors have the advantages of simple structure, good reliability and low cost. They are more suitable to be used as electrical dynamometers to provide dynamic load for bench test systems. But, the speed and torque of induction motors are not easy to be controlled accurately. In this work, an electrical dynamometer based on the induction motor is proposed. In order to get better control performance of torque and speed of induction motor, an improved direct torque control method (DTC) is also developed based on the space vector modulation (SVM) technique. The performance of the proposed dynamometer system is validated in the Matlab/Simulink platform. The simulation results show that the new dynamometer has good torque and stator flux response. And the torque and stator current ripples of it are reduced significantly compared with using the conventional DTC method.

Analysis, design and implementation of direct torque controlled induction motor drive based on slip angle

The conventional direct torque control (DTC) of induction motor drive has two main problems such as higher ripple in torque, flux and variable switching frequency. These problems are mainly due to the hysteresis controllers. Appreciable reduction of torque and flux ripple can be achieved by increasing the inverter switching frequency. Most of the torque ripples reduction methods in literature are centered on this concept. The hysteresis based approach also results in variable switching frequency that depends on operating conditions at particular speed. Hence a method for increasing the switching frequency and at the same time maintaining constant switching frequency is needed. Most researches have chosen the space vector pulse width modulation based DTC (SVM-DTC) scheme. In this paper, first the torque and flux ripple in the conventional DTC method are shown and the improvement achieved by using proposed DTC method based on slip angle is presented. A new method such as slip angle control of induction motor drive based on DTC are proposed, analyzed, simulated, and tested. It is shown that this method progressively reduces torque and flux ripple.

Drive Direct Torque Control of Permanent Magnet Synchronous Motors Based on Discrete Space Vector Modulation

To solve the problems of unsmooth stator flux linkage locus, large torque ripples and big power loss in conventional direct torque control system of permanent magnet synchronous motor, the discrete space vector modulation technique is analyzed, and a new direct torque control method (DSVM-DTC) is proposed in this paper. PI controller and DSVM modulator are used to instead hysteresis controller and switch table in conventional DTC system, which increased the equivalent voltage vectors and selected accurate zero vectors in different sectors. Therefore, the errors of flux and torque can be compensated accurately. Simulation results prove that DSVM-DTC effectively improved the steady-state performance of the system, declined the switching loss, reduced torque ripple, and flux linkage locus is more smooth under the premise of ensuring constant switching frequency.

An Improved Model Predictive Direct Torque Control for Induction Machine Drives

The conventional model predictive direct torque control (MPDTC) method uses all of the voltage vectors available from a two level voltage source inverter for the prediction of the stator flux and stator current, which leads to a heavy computational burden. This paper proposes an improved model predictive direct torque control method. The stator flux predictive controller is obtained from an analysis of the relationship between the stator flux and the torque, which can be used to calculate the desired voltage vector based on the stator flux and torque reference. Then this method only needs to evaluate three voltage vectors in the sector of the desired voltage vector. As a result, the computational burden of the conventional MPDTC is effectively reduced. The time delay introduced by the computational time causes the stator current to oscillate around its reference. It also increases the current and torque ripples. To address this problem, a delay compensation method is adopted in this paper. Furthermore, the switching frequency of the inverter is significantly reduced by introducing the constraint of the power semiconductor switching number to the cost function of the MPDTC. Both simulation and experimental results are presented to verify the validity and feasibility of the proposed method.

Torque Ripple Reduction in Direct Torque Control of Five-Phase Induction Motor Using Fuzzy Controller with Optimized Voltage Vector Selection Strategy

This paper presents a torque ripple reduction method of direct torque control (DTC) using fuzzy controller with optimal selection strategy of voltage vectors in a five-phase induction motor. The conventional DTC method has some drawbacks. First, switching frequency changes according to the hysteresis bands and motor's speed. Second, the torque ripple is rapidly increased in long control period. In order to solve these problems, some/most papers have proposed torque ripple reduction methods by using the optimal duty ratio of the non-zero voltage vector. However, these methods are complicated in accordance with the parameter. If this drawback is eliminated, the torque ripple can be reduced compared with conventional method. In addition, the DTC can be simply controlled without the use of the parameter. Therefore, the proposed algorithm is changing the voltage vector insertion time by using the designed fuzzy controller. Also, the optimized voltage vector selection method is used in accordance with the torque error. Simulation and experimental results show effectiveness of the proposed control algorithm.

Simplified model predictive direct torque control method without weighting factors for permanent magnet synchronous generator‐based wind power system

Conventional model predictive direct torque control (MP-DTC) of permanent magnet synchronous generator (PMSG) suffers from weighing factor tuning work and relatively large calculation amount. This study proposes a simplified MP-DTC method without weighting factors for PMSG-based wind power system. First, the torque and stator flux magnitude are predicted on the stationary reference frame instead of on the synchronous rotating reference frame, hence reducing the calculation amount. Second, a new cost function based on the torque and the reactive torque is developed in this study. As the torque and the reactive torque have the same order of magnitude, the weighting factor which is needed in the conventional MP-DTC system is eliminated. Meanwhile, the stator current and stator flux magnitude can be controlled indirectly by controlling the torque and reactive torque simultaneously, which ensures the stability of the system. Besides, the robustness of the proposed strategy to unknown PMSG parameter variations is improved to a certain extent. The experimental results validate the effectiveness of the proposed method.

A novel direct torque control method for brushless DC motors based on duty ratio control

Conventional direct torque control (DTC) suffers from large torque ripple and nonconstant switching frequency, which are caused by the hysteresis band amplitude and the motor speed. Many methods have been proposed to tackle these problems. However, these methods are usually complicated and parameter dependent. A novel DTC method for brushless DC motors based on duty ratio control is proposed to reduce torque ripple and maintain a constant switching frequency. During each switching period, an active voltage vector and a zero voltage vector are applied. A simple and effective method implemented to calculate the duty ratio relies only on the torque error, reducing the parameter dependence. The proposed method has the advantages of conventional DTC and effectively reduces torque ripple, which improves the performance of conventional DTC. Simulation and experimental results are given to confirm the method’s validity.

SIMULASI PENGATURAN KECEPATAN MOTOR INDUKSI 3 PHASA DENGAN DIRECT TORQUE CONTROL MENGGUNAKAN MATLAB

Induction motors are widely used in the industrial world because they have many advantages, including construction that is very simple and strong, cheap, has high efficiency, quite good power factor, and maintenance is easier. Besides the advantages of induction motors also have weaknesses, one of the disadvantages of an induction motor is not being able to maintain its speed constantly if there is a change in load. If there is a change in load, the speed of the induction motor will decrease. One method of regulating the speed of an induction motor developed in addition to vector control is the Direct Torque Control (DTC) method. The DTC control technique allows direct and separate flux and torque settings and can be done without using a speed sensor. The estimated rotor rotation, torque and flux is carried out by the DTC which is inputted with stator voltage and current. To achieve the desired flux and torque estimation is used as feedback on the control system. In this final assignment, the speed regulation of the induction motor will be simulated using the DTC method using Matlab. The results obtained through the simulation show the length of time to reach the reference speed for speeds of 500rpm and 1000 rpm is around 0.5 seconds. Keywords : Induction motor, Direct Torque Control, Matlab.

Reduction of Torque and Flux Ripples in Space Vector Modulation-Based Direct Torque Control of Asymmetric Permanent Magnet Synchronous Machine

In this paper a study is presented about the reduction of electromagnetic interference (EMI) in Direct Torque Control (DTC) method by the means of chaotic space vector modulation. Space Vector Modulated Direct Torque Control (SV-DTC) is a method developed to reduce current and moment fluctuations which stem from the hysteresis controllers used in classical DTC method. The switching frequency amplitude was changed chaotically in a Space Vector Modulated Direct Torque Control (FFSV-DTC) having a Fixed switching frequency, and Chaotic Space Vector Modulated Direct Torque Control (CAFSV-DTC) method having chaotic amplitude modulated switching frequency was obtained. CAFSV-DTC method was suggested to reduce EMI, acoustic noise and current harmonics which occur in FFSV-DTC method. For this purpose, the proposed CAFSV-DTC method, using a Permanent Magnet Synchronous Motor (PMSM) drive, is compared to Random Amplitude Frequency method (RSV-DTC) and FFSV-DTC. Simulation results indicate that the proposed method yields better results. DOI: http://dx.doi.org/10.5755/j01.eee.22.1.14097

Open-Phase Fault-Tolerant Direct Torque Control Technique for Five-Phase Induction Motor Drives

Direct torque control (DTC) has been widely used as an alternative to traditional field-oriented control (FOC) methods for three-phase drives. The conventional DTC scheme has been successfully extended to multiphase drives in recent times, using hysteresis regulators to independently track the desired torque and flux in symmetrical five-phase induction machines (IMs). The fault-tolerant capability of multiphase drives is an interesting intrinsic advantage for safety-critical applications, where recent research has demonstrated the effectiveness of FOC schemes to perform ripple-free postfault operation. In spite of the utility of DTC methods in normal operation of the multiphase machine, no extension to manage the postfault operation of the drive is found in the literature. In this paper, a novel fault-tolerant DTC scheme is presented. The performance of the proposed method is experimentally validated in a five-phase IM drive considering an open-phase fault condition. Provided tests analyze steady and transient states, including the transition from pre- to postfault operation. Obtained results prove the interest of the proposal, which ensures the open-phase fault-tolerant capability of DTC-controlled five-phase IM drives.

A Bearingless Induction Motor Direct Torque Control and Suspension Force Control Based on Sliding Mode Variable Structure

Aiming at the problems of the large torque ripple and unstable suspension performance in traditional direct torque control (DTC) for a bearingless induction motor (BIM), a new method of DTC is proposed based on sliding mode variable structure (SMVS). The sliding mode switching surface of the torque and flux linkage controller are constructed by torque error and flux error, and the exponential reaching law is used to design the SMVS direct torque controller. On the basis of the radial suspension force mathematical model of the BIM, a radial suspension force closed-loop control method is proposed by utilizing the inverse system theory and SMVS. The simulation models of traditional DTC and the new DTC method based on SMVS of the BIM are set up in the MATLAB/Simulink toolbox. On this basis, the experiments are carried out. Simulation and experiment results showed that the stable suspension operation of the BIM can be achieved with small torque ripple and flux ripple. Besides, the dynamic response and suspension performance of the motor are improved by the proposed method.

Fuel cell/battery hybrid powered unmanned aerial vehicle with permanent magnet synchronous motor

In this study, a model of hybrid powered unmanned aerial vehicle (UAV) is proposed and simulated. The proposed system comprises of some units such as fuel cell, battery, power control, DC/DC buck-boost converter, permanent magnet synchronous motor (PMSM). Proton-exchange membrane fuel cell (PEMFC) is used as main power source. Also, Li-ion battery is used as supplementary power source as well as power charging unit. PMSM is the propulsion source for proposed UAV. Control of PMSM is realised with direct torque control method. Voltage regulation is provided by DC/DC bidirectional buck-boost converter. The simulation of proposed UAV model is achieved in MATLAB/Simulink software. According to simulation results, proposed UAV model can be used for actual applications.

Adaptive MRAC-based direct torque control with SVM for sensorless induction motor using adaptive observer

This paper presents an improved direct torque control (DTC) method for induction motor (IM) drive. The main drawback of the conventional DTC is the use of hysteresis comparators which leads to high torque and flux ripples. The improvement in this paper includes using the space vector modulation to preserve a constant switching frequency and to reduce totally flux and torque ripples. Besides, the torque and stator flux regulation will be done based on model reference adaptive control (MRAC) strategy to ensure a robust control against external disturbance and less sensitivity from machine parameter variation unlike the conventional proportional-integral (PI) controllers. Furthermore, a design of an adaptive observer based on Lyapunov stability is presented for speed/flux and load torque estimation. The observer can improve the control performances and decrease the cost and increase reliability of the global control system by reducing the number of sensors. The proposed strategy will be examined under simulation tests using Matlab/Simulink and experimental implementation with real-time interface (RTI) based on dSpace 1104 board.

Three-Level Inverter-Fed Direct Torque Control of IPMSM With Torque and Capacitor Voltage Ripple Reduction

This paper proposes a new direct torque control (DTC) method for a three-level neutral point clamped (3L-NPC) inverter-fed interior permanent magnet synchronous motor (IPMSM) drive. Theoretically, in comparison to a two-level inverter, a 3L-NPC inverter is advantageous for reducing the torque and flux ripples in DTC drives. Nonetheless, the ripples can still be excessive and detrimental if low switching frequencies are desired. To reduce the torque and flux ripples while maintaining a low average switching frequency, a switching table-based DTC scheme employing two voltage vectors in each sampling period is proposed in this paper. A duty ratio calculation method with minimal parameter dependence is developed, taking into account the dynamic torque and flux characteristics of an IPMSM. In addition, the problems of neutral point voltage fluctuations and smooth voltage vector switching, which are inherited from the 3L-NPC inverter, are addressed. Simulation and experimental results are presented to prove the effectiveness of the proposed method.