The Research of Direct Torque Control Based on Full-Dimensional State Observer

In the article, a mathematical model of the DTC (direct torque control) system of an alternating current electric drive is developed for the tasks of urban electric transport rolling stock, as an alternative to complex vector control of an asynchronous motor, taking into account its relevance, principles of operation and causes of occurrence. The research of the mathematical model of the direct control of the torque of the asynchronous motor in MATLAB was carried out, its main shortcomings, which limit the scope of its application, were revealed. The main task of the DTC system is to identify the stator flux linkage, which is solved by integration with error accumulation. The source of error accumulation is the inaccuracy of determining the active resistance of the stator and its changes during the operation of the asynchronous motor. The DTC system has a disadvantage associated with the appearance of torque ripples and rotor speed fluctuations at low loads.

Abstract-The stator flux observer is a key part in the mathod of Direct Torque Control (DTC). However, the accuracy of the stator flux estimation directly affected the performance of DTC. The traditional induction motor stator flux observation method have been analyzed in This paper. And for the Shortcomings of existing methods, a on-line identification methods based on Radial Basis Function(RBF) have been proposed in the paper. First, the reference model of flux identification should be established according to induction motor u-n mathematical model under the static coordinate system. Then, a RBF neural network can be constructed on this basis. After self-organization learning, on-line identification of stator flux can be realized in the RBF neural network. System simulation has been carried out in Matlab／Simulink. The results show that: the identification method based on the RBF Neural network can improve the induction motor stator flux measurement accuracy, reduce the impact from the interference factors in observation process and the structure is very simple.

In this paper, the torque ripple problem of six-phase asymmetrical brushless DC motor (BLDCM) is studied. First, the basic structure of BLDCM is introduced, and the operation principle of six-phase asymmetrical BLDCM that is studied in the thesis is expounded. Then, the principle of direct torque control (DTC) system of BLDCM is also discussed, and the improved system is proposed, including using the torque hysteresis loop and opening current hysteresis loop, and choosing the improved voltage vector to make the PWM-ON-PWM modulation. Finally, the DTC system simulation model is built, and the system is also tested by the experiment. According to the results of experiment and simulation, the DTC system designed in this thesis can control the six-phase asymmetrical BLDCM stably and reliably, and the problem of high frequency and torque ripple is solved well.

A Direct Torque Control (DTC) strategy for dual-three phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees with isolated neutral points. The proposed control strategy is based on Proportional Integral (PI) regulators implemented in the stator flux synchronous reference frame. To improve the flux estimation, an Adaptive Stator Flux Observer (ASFO) has been used. Doing so, besides a better flux estimation in contrast to open-loop flux estimators, it is possible to use the observed currents to compensate the inverter non-linear behavior (such as dead-time effects), improving the drive performance at low speed. This is particularly important for low voltage/high current applications, as the drive considered in this paper.The advantages of the discussed control strategy are: constant inverter switching frequency, good transient and steady-state performance and less distorted machine currents in contrast to DTC schemes with variable switching frequency. Experimental results are presented for a 10kW dual three-phase induction motor drive prototype.

The traditional direct torque control (DTC) of asynchronous motor has the disadvantages of the flux linkage, large torque ripple and instable switching frequency. To solve the above problems, a new scheme of modulating direct torque control system by adaptive fuzzy PI was put forward. According to the principle of fuzzy control, the regulator can perform the real-time optimization of PI parameters, realizing the good dynamic and static performance of system. In order to verify the feasibility and effectiveness of this scheme, this paper builds a simulation model of direct torque control system based on adaptive fuzzy PI control regulator by using MATLAB and Simulink. The simulation results show that compared with the traditional direct torque control system, the direct torque control system modulated by adaptive fuzzy PI has the merits of obvious reducing in flux and torque ripple, significant improvement on control performance.

To reduce traditional direct torque control (DTC) system low speed control precision and the large torque ripple in low speed, a fuzzy control system of DTC was proposed. On the basis of conventional PI regulator, a fuzzy speed PI regulator was designed according to speed error and its rate of change, which could adjust the proportional coefficient k <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> and integral coefficient k <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</inf> dynamically to adapt the system to the speed variations, and advanced the self-adaptation of speed. In voltage vector fuzzy controller model, the stator flux angle, the stator flux error, and the torque error are reasonably fuzzified into several fuzzy subsets to optimize selection of the voltage vector and decrease the torque ripple. The experimental results show that the proposed fuzzy control system not only can ensure swift speed response, small overshooting, and high steady speed precision, but also can effectively decrease torque ripple in low speed. Additionally, the system improves the observation precision of the stator flux and enhances the robustness of the whole system.

Winches are widely used on board ship’s deck machinery for anchor handling and mooring. The marine winch market was dominated by hydraulic systems and there is a trend to be replaced by more efficient electrical drive system. For both anchoring and mooring control, full load torque is required through the entire speed range including zero speed operation. This poses a challenge for the inverter driven motor control, especially when there is no speed or position sensor. This thesis aims to develop advanced control algorithms of permanent magnet (PM) machine including direct torque control (DTC) and sensorless control for marine winch application. In this thesis, direct torque control, as a new type of high-performance ac driving system after vector control technique, is mainly concerned. Furthermore, since the traditional switch-table based DTC ac motor drive is usually affected by the torque ripple problem and steady-state error problem in torque, this thesis introduced a modified 12-sector DTC control method. The subsystems of traditional DTC system and modified DTC system for permanent magnet synchronous machine (PMSM) are modeled and designed in PSIM software. Then the simulation models of the above two control strategies are also established. Simulation research is conducted and the results are corresponding with theory analysis: the improved system has good dynamic and static performance; less flux and torque ripple especially in the low speed range. The second part of this thesis is to realize sensorless control of DTC control system. Considered the actual situation on board, different methods for high-speed range and low-speed range are discussed. The rotating high frequency (hf) voltage signal injection as low-speed sensorless control method is good for its simplicity and better tracking accuracy, while the back-EMF integral as high-speed method is suitable for its mature industrial applications. And the hf injection method used in this thesis is designed to compatible with the DTC method applied in this thesis, which successfully extended the speed range without sacrificing the simplicity of DTC method.

&lt;span&gt;Multilevel inverter (MLI) is commonly utilized in direct torque control (DTC) for medium and high power applications. The additional voltage vectors generated by MLI can be manipulated to achieve the optimal selection for the inverter switching states in the DTC control systems. Previously, a review of DTC which focused more on the two-level inverter for induction motor as well as a review of the multilevel converter in industrial applications had been implemented individually. However, a review on DTC development in MLI was insufficient in both papers. Therefore, this paper aims to give a comprehensive review of the improvement of DTC via various MLI applications. It is reviewed according to the applicable multilevel inverter topologies in the DTC system. The comparison of DTC by using conventional and multilevel inverter is synthesized. Thus, this review paper will hopefully lead researchers in further research activities actively.&lt;/span&gt;

Flexible Sector Detector-Based Mismatch Supply Voltage in Direct Torque Control Doubly Fed Induction Machine: An Experimental Validation

Direct torque control was introduced in 1980 for induction machine for torque and flux control and developed for MSAP in 1990. DTC is gaining popularity due to its simple control structure and easy implementation. The principle of direct torque control (DTC) of the asynchronous machine was introduced in 1985 by I. Takahashi as an alternative to flux-directed vector control (FOC). It is thanks to its simple control structure that it gains popularity and its easy implementation that it has opened a new horizon in the field of variable speed control of electric drives. Indeed, direct torque control (DTC) has benefited in recent years from significant methodological advances in operation and technological development following the introduction of power electronics and digital electronics and the implementation of possible and very usable control algorithms. In conjunction with these technological advances, the scientific community has developed several control approaches to control the operation of electrical machines. In this context, this article presents a comparative study of the different direct torque control (DTC) strategies and structures of the permanent magnet synchronous machine (MSAP). We propose the algorithm of this control making it possible to provide solutions to the ripples of the torque and the stator flux in order to reduce them by adopting a method of compensating the effects of progression by passing from the six sector DTC (DTC – 6S: classic and modified) then develop the twelve-sector DTC (DTC-12S) whose purpose is to minimize ripples and control the switching frequency of the inverter. The simulation graphs presented will clearly show the difference between the different controls techniques cited.

The direct torque control (DTC) system, which is based on induction machine drive is a developed and simple control method. It allows high dynamic performance with very simple hysteresis control scheme; However, its disadvantages are high current, torque, and flux ripple. In this paper, DTC of induction machine drive has been improved by using the applications of artificial intelligence (AI) approaches to reduce the current, torque, and flux ripples and also get better performance of the machines. At the conclusion of this study, the outcomes of traditional DTC and artificial intelligent methods are compared. By the program MATLAB/SIMULINK, the modeling and simulation results of the DTC system for induction machine (IM) have been proposed.

Deadbeat-direct torque and flux control (DB-DTFC) is a direct torque control (DTC) method that provides the fastest possible torque response with smooth and continuous operation even at the voltage limits. DB-DTFC achieves the smoothest possible torque and flux trajectory tracking performance by using the machine inverse model to select volt-second solutions that will produce the desired torque and flux by the end of each pulsewidth modulation (PWM) interval. Since the DB-DTFC inverse model requires accurate steady-state and dynamic flux estimates, discrete-time stator current and flux linkage observers are needed to properly implement DB-DTFC. The existing high-sampling-frequency stator current and flux linkage observers are formed based on approximate discrete-time models for IPMSMs by assuming high-sampling-frequency (10-kHz) operation. This paper presents a more exact discrete-time model for IPMSMs, such that, even at low sampling frequencies, proper stator current and flux linkage observers can be formed to achieve accurate current and flux linkage estimation. The proposed low-sampling-frequency stator current and flux observers are developed using discrete-time modeling with an inverter-sourced volt-second input model. The proposed observers are shown to be very feasible for real-time implementation, and their experimental evaluation documents the improvement achieved compared to high-sampling-frequency observers, even under machine parameter variations.

PurposeThe direct torque control (DTC) of induction motor (IM) drive is featured by high ripples in the electromagnetic torque and stator flux profiles because they are controlled by two hysteresis regulators. Furthermore, the machine flux is not directly measurable. Hence, it is better to reconstitute it from the instantaneous electrical equations of the machine. Once the stator flux is estimated, we can guarantee a reliable sensorless DTC control. Thus, the purpose of this research work is to ensure fast response and full reference tracking of the IM under sensorless DTC strategy with desired dynamic behavior and low ripple levels.Design/methodology/approachIn this work, an improved DTC strategy, which is DTC_SVM_3L, is suggested. The first step of the designed approach is to substitute the conventional inverter feeding the motor with a three-level inverter because it guarantees reduced switching losses, improved quality of voltage waveform and low-current total harmonic distortion rate. The second aim of this paper is to make the IM operate at a constant switching frequency by using the nearest three vectors-based space vector modulation (SVM) technique rather than hysteresis controllers. The third objective of this study is to conceive a sliding-mode stator flux observer, which can improve the control performances by using a sensorless algorithm to get an accurate estimation, and consequently, increase the reliability of the system and decrease the cost of using sensors. The stability of the proposed observer is demonstrated based on the Lyapunov theory. To overcome the load change disturbance in the proposed DTC control strategy, this paper exhibits a comparative assessment of four speed regulation methods: classical proportional and integral (PI) regulator, fuzzy logic PI controller, particle swarm optimization PI controller and backstepping regulator. The entire control algorithm was tested under different disturbances such as stator resistance and load torque variations.FindingsIt was ascertained that the IM, controlled with three-level inverter, exhibits good performances under the proposed DTC-SVM strategy based on a sliding-mode observer. The robustness of the suggested approach against parameter variations is also proved.Originality/valueThe theoretical development of the proposed control strategy is thoroughly described. Then, simulations using Matlab/Simulink software are launched to investigate the merits of the sensorless DTC-SVM command of three-level inverter-fed IM drive with different speed regulators.

Double-excited AC machines, such as PMSMs, provide fast torque responses and great operating performance. Permanent magnet synchronous motors have an increase in electromagnetic torque that can be demonstrated analytically. Direct Torque Control (DTC) adjusts the angle between the stator and rotor flux connections to achieve rapid torque response. Electrical torque is calculated in a stationary reference frame using DTC’s calculations for electromagnetic torque. Stator flux and torque are variables. There are a variety of techniques for determining the rotor’s location and speed without the use of sensors. As an improvement on standard DTC, a sensor-less approach for detecting rotor position and performing direct torque control will be discussed in this work. MATLAB findings are used to model the sensorless direct torque control technique’s fundamental operation.

Direct torque control or direct torque and flux control have significant advantages in operating motors in the field-weakening (FW) region. The flux can be controlled simply in the stator flux linkage frame, directly affecting back-EMF, torque, and speed. However, controlling the current limit under the stator flux frame has not been investigated extensively, especially for FW operation. This paper analyzes the trajectory of the flux regarding the fed current form inverters and the characteristic current. From the analysis, a novel Direct Flux Control is proposed as a promising controller for interior permanent magnet synchronous motor (IPMSM) functioning across an extensive speed range. Then, the performance of the proposed method is compared with the conventional direct torque control method. The analysis results reveal that the torque and flux ripples of the proposed method are reduced, the maximum speed is increased compared to the conventional controller. Finally, simulation results by using MATLAB/Simulink are provided, and the hardware-in-the-loop validates and demonstrates the feasibility and performance of the proposed method.