A New Integrator for Voltage Model Flux Estimation in a Digital DTC System

The logical choice of stator voltage vector is the key for induction motor direct torque control. This paper proposes a stator voltage vector selection rule based on wiring, according to analyzing the affection caused by the electrical wiring on motor stator voltage amplitude and phase. The rules are tested in direct torque control system. Experimental results show the correctness of the theoretical analysis.

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 new hybrid fuzzy controller for direct torque control (DTC) induction motor drives is presented in this paper. The newly developed hybrid fuzzy control law consists of proportional-integral (PI) control at steady state, PI-type fuzzy logic control at transient state, and a simple switching mechanism between steady and transient states, to achieve satisfied performance under steady and transient conditions. The features of the presented new hybrid fuzzy controller are highlighted by comparing the performance of various control approaches, including PI control, PI-type fuzzy logic control (FLC), proportional-derivative (PD) type FLC, and combination of PD-type FLC and I control, for DTC-based induction motor drives. The pros and cons of these controllers are demonstrated by intensive experimental results. It is shown that the presented induction motor drive is with fast tracking capability, less steady state error, and robust to load disturbance while not resorting to complicated control method or adaptive tuning mechanism. Experimental results derived from a test system are presented confirming the above-mentioned claims.

For the disadvantage of the low flux's observational accuracy of induction motor direct torque control system when it runs in a low velocity, the full order flux observer is used to achieve the stator flux observation.Based on the analysis of four full order flux observer pole placement methods,The impact on observational accuracy and convergence rate was researched with different parameters of the Gain Matrix in the single degree of freedom pole placement method.The simulation results show that to ensure the stability of the system,the impacts on the flux observation were Effectively inhibited when Motor's stator and rotor resistance parameters change through increasing parameter of the Gain Matrix,and the flux observer's robustness was improved.

Direct torque control (DTC) is known for its fast control in AC motor drives due to its simple control structure that directly controls the torque without the need for modulation blocks or frame transformations. However, when used in induction motor (IM) drives it has three main drawbacks: large torque ripples, variable switching frequency, and sector flux-droop at the low-speed region due to the employment of the torque hysteresis controller (THC). Torque ripple minimization can be achieved in DTC drives by replacing the originally proposed two-level inverter with a three-level neutral-point clamped (3L-NPC) inverter. Nevertheless, the switching frequency remains variable and low, which produces an elevated torque ripple and asymmetrical switching signals for the inverter. In addition, sector flux-droop resulting from driving the IM at the low-speed region produces a high current distortion that consequently eliminates the robustness of DTC. To alleviate these problems, an interleaving constant switching frequency torque controller-based DTC (CSFTC-DTC) was implemented. It improves the operation of the IM at the low-speed region by increasing the duty-cycle of the applied active voltage vector and reducing the duration of the applied zero vectors. Although the conventional CSFTC-DTC regulates the stator flux of the IM at the low-speed region and minimizes the total harmonic distortion (THD) of the stator current, it produces a high torque ripple-one of the main disadvantages of classical DTC. In this paper, an interleaving CSFTC-DTC is proposed to subdivide the duty cycle of the applied vectors of the 3L-NPC inverter to limit the influence of the large duty-cycle of the applied vectors on flux-regulation and torque ripples. The simulation and experimental results presented validate the effectiveness of the proposed method over the conventional method.

In this paper, a direct torque and stator flux vector control system is presented. The principle of this method was proposed by Takahashi and Noguchi in 1985. In contrast to the field oriented control, no coordinate transformation and current control loop is required. In practical application, however, problems occur with starting and operation in the zero speed region. This paper shows how, by introducing an additional carrier signal to the torque controller input, a robust start and improved operation in the low speed region can be achieved. The simulation and experimental results which illustrate the performances of the proposed system are presented. Also, nomograms for controller design are given. >

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.

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.

The change of stator resistance has an important influence on the performance of asynchronous motor direct torque control system. Accurate acquisition of stator resistance is very important in high-performance motor control system. According to fuzzy control theory, we devise a stator resistance identifier. On this basis, the direct torque control system of asynchronous motor is designed by using MATLAB software. At the same timethrough this simulation, we find the error of identified stator resistance is small, the system respond is quick, and the robustness is good.

Direct torque control drive (DTC) is well-known due to its fast torque response, simplicity and robustness. But some difficulties arise during steady state and also low speed operation. Stator flux estimation is a crucial issue in a DTC drive, especially in low speed region. An open loop voltage model observer does not work properly due to existence of an open loop integrator and stator resistance variation. In this paper an adaptive flux observer is presented which has the advantage of removing the open loop integration and providing a mechanism to include stator resistance estimation. A precise estimation of stator resistance helps the system to have a desired performance in low speed region. Voltage drops over inverter switches normally had been ignored in voltage calculations, but in low speed region with low voltage values these voltage distortions should be considered. A non-linear inverter model is presented for modeling the voltage distortions. Also for eliminating torque, flux and current pulsations during steady state, instead of classical DTC method a combined DTC-SVM method is used. This method removes the pulsations while maintains the basic advantages of DTC drive.

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.

This paper presents a Neuro-Fuzzy adaptive controller for speed control of a three phase direct torque controlled induction motor drive. The Direct Torque Control (DTC) scheme is one of the most advanced methods for controlling the flux and electromagnetic torque of machines. Control of electromagnetic torque/speed in these drives for high performance applications requires a highly robust and adaptive controller. Adaptive Neural-Fuzzy Inference System (ANFIS) is a hybrid between Artificial Neural Networks (ANN) and Fuzzy Logic Control (FLC) that enhances the execution of direct torque controlled drives and overcomes the difficulties in the physical implementation of high performance drives. MATLAB/SIMULINK implementation of 15 hp, 50 Hz, 4 pole squirrel cage induction motor controlled with the DTC scheme is presented in this paper. The PI controller used for speed control in conventional DTC drives is substituted by the ANFIS based controller. Simulation results show the use of ANFIS decreases the response time along with reduction in torque ripples.

<span>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.</span>

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.

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.