Extending DC Bus Utilization for Induction Motors with Stator Flux Oriented Direct Torque Control

The direct torque control (DTC) is widely used in motion control of electric drives, especially for the switching table based direct torque control (ST-DTC) and the space vector modulation (SVM) based DTC (SVM-DTC). The classical ST-DTC schemes can achieve fast dynamic response but may suffer from distinct torque and flux ripples in steady-state operation. On the other hand, the classical SVM-DTC schemes have lower ripples in torque and flux, but the methods slow down dynamic response of DTC. Different from them, a novel hybrid DTC scheme is proposed for dual three-phase permanent-magnet synchronous motor (PMSM) drives in this paper, which can achieve fast dynamic response of classical ST-DTC scheme and good steady-state performance of classical SVM-DTC scheme simultaneously. The key of the proposed scheme is to implement different torque control methods under dynamic operation mode and steady-state operation mode, respectively. A switching method has been designed to guarantee smooth transition between the two operation modes. Besides, the decoupling control of torque and stator flux is maintained with the proposed control scheme, and the stator flux is controlled stably all along. By experiments on a laboratory prototype, it has been verified that the proposed scheme can achieve both good steady-state and transient performance compared to other control methods for dual three-phase PMSM drives.

A new magnetic-coupled high power factor converter (MCHPFC) with a single switch/single stage is proposed. The proposed converter gives good power factor correction, low current harmonic distortions, and tight output voltage regulation. The prototype shows that the IEC555-2 requirements are met satisfactorily with nearly unity power factor. A proposed MCHPFC is particularly suited for low-power-level power supply applications.

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.

Direct Torque Control (DTC) is known to generate a fast and robust response in asynchronous engines. Yet, during steady state, observable flux, torque and current pulsations arise. This paper presents a study of modified direct torque control applied to a three-phase high performance asynchronous motor. The proposed strategy is based on PI regulators instead of the hysteresis comparators to control both the stator flux and torque whose parameters are determined from modulus and symmetrical optimum criterions. Since the performance of a feedback control system relies on the accuracy of the response signal, an estimator of stator flux and torque is presented. The control system benefits from the advantages of field oriented control (FOC) and conventional direct torque control (DTC) while avoiding some of the disadvantages of either of the two control methods. Performances of the asynchronous motor control are checked by simulations under MATLAB/SIMULINK software.

This paper proposes a novel direct torque control (DTC) scheme to reduce the torque and stator flux ripples for permanent-magnet synchronous motor (PMSM) drives using a relatively low sampling frequency. Unlike the conventional DTC in which the voltage vectors are determined by hysteresis controllers, the proposed DTC uses nonlinear saturation comparators and a duty ratio modulation scheme for switch selection and switching duration determination. Compared to the conventional DTC, the proposed DTC scheme significantly reduces the steady-state torque and flux ripples of PMSMs while preserving most of the intrinsic properties of the conventional DTC, e.g. fast dynamic, robust to disturbances, no coordinate transformation, etc. The effectiveness of the proposed DTC scheme is verified by simulation and experimental results on a 200W PMSM drive system.

This paper proposes the design and implementation of a direct torque controlled induction motor drive system. The method is based on control of decoupling between amplitude and angle of reference stator flux for determining reference stator voltage vector in generating PWM output voltage for induction motors. The objective is to reduce electromagnetic torque ripple and stator flux droop which result in a decrease in current distortion in steady state condition. In addition, the proposed technique provides simplicity of a control system. The direct torque control is based on the relationship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. Experimental results are illustrated in this paper confirming the capability of the proposed system in regards to such issues as torque and stator flux response, stator phase current distortion both in dynamic and steady state with load variation, and low speed operation.

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.

This article proposes a new approach for direct torque control of induction motors. This method is based on direct torque control with pulse width modulation of a current source inverter using SIMULINK/MATLAB simulators for its performance assessment. The proposed control system is realized based on stator-flux-oriented reference. It uses the same method as direct torque control drive systems with a voltage source inverter to estimate the stator flux and electromagnetic torque and, therefore, only needs the stator resistance to control the motor. In this method, stator current components are calculated to directly control the stator flux and electromagnetic torque. Simulation results show the excellent performance of this system. Using simulations, the proposed method is also compared with the direct torque control voltage source inverter system, and it is shown that the proposed method improves induction motor performance and decreases the inverter switching losses. Another main advantage of the proposed control method is that it seriously limits the starting current and feeds the motor with high power quality. A novel switching method in space vector modulation of current source inverter is also proposed, which effectively decreases motor torque ripple and harmonic losses.

Efficient feedback linearization control for an IPMSM of EVs based on improved firefly algorithm

<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>

Recently, many studies have been performed for the variable speed control of an induction motor. Direct torque control (DTC) is an emerging technique for the variable speed control of PWM inverter driven induction motors. DTC allows the direct control of stator flux and instantaneous torque through a simple algorithm. In this paper, an ASIC design technique using VHDL is applied to DTC based speed control of an induction motor. ASIC for DTC based speed control is designed through the descriptions of coordinate transformation, speed controller stator flux and torque estimator, stator flux and torque controller stator flux position detector, FSM (finite state machine) and inverter voltage switching vector. Finally the above system has been implemented on the FPGA (XC4052XL-PG411). Simulation and experiments have been performed to verify the performance of the designed ASIC.

A modified direct torque control (DTC) scheme for interior permanent magnet synchronous machine (IPMSM) is investigated in this paper, which features in very low flux and torque ripple and almost fixed switching frequency. The new scheme provides a variable option for the improvement of DTC controlled IPMSM. Two PI controllers regulate the flux and torque respectively and the stator voltage is generated through SVM unit in the proposed DTC system. Simulation results show that the performance of the proposed DTC system has been improved and the flux and torque ripples are greatly reduced with respect to the conventional DTC.

• Modeling and design of an intelligent control system for electric vehicle applications. • Improvement of direct torque control of DFIM for electric vehicle applications through the use of fuzzy controllers. • Comparative analysis between classical DTC control and DTC based on fuzzy logic of the doubly feed induction motor for electric vehicle applications. Conventional Direct Torque Control (DTC) presents challenges such as significant torque ripples and limited adaptability to load variations. These challenges are exacerbated when applied to electric vehicles (EVs) due to changes in driving speed and the load torque that depends on road conditions. In this context, this work aims to improve the DTC of a Doubly Fed Induction Motor (DFIM) used for electric propulsion. Hysteresis comparators and the control table, responsible for the ripples in conventional DTC, have been replaced by fuzzy logic controllers. Additionally, a fuzzy logic speed controller has been designed to ensure better speed tracking across different ranges (low, medium, and high speed). Simulations performed using Matlab/Simulink allowed for a comparison of the proposed control strategy with conventional DTC. The results show a reduction of 42 % in torque ripples. Furthermore, the proposed control strategy does not show any overshoot compared to the conventional DTC strategy, which shows an overshoot of 1.5 km/h. This improves adaptability to load variations and the precision of dynamic response, optimizing the overall vehicle performance. These improvements result in smoother driving and increased overall efficiency of EVs, demonstrating the practicality and effectiveness of the fuzzy logic control strategy for electric propulsion applications.

This thesis is mainly devoted to the investigation of speed control methods for three phase cage induction motors with particular emphasis being given to Direct Torque Control (DTC) improved techniques.<br/>Classical Direct Torque Control has inherent disadvantages such as: problems during starting resulting from the null states, the compulsory requirement of torque and flux estimators, and torque ripple. In the classical DTC induction motor drive a voltage vector is applied for the entire period, and this causes the stator current and electromagnetic torque exceeds its reference value early during the cycle, causing a high torque ripple. Switching cycles then follows this, in which the zero switching vectors are applied in order to reduce the electromagnetic torque to reference value. This thesis suggests a technique based on applying to the inverter the selected active states just enough time to achieve the torque and flux references values. The rest of the switching period a null state is selected which won't almost change both the torque and the flux. Therefore, a duty ratio has to be determined each switching time. By means of varying the duty ratio between its extreme values (0 up to 1) it is possible to apply any voltage to the motor. The optimum duty ratio per sampling period is a non-linear function of the electromagnetic torque error, the stator flux position and the working point, which is determined by the motor speed and the electromagnetic torque. It is obvious that it is extremely difficult to model such an expression since it is a different non-linear function per working point. Therefore, this thesis is focused on performing a fuzzy-logic-based duty-ratio controller, where the optimum duty ratio is determined every switching period. Additionally, this Fuzzy Controller is adaptive and may be applied to any induction motor.<br/>A stator flux reference optimum controller is also designed, which not only helps to achieve a smaller torque ripple, but also reduces the reactive power consumption of the drive taken from the main supply. This is achieved by changing the stator flux reference value with reference being made to the correspondent torque reference value. Therefore, the stator flux reference value chosen is to be just of sufficient value to produce the desired torque <br/>Simulated results are shown in order to compare the classical DTC and the Fuzzy Logic based DTC.<br/>The control algorithms have been implemented on a PC/DSP based board that facilitates the use of parallelism in software design. A 1.5kW, three-phase induction motor drive has been designed and experimental data obtained from it in order to verify the results achieved by simulation.

Over the past few years, multiple types of modifications have been proposed onto the Direct Torque Control (DTC) scheme. Among others is the implementation of Space Vector Modulation (SVM). In this paper, two new control strategies are proposed onto an SVM-DTC. Instead of using PI torque and flux controllers, a fuzzy logic control method is implemented in the proposed modification to achieve a more constant switching frequency while minimizing the torque error. The fuzzy logic controller controls the voltages in direct and quadratic reference frame (Vd, Vq). This approach fully utilizes the switching capability of the inverter and thus improving the overall system performance. To overcome issues in open loop stator flux such as DC drift and saturation, a closed loop estimation method of stator flux is also proposed based on voltage model and low pass filter. The performance of the proposed control strategy is benchmarked with that of a conventional DTC–SVM. Simulations and experiments were carried out and the results show that the proposed method outperforms the conventional DTC-SVM in terms of DC-offset elimination and overall system robustness. <p class="MsoNormal" style="text-align: justify; text-indent: 36.0pt;"><span style="font-size: 9.0pt; font-family: 'Arial','sans-serif'; color: black;" lang="EN-US">Over the past few years, multiple types of modifications have been proposed onto the Direct Torque Control (DTC) scheme. Among others is the implementation of Space Vector Modulation (SVM). In this paper, two new control strategies are proposed onto an SVM-DTC. Instead of using PI torque and flux controllers, a fuzzy logic control method is implemented in the proposed modification to achieve a more constant switching frequency while minimizing the torque error. The fuzzy logic controller controls the voltages in direct and quadratic reference frame (V<sub>d</sub>, V<sub>q</sub>). This approach fully utilizes the switching capability of the inverter and thus improving the overall system performance. To overcome issues in open loop stator flux such as DC drift and saturation, a closed loop estimation method of stator flux is also proposed based on voltage model and low pass filter. The performance of the proposed control strategy is benchmarked with that of a conventional DTC–SVM. Simulations and experiments were carried out and the results show that the proposed method outperforms the conventional DTC-SVM in terms of DC-offset elimination and overall system robustness. </span></p>