Modified Strategy of Direct Torque Control Applied to Asynchronous Motor Based on PI Regulators

This paper presents a direct torque control (DTC) technique for brushless DC (BLDC) motors with non-sinusoidal back-EMF using four-switch inverter in the constant torque region. This approach introduces a two-phase conduction mode as opposed to the conventional three-phase DTC drives. Unlike conventional six-step PWM current and voltage control schemes, by properly selecting the inverter voltage space vectors of the two-phase conduction mode from a simple look-up table at a predefined sampling time, the desired quasi-square wave current is obtained. Therefore, a much faster torque response is achieved compared to conventional PWM current and especially voltage control schemes. In addition, for effective torque control in two phase conduction mode, a novel switching pattern incorporating with the voltage vector look-up table is designed and implemented for four-switch inverter to produce the desired torque characteristics. Furthermore, to eliminate the low-frequency torque oscillations caused by the non-ideal trapezoidal shape of the actual back-EMF waveform of the BLDC motor, pre-stored back-EMF constant versus position lookup tables are designed and used in the torque estimation. As a result, it is possible to achieve two-phase conduction DTC of a BLDC motor drive using four-switch inverter with faster torque response due to the fact that the voltage space vectors are directly controlled. Therefore, the direct torque controlled four-switch three-phase BLDC motor drive could be a good alternative to the conventional six-switch counterpart with respect to low cost and high performance. A theoretical concept is developed and the validity and effectiveness of the proposed two phase conduction four- switch DTC scheme are verified through the simulations and experimental results.

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.

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.

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.

• 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.

Compared with field orient control (FOC), direct torque control (DTC) is known to provide fast and robust response for induction motors. However, while offering high dynamic performance, classical DTC produces notable torque, flux, and current ripples, and operates with a variable inverter switching frequency. In this paper, a novel torque control scheme for induction motors is proposed. The stator flux and the electrical torque are directly controlled by variable-structure controllers, and stator voltage vectors calculated by the variable-structure controllers are applied to the motor by means of space vector modulation. The proposed scheme therefore provides smooth, fast and robust regulations of the electrical torque and the stator flux. Moreover, the implementation of the scheme is simple. Theoretical analysis shows the asymptotical convergence of electrical torque and stator flux tracking. Simulation and experimental results are provided to evaluate the performance of the proposed scheme.

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

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.

In modern high performance ac drives, field oriented control (FOC) or direct torque control (DTC) schemes are applied to achieve high dynamic operation. Recently, efforts have been made to eliminate the machine shaft sensor in order to reduce costs and increase reliability. Although DTC is often designated as a sensorless scheme, it has similar problems to FOC when operated around zero flux frequency. In this paper, the performance of both schemes is investigated with special emphasis on operation around zero speed. In that operating range it is assumed nowadays that, without a shaft sensor, the flux position can only be determined by exploiting parasitic effects of the machine such as saturation or slotting. Sensorless schemes to estimate the spatial flux position control suffer from reduced accuracy in specific load ranges which degrades the performance of the drive when compared to operation with a shaft sensor. On a test stand FOC and DTC have been realized and the flux position calculated with the use of a speed sensor has been modified with different error functions to test the reaction of both schemes on erroneous flux input values.

This investigation improves the performance of a direct torque controlled permanent magnet synchronous motor (PMSM) using both genetic algorithm (GA) and fuzzy logic. In this approach electromagnetic torque error, stator flux linkage error and stator flux angle are fuzzified using three appropriate fuzzy sets. Therefore the best voltage space vector has been selected in order to minimize torque, flux and current ripples. In this paper direct torque control (DTC) of a PMSM drive is simulated using both conventional table based and fuzzy methods and the PI speed controller is tuned using GA. A comparative study between conventional DTC and proposed approach shows that not only the speed response of the controller has been improved but also torque, flux and stator current ripples have significantly been reduced without any effective change of the inverter switching frequency.

In this work, a direct torque control (DTC) method for multi-machine systems is applied to electric vehicles (EVs). Initially, the DTC control method associated with the model reference adaptive system (MRAS) is used for speed control, and management of the magnetic quantities is ensured by the variable master-slave control (VMSC). In order to increase the technical performance of the studied system, a DTC method has been associated with a fuzzy logic approach. These two control methods are applied to the traction chain of an electric vehicle to highlight its speed, precision, stability, and robustness metric during particular stress tests imposed on the wheel motor. The results obtained in MATLAB/Simulink software made feasible a comparison of two proposed methods based on their technical performances. It should be noted that the direct fuzzy logic torque control (DFTC) has better performance than the DTC associated with the MRAS system as a rise time reduction of 1.4%, an oscillation of torque, and flux amplitude of less than 9%, static steady-state error near zero. The DTFC control method responds favorably to electric vehicle traction chain systems by the nature of the comfort and safety provided.

The transport sector is essential for socio-economic growth; however, the sector contributes a large portion of global carbon dioxide emissions. Consequently, electric vehicles have received increasing attention from various stakeholders in order to provide a solution to the current environmental impact of the transport industry. Current literature on electric vehicle powertrains show that electric vehicles are complex systems, with one of the most essential subsystems being the traction motor control mechanism. As a result, the objective of this paper is to add to the research conducted in the field of electric vehicle powertrains by carrying out comprehensive investigations into the suitability and performance of space vector modulation based direct torque control in the traction motor control system of an electric vehicle with a complete drive system. Initially, a conventional direct torque control mechanism was implemented for control of the traction motor system. The results of the investigation into implementation of conventional direct torque control highlighted the expected issues associated with the mechanism. Implementation of improvements to the conventional direct torque control model, such as the use of a space vector modulation based direct torque control model with closed loop torque control, field-weakening and sensorless control produced significantly favorable results, providing decreased torque and current ripples, operation over a wide speed range, and accurate speed control without the need for mechanical speed sensors. Such results demonstrate that the complete control mechanism investigated is well suited for use in electric vehicle applications.

The objective of this paper is to design and study of duty ratio modulated modified Direct Torque Control drive, especially for Permanent Magnet Synchronous Motor (PMSM). Conventional Direct Torque Control (DTC) is typically associated with torque ripple and stator flux ripple. Duty ratio modulated direct torque control (DDTC) reduces torque ripple and stator flux ripple. For high performance applications the conventional DDTC is again modified to obtain comparatively less torque and flux ripple. In this paper the DDTC is associated with MTPA approach to obtain duty ratio calculation more effectively.

This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC–SVM) and conventional DTC. The scheme proposed in this paper exploits the advantages of both control methods. During the linear region, it allows for a low torque ripple and low current harmonic distortion (THD). During the overmodulation region, it allows for the fastest torque response up to the six-step operation region. In both regions, there is complete independence of the motor parameters. The paper describes a way to provide a smooth transition between the two control schemes. Non-linearities affect the stator flux angle estimation, which leads to the inability to decouple torque and flux. To overcome this problem, a novel PI-based control scheme as well as a simplification on the decoupling terms’ calculation are proposed. Simulation and experimental results are presented to verify the feasibility of the proposed method.

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.