A Novel Overmodulation and Field Weakening Strategy for Direct Torque Control of Induction Machines
ABSTRACT This paper presents a new simple overmodulation strategy in direct torque control (DTC) of induction machines. The strategy increases the inverter voltage limit and therefore extends the constant torque region. The minor modification on the conventional flux weakening method is also introduced to improve the torque capability in the field weakening region and hence improving the operation over a wide speed range. These strategies are implemented with a DTC-constant switching frequency (CSF) based system. To perform the DTC-CSF in overmodulation mode, the flux error status is modified before it is being fed to the voltage vector selection table. With this proposed strategy, a single-mode overmodulation based on stator flux vector control with smooth PWM to six-step transition is developed. This strategy also proposes a dynamic overmodulation to obtain fast torque transient with six-step operation including the field weakening region. The proposed strategy has been verified through computer simulations a
- SourceAvailable from: Ahmad Ghaderi
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- " and  a DTC with constant switching frequency (CSF) is proposed which in it a proportional integrator (PI) controller is used to make the torque error status. However using a PI controller increases the complexity of the controller considering the essentiality of the gain values setting. "
ABSTRACT: DC link voltage of inverters used in electric drive vehicles (EDVs) propulsion systems is limited which leads to the insufficiency of the vehicle speed and acceleration. Therefore the fundamental voltage of EDVs drive system should be increased by operating in the six-step mode at high speeds. Although hysteresis based direct torque control (DTC) is a straightforward approach and has several advantages, this method cannot work in the six-step mode. In this paper a new hysteresis based DTC with over modulation ability for interior permanent magnet synchronous machines (IPMSM) is suggested. In this method, unlike the previously proposed methods, the calculation of the voltage vector or flux reference in different phase angles is not necessary. In the proposed method, the flux trajectory is changed by adjusting the non-switching area and modifying switching table, and thus a seamless transformation between high-frequency switching and six-step square wave is possible. Also in this paper, the dynamic model for an electric vehicle is developed which its traction motor is controlled by proposed DTC. The simulation results prove that the proposed method modify the vehicle performances, notably. These results show that the vehicle with proposed method has a higher top speed and better acceleration. Also it is shown, that the proposed method can improve the vehicle efficiency for various driving cycles. In addition the results confirm the torque discontinuity does not appear in the whole range of vehicle speed.41st Annual Conference of the IEEE Industrial Electronics Society (IECON 2015), JAPAN; 11/2015
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- "Therefore, the torque ripple can be directly controlled by regulating the armature current ripple. Several papers were reported to achieve this requirement, for examples  fully utilized the available DC link voltage through over modulation strategy and  generated the maximum possible voltage vector that is tangential to the flux component to have lower current ripple. Ultimately, all these methods used a vector control which is complicated to be implemented. "
ABSTRACT: This paper describes an approach to develop accurate and simple current controlled modulation technique for brushless DC (BLDC) motor drive. The approach is applied to control phase current based on generation of quasi-square wave current by using only one current controller for the three phases. Unlike the vector control method which is complicated to be implemented, this simple current modulation technique presents advantages such as phase currents are kept in balance and the current is controlled through only one dc signal which represent maximum amplitude value of trapezoidal current (Imax). This technique is performed with Proportional Integral (PI) control algorithm and triangular carrier comparison method to generate Pulse Width Modulation (PWM) signal. In addition, the PI speed controller is incorporated with the current controller to perform desirable speed operation of non-overshoot response. The performance and functionality of the BLDC motor driver are verified via simulation by using MATLAB/SIMULINK. The simulation results show the developed control system performs desirable speed operation of non-overshoot and good current waveforms.MATEC Web of Conferences 01/2014; 13:03007. DOI:10.1051/matecconf/20141303007
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- "Several papers were reported to achieve this requirement, for examples  fully utilized the available DC link voltage through overmodulation strategy and  generated the maximum possible voltage vector that is tangential to the flux component to have a quick change of torque dynamic. Ultimately, all these methods used a vector control which is complicated to be implemented. "
ABSTRACT: This paper presents modeling and simulation of a torque hysteresis controller for brushless DC motors. Brushless DC (BLDC) motors can offer great advantageous compared to other machines used in industrial applications due to its compactness, high torque density, simpler controller and lower maintenance. At first the mathematical modeling of BLDC motor that is suitable to analyze the dynamic performance will be given. A method of torque hysteresis controller will be adapted to drive the motor such that the current (or torque) ripple can be restricted within the predefined band-gap. Moreover, a new current blocking strategy is proposed to prevent the current drained from DC supply when the torque demand is set to zero, that can prolong the capacity voltage of batteries. Some simulation results were carried out using MATLAB/Simulink to verify the proper modeling as well as functionality of the controller.Industrial Electronics and Applications (ISIEA), 2012 IEEE Symposium on; 01/2012