Field-programmable gate array-based torque and stator flux estimator for direct torque control of three-phase induction motor
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Date
2016
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
Direct Torque Control (DTC) has gained acceptance for development of induction motor drive systems since it can provide fast instantaneous torque control with simple control structure. However, the major problems in hysteresis-based DTC are variable switching frequency, high torque ripple and the need for high speed processor. Several methods were previously proposed to minimize the output torque ripple, but require some modifications and knowledge of motor parameters that somehow complicate the simple structure of DTC. Moreover, the effectiveness in minimizing the output torque ripple using those methods can be achieved if a higher switching frequency is applied, with a high speed processor. This thesis presents a novel DTC approach for induction motors based on an improved torque and stator flux estimator and its implementation using DE2 (Cyclone® II 2C35F672C6) Field Programmable Gate Array (FPGA). The DTC performance has significantly improved with the use of FPGA, which can execute the DTC algorithm at higher sampling frequency. The main achievements are: i) solving complicated square root operation in stator flux estimator by modifying non-restoring square root algorithm, ii) increasing the sampling frequency to 200 kHz such that the digital computation performs similar to that of the analog operation, and iii) improving the architecture of the torque and stator flux estimator in order to reduce execution time. The design was achieved in VHDL based on a MATLAB/Simulink simulation model. The Hardware-In-the-Loop (HIL) method is used to verify the functionality of the FPGA estimator. The simulation results were validated experimentally. The execution time of the proposed torque and stator flux estimator is 10 µs and the complete implementation only consumes 2093 logic cells. Thus, it is demonstrated that FPGA implementation of DTC drives can achieve excellent performance.
Description
Thesis (PhD. (Electrical Engineering))
Keywords
Field programmable gate arrays, Automobiles—Motors—Control systems, Automobiles—Motors—Testing