Performance analysis of long term evolution (LTE) network
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An improved Direct Torque Control algorithm for the brushless doubly-fed reluctance machine (BDFRM) has been proposed in this thesis. The conventional DTC method has some well-known advantages such as simple implementation, fast torque and speed response, and independence from machine parameters. However, despite these advantages, the conventional DTC method also has some drawbacks including high torque and speed ripple, variable switching frequency, and poor performance during the transient periods. The main motivation of this thesis is to overcome the disadvantages of the conventional DTC method. The main focus of the work is to adapt the Space Vector Modulation method to the control problem instead of the vector selection method. SVM is a well-known method which can reduce the torque and speed ripple, and provide a fix to the problem to the variation of switching frequency and possible over-frequency. The proposed theory is implemented with simple modification, so that all the advantages of the conventional DTC, such as easy implementation and fast response, still remain, but the issues concerned with torque and current ripple are reduced. This thesis is essentially divided into three main parts. The first part is the theory development which compares the fundamental principles of DTC and the proposed new method. In the second part, the proposed theory is verified as giving improved performance. This was done by comparing the simulation results of the conventional DTC algorithm and the proposed algorithm. The proposed method is shown to significantly reduce the torque and speed ripple, and improve the speed response during the transient period. The third part contains a set of experimental results for verification of the simulation results, the proposed theory and the real time control system are implemented using a TI DSP module, a conventional IGBT inverter kit and a specially constructed prototype which has a radially-laminated rotor with ducts in the form of 4-8-6 pole BDFRM. Transient steps in speed were used to test the control and it was found to work well at low speed and thought the synchronous speed point where drive responses can be challenging.
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