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EN
The aim of this paper is to give a solution to unbalance problem of the input DC voltages of the nine-level NPC-VSI in dq synchronous frame. For that, we used in high voltage and great power applications, one two-level PWM current rectifier-nine-level NPC VSI-PMSM cascade. In the first part, we develop a knowledge model of the Nine-level NPC VSI and propose a space vector modulation of this converter using eight bipolar carriers. After that, this study shows particularly the problem of the stability of the DC voltages of the inverter and its consequence on the performances of the PMSM speed control. Then, we propose a solution to the problem by employed closed loop regulation using classic PI controller mode in d-q synchronous frame. We add a Clamping bridge to stabilize the eight DC input voltages of the nine-level NPC VSI. This cascade found applications in great power and high voltage fields as electrical traction.
2
Content available remote Direct torque control for induction machines using neural networks
EN
In this work, a novel switching vector selector in Direct Torque Control of an induction machine using Artificial Neural Network is studied. In the first part, we describe design of a speed sensor-less Direct Torque Control (DTC) strategy of an induction motor supplied by a two-level voltage source. For this, a conventional look up table is applied which improves the performances. Due to the high computation load, this technique is not convenient for an one-line and real-time control. Thus, a simplified method of choosing the output vector for two-level voltage source inverter-fed induction machine is proposed in the second part, and a novel switching vector selector using Artificial Neural Network (ANN) is trained under the tutor of the method mentioned above. The ANN receives attention as controllers for many industrial applications. Although these networks eliminate the need for mathematical models, they require a lot of training to understand the model of plant or process. In fact, when the stator flux and electromagnetic torque are different from theirs respective references, the output vector can be expediently acquired. Simulation results showed that the ANN structure can replace successfully the conventional look up table of the DTC.
3
Content available remote Feedback and control cascade using seven - Level NPC voltage source inverter
EN
In this paper, the authors present a study of the stability problem of the input DC voltages of the seven-level neutral point clamping (NPC) voltage source inverter (VSI). In the first part, a knowledge model of this converter isdeveloped by using connection functions. In the second part, The authors propose a PWM strategy which uses six bipolar carriers to control the converter. In this part, The inverter is fed by constant input DC voltages. In the last part of the paper, the authors study the stability problem of the input DC voltages of the inverter. Thus, a cascade is studied constituted by three two-level PWM rectifiers - clamping bridge - seven-level NPC VSI. The obtained results show that the input DC voltages of the inverter are not stable. To improve the performances of the proposed cascade and stabilize the input DC voltages, the authors propose in this paper a solution which uses a linear feedback control of this cascade. This study allows to find a solution for the instability problem of the input DC voltages of the inverter. The results obtained with this solution confirm a good performance of the system.
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