Estratégias preditivas para a mitigação da tensão de modo comum em motor de indução trifásico

Abstract

This document presents a comparison between three different strategies that promote the mitigation of the common mode voltage for the AC-DC-AC converter, also known as back-to-back, based on the use of the Predictive Model Control (MPC) to control the rectifier currents, in addition to controlling the flow and speed of the machine indirectly. This work deals with the development of models for each stage of the AC-DC-AC topology, such as the rectifier, DC-link, inverter, and finally, the induction machine. In addition, it is demonstrated how the predictions of the variables to be controlled were performed using the Euler discretization method, in addition to presenting the complete control for the two converters. Along with the presented models, auxiliary structures such as the Phase Locked Loop (PLL) and the stator flux estimator using the full order observer, were also mentioned. Strategy 1 proposes that the mitigation of the common mode voltage (CMV), be performed directly in the quality function, therefore, initially the selection for the rectifier is performed, and from the its CMV, the vector for the inverter is chosen, capable of controlling the flux, the speed and the CMV. Strategies 2 and 3, on the other hand, propose to carry out a pre-selection of the best possible combinations to reduce/cancel CMV. Strategy 2 uses a single check with all 20 best switching possibilities and only one quality function to be minimized, which takes into account rectifier and inverter control. Strategy 3 also proposes a pre-selection of vectors, however using two quality functions. After selecting the rectifier, the three vectors that promote the null CMV are chosen to be verified for the inverter. Given the above, simulation results were obtained for the three strategies for two scenarios, with and without the zero vectors, and experimental results for the three strategies in the scenario without the zero vectors. For all the mentioned scenarios, the three structures were analyzed in relation to the functioning of the control of the variables, such as current, voltage, stator flux and speed, the processing time, in addition to the Total Harmonic Distortion (THD) of the currents of the converters, and mainly the behavior of the individual CMV of each converter and the general CMV, specific to the AC-DC-AC topology. From the simulation and experimental results, it was possible to identify some discussions of the strategies in the two mentioned scenarios. Regarding the control of the variables and the cancellation of the CMV, the strategies obtained similar results, what differentiates the best one to be used are the processing times between them. Regarding the deployment scenarios, the THD of the converter currents is the main topic taken into account.