In this PhD thesis, Eugenio Gubía proposed a solution for the problems of electric motors run from power converters. Controlling motors and electric generators by means of power converters has negative effects with the presence of overtvoltages and high-frequency currents throughout the installation. These effects accelerate the ageing process of the motors and, moreover, can provoke faults in the correct operating of the control circuits.
Thus, in his PhD, Mr Gubia has developed a generic method that can be adapted to each one of the possible installations with the view to identifying the origin of the high-frequency problems and, moreover, to analyse possible solutions. Likewise, the proposed method can be adapted to the design stage of a new installation.
In order to design this method, it was necessary to set up simulation models to reproduce the behaviour of motors, transformers, cables and the power converter, using frequencies in the order of 10 megaHertz. These frequencies are much higher then the tens of kiloHertz used in classical models.
Concretely, in this work it has been possible to reproduce the overvoltages produced as a result of using long connection cables between the inverter and the motor given that, the longer the cable, the greater the probability of overvoltage. This type of cable can be found, for example, in wind-powered generators, which incorporate the generator (the motor) in the upper part of the structure and the power converter at the base.
Garazi Andonegi | Basque research
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