ES395817A1 - Speed control systems for electric motors - Google Patents

Abstract

Improvements in speed control systems for polyphase wound-rotor asynchronous motors, of the type provided with a gradual insertion of resistors in the rotor phases, followed by a periodic interruption of current in these phases, respectively by a controlled semi-conduit device arranged in each one of them closing the mentioned devices in the conductive state the phases on a neutral point, characterized in that the periodical interruption devices each correspond to at least one door rectifier activated by a priming signal, because the signal of Priming is provided by an ignition generator that essentially has three inputs to which they are respectively applied: a first rectangular wave signal whose periodic width is a chosen fraction of the rotor current period, a second voltage signal generated by comparison between the voltage from a device that measures the frequency rotor ia and a speed setpoint voltage, and a third signal that depends on the period of the rotor current and that determined an ignition threshold of the controlled rectifier, said ignition generator containing a first organ that receives the first and second signals so as to produce a tension in saw teeth whose tooth width is determined by the first signal while the slope of the tooth is proportional to the amplitude of the second signal, said tension in saw teeth not providing an effective signal more than when a second organ that it feeds establishes a coincidence with the third signal that determines the ignition threshold, thanks to which the deviation voltage between the set speed and the motor speed has the effect of varying the voltage slope, producing the the rectifier is switched on constantly for a certain fraction of the period of the rotor current and the regulation of ve locity for a corresponding fraction of electrical steps. (Machine-translation by Google Translate, not legally binding)