Frequency Starting of the Electric Drive of the Above Resonance Vibration Machine

Abstract

An above resonance vibration machine with two-shaft unbalanced vibrators for compaction of rigid concrete mixtures in the form is considered. It is noted that for such vibration machines, an unregulated electric drive with an overestimated power of the drive motors is usually used. This enables to quickly overcome the resonant zone during start-up, but in steady state, the drive motors operate with significant underload, which leads to a deterioration in the energy performance of the motors. For the possible replacement of drive motors of excessive power with less powerful ones, the start-up of a resonant vibration machine using a frequency-controlled electric drive was investigated. Using mathematical modelling, a study was conducted to investigate the influence of the basic laws of frequency control on overcoming the resonant zone during start-up. The influence of the laws of frequency control was determined by comparing the maximum displacement of the working body of the vibration machine and the starting current of the motor during frequency and direct start-up. Analysis of the obtained simulation results showed that the basic laws of frequency control do not provide a reduction in the amplitude of oscillations of the working body of the vibration machine and dynamic loads when overcoming the resonant zone during the start-up process, if the frequency start-up time is greater than the direct time. Further studies were carried out with the optimal frequency sweep time for this vibration machine and replacing the drive motors with less powerful ones for the following four cases: with a linear frequency control law, with a stepwise increase in the supply voltage and a linear change in frequency, with a simultaneous stepwise increase in voltage and frequency, with a stepwise increase in frequency and a linear change in voltage. The stepwise increase in the voltage and frequency of the supply was performed at the moment when the value of the supply frequency of the induction motor was equal to the specified resonant frequency of the vibration machine. It is shown that with a linear change in the voltage and frequency of the supply, a decrease in the acceleration of the drive motors in the resonant zone is observed, and a stepwise increase in the frequency leads to "jamming" of the rotors of the drive motors of the vibration machine. It is noted that to overcome the resonant zone during the frequency start-up of induction motors of above resonant vibration machines, it is advisable to use only a step-like increase in voltage, which will allow setting the drive motors with the power required for steady-state operation.