Results of studies of higher harmonics during the operation of ship frequency-controlled asynchronous electric drives

Abstract

One of the directions of scientific and technological progress at sea-based facilities is the use of electrical technologies based on nonlinear elements. It is revealed that the use of such technologies leads to a deterioration in the quality of electricity, mainly due to higher harmonic. The results of theoretical and experimental studies of the higher harmonic components of voltage and current occurring during the operation of ship frequency-controlled asynchronous electric drives are presented. During operation of a frequency-controlled electric drive high current harmonics of mainly 5, 7, 11, 13 orders are emitted into the power supply network, which is due to the presence of a six-phase rectifier. This leads to distortion of the sinusoid of the supply voltage, since the higher harmonic components of the current, propagating through the electrical network, create corresponding voltage drops on its elements. Along with the main harmonic of the voltage of a given frequency, the higher harmonic components of the voltage flow from the autonomous voltage inverter to the stator winding of the asynchronous electric motor, which causes the higher current harmonics and torques of the forward and reverse current sequences in the stator and rotor windings. As a result additional heating of the stator and rotor windings occurs and vibrations of the asynchronous motor shaft at frequencies of 300 and 600 Hz occur. A method for measuring the vibration of a frequency-controlled asynchronous electric drive from the interaction of the moments of the reverse and forward sequences has been developed and experimentally confirmed. A method for calculating the intrinsic frequency of oscillations of the asynchronous motor-load machine system is proposed, confirmed by the example of a laboratory installation. To accurately calculate the natural frequency of the oscillatory system, it is necessary to experimentally measure the moments of inertia of the rotor of an asynchronous motor and the armature of a DC motor.