Lateral And Torsion Vibration Analysis Of VFD Motor-driven Gear Rotor System

Since the beginning of the new century,the state has paid more and more attention to energy conservation and environmental protection,and the energy efficiency of these high energy-consuming enterprises has also received more and more attention.With the transformation of a large number of motor-driven units in various industries using frequency conversion technology,it has greatly promoted energy conservation and emission reduction of enterprises and reduced costs.However,to avoid the failure of the rotor and coupling caused by the torsional vibration problem is the core issue for the promotion and use of variable frequency drive trains.In this paper,the following researches are mainly conducted for the torsional vibration of the VFD driven rotors from electromechanical coupling and laterial-torsion coupling.(1)Comdyn_rotor,a dynamics calculation software for rotor dynamics,was developed in the MATLAB environment.The finite element method was used to establish the finite element model of the rotor system,which can be used for laterial,torsion and laterial-torsion coupled calculations.Comparing with dyrobes,the accuracy of the calculation was verified.(2)A finite element gear shafting coupling model was established by taking an actual motor shafting as an example,and the individual natural frequencies and unbalanced responses of each shaft were analyzed.Based on this,the natural frequency and unbalanced response of the torsional coupled rotor system are calculated,and a new coupled vibration peak appears.The natural frequency and unbalanced responses of the torsional coupled shaft system are calculated.The results show that the calculation of the coupling without calculation and the calculation of the torsion coupling are both inaccurate.The torsional vibration frequency and response will be offset due to the influence of the laterial and torsion coupling,and thus the shaft is calculated.The bending and torsion coupling effects should be considered when calculate torsional vibration.(3)In the MATLAB environment,the torsional vibration initiation and frequency conversion excitation calculation modules were developed,and the modal reduction method was used to reduce the computational complexity.The accuracy of the torsional vibration calculation was verified.The excitation of the synchronous motor and the excitation of the VFD driven motor in the gear coupled shafting system are analyzed.The results show that the torsional vibration is excited at some speeds during start-up,and the resonance frequency coincides with the torsional frequency in the Cambell diagram.Under the excitation of variable frequency harmonics,the torsional vibration phenomenon also occurred in the low speed range of the shaft system,indicating that the frequency conversion drive needs to be calculated and analyzed separately.Finally,the fatigue of the shaft system is calculated.The stress at the shaft coupling is lower than the low-cycle fatigue limit and no fatigue failure occurs.(4)Using the state-space equation to transform the shaft system and verify the accuracy of the results.An electromechanical coupling analysis was performed on the gear coupling model.It was found that the torsional resonance occurs at a rated speed of 1800 rpm when the rotor has a small damping,because the harmonic torque excited by the motor is close to the second-order natural frequency.Next,the influence of the position and damping of the motor speed on the vibration of the shaft system is analyzed.The sensitivity of different measurement positions to vibration is different.Changing the measurement position can reduce torsional resonance.In addition,the torsional resonance generated by the harmonic excitation can also be suppressed by increasing the overall damping of the shaft system.