Generation of torsional excitation in a variable-speed-drive system

Abstract

Torsional vibration issues in elastic drive systems are a well-known topic both in the research area and in the industrial field. A considerable number of papers appear over the last two decades discussing the source of torque and speed ripple in variable speed drive (VSD) technologies and their connection with the mechanical characteristics as the torsional natural frequencies (TNFs). This paper provides a detailed description of the potential mechanical failures in a system equipped with a VSD and it explains which are the sources of torsional excitations focusing on the interactions between electrical side and mechanical side. The effects on the coupling torque of the so called critical speeds will be investigated with both the Campbell diagram and the Waterfall diagram tools in order to predict some potential failures in the drive-shaft

Torsional Vibration Mitigation by Harmonic Inversion through SPWM Carrier Signal Control

“…Also non integer harmonics which have much lower amplitudes than the integer harmonics can be dangerous as they cover higher frequency range [2]. It has to be noted that vibrations may arise also because of other reasons, such as mechanical, due to unbalance of rotating parts; even the control closed loop interaction can amplify the vibrations [3] [4].…”

Review of Medium Voltage High Power Electric Drives

“…This in turn may cause undesired plant shutdowns (171)- (173) . Interactions between the electrical and mechanical sides of the drive system are the main source of magnification of torsional vibration excitations (174) (175) . Due to the DC link voltage fluctuation in VSI, the pulsating air-gap torque spectrum is composed of harmonics and inter-harmonics.…”

“…Due to the DC link voltage fluctuation in VSI, the pulsating air-gap torque spectrum is composed of harmonics and inter-harmonics. Critical operation points, where the rotational speed of the motor causes harmonics and interharmonics coincident with one of the shaft torsional natural frequencies, can cause resonance and lead to system failure (174) (175) . Beside the conventional losses, a recent study shows that additional losses are introduced in the electric motors under torsional vibration (184) .…”

Adjustable Speed Control and Damping Analysis of Torsional Vibrations in VSD Compressor Systems

“…However, there may be harmful interactions in the coupling shaft, such as torsional mode excitations and fatigue cycles. The intrinsic nature of switching-based drives produces a pulsating torque transfer on the transmission components that can match some torsional natural frequencies (TNFs), implying an oscillating behavior of the state variables [4,5]. In fact, crack and/or lifetime reduction can happen if the torque constraints are not satisfied [6].…”

“…As discussed in [4,11], the AC-DC-AC stage produces integer harmonics and interharmonics in torque (referred to DC-link coupling). The overall excitation content transferred to the shaft line is computed in (5), as a function of the motor speed and supply frequency. m, k are integer multipliers according to the following cases:…”