Torsional Vibration Mitigation by Harmonic Inversion through SPWM Carrier Signal Control

Abstract

The paper analyses torsional vibrations caused by electromagnetic torque harmonics in permanent magnet synchronous generators. A vibration mitigation method is proposed based on changing the phase angle of the carrier signal of sinusoidal PWM in order to invert the phase of the torque harmonic causing resonance. Since the frequency has not changed, the system is still in resonance. Thus, after a given time, the torque harmonic should be inverted again. The process is repeated as long as the system is at or near resonance. A criterion is presented to select the exact phase shift of the carrier needed in order to invert the torque harmonic. A method to calculate both the toggle time needed and the frequency range to apply such technique is presented. With the mitigation technique applied, two cases are considered on Matlab/Simulink, namely sustained operation at resonant frequency and accelerating the machine over some critical points.

DC Voltage and Torque Ripple Mitigation in Modular PMSG Drives for Off-Shore Multi-MW WECSs with Linear SPWM modulation

“…Table II summarizes the voltage harmonics present in (10). It should be noted that the harmonic content of the torque along with the corresponding shift in the carrier ψ c coincides with the values in Table II [9]. Figure 5 shows the relation between the change of phase of DC voltage and torque harmonics and the change of the carrier signal phase ψ c .…”

“…Comparing equations (9) and 7, the difference between the parallel and series converters configurations is highlighted such that the disturbance across the DC bus voltage ∆v dcµ has to be controlled.…”

“…In order to identify which harmonics to be cancelled via the sequential command, the derived expressions of v dµ and T eµ as a function of multiples of ψ cµ are the key. By means of (10) and the equations derived in [9], the amplitude of any voltage or torque harmonic can be evaluated at any given speed. The amplitudes of the main harmonics for both voltage and torque reported in Table II are shown in Fig.…”

A Practical Solution for Torsional Vibrations Evasion in Variable Speed Drives

“…An approximate mathematical expression was provided in [7], which accurately calculates the electromagnetic torque (T e ) harmonic amplitudes due to the SPWM modulation. The torsional vibrations in AFPMSG is a local phenomenon occurring on the shaft connecting two rotors.…”

“…Torque harmonics amplitudes as low as 1% of the rated torque can be dangerous [1]. Torsional vibrations is even a bigger concern for high power applications thus various mitigation techniques have been studied [2]- [7]. This paper proposes a practical solution to avoid torsional vibrations in variable speed existing applications, also maintaining low switching losses and better quality waveforms.…”