Current Harmonic Aggregation Cases for Contemporary Loads

Power electronic circuits in modern power supplies have improved the conversion efficiency on the one hand but have also increased harmonic emissions. Harmonic currents from the operation of these units affect the voltage waveforms of the network and could compromise the reliability of the network. Load and source non-linearity can, therefore, limit the renewable source’s hosting capacity in the grid, as a large number of inverter units may increase the harmonic distortions. As a result, voltage and current distortions could reach unbearable levels in devices connected to the network. Harmonic estimation modelling often relies on measurement data, and differences may appear in mathematical simulations as the harmonic aggregation or cancellation may generate different results due to the inaccuracies and limitations of the measurement device. In this paper, the effect of harmonic currents cancellation on the aggregation of different load currents is evaluated to show its impact in the network by presenting a comparison between the measurement and mathematical aggregation of harmonics. Furthermore, the harmonic cancellation phenomenon is also qualified for multiple loads connected to the power supply.

Harmonic Cancellation

This paper reviews the hypothesis of {\em harmonic cancellation}\ according to which an interfering sound is suppressed or canceled on the basis of its harmonicity (or periodicity in the time domain). It defines the concept, discusses theoretical arguments in its favor, and reviews experimental results that support it, or not. If correct, the hypothesis likely draws on time domain processing of temporally-accurate neural representations within the brainstem, as required also by the classic Equalization-Cancellation (EC) model of binaural unmasking. It predicts that a target sound corrupted by interference will be easier to hear if the interference is harmonic than inharmonic, all else being equal. This prediction is borne out in a number of behavioral studies, but not all. The paper reviews those results, with the aim to understand the inconsistencies and come up with a reliable conclusion for, or against, the hypothesis of harmonic cancellation within the auditory system.

A novel adaptive control algorithm for the rejection of harmonics in a standard vibrator

Because of the nonlinear factors in the standard vibrators, the output waveform of the vibrators is usually distorted, especially in the low-frequency band. Traditionally, the harmonic distortion is suppressed by improved design of the vibrator and feedback control. However, these approaches can just suppress the harmonics to some extent. There are still residual harmonic components which cannot be eliminated. In this article, an adaptive control algorithm is proposed to eliminate the harmonics of the vibration calibration system by injecting harmonic components into the control input signal. Weighting vectors of the harmonic components are adaptively updated based on a modified filtered-x least mean square (MFxLMS) algorithm, which has both strong robustness and much less computational complexity. The convergence properties of the proposed MFxLMS algorithm are investigated, and it is further implemented in a real-time controller. Experimental results on a standard vibrator show excellent performances for harmonic cancellation. The harmonic distortion is close to 0% after the implementation of the proposed algorithm.