Harmonic

About: Harmonic is a research topic. Over the lifetime, 44833 publications have been published within this topic receiving 495922 citations. The topic is also known as: overtone & partial.

Statistical properties of wave groups in a random sea state

Abstract: Two apparently distinct approaches to the analysis of wave groups in a random sea state are described. In the first, the probabilities of the group-length G and the length of a ‘high run’ H are defined in terms of a wave envelope function p (t) . These lead naturally to expressions in terms of a single parameter that defines the spectral width. In the second approach, the sequence of wave heights is treated as a Markov chain, with a non-zero correlation only between successive waves. This leads to expressions for G and H in terms of transition probabilities p + and p_. In this paper we find approximate analytic expressions for p + and p _ and that show that the two approaches are roughly equivalent, to order v . Throughout the paper it is emphasized that the concept of a wave group assumes implicitly the neglect of those harmonic components that are either very short or very long compared with the peak frequency o p . That is, some filtering of the original record is implied. For typical records of wind waves it is found that a band-pass filter with upper and lower cut-offs at 1.5 o p and 0.5 o p is the most suitable. Calculations are done for typical records of sea waves, and for some numerically simulated data, and there is agreement between the data and the analysis.

An investigation on the validity of power-direction method for harmonic source determination

Abstract: The power-direction method has been used widely to identify the locations of harmonic sources in a power system. A number of utility-customer disputes over who is responsible for harmonic distortions have been settled with the help of the method. A closer examination of the method, however, reveals that it is unable to fulfil the task of harmonic source detection. Case studies can easily show that the method yields incorrect results. In this paper, problems associated with the method are investigated using case studies and mathematical analysis. The results show that the power direction method is theoretically incorrect and should not be used to determine harmonic source locations. The main cause of the problem is that the direction of active power flow is a function of the phase-angle difference between the two sources. The direction of reactive power flow, on the other hand, has a better correlation with the source magnitudes.

On the parametrization and design of an extended Kalman filter frequency tracker

Abstract: The problem of estimating the frequency of a harmonic signal embedded in broad-band noise is considered. The paper focuses on the extended Kalman filter frequency tracker, which is the application of the extended Kalman filter (EKF) framework to the frequency estimation problem. The EKF frequency tracker recently proposed in the literature is characterized by a vector of three design parameters {q,r,/spl epsi/}, whose role and tuning is still a controversial and unclear issue. In this paper it is shown that a wise parametrization of the extended Kalman frequency tracker is characterized by just one parameter: the /spl epsi/ must be set to zero to achieve the basic property of unbiasedness in a noise-free setting; the performances of the tracker are not influenced independently by q and r; and what really matters is the ratio /spl lambda/=r/q only. The proposed simplification of the extended Kalman filter frequency tracker allows an easier and more transparent tuning of its tracking behavior.

A Repetitive Control Scheme for Harmonic Suppression of Circulating Current in Modular Multilevel Converters

Abstract: In a modular multilevel converter (MMC), the interaction between switching actions and fluctuating capacitor voltages of the submodules results in second- and other even-order harmonics in the circulating currents. These harmonic currents will introduce extra power loss, increase current stress of power devices, and even cause instability during transients. Traditional methods for circulating current harmonic suppression have problems such as limited harmonic rejection capability, limited application area, and complex implementation. This paper presents a plug-in repetitive control scheme to solve the problem. It combines the high dynamics of PI controller and good steady-state harmonic suppression of the repetitive controller, and minimizes the interference between the two controllers. It is suitable for multiple harmonic suppression, easy to implement, and applicable for both single-phase and three-phase MMCs. Simulation and experimental results on a single-phase MMC inverter proved the validity of the proposed control method.