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Harmonic current estimation is required in active power filters for compensation purposes. The most efficient way of calculating the total harmonic current up to the infinite order is to subtract the fundamental component from the distorted current. Direct determination of the fundamental component of a distorted current of mains frequency was realized recently with a third-order modulation integral observer. This article shows that using an exponential modulation function (Exp-MF) for the integral observer will: 1) significantly enhance the robustness of the observer against noise and 2) automatically remove the low-frequency envelope arising from the D/A and A/C sampling processes compared to previous polynomial modulation function. These new and advantageous features are supported with detailed analysis and experimental verification. The robust observer can be implemented in grid-connected power electronics circuits that require the instantaneous information of the fundamental and/or harmonic currents. Practical comparative tests with the adaptive notch filter and recursive discrete Fourier transform (DFT) methods in an active power filter have confirmed the good performance under both the steady and dynamic states of the proposed Exp-MF integral observer.

Parallel operation of multiple grid-connected power converters through LCL filters is known to have the potential problem of triggering oscillations in the ac mains. Such oscillatory frequencies are not integral multiples of the fundamental frequency and, hence, form a new source of interharmonics. Early detection of such oscillations is essential for the parallel power converters to move out of the unstable zone. This paper presents an online observer-based algorithm that can perform fast detection of interharmonics within a specified frequency band. The algorithm has been adopted in a specific and reduced form from an integral observer algorithm for detection of fundamental and interharmonic voltage components in the ac mains. A new method based on the kernel signal for fast interharmonic detection is proposed and practically verified. It has been implemented in a digital controller to detect oscillations such as those occurring between two grid-connected power converters. The practical results indicate that the algorithm can locate such frequency within the specific frequency band within one mains cycle.

Background Fatigue is a complex phenomenon associated with multiple antecedents and detrimental consequences. Although this symptom is prevalent in the older population, it is not easily recognized by nurses and has been under treated. Aim The purpose of this review is to describe the existing research on fatigue on older adults with focus on the lived experience of fatigue, factors related to such fatigue experience and the impact of fatigue on overall health. Methods A systematic search of the literature was undertaken to identify research evidence on fatigue among the older population. Three databases (i.e. OvidMedline, CINAHL and PsycINFO) were searched, resulting in 15 eligible studies. Three aspects about the fatigue phenomenon in older people were identified: the lived experience of fatigue, relating factors of fatigue, and impact of fatigue on overall health. Findings The key findings suggest that fatigue is an overwhelming experience constrains physical capacity and the energy reserve required for appropriate functioning and social participation, as well as worsens their morbidity and mortality outcomes. Yet, its heterogeneous etiologies and multi-dimensional manifestations pose a huge challenge on its diagnosis and treatment. Indeed, there was inadequate research-base evidence on fatigue management for older people. This gap in literature may imply that this problem is poorly recognized and under-treated in older people. Conclusions The findings highlight that fatigue is a substantial problem in older people that deserves early recognition and prompt treatment. Nurses need to be sensitive to the risk factors of fatigue in the older population and conduct a comprehensive fatigue assessment on the high risk case. Although this review only identified limited research-base evidence, the findings do give directions to the development of interventions for fatigue management for older people.