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Electric Circuits and Components
Published in Quamrul H. Mazumder, Introduction to Engineering, 2018
Even though capacitors are generally identified as charge storing devices, they have other useful applications in a circuit depending on the type of capacitor chosen. They can be used in circuits, in conjunction with resistors, and for providing time intervals; an example of such a circuit is shown in Section 8.11 with a 555 timer. They are used for filtering unwanted signal frequencies and suppressing high-frequency voltage transients—explained in more details in Section 8.7.7 for designing a low-pass filter. You can also design other kinds of filtering circuits by combining certain capacitance with appropriate components that is outside the scope of this chapter. If you are interested in learning more about filter design, I would recommend you to read about digital signal processing. In addition, capacitors are used to block unwanted DC voltage in AC systems. Analysis of how a capacitor does this is shown in Section 8.7.6 with some level of calculus.
No-Reference Quality Metric for Degraded and Enhanced Video
Published in H.R. Wu, K.R. Rao, Digital Video Image Quality and Perceptual Coding, 2017
Jorge E. Caviedes, Franco Oberti
To measure noise, most algorithms assume that any image contains small areas of constant brightness (i.e., no details are present). Hence, whatever variation in these areas is nothing but noise. A typical noise measurement algorithm would consist of the following steps: Divide the image into small blocks.Measure the intensity variations for every block.Assuming that the intensity of the noise is much smaller in magnitude than the signal, the block with the least variation (or the average of the blocks with the smallest variation) should correspond to a constant brightness region.Use a set of high-pass filters or a band-pass filter to filter out the DC component. The sum of the outputs of the filters, clipped using perceptual thresholds proposed in [WYSV97], is used to compute the variance or noise.
Novel Approaches to Microgrid Functions
Published in KTM Udayanga Hemapala, MK Perera, Smart Microgrid Systems, 2023
KTM Udayanga Hemapala, MK Perera
A ZSI is composed of a DC source, a two-port network made up of a split-inductor (two inductors, L1, L2), and two capacitors (C1, C2) coupled in an X shape as in Figure 4.11, and it feeds the main converter circuit with DC via impedance source coupling. A voltage or current source might be used as the DC source. A ZSI provides a simplified single-stage power conversion topology as an added benefit. The shoot-through (ST) can no longer kill the inverter, and it adds DC to DC power conversion (buck–boost mode) to the inverter in addition to DC to AC power conversion. It solves the majority of the issues of traditional voltage and current source inverters.
A Review of CMOS Variable Gain Amplifiers and Programmable Gain Amplifiers
Published in IETE Technical Review, 2019
Chunfeng Bai, Jianhui Wu, Xiaoying Deng
The gain of a VGA/PGA with reasonable linearity and gain accuracy is commonly less than 20-dB while the IF section has to provide less than 60-dB gain [68]. This level of gain is usually realized using multiple cascaded amplifiers. If they are directly cascaded, the DC-offset produced at the output terminal of the mixer will be amplified to a considerable value and saturates the succeeding modules. Besides, the DC-offset might cause second-order distortions [69]. Therefore, the DC-offset not only may saturate the amplifiers but also degrades the signal to noise ratio. Hence, methods to implement DCOC are required and they can be classified into two groups: the analogue filtering approach and the digitally assisted calibration.
Mathematical and Experimental Investigation on Advanced PLL for Cascaded H-Bridge Multilevel Inverter in Active Filtering Application
Published in Electric Power Components and Systems, 2019
Soumyadeep Ray, Nitin Gupta, Ram Avtar Gupta
One significant aspect of harmonic current compensation and reference current generation is the design of the overall control system. The main concern while designing control algorithm is simplicity, robustness and accuracy. At the same time, its effectiveness should be tested under normal and distorted source voltage condition. Phase-locked loop (PLL) plays an important role in case of active filtering applications in maximum number of control algorithms. Maximum number of conventional and modified control theories for single- and three-phase SAPF depends on PLL. S. Arya et al. used software PLL for active filtering applications [8] whereas synchronous-reference frame-PLL (SRF-PLL) is commonly used for synchronization which suffers from double-frequency error. PLL also suffers from accuracy issue in distorted voltage condition. Enhanced-PLL (E-PLL) resolves above-mentioned problems to some extent, however, the presence of DC component may degrade dynamic performance of the system. DC component may be present in the existing system due to offset of DC/AC voltage sensors, characteristics mismatch among semiconductor switches, DC offset in analog-to-digital converters, etc. [9]–[12]. The presence of DC component results low-frequency ripple in the PLL loop. It also degrades the performance of amplitude estimation loop. Consequently, several PLLs have been used in the literature but removal of DC components has not been taken care of by the most of the researchers. Meticulous research need to be done in this area for better control performance. S. Labura et al. [9] proposed a PLL structure in order to reject DC offset. This PLL structure used park’s transformation for phase angle measurement. Alpha component of the input voltage signal and polluted input voltage is compared and passed through an integrator circuit for removing DC component from the circuit. Golestan et al. [10] proposed SRF-PLL-based approach for rejecting DC component from polluted supply. Phase detection scheme of this PLL is also working on the basis “abc” to “alpha-beta” transformation. Delayed signal is used for mitigating DC component from polluted input supply. However, computational burden and transformation from “abc” to “alpha-beta” frame are major drawbacks of these PLLs. A. Kulkarni et al. [11], [12] presents an improved version of generalized integrator-based PLL (FR-PLL) in order to get rid of DC offset. Two numbers of second-order GIs are connected in cascaded manner and finally “alpha-beta” component is fed to SRF-PLL. At the same instant, bandwidth selection of SRF-PLL affects dynamic response time. An improved E-PLL-based approach is designed and used for grid-tied photovoltaic (PV) system to get rid of DC components by Verma et al. [13]. Improved E-PLL is capable of exact measurement of phase angle, fundamental component extraction from polluted signal and DC component removal but its effectiveness is tested only in case of normal condition.