Closed-Form Solution of Time-Varying Model and Its Applications for Output Current Harmonics in Two-Stage PV Inverter
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The single-phase photovoltaic (PV) inverter needs significant capacitance to buffer the double-line frequency power pulsation at ac port. The two-stage inverter allows the designer to choose the dc-link voltage and the capacitor size flexibly. With the reduced capacitance, the lifetime of the dc-link capacitor can be prolonged by replacing the electrolytic capacitors with film capacitors. However, the capacitance deduction results in high double-line frequency voltage ripple on dc-link, which increases a series of odd harmonics in the output current. This paper hence analyzes the harmonics caused by the voltage ripple in an inverter with feedback control. The inverter is modeled as a time-varying system by considering the dc-link voltage ripple. A closed-form solution is derived to calculate the amplitude of the ripple-caused harmonics. This analysis helps the designer to understand the effect of the dc-link voltage ripple on current harmonics, evaluate effectiveness of existing approaches, and stimulate new ideas and solutions. The study also derived the theoretical limit to select dc-link capacitance and sampling rate of current reference without violating the grid-tied regulations in power quality. The analysis is verified both by simulation and experimental evaluation.Effects of ripple width in rippled-spectrum signals on ripple density resolution was investigated. Two measurement paradigms were tested: (i) ripple density resolution for discrimination between two rippled signals and (ii) discrimination between a rippled test signal and non-rippled reference signal. The ripple widths varied from 9% to 64% of the ripple frequency spacing. For both paradigms, the ripple density resolution increased with deceasing the ripple width. For discrimination between two rippled signals, the resolution was 8.1 ripples/oct for a ripple width of 64% and increased to 15.1 ripples/oct at the ripple width of 9%. For discrimination between a rippled test and non-rippled reference signal, the resolution was 9.3 ripples/oct at a ripple width of 64% and increased to 85 ripples/oct at a ripple width of 9%. Discrimination between two rippled signals is hypothesized to depend on ripple depth in the excitation pattern; the depth increases with narrowing the ripple width. Discrimination between a rippled test and non-rippled reference signal is hypothesized to depend on temporal processing; the effect of the ripple width appears due to increasing the ratio of the autocorrelated to uncorrelated components of the input signal with narrowing the ripples.
SIGNAL (programming language)
Uncorrelated
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The value of the electrolytic capacitor in the rectifier circuit affects not only the output voltage but also the rip-ple current,the power loss and the life of the capacitor.A mathematical model of the filter capacitance’s ripple current is presented,whose effectiveness is verified by the comparison between the calculation results with the proposed model and the simulation results with the Saber software.The capacitance’s influence on the ripple current and the power loss of the capacitor are analyzed on the basis of the given model.It is concluded that,with the increase of the capacitance,ripple current of the capacitor increases while the power loss increases firstly and then decreases after reaching the maximum.It is proved by experimental results that the proposed model and the analysis results provide more comprehensive considera-tions and a good help on the selection of the capacitance.
Filter capacitor
Rectifier (neural networks)
Tantalum capacitor
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To satisfy the requirements of electronic equipment, a capacitor is developed to work under high ripple current and high voltage, at 105℃ for 2 000 hours. The tests related with the materials, technology, working electrolyte and high ripple current have been down. The results show that the newly developed aluminum electrolytic capacitor can steadily work under 450 V and high ripple current (470 μF, 1.85 A or 56 μF, 0.51 A), at 105℃.
Tantalum capacitor
High Voltage
Film capacitor
Polymer capacitor
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Higher ripple current capacity of electrolytic capacitors are required with the development of the electronic equipment. Discussed is how to enhance ripple current capacity, including material selection, factors causing heating, heat-eliminating methods. The measurement of maximums ripple current capacity and the determination of rated ripple current are presented.
Ripple marks
Filter capacitor
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In the production, capacitance fall-off is a common problem, but the causes are different. Capacitance fall-off will result in capacitance failures and poor stability. Based on the analysis of the failure causes, the solutions are established; therefore, the stable capacitors of low cost are obtained.
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The basic theory of calculation of the capacitance of a capacitor comprised of two cocentric annular plates by the method of (annular) subareas is advanced. Confirming the theory, excellent agreement results between the several available experimentally determined (by electrolytic tank) values for specifically dimensioned capacitors and corresponding calculated values. A family of universal curves is constructed. These afford, by inspection, values of capacitance over the range of geometry of interest in practice.
Polymer capacitor
Film capacitor
Tantalum capacitor
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It is critical for buried target detection via ripple scattering to know the ripple structure, e.g., the ripple height and spatial wavelength. In the present paper, backscattering data from a 300-kHz system show that ripple wavelength and height can potentially be estimated from backscattering images. Motivated by the backscatter data, we have developed a time-domain numerical model to simulate scattering of high-frequency sound by a ripple field. This model treats small-scale scatterers as Lambertian scatterers distributed randomly on the large-scale ripple field. We have found that this approach characterizes the field data well. Numerical simulations are conducted to investigate the possibility of remotely sensing bottom ripple heights and wavelength.
Backscatter (email)
Ripple marks
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This paper analyzes the mechanism of ripple generation,summarizes characteristics of the ripple and its effects on load,and puts forward a discussion of methods for measuring ripple of DC stabilized power supply.
Ripple marks
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Hysteresis
Ripple marks
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When a solid object or wheel is repeatedly dragged on a dry sandy surface, ripple patterns are formed. Although the conditions to form ripple patterns have been studied well, methods to eliminate the developed ripple patterns have not been understood thus far. Therefore, history-dependent stability of the ripple patterns formed on a sandy surface is investigated in this study. First, the ripple patterns are formed by sweeping the flat sandy surface with a flexible plow at a constant speed. Then, the sweeping speed is reduced, and the variation of ripple patterns is measured. As a result, we find that the ripple patterns show hysteresis. Specifically, the increase in amplitude of ripples is observed when the reduced velocity is close to the initial velocity forming the ripple pattern. In addition, splitting of ripples is found when the reduced velocity is further decreased. From a simple analysis of the plow's motion, we discuss the physical mechanism of the ripple splitting.
Hysteresis
Ripple marks
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