Papers by Keyword: Harmonic

Abstract: Nowadays power quality is a critical issue in power system. Moreover the connection of three-phase transformers through underground cables is growing fast in residential, commercial, industrial and rural applications. Due to this increasing situation, the possibilities of having a series connected capacitance and a non-linear inductance, and hence ferroresonance, become more probable. Ferroresonance can also occur in power transformers or reactors by capacitive coupling from neighbouring phases or lines. It is necessary to have a general idea about what would be the best preventive decisions to take in order to avoid unexpected surprises. It is necessary to have an accurate ferroresonance model so that a device that can smoothen the sharp effects of ferroresonance can be found. In this paper, the FACTS device, namely the static synchronous series compensator (SSSC) had been used to mitigate ferroresonance. Results show that using SSSC dramatically decreases and mitigates the ferroresonance shock as well as the instabilities of the network.

Abstract: This paper aims to analyzing and probing the influences of power system harmonics on a differential relay used for distribution transformer protection. The increased use of nonlinear devices in industry, commercial and residential areas can lead to a significant increase the level of harmonic distortion in the power system. This harmonic has the significant effects to the differential protection systems components such as current transformer (CT) and relay. The CT tends to saturate due to the presence of current harmonics in power system, so it will produce magnitude secondary current error and make the differential relay to miss operations. The harmonic distortion effects on the differential protection have been investigated through laboratory test. To determine the CT errors when operates under harmonic condition, the CT has been test with certain level of THD_i. The result of this testing was found that with increasing of the THDi, the magnitude of secondary current error increased and differential relay will operate at no fault conditions.

Abstract: This paper presents a new selective switching strategy for single phase SPWM Inverter that can reduce the power loss and total harmonic distortion. Power loss is always a command issue for inverter system. Power loss occurs during the switching of the inverter. This new selective switching strategy is modified from the typical switching strategy and has been proven to reduce the power loss and harmonics. This project had already been tested on direct power source and also from the solar PV module. This project is focusing on 100W inverter system.

Abstract: This paper proposes a method using non-linear voltage-current characteristics for multiple harmonic sources classification using wavelet hybrid neural network (WHNN). Typical voltage-current characteristics of harmonic sources are non-linear closed curves in the time-domain, referring to the converters, reactors, and non-linear loads. The hybrid neural network is a two-subnetwork architecture, consisting of wavelet layer and a self-organizing feature map (SOFM) network connected in cascade. The effectiveness of the proposed method is demonstrated by numerical tests. The results of multiple harmonic sources show the computational efficiency and accurate classification.

Abstract: Shunt Active Power Filter (SAPF) is a new device for compensating harmonic currents in power system [1]. For unbalanced three-phase four-wire circuits, it need detect the total of harmonic and fundamental negative sequence and zero sequence currents at the same time. Base on traditional method of ip-iq, a detecting method which is suitable for unbalanced three-phase four-wire is proposed and analyzed by mathematical reasoning. At last, correctness of the result is verified by simulation.

Abstract: There are various kinds of damage caused by large amount of harmonic in power grid. The research object of this paper is the harmonic in power grid. A simple and practical harmonic detection program is studied. And the harmonic analysis module is completed. First the principle of harmonic generation is analyzed. And then, the signals of the voltage and current in power grid are collecting. At last, the hardware and software of the module are designed. The signals are analyzed and calculated by the module. The harmonic content is put out. The test proved that the module has the advantages of high precision, good reliability and low cost. It can be used on a variety of equipment.

Abstract: Harmonic analysis is the foundation of harmonic control and compensation. The voltage signals with harmonic component is difficult to analysis under noise environment. This paper proposed a new approach for harmonic analysis based on Hyperbolic S-transform. Firstly, the affection for harmonic analysis by different characters of the hyperbolic window including forward-taper parameter and backward-taper parameter is compared. Secondly, the modified Hyperbolic S-transform with optimal characters is used for harmonic analysis. Finally, the analysis result of the new approach is compared with other methods. Simulation results show the effectiveness and advantages of the new method. It is very satisfied for harmonic analysis under high noise environments.

Abstract: As distribute power generation and micro-grid technology develops, more and more researchers attach importance to the problems of power quality in micro-grid, especially the problem of harmonic. This paper describes the impact and harm harmonic has on the power quality of the power grid. It introduces a revised method of managing micro-grid harmonics which uses an active power filter (APF), and the control method of APF is different from the traditional one. It also establishes the simulation model of micro-grid, analyze the simulation results and experiment in actual micro-grid to verify the effectiveness of the proposed method.

Abstract: The design scheme for PV system connecting the grid is provided, considering the reactive power compensation, harmonic and lightning effects. Solar power generated connects into the nearby medium and low voltage distribution networks by the inverter. The capacity of solar power total is 1.15MWp. The electricity is generated for personal use; the remaining is connected to the grid system. The scheme is reasonable in design; the system is stable and reliable by the practical testing. It can be used in large range popularization and application.

Abstract: Due to a variety of electrical equipment using, the grid power quality severely polluted. For current harmonic signal is generated in hoist converter, the methods is proposed based on Hilbert-Huang Transform (HHT) to detect current harmonic signal and improved Active Power Filter (APF). The simulation mode is established by MATLAB/Simulink software about shunt APF+SPWM inverter hybrid active filter device for harmonic motion detection and suppression simulation. The results show that the harmonic of hoist converter can be detected by this design method real-time and the harmonic can also be suppressed validly.