Advanced Materials Research Vols. 986-987

Abstract: This paper introduces seven-level Cascaded H-bridge (CHB) inverter and work principle. Then, the strongpoint and disadvantage of multi-level inverter usual PWM technologies are analyzed and compared. We find that multi-level cascaded inverter based on three harmonic injection method have two advantages via analysis. The voltage modulation index can increase 1.15. The equivalent switching frequency of H-bridge inverter’s load voltage is N times of each cell switching frequency. At last, H-bridge inverter was investigated with simulation and experiment. The results prove that the analysis is correctness and validity.

Abstract: This paper deals with parameter optimization of virtual impedance of parallel inverter. Conventional design methods determine parameters by observing the changes of amplitude-frequency and phase frequency curves of the equivalent impedance. However, those methods always neglect the dynamic performance of inverters in parallel. This paper proposes a novel method to optimize the coefficients of virtual impedance and experiments show that new method improves the dynamic performance of parallel inverter effectively, as well as stability and flexibility.

Abstract: Temperature is one of the important factors affecting the power generation efficiency of PV cells. In order to improve the efficiency of photovoltaic power generation systems and heat utilization efficiency, we used Matlab/Simulink to build photovoltaic power system analysis model based on thermal power. By changing the heat and illumination input to the photovoltaic cell model and the heat generated by the battery we got the characteristics and temperature characteristics of the photovoltaic cell the system model, the photovoltaic power generation system model and the output power correction, etc. We got the environmental temperature change equation through the actual air temperature and curve fitting and used real and detailed data to compare the data obtained using the equation for online correction. PV cells temperature factor was used to get the PV cells temperature with the environment temperature changes. In order to get PV module thermal /energy efficiency the dates was processed and analyzed by using Matlab and Excel through actual observation data of school 120KW PV power station. The results showed that power generation efficiency increased and year average efficiency PV improved 21.3279% through the use of some heat about PV cells.

Abstract: Electric power industry is related to people's livelihood, economic development, an important foundation for national construction industry. With the deepening of our country comprehensive construction, the demand has increased rapidly, at the same time also have higher requirements for quality of power supply. From the previous electricity use can be gradually increased to cannot accept a power outage, to the power grid voltage waveform, harmonic, frequency and so on each index has a clear requirement, countries have introduced related national standard specification. This aspect shows a gradually increase in the standardization of industrialization in China, on the other hand also puts forward higher demands on distribution power supply departments. One of the goals of the grid is to reduce the failure rate, improve the reliability of power supply. And power grid failure and is the highest percentage of short circuit fault, and the single-phase earth fault and occupy the vast majority of proportion, it is necessary to in-depth analysis of the formation mechanism of single-phase earth fault and damage, so as to find the related protection and remedial measures.

Abstract: In this research, a converter, suitable for the convert station of the HVDC light technology, is proposed and optimized. The converter mainly consists of AC chopper, rectifier transformer, low-pass filters and smoothing reactor. This system can restrain the disturbance of the input power and output the power with high quality. This research is going to analyze the working principle of the converter and then optimize the output wave through filters. Circuit’s simulation is carried out by MATLAB to verify the reliability and feasibility of this converter topology.

Abstract: At present the study mainly for frequency electromagnetic field which is based on a single transmission line meanwhile the value must be in line with the requirements of the workers in the country frequency electromagnetic field. However, for parallel transmission line the maximum of frequency electromagnetic field is still to meet the provisions of the state, therefore in this paper studied the parallel transmission lines. Taking the multiple parallel power lines of China Three Gorges University as an example, the values of electric and magnetic field are calculated and the electromagnetic field is measured based on National standards. Then, compare the measured value with theoretical value, verified the correctness of the superposition algorithm.

Abstract: This paper discusses the post stage power supply circuit’s structure of electronic appliances such as laptops, desktops, mobile phones and digital cameras, which are commonly used in office. The advantages and feasibilities of DC power supply’s substitution for AC are analyzed. On this basis, a DC power supply system consists of photovoltaic cells, batteries, AC/DC modules, DC/AC modules as well as DC loads is brought forward. The main power supply unit, photovoltaic cells, connects the DC bus through a DC regulator circuit. The bus voltage can be maintained stable by real-time adjustment of photovoltaic cells’ output power. The battery module connects the DC bus through a bidirectional Boost-Buck circuit. The charges and discharges of batteries can be real-time controlled according to the bus voltage level. The AC/DC module connects the DC bus as a backup, which can real-time detect the bus voltage to determine whether to start. The DC/AC module can supply power to ordinary AC loads and the DC loads are usually powered from the bus through DC/DC converters.

Abstract: Using Matlab/Simulink software established the simulation model of UHV transformer and UHV power grid.The characteristic of magnetizing inrush current for UHV transformer was obtained by simulation.The paper also analyzed the impact on differential protection from it. Closing resistor inside circuit breaker method was proposed to restrain magnetizing inrush current.The method cuts down the amplitude and accelerated the attenuation speed of it, so as to restrain it. The simulation analysis verified the effectiveness of the method.

Abstract: In order analyze the inter-harmonic affections on the voltage flicker, the relationship between the inter-harmonics and flicker analysis are carried out. In order to be able to accurately determine the level of inter-harmonics to make the electric light flicker, interharmonic-flicker limit curve drawing method based on the voltage flicker constraints is established. And according to IEC lamp-eye-brain model, analog tester flicker and interharmonic-flicker experimental platform are built; limit curve can be drawn through the experimental data. The 2 kinds of harmonic-flicker limit curves for the 220 V, 50 Hz fluorescent lamp are drawn by the 2 methods separately, and the analysis results show that the accuracy of the results obtained by the two methods, the level of interharmonics whether lead to fluorescent flicker can be determined by the curves. The methods have the small amount of calculation, and are practical and easy to implement.

Abstract: Low frequency oscillation caused by system interconnection has been the main factor to threat the secure operation of power grid. It’s significant to research on the problem of low frequency oscillation. This paper summarizes the generation mechanism and analysis methods of low frequency oscillation. Each analysis method has both advantages and disadvantages.