Some people think that we learn our most important lessons in Others think that the knowledge we acquire outside of school is the most Which view do you agree with? Use specific reasons and examples to support your 问题——现实情况——他人的观点——你的观点 Children all around the world are attending Education has become a core issue for every government on earth， and they are all striving hard to achieve higher quality and larger scale of This is by no means coincidence， but indicates the importance of In my point of view， we learn our most important lessons of our life in school， which is reflected by the emphasis of education by 理由一 In schools， students learn the essence of all human The human knowledge is accumulated through all human Knowledge taught in lessons in school are selected and selected over thousands of years， composing the fundamental knowledge a person needed to survive and succeed in For example， the mathematics courses in school lay the basis for every student who is to understand If they know nothing about mathematics， they may well be fooled in the future by banks and other 理由二 Also， the knowledge taught in school is often systematic and reasonable， rather than discrete pieces of Through the process of learning systematically and solving academic problems by reasoning， students only learn the knowledge they are learning， but also learn the most efficient way to view and solve problems around For example， through learning physics and chemistry， students know more about what's happening around us， but more importantly， they grasp some idea of observation， assumption， experimentation and 理由三 And lessons in school often determine students' appetite of literature， art and In schools， student spend much more time learning famous piece of literary works， paintings， sculptures and great compositions， which is definitely different from what they hear and see outside the In this way， their appetites for beauty reach a higher And an appetite for fine arts and literature would bring tremendous benefits to the happiness of their life， considering the huge heritage of fine arts we have!理由四 To conclude， the knowledge taught in school is the true essence of all human knowledge， and school knowledge has a tremendous positive effect on 总结理由，强化结论
Abstract: With the development of power electronics technology， harmonic hazards has become increasingly serious， harmonic governance issues has been On the power source for electronic devices harmonic analysis and concluded that its harm and the corresponding harmonic management principles and comprehensive management， and management of a harmonic Key words: power electronics; harmonics; hazards; inhibitionINTRODUCTIONWith the development of power electronics technology， power electronic devices to the extensive application of power system harmonics caused serious Various power electronic equipment in the transport， metallurgical， chemical and other industrial traffic the extensive application of harmonics in the grid problem is becoming increasingly serious， many low power factor of power electronic devices to the power grid additional burden on the quality of power and influence， Therefore， the power electronic devices harmonic pollution has become hinder the development of power electronics technology major Therefore， inhibition harmonic pollution and improve the power factor of power electronics technology has become a major issue in This paper focus on the key issues of power through electronic harmonic sources and the danger of understanding and analysis， and control of pollution from the relationship between the consideration of a comprehensive management approach on the final harmonic trends in the development of comprehensive management of the A power electronic device - the main source of harmonicsNonlinear load is a harmonic sources， which caused grid voltage distortion， in the voltage several times with the whole of the fundamental frequency Harmonic as the main source of power for various electronic devices mainly AC-DC converter (rectifiers， inverters， chopper， Drives)， as well as bidirectional thyristor controlled switching equipment， as well as internal power system Variable Flow equipment， such as HVDC rectifier valve and the valve， and other Below its harmonics generated an analysis of the 1 RectifierAs a DC power supply devices， rectifiers widely used in various Figure 1 (a) and Figure 1 (b) respectively for the single-phase and three-phase circuits In rectifier devices， AC power supply for the current rectangular wave， rectangular wave of the fundamental frequency for the current and Jibeiai several times for the high-frequency harmonic current waveform Obtained by Fourier series of rectangular wave of high harmonics In fundamental component I1 and the largest ratio of 1 / n， with the trigger control angle α， and the decrease of overlap angle μ for the increase of harmonic wave components have reduced In addition， the existing research results indicate that: Rectifier harmonic current operation mode of the size， has a direct impact， therefore consider adjusting the voltage and current rectifier， it is best to conduct overlap angle， as well as for harmonic phase pressure drop calculations， in order to determine safe and economical operation mode when the control close to 40 ° angle α， overlapping in the 8 ° angle μ about the circumstances are often the most serious state of harmonic， so to go through， as far as possible through the correct choice of regulating transformers tap in order to avoid Harmonic most serious point [1]2 exchange regulatorExchange regulator used for lighting dimming and induction motor speed， and so Figure 2 (a) and 2 (b) respectively for the single-phase and three-phase circuits Exchange regulator and the harmonic frequency rectifier basically the Frequency Converter 3Frequency converter is AC / AC Converter behalf of equipment， when used as mot
