1. 大學物理教學大綱，英文版，機電類
Abstract: With the development of power electronics technology, harmonic hazards has become increasingly serious, harmonic governance issues has been imminent. 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 outlook.
Key words: power electronics; harmonics; hazards; inhibition
INTRODUCTION
With the development of power electronics technology, power electronic devices to the extensive application of power system harmonics caused serious pollution. Various power electronic equipment in the transport, metallurgical, chemical and other instrial 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 obstacles. Therefore, inhibition harmonic pollution and improve the power factor of power electronics technology has become a major issue in the. 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 prospect.
A power electronic device - the main source of harmonics
Nonlinear load is a harmonic sources, which caused grid voltage distortion, in the voltage several times with the whole of the fundamental frequency component. 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 inverter. Below its harmonics generated an analysis of the situation.
1.1 Rectifier
As a DC power supply devices, rectifiers widely used in various occasions. Figure 1 (a) and Figure 1 (b) respectively for the single-phase and three-phase circuits typical. 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 synthesis. 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 reced trend.
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 conct 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].
1.2 exchange regulator
Exchange regulator used for lighting dimming and inction motor speed, and so on. Figure 2 (a) and 2 (b) respectively for the single-phase and three-phase circuits typical. Exchange regulator and the harmonic frequency rectifier basically the same.
Frequency Converter 1.3
Frequency converter is AC / AC Converter behalf of equipment, when used as motor speed control devices, which contain a change with the output frequency band edge, as for the frequency change, the more complicated harmonic content.
Universal Converter 1.4
GM converter input circuits are all from the diode bridge rectifier and DC capacitor components in Figure 3 (a) shows, this circuit impedance input current waveform with the different big difference. In the source impedance relatively small cases, the waveform for the lanky Zhaier high-waveform in Figure 3 (b) solid line shows the contrary, when the source impedance relatively large, its waveform for the dwarf and wide flat waveform Figure 3 (b) shown in dotted line.
In addition to these typical converter will be a great number of harmonics, household appliances is not to be ignored harmonic sources. Such as television sets, battery chargers. Although their indivial capacity little, but because a lot of volume, they injected into the power supply system to the harmonic components can not be ignored.
2 harmonic hazards
Harmonic hazards of the public network include:
1) make a public network components have additional harmonic loss and rece the power generation, power transmission equipment efficiency, a large number of 3rd harmonic flow neutral line, the line will cause overheating or even a fire;
2) impact of the normal work of electrical equipment, in addition to additional wear and tear caused, and also enable a motor mechanical vibration, noise and over-voltage, transformer partial serious overheating, capacitors, cables and other equipment overheating, insulation aging, shortened life expectancy, resulting damage;
3) common cause in the local power grid and parallel resonant series resonance, so that harmonic magnification so that the aforementioned hazards greatly increase, or even lead to serious accidents;
4) will lead to protection and automatic device misoperation, and electrical measuring instrument measurement inaccurate;
5) to neighbouring interfere with communications systems, light, noise and lower the quality of communication, information led to heavy loss of the communications systems do not work properly.
3 harmonic management principles
To improve power quality, we must strengthen the management of the harmonics. In restricted to the utility grid harmonic source harmonic current injection, will be allowed to limit the harmonic voltage within the scope of the principle. First it is necessary to have systems in the harmonic sources and distribution, in the harmonic limit its scope in order to allow access, not curing the management measures must be taken to prevent the spread of harmonics. For this reason the International Electrotechnical Commission (IEC) and the United States have recommended IEEE standards such as IEEE provisions of the current standard harmonic limits shown in Table 1. China Power Grid with the actual level and the standard of other developed countries voltage distortion sine-rate provisions in table 2.
Table 1 harmonic current limits (IEEE519-1992 Provisions)
Isc / IL
H <11
11 <H
<17
17 <H
<23
23 <H
<35H
204.02.01.50.60.35.020-507.03.52.51.00.58.050-10010.04.54.01.50.712.0100-100012.05.55.02.01.015.0> 35THD <> 100015.07.06.02.51.420.0
Table 2 voltage distortion sine-rate limits
Supply voltage / kV voltage distortion sine-rate limits / or 0.3856% 1043531101.5
4 harmonic comprehensive management
At present, China's electric power system harmonics on the management is "pollution first, treatment after" the passive situation,
2. 英語教案
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向前地看
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students under teaching junior grade 2 （50 children）
teaching aids textbook board tape recorder with this lesson,'s record
lesson length one period (40min)
teaching material printed as the textbook shows
new words each volleyball ,.....
teaching procere
step 1 warm-up
sing a song or play a game what can you do i can paly badminton
step 2 leading-in
ask several students can you play volleyball , basketball
where do you play it
how do you play the ball?
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6. 英語教案設計
這個問題秒沉