基于sg3525設(shè)計(jì)單相正弦波spwm逆變電源外文翻譯-wenkub
2022-09-16 14:21:25 本頁面
【正文】 nce voltage, which is set manually or electronically to the desired output. If there is an error in the output voltage, the feedback circuit pensates by adjusting the timing with which the MOSFETs are switched on and off. This part of the power supply is called the switching regulator. The Chopper controller shown in the block diagram serves this purpose. Depending on design/safety requirements, the controller may or may not contain an isolation mechanism (such as optocouplers) to isolate it from the DC output. Switching supplies in puters, TVs and VCRs have these optocouplers to tightly control the output voltage.Openloop regulators do not have a feedback circuit. Instead, they rely on feeding a constant voltage to the input of the transformer or inductor, and assume that the output will be correct. Regulated designs pensate for the parasitic capacitance of the transformer or coil. Monopolar designs also pensate for the magnetic hysteresis of the core.The feedback circuit needs power to run before it can generate power, so an additional nonswitching powersupply for standby is added.Transformer designSMPS transformers run at high frequency. Most of the cost savings (and space savings) in offline power supplies e from the fact that a high frequency transformer is much smaller than the 50/60 Hz transformers formerly used.There are several differences in the design of transformers for 50 Hz vs 500 kHz. Firstly a low frequency transformer usually transfers energy through its core (soft iron), while the (usually ferrite) core of a high frequency transformer limits leakage. Since the waveforms in a SMPS are generally high speed (PWM square waves), the wiring must be capable of supporting high harmonics of the base frequency due to the skin effect, which is a major source of power loss.Power factorSimple offline switched mode power supplies incorporate a simple full wave rectifier connected to a large energy storing capacitor. Such SMPSs draw current from the AC line in short pulses when the mains instantaneous voltage exceeds the voltage across this capacitor. During the remaining portion of the AC cycle the capacitor provides energy to the power supply.As a result, the input current of such basic switched mode power supplies has high harmonic content and relatively low power factor. This creates extra load on utility lines, increases heating of the utility transformers and standard AC electric motors, and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed through the use of filter banks but the filtering is expensive, and the power utility may require a business with a very low power factor to purchase and install the filtering onsite.In 2001 the European Union put into effect the standard IEC/EN6100032 to set limits on the harmonics of the AC input current up to the 40th harmonic for equipment above 75 W. The standard defines four classes of equipment depending on its type and current waveform. The most rigorous limits (class D) are established for personal puters, puter monitors, and TV receivers. In order to ply with these requirements modern switchedmode power supplies normally include an additional power factor correction (PFC) stage.Putting a current regulated boost chopper stage after the offline rectifier (to charge the storage capacitor) can help correct the power factor, but increases the plexity (and cost).Quasiresonant ZCS/ZVSA quasiresonant ZCS/ZVS switch (Zero Current/Zero Voltage) is a design where each switch cycle delivers a quantized 39。它的開關(guān)在一個(gè)非常高的頻率（幾十甚至幾百千赫）比交流的頻率要高，相當(dāng)于變壓器，可充當(dāng)遠(yuǎn)距離傳輸電源。其他優(yōu)勢(shì)包括更小的尺寸和較輕的重量（從消除低頻變壓器具有高體重）和低熱量的產(chǎn)生，還有更高的效率。更確切地可將其稱為電源轉(zhuǎn)換器，但可長時(shí)間不間斷使用。這是一個(gè)較大的特點(diǎn)，這類產(chǎn)品允許用電范圍從120V到240V。特別控制技術(shù)可以采用下列開關(guān)電源，以迫使平均輸入電流跟蹤正弦形狀的交流輸入電壓，因此，設(shè)計(jì)師應(yīng)設(shè)法糾正功率因數(shù)。然而，這種類型的使用可能有害整流階段，因?yàn)樗荒芾枚O管整流的滿負(fù)荷的一半。在高功率開關(guān)模式電源 ，有些可以作為自動(dòng)開關(guān)來使用。開關(guān)是實(shí)施一個(gè)
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