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1、 電氣信息工程學(xué)院 畢業(yè)設(shè)計（論文）外文翻譯外文資料名稱： Pulse width modulation 專 業(yè)： 通信工程 姓 名： 姜 芳 學(xué) 號： 10-2-07 指 導(dǎo) 教 師： 危厚琴 二一四年三月二十八日 Pulse width modulation Pulse Width Modulation (PWM), which is English Pulse Width Modulation abbreviation, referred to as Pulse Width Modulation, is to use. The microprocessor The digital out
2、put to analog circuits to control a very effective technology, widely used in from measurement, communication to power control and transform in many areas. Pulse width modulation is a kind of analog control mode, its according to the corresponding changes in load modulation transistor base or MOS tu
3、beGate bias, to achieve or MOS transistor conduction time change, so as to realize the change of a switching power supply output. This way can make the output of the power supply voltage changes in working conditions remain constant, is to use The microprocessorThe digital signal Analog circuitTo co
4、ntrol a very effective technique. PWM control technologyWith its control is simple, flexible and dynamic response good advantage and become Power electronic technologyThe most widely used control method, also is the people research hot spot .Due to the development of science and technology today has
5、 no boundary between disciplines, combination Modern control theoryIdeas or without resonant wave switch technology will become one of the main development direction of PWM control technology.Background Appeared with the development of electronic technology, a variety of PWM techniques, including: p
6、hase voltage PWM control, pulse width PWM method, random PWM, SPWM method, line voltage PWM control, etc., and in the nimh batteries using the pulse width of the PWM method in intelligent charger, it is to put eachpulseEqual pulse width are listed as a PWM waveform, by changing the cycle can be freq
7、uency modulation pulse train, or change the pulse widthDuty ratioCan regulating, adopt appropriate coordination control method can make the voltage and frequency change.Can adjust the PWM cycle, through the PWM duty cycle and achieve the purpose of control the charging current.The value of the analo
8、g signal can be continuous change, its time and amplitude resolution without restrictions.9 v battery is an analog device, because of its output voltage is not exactly equal to 9 v, but to change over time, and recommend any real value.Similarly, absorb the current from the battery is not limited in
9、 the range of a set of possible values.Analog signals and digital signals differ in that the latter usually only belongs to the predetermined value within a set of possible value, for example in the 0 v, 5 v in the collection value.Analog voltage and current can be directly used for control, such as
10、 to control the volume of the car radio.In the simple simulation of the radio, the volume knob is connected to a variable resistance.Turn the knob, resistance becomes large or small;Through the resistance of the current also will increase or decrease, which changes the drive the speakers current val
11、ue, make corresponding volume become bigger or smaller.Just like the radio, the output of the analog circuit with the input into a linear scale. Although the simulation control may seem intuitive and simple, but it is not always very feasible or economy.One is, the analog circuit is easy to drift ov
12、er time, and therefore difficult to adjust.To solve the problem of precision analog circuits can be very large and bulky (such as old-fashioned family stereo equipment) and expensive.Analog circuits may be severe fever, its power consumption relative to the work device is directly proportional to th
13、e product of the voltage and current on both ends.Analog circuits may also is very sensitive to noise, any disturbance or noise are sure to change the size of the current value.By digitally controlled analog circuits, can greatly reduce the system cost and power consumption.In addition, many micro c
14、ontroller andDSPAre already in the chip contains a PWM controller, this makes the realization of the digital control much easier.The basic principle of Basic principle of pulse width modulation (PWM) : control mode is to control the inverter circuit switching device on and off, make the output end t
15、o get a series of pulse amplitude is equal, using these pulse waveform instead of a sine wave or need.Also is in produce multiple pulse output waveform of half a cycle, make all kinds of the pulse equivalent voltage sine waveform, the output of the obtained smooth and low order harmonics.According t
16、o certain rules of the pulse width modulation, can change the size of the inverter circuit output voltage, also can change the output frequency. For example, the half sine wave shape is divided into N equal parts, can see the sine half-wave as composed of N connected to the pulse waveform.The pulse
17、width is equal, is equal to the / n, but amplitude, and pulse at the top is not straight and level, but a curve, the pulse amplitude according to the sine law of change.If the above with the same number of continuous and pulse sequence instead of wide range of rectangular pulse sequence, make the mi
18、dpoint of the halfway point of the rectangular pulse and the corresponding sine divisions, and make a rectangular pulse and the corresponding sine equal section area (impulse), get a set of pulse sequence, it isPWM waveform.It can be seen that the pulse width is according to the sine law of change.A
19、ccording to the principle of equal impulse effect is the same, the PWM wave and sine half-wave are equivalent.For sine negative half cycle, can also use the same method for PWM waveform.In PWM waveform, the amplitude of the pulse is equal, to the equivalent output sine wave amplitude is changed, as
20、long as the same proportion coefficient change the width of each pulse, therefore in cross - straight - to pay frequency converter, rectifier circuit with uncontrollable diode circuit, PWM pulse voltage is dc side of the inverter circuit output voltage amplitude.Based on the above principle, this pa
21、per in the sine wave frequency, amplitude and pulse number after half a cycle, PWM waveform of the pulse width and interval can be calculated accurately.According to the control circuit of the calculation results of the switch on and off of the device, you can get the required PWM waveform.The speci
22、fic processPulse width modulation (PWM) is an analog signallevel digitally coding Methods.Through high resolution counter The use of Square wave the Duty ratiobe modulation Used for a specific analog signallevelCoding.PWM signalIs still the number, because in any given moment, full of amplitude of t
23、he dc power supply or completely (ON), or completely without (OFF).Voltage or current source is a pass (ON) or OFF (OFF) to repeatpulseSequence is added to the simulation of the load up.Tong is when the dc power supply was added to the load, is broken when power supply was disconnected.As long as en
24、ough bandwidth, any analog value can use PWM coding.Most of the load (whether inductive or capacitive load load) need modulation frequency is higher than 10 hz, usually modulation frequency of 1 KHZ to 200 KHZ.Many internal micro controller contains a PWM controller.PIC16C67 Microchip company, for e
25、xample, it contains two PWM controller, and each one can choose to turn on time and cycle.Duty ratio is the turn on time and the ratio of the cycle;The reciprocal of frequency modulation period.Perform PWM before operation, the microprocessor in the software required for the following work:1, the se
26、t provides a square waveThe timer/ counter cycle2, set in the PWM control register on time3, set the direction of the PWM output, the output is a generalI/Opin4, start the timer5, can make the PWM controllerAdvantagesAn advantage of PWM is from the processor toControlled systemSignals are digital fo
27、rm, the need forD/a conversion.Keep signals into digital form to minimize noise.Noise only in strong enough to logic 1 change to logic 0 or logic 0 for the logic 1, also can affect the digital signal.To the noise resistance ability enhancement is PWM another advantage compared with the simulation co
28、ntrol, and its will be the main cause of PWM are used for communication in some time.From analog signal to the PWM can greatly extend the communication distance.At the receiving end, through properRCorLCNetwork can filter out high frequency square wave modulation and signal to analog form.In short,
29、the economy of PWM, saving space, strong antinoise performance, is a worthy of the engineers in many effective technology used in the design application.The specific application (1) PWM method to control the charging current software:The basic idea of this method is to use single chip microcomputer
30、with PWM port, under the premise of without changing PWM square-wave cycle, adjust the micro controller PWM control register by using the method of software to adjust the PWM duty cycle, so as to control the charging current.This method is required and must have the ADC port MCU PWM port these two c
31、onditions must be, in addition to the digits as far as possible high ADC, MCU work fast as possible.Before adjust the charging current, single chip microcomputer to quickly read the size of the charging current, then set the charging current and the actual reading of the charging current, if the act
32、ual current is small to increase the charging current adjustment in the direction of the PWM duty cycle;If the actual current is big, to reduce the charging current adjustment in the direction of the PWM duty cycle.Should pay attention to in the process of the adjustment of the software PWM ADC read
33、ing error introduced and power supply voltage ripple interference, reasonable use the digital filtering technique such as arithmetic average method.(2) PWM in the application of thrust modulation:In 1962, Nicklas and so on, proposed the theory of pulse modulation is pointed out that using the jet pu
34、lse is simple and effective control scheme for spacecraft control, at the same time can make the time or energy to achieve optimal control.PWM motor control mode is in each pulse cycle, by changing the time duration of the valve in the open or closed position to alter the flow through the valve of t
35、he gas flow, which changes the total thrust effect, for mass flow rate of the same system, can get through itPulse width modulation technologyTo obtain the effect of the variable thrust.Pulse width modulation usually 15, there are two ways: the first kind of pulse width modulation (PWM), for whole t
36、o controller design of controlled objects, and according to the control requirements of the force size, on the wholeThe system modelMathematical calculating dynamic transformation, and the fixed power output should be continuous function of time and start time;The second as the pulse width modulator
37、, regardless of the control object model, but according to the input attenuation dynamic accumulation, and then after some algorithm transform, determine the duration of the output.This way is very simple, and can achieve same output function approximation.Pulse width modulation control technology o
38、f simple structure, easy to implement, technology is mature,RussiaHas successfully applied its remote rockets point of viewA stable systemIn the control.But when the modulation quantity is zero, positive and negative to cancel out the control function of the control efficiency was obviously lower th
39、an that of variable flow rate systems.And the system response has certain hysteresis, its frequency must be greater than the switchKKVItself inherent frequency, otherwise not only not modulation effect, even catastrophic consequences.(3) In the application of the LED:In LED control PWM function in p
40、ower supply section, PWM pulse frequency is usually greater than 100 hz, the eye wont be shine.脈沖寬度調(diào)制 脈沖寬度調(diào)制(PWM)，是英文“Pulse Width Modulation”的縮寫，簡稱脈寬調(diào)制，是利用微處理器的數(shù)字輸出來對模擬電路進(jìn)行控制的一種非常有效的技術(shù)，廣泛應(yīng)用在從測量、通信到功率控制與變換的許多領(lǐng)域中。脈沖寬度調(diào)制是一種模擬控制方式，其根據(jù)相應(yīng)載荷的變化來調(diào)制晶體管基極或MOS管柵極的偏置，來實(shí)現(xiàn)晶體管或MOS管導(dǎo)通時間的改變，從而實(shí)現(xiàn)開關(guān)穩(wěn)壓電源輸出的改變。這種方式能使電源的
41、輸出電壓在工作條件變化時保持恒定，是利用微處理器的數(shù)字信號對模擬電路進(jìn)行控制的一種非常有效的技術(shù)。 PWM控制技術(shù)以其控制簡單，靈活和動態(tài)響應(yīng)好的優(yōu)點(diǎn)而成為電力電子技術(shù)最廣泛應(yīng)用的控制方式，也是人們研究的熱點(diǎn)。由于當(dāng)今科學(xué)技術(shù)的發(fā)展已經(jīng)沒有了學(xué)科之間的界限，結(jié)合現(xiàn)代控制理論思想或?qū)崿F(xiàn)無諧振波開關(guān)技術(shù)將會成為PWM控制技術(shù)發(fā)展的主要方向之一。 背景介紹 隨著電子技術(shù)的發(fā)展，出現(xiàn)了多種PWM技術(shù)，其中包括：相電壓控制PWM、脈寬PWM法、隨機(jī)PWM、SPWM法、線電壓控制PWM等，而在鎳氫電池智能充電器中采用的脈寬PWM法，它是把每一脈沖寬度均相等的脈沖列作為PWM波形，通過改變脈沖列的周期可以調(diào)
42、頻，改變脈沖的寬度或占空比可以調(diào)壓，采用適當(dāng)控制方法即可使電壓與頻率協(xié)調(diào)變化。可以通過調(diào)整PWM的周期、PWM的占空比而達(dá)到控制充電電流的目的。 模擬信號的值可以連續(xù)變化，其時間和幅度的分辨率都沒有限制。9V電池就是一種模擬器件，因?yàn)樗妮敵鲭妷翰⒉痪_地等于9V，而是隨時間發(fā)生變化，并可取任何實(shí)數(shù)值。與此類似，從電池吸收的電流也不限定在一組可能的取值范圍之內(nèi)。模擬信號與數(shù)字信號的區(qū)別在于后者的取值通常只能屬于預(yù)先確定的可能取值集合之內(nèi)，例如在0V,5V這一集合中取值。模擬電壓和電流可直接用來進(jìn)行控制，如對汽車收音機(jī)的音量進(jìn)行控制。在簡單的模擬收音機(jī)中，音量旋鈕被連接到一個可變電阻。擰動旋鈕時
43、，電阻值變大或變??；流經(jīng)這個電阻的電流也隨之增加或減少，從而改變了驅(qū)動揚(yáng)聲器的電流值，使音量相應(yīng)變大或變小。與收音機(jī)一樣，模擬電路的輸出與輸入成線性比例。 盡管模擬控制看起來可能直觀而簡單，但它并不總是非常經(jīng)濟(jì)或可行的。其中一點(diǎn)就是，模擬電路容易隨時間漂移，因而難以調(diào)節(jié)。能夠解決這個問題的精密模擬電路可能非常龐大、笨重（如老式的家庭立體聲設(shè)備）和昂貴。模擬電路還有可能嚴(yán)重發(fā)熱，其功耗相對于工作元件兩端電壓與電流的乘積成正比。模擬電路還可能對噪聲很敏感，任何擾動或噪聲都肯定會改變電流值的大小。通過以數(shù)字方式控制模擬電路，可以大幅度降低系統(tǒng)的成本和功耗。此外，許多微控制器和DSP已經(jīng)在芯片上包含了
44、PWM控制器，這使數(shù)字控制的實(shí)現(xiàn)變得更加容易了。 基本原理 脈寬調(diào)制（PWM）基本原理：控制方式就是對逆變電路開關(guān)器件的通斷進(jìn)行控制，使輸出端得到一系列幅值相等的脈沖，用這些脈沖來代替正弦波或所需要的波形。也就是在輸出波形的半個周期中產(chǎn)生多個脈沖，使各脈沖的等值電壓為正弦波形，所獲得的輸出平滑且低次諧波少。按一定的規(guī)則對各脈沖的寬度進(jìn)行調(diào)制，即可改變逆變電路輸出電壓的大小，也可改變輸出頻率。例如，把正弦半波波形分成N等份，就可把正弦半波看成由N個彼此相連的脈沖所組成的波形。這些脈沖寬度相等，都等于 /n ，但幅值不等，且脈沖頂部不是水平直線，而是曲線，各脈沖的幅值按正弦規(guī)律變化。如果把上述脈沖
45、序列用同樣數(shù)量的等幅而不等寬的矩形脈沖序列代替，使矩形脈沖的中點(diǎn)和相應(yīng)正弦等分的中點(diǎn)重合，且使矩形脈沖和相應(yīng)正弦部分面積（即沖量）相等，就得到一組脈沖序列，這就是PWM波形?？梢钥闯?，各脈沖寬度是按正弦規(guī)律變化的。根據(jù)沖量相等效果相同的原理，PWM波形和正弦半波是等效的。對于正弦的負(fù)半周，也可以用同樣的方法得到PWM波形。 在PWM波形中，各脈沖的幅值是相等的，要改變等效輸出正弦波的幅值時，只要按同一比例系數(shù)改變各脈沖的寬度即可，因此在交直交變頻器中，整流電路采用不可控的二極管電路即可，PWM逆變電路輸出的脈沖電壓就是直流側(cè)電壓的幅值。根據(jù)上述原理，在給出了正弦波頻率，幅值和半個周期內(nèi)的脈沖數(shù)
46、后，PWM波形各脈沖的寬度和間隔就可以準(zhǔn)確計算出來。按照計算結(jié)果控制電路中各開關(guān)器件的通斷，就可以得到所需要的PWM波形.具體過程 脈沖寬度調(diào)制（PWM）是一種對模擬信號電平進(jìn)行數(shù)字編碼的方法。通過高分辨率計數(shù)器的使用，方波的占空比被調(diào)制用來對一個具體模擬信號的電平進(jìn)行編碼。PWM信號仍然是數(shù)字的，因?yàn)樵诮o定的任何時刻，滿幅值的直流供電要么完全有（ON），要么完全無（OFF）。電壓或電流源是以一種通（ON）或斷（OFF）的重復(fù)脈沖序列被加到模擬負(fù)載上去的。通的時候即是直流供電被加到負(fù)載上的時候，斷的時候即是供電被斷開的時候。只要帶寬足夠，任何模擬值都可以使用PWM進(jìn)行編碼。多數(shù)負(fù)載（無論是電感
47、性負(fù)載還是電容性負(fù)載）需要的調(diào)制頻率高于10Hz，通常調(diào)制頻率為1kHz到200kHz之間。許多微控制器內(nèi)部都包含有PWM控制器。例如，Microchip公司的PIC16C67內(nèi)含兩個PWM控制器，每一個都可以選擇接通時間和周期。占空比是接通時間與周期之比；調(diào)制頻率為周期的倒數(shù)。 執(zhí)行PWM操作之前，這種微處理器要求在軟件中完成以下工作：1、設(shè)置提供調(diào)制方波的片上定時器/計數(shù)器的周期2、 在PWM控制寄存器中設(shè)置接通時間3、設(shè)置PWM輸出的方向，這個輸出是一個通用I/O管腳4、啟動定時器5、使能PWM控制器優(yōu)點(diǎn) PWM的一個優(yōu)點(diǎn)是從處理器到被控系統(tǒng)信號都是數(shù)字形式的，無需進(jìn)行數(shù)模轉(zhuǎn)換。讓信號保
48、持為數(shù)字形式可將噪聲影響降到最小。噪聲只有在強(qiáng)到足以將邏輯1改變?yōu)檫壿?或?qū)⑦壿?改變?yōu)檫壿?時，也才能對數(shù)字信號產(chǎn)生影響。對噪聲抵抗能力的增強(qiáng)是PWM相對于模擬控制的另外一個優(yōu)點(diǎn)，而且這也是在某些時候?qū)WM用于通信的主要原因。從模擬信號轉(zhuǎn)向PWM可以極大地延長通信距離。在接收端，通過適當(dāng)?shù)腞C或LC網(wǎng)絡(luò)可以濾除調(diào)制高頻方波并將信號還原為模擬形式。 總之，PWM既經(jīng)濟(jì)、節(jié)約空間、抗噪性能強(qiáng)，是一種值得廣大工程師在許多設(shè)計應(yīng)用中使用的有效技術(shù)。具體應(yīng)用 (1) PWM軟件法控制充電電流:該方法的基本思想就是利用單片機(jī)具有的PWM端口，在不改變PWM方波周期的前提下，通過軟件的方法調(diào)整單片機(jī)的P
49、WM控制寄存器來調(diào)整PWM的占空比，從而控制充電電流。該方法所要求的單片機(jī)必須具有ADC端口和PWM端口這兩個必須條件，另外ADC的位數(shù)盡量高，單片機(jī)的工作速度盡量快。在調(diào)整充電電流前，單片機(jī)先快速讀取充電電流的大小，然后把設(shè)定的充電電流與實(shí)際讀取到的充電電流進(jìn)行比較，若實(shí)際電流偏小則向增加充電電流的方向調(diào)整PWM的占空比；若實(shí)際電流偏大則向減小充電電流的方向調(diào)整PWM的占空比。在軟件PWM的調(diào)整過程中要注意ADC的讀數(shù)偏差和電源工作電壓等引入的紋波干擾，合理采用算術(shù)平均法等數(shù)字濾波技術(shù)。 (2) PWM在推力調(diào)制中的應(yīng)用:1962年，Nicklas等提出了脈沖調(diào)制理論，指出利用噴氣脈沖對航天
50、器控制是簡單有效的控制方案，同時能使時間或能量達(dá)到最優(yōu)控制。脈寬調(diào)制發(fā)動機(jī)控制方式是在每一個脈動周期內(nèi)，通過改變閥門在開或關(guān)位置上 停留的時間來改變流經(jīng)閥門的氣體流量，從而改變總的推力效果，對于質(zhì)量流率不變的系統(tǒng)，可以通過脈寬調(diào)制技術(shù)來獲得變推力的效果。脈寬調(diào)制通常有兩種方法15：第一種為整體脈寬調(diào)制，對控制對象進(jìn)行控制器設(shè)計，并根據(jù)控制要求的作用力大小，對整個系統(tǒng)模型進(jìn)行動態(tài)的數(shù)學(xué)解算變換，得出固定力輸出應(yīng)該持續(xù)作用的時間和開始作用時間；第二種為脈寬調(diào)制器，不考慮控制對象模型，而是根據(jù)輸入進(jìn)行“動態(tài)衰減”性的累加，然后經(jīng)過某種算法變換后，決定輸出所持續(xù)的時間。這種方式非常簡單，也能達(dá)到輸出作用近似相同。脈寬調(diào)制控制技術(shù)結(jié)構(gòu)簡單、易于實(shí)現(xiàn)、技術(shù)比較成熟，俄羅斯已經(jīng)將其成功地應(yīng)用于遠(yuǎn)程火箭的角度穩(wěn)定系統(tǒng)控制中。但是當(dāng)調(diào)制量為零時，正反向的控制作用相互抵消，控制效率明顯比變流率系統(tǒng)低。而且系統(tǒng)響應(yīng)有一定的滯后，其開關(guān)的頻率必須遠(yuǎn)大于KKV本身的固有頻率，否則不但起不到調(diào)制效果，甚至?xí)l(fā)生災(zāi)難性后果。 (3) 在LED中的應(yīng)用:在LED控制中PWM作用于電源部分，脈寬調(diào)制的脈沖頻率通常大于100Hz，人眼就不會感到閃爍。
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