電氣專業(yè)畢業(yè)論文外文翻譯分析解析

1、本科畢業(yè)設計外文文獻及譯文文獻、資料題目：Designing Stable Control Loops文獻、資料來源：期刊文獻、資料發(fā)表（出版）日期：2010.3.25 院 （部）： 信息與電氣工程學院專 業(yè)： 電氣工程與自動化班 級： 姓 名： 學 號： 指導教師： 翻譯日期： 2011.3.10外文文獻：Designing Stable Control LoopsThe objective of this topic is to provide the designer with a practical review of loop compensation techniques appl

2、ied to switching power supply feedback control. A top-down system approach is taken starting with basic feedback control concepts and leading to step-by-step design procedures, initially applied to a simple buck regulator and then expanded to other topologies and control algorithms. Sample designs a

3、re demonstrated with Math cad simulations to illustrate gain and phase margins and their impact on performance analysis. I. INTRODUCTIONInsuring stability of a proposed power supply solution is often one of the more challenging aspects of the design process. Nothing is more disconcerting than to hav

4、e your lovingly crafted breadboard break into wild oscillations just as its being demonstrated to the boss or customer, but insuring against this unfortunate event takes some analysis which many designers view as formidable. Paths taken by design engineers often emphasize either cut-and-try empirica

5、l testing in the laboratory or computer simulations looking for numerical solutions based on complex mathematical models. While both of these approach a basic understanding of feedback theory will usually allow the definition of an acceptable compensation network with a minimum of computational effo

6、rt.II. STABILITY DEFINEDFig. 1. Definition of stabilityFig. 1 gives a quick illustration of at least one definition of stability. In its simplest terms, a system is stable if, when subjected to a perturbation from some source, its response to that perturbation eventually dies out. Note that in any p

7、ractical system, instability cannot result in a completely unbounded response as the system will either reach a saturation level or fail. Oscillation in a switching regulator can, at most, vary the duty cycle between zero and 100% and while that may not prevent failure, it wills ultimate limit the r

8、esponse of an unstable system.Another way of visualizing stability is shown in Fig. 2. While this graphically illustrates the concept of system stability, it also points out that we must make a further distinction between large-signal and small-signal stability. While small-signal stability is an im

9、portant and necessary criterion, a system could satisfy thisrt quirement and yet still become unstable with a large-signal perturbation. It is important that designers remember that all the gain and phase calculations we might perform are only to insure small-signal stability. These calculations are

10、 based upon and only applicable to linear systems, and a switching regulator is by definition a non-linear system. We solve this conundrum by performing our analysis using small-signal perturbations around a large-signal operating point, a distinction which will be further clarified in our design pr

11、ocedure discussion。Fig. 2. Large-signal vs. small-signal stabilityIII. FEEDBACK CONTROL PRINCIPLESWhere an uncontrolled source of voltage (or current, or power) is applied to the input of our system with the expectation that the voltage (or current, or power) at the output will be very well controll

12、ed. The basis of our control is some form of reference, and any deviation between the output and the reference becomes an error. In a feedback-controlled system, negative feedback is used to reduce this error to an acceptable value as close to zero as we want to spend the effort to achieve. Typicall

13、y, however, we also want to reduce the error quickly, but inherent with feedback control is the tradeoff between system response and system stability. The more responsive the feedback network is, the greater becomes the risk of instability. At this point we should also mention that there is another

14、method of control feedforward.With feed forward control, a control signal is developed directly in response to an input variation or perturbation. Feed forward is less accurate than feedback since output sensing is not involved, however, there is no delay waiting for an output error signal to be dev

15、eloped, andfeedforward control cannot cause instability. It should be clear that feed forward control will typically not be adequate as the only control method for a voltage regulator, but it is often used together with feedback to improve a regulators response to dynamic input variations.The basis

16、for feedback control is illustrated with the flow diagram of Fig. 3 where the goal is for the output to follow the reference predictably and for the effects of external perturbations, such as input voltage variations, to be reduced to tolerable levels at the output Without feedback, the reference-to

17、-output transfer function y/u is equal to G, and we can express the output asy = GuWith the addition of feedback (actually the subtraction of the feedback signal)y = Gu - yHGand the reference-to-output transfer function becomesy/u=G/1+GHIf we assume that GH _ 1, then the overall transfer function si

18、mplifies toy/u=1/HFig. 3. Flow graph of feedback controlNot only is this result now independent of G,it is also independent of all the parameters of the system which might impact G (supply voltage, temperature, component tolerances, etc.) and is determined instead solely by the feedback network H (a

19、nd, of course, by the reference).Note that the accuracy of H (usually resistor tolerances) and in the summing circuit (error amplifier offset voltage) will still contribute to an output error. In practice, the feedback control system, as modeled in Fig. 4, is designed so thatG _ H and GH _ 1 over as

20、 wide a frequency range as possible without incurring instability. We can make a further refinement to our generalized power regulator with the block diagram shown in Fig. 5. Here we have separated the power system into two blocks the power section and the control circuitry. The power section handle

21、s the load current and is typically large, heavy, and subject to wide temperature fluctuations. Its switching functions are by definition, large-signal phenomenon, normally simulated in most stability analyses as just a two states witch with a duty cycle. The output filter is also considered as a pa

22、rt of the power section but can be considered as a linear block. Fig. 4. The general power regulatorIV. THE BUCK CONVERTER The simplest form of the above general power regulator is the buck or step down topology whose power stage is shown in Fig. 6. In this configuration, a DC input voltage is switc

23、hed at some repetitive rate as it is applied to an output filter. The filter averages the duty cycle modulation of the input voltage to establish an output DC voltage lower than the input value. The transfer function for this stage is defined bytON=switch on -timeT = repetitive period (1/fs)d = duty

24、 cycleFig. 5. The buck converter. Since we assume that the switch and the filter components are lossless, the ideal efficiency ofThis conversion process is 100%, and regulation of the output voltage level is achieved bycontrolling the duty cycle. The waveforms of Fig.6 assume a continuous conduction

25、 mode (CCM)Meaning that current is always flowing through the inductor from the switch when it is closed,And from the diode when the switch is open. The analysis presented in this topic will emphasizeCCM operation because it is in this mode that small-signal stability is generally more difficultto a

26、chieve. In the discontinuous conduction mode (DCM), there is a third switch condition in which the inductor, switch, and diode currents are all 5-4 zero. Each switching period starts from the same state (with zero inductor current), thus effectively reducing the system order by one and making small-

27、signal stable performance much easier to achieve. Although beyond the scope of this topic, there may be specialized instances where the large-signal stability of a DCM system is of greater concern than small-signal stability. There are several forms of PWM control for the buck regulator including, F

28、ixed frequency (fS) with variable tON and variable tOFF Fixed tON with variable tOFF and variable fS Fixed tOFF with variable tON and variable fS Hysteretic (or “bang-bang”) with tON, tOFF, and fS all variable Each of these forms have their own set of advantages and limitations and all have been suc

29、cessfully used, but since all switch mode regulators generate a switching frequency component and its associated harmonics as well as the intended DC output, electromagnetic interference and noise considerations have made fixed frequency operation by far the most popular. With the exception of hyste

30、retic, all other forms of PWM control have essentially the samesmall-signal behavior. Thus, without much loss in generality, fixed fS will be the basis for our discussion of classical, small-signal stability. Hysteretic control is fundamentally different in that the duty factor is not controlled, pe

31、r se. Switch turn-off occurs when the output ripple voltage reaches an upper trip point and turn-on occurs at a lower threshold. By definition, this isa large-signal controller to which small-signal stability considerations do not apply. In a small signal sense, it is already unstable and, in a math

32、ematical sense, its fast response is due more to feed forward than feedback.REFERENCES1 D. M. Mitchell, “DC-DC Switching Regulator Analysis”, McGraw-Hill, 1988,DMMitchell Consultants, Cedar Rapids, IA, 1992(reprint version).2 D. M. Mitchell, “Small-Signal Mathcad Design Aids”, (Windows 95 / 98 versi

33、on), e/jBLOOM Associates, Inc., 1999.3 George Chryssis, “High-Frequency Switching Power Supplies”, McGraw-Hill BookCompany, 1984.4 Ray Ridley, “A More Accurate Current- Mode Control Model”, Unitrode SeminarHandbook, SEM-1300, Appendix A2.5 Lloyd Dixon, “Control Loop Design”, Unitrode Seminar Handboo

34、k, SEM-800.6 Lloyd Dixon, “Control Loop Design SEPIC Preregulator Design”, Unitrode SeminarHandbook, SEM-900, Topic 7.7 Lloyd Dixon, “Closing the Feedback Loop”, Unitrode Seminar Handbook, SEM-300.中文翻譯：控制電路設計摘要：本篇論文的寫作目的，是為給設計師們提供一個實際性的說明，那就是線性補償技術在電源轉換與電流反饋操作中是如何應用的。一個組織管理嚴密的系統(tǒng)電路需要一開始就有一個基礎的電流反饋操作理

35、論的支持，并且通過一步步的設計步驟，從初步階段應用到一個簡單升壓調節(jié)器，然后再擴展到其他的拓撲學與算數(shù)控制學中去。matchad模擬器也驗證了設計樣本中幅相裕度整定在分布設計中是存在的，并且還影響著實驗的分析報告。一、簡介：驗證所提議的電源供給解決方案的穩(wěn)定性，一直就是電路設計過程中一個極具挑戰(zhàn)性的方面。最讓你感到窘迫的，并不是你最為得意之作的電路板正在實驗的重要階段中，被突然闖入的無序振蕩所打亂，而是你實驗恰恰驗證了許多電路設計者感到最為頭疼的數(shù)據(jù)分析。電路設計師常常強調，在實驗室里要注重切換實驗的實用價值，或者是以復雜的數(shù)學模式為電腦集成系統(tǒng)所需要的數(shù)據(jù)處理。然而這兩者的方向都是以電路設計

36、的前提為基礎。于是，對反饋原理最基本的理解將幫助我們去定義接受性補償網(wǎng)系統(tǒng)的最小值計算范圍。二、穩(wěn)定性的界定：圖1 穩(wěn)定的定義 圖1直接展示了至少一個關于穩(wěn)定性的界定。用最簡潔的術語來說，如果一個電路系統(tǒng)是穩(wěn)定的，就算被從某些來源說產生的微擾所壓制時，返回的微擾的也將會一并抵消。需要注意的是，在任何實用電路中，不穩(wěn)定性不會導致一個完全無束縛的反應，這就如同電路既會達到飽和狀態(tài)也會處于缺損狀態(tài)一樣。正在調節(jié)器轉化過程中的振蕩極有可能在零和百分之一百間的負荷周期中波動，并且這種變化不可能阻止失敗，它將最終制約不穩(wěn)定電路的回流電。圖2 展示的是另外一個設想的穩(wěn)定性。盡管該圖形象地展示了電路穩(wěn)定性的觀

37、點，但與此同時，也指出了我們必須將大信號的穩(wěn)定性與小信號的穩(wěn)定性嚴格區(qū)分開來。然而小信號的穩(wěn)定性是一個非常重要和非常需要的判斷標準，一個電路也可以滿足這個要求，并且會與一個大信號的微擾一起變得不穩(wěn)定。重要的是，電路設計師們需要記得，所有我們可能執(zhí)行的幅相裕度整定計算僅僅只是確保了小信號的穩(wěn)定性。這些計算結果主要依靠并且只適用于線性電路，和一個轉換調節(jié)器被定義為非線性的電路。我們通過用圍繞小信號直流工作點周圍小信號的微擾，來演算我們的分析結果，去解決這個迷團。這之中的具體差別將會在接下來的設計過程的有關探討來說明。圖2 強信號和弱信號三、反饋電流控制原理：展示的是一個最基本的調節(jié)器，在這里，不受

38、控制的電壓來源（或者電流，或者功率）將會被應用到電路的輸入，且在輸出過程中被這個不受控制的電壓（電流或者功率）的預期值完全的掌控。電流控制的基礎是一些基準電壓的結構，任何在輸出電流和基準電壓之間的偏差都是會導致電路的錯誤。在一個反饋操作電路中，負反饋回流電是用來減少在可接受的標準內這種錯誤就如我們希望能從一開始付出努力，一直堅持到最后能成功一樣。然而，按照典型的案例來說，我們也希望讓錯誤不會那么快的發(fā)生，但是回流電控制電路本身就存在著頻率響應與電路穩(wěn)定性的互換?；亓麟娐返念l率響應越多，不穩(wěn)定的危險性就越大。在這一點上我們應該注意，另外一個控制方法前反饋。通過前反饋的控制，一個控制信號將被直接地

39、發(fā)展到去回應一個輸出波動或者微擾中。前反饋沒有回流電那么精準，因為檢測輸出電流不是那么復雜難懂，然而，無法否認的是，等待一個輸出電流的錯誤信號會被發(fā)現(xiàn)，而且前反饋控制無法產生不穩(wěn)定性。需要清楚表明的是，典型的前反饋控制將不像只有一個電壓調節(jié)器的控制線路那么有效，但是前反饋的控制經(jīng)常被用于和反饋一起去加快調節(jié)器對動態(tài)輸入變動的響應頻率。圖3中的電流圖闡述了反饋控制的基礎，目標就是為了輸出功率能跟著可以預測的基準電壓，為了將外部微擾的影響，如同輸出功率的變動一樣，能會被減少到輸出功率所能接受的等級上。圖3 反饋控制流圖如果沒有反饋電，基準電壓到輸出功率的轉換函數(shù)y/u就跟G是一樣的，我們可以這樣表

40、達輸出功率：y=Gu另外反饋電流（實際上是反饋信號的減法）：y = Gu - yHG之后r基準電壓與輸出功率的轉換函數(shù)：Y=Gu=1 + GH如果我們假設GH=1，那么整體的轉換函數(shù)就是： y/u=1/h這個函數(shù)不僅使得G現(xiàn)在成為獨立，它還使所有的電路參數(shù)都變得獨立，這這可能會影響G（供給功率、溫度、元件公差，等等）并且被只被回流電路H（并且，理所當然的，被基準電壓作用）所代替來決定它。值得一提的是，H的準確性（通常稱為電阻的公差）和電路的總和（錯誤放大補償功率）將繼續(xù)造成輸出電流的錯誤。在實際中，反饋控制電路，如圖4的模型所示，如此設計是為了使G ：H和GH=1的振動頻率能越大范圍越好并且不會產生任何不穩(wěn)定性。我們可以進一步的改良概括功率調節(jié)器就像圖4所見到的一樣。在這里我們有單獨分