【正文】 起動的電路和特性 a)電路圖 b)特性圖 1．起動過程如下： ① 串聯(lián)起動電阻 1aR 、 2aR 、 2aR 、 3aR 、 4aR 和 5aR 起動 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 13 起動前開關(guān) 1K 、 2K 、 3K 、 4K 和 5K 斷開，使得電樞電路中串入電阻 1aR 、2aR 、 3aR 、 4aR 和 5aR ，加上電樞電路自身電阻 aR ，電樞電路的總電阻為 543215 aaaaaa RRRRRRR ?????? 加上勵磁電壓 fU ，保 持勵磁電流 fI 為額定值不變，然后加上電樞電壓 aU ，這時電動機(jī)的機(jī)械特性如圖中的人為特性 m f 。 ④ 切除起動電阻 3aR 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 14 當(dāng)工作 點到達(dá) k 點，即電磁轉(zhuǎn)矩 T 等于切換轉(zhuǎn)矩 2T 時，再合上開關(guān) 3K ，切除起動電阻 3aR ，電樞電路的總電阻變?yōu)? 212 aaa RRRR ??? 這時電動機(jī)的機(jī)械特性變?yōu)槿藶樘匦?bjn0 ，切除 3aR 的瞬間，轉(zhuǎn)速來不及改變，工作點由 j 點平移到 c 點，使這時的電磁轉(zhuǎn)矩 T 仍等于 1T ，電動機(jī)繼續(xù)加速，工作點沿 c 點向 i 點移動。工作點由 h 點移到 a 點，最后穩(wěn)定在 g 點，至此，整個起動過程結(jié)束。 目前 MATLAB 產(chǎn)品族可以用來進(jìn)行： 數(shù)值分析、數(shù)值和符號計算、工程和科學(xué)繪圖、控制系統(tǒng)的設(shè)計與仿真、數(shù)字圖像處理、數(shù)字信號處理、通訊系統(tǒng)設(shè)計與仿真、財務(wù)與金融工程。利用 M 語言還開發(fā)了相應(yīng)的 MATLAB 專業(yè)工具箱函數(shù)供用戶直接使用。 SIMULINK 提供了利用鼠標(biāo)拖放的方法建立系統(tǒng)框圖模型的圖形界面，而且 SIMULINK 還提供了豐富的功能塊以及不同的專業(yè)模塊集合，利用 SIMULINK 幾乎可以做到不書寫一行代碼完成整個動態(tài)系統(tǒng)的建模工作。利用 RTW 生成的代碼簡潔、可靠、易讀。 另外， MATLAB 開放性的可擴(kuò)充體系允許用戶開發(fā)自定義的系統(tǒng)目標(biāo)，利用 RealTime Workshop Embedded Coder 能夠直接將 SIMULINK 的模型轉(zhuǎn)變成效率優(yōu)化的產(chǎn)品級代碼。 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 18 MATLAB 結(jié)合第三方軟硬件產(chǎn)品組成了在不同領(lǐng)域內(nèi)的完整解決方案，實現(xiàn)了從算法開發(fā)到實時仿真再到代碼生成與最終 產(chǎn)品實現(xiàn)的完整過程。除此之外， SIMULINLK 還支持 Stateflow，用來仿真事件驅(qū)動過程。用戶可以通過將塊組成子系統(tǒng)建立多級模型。仿真結(jié)果可以在運行的同時通過示波器或者圖形窗口顯示。 （ 5）專用模型庫 SIMULINLK 的模型庫可以通過專用元件集進(jìn)一步擴(kuò)展。 即在 MATLAB的命令窗口中直接鍵入如下命令： 如下圖便是 SIMULINLK 的模塊庫瀏覽器： SIMULINK 模塊庫瀏覽器主要用于瀏覽及選擇模塊。 繪制仿真線路 一．先打開 SIMULINLK 的模塊庫瀏覽器和模型編輯窗 ,默認(rèn)情況下模型名為“ Untitled”。 三．連接信號線。 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 22 圖 仿真線路圖 其中 Starter 模塊是封裝的子模塊，其內(nèi)部結(jié)構(gòu)如下圖。 2． Workspace I/O 頁，作用是管理模型從 MATLAB 工作空間的輸入和對它的輸出。然后選中模塊，右擊鼠標(biāo)，在彈出的快捷菜單中單擊 Block parameters 選項，即可打開該模塊的參數(shù)設(shè)置對話框。 一．電流與轉(zhuǎn)速關(guān)系仿真結(jié)果： 圖 電流與轉(zhuǎn)速關(guān)系仿真結(jié)果圖 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 24 由電流與轉(zhuǎn)速關(guān)系仿真結(jié)果可看出電流 Ia 與轉(zhuǎn)速 w 成線性關(guān)系變化，當(dāng)電流 Ia 增大時，會促使反電動勢增加，因此轉(zhuǎn)速 w 隨之增大，起動后達(dá)到穩(wěn)定。此外由于啟動級數(shù)較多，轉(zhuǎn)速上升較為平穩(wěn)。這說明了本方法的有效性。 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 26 總結(jié) 本篇論文主要討論了基于 MATLAB 的直流電機(jī)分級起動過程模擬。最后是對整個設(shè)計論文的修改與整理。電機(jī)與拖動基礎(chǔ)。而這些應(yīng)該歸功于我的學(xué)校。在 朱 老師的悉心指導(dǎo)下，我對畢業(yè)設(shè)計的認(rèn)識從一團(tuán)糟到有了初步的認(rèn)識到明確了任務(wù)目標(biāo)，再到基本工作的組織和完成以及對工作任務(wù)的檢查和整理。 an electrical power source is connected to the rotor coil through the mutator and its brushes, causing current to flow in it, producing electromagism. The mutator causes the current in the coils to be switched as the rotor turns, keeping the magic poles of the rotor from ever fully aligning with the magic poles of the stator field, so that the rotor never stops (like a pass needle does) but rather keeps rotating indefinitely (as long as power is applied and is sufficient for the motor 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 30 to overe the shaft torque load and internal losses due to friction, etc.) Many of the limitations of the classic mutator DC motor are due to the need for brushes to press against the mutator. This creates friction. Sparks are created by the brushes making and breaking circuits through the rotor coils as the brushes cross the insulating gaps between mutator sections. Depending on the mutator design, this may include the brushes shorting together adjacent sections— and hence coil ends— momentarily while crossing the gaps. Furthermore, the inductance of the rotor coils causes the voltage across each to rise when its circuit is opened, increasing the sparking of the brushes. This sparking limits the maximum speed of the machine, as toorapid sparking will overheat, erode, or even melt the mutator. The current density per unit area of the brushes, in bination with their resistivity, limits the output of the motor. The making and breaking of electric contact also causes electrical noise , and the sparks additionally cause RFI. Brushes eventually wear out and require replacement, and the mutator itself is subject to wear and maintenance (on larger motors) or replacement (on small motors). The mutator assembly on a large machine is a costly element, requiring precision assembly of many parts. On small motors, the mutator is usually permanently integrated into the rotor, so replacing it usually requires replacing the whole rotor. Large brushes are desired for a larger brush contact area to maximize motor output, but small brushes are desired for low mass to maximize the speed at which the motor can run without the brushes excessively bouncing and sparking (parable to the problem of valve float in internal bustion engines).Small brushes are also desirable for lower cost. Stiffer brush springs can also be used to make brushes of a given mass work at a higher speed, but at the cost of greater friction losses (lower efficiency) and accelerated brush and mutator wear. Therefore, DC motor brush design entails a tradeoff between output power, speed, and efficiency/wear. Brushless DC motors Some of the problems of the brushed DC motor are eliminated in the brushless design. In this motor, the mechanical rotating switch or mutator/brush gear 安徽建筑大學(xué)畢業(yè)設(shè)計（論文） 31 assembly is replaced by an external electronic switch synchronised to the rotor39。 health. Brushless motors are usually used in small equipment such as puters and are generally used to get rid of unwanted heat. They are also very quiet motors which is an advantage if being used in equipment that is affected by vibrations. Modern DC brushless motors range in power from a fraction of a watt to many kilowatts. Larger brushless motors up to about 100 kW rating are used in electric vehicles. They also find significant use in highperformance electric model aircraft. Coreless or ir。s bearings. Without a