【正文】 可以考慮基頻以下和基頻以上兩種情況。當(dāng)電動勢值較高時，可以忽略定子繞組的漏磁阻抗壓降，認為定子相電壓約等于，則/=常值，即恒壓頻比的控制方式。圖61 異步電動機變頻調(diào)速的控制特性把基頻以下和基頻以上兩種情況的控制特性畫在圖61上。在基頻以下，磁通恒定時轉(zhuǎn)矩也恒定，屬于“恒轉(zhuǎn)矩調(diào)速”，在基頻以上，轉(zhuǎn)速升高時轉(zhuǎn)矩降低，屬于“恒功率調(diào)速”。但是由于同步電動機的轉(zhuǎn)子結(jié)構(gòu)與異步電動機不同，其矢量坐標(biāo)變換有自己的特點，這些主要特點是：定子有三相交流繞組，轉(zhuǎn)子為直流勵磁或永磁。忽略阻尼繞組的效應(yīng)。暫先忽略定子電阻和漏抗的影響。圖62 二極同步電動機的物理模型圖中，定子三相繞組軸線A、B、C是靜止的，三相電壓、和三相電流、都是平衡的，轉(zhuǎn)子以同步轉(zhuǎn)速旋轉(zhuǎn)，轉(zhuǎn)子上的勵磁繞組在勵磁電壓供電下流過勵磁電流。在同步電動機中，除轉(zhuǎn)子直流勵磁外，定子磁動勢還產(chǎn)生電樞反應(yīng)，直流勵磁與電樞反應(yīng)合成起來產(chǎn)生氣隙磁通，合成磁通在定子中敢于的電動勢與外加電壓基本平衡。圖63 磁動勢和磁通的空間矢量圖圖64 電壓、電流和磁鏈的時間向量圖圖64畫出了定子一相繞組的電壓、電流與磁鏈的時間相量圖。加入了矢量運算器，用來控制同步電動機的定子電流和勵磁電流，即可實現(xiàn)同步電動機的矢量控制，其原理如圖65所示。圖65 同步電動機基于電流模型的矢量控制系統(tǒng)根據(jù)機電能量轉(zhuǎn)換原理，同步電動機的電磁轉(zhuǎn)矩可以表達為：旋轉(zhuǎn)磁動勢幅值：整理以后得其中，上式表明，經(jīng)矢量分解后，同步電動機的轉(zhuǎn)矩公式獲得了和直流電動機轉(zhuǎn)矩一樣的表達式。如圖65所示，同步電動機矢量控制系統(tǒng)采用了和直流電動機調(diào)速系統(tǒng)相似的雙閉環(huán)控制結(jié)構(gòu)。與此同時，乘以系數(shù)即得合成勵磁電流的給定信號，另外，按功率因數(shù)要求還可得定子電流勵磁分量給定信號。通過ACR和AFR實行電流閉環(huán)控制，可使實際電流、以及跟隨其給定值變化，獲得良好的動態(tài)性能。第七章 Auto CAD 2004繪圖 CAD簡介Auto CAD是由美國Autodesk公司開發(fā)的大型計算機輔助繪圖軟件，主要用來繪制工種圖樣。當(dāng)前Auto CAD已經(jīng)廣泛應(yīng)用于機械、電子、服裝、建筑等設(shè)計領(lǐng)域。作為一個通用的工種設(shè)計平臺，Auto CAD還擁有強大的人機交互能力和簡便的操作方法，十分方便廣大普通用戶，下面介紹一下Auto CAD的主要功能。精確定位定形功能：Auto CAD提供了坐標(biāo)輸入、對象捕捉、柵格捕捉、追蹤等功能，利用這些功能可以精確地為圖形對象定位和定形。圖形輸出功能：圖形輸出包括屏幕顯示和打印出圖，Auto CAD提供了方便的縮放和平移等屏幕顯示工具，模型空間、圖紙空間、布局、發(fā)布和打印等功能極大地豐富了出圖選擇。 輔助設(shè)計功能：可以查詢繪制好的圖形的長度、面積、體積和力學(xué)性能等；提供多種軟件的接口，可方便地將設(shè)計數(shù)據(jù)和圖形在多個軟件中共享，進一步發(fā)揮各軟件的特點和優(yōu)勢。通過DXF、IGES等圖形數(shù)據(jù)接口，可以實現(xiàn)Auto CAD和其他系統(tǒng)的集成。在實際工作生產(chǎn)中，設(shè)計師會利用已有的定子沖片圖設(shè)計電機繞組，主要是因為這樣可以有效的節(jié)省設(shè)計步驟，充分的利用已有資源。圖71 定子沖片圖跟定子沖片圖一樣，在實際工作生產(chǎn)中，設(shè)計師會利用已有的轉(zhuǎn)子沖片圖設(shè)計電機繞組，主要是因為這樣可以有效的節(jié)省設(shè)計步驟，充分的利用已有資源。圖72 轉(zhuǎn)子沖片圖在設(shè)計電機繞組完成以后，根據(jù)設(shè)計結(jié)果需要畫出繞組圖。因此必須全面地、綜合地看問題，并能因時因地制宜，針對具體情況采取不同的解決方案。 通過這次畢業(yè)設(shè)計，尤其在手工核算過程中，我重新溫習(xí)了關(guān)于《電機學(xué)》、《電機設(shè)計》等方面的知識，加強了自己較為薄弱的基礎(chǔ)知識。手工核算主要的目的主要是使我們熟悉電機設(shè)計的一般步驟、程序，對電機各參量的相互聯(lián)系有更實際的認識，為下一步的優(yōu)化設(shè)計打下基礎(chǔ)。經(jīng)過這一個學(xué)期的做畢業(yè)設(shè)計的過程。作為一名工科的學(xué)生，我更深深地體會到知識更新、學(xué)無止境的重要性，因此，在今后的工作和生活當(dāng)中，將不斷地積極求學(xué)進取，生命不息，讀書不止，這樣才能豐富和完善自己。致謝本次畢業(yè)設(shè)計歷時三個多月，從選題、開題報告、復(fù)算過程到CAD繪制沖片圖、繞組圖，完成論文。本次畢業(yè)設(shè)計的完成過程中，還得到了黃教授門下研究生王愛鳳學(xué)姐的幫助，在此一并表示感謝。(2) ia0, ib0 and ic0。(4) ia0, ib0 and ic0。(6) ia0, ib0 and ic0.It is very important and difficult to detect the zerocross point or the polarity of each phase , if the zerocross point is detect directly through A/D converter of DSP or MCU, bigger measurement deviation will be led especially under the condition of small current, which will result in bigger deadtime pensation deviation and also affect the result of deadtime pensation. Therefore, this paper adopts an indirectly method to detect the zerocross point of phase current, which is based on the current vector angle φ in the twophase static reference frame.For convenient analysis and illustration, place the threephase currents ia, ib, ic in the threephase static reference frame and the two current ponents iα , iβ of the current vector in the twophase static reference frame into the same figure, which is shown in . According to the polarity of threephase currents ia, ib, ic, the iα iβ plane in the twophase static reference frame can be divided into six sectors: I(1), II(2), III(3), IV(4), V(5) and VI(6). For each sector in the iαiβ plane, there is a corresponding deadtime pensation rule. In other words, once the sector which the current vector belongs to is known, the deadtime effect can be pensated according to the corresponding pensation , recognizing the sector number of the current vector is the key problem. In this paper, the sector number is determined by thecurrent vector angle φ which can be calculated through the α and β axis ponents of the stator current vector. Equation (1) shows the calculation method of the current vector φ, and equation (2) shows the relationship between the sector number and the current vector φ. φ=kπ+arctan（iβ/iα） (k = 0,1). Current Polarity and Current Vector Angle ?TABLE IDEADTIME COMPENSATION RULES TABLE OF SVPWM(2)For threephase voltage source inverter, the essence of deadtime pensation is to pensating the voltage deviation. However, in the digital motor driving and control system, voltage regulation is implemented through pulse width modulation, that is, through regulating the duty cycle of voltage pulse which has something to do with the pulse width T in one PWM period Tpwm. Therefore, in fact it is the pulse width T that is pensated in the practical application. TABLE I shows the deadtime pensation rules corresponding with the polarity of threephase currents ia,ib,ic and the sector number of the current vector in the iαiβ plane. It can be seen that for different sectors of the iαiβ plane, the pensation values are correspondingly different. In one word, the proposed deadtime pensation method can be carried out through the following steps:(1) Calculate the current vector angle φ through the α and β axis ponents of the stator current vector in the twophase static reference frame according to equation (1).(2) Determine the sector number through the current vector angle φ according to equation (2).(3) Execute the deadtime pensation algorithm according to the pensation rules table TABLE I.III. EXPERIMENTSIn order to test and verify the proposed deadtime pensation method of SVPWM, experiments are established and made. The experiment system consists of PMSM, threephase voltage source inverter, control platform, dynamometer, heat dissipation system, et type of IGBT in the inverter is CM600DY24A produced by Mitsubishi. The control platform is based on DSP TMS320F2812 produced by Texas is a special motor control DSP which has many advantages and can implement highperformance motor control such as FOC (Field Oriented Control) and DTC (Direct Torque Control). The main parameters of the control objectPMSM used in experiments are listed in TABLE II.For different pulse width pensation values of , and , the deadtime pensation experiments are all made. shows the experiment waveforms of threephase stator currents and the sector number of stator current vector for different pulse width pensation values, and shows the corresponding frequency spectrums.TABLE IIMAIN PARAMETERS OF PMSM USED