【正文】 到相應(yīng)的低阻抗輸出。當(dāng)SD輸入高電平時兩路均關(guān)閉。高抗噪聲平移位電路將邏輯信號送到輸出驅(qū)動級。由于每個高電壓DMOS電平轉(zhuǎn)換器僅在 很狹窄的脈沖持續(xù)期內(nèi)才導(dǎo)通，所以功率很低。單片機(jī)選擇依據(jù)：(1)性能因素。(2)安全因素。 PIC單片機(jī)特點(diǎn)：PIC (Periphery Interface Chip)系列單片機(jī)是美國Microchip公司生產(chǎn)的產(chǎn)品。PIC系列單片機(jī)具有高，中，低3個檔次，可以滿足不同用戶開發(fā)的需求，適合在各個領(lǐng)域中的應(yīng)用。圖34 PIC系列單片機(jī)哈佛總線結(jié)構(gòu)(3) RISC技術(shù) RISC (Reduced Instruction Set Computer)是指精簡指令集計算機(jī)。(5)功耗低 由于PIC系列單片機(jī)采用CMOS結(jié)構(gòu)，使其功率消耗極低。(9)程序存儲器版本齊全Microchip公司提供的產(chǎn)品是一個單片機(jī)系列，可供選擇的存儲器類別和產(chǎn)品封裝工藝的形式較多，為產(chǎn)品的不同試驗(yàn)階段和不同應(yīng)用場合可提供一個全方位的選擇內(nèi)容和不同的性能檔次。電池欠壓信號：電池電壓經(jīng)分壓后接單片機(jī)管腳3。帶8位AID轉(zhuǎn)換輸入 8位定時器/計數(shù)器TMRO，帶8位預(yù)分頻 內(nèi)置上電復(fù)位電路(POR) 內(nèi)置自振式(RC振蕩)看門狗 在眾多的電樞電壓控制方法中，脈寬調(diào)制 PWM( PulseWidth Modulation)技術(shù)因?yàn)樾栌玫拇蠊β士煽仄骷?、線路簡單、調(diào)速范圍寬、電流波形系數(shù)好、附加損耗小、功率因數(shù)高的優(yōu)點(diǎn)，從而得到廣泛應(yīng)用。 時鐘電路 如圖35所示，單片機(jī)的10腳外接16Mhz晶體。2 剎車圖38 剎車圖電動自行車標(biāo)準(zhǔn)要求電動車在剎車制動時，控制器應(yīng)能自動切斷對電動機(jī)的供電。同時也有少數(shù)高檔車采用霍爾元件做開關(guān)，剎車時輸出高電平給控制器，實(shí)現(xiàn)剎車斷電功能，即高電位剎車，也稱之為電子剎把。面板顯示電路如圖39所示：圖39 面板顯示電路圖1 74LS164引腳圖74LS164為8位移位寄存器（串行輸入，并行輸出）圖310 74LS164引腳圖如圖310所示，當(dāng)清除端（CLEAR）為低電平時，輸出端（QA－QH）均為低電平。 引出端符號 CLOCK ：時鐘輸入端。但是，由于它采用的是雙極型熔絲工藝，一旦編程以后不能修改，因而不適應(yīng)研制工作中經(jīng)常修改電路的需要。按照霍爾器件的功能可將它們分為:霍爾線性器件和霍爾開關(guān)器件。此外，其工作溫度范圍寬，可達(dá)55 0C~150oC。轉(zhuǎn)子位置傳感器的主要技術(shù)指標(biāo)為：輸出信號的幅值、精度，響應(yīng)速度，工作溫度，抗干擾能力，損耗，體積重量，安裝方便性以及可靠性等。當(dāng)霍爾元件按要求通以電流并置于外磁場中，即輸出霍爾電勢信號，當(dāng)其不受外磁場作用時，其輸出端無信號。電角度，永磁體的極弧寬度為180176。電角的矩形波信號。圖312 霍爾元件式位置傳感器結(jié)構(gòu)（2）電磁式位置傳感器電磁式位置傳感器的定子由磁芯、高頻激磁繞組和輸出繞組組成。電磁式位置傳感器輸出信號較大，一般不需要經(jīng)過放大便可直接驅(qū)動開關(guān)管，但此輸出電壓是交流，必須先整流。遮光盤處于發(fā)光二極管和光敏三極管中間，盤上開有一定角度的窗口。它省去了轉(zhuǎn)子位置傳感器，因而電機(jī)結(jié)構(gòu)簡單、體積小、可靠性高。2 霍爾器件在無刷直流電機(jī)中的應(yīng)用當(dāng)霍爾傳感器用作無刷直流電機(jī)轉(zhuǎn)子位置信息檢測裝置時，將其安放在電機(jī)定子的適當(dāng)位置，霍爾器件的輸出與控制部分相連。電流信號經(jīng)過LM358放大，由單片機(jī)PIC16F72A/D通道RA1（管腳2）輸入，并進(jìn)行控制處理。電流采樣方式可采取直接采樣兩相電流的方法或采樣直流母線電流的方法?？紤]到本控制系統(tǒng)的成本問題，本系統(tǒng)采用第一種電流采樣方式。它的使用范圍包括傳感放大器、直流增益模塊和其他所有可用單電源供電的使用運(yùn)算放大器的場合。 電源電路圖317 電源電路圖如圖317所示，36V電池送入U1U1U15穩(wěn)壓器輸出+15V和+5V給PIC單片機(jī)和IR2110供電。欠壓檢測是根據(jù)需要設(shè)定欠壓值, 然后采樣當(dāng)前電源電壓, 若電壓低于設(shè)定值,則關(guān)閉輸出, 相反, 則進(jìn)行限流保護(hù)檢測。直流無刷電機(jī)的3個霍爾元件組合起來有8種狀態(tài), 其中6種是有效的, 對應(yīng)1個輸出的狀態(tài)。2 啟動理論上講, 轉(zhuǎn)子位置過磁場換相臨界點(diǎn)時, 電流換相的速度越快越好。設(shè)電動自行車運(yùn)行在最高速20km/s(這是國家法律規(guī)定的速度限制), , 。定時器在每個時間周期增加1。須注意對有的定時器計數(shù)值寄存器寫的時候, 會把預(yù)分頻值清除, 因此必須在寫計數(shù)值的同時重新寫預(yù)分頻值控制字。4 剎車控制剎車控制在主程序里面, 主程序時刻檢測剎車信號, 當(dāng)有剎車信號, 關(guān)斷波的輸出若沒有剎車信號, 根據(jù)轉(zhuǎn)把輸入的電壓, 控制波的輸出。軟件定時器根據(jù)調(diào)速要求產(chǎn)生直流斬波電壓，采用中斷方式運(yùn)行，改變斬波電壓只需在對應(yīng)單元寫入控制值。 本文所設(shè)計的基于PIC單片機(jī)的無刷直流電機(jī)控制器具有硬件結(jié)構(gòu)簡單、保護(hù)功能完善、軟件采用模塊化設(shè)計易于用戶二次開發(fā)等特點(diǎn)。致 謝在做畢業(yè)設(shè)計這段時間里，胡老師給了我很多指導(dǎo)和建議，讓我對無刷電機(jī)控制系統(tǒng)有了很多了解，并學(xué)到了很多對我有用的東西。 however, the windings are distributed in a different manner. Most BLDC motors have three stator windings connected in star fashion. Each of these windings are constructed with numerous coils interconnected to form a winding. One or more coils areplaced in the slots and they are interconnected to make a winding. Each of these windings are distributed over the stator periphery to form an even numbers of poles. There are two types of stator windings variants: trapezoidal and sinusoidal motors. This differentiation is made on the basis of the interconnection of coils in the stator windings to give the different types of back Electromotive Force (EMF). Refer to the “What Is Back EMF” section for more information.As their names indicate, the trapezoidal motor gives a back EMF in trapezoidal fashion and the sinusoidal motor!ˉs back EMF is sinusoidal, as shown in Figure and Figure2. In addition to the back EMF, the phase current also has trapezoidal and sinusoidal variations in the respective types of motor. This makes the torque output by a sinusoidal motor smoother than that of a trapezoidal motor. However, this es with an extra cost, as the sinusoidal motors take extra winding interconnections because of the coils distribution on the stator periphery, thereby increasing the copper intake by the stator windings.Depending upon the control power supply capability, the motor with the correct voltage rating of the stator can be chosen. Fortyeight volts, or less voltage rated motors are used in automotive, robotics, small arm movements and so on. Motors with 100 volts, or higher ratings, are used in appliances, automation and in industrial applications.RotorThe rotor is made of permanent magnet and can vary from two to eight pole pairs with alternate North (N) and South (S) poles.Based on the required magnetic field density in the rotor, the proper magnetic material is chosen to make the rotor. Ferrite magnets are traditionally used to make permanent magnets. As the technology advances, rare earth alloy magnets are gaining popularity. The ferrite magnets are less expensive but they have the disad vantage of low flux density for a given volume. In contrast, the alloy material has high magnetic density per volume and enables the rotor to press further for the same torque. Also, these alloy magnets improve the sizetoweight ratio and give higher torque for the same size motor using ferrite magnets.Neodymium (Nd), Samarium Cobalt (SmCo) and the alloy of Neodymium, Ferrite and Boron (NdFeB) are some examples of rare earth alloy magnets. Continuous research is going on to improve the flux density to press the rotor further.Figure4 shows cross sections of different arrangements of magnets in a rotor.Hall SensorsUnlike a brushed DC motor, the mutation of a BLDC motor is controlled electronically. To rotate the BLDC motor, the stator windings should be energized in a sequence. It is important to know the rotor position in order to understand which winding will be energized following the energizing sequence. Rotor position is sensed using Hall effect sensors embedded into thestator.Note: Hall Effect Theory: If an electric current carrying conductor is kept in a magnetic field, the magnetic field exerts a transverse force on the moving charge carriers which tends to push them to one side of the conductor. This is most evident in a thin flat conductor. A buildup of charge at the sides of the conductors will balance this magnetic influence, producing a measurable voltage between the two sides of the conductor. The presence of this measurable transverse voltage is called the Hall effect after E. H. Hall who discovered it in 1879.