隨著油價的不斷上漲和人們環保意識的增強，電動自行車以其價格低、綠色環保，使用安全方便等優點越來越受到消費者的喜愛。評價電動自行車質量好壞的重要參數之一是其蓄電池的使用壽命。而蓄電池的充電過程對其壽命影響最大。研究表明：過充電，可使蓄電池發熱，電解液失水；而充電不足，則可使蓄電池內化學反應不充分，長期充電不足會導致蓄電池容量下降。由此可見，充電器性能的好壞直接影響著蓄電池的使用效果和使用壽命。目前市場上的充電器存在的主要不足，第一不是從副邊繞組直接獲得取樣信號，因而穩壓效果不理想；第二是輸出電流和電壓調節范圍窄，因而只適用于固定負載。為此，本文介紹了一種以單片機為控制器的通用智能充電器的設計方案。該裝置能根據蓄電池的充電特性或實時監測到的充電狀態，來智能化地調節充電電壓和充電電流，而且調節范圍寬，并具有過流、過壓、過溫等保護功能。

1 系統結構

    本智能充電器的結構如圖1所示。該系統主要由電源變換電路、采樣電路、微處理器，脈寬調制器、鍵盤、顯示器和溫度傳感器等部分組成，是一個閉環的智能充電系統。


2硬件電路

   本智能充電器的硬件電路如圖2所示，整個電路分為開關電源部分、以單片機為主的控制電路和以UC3842為核心的脈寬調制電路三部分

2．1開關電源設計

   本設計采用電流控制型脈寬調制方式。其整個工作過程是將交流輸入經濾波、整流后變為直流高壓，再由開關管斬波、高頻變壓器降壓后得到高頻矩形電壓，最后經過輸出整流濾波獲得所需要的直流輸出電壓。系統對開關電源的要求是其交流輸入電壓范圍為90～270 V，能同時輸出+5V(作為控制部分電源)及12～60 V(主回路)的電壓。輸出電流為1～3 A。

2．2單片機控制電路設計

   單片機控制電路主要由單片機AT89S52、ADC(TLC0832)、多路選擇開關(CD4051)、數字電位器(X9C102)、數字溫度傳感器DSl8820、取樣電阻R_s和R_w、2×4鍵盤、液晶顯示(CONl6)等組成。

    本部分設(she)(she)計(ji)時(shi)(shi)(shi)(shi)應(ying)先根據蓄(xu)(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)型(xing)號(hao)參(can)數，來通(tong)(tong)過(guo)(guo)(guo)鍵盤設(she)(she)計(ji)與之(zhi)對應(ying)的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)、充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)以及(ji)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)(shi)間，當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路接上(shang)(shang)蓄(xu)(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池后(hou)，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)(guo)(guo)程開始，此后(hou)由(you)單(dan)片(pian)機通(tong)(tong)過(guo)(guo)(guo)取樣(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)RM檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，若檢測到(dao)(dao)蓄(xu)(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池因過(guo)(guo)(guo)渡(du)放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)而(er)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)于正常范圍。那么，為了(le)避免(mian)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)過(guo)(guo)(guo)大而(er)造成蓄(xu)(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池損(sun)壞，應(ying)先對蓄(xu)(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池實行穩定(ding)(ding)的(de)小(xiao)(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(本設(she)(she)計(ji)程序中設(she)(she)為l／5的(de)設(she)(she)定(ding)(ding)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu))，同時(shi)(shi)(shi)(shi)，單(dan)片(pian)機開始計(ji)時(shi)(shi)(shi)(shi)，之(zhi)后(hou)單(dan)片(pian)機將不斷檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)和充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)并(bing)顯示(shi)在(zai)液晶屏上(shang)(shang)，隨著充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)進行，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不斷上(shang)(shang)升，當(dang)上(shang)(shang)升到(dao)(dao)正常范圍時(shi)(shi)(shi)(shi)，單(dan)片(pian)機可(ke)通(tong)(tong)過(guo)(guo)(guo)控制數字電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位器(qi)(qi)來調節輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，從而(er)轉(zhuan)入大電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)恒流(liu)(liu)(liu)(liu)(liu)(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(即設(she)(she)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu))方式，此后(hou)，單(dan)片(pian)機一(yi)直(zhi)保持不停(ting)地檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)達到(dao)(dao)設(she)(she)定(ding)(ding)值(zhi)時(shi)(shi)(shi)(shi)，單(dan)片(pian)機發出(chu)指令，以增大數字電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位器(qi)(qi)的(de)阻(zu)值(zhi)，并(bing)通(tong)(tong)過(guo)(guo)(guo)脈寬調制減小(xiao)(xiao)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。從而(er)使(shi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)減小(xiao)(xiao)，當(dang)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)減小(xiao)(xiao)到(dao)(dao)1／5的(de)設(she)(she)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)時(shi)(shi)(shi)(shi)，再轉(zhuan)為涓流(liu)(liu)(liu)(liu)(liu)(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，最后(hou)在(zai)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)(shi)間到(dao)(dao)時(shi)(shi)(shi)(shi)關閉電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源，這樣(yang)就避免(mian)了(le)因電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池溫升過(guo)(guo)(guo)快或嚴重極化而(er)影(ying)響充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)質量，提(ti)高蓄(xu)(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)使(shi)用壽命。當(dang)檢測到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)、充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)(liu)和溫度超過(guo)(guo)(guo)設(she)(she)定(ding)(ding)值(zhi)的(de)1／10倍時(shi)(shi)(shi)(shi)(由(you)程序設(she)(she)定(ding)(ding))，單(dan)片(pian)機立(li)即輸出(chu)報警信號(hao)報警。同時(shi)(shi)(shi)(shi)使(shi)繼(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)動作并(bing)切斷總電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源，以提(ti)高充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)安全性(xing)(xing)和可(ke)靠性(xing)(xing)。

   顯示器可用于顯示單片機實時采樣到的蓄電池電壓、充電電流、已充電時間和蓄電池的溫度，鍵盤則用于設定充電電壓(充電極限電壓)、恒流充電電流(極限充電電流)和充電時間。電路中的單片機可通過串口RS232和上位機相連，以用于存儲數據和虛擬顯示充電參數的設定。當檢測到充電電流為零時，單片機轉入休眠狀態。而當檢測到充電電流不為零時，單片機被激活。

2．3 PWM控制器設計

   PW M控制器部分是以UC3842為核心。UC3842芯片內含有5.0 V基準電壓穩壓器、高增益誤差放大器和脈沖寬度比較器，它可以控制芯片內的驅動器。而驅動器則可提供25 mA的輸出電流．可直接驅動NOSFET調整管，從而調整充電器的輸出電壓和電流。由于該驅動器同時具有過流、過壓保護，工作電源電壓可以在8～40 V，而啟動電流小于1 mA，工作溫度為O～70℃，因而是目前較理想的新型脈寬調制器。

   該PWM控制器在啟動時，是由R₁、R_w。為UC3842提供啟動電壓，待其工作后，其輔助繞組3、4端的電壓經D₁整流、C₄、C₅濾波、DW₁穩壓后得到的16 V直流電壓，一路加到UC38427的7腳為其供電，另一路經R3和數字電位器X9C102分壓后加到UC3842的2腳。以作為脈寬調制的輸入信號。一般在這類電源的設計中，輸出電壓取樣可與UC3842的供電電壓相連。為了反映輸出電壓變化，本設計沒有加穩壓管，但這會使UC3842的工作電壓不穩，輸出諧波成分增多，為了克服此不足，本設計中UC3842的供電電壓采用由3、4繞組端壓單獨整流、濾波、穩壓后，提供給UC3842芯片16 V的穩定電壓。充電電壓的調節是將電池電壓經外環電壓取樣電路R₁₂、R_M取樣，再經多路電子開關選擇、MD變換，單片機處理后，送入數字電位器，以控制數字電位器的有效電阻。從而間接控制UC3842的2腳電壓，進而控制脈沖占空比，以改變充電電壓。

   當充電器輸出電壓偏高時，反饋回UC3842的2腳電壓也升高(超過參考電壓2.5 V)之后，驅動信號的脈沖占空比減小，使輸出電壓下降，從而達到穩壓的目的。充電電流的調節主要是先將充電電流經外環電流取樣電阻R_s取樣和LM358放大(可用R1調節放大倍數)、多路電子開關選擇、MD變換，再送單片機處理，然后調節數字電位器的阻值。其調節過程與電壓調節相似，實際上，電流調節也是通過電壓調節實現的。

2．4．保護電路設計

   當過流或短路時，內環取樣電阻R₁₀兩端的電壓升高。當3腳電壓超過1伏時，通過UC3842的內部調制可使其停止脈寬輸出，開關管截止，輸出電壓和電流均為0，從而保護電源。過壓時，DW₁和DW₂會擊穿而短路，也會造成過流保護，DW₂可用以保護場效應管和UC3842。而當發生欠壓時，即當UC3842的7腳電壓降至10 V以下時，UC3842將啟動欠壓鎖定電路而關閉開關控制器。內環的這種反饋調整是在輸出電壓尚未發生變化時，通過檢測內環電流使脈寬提前得到調整，(前饋控制)，從而加快了變換器對異常情況的動態響應速度。以便更加快速有效地起到保護作用。當然，外環電流、電壓的取樣(R_s、R_w)亦可通過單片機的調節作用來達到對異常情況的保護，但響應速度比內環慢5～10個工頻周期，因此，外環取樣主要是調節充電電流和充電電壓，兼作二次保護，而內環取樣則是主要的，它是一次的保護，這種雙環保護方式會更加安全可靠。

3軟件設計

   在程序的初始階段，首先是對單片機進行初始化，即根據不同的電池設定不同的充電參數，選擇不同的充電策略。其后是判斷電池是否連接正確，根據電池電壓值判斷應該進入哪一個充電階段(即小電流預充電，大電流恒流充電或恒壓涓流充電方式)。在預充階段，應降低充電電壓，而在恒流方式時，應不斷檢測充電電流是否達到恒定電流(如1.8 A)，如果小于1.8 A，則抬高電池兩端的電壓，使之達到1.8 A，以上調節過程均可采用比例控制。在電池兩端電壓達到設定值后，系統再進入涓流充電模式。該充電器的程序流程如圖3所示。圖3中，I_s為設定的充電電流(即恒流充電電流)，U_min為蓄電池的放電極限電壓，U_max為蓄電池的充電極限電壓。


4應用試驗

   本設計選用了電動自行車常用的36 V／12 Ah鉛酸蓄電池作為測試對象，其恒壓充電電壓設定為43 V，恒流充電電流Is為1.8 A，起始時，隨著充電的進行，充電電流幾乎維持1.8 A不變，但電池電壓不斷升高，當充電3小時后。電壓上升減慢；當充電到4小時后，充電電壓接近43 V；之后電壓上升更加緩慢。而且充電下降較快。當充到43 V時，充電器自動停止。從測試數據來看，該設計達到了恒流快充，恒壓涓充，充滿自行關斷的設計要求。

5結束語

   本文設計的過度放電預充、恒流快充、恒壓涓充、智能控制的充電方案，能很好地解決電動自行車用電池在充電過程中存在的過充電、充電不足和發熱等問題，并能根據不同電池選擇不同的充電方案。而且具有通用性。能實時檢測并顯示充電電流、充電電壓、充電時間和蓄電池溫度等參數。由于電路具有內外環控制，符合最優控制規律。最具有過流、過壓和超溫保護功能，同時由于UC3842采用穩壓供電，因此，不但諧波污染程度低，原副邊電氣隔離安全可靠，同時還可根據負載情況通過單片機來進行控制，并可實現跳周期模式工作。故可提高電源的效率。