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MPPT工作流程及算法和硬件的選擇

在光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)控(kong)制系統中，因為日(ri)照、溫度等條件的變(bian)(bian)化，光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)的輸(shu)(shu)(shu)出(chu)功率也(ye)是在不斷變(bian)(bian)化的，為保證使得光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)的輸(shu)(shu)(shu)出(chu)功率保持在最(zui)大(da)點，需要調整(zheng)光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(日(ri)照強度發生變(bian)(bian)化時(shi)，短路(lu)電(dian)(dian)(dian)(dian)流(liu)變(bian)(bian)化大(da)，開(kai)路(lu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)受(shou)影(ying)響(xiang)小(xiao);環境(jing)溫度發生變(bian)(bian)化時(shi)，短路(lu)電(dian)(dian)(dian)(dian)流(liu)受(shou)影(ying)響(xiang)小(xiao)，開(kai)路(lu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)變(bian)(bian)化大(da))。另外，光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)的輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)和電(dian)(dian)(dian)(dian)流(liu)也(ye)和負載有很大(da)關系，負載大(da)，輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)大(da)，輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)流(liu)小(xiao);負載小(xiao)，輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)小(xiao)，輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)流(liu)大(da)。光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)的MPP中的電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)是指光(guang)(guang)(guang)伏(fu)(fu)(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)的輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)。

MPPT算法選擇

目前，MPPT算法有開(kai)路電(dian)壓比率(離(li)線(xian))、短路電(dian)流比率(離(li)線(xian))、觀(guan)察調(diao)節(在(zai)(zai)線(xian))、極(ji)限(xian)追蹤(zong)控制法(在(zai)(zai)線(xian))。

開(kai)路(lu)電壓比(bi)率(lv)法(fa)(fa)——這(zhe)可以說(shuo)是(shi)非常經典也相當古老的(de)(de)(de)方法(fa)(fa)了，又名(ming)“固定電壓法(fa)(fa)”。簡單(dan)來(lai)(lai)說(shuo)，算(suan)法(fa)(fa)基于(yu)最(zui)大(da)功率(lv)電壓和(he)開(kai)路(lu)電壓的(de)(de)(de)線性關系(xi)(xi)(xi)式 ，系(xi)(xi)(xi)數 取(qu)值由設計(ji)(ji)師決定，一(yi)(yi)般介(jie)于(yu)0.71到0.78之間，大(da)多(duo)數設定為0.76。MPPT在(zai)(zai)追蹤(zong)(zong)時，首(shou)先(xian)開(kai)路(lu)DC端來(lai)(lai)測量(liang)開(kai)路(lu)電壓，然后通過(guo)算(suan)法(fa)(fa)來(lai)(lai)計(ji)(ji)算(suan)最(zui)大(da)功率(lv)電壓并且(qie)定位最(zui)大(da)功率(lv)點。MPPT會保持(chi)在(zai)(zai)該功率(lv)點一(yi)(yi)段時間，然后重(zhong)復開(kai)路(lu)測算(suan)并且(qie)重(zhong)新定位。固定電壓法(fa)(fa)的(de)(de)(de)最(zui)大(da)優點就是(shi)制(zhi)作(zuo)(zuo)便宜并且(qie)應(ying)用簡單(dan)。相反(fan)，缺點也十分明顯：精確(que)值和(he)追蹤(zong)(zong)效率(lv)較(jiao)低。盡(jin)管固定電壓法(fa)(fa)被(bei)稱(cheng)之為“追蹤(zong)(zong)”算(suan)法(fa)(fa)，事(shi)實上(shang)它依(yi)(yi)然是(shi)在(zai)(zai)整個工作(zuo)(zuo)循環中(zhong)的(de)(de)(de)一(yi)(yi)個計(ji)(ji)算(suan)設定值而非即時追蹤(zong)(zong)值。其次(ci)，此方法(fa)(fa)完全且(qie)單(dan)純依(yi)(yi)賴于(yu)組串(chuan)的(de)(de)(de)開(kai)路(lu)電壓值而放棄了對于(yu)工作(zuo)(zuo)電流的(de)(de)(de)追蹤(zong)(zong)。當局部(bu)陰影出(chu)現(xian)在(zai)(zai)陣列時，實際(ji)最(zui)大(da)功率(lv)點和(he)MPPT設定功率(lv)點就會出(chu)現(xian)相當大(da)的(de)(de)(de)偏差(cha)，偏差(cha)范(fan)圍取(qu)決于(yu)陰影遮蓋(gai)程度。最(zui)后，每(mei)次(ci)機器進(jin)行開(kai)路(lu)電壓測量(liang)時，太陽能系(xi)(xi)(xi)統是(shi)無法(fa)(fa)輸(shu)出(chu)功率(lv)的(de)(de)(de)，隨著(zhu)時間和(he)次(ci)數累(lei)計(ji)(ji)此算(suan)法(fa)(fa)會造成一(yi)(yi)定量(liang)的(de)(de)(de)能量(liang)流失。總(zong)體來(lai)(lai)說(shuo)，差(cha)評。

短路電(dian)(dian)(dian)(dian)(dian)流(liu)比(bi)(bi)率(lv)法——和固定電(dian)(dian)(dian)(dian)(dian)壓法的(de)(de)算法相似(si)，可(ke)以(yi)表(biao)述為 ， 是(shi)(shi)一(yi)個(ge)變量(liang)系(xi)數(shu)，通常(chang)變化范圍在0.78至(zhi)0.92。和固定電(dian)(dian)(dian)(dian)(dian)壓法不(bu)同的(de)(de)是(shi)(shi)，短路電(dian)(dian)(dian)(dian)(dian)流(liu)比(bi)(bi)率(lv)法要(yao)求在轉(zhuan)換器(qi)內置一(yi)個(ge)高頻開關來測量(liang)短路電(dian)(dian)(dian)(dian)(dian)流(liu)。比(bi)(bi)較推薦的(de)(de)是(shi)(shi)在組串(chuan)和DC link的(de)(de)電(dian)(dian)(dian)(dian)(dian)容之間(jian)安(an)裝一(yi)個(ge)FET(field-effect transistor)。由(you)于電(dian)(dian)(dian)(dian)(dian)流(liu)受到光照強度的(de)(de)影響(xiang)非常(chang)大，通常(chang)機器(qi)還(huan)需要(yao)一(yi)個(ge)DSP(digital signal processor)來保證(zheng)IV曲線的(de)(de)全掃描(miao)和數(shu)據(ju)的(de)(de)準(zhun)確度。這也讓(rang)短路電(dian)(dian)(dian)(dian)(dian)流(liu)比(bi)(bi)率(lv)法設計更加復雜且難以(yi)應用。差(cha)評(ping)。

觀察調節法——站在(zai)巨人肩(jian)頭發展出(chu)(chu)來的(de)(de)(de)算法你(ni)敢不(bu)服?目(mu)前，P&O依然應(ying)用在(zai)世界各大主流的(de)(de)(de)逆變器中也是(shi)(shi)最廣泛(fan)的(de)(de)(de)被應(ying)用的(de)(de)(de)算法，沒有(you)之(zhi)一(yi)(yi)。相比于ESC，P&O可(ke)(ke)以(yi)在(zai)更短(duan)的(de)(de)(de)時(shi)間內(nei)追(zhui)蹤時(shi)觸碰更大的(de)(de)(de)區(qu)域，掃描(miao)更多地數據。這進一(yi)(yi)步提高了(le)P&O的(de)(de)(de)追(zhui)蹤效(xiao)率和準確率。由于它(ta)在(zai)短(duan)時(shi)間內(nei)可(ke)(ke)以(yi)處理(li)大量的(de)(de)(de)數據，這也一(yi)(yi)定(ding)(ding)程(cheng)度抵制(zhi)了(le)突變光照(zhao)強度對(dui)于追(zhui)蹤精確度的(de)(de)(de)影響。缺點的(de)(de)(de)話，由于它(ta)掃描(miao)的(de)(de)(de)范圍較大，會(hui)一(yi)(yi)定(ding)(ding)程(cheng)度的(de)(de)(de)導(dao)致輸出(chu)(chu)功(gong)率缺乏穩定(ding)(ding)性，但(dan)是(shi)(shi)抖動(dong)程(cheng)度基本都在(zai)±4%以(yi)內(nei)。所(suo)以(yi)我(wo)還要給它(ta)32個贊!P&O還有(you)一(yi)(yi)個姐妹版本，還是(shi)(shi)“爬山”邏輯，但(dan)是(shi)(shi)并入了(le)“試錯”法(trial and error)。處理(li)器會(hui)根(gen)據下一(yi)(yi)刻追(zhui)蹤點的(de)(de)(de)移(yi)動(dong)趨(qu)勢，比較功(gong)率的(de)(de)(de)正增(zeng)量或負增(zeng)量。如果功(gong)率持續(xu)增(zeng)加，處理(li)器將會(hui)繼續(xu)同方向移(yi)動(dong)追(zhui)蹤點，不(bu)停比較直(zhi)到功(gong)率達到峰(feng)值。

極限追蹤控制法——該算法第一次提(ti)出在19世紀20年代(dai)，也(ye)是(shi)(shi)目前(qian)全球最流行(xing)的(de)“觀測調節法”(Perturb and Observe)的(de)前(qian)身。算法的(de)創新(xin)點是(shi)(shi)引入了向量(liang)在P-V曲(qu)線中(zhong)。處理器根據電壓的(de)增(zeng)量(liang)或減(jian)量(liang)來(lai)比較對應的(de)功率增(zeng)減(jian)量(liang)，進(jin)而確定追蹤功率點的(de)移動(dong)方向。具體判定方法請(qing)參照圖二，一目了然。

ESC算(suan)(suan)(suan)法(fa)(fa)的(de)(de)(de)(de)巨大(da)成功是相(xiang)比于(yu)之(zhi)前的(de)(de)(de)(de)固定(ding)電壓(ya)法(fa)(fa),通(tong)過漸進向(xiang)(xiang)量引入了(le)(le)“爬山法(fa)(fa)”的(de)(de)(de)(de)概念，進而開啟了(le)(le)動態追(zhui)蹤的(de)(de)(de)(de)算(suan)(suan)(suan)法(fa)(fa)。ESC極大(da)地拓寬(kuan)了(le)(le)MPPT對于(yu)DC端輸(shu)入能量的(de)(de)(de)(de)捕(bu)捉，顯(xian)著(zhu)地提高了(le)(le)追(zhui)蹤效率(lv)(lv)。由于(yu)ESC對于(yu)后代MPPT算(suan)(suan)(suan)法(fa)(fa)的(de)(de)(de)(de)影響(xiang)深遠，導致它(ta)(ta)的(de)(de)(de)(de)短板(ban)也(ye)一(yi)并被繼(ji)承下來并至(zhi)今“禍(huo)害”眾多一(yi)線品牌的(de)(de)(de)(de)逆變器。ESC對于(yu)陡然變化的(de)(de)(de)(de)光照反應強烈，舉個通(tong)俗(su)例子，MPPT正(zheng)專注的(de)(de)(de)(de)比較著(zhu)功率(lv)(lv)和電壓(ya)的(de)(de)(de)(de)變量，“嗯，正(zheng)向(xiang)(xiang)移動的(de)(de)(de)(de)電壓(ya)同步伴隨著(zhu)功率(lv)(lv)的(de)(de)(de)(de)增加，明顯(xian)最(zui)大(da)功率(lv)(lv)點還在正(zheng)向(xiang)(xiang)(右(you)邊(bian))，那(nei)我繼(ji)續向(xiang)(xiang)右(you)移動”。此時云層擋住(zhu)了(le)(le)陽光，稍(shao)(shao)稍(shao)(shao)影響(xiang)了(le)(le)輸(shu)入的(de)(de)(de)(de)直(zhi)流功率(lv)(lv)，使之(zhi)略微下降，“慢著(zhu)!正(zheng)向(xiang)(xiang)移動的(de)(de)(de)(de)電壓(ya)竟然導致功率(lv)(lv)減小了(le)(le)!我肯定(ding)錯過了(le)(le)最(zui)大(da)功率(lv)(lv)點，快掉(diao)頭!”于(yu)是，追(zhui)蹤點就離它(ta)(ta)的(de)(de)(de)(de)歸宿越來越遠的(de)(de)(de)(de)地方飄去。。。我在實驗室模擬測(ce)試時，親眼看到最(zui)多達到70%左(zuo)右(you)的(de)(de)(de)(de)偏差。基于(yu)ESC這種一(yi)級(first stage)追(zhui)蹤的(de)(de)(de)(de)設計(ji)理念，這種現象，無解。但是欣賞(shang)它(ta)(ta)對后世的(de)(de)(de)(de)正(zheng)面影響(xiang)以及理念創新，還是好(hao)評!

綜合考慮，MPPT的(de)(de)算(suan)法采用極(ji)限追蹤控制法來(lai)進行軟件實現，即采集PN側電(dian)(dian)壓(ya)、流向PN側的(de)(de)電(dian)(dian)流數據，計(ji)算(suan) 、 和 ，判斷 與 的(de)(de)關系， 大(da)于 ，此時應按 減小PN側的(de)(de)目標(biao)電(dian)(dian)壓(ya);若 小于 ，此時應按 增加PN側的(de)(de)目標(biao)電(dian)(dian)壓(ya)。

MPPT硬(ying)件選擇(ze)

MPPT的實現(xian)是(shi)(shi)通(tong)過調節光(guang)伏(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)輸(shu)(shu)出電(dian)(dian)(dian)(dian)壓(ya)來實現(xian)的，若光(guang)伏(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)輸(shu)(shu)出電(dian)(dian)(dian)(dian)壓(ya)直接(jie)連(lian)接(jie)到DC/AC的PN側，那(nei)么光(guang)伏(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)輸(shu)(shu)出電(dian)(dian)(dian)(dian)壓(ya)波動就會直接(jie)影響PN側電(dian)(dian)(dian)(dian)壓(ya)，最(zui)好是(shi)(shi)在光(guang)伏(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)和(he)DC/AC之間(jian)加一(yi)(yi)個(ge)中(zhong)間(jian)環節，通(tong)過這(zhe)個(ge)中(zhong)間(jian)環節來調整輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)壓(ya)，保持輸(shu)(shu)出電(dian)(dian)(dian)(dian)壓(ya)穩定，增加或減小輸(shu)(shu)出電(dian)(dian)(dian)(dian)流。這(zhe)個(ge)功(gong)能(neng)一(yi)(yi)般(ban)有BUCK、BOOST、BUCK-BOOST、CUK電(dian)(dian)(dian)(dian)路(lu)和(he)開(kai)關電(dian)(dian)(dian)(dian)路(lu)可以選擇(ze)，但BUCK電(dian)(dian)(dian)(dian)路(lu)是(shi)(shi)連(lian)續(xu)向負(fu)載供電(dian)(dian)(dian)(dian)、間(jian)接(jie)從電(dian)(dian)(dian)(dian)源取電(dian)(dian)(dian)(dian);BOOST電(dian)(dian)(dian)(dian)路(lu)時間(jian)接(jie)向負(fu)載供電(dian)(dian)(dian)(dian)、連(lian)續(xu)從電(dian)(dian)(dian)(dian)源取電(dian)(dian)(dian)(dian)，為保證(zheng)光(guang)伏(fu)(fu)(fu)電(dian)(dian)(dian)(dian)池(chi)板的發電(dian)(dian)(dian)(dian)效率得(de)到較好使用(yong)，一(yi)(yi)般(ban)選擇(ze)BOOST電(dian)(dian)(dian)(dian)路(lu)來實現(xian)MPPT。

選(xuan)擇BOOST電路來實現MPPT算法(fa)，其結構拓(tuo)撲如(ru)下圖。

考(kao)慮成(cheng)本問題(ti)，再加上光(guang)伏電池輸(shu)出(chu)的所有(you)最大功率點對應的輸(shu)出(chu)電壓差別(bie)不是很大，MPPT不使用(yong)DC/DC電路來實現(xian)，在(zai)現(xian)有(you)的DC/AC平臺(tai)上進行實現(xian)。

MPPT程序實現(xian)

變流器的(de)工作(zuo)流程為：

 啟動——預(yu)充電——PN側抬(tai)壓——接入光伏電池(chi)——輸出(chu)(MPPT)。

可(ke)以確定，MPPT的作(zuo)用是(shi)在電壓(ya)環上(shang)作(zuo)用，并且是(shi)在變流器進入工(gong)作(zuo)狀態后(hou)開始工(gong)作(zuo)。

 采(cai)用(yong)現有的DC/AC平臺(tai)來實現MPPT，存在(zai)兩(liang)個問題(ti)：控(kong)制步長(時間間隔(ge))問題(ti)、擾動(dong)步長 問題(ti)、判斷精度問題(ti)。

控制(zhi)步(bu)(bu)長(chang)問(wen)題——PN側電壓(ya)在MPPT過程中會產生一(yi)(yi)(yi)定的(de)(de)(de)波動，但因為(wei)對(dui)于(yu)光伏電池(chi)來(lai)說(結合下(xia)面兩(liang)圖)，其最大(da)功(gong)率點對(dui)應(ying)的(de)(de)(de)電壓(ya)大(da)致(zhi)都(dou)在一(yi)(yi)(yi)個不(bu)大(da)的(de)(de)(de)范圍(wei)內，并且(qie)都(dou)接近開路電壓(ya)，所以(yi)，對(dui)于(yu)在DC/AC上(shang)實(shi)現MPPT，要考(kao)慮(lv)多長(chang)時間(jian)對(dui)PN側目標(biao)電壓(ya)進行一(yi)(yi)(yi)次(ci)更新(xin)。目前State Manage函數是0.1ms進入一(yi)(yi)(yi)次(ci)，可以(yi)考(kao)慮(lv)MPPT的(de)(de)(de)控制(zhi)步(bu)(bu)長(chang)為(wei)0.2~0.5ms，步(bu)(bu)長(chang)暫定為(wei)0.3ms。

相同光(guang)照、不同溫(wen)度

相同溫度，不同光照

擾動步(bu)長問題——考慮在變流器進入工作狀態后，其(qi)PN側電(dian)(dian)(dian)壓(ya)(ya)(ya)為(wei)較(jiao)穩定的(de)(de)值(zhi)(zhi)，即使光照強度、環境溫度發生變化(hua)，光伏(fu)(fu)電(dian)(dian)(dian)池的(de)(de)最大(da)功率(lv)點電(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)(de)變動范圍不會很大(da)。根(gen)據其(qi)采集回(hui)來的(de)(de)PN側電(dian)(dian)(dian)壓(ya)(ya)(ya)和光伏(fu)(fu)電(dian)(dian)(dian)池輸出(chu)電(dian)(dian)(dian)流，并計算和前一時刻的(de)(de)功率(lv)差值(zhi)(zhi) ，根(gen)據電(dian)(dian)(dian)導增量法進行(xing)判斷，然(ran)后在目標(biao)跟蹤(zong)電(dian)(dian)(dian)壓(ya)(ya)(ya)上增加或減小一定的(de)(de)步(bu)長 。因為(wei)在光伏(fu)(fu)電(dian)(dian)(dian)池開(kai)始工作后，PN側電(dian)(dian)(dian)壓(ya)(ya)(ya)不是(shi)從0開(kai)始的(de)(de)，而是(shi)在光伏(fu)(fu)電(dian)(dian)(dian)池最大(da)功率(lv)點對(dui)應電(dian)(dian)(dian)壓(ya)(ya)(ya)附近，所以 的(de)(de)值(zhi)(zhi)會比較(jiao)小，K值(zhi)(zhi)的(de)(de)設(she)置通(tong)過調試程序獲得(de)，K暫定為(wei)5。

判斷精度問題——由導納法的(de)(de)工作流程(cheng)圖(下圖)可以知道，在(zai)(zai)流程(cheng)中(zhong)(zhong)(zhong)存(cun)在(zai)(zai) 、 與0的(de)(de)關系(xi)的(de)(de)判斷，程(cheng)序中(zhong)(zhong)(zhong)總是會存(cun)在(zai)(zai)誤(wu)差，并且檢測中(zhong)(zhong)(zhong)也(ye)會存(cun)在(zai)(zai)，如果以0為(wei)判斷準值(zhi)，考慮實際應用中(zhong)(zhong)(zhong)的(de)(de)誤(wu)差因(yin)素(su)，用一(yi)個小的(de)(de)閥值(zhi)來替代0。閥值(zhi)暫定為(wei)0.1V和0.1A。

MPPT算法C程序實現

#include "16F877.h"

#device ADC = 8 // 一個8位寄存器ADC模(mo)式

#fuses HS, NOWDT, PUT, NOPROTECT, BROWNOUT, NODEBUG, NOLVP // High-Speed 20MHz, No Watchdog, No Protection, Brownout Protection,

#use delay(clock=20000000) // 20MHz Crystal

//int is defined as 8-bit unsigned integer using CCS compiler

void main (void)

{

signed int direction;

int delta;

int pwm;

int upperbound;

int lowerbound;

float power;

float powerold;

float voltage;

float voltagedrop;

float voltagedifference;

float currentma;

float measuredvoltage;

float measuredvoltagedrop;

direction = 1; // Set initial direction to positive

delta = 1; // Amount by which to adjust the PWM - 7-bit resolution so duty step of 2%

pwm = 26; // Initial position of the PWM - 50% Duty Cycle with 7-bit resolution.

upperbound = 49; // Upper bound of the PWM %

lowerbound = 1; // Lower bound of the PWM %

power = 0; // Initial Value of Power

setup_adc(ADC_CLOCK_DIV_32); // ADC clock

setup_adc_ports(ALL_ANALOG); // Set all inputs to analog

output_low(PIN_C1); // Set CCP1 output low

setup_ccp1(ccp_pwm); // setup pin CCP1 (RC2) to do PWM

setup_timer_2(T2_DIV_BY_1,12,1); // 384.615kHz

while (1)

{

//delay_ms(1000) // Wait 1 Second

set_adc_channel(0); // Select RA0

//delay_ms(20); // Wait to Read ADC

measuredvoltage = read_adc(); // Read the voltage input from ADC channel 0

set_adc_channel(1); // Select RA1

//delay_ms(20); // Wait to Read ADC

measuredvoltagedrop = read_adc(); // Read the Voltage dropped across the R from ADC channel 1

voltage = measuredvoltage/51; // Measured Voltage is 51 steps per Volt at a Reference Voltage of 5V

voltagedrop = measuredvoltagedrop/51;

voltagedifference = voltage - voltagedrop;

currentma = voltagedifference; // Calculating Current using 1K Resistance

powerold = power; // Calculate the Power from the inputs

power = voltage * currentma;

pwm = pwm + direction*delta; // Adjust Pulse Width Modulation Value by Delta value

if (power < powerold) // If at top of curve, change direction

{

direction = -direction;

continue;

}

if (pwm > upperbound) // If at maximum PWM, Stop here

{

pwm = upperbound;

continue;

}

if (pwm < lowerbound) // If at mi

nimum PWM, Stop here

{

pwm = lowerbound;

continue;

}

set_pwm1_duty(pwm); // Set PWM Mark-Space Radio to approx 50%

}

}