Iyini i-PWM?

I-PWM imele i-Pulse Width Modulation. Uvula futhi uvale i-voltage ngefrikhwensi engashintshi, ushintsha isilinganiso{1}sesikhathi sokuvala{2}}ukuze ulawule ukulethwa kwamandla okumaphakathi. Yilokho kuphela. Okusele kumane kubhekane nemiphumela.

Thatha umphakeli we-12V oshayela i-LED edinga i-3V. Ngokuvamile ungasebenzisa isilawuli noma isilawuli somugqa, ushise i-9V njengokushisa. Imfucuza eyisiphukuphuku. Nge-PWM uvula futhi uyivale i-12V egcwele ngokushesha ngokwanele ukuthi ubukhulu be-thermal be-LED buyilinganisele ngaphandle. 25% umjikelezo womsebenzi ukunika cishe okulingana ne-3V. I-LED ibona u-12V → 0V → 12V → 0V mhlawumbe ngu-1kHz, kodwa ayikwazi ukuphola futhi ishise ngokushesha, ukuze ukukhanya kuhlale kungashintshi.

Imvamisa ibalulekile. Ihamba kancane kakhulu (ngaphansi kuka-100Hz) futhi uthola ukucwayiza okubonakalayo. Abanye abantu babona ukucwayiza kufika ku-200Hz. Ngokuvamile ngisebenzisa i-LED dimming ngo-20kHz ukuze nje ngiphephe-futhi ngiyigcine ingaphandle kwebanga elizwakalayo uma kukhona ukuhlangana komshini. Ukushintsha isivinini kuthinta nokulahlekelwa, kodwa sizofika kulokho.

Izibalo: uma isikhathi sakho singu-T futhi{0}}isikhathi singu-t, umjikelezo womsebenzi D=t/T. Kulula. Amandla alethwayo cishe angu-D × V_supply × I_load, khipha ukulahlekelwa. Lokho kulahlekelwa yilapho izinto ziba mnandi.

Isizathu sokuqala: ukusebenza kahle. I-MOSFET ku-saturation yehla mhlawumbe ngo-0.1-0.2V kumaza afanele. I-MOSFET icishiwe idonsa ama-microamp. Ngakho-ke kungenzeka ukuthi uyachitha (0.1V × wamanje) noma empeleni akukho lutho. Qhathanisa lokho nesilawuli somugqa esilahla i-9V ngokugcwele ngokuqhubekayo. Umehluko wempilo yebhethri ungu-40-50x kwezinye izimo, hhayi ihaba.

Okwesibili: ungasebenzisa amandla ashibhile. Udinga ukushayela injini engu-48V ngesivinini esiguquguqukayo? Ngokulawulwa kwe-analog udinga ukunikezwa okubizayo okuguquguqukayo okungu-0-48V. Nge-PWM usebenzisa ukunikezwa okungaguquki okungu-48V (okushibhile) kanye ne-MOSFET (nayo ishibhile). Kwenziwe.

Isizathu sesithathu akekho okhuluma ngaso: ukuthenga. Zama ukuthola ukunikezwa okuhle kwe-analog eguquguqukayo ngevolumu. Izikhathi zokuhola zingamaviki angama-26 ubuncane kubakhiqizi abahloniphekile. Ama-MOSFET? Konke kusesitokweni kwa-Digikey. Uma ukukhiqizwa kukumemeza, lokhu kubaluleke ngaphezu kwezindleko ze-BOM.

PWM

I-EMI izokulimaza. Okokuqala ngenza ibhodi-yamanje ye-PWM ephezulu (120A yemoto ye-DC), yabulala ibhasi le-CAN emotweni efanayo. Akuwona amaphakethe onakele-afile ngokuphelele. Kuvele ukuthi ukukhala kwesango lami kwakuhlangana endaweni ye-chassis, kwehlisa ama-spikes angu-40V kubhangqa ehlukile ye-CAN. Kwengezwe ubuhlalu be-ferrite, isisekelo esinyakazayo, kusenezinkinga. Ekugcineni kwadingeka ukuthi kwengezwe isihlungi se-pi esiphakelini senjini futhi kuhlukaniswe izindiza eziphansi ngoxhumano lwephoyinti elilodwa{9}}. Uthathe ama-rev ebhodi amathathu.

Ukushayela kwesango kunzima kunalokho okubukeka. Udinga i-impedance ephansi ukusuka kumshayeli wakho ukuya esangweni le-MOSFET{1}}ukulandelela izindaba ze-inductance ku-high di/dt. Ngibone i-10nH ye-trace inductance ibangela ukukhuphuka kwamandla kagesi angu-50V ngesikhathi sokushintsha (V=L × di/dt). Lokho kwanele ukubhoboza nge-60V elinganiselwe i-MOSFET. Abantu bayaphikisana ngezibalo kodwa ngizibonele ku-scope: i-3A/ns ukushintsha i-current ibe yi-10nH ikunikeza i-30V spike. Engeza i-voltage yokuhlinzeka futhi usungaphezu kwesilinganiso esiphezulu esiphelele.

Bese kuba khona{0}}ukushutha-ku-H-emabhulohweni. KUFANELE ube nesikhathi esinqunyiwe phakathi kokuvala-i-FET yohlangothi oluphansi nokuvula-uhlangothi oluphezulu (ngokuphambene nalokho). I-Zero deadtime isho ukuthi womabili ama-FET aziphatha ngesikhathi esisodwa-ukuqondisa ngqo kusuka ekunikezeni kuye emhlabathini ngokusebenzisa ukumelana nesiteshi se-FET. 50U-A ukuya ku-0.01Ω kabili kusewu-1000A kuma-microseconds ngaphambi kokuba izinto ziqhume. Imodi yokwehluleka iyamangalisa: i-crater encane ku-silicon, i-FET iba mfushane unomphela, ikhipha konke okunye kuketango.

Kepha isikhathi esiningi sokufa kanye ne-diode yomzimba iqhuba ngesikhathi sokufa. Ama-diode omzimba asabekayo-ukuwa ukuya phambili okuphezulu (1-2V), ukululama kancane. Ulahlekelwa ukusebenza kahle futhi ukhiqize ukushisa okwengeziwe. Ukuhwebelana kuvame ukuba ngu-100-500ns omisiwe kuye ngezici zokushintsha ze-FET yakho.

Umzwelo wokuqala wawo wonke umuntu: imvamisa ephezulu=ama-inductors/capacitor amancane=ashibhe. Ngezinye izikhathi kuyiqiniso. Kodwa ukushintsha ukulahlekelwa kuyanda ngokuvama-ulahlekelwa amandla njalo uma izinguquko ze-FET. ESwitching ≈ 0.5 × Vsupply × Iload × (trise + tfall) × fsw. Phinda kabili imvamisa, kabili ukulahleka kokushintsha.

Kumadrayivu ezimoto, i-20kHz ijwayelekile. Ngaphezulu kokuzwakalayo, izikhathi ezingaguquki zemishini azinandaba. Kodwa kukhompuyutha ephathekayo ubona u-300kHz-1MHz. Kungani? Izibuthe ezincane. I-inductor engu-1MHz ngokomzimba ingu-1/50 usayizi we-20kHz one-inductance efanayo. Lokho kukhulu kumadivayisi aphathekayo. Ukuhwebelana udinga ama-FET asheshayo (i-Qg ephansi), isakhiwo esingcono, idizayini yomshayeli ecophelela kakhulu.

Umsindo (ama-amps e-Class D) usebenzisa u-250kHz-1MHz. Ngaphansi kuka-200kHz futhi ungezwa imvamisa yenkampani yenethiwekhi njengokukhala-okuphezulu. Ngaphezulu kwe-1MHz futhi uqala ukulwa nokuphazanyiswa komsakazo we-AM. Imiklamo eminingi ihlala ku-400-500kHz, isihlungi esidlula kancane mhlawumbe esingu-50kHz ukuze sikhiphe inkampani yenethiwekhi.

Isibonelo sangempela: wenze isiguquli sebuck esingu-500kHz kanye, sazama ukuya ku-1MHz ukuze sinciphise ibhodi. Ukusebenza kahle kwehle ngo-4% (88% kuya ku-84%). Lokho kungu-8W ukushisa okwengeziwe endaweni engu-200W. Idinga i-heatsink enkulu, ilahlekelwe yikho konke ukonga kwesikhala kusuka ku-inductor encane. Ihlala ku-500kHz.

PWM

I-8-bit PWM (izinyathelo ezingu-256) izwakala kahle uze uzame ukufiphalisa i-LED ngokushelela ukusuka ku-100% ukuya ku-0%. Ngaphansi kuka-10% womjikelezo womsebenzi uthola izinyathelo ezibonakalayo zokukhanya. Iso lomuntu liyi-logarithmic-lizwela kakhulu izinguquko emazingeni okukhanya aphansi. Udinga u-12-bit (izinyathelo ezingu-4096) ubuncane bokufiphalisa okubushelelezi kubo bonke ububanzi.

Kodwa nakhu okubambekayo: i-12-bit ku-20kHz isho ukuthi udinga iwashi lesikhathi elingu-20kHz × 4096=81.92MHz. Akuwona wonke ama-micro angakwenza lokho. Futhi uma udinga iziteshi eziningi ezizimele ze-PWM ku-12-bit, ubheka okokujikeleza kwesikhathi okuzinikele noma i-FPGA.

Indlela yokusebenza: sebenzisa i-8-bit PWM kodwa ulungise imvamisa ngokushintshashintsha. Ekukhanyeni okuphezulu sebenzisa u-20kHz, ekukhanyeni okuphansi kwehla ku-100Hz. Ikunikeza izinyathelo ezingcono lapho uzidinga khona. Kepha manje une-EMI eguquguqukayo okufanele ubhekane nayo. Akukho lutho lwamahhala.

Ama-VFD wezimboni (ama-variable frequency drives) ashintsha amakhulu ama-amps ku-480VAC. Isu lokulawula liyinkimbinkimbi kakhulu-ukushintsha i-space vector, inkambu-yokulawula okuqondisiwe, noma ngabe yini-kodwa ngaphansi kwayo kusalokhu i-PWM ishintsha ama-IGBT ayisithupha-ebhulohweni lezigaba ezintathu.

Umehluko kulesi sikali:

Abashayeli bamasango badinga izinsiza ezingazodwa ze-15V. Lokho yizinto eziyisi-6 ezihlukanisiwe ezintanta ngamandla ahlukene afika ku-680VDC (okulungisiwe okungu-480VAC). Umshayeli ngamunye udinga amandla akhe, isivimbeli sesango saso (0.5-2Ω esijwayelekile), isivikelo saso esidlulele.

Isikhathi esimisiwe sikhuphuka sibe ngu-2-5µs ngoba ama-IGBT anensa kunama-MOSFET

Izihlungi ze-dv/dt kokuphumayo ngenxa yokuthi amandla ekhebula le-motor kanye namaphethelo ashintshayo abangela amaza amakhulu-amamodi avamile. Ngilinganise u-20A wemodi evamile-kukhebula yemoto engu-5HP, ehluke ngokuphelele kumotho wamanje. Yingakho udinga izintambo ezivikelwe kanye nesisekelo esifanele.

I-Thermal: ngisho nokulahlekelwa okungu-2% ku-50kW kungu-1kW wokushisa. Ukupholisa amanzi ngokushintsha kokugeleza kanye nezinsimbi zokushisa. Uma ukugeleza kwesipholisi kwehla ngaphansi komkhawulo, isilawuli sikhubaza okukhiphayo ngokushesha. Amasistimu abonwe esha ngoba othile ukhohlwe ukuhlola izinga lokupholisa.

Ukukhethwa kwengxenye kuba yinqaba. I-IGBT elinganiselwe ngo-100A ngokuqhubekayo ingase ibambe kuphela u-80A ku-50℃ambient, 60A ku-70 degree. Kodwa ukuqala injini enkulu idonsa i-6x ekalwe okwamanje imizuzwana embalwa. Ngakho-ke usayizi wakho wokuphakama, hhayi{9}}umbuso ozinzile, bese unciphisa izinga lokushisa. Qeda nge-300A IGBT yohlelo lokusebenza lwe-"100A". Izindleko ze-BOM zenza ukuthenga kungajabulisi kakhulu.

Izibali zesikhathi ze-STM32: eziningi zine-16-bit PWM, ezinye izinhlobo ziya ku-32-bit kodwa awuvamisile ukuyidinga. Okubaluleke kakhulu inani lokuqhathanisa iziteshi kanye nemiphumela ehambisanayo. I-TIM1 ne-TIM8 ochungechungeni lwe-F4 baneziteshi ezine eziqhathaniswayo ngayinye enemiphumela ehambisanayo kanye nokufakwa kwesikhathi esimisiwe esihlelekayo. Perfect for motor control.

Inkinga: zonke iziteshi ze-PWM kusibali sikhathi esisodwa zivumelaniswa kwikhawunta efanayo. Uma udinga amafrikhwensi azimele, udinga izikhathi ezihlukene. Futhi ziningi kuphela izibali sikhathi ezinezici ezithuthukile. Ku-STM32F4 uthola i-TIM1, i-TIM8 yokulawula okuthuthukile. I-TIM2-5 ye-PWM eyisisekelo. I-TIM9-14 iyi-16-bit ngaphandle kwesizukulwane esidala. Uphela ngokushesha uma uhlelo lokusebenza ludinga amasiginali amaningi e-PWM ahlukene.

Kubonwe amadizayini lapho ancipha khona-i-bang PWM kusofthiwe ngoba iphelelwe iziteshi zesibali sikhathi. Umbono omubi. I-Jitter, i-CPU ngaphezulu, ukuguqulwa okubalulekile lapho okunye kuphazamisa umlilo. Vele ukhokhe i-$2 eyengeziwe nge-micro enezibali-sikhathi ezengeziwe noma usebenzise i-PWM IC yangaphandle (njenge-PCA9685). Ikusasa lakho lizokubonga.

I-ESP32 inamashaneli e-PWM angu-16 esebenzisa iperipheral ye-LED PWM. Kuzwakala kukuhle, ngaphandle kokuthi wonke athathwe ewashini elilodwa le-80MHz APB futhi abelana ngezihlukanisi ngamaqembu. Ufuna amafrikhwensi ahlukene? Ngethemba ukuthi ziyizinombolo eziphelele. Futhi ukulungiswa kuncipha njengoba imvamisa inyuka ngoba isebenzisa iwashi lesisekelo elifanayo. Ku-20kHz uthola u-12-bit, ku-40kHz wehlele ku-11-bit, njll. I-Datasheet ayikwenzi lokhu kucace.

Sabalalisa-i-spectrum PWM: esikhundleni samafrikhwensi alungisiwe, uyawuhlukanisa ±10% ngokungahleliwe. Isabalalisa i-EMI ebangeni elibanzi lefrikhwensi, inciphisa ukukhishwa okuphezulu. Isiza ukudlula ukuhlolwa kwe-FCC/CE ngaphandle kwehadiwe yokuhlunga eningi. Ama-chips amaningi esimanje e-SMPS analokhu okwakhelwe ngaphakathi. I-Cypress PSoC ikuvumela nokuthi ulawule iphethini ye-dithering-sawtooth, triangular, pseudo{7}}okungahleliwe.

I-Interleaved PWM: sebenzisa iziguquli eziningi ngaphandle kwesigaba. Iziguquli ezimbili ku-180℃phase shift zisho ukuthi i-capacitor yokufaka ibona uhhafu wamanje we-ripple. Iziguquli ezine ku-90℃phase shift{4}}ikota ye-ripple. Kodwa manje udinga ukuvumelanisa kwesigaba okunembayo phakathi kwamashaneli nokulinganisa kokulayisha ukuze abelane ngokwamanje ngokulinganayo. Ngokuvamile idinga isilawuli esizinikele i-IC ngaphandle uma i-micro yakho inezinsiza ezanele.

Ama-GaN FET angashintsha abe ngaphansi kuka-10ns. Ivula amafrikhwensi angu-10MHz+ PWM{4}}ama-inductors abe mancane, cishe amathrekhi e-PCB nje. Kodwa: ukwakheka kwebhodi kubalulekile, isango lokushayela lidinga ukunakwa okujulile, noma yikuphi ukuthungathwa kubangela ukuqhuma okukhulu. Hhayi kwabaqalayo. Ubone indandatho yedizayini ye-GaN ku-2x VDD ngoba othile usebenzise umshayeli wesango ojwayelekile onobude obungu-5cm bokulandela umkhondo. I-FET ayizange isinde.

PWM

Ezintweni eziningi: 20kHz, i-hardware timer PWM, -ukulungiswa kwebhithi elingu-10. Inala yokulawula imoto kanye nokufiphala kwe-LED. Engeza umshayeli wesango i-IC (isilinganiso esiphezulu se-2A esiphezulu samanje), amakepisi e-ceramic e-ESR aphansi khona kanye kumsele we-FET, indiza ephansi enamafutha. Hlola ama-waveforms ashintshayo nge-scope ku-prototype yokuqala, lindela ukuphindaphinda kanye.

Kunoma yini engaphezu kuka-10A okuqhubekayo, ukulingisa okushisayo ngaphambi kwesakhiwo. Ngisebenzisa i-ANSYS kodwa ngisho ne-FEA eyisisekelo ibamba izinkinga eziningi. Khipha izendlalelo zethusi ezilahlekelwe njengemithombo yokushisa, setha izimo zomngcele, hlola ukuthi ingabe kukhona yini okufika ku-125℃junction temp at max ambient. Imvamisa udinga ama-heatsink noma umoya ophoqelelwe uma ushintsha ngaphezu kuka-50W.

Futhi ihlole ezingeni lokushisa. Ukuhlolwa kwezinga lokushisa kwegumbi kubamba cishe u-60% wezinkinga. Ibhokisi elishisayo-elingu-70℃ambient amahora angu-8 lithola okunye-i-thermal runaway, gate threshold shift, capacitor ESR ukwanda. Kungibize ngesonto kanye lapho idizayini isebenze kahle ku-25℃kodwa i-FET yabambelela ku-65℃ngoba angizange ngibale i-threshold voltage temperature coefficient.

Lokho yi-PWM. Umqondo olula, imininingwane engapheli.

Okokugcina: uma wenza-izinto ze-PWM ezisebenza ngebhethri, ungashibhisi ngamaseli. Izame{2}}ukuqamba amaphakethe e-lithium kanye{3}}ayikwazanga ukuphatha i-ripple current, i-voltage encibilikile ngaphansi komthwalo, yonke isistimu yaba nsundu. Kushintshelwe kokufanelei-ionic lithium ibhethriamamojula anesilinganiso C-esihloniphekile, inkinga inyamalele. I-$15 eyengeziwe ngephakethe ingisindise ezingcingweni ezintathu zosekelo ngesonto.