Menene PWM? {0} Polinovel

PWM yana nufin Modulation Nisa na Pulse. Kuna kunna wutar lantarki da kashewa a ƙayyadaddun mitar, canza ƙimar lokacin kunnawa zuwa lokacin kashewa{2}} don sarrafa matsakaicin isar da wutar lantarki. Shi ke nan. Sauran yana magance sakamakon kawai.

Ɗauki wadatar 12V tana tuƙi LED mai buƙatar 3V. A yadda aka saba za ku yi amfani da resistor ko linzamin kwamfuta, ƙone 9V azaman zafi. Sharar banza. Tare da PWM kuna kunnawa da kashe cikakken 12V da sauri sosai wanda yawan zafin zafin wutar LED ɗin ya fitar da shi{7}}% sake zagayowar aikin yana ba ku kusan 3V daidai. LED yana ganin 12V → 0V → 12V → 0V a wata kila 1kHz, amma ba zai iya kwantar da hankali da zafi da sauri ba, don haka haske yana dawwama.

Matsaloli masu yawa. Yayi jinkiri sosai (a ƙarƙashin 100Hz) kuma kuna samun flicker bayyane. Wasu mutane suna ganin flicker har zuwa 200Hz. Yawancin lokaci ina sarrafa LED dimming a 20kHz kawai don zama lafiya -kuma yana kiyaye shi daga kewayon sauti idan akwai wani haɗin gwiwa na inji. Saurin sauyawa yana shafar asarar kuma, amma za mu kai ga hakan.

Lissafi: idan jinin haila T ne kuma akan -lokacin t, zagayowar aikin D=t/T. Sauƙi. Ikon isarwa shine kusan D × V_supply × I_load, ban da asara. Wadancan asarar sune inda abubuwa ke da ban sha'awa.

Dalili na farko: inganci. MOSFET a cikin jikewa ya ragu watakila 0.1-0.2V a madaidaicin igiyoyin ruwa. MOSFET kashe yana zana microamps. Don haka ko dai kuna watsawa (0.1V × halin yanzu) ko kuma ba komai. Kwatanta hakan da mai sarrafa linzamin kwamfuta yana faɗuwar 9V a cikakken halin yanzu ci gaba. Bambancin rayuwar baturi shine 40-50x a wasu lokuta, ba ƙari ba.

Na biyu: zaka iya amfani da kayan wuta mai rahusa. Kuna buƙatar tuƙi motar 48V akan saurin canji? Tare da kulawar analog kuna buƙatar wadatar 0-48V mai tsada mai tsada. Tare da PWM kuna amfani da ƙayyadaddun wadatar 48V (mai arha) da MOSFET (kuma mai arha). Anyi.

Dalili na uku babu wanda ya yi magana game da: sayayya. Gwada samar da ingantaccen wadatar analog mai canzawa a girma. Lokacin jagora shine mafi ƙarancin makonni 26 daga masana'anta masu kyau. MOSFETs? Komai yana nan a hannun Digikey. Lokacin da samarwa ke kururuwa a gare ku, wannan yana da mahimmanci fiye da farashin BOM.

PWM

EMI zai ba ku mamaki. Da farko na yi babban jirgi na PWM na yanzu (120A don injin DC), ya kashe bas ɗin CAN akan abin hawa ɗaya. Ba a lalata fakiti ba{4}}matattu gaba ɗaya. Juyowa tayi tana ringing ɗin gate ɗina yana haɗawa ta cikin ƙasan chassis, yana haifar da ƙwanƙwasa 40V akan nau'in CAN daban. Ƙara beads na ferrite, wuraren motsa jiki, har yanzu suna da matsala. Daga ƙarshe sai an ƙara matatar pi akan wadatar mota sannan a raba jiragen ƙasa tare da haɗin maki ɗaya-. Ya ɗauki bita guda uku.

Tuƙin ƙofar yana da wahala fiye da yadda ake gani. Kuna buƙatar ƙaramin takura daga direban ku zuwa ƙofar MOSFET{1}}matsalolin inductance a babban di/dt. Na ga 10nH na alamar inductance yana haifar da karuwar wutar lantarki 50V yayin sauyawa (V=L × di/dt). Wannan ya isa a buga ta hanyar MOSFET mai nauyin 60V. Mutane suna jayayya game da lissafi amma na gan shi akan iyakar: 3A/ns yana canza halin yanzu zuwa 10nH yana ba ku karu 30V. Ƙara ƙarfin wutar lantarki na wadata kuma kun wuce cikakkiyar ƙimar ƙima.

Sannan akwai harbi - ta cikin gadoji na H{1}. Dole ne ku sami lokacin ƙarshe tsakanin kashe ƙananan -gefen FET da kunna babban- gefen (da akasin haka). Ƙayyadaddun lokaci yana nufin duka FETs suna yin aiki lokaci ɗaya- kai tsaye daga samarwa zuwa ƙasa ta hanyar juriya na tashar FET{7}A zuwa 0.01Ω sau biyu har yanzu 1000A na miktoci kafin abubuwa su fashe. Yanayin gazawar yana da ban mamaki: ƙaramin rami a cikin siliki, FET yana ɗan gajeren gajere, yana fitar da duk abin da ke cikin sarkar.

Amma lokacin mutuwa da yawa kuma diode na jiki yana gudana a lokacin matattu. Diodes na jiki yana da muni{1}} babban digo na gaba (1{5}}2V), jinkirin dawowa. Kuna rasa inganci kuma kuna haifar da ƙarin zafi. Cinikin-kashe yawanci shine lokacin ƙarewar 100-500ns ya danganta da halayen FET ɗin ku.

Hankalin kowa na farko: mafi girman mitoci=ƙananan inductor/capaccitors=mai rahusa. Wani lokaci gaskiya. Amma canza hasara yana ƙaruwa tare da mita{4}} kuna rasa kuzari a duk lokacin da FET ta canza. ESwitching ≈ 0.5 × Vsupply × Iload × (trise + tfall) × fsw. Sau biyu mitar, ninka asarar sauyawa.

Don tuƙin mota, 20kHz na kowa ne. Sama da abin ji, madannin lokaci na inji ba su damu ba. Amma a cikin wutar lantarki na kwamfutar tafi-da-gidanka kuna ganin 300kHz{13}}1 MHz. Me yasa? Karamin maganadisu. Inductor 1MHz shine a zahiri 1/50 girman girman 20kHz daya tare da inductance iri ɗaya. Wannan yana da girma ga na'urori masu ɗaukuwa. Ciniki-kashe shine kuna buƙatar FETs masu sauri (ƙananan Qg), mafi kyawun shimfidawa, ƙarin ƙirar direba mai hankali.

Audio (Class D amps) yana tafiyar da 250kHz{4}}1 MHz. A ƙasa da 200kHz kuma kuna iya jin mitar mai ɗaukar hoto azaman ƙarar ƙarar ƙarar ƙararrawa. Sama da 1MHz kuma kun fara faɗa tare da tsangwama na rediyo na AM. Yawancin ƙira suna daidaitawa a 400-500kHz, matattara mai ƙarancin wucewa a watakila 50kHz don cire mai ɗauka.

Misali na gaske: yayi mai sauya buck 500kHz sau ɗaya, yayi ƙoƙarin zuwa 1MHz don rage allon. Ingancin ya ragu 4% (88% zuwa 84%). Wannan shine ƙarin zafi na 8W a cikin wadatar 200W. Ana buƙatar babban heatsink, rasa duk ajiyar sararin samaniya daga ƙaramin inductor. Ya kasance a 500kHz.

PWM

8 -bit PWM (matakai 256) yana da kyau har sai kun yi ƙoƙarin rage LED ɗin a hankali daga 100% zuwa 0%. A ƙasa da 10% na sake zagayowar aiki za ku sami matakan bayyane a cikin haske. Idon mutum yana da logarithmic-ya fi kulawa da canje-canje a ƙananan matakan haske. Bukatar 12-bit (matakai 4096) mafi ƙanƙanta don raguwa mai santsi a cikin cikakken kewayon.

Amma ga abin kama: 12-bit a 20kHz yana nufin kuna buƙatar agogon ƙidayar 20kHz × 4096=81.92MHz. Ba duk micros ba ne ke iya yin hakan. Kuma idan kuna buƙatar tashoshi na PWM masu zaman kansu da yawa a 12-bit, kuna kallon keɓantattun abubuwan ƙidayar lokaci ko FPGA.

Aiki: yi amfani da 8{6}}bit PWM amma daidaita mitar da ƙarfi. A babban haske yana gudu 20kHz, a ƙaramin haske ya ragu zuwa 100Hz. Yana ba ku mafi kyawun matakai inda kuke buƙatar su. Amma yanzu kuna da EMI mai canzawa-mita don magancewa. Babu wani abu kyauta.

VFDs masana'antu (masu sarrafa mitoci masu canzawa) suna canza ɗaruruwan amps a 480VAC. Dabarar sarrafawa ta fi rikitarwa -Model vector na sararin samaniya, filin{3}}madaidaicin iko, komai-amma a ƙarƙashinsa har yanzu PWM tana canza IGBT shida a cikin gada guda uku{{5}.

Bambance-bambance a wannan sikelin:

Direbobin ƙofa suna buƙatar keɓaɓɓen kayayyaki 15V. Wannan keɓaɓɓen kayayyaki 6 ke shawagi a wurare daban-daban har zuwa 680VDC (gyara 480VAC). Kowane direba yana buƙatar ikon kansa, nasa mai tsayayyar kofa (0.5-2Ω na al'ada), nasa kariya ta wuce gona da iri.

Lokacin mutuwa yana ƙaruwa zuwa 2-5µs saboda IGBTs suna da hankali fiye da MOSFETs

dv/dt tana tacewa akan fitarwa saboda ƙarfin kebul na motar da kuma saurin sauya gefuna yana haifar da manyan igiyoyin ruwa na gama gari{0}}. Na auna 20A na gama-gari{3}} akan kebul na motar 5HP, gaba ɗaya daban da na yanzu. Shi ya sa kuke buƙatar igiyoyi masu kariya da ƙasa mai kyau.

Thermal: ko da 2% asarar a 50kW shine 1kW na zafi. Mai sanyaya ruwa tare da madaidaicin magudanar ruwa da maƙallan zafin jiki. Idan kwararar mai sanyaya ta faɗi ƙasa ƙasa, mai sarrafawa yana kashe abubuwan da aka fitar nan take. Abubuwan da aka gani suna ƙonewa saboda wani ya manta don duba matakin sanyaya.

Zaɓin ɓangaren yana samun ban mamaki. Wani IGBT da aka ƙididdige don ci gaba na 100A zai iya ɗaukar 80A kawai a yanayin yanayin digiri 50, 60A a digiri 70. Amma fara babban mota yana jan 6x rated current na daƙiƙa da yawa. Don haka kuna girma don kololuwa, ba tsayayye ba{9}}, sa'an nan ku ƙi zafin jiki. Ƙare da 300A IGBT don aikace-aikacen "100A". Kudin BOM yana sa sayayya mara dadi sosai.

STM32 masu ƙidayar lokaci: yawancin suna da 16-bit PWM, wasu samfuran suna zuwa 32-bit amma ba kasafai kuke buƙata ba. Abin da ya fi mahimmanci shi ne adadin kwatanta tashoshi da abubuwan da suka dace. TIM1 da TIM8 akan jerin F4 suna da tashoshi huɗu na kwatanta kowannensu tare da ƙarin kayan aiki da shigar da lokacin mutuwa. Cikakke don sarrafa mota.

Matsala: duk tashoshi na PWM akan mai ƙidayar lokaci ɗaya suna aiki tare da counter iri ɗaya. Idan kuna buƙatar mitoci masu zaman kansu, kuna buƙatar masu ƙidayar lokaci daban. Kuma akwai masu ƙidayar lokaci da yawa tare da abubuwan ci gaba. A kan STM32F4 kuna samun TIM1, TIM8 don sarrafa ci gaba. TIM2-5 don ainihin PWM. TIM9-14 sune 16-bit ba tare da tsarawar lokaci ba. Kuna ƙarewa da sauri idan aikace-aikacen yana buƙatar keɓaɓɓen sigina na PWM.

Ana ganin ƙira inda suka ciza PWM a cikin software saboda sun ƙare tashoshi masu ƙidayar lokaci. Mummunan ra'ayi. Jitter, CPU sama, jujjuya fifiko lokacin da wasu ke katse wuta. Kawai ku biya ƙarin $2 don micro tare da ƙarin masu ƙidayar lokaci ko amfani da PWM IC na waje (kamar PCA9685). Kai na gaba zai gode maka.

ESP32 yana da tashoshi 16 PWM ta amfani da gefen PWM na LED. Yayi kyau sosai, sai dai duk an samo su daga agogon APB 80MHz guda ɗaya kuma ana raba masu rarraba cikin ƙungiyoyi. Kuna son mitoci daban-daban? Da fatan sun kasance ma'auni na lamba. Hakanan ƙuduri yana raguwa yayin da mita ke ƙaruwa saboda yana amfani da agogon tushe iri ɗaya. A 20kHz kana samun 12-bit, a 40kHz kana kasa zuwa 11-bit, da dai sauransu. Datasheet ba ya bayyana wannan a fili.

Yada -Bakan PWM: maimakon tsayayyen mitar, kuna karkatar da shi ±10% ba da gangan ba. Yana yada EMI a cikin kewayon mitar mitoci mai faɗi, yana rage yawan hayaƙi. Yana taimakawa wuce gwajin FCC/CE ba tare da kayan aikin tacewa ba. Yawancin guntuwar SMPS na zamani suna da wannan ginannun ciki. Cypress PSoC har ma yana ba ku damar sarrafa tsarin dithering -sawtooth, triangular, pseudo- bazuwar.

PWM Interleaved: Gudun masu juyawa da yawa daga lokaci. Masu juyawa biyu a 180 digiri motsi na nufin mai shigar da capacitor yana ganin rabin ripple halin yanzu. Masu juyawa huɗu a 90 digiri motsi - kwata na ripple. Amma yanzu kuna buƙatar daidaitaccen aiki tare tsakanin tashoshi da daidaita nauyi don su raba halin yanzu daidai. Yawancin lokaci yana buƙatar keɓaɓɓen mai sarrafa IC sai dai idan micro ɗinku yana da isassun albarkatu.

GaN FETs na iya canzawa cikin ƙasa da 10ns. Yana buɗe mitoci 10MHz+ PWM{4}}inductors sun zama ƙanƙanta, kusan kawai alamun PCB. Amma: shimfidar allo yana da mahimmanci, tuƙin ƙofa yana buƙatar kulawa sosai, duk wani inductance yana haifar da wuce gona da iri. Ba don masu farawa ba. Duba zoben ƙirar GaN zuwa 2x VDD saboda wani ya yi amfani da madaidaicin direban ƙofa mai tsayin 5cm. FET ba ta tsira ba.

PWM

Don mafi yawan kaya: 20kHz, hardware mai ƙidayar lokaci PWM, 10{5}} ƙudurin bit. Yawaita don sarrafa motoci da dimming LED. Ƙara direban kofa IC (2A mafi ƙanƙanta na halin yanzu), ƙananan iyakoki na yumbu na ESR daidai a magudanar ruwa ta FET, jirgin ƙasa mai kitse. Bincika fasalin motsin motsi tare da iyaka akan samfurin farko, sa ran sake maimaita sau ɗaya.

Don wani abu sama da 10A ci gaba, simintin thermal kafin shimfidawa. Ina amfani da ANSYS amma har ma na asali FEA yana kama mafi yawan matsaloli. Fitar da yadudduka na jan karfe tare da asara azaman tushen zafi, saita yanayin iyaka, bincika idan wani abu ya kai madaidaicin digiri 125 a max na yanayi. Yawancin lokaci kuna buƙatar heatsinks ko iska mai tilastawa idan kuna canzawa fiye da 50W.

Kuma gwada shi a yanayin zafi. Gwajin zafin daki yana iya kama kashi 60% na al'amura. Hot{3}}akwatin a yanayin yanayin digiri 70 na tsawon awanni 8 yana samun sauran{6}}magudanar zafi, motsi bakin kofa, haɓakar ESR capacitor. Kudin ni a mako guda sau ɗaya lokacin da ƙira ta yi aiki mai kyau a digiri 25 amma FET ta ƙare a digiri 65 saboda ban ƙididdige ƙimar ƙimar ƙarfin wutar lantarki ba.

PWM ke nan. Ra'ayi mai sauƙi, cikakkun bayanai marasa iyaka.

Abu na ƙarshe: idan kuna yin batir{0} abubuwan PWM masu ƙarfi, kar ku yi arha akan sel. An gwada wasu babu{2}} fakitin lithium suna sau ɗaya-ba zai iya ɗaukar ripple current ba, ƙarfin lantarki ya ragu a ƙarƙashin kaya, gabaɗayan tsarin ya dushe. An canza zuwa daidaibatirin lithium ionicsamfura masu inganci C{0}, matsala ta ɓace. Ƙarin $15 akan kowane fakiti ya cece ni daga kiran tallafi guda uku a mako.