Študija sinhronega usmerjanja pri alternatorjih

Cernatič, Jurij (author), Nemec, Mitja (mentor)

Naloga sistematično obravnava izgradnjo sistema za trifazno sinhrono usmerjanje v novi izvedbi, na osnovi mikrokrmilnika. Za vir trifazne napetosti smo uporabili nekoliko predelan 12 V avtomobilski alternator. V uvodnem delu smo najprej na kratko predstavili zgradbo in delovanje 12 V avtomobilskega alternatorja, nato pa smo nadaljevali z razlago trifaznega usmernika in procesa komutacije toka. Izpostavili smo glavno pomanjkljivost diodnega usmernika in možno rešitev – sinhrono usmerjanje. Opisali smo nekaj obstoječih krmilnikov za sinhrono usmerjanje ter navedli njihove slabosti. Osrednji del smo namenili razlagi razvoja in izgradnje sistema za sinhrono usmerjanje. Podali smo splošne zahteve, razložili izbor ustreznega MOSFET elementa ter opisali posamezne sklope strojnega dela sinhronega usmernika. V nadaljevanju smo podrobneje pojasnili zgradbo in delovanje programske opreme, predvsem modulov za pulzno-širinsko modulacijo, ter način za sinhronizacijo sistema na frekvenco vhodne napetosti. Podali smo tudi blokovne diagrame glavnih sklopov programa. V zadnjem delu smo najprej predstavili merilni sistem, na katerem smo izvajali meritve s trifaznim sinhronim usmernikom. Opisali smo tudi težave, s katerimi smo se srečali pri izvajanju meritev. V nadaljevanju so predstavljeni rezultati meritev, kjer smo ugotovili, da so se izgube pri uporabi sinhronega usmerjanja občutno zmanjšale, in sicer tudi do desetkrat. Pri povečanju območja delovanja MOSFET-ov s 120° na 145° pa so se izgube zmanjšale za približno 40 %. Posledica zmanjšanja izgub se je izkazala tudi kot upad temperature MOSFET tranzistorjev med delovanjem, kar smo potrdili preko meritev s termografsko kamero. V zaključku smo strnili celoten potek razvoja trifaznega sinhronega usmernika in opisali rezultate, ki jih njegova uporaba prinaša. Izpostavili smo najzahtevnejše dele razvoja ter težave, ki so se pojavile pri meritvah. Čeprav izdelan sistem prinaša precejšnje zmanjšanje izgub in odpravlja določene pomanjkljivosti alternativnih izvedb, smo se vprašali, ali je izvedba v takšni obliki stroškovno sprejemljiva.

• Language: Slovenian
• Keywords: sinhrono usmerjanje, komutacija, MOSFET, izkoristek
• Work type: Master's thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2018
• PID: 20.500.12556/RUL-101752
• Publication date in RUL: 03.07.2018

Secondary language

• Language: English
• Title: Study of synchronous rectification in alternators

Abstract

The present thesis systematically deals with the designing of a system for a three-phase synchronous rectification based on a microcontroller. A modified 12 V automotive alternator was used as a three-phase voltage source. In the introductory part we explained the structure and the operation/functioning of a 12 V automotive alternator. Later on we focused on explaining of a three-phase rectifier working principles and current commutation process. We presented the main disadvantage of a diode rectifier and proposed a possible solution – synchronous rectification. Later on, a few currently available drivers for synchronous rectification were analyzed and their drawbacks pointed out. In the main part we explained the development and construction process of a system for synchronous rectification. General requirements and MOSFET selection criteria were given and explained. We also explained the different subparts of the synchronous rectifier hardware. Further on, we focused on the software development process, with emphasis on the pulse-width modulation modules and a manner of system synchronization with input voltage frequency. Software block diagrams were also given. In the last part we introduced a measurement system which was used to take measurements on the three-phase synchronous rectifier. We also described the encountered difficulties while taking measurements. Later we presented the results of the measurements in which we found that the losses were substantially reduced by up to the factor of ten. When the MOSFET operation area was increased from 120° to 145°, losses were reduced by approximately 40 %. MOSFET operating temperatures were also reduced, which we confirmed by using thermal imaging camera. In conclusion we summed up the development process of the three-phase synchronous rectifier and described the results of using one. We pointed out the most challenging parts of the development process and the difficulties we encountered during the process of taking the measurements. Although the system itself brings significant loss reduction and outperforms some of the currently available solutions, we questioned its financial viability.

• Keywords: synchronous rectification, commutation, MOSFET, efficiency