| Abstract | U radu je razmatrana složena struktura sustava regulacije glavnog elektromotornog pogona tiristorizirane lokomotive serije BDŽ 46 (6-osovinska lokomotiva trajne snage 5100 kW, napona napajanja 25 kV, 50 Hz, sa istosmjernim vučnim motorima sa serijskom uzbudom). Realizirani su matematički modeli elemenata energetskog kruga elektromotornog pogona kao i pripadajućih upravljačko-regulacijskih sklopova. Nakon toga je ostvarena sinteza spomenutih modela, u cilju dobivanja modela osnovnih struktura sustava regulacije za karakteristične radne režime – režim vuče i režim elektrootporničkog kočenja. Opis glavnog EMP lokomotive sadržan je u drugom poglavlju. Glavni EMP lokomotive serije BDŽ 46, sastavljen je od glavnog transformatora, tri sekventno upravljana para tiristorskih ispravljača, šest istosmjernih vučnih motora sa serijskom uzbudom (nazivne snage 850 kW), prigušnica za glađenje ispravljene struje, pripadnih pogonskih sklopova, kočnih otpornika te pripadajućih sklopnika vuče/kočenja i preklopki smjera. U okviru drugog poglavlja posebno su obrazloženi specifični zahtjevi na glavni elektromotorni pogon lokomotive u cijelosti (uključujući i pripadni upravljačko-regulacijski sustav), koji proizlaze iz specifičnih uvjeta rada pogona (promjenjivost adhezijskih uvjeta između kotača i tračnica, različita opterećenja pogonskih osovina, karakteristični režimi rada i dr.). U cilju što boljeg iskorištenja raspoložive vučne sile, nužno je odabrati pravilan način upravljanja glavnim elektromotornim pogonom lokomotive. Prilikom odabira koncepcije upravljanja pogonom, ključni značaj ima razumijevanje procesa koji se događaju između kontaktnih površina kotača i tračnica. Stoga je problematici adhezije također posvećena određena pozornost. Treće poglavlje obuhvaća kratki opis sklopovske i programske osnove kojom je ostvarena primijenjena upravljačko-regulacijska struktura. U osnovi, radi se o kaskadnoj strukturi s nadređenim krugom regulacije brzine i podređenim krugovima regulacije struje vučnih motora. Konfiguracija energetskog kruga glavnog elektromotornog pogona mijenja se, ovisno o režimu rada. U režimu vuče, motori glavnog EMP lokomotive raspodijeljeni su tako da formiraju tri nezavisno upravljive dvomotorne jedinice, za razliku od situacije u režimu elektrootporničkog kočenja, kada se uzbude svih šest strojeva (spojene u seriju) napajaju iz istog ispravljača. Stoga se i upravljačko-regulacijska struktura glavnog EMP lokomotive mijenja u skladu s radnim režimom, prilagođavajući se promjenama u konfiguraciji energetskog kruga pogona. U režimu vuče, slabljenje polja ostvaruje se u tri stupnja, shuntiranjem uzbude vučnih motora. Ovakav način upravljanja poljem postavlja dodatna ograničenja na mogućnost nezavisnog upravljanja vučnim motorima unutar iste dvomotorne jedinice, što izravno utječe i na mogućnost maksimalnog iskorištenja raspoložive vučne sile. Svaki regulacijski krug struje ima pridružene regulacijske petlje koje imaju zadatak da nivo pojedinih električkih i mehaničkih pogonskih veličina održavaju u granicama dozvoljenog. Tu spada regulator nivoa torzionih oscilacija, regulator napona, regulator automatskog odabira radne točke i dr. Stoga su u trećem poglavlju prikazani načini djelovanja nekih od spomenutih regulacijskih petlji, ilustrirani snimkama odgovarajućih vremenskih valnih oblika. Nužna pretpostavka za analizu i istraživanje statičkih i dinamičkih karakteristika sustava regulacije glavnog EMP lokomotive je raspolaganje odgovarajućim matematičkim modelima pojedinih elemenata energetskog kruga, pripadajućih upravljačko-regulacijskih struktura te sustava u cjelini. Spomenuti matematički modeli opisani su u četvrtom poglavlju, u sklopu čega su i identificirani parametri modela (na osnovu vlastitih mjerenja ili dostupnih proračuna i izvještaja o ispitivanju komponenti energetskog kruga). Matematički model sekventno upravljanog para tiristorskih ispravljača postavljen je na srednjim vrijednostima napona i struja i to za kontinuirano područje vođenja (pri normalnim opterećenjima glavnog EMP lokomotive, ispravljači praktički ne dolaze u diskontinuirani režim vođenja). Statičke karakteristike ispravljača određene su uvažavajući utjecaj glavnog transformatora, kontaktnog voda i transformatora elektrovučne podstanice preko kojih se napaja glavni EMP lokomotive. Matematički model vučnog kruga sastoji se od matematičkog modela vučnog motora i prigušnice za glađenje ispravljene struje. Armaturni namot vučnog motora nadomješten je serijskim R-L krugom, baš kao i prigušnica za glađenje ispravljene struje. Razlika je jedino u tome što je pretpostavljeno da se parametri armaturnog R-L kruga ne mijenjaju s iznosom struje, dok se dinamički induktivitet prigušnice za glađenje ispravljene struje dosta mijenja s iznosom struje kroz prigušnicu. Uzbudni krug nadomješten je serijskom R-L kombinacijom uzbudnog namota, kojoj su paralelno spojeni otpori za shuntiranje uzbude. Dinamički induktivitet uzbudnog namota mijenja se ovisno o struji magnetiziranja. U cilju uzimanja u obzir utjecaja vrtložnih struja, u paralelu s dinamičkim induktivitetom uzbudnog namota spojena je nadomjesna impedancija (u općem slučaju sačinjena od n paralelno spojenih R-L grana). Matematički model pogonskog sklopa izveden je, korištenjem pristupa koncentriranih masa, za opći slučaj, koji dozvoljava i analizu pojave torzionih oscilacija. Međutim za potrebe makro modela lokomotive/vlaka koristi se njegov oblik za dinamički stabilno stanje (nema torzionih oscilacija). Moment tereta motora, određen iznosom ostvarenih odrivnih sila između kotača i tračnica, modeliran je adhezijskom karakteristikom. Adhezijska karakteristika zadana je analitički ili pomoću krivulje zadane konačnim brojem točaka. Model translatornog gibanja omogućuje uvažavanje različite geometrije pruge kao i različitih sastava vlakova (s obzirom na masu i dužinu), korištenjem tzv. mjerodavnog otpora pruge. Mjerodavni otpor pruge dobiva se iz građevinskog presjeka pruge, a njegovo uvođenje motivirano je isključivo željom za skraćivanjem računanja otpora pruge za složenije kompozicije. Peto poglavlje obuhvaća programsku realizaciju simulacijskih modela, na osnovu matematičkih modela predstavljenih u četvrtom poglavlju. Tako su, svođenjem kompletnog glavnog EMP lokomotive na jednu dvomotornu jedinicu (ili čak na samo jedan vučni motor), dobiveni simulacijski modeli za režima vuče i režim elektrootporničkog kočenja. Simulacijom dobivenih modela, koji opisuju ponašanje jednog vučnog motora, istraženo je dinamičko ponašanje nekih pogonskih varijabli pri vuči i elektrootporničkom kočenju lokomotive u strojnoj vožnji, s lakšim teretnim vlakom (ukupne bruto mase oko 500 tona) te težim teretnim vlakom (ukupne bruto mase oko 1500 tona). Dobiveni su rezultati koji se u dobroj mjeri podudaraju s eksperimentalno snimljenim podacima te predstavljaju dobru osnovu za daljnju razradu dobivenih modela za potrebe istraživanja prijelaznih pojava te statičkih i dinamičkih karakteristika elektromotornog pogona lokomotive, ali i drugih vozila s električnom vučom. |
| Abstract (english) | The thesis deals with the complex structure of the automatic control system of the main electrical drive of the thyristorised locomotive series BDŽ 46 (6-axle locomotive with continuous power rating of 5100 kW, rated supply voltage 25 kV, 50 Hz, axles driven by series wound DC motors), obtained after reconstruction of diode locomotive for Bulgarian State Railways. Through synthesis of the mathematical models of the elements of the electrical drive's power circuit, and corresponding control circuits, mathematical models of the basic structures of the main electrical drive of the thyristorised locomotive were obtained – for motoring as well as for electro-resistance braking. Second chapter provides a description of the main electrical drive of the locomotive, that consists of main power transformer, three sequentially controlled pairs of seriesconnected semi-controllable thyristor rectifiers, smoothing reactors for rectified current, six series wound DC traction motors (with continuous power rating of 850 kW) and all the appropriate transmissions and switching gear (contactors etc.). Within second chapter the specific requirements on main electrical drive in total (including its automatic control system), as a consequence of specific operating conditions (variability of adhesion conditions between wheel and rail, various vertical axle loads, specific service conditions etc.) were elaborated more in detail. In order to obtain maximum possible utilization of available traction force it is necessary to choose the appropriate control algorithm for each particular drive system. During the selection process of the control conception for the main electrical drive of the locomotive, understanding of processes, which take place between the contact surfaces of the wheels and rails (in order to gain a tractive effort), is crucial. Therefore, certain attention was also paid to the adhesion related topics. Third chapter contains brief description of the software and hardware base that was used to implement selected structure of the automatic control system. In fact, it is based on multiloop cascade control, with outer speed control loop and subordinated current control loops. Configuration of power circuit changes according to the specific service conditions. In motoring configuration, series wound DC traction motors are connected in such way to form three separately controlled drive units (each of them consists of two motors connected in series). In electro-resistance braking configuration, braking resistance shorts armature windings of each motor, while all six excitation windings are connected in series and supplied from the same semi-controlled thyristor rectifier. Therefore, structure of the control system changes with respect to specific service conditions, in order to alter its characteristics according to the changes in power circuit configuration. Field weakening is achieved in three discrete stages by connecting additional shunt resistance in parallel with the excitation winding of the series wound DC traction motor. This way of field weakening (instead of continuous one) puts additional limitations on potentials to independently control motors within the same 2-motor drive unit. That has direct impact on possibilities to gain a maximum available tractive effort. Each current control loop has several subordinated control loops that take care to maintain the level of electrical and mechanical state variables (e.g. torsional vibrations, wheel slip, motor voltage etc.) within the limits that define safe operating area. Third chapter also provides a short description of their structure and dynamic behavior, illustrated by time diagrams of corresponding physical quantities. Basic requirement for the purpose of analysis and investigations of static and dynamic behavior of the main electrical drive of the locomotive is availability of appropriate mathematical models of all components of its power circuit and corresponding automatic control system, as well as of the system as a whole. These models are defined in the fourth chapter, and their parameters were identified on the basis of available measurements and previous calculations and test protocols (for some major components of electrical drive). Mathematical model of the sequentially controlled pair of semi-controlled thyristor based rectifiers that supply traction motors, are determined for the continuous current domain (at regular loads of the main electrical drive of the locomotive, the controllable rectifiers practically do not operate in the discontinuous current domain). Their static characteristics were determined taking into account influence of the complete supply network (main power transformer, overhead line impedance and transformer of the railway power substation). Mathematical model of traction circuit consists of the mathematical load of the series wound DC traction motor and assigned reactor for smoothing of the rectified current. Armature winding is represented by series connected R-L combination, as well as reactor for smoothing the rectified current. The only difference is that it was supposed that parameters of the armature winding R-L combination do not change their value with respect to armature current, while dynamical inductance of the smoothing reactor changes considerably with respect to its current (this is taken into account by reactor's nonlinear characteristic). Excitation circuit is substituted by series connected R-L combination of the series wound excitation winding, in parallel with four shunt resistances (basic and three additional shunts). Dynamical inductance of the excitation winding also varies according to the magnetizing current that flows through it. In order to take into account the effect of the eddy currents on dynamic behavior of the motor, additional equivalent impedance (that generally consists of n parallel connected R-L combinations) was added in parallel with the dynamic inductance of the excitation winding. General form of the mathematical model of the transmission system was determined, using concentrated masses approach, which enables analysis of torsional vibrations related problems. Dynamically stable state of this model (without torsional vibrations) was used in macro model of the locomotive/train. Motor load torque, which is determined by friction between contact surfaces of wheels and rails, was modeled by means of adhesion characteristics. Adhesion characteristics were defined by analytical expression or by nonlinear characteristics determined by finite number of points. Fifth chapter contains description of software implementation of simulation models, based on mathematical models presented in Chapter 4. Thus, by replacing a complete main electrical drive of the locomotive by one 2-motor drive unit (or even just a single traction motor), simulation models for motoring and braking were obtained. The dynamical behavior of variables of a single traction motor, of the main electrical drive, during locomotive acceleration and braking was investigated by simulation on digital computer for single locomotive, and for trains of approximately 500 and 1500 tons, respectively. The results obtained by simulation on digital computer give on the whole a good agreement with the experimentally obtained results. Therefore developed simulation models represent good base for their further improvement and application in investigation of static and dynamic characteristics of the main electrical drive of the locomotive, as well as for other vehicles that employ electrical traction. |
