The University of New South Wales FINAL EXAMINATION. Session ELEC4613 ELECTRIC DRIVE SYSTEMS. 1. Time allowed 3 hours

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1 The University of New South Wles FINAL EXAMINATION Session 010 ELEC4613 ELECTRIC DRIVE SYSTEMS 1. Tie llowed 3 hours. Reding tie: 10 inutes 3. Totl nuber of questions in this pper = SIX 4. Answer ny FOUR Questions 5. All questions crry the se rk. Mrks for ech question re indicted beside the question. 6. Totl rk for this pper equls 80.This ex contributes 65% of the totl course ssessent. 7. Print your ne, student ID nd question nuber on the front pge of ech nswerbook. 8. A seprte nswerbook ust be used for nswering ech question Drwing instruents y be brought into the exintion roo. Cndidtes should use their own UNSW-pproved electronic clcultors. This is closed book exintion. Assuptions de in nswering the questions should be stted explicitly. All nswers ust be written in ink. Except where they re expressly required, pencils y only be used for drwing, sketching or grphicl work. This question pper y be retined by the cndidte. 1/6

2 QUESTION 1 () Develop n expression for the trnsfer chrcteristic between shft speed nd rture input voltge v of seprtely excited DC otor with pure inerti lod (i.e., negligible dping D nd lod torque T L ). Express the trnsfer chrcteristic in the for: G 1 s 1/ K 1 s s 1 E [6 rks] where K E is the otor bck ef constnt in V/rd/sec nd τ nd τ re the electricl nd echnicl tie constnts, respectively, of the otor. These re given by L nd R J K T E R K T Show tht dping rtio nd un-dped nturl frequency n of the otor trnsfer chrcteristic re given by [6 rks] 1 nd n 1 A pernent gnet DC servo otor hs the following preters: K E = K T = 0.5 N/p R = 0.4 L = 3 H J T = kg- D 0 T L 0 Find the nd n of the drive. [4 rks] (d) If DC supply is suddenly pplied to the rture of the otor of 1, coent qulittively with sketch whether the rise of speed of the otor will be over- or under-dped. [4 rks] /6 Plese see over for Question

3 QUESTION A 105 kw, 30 V, 1500 rev/in seprtely excited DC otor is driven fro three-phse fullycontrolled thyristor bridge converter. The rted current of the otor is 450A nd the rture resistnce, R, is The voltge constnt of the otor, K E, is 0.14 V/rev/in. Assue tht sufficient inductnce is present in the rture circuit to ke the rture current continuous. The converter output voltge drops with lod current t the rte of 0.06V/Ap due to its source inductnce. () In which qudrnt(s) does this drive operte? [ rks] Cn this drive be brked by the converter without ltering ny connections to the otor? [ rks] Find the input supply voltge (in RMS vlue) to the converter for opertion of the drive t the rted speed nd rted lod. [3 rks] (d) Clculte the firing ngle of the converter when the drive is to be operted t 750 rev/in with rted lod. [3 rks] (e) If the otor is to be brked fro 750 rev/in rpidly by reversing the converter connections, clculte the firing ngle α ieditely fter reversl of rture connection. Assue tht the xiu brking current in the otor is to be liited to twice the rted rture current. [5 rks] (f) If the firing ngle is controlled such tht the xiu brking current is intined up to zero speed, estite the shortest tie tken by the otor speed to drop to zero (i.e., to stndstill) fro 750 rev/in? Assue tht the totl inerti of the drive syste referred to the otor is 50 kg- nd tht ll other lods cn be neglected. [5 rks] Given: The DC output voltge of 3-phse fully controlled thyristor bridge converter for firing ngle, ssuing continuous conduction nd zero voltge drop due to source inductnce is given by V 3V x cos where V x is the pek of the line-line supply voltge to the converter. 3/6 Plese see over for Question 3

4 QUESTION 3 () Derive the reltionship between slip s nd firing ngle in the slip power recovery (sttic Scherbius) schee of wound-rotor induction otor drive (see Figure 1). Drw the torque-speed chrcteristics of such drive for firing ngles of = 90, 10, 140 nd 160 degrees. (1 rks) AC Mins I d V V d V di Wound Rotor IM Slip Rings 3-f Diode Bridge Rectifier Figure 1 Vrible Resistor 3-f 3-f Thyristor Trnsforer Bridge Converter V 1 A three-phse, Y-connected, 415V, 100kW, 50Hz, 4-pole wound rotor induction otor controls the speed of pup. It is driven with slip power recovery (sttic Scherbius) schee. The turns-rtio between the sttor nd rotor windings of the otor is = nd the secondry to priry winding of the trnsforer connected between the rotor circuit nd the AC ins is n =. (i) Find the firing ngle of the fully-controlled thyristor converter of the sttic Scherbius drive when the otor runs t 100 rev/in nd develops full lod. (4 rks) (ii) Find the required DC bus voltge V di t the input of the thyristor converter when the otor runs t 600 rev/in nd develops full lod. (4 rks) Plese see over for Question 4 4/6

5 QUESTION 4 A three-phse, 415V, 1470 rev/in, 50 Hz, 4-pole squirrel-cge induction otor hs the following preters: R 1 = 0.8, R = 0.3, 1 X X 0.6, X = 45 where R, X re the rotor preters referred to the sttor winding. The otor is driven fro VS inverter with constnt voltge to frequency rtio (V/f drive) in order to operte the otor with constnt ir-gp flux. () Show tht the slip frequency when xiu torque is developed under such drive is given by [5 rks] for f1 f sf1 X where f o is the bse frequency of the supply. Using the expression found in () nd by ignoring the voltge drop in the sttor ipednce, show tht the xiu developed torque t ny operting frequency f 1 is given by T x 3p K f o [10 rks] 4 X where p = nuber of pole pirs K = rted ir-gp flux t bse frequency = E o /f o Find the required strting frequency of the otor if it ust be strted with the xiu developed torque. [5 rks] Plese see over for Question 5 5/6

6 QUESTION 5 () Show, with help of phsor digr, tht the developed power per-phse in slient pole synchronous chine is given by VE f V X d X q P sin sin Xd XdX q W where V is the sttor phse voltge, E f is the field induced phse ef, δ is the torque ngle, X d nd X q re the d- nd q-xis synchronous rectnces, respectively. The resistnce of the sttor winding is ssued negligible. [10 rks] A 4-pole, 3-phse, 50 Hz, Y-connected, slient-pole synchronous otor with pernent gnet excittion hs the following preters: X d = 5 /phse t 50 Hz; X q = 10.5 /phse t 50 Hz; R 0 /phse ner bse speed. The sttor induced voltge (ef)/phse is found to be 170 V RMS when the otor runs t 150 rev/in. The otor is driven fro voltge-source inverter. The inverter switching control is such tht the otor lod ngle δ is liited t 10, t which xiu torque is developed. The RMS inverter output voltge is de proportionl to frequency (i.e. constnt V/f control). It supplies 30V RMS, to the otor t 50 Hz. Clculte the xiu torque the otor will develop while running t 150 rev/in. [10 rks] QUESTION 6 Describe the following: () The effect of discontinuous conduction of converter current on the speed regultion chrcteristic of otor drive. The effect of converter output current ripple on the perfornce nd de-rting of otor. The role of n inner current controller in n electric drive. [0 rks] END OF PAPER 6/6