Question

DC-DC Converter Machine Drives D QUE D EA TI C+ ata at I A separately excited DC motor is powered by a full bridge power converter using MOSFET power transistors and freewheeling diodes as shown above, Converter: Vs - 250 V Switching frequency - 5 kHz. Two-quadrant mode: Q3 always open and Q4 always closed. Assume ideal switches and diodes. DC machine: R-50 m2 LA = 300 H Ex -0.2 V/(r/min) Ignore rotational losses and brush voltage drop Answer the following: a) Calculate the highest shaft speed that can be obtained with this DC machine drive.(Ans:1250 rpm) (b) With a duty cycle of D-0.75 and armature current of 11 = 300 A calculate the speeds of the DC motor drive with two-quadrant switching.(Ans: 862.5 rpm) (c) Calculate the supply powers of the converter to the DC machine for the operating condition of (b) with two-quadrant switching. (Ans: 56.25 kW) (d) Draw the supply voltage waveforms VA-12(t) for the operating condition of (b) with two- quadrant switching. (e) With the speed of the drive at 387 r/min and 11 --300 A, calculate the duty cycles and converter powers with two-quadrant switching. (Ans: 0.25) (1) Draw the armature current waveforms for the operating conditions of (e) with two-quadrant switching and calculate the Aix (Ans: 31.27 A)

Answer 1

PAGE 1 a) EG=D Vg - fala Ja 0 10=1 66 is at mar fo- le Eь Speed (N) at Eb marinum s 60 250 10.2 N = 1250 gpm. b) Ef = Ous - John 0.75 x 950 - 300 X 0'05 1725 172.5 N = 862.5 ppm. Na Eb => EA C) Pouka (P) = our la 0.75 x 250 x 360 56250 Pin = 56.25kW vit d) Al-An Ve 3500 P, ON P₂ON By ON 07 t 17 - +0.75 T >40157- t T CS$canned with CamScanner

P, on, Py ON ( I at Quadrant Motering Mode) YAI-VA2= Uq PAGE 2 Di y la Eb f Ra wurm. A2 k. MAI-A → Q2 ON clina quadrant Regenerative breaking) o of En umfa Ia Az AL Dy Q2 * VAI A2 0 Given Speed (N) = 387 sp. 77.4 387 *02- Eb = N E Ef a Dug - Para D(250) + 360 X0-05 774 D C 250) 624 D = 02496 D= 0.25 CSscanned with CamScanner

PAGE 3 ff) L = 300uH D = 0.25 ug 250, f=5Hz, VAI-AL & T r DTI la Laman AIL 41 Anderlo Ho Jamin l L t This anka Buck converter. Same APL = I CI-DID Lxf 250 x C1-0.25) X0.05 300 xotx 5x100 Age = 31.25 A CScanned with CamScanner