EE4763 power electronics spring 2016 :homework 2...university of texas,san antonio

EE4763 Power Electronics Spring 2016

Homework 2

Assigned: Feb 1, 2016

Due: Feb 10, 2016 (before start of class)

Do the following problems from the textbook; ’Power Electronics”, by N. Mohan, Wiley, ISBN: 9781118074800

3.8

3.9

3.10

3.15

3.16

3.17

Problem 7

A buck-boost converter shown in Fig. 1 is operating under Continuous Conduction Mode (CCM) with the following specifications: Vin = 300V , Vo = 400V , R = 100Ω and Fs = 100kHz. The value of inductance L is large enough such that the ripple in the inductor current is negligible.

(i) Determine the duty cycle of operation D

(ii) What is the average value of inductor current īL?

(iii) Determine the switching loss in the Mosfet given tri = 20ns, tfi = 25ns, trv = 30ns and tfv = 30ns.

1

−

iL

L

+

−

+

−

vsw

Vin

C

+

R −

Vo

+

Figure 1: Buck-Boost Converter for Problem 1

Problem 8

A boost converter shown in Fig. 2 is operating with the following specifications: Vg = 300V , Vo = 400V , Po = 4000W and Fs = 20kHz.

(i) Calculate the value of inductance L such that the peak-peak ripple in inductor current ΔiL(pk−pk) = 2A.

(ii) Plot the Inductor current iL(t)

(iii) Calculate the critical value of load power Po below which the converter goes into Discontinuous Conduction Mode (DCM)

iD

− +

+

−R

Vin +

−C

L

Vo

+

−

vsw

iL

Figure 2: Boost Converter for Problem 8

2