EEE 472/591 – Power Electronics and Power Management Sample Final Exam

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EEE 472/591 – Power Electronics and Power Management

Sample Final Exam

Duration: 110 minutes Open book and open notes

Instructions:  Use of calculators allowed but not computers. Show all intermediate steps.

Problem 1 (30 points):

The converter uses unipolar PWM and interfaces a dc voltage source (500 V) and ac voltage source of vs = 340sin (377t) V . The current from the grid is to be controlled is  = 12 sin(377t) A.

(a) Draw the average model of the given converter

(b) Calculate vAB (t ) for the given requirement

(c) Calculate the control voltage vcA (t) for pole-A

(d) Calculate id (t )

Problem 2 (30 points):

It is given that Vd = 500 V, vac = 350 sin(377t) V, L = 1 mH and the switching frequency is 20 kHz. The converter uses unipolar PWM and is operating with vcA = -vcB = 0.7 sin (377t +30) V.

(a) Calculate the expression for the CCA value of iL(t)

(b) Draw the following four instantaneous waveforms over one switching period around 4 ms.

You may neglect the high frequency ripple in the inductor current. Show all relevant information.

(1) vAN (t), (2) vBN (t), (3) vAB (t) and (4) iL (t)

(c) What are the required peak voltage and peak current ratings for the four switches?

Problem 3 (20 points):

A two-phase, interleaved (phase-shifted) boost DC-DC converter is shown below.  Both phases (i.e., both boost converters) operate at a switching frequency of 200 kHz and duty ratio of 0.5. The input current is shared equally by the two phases.

(a) Draw the gate drive signals q1(t) and q2(t).

(b) Calculate the output voltage, Vo.

(c) Draw the waveforms of iL1(t), iL2(t) and iin(t) over one switching period.

Problem 4 (20 points):

A buck converter has an input voltage of 100 V and output voltage of 60 V with a load current of 5 A.  The switching frequency is 200 kHz.  The MOSFET has an RDS ON  of 50 milli ohms, turn-on transition time, ton = 50 ns, and turn-off transition time toff = 40 ns.  The diode has a forward drop of 0.7 V. Neglect inductor current ripple.

(a) Calculate the conduction loss and switching loss in the MOSFET

(b) Calculate the conduction loss in the diode