Download Problem Set #11 - Power Electronics III | ECEN 5817 and more Assignments Electrical and Electronics Engineering in PDF only on Docsity! Problem Set 11 Power Electronics 3 Spring, 2006 1 Analysis of effect of magnetizing current on zero-voltage switching in the zero-voltage transition full- bridge converter . Figure 1 illustrates a full-bridge zero-voltage transition (ZVT) converter, with the mag- netizing inductance L M and magnetizing current i M ( t ) explicitly identified. As noted in class, the magne- tizing current can assist in the zero-voltage switching process, especially at light load, and a small air gap is often added to the transformer for this purpose. (a) Sketch the waveforms of v M ( t ) and i M ( t ), along with the v 2 ( t ), v 4 ( t ), v s ( t ), and i c ( t ) waveforms, for all twelve intervals within a switching period. Label salient features. You may assume that the magnetizing inductance L M is large relative to the commutating inductance L c , so that the mag- netizing current i M ( t ) does not exhibit a significant resonant (ringing) component. (b) Sketch the state-plane diagram ( j c vs. m 2 ) for this converter. Label salient features. (c) Show that the peak magnetizing current is given by: with k M = L M / L c , and M = V / nV g . Hence derive an expression that guarantees zero-voltage switching at no load. Also derive an expression for the conversion ratio M . (d) Design a ZVT converter to meet the following specifications: V g = 385 V Output: 28 V at 500 W Switching frequency: 500 kHz MOSFET output capacitances C leg 1 to C leg 4 : 300 pF Design for M = 0.75, and obtain zero-voltage switching at all load powers from 500 W to 0 W. You should specify: The phase shift φ at full load The required values of L c and L M The turns ratio n ic(t) Lc + –Vg Q1 Q2 Q3 Q4 D1 D2 D3 D4 + v2(t) – Cleg1 Cleg2 Cleg4 Cleg3 + v4(t) – + vs(t) – D5 D6 I1 : n : n + V – ig(t) + vo(t) – + vM(t) – LM iM(t) Fig. 1 A zero-voltage transition full-bridge converter with significant magnetizing current. IMp = VTs 4nL M JMp = Mπ 2Fk M
