11-04-2012, 11:37 AM
CHARACTERISTIC CURVES OF THE ZERO VOLTAGE TRANSITION CONVERTER
introduction
In order to properly design the converter, charactenstic curves showing the
relationship between switch voItages, currents and various auxiIiary circuit component
values are needed. Using the analyticaI equations denved in Section 2.4 of Chapter 2
these curves can be drawn both for Mode I and for Mode2. Due to the nature of
equations in Section 2.4, the closed form solution of the equations can only be obtained
by using an iterative method.
description of program
The working of the program in Mode 1 is as follows:
1). An initial value Vc,, which is the voltage across the resonant capacitor before the
switching cycle begins, is assumed-
2). Step by step the equations derived in Chapter 2 for Mode 1 are solved for each
interval using the initia1 and final operating conditions of each interval.
DEFINITIOOFN V ARIABLEUSSE D IN CHARACTEFUSTCIC~ V E S
The variables used in drawing the characteristic curves are defined in this section
as follows:
1) Base voltage is the constant dc output voltage required fYom the converter. Thus base
voltage is Vb = 400 V.
2) Base current Ib is taken as the maximum current that is drawn fkom the input of the
converter just before the auxiliary circuit is activated. For ac input with PFC the
maximum current dratm will be at the peak of the ac voltage wave. The maximum
current aIso depends on the nns magnitude of the input voltage.
AUXILIARY CIRCUICTH ARACTERISCTUIRCV ESW HEN CONVERTER OPERATES
Most of the cuves drawn here are to aid in the rating of the auxiliary circuit
devices. Peak and rms values are used to rate switches while peak and average values are
used for selection of the diodes.
conclusion
In this chapter characteristic curves based on the steady state analysis of Chapter
2 were presented. From these curves certain insights towards the working of the converter
were gained. The curves were drawn for that particuIar point on the input AC wave where
the ZVS turn-on interval is the least which is same as the point when input current is
maximum. This makes up the worst case condition of the converter.