The parallel resonant converter as a single-phase high-quality rectifier.It is desired to utilize a transformer-isolated parallel resonant dc-dc converter in a single-phase low-harmonic rectifier system.By
properly varying the converter switching frequency,a near-ideal rectifier system that can be modeled as
in Fig.18.12 is obtained.You may utilize the results of Section 19.5.2 to answer this problem.The parallel resonant tank network contains an isolation transformer having a 1: nturns ratio.You may use either
approximate graphical analysis or computer iteration to answerparts (b) and (c).
(a)
(b)
(c)
(d)
Plot the normalized input characteristics (normalized input voltage = normalized
input current of the parallel resonant converter, operated in the continuous conduction mode above resonance.Plot curves forF= = 1.0, 1.1, 1.2, 1.3, 1.5, and 2.0.Compare
these characteristics with the desired linear resistive input characteristic =
The converter is operated open-loop, with F=1.1.The applied normalized input voltage is a rectified sinusoid of unity magnitude:= Sketch the resulting normalized input current waveform Approximately how large is the peak current?The crossover dead time?
A feedback loop is now added, which regulates the input current to follow the input voltage such
that = You may assume that the feedback loop operates perfectly.For the case
and with the same applied (t) waveform as in part (b), sketch the switching frequency waveform for one ac line period [i.e., show how the controller mustvaryFto regulate
.What is the maximum value ofF?Note:In practice, the converter would be designed to
operate with a smaller peak value of ,so that the switching frequency variations would be better behaved.
Choose element values (tank inductance, tank capacitance, and transformer turns ratio) such that
the converter of part (c) meets the following specifications:
Ac input voltage 120 Vrms, 60 Hz
DC output voltage 42 V
Average power 800 W
Maximum switching frequency 200 kHz
Refer the elementvalues tothe primary side of the transformer