To explain the operating mode of the NCC, assume that the load current is flowing through diode D2, resulting from a positive load current. At a given time, the controller demands turn off of S2. To achieve the commutation, both switches Sbd1 and Sbd2 in the bi-directional switch are first turned on when the voltage at point c is equal to uDC /2. Then S2 is turned off at zero voltage (and zero current because D2 was conducting). During the following half period of the resonance, the load current is supplied through Sbd1 and the voltage across S1 decreases. When the voltage at point c reaches uDC /2, the voltage across S1 is zero. Then, first Sbd2 is turned off, then S1 is turned on and finally Sbd1 may be turned off. The commutation process is depicted in Figure 47.
Figure 47. Illustration of the commutation procedure for the NCC.
The NCC is suitable both for discrete pulse modulation (DPM), and pulse width modulation (PWM). Both techniques are described in several papers concerning different resonant converters and a brief survey is given in (Munk-Nielsen, 1997).
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