Equation (10) defines the periodic nonlinear carrier waveform
in the NLC controller of Fig. 1. Operation of the
controller is illustrated by the waveforms of Fig. 2. Note that
the ideal waveform is not realizable because
, but can simply be clamped at the beginning of a
switching period. With the nonlinear-carrier waveform defined
by (10), the required current shaping (3) can also be expressed
as
(11)
A. Current Distortion in the DCM
The basic assumption in the derivation of the NLC controller
is that the converter operates in the CCM. In the DCM, the
relation (5) is not valid, and the resulting input current does not
exactly follow the input voltage. The purpose of this section
is to determine conditions for operation in the CCM and to determine the current distortion caused by operation in the
DCM.
In the DCM, the switch current is zero at the beginning of
any switching cycle, . The average switch current
can be found as a function of the switch duty ratio
(12)
The condition for operation in the CCM is