  Switch-mode power converters are used in various applications to convert
between different voltage (or current) levels. They use transistors to switch
on and off the input voltage to generate a pulsed voltage whose arithmetic
average is the desired output voltage of the converter. After smoothening by
filters, the converter output is used to supply devices. The simulation of
these switch-mode power converters by conventional time discretization is
computationally expensive since a high number of time steps is necessary to
properly resolve the unknown state variables and detect switch events of the
excitation. This paper proposes a multirate method based on the concept of
Multirate Partial Differential Equations (MPDEs), which splits the solution
into fast varying and slowly varying parts. The method is developed to work
with pulse width modulated (PWM) excitation with a constant switching cycle and
varying duty cycle. The important case of varying duty cycles in the MPDE
framework is addressed for the first time. Switching event detection is no
longer necessary and a much smaller number of time steps for a decent
resolution are required, thus leading to a highly efficient method.
