Depending on the analysis to be carried on, several choices are offered to the designer.

Small-Signal Model (SSM)- It assumes that the variations
of concern (e.g. output or input voltages) are small around a
steady-state DC operating point. In this case, second-order
AC cross-products can be neglected and the model is linear
around its operating point. The SSM is then usually employed
for harmonic simulations where the AC transfer functions
are of interest. Do not use a SSM to simulate a 100%
transient load span, the result would be wrong since AC
cross-products could no longer be negligible. Some SSM
models can find their DC point alone, some not and the operating
point must then be fed by the designer

Vincent BELLO has been the first in the 80’s to
port MIDDLEBROOK’s non-linear state-space average
models to the SPICE domain [1]. In BELLO’s models, the
previous AC terms were no longer neglected but rather dynamically
multiplied by some POLY SPICE2 statements.
Large-signal variations could then be simulated and allowed

the user to visualize the effects of a 0 to 100% duty-cycle
sweep. These large-signal models (LSM) are best suited for
TRANSIENT runs.

State-space averaging (SSA) method

PWM switch model

	Created by Stephen Thomas over 6 years ago

Note on Converter Models, created by Stephen Thomas on 22/12/2017.