Linearize Event-Based Subsystems (Externally
Scheduled Subsystems)
Linearizing Event-Based Subsystems
Event-based subsystems (triggered subsystems) and other event-based models require
special handling during linearization.Executing a triggered subsystem depends on previous signal events, such as zero
crossings. However, because linearization occurs at a specific moment in time, the trigger
event never happens.An example of an event-based subsystem is an internal combustion (IC) engine. When an
engine piston approaches the top of a compression stroke, a spark causes combustion.
The timing of the spark for combustion is dependent on the speed and the position of the
engine crankshaft.In the scdspeed model, triggered subsystems generate events when the pistons reach
both the top and bottom of the compression stroke. Linearization in the presence of such
triggered subsystems is not meaningful.Approaches for Linearizing Event-Based Subsystems
You can obtain a meaningful linearization of triggered subsystems, while still preserving
the simulation behavior, by recasting the event-based dynamics as one of the following:- Lumped average model that approximates the event-based behavior over time.
- Periodic function call subsystem, with Normal simulation mode.
In the case of periodical function call subsystems, the subsystem linearizes to the
sampling at which the subsystem is periodically executed.In many control applications, the controller is implemented as a discrete controller,
but the execution of the controller is driven by an external scheduler. You can use such
linearized plant models when the controller subsystem is marked as a Periodic
Function call subsystem.If recasting event-based dynamics does not produce good linearization results, try
frequency response estimation. See “Estimate Frequency Response Using Linear Analysis
Tool” on page 5-7.Linearize Event-Based Subsystems (Externally Scheduled Subsystems)