MATLAB: Is the pulse generated by the Pulse Generator block delayed when placed in an Enabled Subsystem using Simulink 7.6 (R2010b)

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I have placed a Pulse Generator block within an enabled subsystem (phase = 0). I expect the output of this subsystem to go high as soon as the subsystem is enabled. However, this is not always the case.

Best Answer

If the Pulse Generator block is not reset when the enabled subsystem is enabled, then there may be a delay in the output. To work around this issue, see the attached model that uses a Discrete-Time Integrator block to obtain the expected signal.

For more information consult the documentation by executing the following at the MATLAB prompt:

doc 'discrete-time integrator'

Related Solutions

MATLAB: When linearizing a Simulink model, are there any blocks with behaviors that can pose difficulties

This change has been incorporated into the documentation in Release 14 Service Pack 3 (R14SP3). For previous releases, read below for any additional information:

The Simulink linearization functions are able to provide linearizations for a wide array of Simulink models. However, the model must fundamentally still be linearizable, which means that it should not contain large discontinuities or event-based actions.

In particular, the following block features will likely cause problems:

Triggered Subsystems-- Triggered Subsystems, Triggered-Enabled Subsystems, Function-Call Subsystem, and other event-based conditionally executed Subsystems will not linearize correctly, since a trigger is an event that is defined by the level of a signal in the past and the current time, so they do not exhibit continuous behavior. Note that Enabled Subsystems are supported for linearization in Simulink 5.0 (R13) and later, and action subsystem (If-Then-Else, Switch-Case) are supported for linearization in Simulink 6.0 (R14) and later.
Integrator blocks with externally supplied initial conditions-- The block driving the Integrator initial condition port must be an Initial Condition (IC) block or a Constant block. For more information, see the following Related Solution 1-OERRA.
Continuous or discrete integrator blocks which are near the saturation point-- For example, an Integrator block with an initial state of 90, an input of 1, and an upper limit of 90 will give problematic results since the block's linearization is numerically computed. If your model is near at a saturation point it is best to turn off the "Limit Output" checkbox before linearizing.

Also, an enhancement to the linearization of the Integrator block has been made for Release 14 SP1 (R14SP1). It now has an "Ignore limit and reset when linearizing" option. Selecting this option will cause Simulink linearization commands to treat this block as unresettable and as having no limits on its output, regardless of the settings of the block's reset and output limitation options. This allows you to linearize a model around an operating point that causes the integrator to reset or saturate.

MATLAB: How to have a Pulse Generator block that will start from 0 phase whenever the enabled subsystem it resides in is enabled in Simulink 7.8 (R2011b)

The ability to reset the state of a signal such as a Pulse Generator is currently not available in Simulink 7.8 (R2011b). This is because the Pulse Generator signal works under the following calculation, which is based on simulation time:

   if (t >= PhaseDelay) && Pulse is on
     Y(t) = Amplitude
   else
     Y(t) = 0
   end

As a workaround, the pulse generator can be connected to an external time signal which is fed by a Counter Free-Running block. Whenever the subsystem is re-enabled, the counter is reset to zero to denote zero time and therefore zero phase.

One thing to note with this is that the counter is incremented by 1 at every time step, so the period of the pulse generator signal will need to be "normalized" to account for the simulation time step size.

Please see the attached model for more information on this workaround. The pulse generator signal is interrupted with a negative pulse. When the enabled subsystem is re-enabled after this interruption, the pulse begins from its zero-phase point no matter what time the simulation is in.

Best Answer

Related Solutions

MATLAB: When linearizing a Simulink model, are there any blocks with behaviors that can pose difficulties

MATLAB: How to have a Pulse Generator block that will start from 0 phase whenever the enabled subsystem it resides in is enabled in Simulink 7.8 (R2011b)

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