AC Sweep
Purpose
Perform AC sweep
Library
PLECS Extras / Analysis Tools
Description
The AC Sweep block enables you to determine the transfer function of a generic system from a single input to one or more outputs. The analysis is performed by injecting a small sinusoidal signal at different frequencies into the system and extracting the same frequencies from the system output(s) by Fourier analysis. The perturbation signal is available at the block output. The system outputs to be analyzed must be fed into the block's input port.
An ac sweep can be started either by clicking the button Start analysis or with the MATLAB command
placsweep(block);
where block is the Simulink handle or the full block path of the AC Sweep block. The block handle or path can be followed by parameter/value pairs that override the settings in the dialog box.
For additional information see section AC Analysis.
Parameters
- System period length
- The period length of the unperturbed system.
- Simulation start time
- The simulation start time for the ac sweep.
- Frequency sweep range
- A vector containing the lowest and highest perturbation frequency.
- Frequency sweep scale
- Specifies whether the sweep frequencies should be distributed on a linear or logarithmic scale.
- Number of points
- The number of data points generated.
- Amplitude at first freq
- The amplitude of the perturbation signal at the lowest
frequency. The amplitudes at the other frequencies are calculated as
- Show reference input
- If this parameter is set to on, the block will show an additional
input port, and the signal that is connected to it is used to determine the
spectrum
for the calculation of the transfer function
. Otherwise,
is determined by the internally generated perturbation signal.
- Method
- Specifies the method to use for obtaining the steady-state operating point of
the system for each perturbation frequency.
Brute force simulation simply simulates the system on a cycle-by-cycle basis until the difference between the state variables at the beginning and end of a cycle become sufficiently small. With this setting the parameter Max number of iterations actually limits the number of cycles until a steady state is reached.
Steady-state analysis performs a steady-state analysis for each perturbation frequency.
Start from model initial state uses the initial state values specified in the model - either in the individual blocks or in the simulation parameters.
Start from unperturbed steady state performs a steady-state analysis of the unperturbed system to determine the initial state vector for the ac sweep.
- Termination tolerance
- The relative error bound for all state variables. The analysis
continues until
for each state variable.
- Max number of iterations
- The maximum number of iterations allowed.
- Output variable
- The name of a MATLAB variable used to store the transfer function at the end of an analysis. If the analysis was run interactively from the GUI, the variable is assigned in the MATLAB base workspace. If the analysis was run with the placsweep command, the variable is assigned in the caller's workspace.
- Plot bode diagram
- Specifies whether to plot the transfer function in a bode diagram.
- Display level
- Specifies the level of detail of the diagnostic messages displayed in the command window (iteration, final, off).
- Hidden model states
- Specifies how to handle Simulink blocks with 'hidden' states, i.e. states that are not stored in the state vector (error, warning, none).