Second-Order Low-Pass Filter (Discrete or Continuous)
Discrete-time or continuous-time second-order low-pass filter
Simscape / Electrical / Control / General Control
The Second-Order Low-Pass Filter (Discrete or Continuous) block implements a second-order low pass filter in conformance with IEEE Std 421.5-2016. In the standard, the filter is a single input, single output signal conditioner that is used in the Power System Stabilizer PSS1A.
In the PSS1A, the filter accounts for some of the low-frequency effects of high-frequency torsional filters. It can also help shape the gain and phase characteristics of the stabilizer.
To switch between continuous and discrete implementations of the Second-Order Low-Pass Filter (Discrete or Continuous) block, adjust the Sample time parameter value.
To specify the initial conditions of this block, set Initialization to:
Inherited from block input— The block sets the state and output initial conditions to the initial input.
Specify as parameter— The block sets the state initial condition to the value of Initial state.
u — Filter input
scalar or vector
y — Filtered output
scalar or vector
Filtered output. The output has the same number of elements as the input.
Coefficient of s, A1 — A1 coefficient
0.1 (default) | positive scalar
A1, the signal conditioning frequency filter coefficient of s.
Coefficient of s^2, A2 — A2 coefficient
0.2 (default) | positive scalar
A2, the signal conditioning frequency filter coefficient of s2.
Initialization — Initial state specification
Inherited from block
input (default) |
Specify as parameter
Specify the initial state condition for this block. For more information, see Initial Conditions.
Initial state — Initial state
0 (default) | real number
Block initial state.
To enable this parameter, set Initialization to
Specify as parameter.
Sample time (-1 for inherited) — Block sample time
-1 (default) | 0 | positive scalar
Time between consecutive block executions. During execution, the block produces outputs and, if appropriate, updates its internal state. For more information, see What Is Sample Time? and Specify Sample Time.
For inherited discrete-time operation, specify
discrete-time operation, specify a positive integer. For continuous-time operation,
If this block is in a masked subsystem, or other variant subsystem that allows you to switch between continuous operation and discrete operation, promote the sample time parameter. Promoting the sample time parameter ensures correct switching between the continuous and discrete implementations of the block. For more information, see Promote Block Parameters on a Mask.
 IEEE Recommended Practice for Excitation System Models for Power System Stability Studies. IEEE Std 421.5-2016. Piscataway, NJ: IEEE-SA, 2016.
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Introduced in R2018b