genfrd

Generalized frequency response data (FRD) model

Description

Generalized FRD (genfrd) models arise when you combine numeric FRD models with models containing tunable components (Control Design Blocks). genfrd models keep track of how the tunable blocks interact with the tunable components. For more information about Control Design Blocks, see Generalized Models.

Construction

To construct a genfrd model, use series, parallel, lft, or connect, or the arithmetic operators +, -, *, /, \, and ^, to combine a numeric FRD model with control design blocks.

You can also convert any numeric LTI model or control design block sys to genfrd form.

frdsys = genfrd(sys,freqs,frequnits) converts any static model or dynamic system sys to a generalized FRD model. If sys is not an frd model object, genfrd computes the frequency response of each frequency point in the vector freqs. The frequencies freqs are in the units specified by the optional argument frequnits. If frequnits is omitted, the units of freqs are 'rad/TimeUnit'.

frdsys = genfrd(sys,freqs,frequnits,timeunits) further specifies the time units for converting sys to genfrd form.

For more information about time and frequency units of genfrd models, see Properties.

Input Arguments

sys	A static model or dynamic system model object.
freqs	Vector of frequency points. Express frequencies in the unit specified in frequnits.
frequnits	Frequency units of the genfrd model, specified as one of the following values: 'rad/TimeUnit' 'cycles/TimeUnit' 'rad/s' 'Hz' 'kHz' 'MHz' 'GHz' 'rpm' Default: 'rad/TimeUnit'
timeunits	Time units of the genfrd model, specified as one of the following values: 'nanoseconds' 'microseconds' 'milliseconds' 'seconds' 'minutes' 'hours' 'days' 'weeks' 'months' 'years' Default: 'seconds'

Properties

Blocks	Structure containing the control design blocks included in the generalized LTI model or generalized matrix. The field names of Blocks are the Name property of each control design block. You can change some attributes of these control design blocks using dot notation. For example, if the generalized LTI model or generalized matrix M contains a realp tunable parameter a, you can change the current value of a using: M.Blocks.a.Value = -1;
Frequency	Frequency points of the frequency response data. Specify Frequency values in the units specified by the FrequencyUnit property.
FrequencyUnit	Frequency units of the model. FrequencyUnit specifies the units of the frequency vector in the Frequency property. Set FrequencyUnit to one of the following values: 'rad/TimeUnit' 'cycles/TimeUnit' 'rad/s' 'Hz' 'kHz' 'MHz' 'GHz' 'rpm' The units 'rad/TimeUnit' and 'cycles/TimeUnit' are relative to the time units specified in the TimeUnit property. Changing this property changes the overall system behavior. Use chgFreqUnit to convert between frequency units without modifying system behavior. Default: 'rad/TimeUnit'
InputDelay	Input delay for each input channel, specified as a scalar value or numeric vector. For continuous-time systems, specify input delays in the time unit stored in the TimeUnit property. For discrete-time systems, specify input delays in integer multiples of the sample time Ts. For example, InputDelay = 3 means a delay of three sample times. For a system with Nu inputs, set InputDelay to an Nu-by-1 vector. Each entry of this vector is a numerical value that represents the input delay for the corresponding input channel. You can also set InputDelay to a scalar value to apply the same delay to all channels. Default: 0
OutputDelay	Output delays. OutputDelay is a numeric vector specifying a time delay for each output channel. For continuous-time systems, specify output delays in the time unit stored in the TimeUnit property. For discrete-time systems, specify output delays in integer multiples of the sample time Ts. For example, OutputDelay = 3 means a delay of three sampling periods. For a system with Ny outputs, set OutputDelay to an Ny-by-1 vector, where each entry is a numerical value representing the output delay for the corresponding output channel. You can also set OutputDelay to a scalar value to apply the same delay to all channels. Default: 0 for all output channels
Ts	Sample time. For continuous-time models, Ts = 0. For discrete-time models, Ts is a positive scalar representing the sampling period. This value is expressed in the unit specified by the TimeUnit property of the model. To denote a discrete-time model with unspecified sample time, set Ts = -1. Changing this property does not discretize or resample the model. Default: 0 (continuous time)
TimeUnit	Units for the time variable, the sample time Ts, and any time delays in the model, specified as one of the following values: 'nanoseconds' 'microseconds' 'milliseconds' 'seconds' 'minutes' 'hours' 'days' 'weeks' 'months' 'years' Changing this property has no effect on other properties, and therefore changes the overall system behavior. Use chgTimeUnit to convert between time units without modifying system behavior. Default: 'seconds'
InputName	Input channel names, specified as one of the following: Character vector — For single-input models, for example, 'controls'. Cell array of character vectors — For multi-input models. Alternatively, use automatic vector expansion to assign input names for multi-input models. For example, if sys is a two-input model, enter: sys.InputName = 'controls'; The input names automatically expand to {'controls(1)';'controls(2)'}. You can use the shorthand notation u to refer to the InputName property. For example, sys.u is equivalent to sys.InputName. Input channel names have several uses, including: Identifying channels on model display and plots Extracting subsystems of MIMO systems Specifying connection points when interconnecting models Default: '' for all input channels
InputUnit	Input channel units, specified as one of the following: Character vector — For single-input models, for example, 'seconds'. Cell array of character vectors — For multi-input models. Use InputUnit to keep track of input signal units. InputUnit has no effect on system behavior. Default: '' for all input channels
InputGroup	Input channel groups. The InputGroup property lets you assign the input channels of MIMO systems into groups and refer to each group by name. Specify input groups as a structure. In this structure, field names are the group names, and field values are the input channels belonging to each group. For example: sys.InputGroup.controls = [1 2]; sys.InputGroup.noise = [3 5]; creates input groups named controls and noise that include input channels 1, 2 and 3, 5, respectively. You can then extract the subsystem from the controls inputs to all outputs using: sys(:,'controls') Default: Struct with no fields
OutputName	Output channel names, specified as one of the following: Character vector — For single-output models. For example, 'measurements'. Cell array of character vectors — For multi-output models. Alternatively, use automatic vector expansion to assign output names for multi-output models. For example, if sys is a two-output model, enter: sys.OutputName = 'measurements'; The output names automatically expand to {'measurements(1)';'measurements(2)'}. You can use the shorthand notation y to refer to the OutputName property. For example, sys.y is equivalent to sys.OutputName. Output channel names have several uses, including: Identifying channels on model display and plots Extracting subsystems of MIMO systems Specifying connection points when interconnecting models Default: '' for all output channels
OutputUnit	Output channel units, specified as one of the following: Character vector — For single-output models. For example, 'seconds'. Cell array of character vectors — For multi-output models. Use OutputUnit to keep track of output signal units. OutputUnit has no effect on system behavior. Default: '' for all output channels
OutputGroup	Output channel groups. The OutputGroup property lets you assign the output channels of MIMO systems into groups and refer to each group by name. Specify output groups as a structure. In this structure, field names are the group names, and field values are the output channels belonging to each group. For example: sys.OutputGroup.temperature = [1]; sys.OutputGroup.measurement = [3 5]; creates output groups named temperature and measurement that include output channels 1, and 3, 5, respectively. You can then extract the subsystem from all inputs to the measurement outputs using: sys('measurement',:) Default: Struct with no fields
Name	System name, specified as a character vector. For example, 'system_1'. Default: ''
Notes	Any text that you want to associate with the system, stored as a string or a cell array of character vectors. The property stores whichever data type you provide. For instance, if sys1 and sys2 are dynamic system models, you can set their Notes properties as follows: sys1.Notes = "sys1 has a string."; sys2.Notes = 'sys2 has a character vector.'; sys1.Notes sys2.Notes ans = "sys1 has a string." ans = 'sys2 has a character vector.' Default: [0×1 string]
UserData	Any type of data you want to associate with system, specified as any MATLAB® data type. Default: []
SamplingGrid	Sampling grid for model arrays, specified as a data structure. For model arrays that are derived by sampling one or more independent variables, this property tracks the variable values associated with each model in the array. This information appears when you display or plot the model array. Use this information to trace results back to the independent variables. Set the field names of the data structure to the names of the sampling variables. Set the field values to the sampled variable values associated with each model in the array. All sampling variables should be numeric and scalar valued, and all arrays of sampled values should match the dimensions of the model array. For example, suppose you create a 11-by-1 array of linear models, sysarr, by taking snapshots of a linear time-varying system at times t = 0:10. The following code stores the time samples with the linear models. sysarr.SamplingGrid = struct('time',0:10) Similarly, suppose you create a 6-by-9 model array, M, by independently sampling two variables, zeta and w. The following code attaches the (zeta,w) values to M. [zeta,w] = ndgrid(<6 values of zeta>,<9 values of w>) M.SamplingGrid = struct('zeta',zeta,'w',w) When you display M, each entry in the array includes the corresponding zeta and w values. M M(:,:,1,1) [zeta=0.3, w=5] = 25 -------------- s^2 + 3 s + 25 M(:,:,2,1) [zeta=0.35, w=5] = 25 ---------------- s^2 + 3.5 s + 25 ... For model arrays generated by linearizing a Simulink® model at multiple parameter values or operating points, the software populates SamplingGrid automatically with the variable values that correspond to each entry in the array. For example, the Simulink Control Design™ commands linearize (Simulink Control Design) and slLinearizer (Simulink Control Design) populate SamplingGrid in this way. Default: []

Tips

• You can manipulate genfrd models as ordinary frd models. Frequency-domain analysis commands such as bode evaluate the model by replacing each tunable parameter with its current value.

Version History

Introduced in R2011a