Disturbance Compensator

Modify control actions to compensate for unknown dynamics and disturbances

Since R2024a

• 

Libraries:
Simulink Control Design / Disturbance Observer

Description

Use the Disturbance Compensator block to modify control actions of a nominal controller to reject and compensate for disturbances in your model. To compensate for disturbances, the Disturbance Compensator block uses an extended state observer to estimate total disturbances in the model and returns the modified controller actions you can use as plant input.

The block extends the implementation of ESO described in the previous section as follows.

$$\begin{array}{c}\dot{x}/x^{+}=Ax+B_{u}u+B_{d}d\\ y_m=C_{m}x\\ u=u_0+K_d\widehat{d}\end{array}$$

Here:

• x is the plant states.

• $$\dot{x}$$ is the state derivative in continuous time and x⁺ is the state update x[k+1] in discrete time.

• A, B_u, and C_m are the plant dynamics.

• y_m is the measurable plant output.

• B_d is the disturbance input matrix.

• d is the total disturbances in the model, including unknown dynamics and internal and external disturbances.

• u is the modified controller action.

• u₀ is the nominal controller action.

• K_d is the compensation gain matrix.

The block does not require you to provide an actual model of the plant. You can specify the dynamics obtained from a physical representation or an approximation of the plant. Therefore, the accuracy of disturbance rejection will depend on the accuracy of the plant approximation you provide.

For more information, see Control Design and Disturbance Compensation Using Extended State Observers

Examples

Compensate for Disturbances in Spring-Mass-Damper System

Compensate for disturbances in a spring-mass-damper system using the Disturbance Compensator block.

• Since R2024a
• Open Live Script

Ports

Input

u — Known inputs

scalar | vector

Specify the known inputs of the model as an N_u-by-1 signal, where N_u is the number of inputs in the model.

y — Measured outputs

scalar | vector

Specify the measured outputs of the model N_y-by-1 signal, where N_y is the number of outputs in the model.

A — State matrix

scalar | vector | matrix

Specify the state matrix as an N_x-by-N_x signal, where N_x is the number of states in the model.

Dependencies

To enable this port, select the Use external source for model matrices (A,Bu,Cm) and Use external source for L parameters.

Bu — Input matrix

scalar | vector | matrix

Specify the input matrix as an N_x-by-N_u signal, where N_x is the number of states and N_u is the number of inputs in the model.

Dependencies

To enable this port, select the Use external source for model matrices (A,Bu,Cm) and Use external source for L parameters.

Cm — Output matrix

scalar | vector | matrix

Specify the output matrix as an N_y-by-N_x signal, where N_x is the number of states and N_y is the number of outputs in the model.

Dependencies

To enable this port, select the Use external source for model matrices (A,Bu,Cm) and Use external source for L parameters.

Bd — Disturbance matrix

scalar | vector | matrix

Specify the disturbance matrix as an N_x-by-N_d signal, where N_x is the number of states and N_d is the number of disturbances in the model.

Dependencies

To enable this port, select the Use external source for matrix Bd and Use external source for L parameters.

S0 — Initial conditions

scalar | vector

Specify the initial conditions for the extended states as a scalar or vector with length N_x + N_d, where N_x is the number of states and N_d is the number of disturbances int the model.

Dependencies

To enable this port, select Use external source for initial conditions S0 (x0,d0).

L — Observer matrix

scalar | vector | matrix

Specify the observer matrix as an (N_x+N_d)-by-N_y signal.

Dependencies

To enable this port, select Use external source for matrix L.

Kd — Compensation gain matrix

scalar | vector | matrix

Specify the compensation gain matrix K_d as anN_u-by-N_d signal.

Dependencies

To enable this port, select Use external source for matrix Kd.

Output

dhat — Estimated disturbances

vector

Estimated disturbances in the model, returned as an N_d-by-1 signal, where N_d is the number of disturbances in the model.

xhat — Estimated states

vector

Estimated states of the model, returned as an N_x-by-1 signal, where N_x is the number of states in the model.

Dependencies

To enable this port, select Output estimated model states xhat.

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Parameters Tab

Time domain — Controller time domain

discrete-time (default) | continuous-time

Specify the controller time domain.

When you select discrete-time, specify the sample time using the Sample time parameter.

LTI state-space variable — Known plant dynamics

ss object | idss object

Specify the known plant dynamics as a state-space model object. You can obtain this model from a physical representation or an approximation of the plant.

Use external source for model matrices (A,Bu,Cm) — Specify model matrices at block input ports

off (default) | on

Select this option to specify the model matrices A, B_u, and C_m using the block input ports A, Bu, and Cm, respectively.

Dependencies

To enable this parameter, you must also select the Use external source for L parameter.

Number of states — Number of states in the model

1 (default) | positive integer

When you specify model matrices as block inputs, use this parameter to specify the number of states in the model.

Dependencies

To enable this parameter, select the Use external source for model matrices (A,Bu,Cm) and Use external source for L parameters.

Number of inputs — Number of inputs in the model

1 (default) | positive integer

When you specify model matrices as block inputs, use this parameter to specify the number of inputs in the model.

Dependencies

To enable this parameter, select the Use external source for model matrices (A,Bu,Cm) and Use external source for L parameters.

Number of outputs — Number of outputs in the model

1 (default) | positive integer

When you specify model matrices as block inputs, use this parameter to specify the number of outputs in the model.

Dependencies

To enable this parameter, select the Use external source for model matrices (A,Bu,Cm) and Use external source for L parameters.

Specify gain k (such that Bd = k*Bu) — Gain value for computing disturbance input matrix

1 (default) | nonzero scalar

Specify the gain value k for computing disturbance matrix B_d such that B_d = k×B_u.

Use external source for matrix Bd — Specify disturbance matrix at block input port

off (default) | on

Select this option to specify the disturbance matrix B_d using the block input port Bd.

Dependencies

To enable this parameter, you must also select the Use external source for L parameter.

Number of disturbances — Number of disturbances in the model

1 (default) | positive integer

When you specify disturbance matrices as a block input, use this parameter to specify the number of inputs in the model.

Dependencies

To enable this parameter, select the Use external source for matrix Bd and Use external source for L parameters.

Initial conditions — Initial conditions for the extended states

0 (default) | scalar | vector

Specify the initial conditions for the extended states as a scalar or vector with length N_x + N_d, where N_x is the number of states and N_d is the number of disturbances int the model.

Use external source for initial conditions S0 (x0,d0) — Specify initial conditions at block input port

off (default) | on

Select this option to specify the initial conditions using the block input port S0.

Tuning Tab

Bandwidth (rad/s) — Observer bandwidth

1 (default) | positive scalar

Specify the observer bandwidth ω_o as a positive scalar.

Spacing (rad/s) — Observer bandwidth spacing

0.01 (default) | positive scalar

Specify the spacing for the closed-loop poles. For given observer bandwidth ω_o and pole spacing δ, the block places the closed-loop poles at $$\left[\begin{array}{ccccc}{\omega }_o& {\omega }_o+\delta & {\omega }_o+\delta \times 2& \dots & {\omega }_o+\delta \times n\end{array}\right]$$, where n is the number of closed-loop poles.

Use external source for matrix L — Specify observer matrix at block input port

off (default) | on

Select this option to specify the observer matrix using the block input port L.

Use external source for matrix Kd — Specify compensation gain matrix at block input port

off (default) | on

Select this option to specify the observer matrix using the block input port Kd.

Block Tab

Limit output (u) — Limit block output to specified saturation limits

off (default) | on

Option to limit block output to specified saturation limits. Specify the output saturation limits using the Upper limit and Lower limit parameters.

Upper limit — Upper saturation limit for block output

inf (default) | scalar

Specify the upper limit for the block output. The block output is held at this value whenever it would otherwise exceed this value.

Dependencies

To enable this parameter, select the Limit output (u) parameter.

Lower limit — Lower saturation limit for block output

–inf (default) | scalar

Specify the lower limit for the block output. The block output is held at this value whenever it would otherwise go below this value.

Dependencies

To enable this parameter, select the Limit output (u) parameter.

Data type — Floating point precision

double (default) | single

Specify the floating-point precision based on simulation environment or hardware requirements.

For continuous-time models, the block only supports double data type.

Time delay — Specify time delays

1 (default) | positive scalar | vector

Specify time delays in the model as a scalar or vector of length N_u, where N_u is the number of inputs in the model.

For discrete-time models, specify the delay as an integer multiple k of the sample time. The delay in discrete time is given by T_d = k×T_s.

Dependencies

To enable this parameter, select the Specify input delays parameter.

Output estimated model states xhat — Output estimated states at block output port

off (default) | on

Select this option to output estimated model states at the block output xhat.

Output estimated model states dhat — Output estimated disturbances at block output port

off (default) | on

Select this option to output estimated model states at the block output dhat.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2024a