Integrator¶

Integrator mask¶

This block implements an integrator with saturation.

This filter solves some of the limitations of standard Simulink integrator blocks:

When using continuous-time Simulink blocks, the generated code discretizes the continuous-time parameters in each cycle. This is computationally demanding and will increase the input-output delay of the control network. Such an increase in delay may be problematic in performance-critical applications.
When using discrete-time Simulink blocks, the configuration of the filter becomes more difficult. Firstly, control engineers are generally more familiar with continuous-time formulations. Secondly, the discrete-time filter parameters depend on the sample time of the system. When the sample time changes, the response of the filter changes as well.

Implementation¶

The integrator is implemented in discrete-time as shown below.

Simulink integrator configuration¶

Simulink integrator implementation¶

The filter is discretized assuming a fixed sample rate. That means only fixed-step solvers can be used during simulation. An error will be triggered when attempting to simulate with a variable-step solver.

The Reset input can be used to reset the state of the integrator.

Hint

When connected to the (inverted) CloseLoopRequest signal, the Reset input can be used to guarantee that the integrator output is zero when the control loop is opened.

The Lock input can be used to disconnect the input from the integrator.

Hint

Locking can be useful when using a control output saturation. When the control output saturates, the integrator state will keep accumulating, eventually preventing the control output from leaving the saturated state. This can be prevented by setting the Lock input to true when saturating the control output.

Parameters and Dialog Box¶

Show discrete-time parameters in diagnostics view: When checked, the discrete-time parameters of the Integrator block are printed to the diagnostics view. This option only affects the Simulink environment, the discrete-time parameters can always be evaluated in PMP.

Integrator dialog¶

Frequency: Parameter setting the integrator bandwidth. In other words, this sets the frequency for which the integrator gain is one (0 dB).

Hint

Due to the frequency response of an integrator (20 dB/dec magnitude decay), the configuration of the bandwidth resembles the configuration of an integral gain. I.e. doubling the integrator frequency effectively means doubling the integrator gain.
LowerClip & UpperClip: Parameter setting the lower and upper bound of the integrator saturation.

The saturation limits are ignored when LowerClip ≥ UpperClip.

Note

Whenever saturation becomes active, the Saturated output will become true. Otherwise, it will be false.

Data Type Support¶

Input ports: The input port Input accepts only signals of type single.

The input port Reset accepts only signals of type boolean.

The input port Lock accepts only signals of type boolean.
Dialog parameters: All dialog parameters must be of type single. Please note, entering double values will give a warning that precision loss may occur.

Code generation¶

Filter name

The integrator name is inherited from Simulink. To ensure that all integrators have a unique name in PMP, the integrator name is prefixed with the name of its parent subsystems. For example, the name of filter Integrator1 in Subsystem modelname/SubsystemFoo/SubsystemBar becomes SubsystemFoo_SubsystemBar_Integrator1.

Signals

The following signals are generated in PMP:

Integrator-signals¶
Signal Name	Access	Data type	Description
Frequency	RW	Float	Integrator bandwidth.
Ki	R	Float	Integrator anti wind-up lower saturation
LowerClip	RW	Float	Integrator anti wind-up lower saturation.
UpperClip	RW	Float	Integrator anti wind-up upper saturation.