FB_ExtendedStateObserver (Function Block)

Estimates the process output and total disturbance for use in an Active Disturbance Rejection Controller (ADRC).

The observer tracks two states:

Z1 estimate of the process output.
Z2 estimate of the total disturbance, including unmodelled dynamics, nonlinearities, and external disturbances.

The observer gain is derived from Wo and b0. A higher Wo tracks disturbances faster but amplifies sensor noise.

Note

The block is FINAL and must be instantiated, not extended. Use FB_init to set fWo and fB0 at declaration time.

Extends: FB_SoComponent

Properties

B0

Type: LREAL

Gets or sets the estimated plant gain (b0).

This is the ratio of how much the output changes per unit of control signal. For example, if a 10% heater output raises the temperature at 2°C/s, then b0 = 0.2. This does not need to be exact because the observer treats inaccuracies as part of the disturbance and cancels them.

InputU

Type: LREAL

Gets or sets the control signal from the previous cycle.

Set this to the controller output before calling Run().

InputY

Type: LREAL

Gets or sets the measured process output.

Set this to the feedback value before calling Run().

Wo

Type: LREAL

Gets or sets the observer bandwidth in rad/s.

Controls how quickly the observer tracks the process output and disturbances. Typically set to 3–10 times Wc. A value of 10 means the observer reacts roughly 10 times faster than the controller.

Too high amplifies sensor noise and risks numerical instability, for a 10ms task cycle, keep Wo below 100 rad/s. Too low and disturbances are not rejected fast enough.

Z1

Type: LREAL

Gets the estimated process output.

Z2

Type: LREAL

Gets the estimated total disturbance.

A large value indicates significant unmodelled dynamics or external disturbance acting on the process.

Methods

FB_init

Inputs

Name	Type	Description
`bInitRetains`	`BOOL`	if TRUE, the retain variables are initialized (warm start / cold start)
`bInCopyCode`	`BOOL`	if TRUE, the instance afterwards gets moved into the copy code (online change)
`fWo`	`LREAL`	Observer bandwidth in rad/s.
`fB0`	`LREAL`	Estimated plant gain.

Reset

Clears the observer state. Z1 and Z2 are set to zero.

Run

Advances the observer by one time step.

Note

Must be called once per cycle on a single PLC task. If the measured cycle time is zero the method returns early without updating the state.

Uses Forward Euler discretisation. For stability, ensure Wo satisfies Wo \* T < 1 where T is the task cycle time in seconds. For a 10ms task, Wo should not exceed 100 rad/s.