ABB ACSM1 Series, Firmware Manual

Page: 277 / 334

Standard function blocks
277
Operation The PID controller can be used for closed-loop control systems. The controller includes
anti-windup correction and output limitation.
The PID controller output (Out) before limitation is the sum of the proportional (U
P
),
integral (U
I
) and derivative (U
D
) terms:
Out
unlimited
(t) = U
P
(t) + U
I
(t) + U
D
(t)
U
P
(t) = P × Dev(t)
U
I
(t) = P/tI × [
∫
Dev(
τ
)d
τ
+ tC × (Out(t) - Out
unlimited
(t))]
U
D
(t) = P × tD × d(Dev(t))/dt
Integrator:
The integral term can be cleared by setting I_reset to 1. Note that the anti-windup
correction is simultaneously disabled. When I_reset is 1, the controller acts as a PD
controller.
If integration time constant tI is 0, the integral term will not be updated.
Smooth return to normal operation is guaranteed after errors or abrupt input value
changes. This is achieved by adjusting the integral term so that the output will retain its
previous value during these situations.
Limitation:
The output is limited by the defined minimum and maximum values, OLL and OHL:
If the actual value of the output reaches the specified minimum limit, output O=LL is set
to 1.
If the actual value of the output reaches the specified maximum limit, output O=HL is set
to 1.
Smooth return to normal operation after limitation is requested if and only if the
anti-windup correction is not used, i.e. when tI = 0 or tC = 0.
Error codes:
Error codes are indicated by the error output (ERROR) as follows
Balancing:
The balancing function (BAL) permits the output signal to track an external reference
and gives a smooth return to the normal operation. If BAL is set to 1, the output (Out) is
set to the value of the balance reference input (BAL_ref). Balance reference is limited by
the defined minimum and maximum limits (OLL and OHL).
Anti-windup:
Anti-windup correction time constant is defined by input tC. If tC = 0 or tI = 0,
anti-windup correction is disabled.
Error code Description
1 The minimum limit (OLL) exceeds the maximum limit (OHL).
2 Overflow with Up, Ui, or Ud calculation