What is Integral windup?

A phenomenon in which the integral term of a PID controller keeps accumulating the error and grows excessively while the manipulated variable is saturated at an upper or lower limit of the actuator. Even after the error changes sign, the manipulated variable stays saturated until the accumulated integral comes down, causing a large overshoot and a long oscillation. It is prevented by anti-windup measures such as conditional integration (clamping), which stops integrating during saturation, back-calculation, which feeds the difference between the values before and after limiting back into the integrator, and the use of the velocity form of PID.

Japanese name: 積分ワインドアップ

Integral windup appears in 2 practice questions across 1 topic, including Control Engineering Basics.

Field: Control Engineering Basics

Try it: questions about Integral windup

Which of the following correctly describes integral windup?

AA phenomenon in which the derivative term amplifies noise and the manipulated variable keeps oscillating finely; it is prevented by adding a low-pass filter to the derivative
BA phenomenon in which a steady-state error persists because the sampling period in the integral calculation was made too long
CA phenomenon in which the integral term keeps accumulating the error while the manipulated variable is stuck at its upper limit, so the manipulated variable does not come down for a while even after the error changes sign, causing a large overshoot

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Answer: C. A phenomenon in which the integral term keeps accumulating the error while the manipulated variable is stuck at its upper limit, so the manipulated variable does not come down for a while even after the error changes sign, causing a large overshoot

Manipulated variables such as a motor voltage or a valve opening have upper and lower limits. When a large error continues and the manipulated variable saturates at its upper limit, the manipulated variable cannot increase any further, yet the integral term keeps accumulating the error and grows large. Even after the controlled variable passes the setpoint and the error changes sign, the manipulated variable stays at its upper limit until the accumulated integral comes down, which causes a large overshoot and a long oscillation. As a countermeasure, anti-windup is used, which stops integrating or limits the integral while the output is saturated.

Positional PI control is implemented on a microcontroller, with the duty cycle of a PWM signal (0 to 100%) as the manipulated variable. Which of the following is a correct countermeasure against integral windup?

AWhile the output is saturated, increase the proportional gain to get out of saturation sooner
BIf the integral term is calculated in floating point no overflow occurs, so no special measure is needed
CWhile the output is saturated, stop integrating if the error would deepen the saturation, or feed the difference from the limited value back into the integrator, to hold down the integral

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Answer: C. While the output is saturated, stop integrating if the error would deepen the saturation, or feed the difference from the limited value back into the integrator, to hold down the integral

The first method is conditional integration (clamping): while the output is saturated and the error would deepen the saturation, the integral is not updated. The second is back-calculation: the difference between the value calculated before limiting and the value actually output is multiplied by a coefficient and fed back into the integrator to pull the integral back. In the velocity form of PID control, which calculates the change in the manipulated variable, simply limiting the output makes windup unlikely. When calculating in integer fixed point, overflow of the integral variable itself must also be guarded against, for example with saturating arithmetic.

Integral windup in the explanations

As a countermeasure, anti-windup is used, which stops integrating or limits the integral while the output is saturated.
Which of the following correctly describes integral windup?
In the velocity form of PID control, which calculates the change in the manipulated variable, simply limiting the output makes windup unlikely.
Positional PI control is implemented on a microcontroller, …