Limitations of PID controllers

Abstract

The objective of the paper is to outline the limitations of classical PID controllers acting on the error signal for control of a plant modelled as a linear transfer function.It is shown how a modified form of controller, a PI-PD controller, which corresponds to PI control of a plant transfer function changed by the PD feedback can produce improved control in several situations. This implementation avoids the derivative kick problem associated with derivative action in the forward path, which still exists when a filter is included. Further, the PD in the inner feedback loop enables placement of the open loop poles in appropriate positions thereby providing good control for open loop system transfer functions having resonances, unstable, or integrating poles. The simulation results show significantly improved performance of the proposed control method particularly for the latter processes.

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“…In CLCS, the most common controller used is the proportional-integral-derivative (PID) controller. This high usage is because most engineers understand how to vary the three parameters [3], based on the past (I), present (P), and future (D) control error [1] for achieving the intended CLCS behavior. However, PID controllers do not work well for nonlinear processes as well as for processes with small dead-times [3].…”

“…This high usage is because most engineers understand how to vary the three parameters [3], based on the past (I), present (P), and future (D) control error [1] for achieving the intended CLCS behavior. However, PID controllers do not work well for nonlinear processes as well as for processes with small dead-times [3]. Further, depending on its parameter, PID controllers are prone to over-and undershot or reach the set-point very slow [28].…”

Mitigation of Derivative Kick Using Time-Varying Fractional-Order PID Control

“…1 is proven to be useful in improving the closed loop control performance, there exists a general problem caused by the derivative kick, that is, an instant response of the controller that generates a huge spike in the designed control signal U (s) for a step input command. Even though, many researches focus on the improvement of overshoot and settling time [10]- [12] on FOPID controller design, the spike in the control signal is often overlooked. Such a spike is harmful to the control systems and may result in damage to the system devices.…”

“…Most literatures are focused on the controlling aspect of the plant with a reduced error management and not much on the peak values of the control signal leaving the PID controller. There is always a compromise between overshoot, settling time, and the voltage spike, called the derivative kick, coming from the derivative control from the PID controller [10]- [12]. This voltage spike can be attributed to sudden changes to the setpoint, which will give rise to an impulse signal coming from the controller output.…”

“…The output signal coming from the controller is then fed to control elements such as: electric motors, electronics or control valves, which may be damaged by such sudden high voltage spikes. To mitigate this derivative kick, several researchers have applied the parallel controller structures such as the PI-PD [10], I-PD [11], [12], and the most recent fractionalorder proportional integral-derivative (FOPI-D) controller [13]. The PI-PD controller design provides a good overall control of unstable and resonant system's responses to setpoint changes.…”