The ability of PI and PID controllers to compensate many practical processes has led to their wide acceptance in industrial applications The requirement to choose two or three controller parameters is most easily done using tuning rules Starting with a general discussion of industrial practice, the chapter will provide an outline of tuning rules for continuous-time PI and PID control of time-delayed single-input, single-output (SISO) processes

An Overview of Tuning Rules for the PI and PID Continuous-Time Control of Time-Delayed Single-Input, Single-Output (SISO) Processes

Modeling and control of reverse osmosis desalination process using centralized and decentralized techniques

In this paper, we introduce a new vulnerability of cyber-physical systems to malicious attack. It arises when the physical system, that is modeled as a continuous-time LTI system, is controlled by a digital controller, i.e., the output is measured only at discrete sensing times. Since the anomaly detector monitors the output signal, nothing abnormal can be detected through the output if the output looks normal at sensing times. This implies that if an (actuator) attack drives the internal states passing through the kernel of the output matrix at each sensing time, then the attack compromises the system while it remains stealthy. We show that this type of attack is feasible when the control system uses multi-rate sampling, and the sampling rate for input signal is higher than that for output measurements. Simulation results for the X-38 vehicle illustrate this new attack strategy possibly brings disastrous consequences.

Zero-stealthy attack for sampled-data control systems: The case of faster actuation than sensing

Dynamic simulation of the reverse osmosis process for seawater using LabVIEW and an analysis of the process performance

In this paper, we propose a Generalized Gain Margin (GGM) as a gain margin like stability metric for Nonlinear (NL) systems under regular perturbation. Four timedomain GGM assessment methods for Linear Time-Invariant (LTI) systems are provided, and the GGM equivalence between linear and NL systems, for both time-invariant and time-varying cases, at the equilibrium point is established, which makes it possible to develop GGM assessment methods for NL systems in the subsequent investigation using the corresponding GGM estimating methods for linear systems. However, unlike the linear systems, the GGM of the NL system may be reduced when the size of Domain of Attraction (DOA) is imposed, which is shown by examples. The main results in this paper facilitate generalization to Linear Time-Varying (LTV) systems and Nonlinear Time-Varying (NLTV) systems in future work.

Generalized gain margin for nonlinear systems

Mathematical models that adequately represent steady state and transient behaviour of desalination process comprising of equalisation tank, reverse osmosis (RO) system using a constant rate of transfer of diffusing substance per unit area of the cylinder surface and a potable water tank system are developed. A solute mass transport model is solved using the partial differential equation parabolic elliptical numerical technique using Crank–Nicholson method is inbuilt. Solution of this model shows decline in the permeate flux in the RO membrane. The theoretical transient and steady state models are compared with experimental results. The comparison shows that both the transient and steady state models are matching with the experimental results. A Transfer function model has also been developed to represent input–output relations. The decrease in flux in the RO membrane was compared with the experimental results.

Development of a transient model for the desalination of sea/brackish water through reverse osmosis

Multi-rate controllers are useful in providing fast control updates using slow measurements. The multi-rate control loop involves up-sampling, down-sampling, and systems considered at different timescales. The challenge is then, to present complete frequency domain model of the loop. This paper presents the frequency domain model of the loop which is suitable for analysis and design of controllers. The approach is illustrated through a numerical example.

Design of digital multi-rate controller using frequency domain analysis

The control of various processes using a proportional-integral (PI) controller is investigated in this work A new tuning rule based on the ultimate gain and phase margin specification is proposed The tuning rule is given by analytical approximations To obtain the tuning rule, a control signature is formulated using the ultimate properties of the system The PI controller parameters are related with process model parameter to yield a model based tuning rule Simulation examples are provided to demonstrate the performance and robustness of the present tuning rule The new tuning rule requires a relatively small computational effort and is particularly useful for online applications

Model Based PI Tuning Rule with Ultimate Gain and Phase Margin Criteria

The ripple voltage waveform of DC-DC buck converter is used for system identification Based on the parameters identified and using the user specification of gain margin and phase margin, PI controller parameter tuning rule is proposed The closed loop performance with line and load variation of the buck converter is simulated using MATLAB/SIMULINK and analyzed The robustness measure of the PI controller on the performance is also studied

Rames C. Panda

Papers

Development of a transient model for the desalination of sea/brackish water through reverse osmosis

Design of digital multi-rate controller using frequency domain analysis

Model Based PI Tuning Rule with Ultimate Gain and Phase Margin Criteria

System Identification and controller tuning rule for DC-DC converter using ripple voltage waveform