Diagnosis of a unit-wide disturbance caused by saturation in a manipulated variable

It is well known that faulty control valves with friction in the moving parts lead to limit cycle oscillations which can propagate to other parts of the plant. However, a control loop with healthy valve can also undergo oscillatory behavior. The root cause of a unit-wide oscillation in a distillation column was traced to a pressure control loop in a case study at Mitsui Chemicals. The diagnosis was made by means of a new technique of pattern matching of the time-resolved frequency spectrum using a wavelet analysis tool. The method identified key characteristics shared by measurements at various places in the column and quantified the similarities. Non-linearity was detected in the time trend of the pressure measurement, a result which initially suggested the root cause was a faulty actuator or sensor. Further analysis showed, however, that the source of non-linearlity was periodic saturation of the manipulated variable caused by slack tuning. The problem was remidied by changing the controller tuning settings and the unit-wide disturbance then went away

Signal Identification In Discrete-Time Based On Internal-Model-Principle

This work presents an implementation of a signal identification algorithm which is based on the internal model principle. By using several internal models in feedback with a tuning function, this algorithm can decompose a signal into narrow-band signals and identify the frequencies, amplitudes and relative phases. A desired band-pass filter response can be achieved by selecting appropriate coefficients of the controllers and tuning functions, which can reject the noise and improve the performance. To achieve a result with fast transient characteristics, this system is then modified by adding a low-pass filter. This work is based on the previous work in continuous time. However, a discrete implementation should be much more practical. The simulation result shows a good tracking of the original signal with minimal response to measurement noise

A path planning and path-following control framework for a general 2-trailer with a car-like tractor

Maneuvering a general 2-trailer with a car-like tractor in backward motion is a task that requires significant skill to master and is unarguably one of the most complicated tasks a truck driver has to perform. This paper presents a path planning and path-following control solution that can be used to automatically plan and execute difficult parking and obstacle avoidance maneuvers by combining backward and forward motion. A lattice-based path planning framework is developed in order to generate kinematically feasible and collision-free paths and a path-following controller is designed to stabilize the lateral and angular path-following error states during path execution. To estimate the vehicle state needed for control, a nonlinear observer is developed which only utilizes information from sensors that are mounted on the car-like tractor, making the system independent of additional trailer sensors. The proposed path planning and path-following control framework is implemented on a full-scale test vehicle and results from simulations and real-world experiments are presented.Comment: Preprin

Theory and application of time-frequency analysis to transient phenomena in electric power and other physical systems

textThis dissertation provides a new theoretical scheme of signal processing: cross time-frequency analysis. The proposed cross time-frequency analysis is applied to various types of real-world signals and systems in order to verify the feasibility and applicability of the proposed theory. The application of time-frequency analysis is focused on electric power and other physical systems. Unfortunately, classical Fourier-based methodologies and power quality indices are not directly applicable for the assessment and localization of transient power quality phenomena. Hence, in this dissertation, application of time-frequency analysis is discussed for the assessment and localization of transient power quality events. Through the use of joint time and frequency localized “energy” distributions, a set of time-frequency based transient power quality indices are presented and applied to real-world disturbance signals. Also, a solution for the spatial localization of transient disturbances is presented. It rests upon calculating a time and frequency localized “phase difference” via cross time-frequency analysis. By evaluating the phase difference of voltage and current at the time and frequency of interest and at different spatial points, one can identify the direction of transient disturbance energy flow in order to pinpoint the location of the transient disturbance source. In addition, applications of time-frequency theory have been extended to various types of real-world physical signals and systems. A new reflectometry methodology, time-frequency domain reflectometry, is proposed and demonstrated with experimental results. Also, cross time-frequency analysis has been utilized for the characterization of ocean wave group propagation, and applied to transient postural sway signals to identify the effects of aging and sensory systems on human postural control systems.Electrical and Computer Engineerin