Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Accurate modeling of liquid flow systems is necessary for the effective operation of the plant under different conditions. The plant dynamics may change with time, and due to this, the operation may not be satisfactory. In this article, relay autotuning of a liquid flow-line is proposed. Well-known describing function approximation is utilized for the estimation of gain of relay used in a feedback loop to excite the plant to be identified. The expressions are derived for the identification of a class of overdamped second-order plus dead-time and first-order plus dead-time plant dynamics. The identification method tested on different standard systems shows that the proposed method has good identification accuracy. Therefore, the proposed identification method is applied to a liquid flow line pressure control system. The experimental results show that an accurate dynamic model is extracted using the proposed method with a minimal set of data from an obtained limit cycle oscillation. The measured quantities of the limit cycle are utilized in the derived explicit expressions for the identification of unknown variables of the dynamic plant model. A distributed process control system is utilized here as a standard industrial platform to design virtual relay and conduct the proposed autotuning. The efficiency of the modeling method is demonstrated through the comparison of Nyquist and relay response plots with the transfer functions obtained from the MATLAB system identification toolbox. © The Author(s) 2020.

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Department of Control and Automation

School of Electrical Engineering

Vellore Campus

Transactions of the Institute of Measurement and Control

Transfer function identification of a liquid flow-line pressure control system from simple relay auto-tuning

In this brief, an online relay autotuning scheme for parameter estimation of a class of time delayed systems is presented. The identification method comprises a relay and a proportional-derivative (PD) controller which helps in yielding sustained oscillation or limit cycles at the system output around the user defined setpoint. Along with the relay and controller parameters, the important limit cycle information are measured and further substituted in the derived set of mathematical expressions required for the estimation of system unknown dynamic in the form of under-damped second-order plus dead-time (SOPDT) model. Simulations of well known model dynamics from the literature are considered to illustrate the efficacy of the proposed scheme in presence of noise and static load disturbance. For the real-time validation of the proposed scheme, a pipe-line water pressure control system is identified as under-damped SOPDT transfer function model. © 2004-2012 IEEE.

IEEE Transactions on Circuits and Systems II: Express Briefs

Parameter Identification of Delayed Under-Damped Systems Using On-Line Relay Autotuning

In this brief, the dynamics of a DC-DC buck converter is modeled using the limit cycle oscillations (LCO) induced by relay feedback test. The mathematical modeling of the converter is done based on sustained oscillatory output conditions and measurements made on LCO. The method is capable of identifying the model in presence of parameter variations. With the precise information of losses of the components available in the LCO, it is possible to get an accurate dynamic model of the converter. The identified dynamic model is validated with the step response. Also, the performance of the model is tested under different parameter perturbations. The proposed method is verified by simulation and experimental results. © 2004-2012 IEEE.

Modeling and Estimation of DC-DC Buck Converter Dynamics Using Relay Feedback Output With Performance Evaluation

In this paper, identification and control of a process whose dynamics can be described by a second-order-plus-dead-time (SOPDT) stable/unstable model is presented. Using the state-space approach and limit cycle information, analytical expressions are derived to identify the process dynamics. The wavelet decomposition is performed to recover a noise-free limit cycle output which is generally contaminated by measurement noise. The proportional–integral–derivative controller connected in the feedback loop is designed primarily to get good load disturbance rejection for the identified process. Reference tracking is achieved with the help of a set-point filter. The direct synthesis method with single tuning parameter is used to tune the controller parameters. The best value of the tuning parameter is selected using the particle swarm optimization algorithm in such a way that a good performance measure of the closed-loop system is achieved. © 2017, Springer-Verlag GmbH Germany.

International Journal of Dynamics and Control

Identification and PID tuning techniques for stable and unstable SOPDT processes

Accurate dynamics of power converters are necessary to achieve good control performance. In this study, the dynamical model of the DC-DC buck converter is identified by the relay feedback method. The relay is connected in the closed loop to produce a limit cycle output. The important information of the oscillatory output is used for the identification. The relay is approximated using dual-input describing function (DIDF) in the mathematical modelling. DIDF can handle symmetric and asymmetric limit cycle outputs. The converter is modelled as a second-order plus dead-time system. Using the gain and phase angle criteria, analytical expressions are derived to estimate the dynamics. The converter dynamics obtained from the proposed method are compared with that estimated using the state-space averaging method. The model is also identified from the realtime experiment. To check the efficacy of the identified model, a model validation test is performed. © The Institution of Engineering and Technology 2018.

IET Circuits, Devices and Systems

Identification of DC-DC buck converter dynamics using relay feedback method with experimental validation

In this paper critically damped system is identified using online relay feedback test. Relay test comprises of a PID controller connected in parallel with the relay. Limit cycle information ultimate gain and frequency are used for the identification process. The objective of the proposed method is to identify an nth order critically damped system with the same order. Simple expressions for the process parameters are derived which can be used for higher order critically damped systems. The proposed identification method is tested with different examples. Identification is also done under load disturbance using DIDF (Dual input describing function). © 2016 IEEE.

1st IEEE International Conference on Power Electronics, Intelligent Control and Energy Systems, ICPEICES 2016

Identification of higher order critically damped systems using relay feedback test

The process parameters for first-order-plus-dead-time (FOPDT) and second-order-plus-dead-time (SOPDT) stable processes are obtained using relay feedback test with the help of dual input describing function (DIDF). The limit cycle data is used to identify the unknown process parameters. This paper presents identification of stable FOPDT and SOPDT process for the cases with and without load disturbance. The relay settings are unchanged during load disturbance. The bias caused due to load is incorporated in the relay approximation using DIDF. This is used to obtain the parameters for both the cases. An on-line relay feedback test using a proportional integral and derivative (PID) controller is performed to obtain the unknown parameters. © 2016 IEEE.

11th International Conference on Industrial and Information Systems, ICIIS 2016 - Conference Proceedings

Estimation of stable FOPDT and SOPDT process using dual input describing function

Voltage support to the Distribution Node (DN) is necessary requirement due to fluctuations of time varying reactive load. The Photovoltaic's Arrays (PAs) and Electric Vehicles (EVs) provide active and reactive power support to DN. Voltage support can be achieved at DN node from RES and EVs. In this paper, coordination of EVs and PAs are integrated with DN to improve the voltage profile. The coordination can be achieved by providing active and reactive power support through PAs and the EVs charge/discharge (support/inject) based on the node voltage. The bulk numbers of EVs are connected to the DN through point of common coupling (PCC) which is called as Charging Station (CS). Many PAs are used to generate power for DN support; it's known as DN Supporting Point (DNSP). The main focus of this work is to predict the most accurate location of CS and DNSP. A 33kV Distribution System (DS) of Guwahati city is modeled in MATLAB Simulink environment with four types of active and reactive load profiles. Typical DS having 48 nodes, the CS and DNSP are connected in each node of the DS. To control the power flow of the CS and DNSP, fuzzy based control strategies and optimal aggregator has been implemented. Also, probability distribution function has been used to find the scheduled arrival of EVs at CS. Voltage, power and energy of the CS and DNSP are compared. © 2014 IEEE.