Li-Hua Xie

Nanyang Technological University, Singapore, Singapore

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Publications (4)2.52 Total impact

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    ABSTRACT: This paper presents a new control-loop configuration criterion for multivariable processes. Both the steady-state and transient information of the process transfer function are investigated. A new interaction measurement, relative normalized gain array, is proposed for evaluating control-loop interactions. Consequently, a new loop pairing criterion based on the relative normalized gain array is proposed for control structure configuration. The main contribution of this work is that it systematically analyzed the process transferring characteristics from both steady-state and transient perspectives and derived a feasible solution for the problem. Several examples, for which the conventional relative gain array based loop pairing criterion gives an inaccurate interaction assessment, are employed to demonstrate the effectiveness of the proposed interaction measure and loop pairing criterion.
    Journal of Process Control. 01/2009;
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    ABSTRACT: This paper presents the new development of the boiler-turbine coordinated control strategy using fuzzy reasoning and autotuning techniques. The boiler-turbine system is a very complex process that is a multivariable, nonlinear, slowly time-varying plant with large settling time and a lot of uncertainties. As there exist strong couplings between the main steam pressure control loop and the power output control loop in the boiler-turbine unit with large time-delay and uncertainties, automatic coordinated control of the two loops is a very challenging problem. This paper presents a new coordinated control strategy (CCS) which is organized into two levels: a basic control level and a high supervision level. Proportional-integral derivative (PID) type controllers are used in the basic level to perform basic control functions while the decoupling between two control loops can be realized in the high level. A special subclass of fuzzy inference systems, called the Gaussian partition with evenly (GPE) spaced midpoints systems, is used to self-tune the main steam pressure PID controller's parameters online based on the error signal and its first difference, aimed at overcoming the uncertainties due to changing fuel calorific value, machine wear, contamination of the boiler heating surfaces and plant modeling errors. For the large variation of operating condition, a supervisory control level has been developed by autotuning technique. The developed CCS has been implemented in a power plant in China, and satisfactory industrial operation results demonstrate that the proposed control strategy has enhanced the adaptability and robustness of the process. Indeed, better control performance and economic benefit have been achieved.
    IEEE Transactions on Control Systems Technology 12/2005; · 2.52 Impact Factor
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    ABSTRACT: First Page of the Article
    Control and Automation, 2002. ICCA. Final Program and Book of Abstracts. The 2002 International Conference on; 02/2002
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    ABSTRACT: A cooling coil unit (CCU) is nonlinear in nature. Existing CCU models for control and optimization are either linear approximations around working point or very complex nonlinear ones, resulting in difficulties for real time applications. Therefore, a simple yet accurate CCU engineering model is very important to obtain a better performance for Heating, Ventilating, and Air-Conditioning (HVAC) systems. In this paper, a technique for developing a simple yet accurate engineering CCU model is presented. The modeling technique is based on energy balance and heat transfer principles. Commissioning information is then used to estimate up to maximum three model parameters by either linear or non-linear least-squares method. Experiment shows that the method is robust and gives a good match to the real performance over the entire operating range compared with methods presented in the literature. This model is expected to have wide applications in control and optimization of HVAC systems. The modeling methodology can also be extended to other heat exchangers. 1 INTRUDUCTION Heating, Ventilating, and Air-Conditioning (HVAC) systems provide a specified ambient environment for the occupants with comfortable temperature, humidity, etc. In HVAC systems, cooling coils play an essential role (Skimin 1995, Kreith & West 1997), which transfer cooling load from air loop to chilled water loop by forcing air flow over the coil and into the space to be conditioned. The performance of coils, which is embodied through their heat transfer properties, directly influences the performance of HVAC systems. Therefore, a simple, reliable and yet accurate engineering model is very important for system control and optimization applications.