Time-delay systems: an overview of some recent advances and open problems

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

International Journal of Computer and Applications

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Power Electronics Converters Applications And Design

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L2 Gain And Passivity Techniques In Nonlinear Control

Load frequency control of a realistic power system with multi-source power generation

Brief Obtaining controller parameters for a new Smith predictor using autotuning

A new control structure with a tuning method to design a PID load frequency controller for power systems is presented. Initially, the controller is designed for single area power system, then it is extended to multi-area case. The controller parameters are obtained by expanding controller transfer function using Laurent series. Relay based identification technique is adopted to estimate power system dynamics. Robustness studies on stability and performance are provided, with respect to uncertainties in the plant parameters. The proposed scheme ensures that overall system remains asymptotically stable for all bounded uncertainties and for system oscillations. Simulation results show the feasibility of the approach and the proposed method improves the load disturbance rejection performance significantly even in the presence of the uncertainties in plant parameters.

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A new control scheme for PID load frequency controller of single-area and multi-area power systems

A set of general expressions is derived from a single asymmetrical relay feedback test for online plant identification. The expressions also remain valid for an odd symmetrical limit cycle test method. Using the expressions, the exact parameters of open-loop stable and unstable first-order plus time delay (FOPDT) and second-order plus time delay (SOPDT) transfer function models may be obtained from simple measurements made on the limit cycle. The approach can also be used to identify transfer functions of integrating processes. Conditions for the existence of limit cycles in unstable FOPDT and SOPDT processes are derived. The design of controllers for these processes is then considered and a simple, but very effective, approach using standard forms with a variable zero is presented. The advantages of using PI-PD control, compared with conventional PID or PI-D control, particularly for unstable and integrating processes is clearly shown. Examples are given to illustrate the value of the proposed general identification method and the improved system performance provided by the proposed controllers.

Autotuning and controller design for processes with small time delays

A modified Smith predictor and a simple but very effective controller design procedure is proposed for time delay processes. The controller has a simple structure whose high performance particularly for unstable and integrating process is clearly shown. Design of the controllers is based on standard forms of the closed-loop system response with a variable zero and on the optimum stability approach of De Paor and O'Malley (1989) for a proportional controller for an unstable process. Illustrative examples show the superiority of the proposed controller design method over previously published approaches in terms of both closed-loop performance and robustness.

Somanath Majhi

Papers

Load frequency control of a realistic power system with multi-source power generation

Brief Obtaining controller parameters for a new Smith predictor using autotuning

A new control scheme for PID load frequency controller of single-area and multi-area power systems

Autotuning and controller design for processes with small time delays

Modified Smith predictor and controller for processes with time delay