Automatic generation control of an interconnected hydrothermal power system considering superconducting magnetic energy storage Rajesh Joseph Abraham, D. Das * , Amit Patra Department of Electrical Engineering, Indian Institute of Technology, Kharagpur 721 302, India Received 3 February 2006; received in revised form 18 November 2006; accepted 8 January 2007 Abstract This paper presents the analysis of automatic generation control (AGC) of an interconnected hydrothermal power system in the pres- ence of generation rate constraints (GRCs). The improvement of AGC with the addition of a small capacity superconducting magnetic energy storage (SMES) unit in either, as well as in both the areas are studied. Time domain simulations are used to study the performance of the power system and control logic. The optimal values of the integral gain settings are obtained using integral squared error (ISE) technique by minimising a quadratic performance index. Suitable method for controlling the SMES unit is described. Analysis reveals that SMES unit fitted in either of the areas is as effective as SMES units fitted in both the areas and improves the dynamic performances to a considerable extent following a load disturbance in either of the areas. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: AGC; Hydrothermal; Power system; SMES 1. Introduction Electric power systems operating in an interconnected grid are normally composed of control areas or regions and interconnected through tie-lines. Each control area is obliged to manage in parallel, the important tasks of covering the customers load requirements as well as main- taining the interchanged power and the system frequency at their respective scheduled values so that the power sys- tem remains at its nominal state characterised by nominal system frequency, voltage profile and load flow configura- tion. To maintain the power system in its nominal state, at each instant, the generated power should exactly match the demanded power plus the associated system losses. But in a practical power system, the load is changing con- tinuously. Further, the ability of the generation to track the changing load is limited due to physical/technical con- siderations. Thus, the exact power generation–consump- tion equilibrium and hence, the nominal state of the power system cannot be satisfied in practice. Thus, auto- matic generation control (AGC) of an interconnected power system is concerned with two main objectives: instantaneously matching the generation to the system load and adjusting the system frequency and tie-line load- ings at their scheduled values as close as possible so that, the quality of the power delivered is maintained at the requisite level. Literature survey shows that, most of the works con- cerned with AGC of interconnected power systems pertain to tie-line bias control strategy [1–10]. Supplementary con- trollers are designed to regulate the area control errors to zero effectively. Even in the case of small load disturbances and with the optimised gain for the supplementary control- lers, the power frequency and the tie-line power deviations persist for a long duration. In these situations, the governor system may no longer be able to absorb the frequency fluc- tuations due to its slow response [1]. Thus, to compensate for the sudden load changes, an active power source with fast response such as an superconducting magnetic energy 0142-0615/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijepes.2007.01.004 * Corresponding author. Tel.: +91 3222 79507; fax: +91 3222 55303. E-mail address: ddas@ee.iitkgp.ernet.in (D. Das). www.elsevier.com/locate/ijepes Electrical Power and Energy Systems 29 (2007) 571–579