Multi-Area Frequency and Tie-Line Power Flow Control by Fuzzy Gain Scheduled SMES

Abstract

Generation and distribution of electric energy with good reliability and quality is very important in power system operation and control. This is achieved by Automatic Generation Control (AGC). In an interconnected power system, as the load demand varies randomly, the area frequency and tie-line power interchange also vary. The objective of Load Frequency Control (LFC) is to minimize the transient deviations in these variables and to ensure for their steady state values to be zero. The LFC performed by only a governor control imposes a limit on the degree to which the deviations in frequency and tie-line power exchange can be minimized. However, as the LFC is fundamentally for the problem of an instantaneous mismatch between the generation and demand of active power, the incorporation of a fast-acting energy storage device in the power system can improve the performance under such conditions. But fixed gain controllers based on classical control theories are presently used. These are insufficient because of changes in operating points during a daily cycle [Benjamin et al., 1978; Nanda et al., 1988; Das et al., 1990; Mufti et al., 2007; Nanda et al., 2006 & Oysal et al., 2004] and are not suitable for all operating conditions. Therefore, variable structure controller [Benjamin et al., 1982; Sivaramaksishana et al., 1984; Tripathy et al., 1997 & Shayeghi et al., 2004] has been proposed for AGC. For designing controllers based on these techniques, the perfect model is required which has to track the state variables and satisfy system constraints. Therefore it is difficult to apply these adaptive control techniques to AGC in practical implementations. In multi-area power system, if a load variation occurs at any one of the areas in the system, the frequency related with this area is affected first and then that of other areas are also affected from this perturbation through tie lines. When a small load disturbance occurs, power system frequency oscillations continue for a long duration, even in the case with optimized gain of integral controllers [Sheikh et al., 2008 & Demiroren, 2002]. So, to damp out the oscillations in the shortest possible time, automatic generation control including SMES unit is proposed. Therefore, in the proposed control system, with an addition of the simple SMES controller, a supplementary controller with KIi (as shown in Fig. 6) is designed in order to retain the