DISCRETE-TYPE AUTOMATIC GENERATION CONTROL OF TWO-AREA THERMAL SYSTEM WITH SEVERAL TYPES OF INTERCONNECTION

Abstract

The performance of automatic generation control (AGC) of interconnected power system is quite dependent to the generation rate limitations of power plants utilised for AGC. The excellent performance may be achieved by utilising fast acting generation plants. However, in the power system having thermal plants, the power generation can change only at a specified maximum rate, therefore the strategy of AGC for such thermal system must be determined considering the generation rate limitation. This paper presents a method of designing discrete-type regulators for AGC of a two-area reheat-type thermal system considering the generation rate limitation. In the two-area system, several types of interconnection, i.e., by AC tie-line, by DC tie-line, and by AC and DC parallel tie-lines, are considered. The construction of the regulators for the thermal plants is based on the well known TBC or FFC. Furthermore, the DC tie-line power is also modulated by a regulator of discrete-type. The parameters of regulators are optimised by minimising a discrete-type quadratic performance index with a term for presenting the generation rate limitation of the thermal plant. The minimisation is achieved by using a Newton-Raphson iterative algorithm. The control effects both by the proposed AGC and by the DC tie-line power modulation are examined by simulating the model two-area system. The results prove that the proposed regulators can act efficiently under various sizes of load changes, and that the higher frequency mode of oscillations caused by the load changes can be damped effectively by controlling the DC tie-line power. Furthermore, the effects of regulator sampling time to the AGC performance are also investigated.