Accuracy of the “two-load method” considering induction motor load in power system network aggregation

The authors once proposed a practical power system aggregation method for network, generators, and their control systems. Since the main object then was to explain all of the new method, some issues were left unsolved in aggregation accuracy compared with the other methods. Mainly three issues as follows still remain unsolved. (1) To assess “Two-load method” that maintains power system loss like the proposed method. (2) To assess error caused only by network aggregation. (3) To assess cases with static load model. When “two-load method” is applied on detailed systems that consider load branch impedance, negative loads appear very often. As a measure, the paper introduces a new understanding of two-load method: A pair of positive and negative imaginary constant impedance loads having the same magnitude are added. Aggregation accuracy of three aggregation methods are compared on existing four local systems with small hydro generators having the same machine constants and control systems. “Two-load method” is not superior to “two-element method” and inferior to “three-element method” with induction motor load. Difference of aggregation accuracy of the three methods is not significant with static load. © 2019 The Institute of Electrical Engineers of Japan.