Power system monitoring ensuring direct observation of critical buses and transmission lines using a bi-level approach

Finding minimum number of connecting lines is as important as locating phasor measurement units (PMUs) for full observability of power system. Therefore, a PMU placement method should determine both optimum buses and lines, since utilities can make better decisions for monitoring of power system with this information. Moreover, it is necessary to provide direct observation of critical buses and transmission lines to improve monitoring of the system and perform critical analyses such as dynamic vulnerability assessment. To achieve these goals, this paper presents a bi-level method. In this method, the problem of finding minimum number of connecting lines is separated from the problem of PMU placement and is moved to the upper level. Furthermore, due to the differences between the definitions of problems, different optimization methods are used in each level. A line redundancy factor (LRF) is also added to the upper level to penalize the excessive lines. The effectiveness of the proposed method is demonstrated on 4 test power systems. Results show that this method can find the optimal combination of buses and lines to provide observability of power system.