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Optimal reactive power dispatch (ORPD) is a key instrument to achieve secure and economic operation of power systems. Due to complex characteristics of ORPD, heuristic optimization has become an effective solver. A novel heuristic optimization algorithm namely the Mean-Variance Mapping Optimization (MVMO) is proposed to handle the ORPD problem. The concept, mechanism and implementation of MVMO are discussed in this paper. Based on the IEEE 57-and 118-bus systems, MVMO is compared with some basic and enhanced evolutionary algorithms. Simulation results show that MVMO is an excellent algorithm for ORPD and should deserve more attention. The superiority to the other algorithms is very pronounced in the IEEE 118-test case.

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Voltage stability has become a serious treat of modern power system operation nowadays. To tackle this problem properly, load shedding is one of the effective countermeasures. However, its consequences might result in huge technical and economic losses. Therefore, this control measure should be optimally and carefully carried out. This paper proposes an ant colony optimization (ACO) based algorithm for solving the optimal load shedding problem. Two principal concerns of the problem are addressed. The appropriate load buses for the shedding are identified by sensitivities of voltage stability margin with respect to the load change at different buses. Then, the amount of load shedding at each bus is determined by applying ACO to solve a nonlinear optimization problem formulated in the optimal power flow framework. The performance of the proposed ACO based method is illustrated with a critical operating condition of the IEEE 30-bus test system.

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