In the near future, many distributed generation systems, such as photovoltaic or wind power generation, will be interconnected to the electric power distribution systems of Japan. Therefore, we must make the best use of the distributed generation systems considering their influence on power quality, stability, and so on.
This paper investigates the influence of distributed generation systems on the voltage characteristics in distribution systems by a stochastic approach. Firstly, we calculate the node voltage fluctuations in a test distribution system using the stochastic power flow, and show that the voltage characteristics deteriorate after interconnecting distributed generation systems. Secondly, we formulate the problem of voltage characteristics improvement as the nonlinear optimization problem which has the following objective functions: 1) minimize the total voltage fluctuations throughout a distribution system; 2) regulate the node voltage at a specified value considering voltage fluctuations. These problems can be also solved using the stochastic power flow. The simulation results show that the node voltage fluctuations can be minimized by controlling the parameters regarding the reactive power of distributed generation systems, and the stochastic power flow is effective in calculating the practical value of reactive power of distributed generation systems in order to regulate the node voltage.
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