According to the government's policy to demonstrate and expand the renewable energy sources, distributed generators such as PV (photovoltaic) and WP (wind power) systems are installed and operated in distribution systems. However, there are many issues related to power quality problems including over-voltage and under-voltage of customers. Especially Blackouts-the total loss of electrical power-serve as a reminder of how dependent the modern world and particularly urban areas have become on electricity and the appliances it powers. In order to overcome these problems, the electric power company have installed a Step Voltage Regulator (SVR) in primary feeders interconnected with distributed generators, and also have established the technical guidelines for the distributed generators to stabilize the customer voltages in distribution systems. However, it is difficult to maintain the customer voltages within allowable limit. Therefore, this paper analyzes the problem of voltage control by SVR in distribution system with large scale PV systems, and presents operating range and voltage control limit of Small Hydropower Generator (SHG) with PF control function. In addition, this paper evaluates the voltage impact in primary feeders depending on voltage control modes of SHG, and then proposes optimal voltage control algorithm. Furthermore, from the simulation results base on the proposed algorithm, it is confirmed that it can contribute to voltage stabilization in distribution system interconnected with large scale PV systems.

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Solar cells in a PV module are connected in series and parallel to produce a higher voltage and current.The PV module has performance characteristics depending on solar radiation and temperature. In addition, the PV system causes power loss by special situations, including the shadows of the surrounding environment, such as nearby buildings and trees. In other words, an increase in power loss and a decrease in life cycle can occur because of the partial shadow and hot-spot effect. Therefore, this paper proposes the optimal configuration algorithm of a bypass diode to improve the output of a PV module and one of a PV array to minimize the loss of the PV array. In addition, this paper presents a model of a PV module and PV array based on the PSIM S/W. The simulation results confirmed that the proposed optimal configuration algorithms are useful tools for improving the performance of PV system.