太陽光発電が大量に連系された系統の電圧に関する基礎特性;太陽光発電が大量に連系された系統の電圧に関する基礎特性;Fundamental Voltage Characteristics in Power System with a Large Penetration of Photovoltaic Generation

Recently, because of global warming, the attention to the renewable energy sources such as photovoltaic generations has increased. In Japan, a lot of photovoltaic generations will be installed to the power system, especially to the distribution system, in future. This will make the power flow in the power system changed. That is to say that the forward power flow (power flow from higher voltage system to lower voltage system) reduces, or moreover, that the reverse power flow (power flow from lower voltage system to higher voltage system) occurs. Because of the changed in power flow, the voltage characteristics will be also changed. Consequently, it is expected that the penetration of photovoltaic generation has some impacts on voltage stability. In recent studies, the change in voltage characteristics is mentioned, but the amount of photovoltaic generations is not so large. Moreover, only the distribution system is considered. In this paper, the fundamental voltage characteristics are studied by the simple power system model (Fig. 1) which consists of one infinite bus, one load, and one photovoltaic generation. By PV curve which is the relation between power (P) and voltage (V) at load, the steady state characteristics can be discussed. PV curve in which there is no photovoltaic generation (Case1) and one in which there is photovoltaic generation (Case2) are shown in Fig. 2. In Fig. 2, the area where PL (power consumed at load) is negative is shown. In Case1, reverse power flow occurs in the area PL is negative. It is indicated by Fig. 2 that PV curve has not only right nose (forward power flow limit) but also left nose (reverse power flow limit). When the output from photovoltaic generation increases, PV curve moves to the right hand. When the output from photovoltaic generation is very large, such as Case2, the left nose can be appeared on the area where PL is positive. PV curve also indicates that, when the reverse power flow increases (PL reduces), voltage drops. This is opposite to the