1. Field of the Invention
This invention is related to a power system which converts DC output from a DC power source such as a solar cell and a fuel cell to AC output by an inverter and supplies to a load, and is intended for an efficient operation of the inverter.
2. Description of Prior Art
A solar power generating system which uses solar cells becomes popular as a clean power system.
FIG. 5 is a schematic view illustrating a conventional solar power generating system for domestic use. DC sources 101 comprising of a plurality of solar cells are placed on a house roof. DC output from the plurality of DC sources is accumulated and flowed into a connection box 102. The DC output from the connection box 102 is converted to AC output by an inverter 103, and is supplied to a load 105 as home electric appliance through a panelboard 104. Electricity can be also supplied to the loads 105 from a commercial power supply 106. When electricity runs short, for example at night, electric power is supplied from the commercial power supply 106.
In the meanwhile, efficiency of an inverter dips sharply at a time of low output. To solve the problem, Patent Abstracts of Japan, publication number 06165513, for example, provides a method for operating a plurality of inverters in parallel and determining how many inverters should be operated by judging a total output current of inverters.