Patent ID: 7554220

Claim:
A stable power supply apparatus comprising: a secondary battery for charging and discharging DC power; a converter connected between said secondary battery and a system bus line of a power transmission power supply or between said secondary battery and a load connected to the system bus line and having a wide-gap bipolar semiconductor device as a switching device, for converting AC inputted from said system bus line into DC and outputting to said secondary battery, and for converting DC output from said secondary battery into AC and outputting to said system bus line; a detection apparatus for detecting at least a voltage of said system bus line and for detecting a supply and demand state of the power on the basis of the detected voltage; and a control circuit for controlling said converter so that the converter is operated under a rated power of the converter to charge said secondary battery when the supply and demand state is balanced and to discharge said secondary battery for supplying power to said system bus line when the demand becomes larger than the supply on the basis of the detected output of said detection apparatus, and so that the converter is operated under the power that is 3 to 30 times the rated power when an instantaneous voltage drop wherein the voltage of the system bus line lowers significantly is detected on the basis of the detected output of the detection apparatus.