Patent ID: 6556459
Filing Date: 2003-04-29
Classification: H02J

Abstract:
An uninterruptible power supply comprising:a first feeding path to feed an AC power to a load from a utility power supply through an AC switch made up of a pair of antiparallelly connected thyristors; a second feeding path including a voltage control type power converter, the power converter using a DC power supply as its source and performing an inverter operation of converting a DC power into an AC power and feeding the converted AC power to the load; a reference sinusoidal voltage generation circuit to produce a reference sinusoidal voltage; and a control command generation means to, based on the reference sinusoidal voltage, output to the power converter a voltage control command to cause the power converter to perform the inverter operation, wherein, while the voltage control command is being output from the control command generation means, the AC switch is turned off and the feeding of the AC power to the load is switched over from the first feeding path to the second feeding path; wherein the reference sinusoidal voltage generation circuit includes: a sinusoidal voltage generation means to generate a synchronous sinusoidal voltage Vref1, a high synchronous sinusoidal voltage Vref2 and a low synchronous sinusoidal voltage Vref3, wherein the synchronous sinusoidal voltage Vref1 is synchronized with the utility power supply and, when used as the reference sinusoidal voltage, causes an output voltage of the power converter to become almost equal to a voltage of the utility power supply, the high synchronous sinusoidal voltage Vref2 is in phase with the synchronous sinusoidal voltage Vref1 and higher in amplitude than the synchronous sinusoidal voltage Vref1, and the low synchronous sinusoidal voltage Vref3 is in phase with the synchronous sinusoidal voltage Vref1 and lower in amplitude than the synchronous sinusoidal voltage Vref1; a current detection means to detect a current flowing through the AC switch; and a sinusoidal voltage selection means to select the synchronous sinusoidal voltage Vref1, the high synchronous sinusoidal voltage Vref2 or the low synchronous sinusoidal voltage Vref3 and output the selected voltage as the reference sinusoidal voltage to the control command generation means, wherein when the voltage control command is not output, the sinusoidal voltage selection means selects the synchronous sinusoidal voltage Vref1 and wherein when the voltage control command is output, the sinusoidal voltage selection means selects the high synchronous sinusoidal voltage Vref2 if an output of the current detection means has a positive polarity, selects the low synchronous sinusoidal voltage Vref3 if the output of the current detection means has a negative polarity, and selects the synchronous sinusoidal voltage Vref1 if the output of the current detection means is zero.