Uninterruptible power supply and method of turning off AC switch for uninterruptible power supply

An uninterruptible power supply comprising:

• a power failure detection means to detect a power failure in a utility power supply;
• an AC switch having a pair of antiparallelly connected thyristors, the AC switch being adapted to conduct to feed an AC power from the utility power supply to a load when the utility power supply is normal and, the AC Switch being turned off when the utility power supply fails;
• a DC power supply;
• a voltage control type power converter arranged between the AC switch and the DC power supply, wherein when the utility power supply is normal, the power converter performs a rectifier operation of converting the AC power from the utility power supply into a DC power and charging the DC power supply with the DC power and performs an active filter operation of compensating for a harmonic current and a reactive current flowing into the load and wherein at other times the power converter uses the DC power supply as its source and performs mainly 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 and a current control command to cause the power converter to perform the rectifier operation and the active filter operation;
• 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 power failure detection means does not detect a power failure and the voltage control command is not output, the sinusoidal voltage selection means selects the synchronous sinusoidal voltage Vref1 and wherein when the power failure detection means detects a power failure and 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.

An uninterruptible power supply comprising:

• a power failure detection means to detect a power failure in a utility power supply;
• an AC switch having a pair of antiparallelly connected thyristors, the AC switch being adapted to conduct to feed an AC power from the utility power supply to a load when the utility power supply is normal and, the AC Switch being turned off when the utility power supply fails;
• a DC power supply;
• a voltage control type power converter arranged between the AC switch and the DC power supply, wherein when the utility power supply is normal, the power converter performs a rectifier operation of converting the AC power from the utility power supply into a DC power and charging the DC power supply with the DC power and performs an active filter operation of compensating for a harmonic current and a reactive current flowing into the load and wherein at other times the power converter uses the DC power supply as its source and performs mainly an inverter operation of converting a DC power into an AC power and feeding the converted AC power to the load;
• a phase shift type 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 and a current control command to cause the power converter to perform the rectifier operation and the active filter operation;
• wherein the phase shift type reference sinusoidal voltage generation circuit comprises:
• a phase shift type sinusoidal voltage generation means to generate a synchronous sinusoidal voltage Vref1, a leading sinusoidal voltage Vref4 and a lagging sinusoidal voltage Vref5, 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 in amplitude to a voltage of the utility power supply, the leading sinusoidal voltage Vref4 is equal in amplitude to and leading in phase the synchronous sinusoidal voltage Vref1, and the lagging sinusoidal voltage Vref5 is equal in amplitude to and lagging in phase the synchronous sinusoidal voltage Vref1;
• a current detection means to detect a current flowing through the AC switch;
• and
• a phase shift type sinusoidal voltage selection means to select the synchronous sinusoidal voltage Vref1, the leading sinusoidal voltage Vref4 or the lagging sinusoidal voltage Vref5 and output the selected voltage as the reference sinusoidal voltage to the control command generation means, wherein when the power failure detection means does not detect a power failure and the voltage control command is not output, the phase shift type sinusoidal voltage selection means selects the synchronous sinusoidal voltage Vref1 and wherein when the power failure detection means detects a power failure and the voltage control command is output, the phase shift type sinusoidal voltage selection means selects the leading sinusoidal voltage Vref4 or the lagging sinusoidal voltage Vref5, whichever is larger than the synchronous sinusoidal voltage Vref1 if an output of the current detection means has a positive polarity, selects the leading sinusoidal voltage Vref4 or the lagging sinusoidal voltage Vref5, whichever is smaller than the synchronous sinusoidal voltage the 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.