US 8,527,106 B2 · System stabilization device

Abstract

A control unit of a system stabilization device uses a fluctuation detection block (60) to determine fluctuation components included in the active component and reactive component currents of a system current and fluctuation components included in the frequency signal and the amplitude signal of a system voltage. The high frequency cut-off of the fluctuation detection block (60) is set to be f1; the low frequency cut-off is set to be f2. The fluctuation detection block (60) is composed of a low-pass filter (61) with a time constant of T1, a low-pass filter (62) with a time constant of T2, a subtracter (63) which outputs the difference, between the output signals of the filter (61) and the filter (62), and a feedback circuit (64) which provides feedback on the output of the subtracter (63) to the filters (61, 62). Thus, stability is ensured without using a current detector.

A system stabilization device provided in a distribution system which, when a power system is normal, is connected to the power system, and when an abnormality occurs in the power system, is cut off from the power system, and to which a dispersed generation plant and a load are connected,

the system stabilization device having a control unit, and a power converter which performs a converting action and an inverting action in accordance with a gate signal fed from the control unit,
wherein when the power system is normal, the control unit
determines a first active component of a system current and a first reactive component of the system current, the system current flowing from the power system into the distribution system;
determines a first fluctuation component included in the first active component of the system current by a first fluctuation detection block, and uses the first fluctuation component as a first current command for the first active component;
determines a second fluctuation component included in the first reactive component of the system current by a second fluctuation detection block, and uses the second fluctuation component as a second current command for the first reactive component;
further determines a second active component of an alternating current output current and a second reactive component of the alternating current output current, the alternating current output current being outputted from the power converter;
and
outputs the gate signal for reducing a first current deviation, which is a first deviation between the first current command for the first active component and the second active component of the alternating current output current, to zero, and also reducing a second current deviation, which is a second deviation between the second current command for the first reactive component and the second reactive component of the alternating current output current, to zero, and
when the abnormality occurs in the power system, the control unit
determines, from a system voltage of the distribution system, a frequency signal showing a frequency of the system voltage and an amplitude signal showing an amplitude of the system voltage;
determines a third fluctuation component included in the frequency signal by a third fluctuation detection block, and uses the third fluctuation component as a third current command for a third active component;
determines a fourth fluctuation component included in the amplitude signal by a fourth fluctuation detection block, and uses the fourth fluctuation component as a fourth current command for a third reactive component;
further determines the second active component of the alternating current output current and the second reactive component of the alternating current output current, the alternating current output current being outputted from the power converter;
and
outputs the gate signal for reducing a third current deviation, which is a third deviation between the third current command for the third active component and the second active component of the alternating current output current, to zero, and also reducing a fourth current deviation, which is a fourth deviation between the fourth current command for the third reactive component and the second reactive component of the alternating current output current, to zero, and
when a first cut-off frequency on a high frequency side of a pass band frequency of a fluctuation detection block is set to be f1, a second cut-off frequency on a low frequency side of the pass band frequency is set to be f2, a first time constant of a first low-pass filter for noise removal which has the first cut-off frequency of f1 is set to be T1, and a second time constant of a second low-pass filter for setting a fluctuation detection time which has the second cut-off frequency of f2 is set to be T2, the first fluctuation detection block, the second fluctuation detection block, the third fluctuation detection block, and the fourth fluctuation detection block are each composed of a first filter having first order lag characteristics with the first time constant of T1, a second filter having first order lag characteristics with the second time constant of T2, a subtracter which performs subtraction between a first signal outputted from the first filter and a second signal outputted from the second filter and outputs a resulting difference, and a feedback circuit for providing the first filter and the second filter with feedback on an output of the subtracter.

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System stabilization device

Life of this patent

System stabilization device

Life of this patent

Abstract

Claims8