Patent ID: 8457804
Filing Date: 2013-06-04
Classification: G05B,H02J,Y02E

Abstract:
1. A system stabilizing 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 stabilizing 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 detecting 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 detecting block, and uses the second fluctuation component as a second current command for the first reactive component; further determines a second active component of a converter current and a second reactive component of the converter current, the converter current being inputted to and 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 converter 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 converter 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 detecting 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 detecting 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 converter current and the second reactive component of the converter current, the converter current being inputted to and 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 converter 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 converter current, to zero, and when a first cut-off frequency on a high frequency side of a pass band frequency of a fluctuation detecting 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, 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, an oscillation coefficient is set to be ζ, a setting number is set to be α, a gain is set to be G, a first value obtained by multiplying T1 by α is set to be T3, and a second value obtained by dividing T2 by α is set to be T4, 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 a third time constant of T3; a second filter having first order lag characteristics with a fourth time constant of T4; 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; an amplifier for multiplying an output of the subtracter by the gain G, and outputting a resulting product; a rating limiter which, when an amplification signal outputted from the amplifier is smaller than a preset rated value, allows the amplification signal to pass unchanged, but when the amplification signal is equal to or larger than the preset rated value, restricts a signal value of the amplification signal to a rated value and then allows the amplification signal to pass; and an overcompensation inhibiting unit, the oscillation coefficient ζ expressed by a Formula (01) is set at a third value larger than 1, and the setting number α and the gain G are set using the Formula (01), a Formula (02) and a Formula (03), and if a first state where the signal value of the amplification signal is restricted to the rated value by the rating limiter continues for a time equal to or longer than a preset constant time, the overcompensation inhibiting unit changes the fourth time constant of the second filter to a value smaller than T4, but if a second state where the amplification signal passes unchanged through the rating limiter is reached, the overcompensation inhibiting unit returns the fourth time constant of the second filter to T4.