Capacitor polarity-based var correction controller for resonant line conditions and large amplitude line harmonics
First Claim
1. A static VAR compensator, comprising:
- an output node connected to a power line carrying a power signal;
a reactive power compensation element connected to said output node, includinga compensating capacitor, anda plurality of switching devices for selectively connecting said compensating capacitor to said output node for a predetermined compensation period, said predetermined compensation period being transformed into an incomplete compensation period under certain physical conditions;
a compensation assessment circuit connected to said reactive power compensation element; and
a controller connected to said compensation assessment circuit to identify said incomplete compensation period and to produce control signals for said plurality of switching devices of said reactive power compensation element such that said reactive power compensation element conditions said power signal to account for said incomplete compensation period.
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Abstract
The invention is a static VAR compensator (SVC) which provides optimized power factor correction in the presence of resonant line conditions and large amplitude harmonics. A gate drive signal is applied to the solid state devices of the SVC during only a minor fraction of the fundamental cycle to prevent damage to the solid state devices and the capacitors of the SVC, otherwise caused by resonant line conditions or large amplitude harmonics. This relatively short gate drive signal, in the presence of large amplitude harmonics, will force the solid state electronic components to turn-off prematurely. As a result, the capacitors of the SVC provide incomplete reactive power compensation. Feedback from a capacitor polarity circuit is used to determine switched capacitor status at a specific instant in each cycle. A VAR correction controller, responsive to the feedback, executes a control scheme to account for incomplete reactive power compensation.
50 Citations
20 Claims
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1. A static VAR compensator, comprising:
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an output node connected to a power line carrying a power signal; a reactive power compensation element connected to said output node, including a compensating capacitor, and a plurality of switching devices for selectively connecting said compensating capacitor to said output node for a predetermined compensation period, said predetermined compensation period being transformed into an incomplete compensation period under certain physical conditions; a compensation assessment circuit connected to said reactive power compensation element; and a controller connected to said compensation assessment circuit to identify said incomplete compensation period and to produce control signals for said plurality of switching devices of said reactive power compensation element such that said reactive power compensation element conditions said power signal to account for said incomplete compensation period. - View Dependent Claims (2, 3, 4, 5, 6, 12, 13)
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7. A static VAR compensator, comprising:
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a power line output node for connection to a power line carrying a power signal; a parameter measurement circuit to continuously sample said power signal and obtain a measured power signal; a plurality of compensating capacitors, with associated increment VAR values; a plurality of capacitor polarity circuits, each of said capacitor polarity circuits being connected to one of said plurality of compensating capacitors and generating a capacitor polarity signal; a plurality of thyristor strings, each of said thyristor strings connecting a selected compensating capacitor of said plurality of compensating capacitors to said power line output node to provide capacitive reactive power conditioning to said power signal for a complete compensation period of one-half cycle of said power signal, said complete compensation period being transformed into an incomplete compensation period in response to certain physical conditions; a plurality of gate drive circuits corresponding to said plurality of thyristor strings to fire said plurality of thyristor strings; and a controller connected to said parameter measurement circuit, said plurality of capacitor polarity circuits, and said plurality of gate drive circuits to identify said incomplete compensation period of one or more of said plurality of compensating capacitors in a previous cycle of said power signal and to produce gate drive signals to be applied to said gate drive circuits to provide capacitive reactive compensation in one or more subsequent cycles of said power signal to account for said incomplete compensation period. - View Dependent Claims (8, 9, 10, 11, 14, 15)
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16. A method of operating a static VAR compensator including a power line output node for connection to a power line carrying a power signal, a plurality of compensating capacitors, a plurality of thyristor strings each of said thyristor strings connecting a selected compensating capacitor of said plurality of compensating capacitors to said power line output node to provide capacitive reactive power conditioning to said power signal, and a plurality of gate drive circuits corresponding to said plurality of thyristor strings to fire said plurality of thyristor strings, the method comprising the steps of:
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providing a plurality of compensation assessment circuits to generate compensation assessment output signals when one or more of said plurality of compensating capacitors provides incomplete reactive compensation to said power signal in a first cycle; and generating gate drive signals, for application to said plurality of gate drive circuits in a second cycle, that force said plurality of compensating capacitors to provide reactive compensation in response to said incomplete reactive compensation to said power signal in said first cycle. - View Dependent Claims (17, 18, 19, 20)
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Specification