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Variable shunt and series connected reactors are used in a complimentary combination in an electric arc furnace to provide improved flicker control. A power control system for an time-varying AC load, such as an electric arc furnace, connected to an AC power supply line includes a first variable rea

Variable shunt and series connected reactors are used in a complimentary combination in an electric arc furnace to provide improved flicker control. A power control system for an time-varying AC load, such as an electric arc furnace, connected to an AC power supply line includes a first variable reactance intermediate the power supply line and the load, and a second variable reactance connected in parallel with the power supply line. A control system is provided for (i) monitoring load current and adjusting the first variable reactance in response to changes in the monitored load current; and (ii) monitoring reactive power draw by the load and adjusting the second variable reactance in response to changes in the monitored reactive power draw. The first variable reactance and second variable reactance are each primarily used to mitigate flicker at different times during the load operation.

대표청구항 ▼

Variable shunt and series connected reactors are used in a complimentary combination in an electric arc furnace to provide improved flicker control. A power control system for an time-varying AC load, such as an electric arc furnace, connected to an AC power supply line includes a first variable rea

Variable shunt and series connected reactors are used in a complimentary combination in an electric arc furnace to provide improved flicker control. A power control system for an time-varying AC load, such as an electric arc furnace, connected to an AC power supply line includes a first variable reactance intermediate the power supply line and the load, and a second variable reactance connected in parallel with the power supply line. A control system is provided for (i) monitoring load current and adjusting the first variable reactance in response to changes in the monitored load current; and (ii) monitoring reactive power draw by the load and adjusting the second variable reactance in response to changes in the monitored reactive power draw. The first variable reactance and second variable reactance are each primarily used to mitigate flicker at different times during the load operation. es the gain to a value larger than a normal value only when the DC voltage sensed at least equals a threshold voltage. 7. The power conversion apparatus as defined in claim 5, wherein, in response to one of the DC voltage sensed and the deviation, a modulation factor bias produced by said modulation and phase circuit is added to a normal modulation to provide the control signal to said self-commutated power converter. 8. The power conversion apparatus as defined in claim 5, wherein said voltage control circuit includes a subtracter for producing the deviation. 9. A power conversion apparatus connected to an AC system, comprising: a voltage control circuit providing feedback control of a DC voltage of a converter; a subtracter for obtaining a deviation of a detected DC voltage from an active voltage command value, said voltage control circuit changing a control gain applied to the DC voltage according to one of the detected DC voltage and the deviation of the detected DC voltage from a DC voltage command value; and means for detecting a system fault in the AC system, wherein, during continuation of the system fault, a DC voltage command value is decreased in said voltage control circuit. 10. A power conversion apparatus connected to an AC system, comprising: a voltage control circuit providing feedback control of a DC voltage of a converter; a subtracter for obtaining a deviation of a detected DC voltage value from an active voltage command value, said voltage control circuit changing a control gain applied to the DC voltage according to one of the detected DC voltage and the deviation of the detected DC voltage from a DC voltage command value; and means for detecting a system fault in the AC system, wherein, during continuation of the system fault and during a period of time after clearance of the system fault, an integral term of said voltage control circuit is set to zero when absolute value of the deviation of the detected DC voltage value from the DC voltage command value is smaller than a set value. [US_PATENT]US-5325490, 19940600, Brasseur, 395/325; US-5473766, 19951200, Shaver, 395/500; US-5530887, 19960600, Harper et al., 395/800; US-5551012, 19960800, Chuang et al., 395/500; US-5610801, 19970300, Begis, 361/784; US-5678011, 19971000, Kim et al., 395/282; US-5734872, 19980300, Kelly, 395/500; US-5848250, 19981200, Smith et al., 395/309; US-5987553, 19991100, Swamy et al., 710/129; US-6052794, 20000400, Polzin et al., 713/500; US-6066981, 20000500, Craig et al., 327/565; US-6161177, 20001200, Anderson, 713/002