Abstract: An output power control method of a wind generator includes: when a disturbance occurs, increasing output power of the wind generator by adding the active power proportional to kinetic energy stored in the wind generator at the instant of a disturbance, wherein the increasing of output power calculates an increment of the output power by using a mechanical input curve and an electrical output curve at a corresponding wind speed of the wind generator, and the increment of the output power is determined as a constant which makes the mechanical input curve of the wind generator and the electrical output curve intersect at least at one point according to each input wind speed, and when an intersection determined above is formed at a rotor speed lower than ?min, the increment of the output power is determined as a maximum constant value which makes the rotor speed reach a predetermined point.

Abstract: A three-level SEPIC converter circuit includes: an input inductor connected to one side of an input terminal; first and second switches connected between the input inductor and the other side of the input terminal in series; a first capacitor and a first diode connected between the first switch and one side of an output terminal in series; a second diode and a second capacitor connected between the other side of the output terminal and the other side of the input terminal in series; first and second output capacitors connected between the output terminals; and an output inductor connected between a node between the first capacitor and the first diode and a node between the second capacitor and the second diode, wherein a node between the first switch and the second switch and a node between the first output capacitor and the second output capacitor are connected.

Abstract: An inertial control method of a wind turbine includes the steps of: acquiring frequency information of a power grid; calculating a time variant droop coefficient when the frequency information is reduced below a preset range; and controlling the wind turbine using the calculated time variant droop coefficient, wherein the step of calculating a time variant droop coefficient includes the steps of: collecting rotor speed information changing according to the inertial control; and calculating the time variant droop coefficient using the collected rotor speed information.

Abstract: A system and method for controlling voltage at a point of common coupling of a wind farm including a plurality of wind turbines is provided. The method includes: calculating a first voltage error value, which is a difference between a reference voltage value of the point of common coupling and an actual voltage value of the point of common coupling; calculating a compensation reference voltage value based on the first voltage error value; calculating a second voltage error value by subtracting a voltage value of an output terminal of a wind turbine from a sum of a reference voltage value of the wind turbine and the compensation reference voltage value; calculating a reactive power compensation value corresponding to the second voltage error value; and injecting a reactive current corresponding to the reactive current compensation value into a power grid.

Abstract: A system and method for controlling voltage at a point of common coupling of a wind farm including a plurality of wind turbines is provided. The method includes: calculating a first voltage error value, which is a difference between a reference voltage value of the point of common coupling and an actual voltage value of the point of common coupling; calculating a compensation reference voltage value based on the first voltage error value; calculating a second voltage error value by subtracting a voltage value of an output terminal of a wind turbine from a sum of a reference voltage value of the wind turbine and the compensation reference voltage value; calculating a reactive power compensation value corresponding to the second voltage error value; and injecting a reactive current corresponding to the reactive current compensation value into a power grid.

Abstract: A high efficiency DC/DC converter with high conversion ratio is provided. The DC/DC converter includes a power switch for selectively switching an electrical connection between one side of a power supply and anodes of a first diode and a second diode, a first capacitive element whose one side is connected to a cathode of the first diode, a second capacitive element whose one side is connected to a cathode of the second diode, a first-first switch for selectively switching an electrical connection between the other side of the first capacitive element and the other side of the power supply, and a second-first switch for selectively switching an electrical connection between the other side of the first capacitive element and one side of the second capacitive element.

Abstract: A time variant droop-based inertial control method of a wind generator includes the steps of acquiring a nominal frequency value and a system frequency value of a power system; calculating a difference between the system frequency value and the nominal frequency value; calculating a rate of change of the system frequency; acquiring a droop coefficient Rvariant using the rate of change of the system frequency; and controlling the wind generator based on the difference between the system frequency value and the nominal frequency value and the droop coefficient Rvariant.

Abstract: The present invention relates to a method of controlling a wind farm. A method of controlling inertia in a wind farm includes obtaining information about the frequency of an electrical grid which has been received from the electrical grid or calculated using the voltage of the wind turbine, receiving information about the rotor speed of the wind turbine, calculating the kinetic energy of the wind turbine using the information about the rotor speed, calculating an individual droop coefficient of the wind turbine using the calculated kinetic energy, and controlling the wind turbine using the calculated droop coefficient.

Abstract: A high efficiency DC/DC converter with high conversion ratio is provided. The DC/DC converter includes a power switch for selectively switching an electrical connection between one side of a power supply and anodes of a first diode and a second diode, a first capacitive element whose one side is connected to a cathode of the first diode, a second capacitive element whose one side is connected to a cathode of the second diode, a first-first switch for selectively switching an electrical connection between the other side of the first capacitive element and the other side of the power supply, and a second-first switch for selectively switching an electrical connection between the other side of the first capacitive element and one side of the second capacitive element.

Abstract: The present invention relates to a method and system for controlling a wind farm when a ramp up or ramp down rate of the wind farm does not satisfy a grid-code or corresponding criteria due to an abrupt change in wind speed. The method and system for controlling a wind farm includes the steps of measuring speed and direction of wind performed outside the wind farm, sequentially controlling wind turbines if the wind speed abruptly changes considering a time for the wind to arrive at the wind turbines, determining the number of wind turbines to be controlled simultaneously so that the wind farm may satisfy the grid-code at this point, grouping the wind turbines, determining a control sequence and a control time of each group, and adjusting a control end time if stopping times of adjacent groups are overlapped when the wind turbines are stopped.

Abstract: The present invention relates to a method and system for controlling a wind farm when a ramp up or ramp down rate of the wind farm does not satisfy a grid-code or corresponding criteria due to an abrupt change in wind speed. The method and system for controlling a wind farm includes the steps of measuring speed and direction of wind performed outside the wind farm, sequentially controlling wind turbines if the wind speed abruptly changes considering a time for the wind to arrive at the wind turbines, determining the number of wind turbines to be controlled simultaneously so that the wind farm may satisfy the grid-code at this point, grouping the wind turbines, determining a control sequence and a control time of each group, and adjusting a control end time if stopping times of adjacent groups are overlapped when the wind turbines are stopped.

Abstract: Provided an error compensating method for an instrument transformer, in which an error of an instrument transformer is compensated by reflecting hysteresis characteristics of iron core. When such error compensation is performed, a hysteresis loop indicating the relationship between magnetic flux and excitation current is not used as it is, but core-loss resistances and magnetic flux-excitation current curves are used, thereby achieving more precise compensation. According to the present invention, an error of an instrument transformer can be significantly reduced. Therefore, it is possible to manufacture an instrument transformer with high accuracy and to significantly reduce the size of the instrument transformer. Further, a material with high permeability does not need to be used in order to increase the accuracy.

Abstract: Disclosed is a compensated current differential relaying method and system for protecting a transformer more correctly by calculating and estimating an exciting current including a core-loss current and a magnetizing current, and, in particular, to a compensated current differential relaying method and system which can protect the transformer correctly irrespective of the level of remanent flux.

Abstract: Disclosed is a compensated current differential relaying method and system for protecting a transformer more correctly by calculating and estimating an exciting current including a core-loss current and a magnetizing current, and, in particular, to a compensated current differential relaying method and system which can protect the transformer correctly irrespective of the level of remanent flux.

Abstract: Disclosed herein is a method of compensating for the distorted secondary/ current of a current transformer. The method includes steps (a), (b) and (c). At step (a), the saturated section of the current transformer is detected. At step (b), fault current generated during a fault in a power system is represented using an AutoRegressive (AR) model, with the fault current being assumed to be a combination of a Direct Current (DC) offset component, a fundamental wave component and harmonic components. At step (c), coefficients of the AR model are estimated and the secondary current during saturation of the current transformer is compensated, based on the secondary current data sampled in the unsaturated section.

Abstract: A method for preventing the unwanted maloperation of a protective relay system that is caused by the imprecise detection of an actual secondary current value resulting from a measured secondary current being distorted comprises the steps of calculating difference values for sampled secondary currents; comparing absolute values of the difference values with a predetermined critical value, and determining a saturation starting moment of a current transformer when one of the absolute values exceeds the predetermined critical value; obtaining a magnetizing current at the saturation starting moment using the difference values if the saturation starting moment is determined, and obtaining a magnetic flux value in a steel core of the current transformer from a magnetization curve using the magnetizing current; calculating a magnetic flux value at a time after the saturation starting moment using a secondary current value measured at that time and the magnetic flux value obtained at the saturation starting moment so

Abstract: Disclosed is a relaying method for protecting a transformer by using a difference of current. A decision function, related to the rate of change of a primary current, a secondary current, or a differential current, is used for determining whether a detected abnormal current is due to the inrush or internal fault.

Abstract: The present invention relates to a method for preventing the unwanted maloperation of a protective relay system that is caused by the imprecise detection of an actual secondary current value resulting from a measured secondary current being distorted.

Abstract: The present invention relates to a relaying method using the ratio of induced voltages or the ratio of flux linkage increments. The protective relaying method for power transformers with one or more phases includes the first step of obtaining primary and secondary voltages and currents of the transformer; the second step of calculating induced voltages, induced voltage differences, ratio of primary and secondary induced voltages, or ratio of primary and secondary induced voltage differences from the currents and the voltages; the third step of calculating at least one predetermined decision parameter derived from at least one predetermined equation; the fourth step of deciding whether an internal winding fault occurs by comparing the decision parameter to the induced voltages, the induced voltage differences, the ratio of primary and secondary induced voltages, or the ratio of primary and secondary induced voltage differences.

Abstract: Disclosed is a relaying method for protecting a transformer by using a difference of current. A decision function, related to the difference of a primary current, a secondary current, or a differential current is used for determining whether a detected abnormal current is due to the inrush or internal fault.