Abstract: A method of controlling output levels of an MMC converter to reduce fluctuation in a power grid frequency, which adjusts an output level of the MMC converter in response to a change in a power grid frequency of a power grid system in the MMC converter connected to a grid system, is proposed. The method includes a detection step of detecting a power grid frequency of a grid connected to the MMC converter in real time, a comparison step of comparing the detected power grid frequency with a preset reference power grid frequency, and an adjustment step of adjusting a number of output levels of the MMC converter to reduce a difference between the detected power grid frequency and the reference power grid frequency when the detected power grid frequency and the reference power grid frequency are different from each other.

Abstract: Disclosed is a modular multilevel converter sub-module, including: a normal circuit which includes a first switching element and a second switching element connected in series and a first diode and a second diode respectively connected to be parallel to the first switching element and the second switching element to offset a counter electromotive force generated in the first switching element and the second switching element, a fault DC current blocking circuit which includes a capacitor connected to the normal circuit in parallel and applies a capacitor voltage to a DC fault path as a reverse voltage with respect to a fault voltage, and a bypass circuit which includes a third switch element, is connected to the fault DC current blocking circuit in parallel, and determines an output voltage and a direction of an arm current to provide a DC fault current bypass path when a DC fault current occurs.

Abstract: A modular multilevel converter (MMC) includes multiple converter arms, each converter arm having: N submodules connected to each other in series, N being an integer equal to or greater than 2; and a circuit opening unit connected to the N submodules in series to open a circuit of the converter arm, wherein the N submodules has n submodules including full-bridge circuits and N?n submodules including half-bridge circuits, n being less than N.

Abstract: Disclosed is a modular multilevel converter sub-module, including: a normal circuit which includes a first switching element and a second switching element connected in series and a first diode and a second diode respectively connected to be parallel to the first switching element and the second switching element to offset a counter electromotive force generated in the first switching element and the second switching element, a fault DC current blocking circuit which includes a capacitor connected to the normal circuit in parallel and applies a capacitor voltage to a DC fault path as a reverse voltage with respect to a fault voltage, and a bypass circuit which includes a third switch element, is connected to the fault DC current blocking circuit in parallel, and determines an output voltage and a direction of an arm current to provide a DC fault current bypass path when a DC fault current occurs.

Abstract: A method of controlling output levels of an MMC converter to reduce fluctuation in a power grid frequency, which adjusts an output level of the MMC converter in response to a change in a power grid frequency of a power grid system in the MMC converter connected to a grid system, is proposed. The method includes a detection step of detecting a power grid frequency of a grid connected to the MMC converter in real time, a comparison step of comparing the detected power grid frequency with a preset reference power grid frequency, and an adjustment step of adjusting a number of output levels of the MMC converter to reduce a difference between the detected power grid frequency and the reference power grid frequency when the detected power grid frequency and the reference power grid frequency are different from each other.

Abstract: The present invention relates to an MMC converter system which can quickly cut off fault current by installing a plurality of disconnecting switch units on a line connected between two MMC converter devices. The MMC converter system comprises: a first MMC converter device including a plurality of serially connected sub modules; a second MMC converter device including a plurality of serially connected sub modules; a first disconnecting switch unit installed on a line between the first and second MMC converter devices; and a second disconnecting switch unit connected in series to the first disconnecting switch unit on the line, wherein each of the first and second disconnecting switch units comprises a mechanical switch installed on the line so as to open and close the line and a diode connected in parallel to the mechanical switch, and the two diodes are installed in opposite directions to each other.

Abstract: The present invention relates to an MMC converter system which can quickly cut off fault current by installing a plurality of disconnecting switch units on a line connected between two MMC converter devices. The MMC converter system comprises: a first MMC converter device including a plurality of serially connected sub modules; a second MMC converter device including a plurality of serially connected sub modules; a first disconnecting switch unit installed on a line between the first and second MMC converter devices; and a second disconnecting switch unit connected in series to the first disconnecting switch unit on the line, wherein each of the first and second disconnecting switch units comprises a mechanical switch installed on the line so as to open and close the line and a diode connected in parallel to the mechanical switch, and the two diodes are installed in opposite directions to each other.

Abstract: Provided is an MMC and a DC failure blocking method therefor, the MMC and the method being capable of DC failure blocking and reducing loss using a combination of half-bridge submodules and full-bridge submodules for converter arms of the MMC. According to the present invention, there is provided a modular multilevel converter (MMC) including multiple converter arms, each converter arm having: N (N?2, an integer) submodules connected to each other in series; and a circuit opening unit connected to the N submodules in series to open a circuit of the converter arm, wherein the N submodules are n (n<N) submodules including full-bridge circuits and N-n submodules including half-bridge circuits.

Abstract: Disclosed is a power control system for a plurality of energy storage devices, including: a first converter configured to perform a voltage conversion, the first converter having one end connected to a first power system and another end connected to a direct current (DC) linker; a second converter configured to perform a voltage conversion, the second converter having one end connected to a second power system and another end connected to the DC linker; a first energy storage device configured to store electric energy; a direct current-to-direct current (DC-DC) converter configured to perform a voltage conversion, the DC-DC converter having one end connected to the first energy storage device and another end connected to the DC linker; a second energy storage device connected to the DC linker and configured to store electric energy, and a control device.

Abstract: Provided are a multi-level converter having more than one converter arm in which a plurality of sub-modules are connected in series, multi-level converter comprising, a first bypass circuit connected in parallel to at least one sub-module included in more than one converter arm on a first side and including a first switching device, a second bypass circuit connected in parallel to more than one converter arm on a second side and including a diode, a second switching device included in more than one converter arm and having a first end connected in series to at least one sub-module and a second end connected to a first end of first bypass circuit at a single node and a third switching device included in more than one converter arm and having a first end connected in series to at least one sub-module and a second end connected to a first end of second bypass circuit at a single node.

Abstract: The present disclosure provides a method for controlling a multilevel converter, the method including, detecting modulation state values and current directions of sub-modules, and designating, by one sub-module, an average number of switching for each period of an output waveform, wherein the step of designating the average number of switching includes, grouping the sub-modules according to being in ON state or in OFF state, comparing the number of sub-modules in previous ON state and the number of sub-modules in OFF state to obtain a difference therebetween, and changing a state as much as the difference, comparing a sub-module of ON state in charged state and in discharged state with a sub-module of OFF state, and changing the compared states of sub-modules of ON state and OFF state.

Abstract: Disclosed is a power control system for a plurality of energy storage devices, including: a first converter configured to perform a voltage conversion, the first converter having one end connected to a first power system and another end connected to a direct current (DC) linker; a second converter configured to perform a voltage conversion, the second converter having one end connected to a second power system and another end connected to the DC linker; a first energy storage device configured to store electric energy; a direct current-to-direct current (DC-DC) converter configured to perform a voltage conversion, the DC-DC converter having one end connected to the first energy storage device and another end connected to the DC linker; a second energy storage device connected to the DC linker and configured to store electric energy, and a control device.

Abstract: Provided are a multi-level converter having more than one converter arm in which a plurality of sub-modules are connected in series, multi-level converter comprising, a first bypass circuit connected in parallel to at least one sub-module included in more than one converter arm on a first side and including a first switching device, a second bypass circuit connected in parallel to more than one converter arm on a second side and including a diode, a second switching device included in more than one converter arm and having a first end connected in series to at least one sub-module and a second end connected to a first end of first bypass circuit at a single node and a third switching device included in more than one converter arm and having a first end connected in series to at least one sub-module and a second end connected to a first end of second bypass circuit at a single node.

Abstract: A method of controlling a multilevel converter is provided. In the method of controlling a multilevel converter according to an embodiment, a sub-module having the maximum voltage and a sub-module having the minimum voltage respectively are extracted from among a plurality of sub-modules. An amount of state variation of each of the plurality of sub-modules is determined. When the amount of state variation is not determined to be 0, a direction of a current flowing through the plurality of sub-modules is detected. A subsequent state of at least one sub-module is determined according to at least one of the amount of the state variation and current direction. Subsequently an arrangement time for sub-module values can be efficiently reduced while the number of the sub-modules increases in the voltage balancing.

Abstract: The present disclosure provides a method for controlling a multilevel converter, the method including, detecting modulation state values and current directions of sub-modules, and designating, by one sub-module, an average number of switching for each period of an output waveform, wherein the step of designating the average number of switching includes, grouping the sub-modules according to being in ON state or in OFF state, comparing the number of sub-modules in previous ON state and the number of sub-modules in OFF state to obtain a difference therebetween, and changing a state as much as the difference, comparing a sub-module of ON state in charged state and in discharged state with a sub-module of OFF state, and changing the compared states of sub-modules of ON state and OFF state.

Abstract: This invention relates to a PMU-based controlled system separation method to protect against a catastrophic blackout. The method includes the steps of performing an offline analysis of an electrical transmission network to partition generators into a number of coherent groups, performing online monitoring of the transmission network to determine a separation interface and frequencies and damping ratios of dominant inter-area modes, and estimating the risk of system separation to perform real-time control.

Abstract: This invention relates to a PMU-based controlled system separation method to protect against a catastrophic blackout. The method includes the steps of performing an offline analysis of an electrical transmission network to partition generators into a number of coherent groups, performing online monitoring of the transmission network to determine a separation interface and frequencies and damping ratios of dominant inter-area modes, and estimating the risk of system separation to perform real-time control.

Abstract: An apparatus and method to suppress a low speed ripple current to a motor include a power supply unit to supply single-phase alternating current (AC) power. A rectifying and smoothing unit rectifies and smoothes the single-phase AC power and outputs a direct current (DC) voltage indicative thereof. An inverter receives and converts the DC voltage to a motor driving current to drive the motor. A controller compares an envelope detected from a ripple current in the motor driving current and a DC component extracted from the ripple current and generates a compared result therefrom, and controls an output voltage from the inverter according to the compared result.

Abstract: An apparatus and method to suppress a low speed ripple current to a motor include a power supply unit to supply single-phase alternating current (AC) power. A rectifying and smoothing unit rectifies and smoothes the single-phase AC power and outputs a direct current (DC) voltage indicative thereof. An inverter receives and converts the DC voltage to a motor driving current to drive the motor. A controller compares an envelope detected from a ripple current in the motor driving current and a DC component extracted from the ripple current and generates a compared result therefrom, and controls an output voltage from the inverter according to the compared result.