Abstract: A power conversion device includes a power converter connected between a multi-phase alternating-current circuit and a direct-current circuit, and a control device to control the power converter. The control device detects an unbalanced component indicating a voltage unbalanced component or a current unbalanced component of the alternating-current circuit and limits a magnitude of an alternating current flowing between the power converter and the alternating-current circuit based on the unbalanced component.

Abstract: In a power conversion system, a first power converter is connected between a first AC power system, and a first DC main line and a DC return line. A second power converter is connected between the first AC power system, and the DC return line and a second DC main line. A first control device controls the first power converter in accordance with a first active power command value. A second control device controls the second power converter in accordance with a second active power command value. A common control device sets the first active power command value and the second active power command value by distributing a command value of total active power output from the entire power conversion system to the first AC power system. The common control device makes the first active power command value and the second active power command value different from each other.

Abstract: A power conversion device includes a self-commutated power converter that performs power conversion between an AC circuit and a DC circuit, and a control device that controls switching operation of a switching element included in the self-commutated power converter. The control device performs first control to increase a switching frequency of the switching element when a control command value for the self-commutated power converter becomes equal to or greater than a first threshold value.

Abstract: A power conversion system includes a plurality of power conversion devices connected to a plurality of AC systems, respectively. The power conversion devices are further connected to a common DC circuit. The power conversion system further includes a start-up device to start up each power conversion device. The start-up device selects an AC system that satisfies a defined condition relating to power supply capability from among the plurality of AC systems based on system information of the plurality of AC systems and starts up a power conversion device connected to the selected AC system.

Abstract: A power converter includes an arm in which a plurality of converter cells are connected in series, each of the converter cells including at least two switching elements, a power storage element, and a pair of output terminals. A control device controls the power converter. The converter cell includes a switch to have the converter cell bypassed. When the control device senses failure of the converter cell, it has the failed converter cell within the arm bypassed and controls a normal converter cell within the arm to suppress a ratio of a harmonic component in an arm current that increases due to the failure.

Abstract: A power conversion device includes a power converter including a plurality of arms each having a plurality of converter cells connected to each other in cascade. Each converter cell includes a capacitor electrically connected to input/output terminals through a plurality of switching elements. A control device performs AC current control in accordance with a deviation between a detected AC current and an AC current command value and individual voltage control in accordance with a deviation between a voltage of each individual capacitor and an individual voltage command value. The control device calculates an evaluation value indicating the degree of variations in voltage of the individual capacitors. When the evaluation value is greater than a threshold value, the control device changes control of the power converter such that arm current flowing through each of the arms increases while the AC current control and the individual voltage control are being performed.

Abstract: A power conversion system includes: a first power converter to perform power conversion between a first AC system and a DC circuit; and a second power converter to perform power conversion between a second AC system and the DC circuit. Each of the first power converter and the second power converter includes a plurality of submodules connected in series. Each of the plurality of submodules includes a plurality of switching elements and a capacitor. A first fundamental frequency of the first AC system is greater than a second fundamental frequency of the second AC system. A first average voltage value of a capacitor in a first submodule included in the first power converter is larger than a second average voltage value of a capacitor in a second submodule included in the second power converter.

Abstract: A power conversion device includes a plurality of leg circuits and a control device. The control device controls an output voltage at a first converter cell, which is controlled not based on the circulating current, based on a first voltage instruction value. The control device controls an output voltage at a second converter cell using a first value based on a deviation between a circulating current and a circulating current instruction value and a second value based on a deviation between a capacitor voltage and a capacitor voltage instruction value in the second converter cell. When the capacitor voltage at the second converter cell is less than a first threshold, the control device linearly combines an auxiliary voltage instruction value including at least one of a DC component and a fundamental AC component of the AC circuit with the first value and the second value.

Abstract: A power conversion device includes a power conversion circuit unit including a plurality of leg circuits, and a control device. Each of the leg circuits includes a plurality of first converter cells each having a capacitor and connected in series to each other and a plurality of second converter cells each having the capacitor and connected in series to each other. The plurality of first converter cells are controlled not based on a circulating current circulating between the plurality of leg circuits, and the plurality of second converter cells are controlled based on the circulating current. The control device stops a switching operation of at least one second converter cell in the plurality of second converter cells when a voltage at the capacitor in the second converter cell becomes less than a first threshold.

Abstract: A power conversion device includes a power conversion circuit unit including a plurality of leg circuits. Each of the leg circuits includes a plurality of converter cells each having a capacitor and connected in series to each other. Each of the plurality of converter cells is a first converter cell including at least two switching elements or a second converter cell including at least four switching elements. The power conversion device further includes a control device. The control device operates the plurality of the first converter cells that are controlled not based on a circulating current circulating between the plurality of leg circuits as a voltage source that outputs a circulating voltage in a circulation circuit indicating a closed circuit that does not include a DC circuit and an AC circuit, and operates the plurality of the second converter cells to control the circulating current in the circulation circuit.

Abstract: A power conversion device includes a power conversion circuit unit including a plurality of leg circuits, and a control device. Each of the leg circuits includes a plurality of first converter cells each having a capacitor and connected in series to each other and a plurality of second converter cells each having the capacitor and connected in series to each other. The plurality of first converter cells are controlled not based on a circulating current circulating between the plurality of leg circuits, and the plurality of second converter cells are controlled based on the circulating current. The control device executes control processing for increasing a current flowing through the second converter cell when a voltage at the capacitor in the second converter cell is less than a first threshold value.

Abstract: A power converter includes at least one arm having a plurality of converter cells cascaded to each other. Each of the converter cells includes a pair of input/output terminals, a plurality of switching elements, and a power storage element. The power storage element is electrically connected to the input/output terminals through the switching elements. A control device generates a control signal for controlling on and off of the switching elements of each converter cell. The control device generates the control signal by pulse width modulation control based on a modulation command signal including an AC component having a fundamental frequency and corresponding to a command value of an output voltage between the input/output terminals, in each converter cell, such that a harmonic component included in the output voltage and having a predetermined frequency that is an integer multiple of the fundamental frequency is suppressed.

Abstract: A voltage evaluation value generator receives voltage detection values of power storage elements of all of converter cells included in a power converter and generates a first voltage evaluation value of each power storage element of all of the converter cells and a second voltage evaluation value of each power storage element in a plurality of converter cells included in each of a plurality of groups obtained by classifying all of the converter cells in advance, without using a mean value of voltage detection values. A voltage macro controller uses the voltage evaluation value to calculate a control value set in common to at least the converter cells in the same group for controlling deficiency and excess of stored energy in all of the converter cells and the converter cells in each group.

Abstract: A control device includes: a phase error calculation unit to calculate a phase error between a phase of a voltage command for the power converter and a phase of a point-of-interconnection voltage; and an isolated system determination unit to determine whether the AC power system has shifted from an interconnected system to an isolated system, based on the phase error and a magnitude of the point-of-interconnection voltage, the interconnected system being the AC power system connected to a generator, the isolated system being the AC power system not connected to the generator. The isolated system determination unit determines that the AC power system has shifted from the interconnected system to the isolated system, when at least a first condition is met that the phase error is outside a reference range and the magnitude of the point-of-interconnection voltage is greater than a first voltage threshold.

Abstract: A control device includes: a phase generation unit to generate a phase of a voltage command for the power converter; a voltage control unit to generate a voltage value of the voltage command; and a command unit to output the voltage command having the phase and the voltage value to the power converter. The voltage control unit includes: a voltage compensator unit to compute a compensation voltage value, based on a voltage deviation of a point-of-interconnection voltage from a reference voltage; a droop calculator unit to compute a first droop value in accordance with a magnitude of a point-of-interconnection current, when the AC power system is an isolated system, the isolated system being the AC power system not connected to a generator; and a calculation unit to calculate the voltage value of the voltage command, based on a difference between the compensation voltage value and the first droop value.

Abstract: A power converter includes an arm in which a plurality of converter cells are connected in series, each of the converter cells including at least two switching elements, a power storage element and a pair of output terminals. A control device controls the power converter. The converter cell includes a switch to have the converter cell bypassed. When the control device senses failure of the converter cell, it has the failed converter cell bypassed, estimates an output voltage lost by bypassing the failed converter cell, and has a normal converter cell supply the estimated output voltage of the failed converter cell.

Abstract: A power conversion device includes a conversion circuit constituted of a plurality of arm circuits and a bypass circuit. The bypass circuit includes a full-wave rectification circuit, a positive-side connection arm, and a negative-side connection arm. The full-wave rectification circuit is connected between a plurality of AC connections, a positive-side intermediate node, and a negative-side intermediate node, and configured to convert AC voltages generated at the plurality of AC connections into a DC voltage across the positive-side intermediate node and the negative-side intermediate node and output the DC voltage. The positive-side connection arm blocks a current in a direction from a positive-side DC terminal toward the positive-side intermediate node. The negative-side connection arm is connected between the negative-side intermediate node and a negative-side DC terminal and blocks a current in a direction from the negative-side intermediate node toward a negative-side DC terminal.

Abstract: A power converter includes an arm in which a plurality of converter cells are connected in series, each of the converter cells including at least two switching elements, a power storage element, and a pair of output terminals. A control device controls the power converter. The converter cell includes a switch to have the converter cell bypassed. When the control device senses failure of the converter cell, it has the failed converter cell within the arm bypassed and controls a normal converter cell within the arm to suppress a ratio of a harmonic component in an arm current that increases due to the failure.

Abstract: A power converter includes an arm in which a plurality of converter cells are connected in series, each of the converter cells including at least two switching elements, a power storage element, and a pair of output terminals. A control device controls voltages of the plurality of converter cells by phase shift PWM control using a carrier signal for each converter cell. The converter cell includes a switch to have the converter cell bypassed. When the control device senses failure of the converter cell within the arm, it has a failed converter cell within the arm bypassed and rectifies uneven intervals among phases of carrier signals of a plurality of normal converter cells within the arm caused by failure of the converter cell.

Abstract: A power converter includes an arm in which a plurality of converter cells are connected in series, each of the converter cells including at least two switching elements, a power storage element and a pair of output terminals. A control device controls the power converter. The converter cell includes a switch to have the converter cell bypassed. When the control device senses failure of the converter cell, it has the failed converter cell bypassed, estimates an output voltage lost by bypassing the failed converter cell, and has a normal converter cell supply the estimated output voltage of the failed converter cell.