Abstract: A power converter includes at least one arm for each phase, and each arm is formed by connecting, in series, a plurality of converter cells each having a plurality of semiconductor switching elements and a DC capacitor. A control device generates, for each arm, an arm voltage command for the plurality of convener cells, to control the power converter. The control device includes a voltage information calculation unit for calculating a voltage information value on the basis of voltage of at least one DC capacitor in the power converter, and a overall voltage control unit for changing a voltage total value of all the DC capacitors so that the voltage information value becomes close to a set lower limit value.

Abstract: A first voltage control circuitry controls a first representative value, i.e., an average-value corresponding value of DC capacitor voltages of all converter cells to follow an overall voltage command value. A phase balance control circuitry controls second representative values, i.e., average-value corresponding values of DC capacitor voltages of the converter cells in leg circuits for respective phases to follow the first representative value. A positive-negative balance control circuitry controls deviations of third representative values, i.e., average-value corresponding values of the DC capacitor voltages of the converter cells in the positive and negative arms of the leg circuits for respective phases to become zero between the positive and negative arms. An individual balance control circuitry controls DC capacitor voltages of all the converter cells to follow the third representative values.

Abstract: A controlling circuitry of a power conversion device has a first control mode for controlling circulation current circulating among leg circuits for the respective phases in a power converter so that an AC component having a frequency that is an even multiple other than a multiple of 3 with respect to the frequency of a fundamental component of AC is contained in the circulation current, and determines whether to make the first control mode active or inactive, on the basis of the voltage value of an energy storage element.

Abstract: In an MMC-based power conversion device, a control device generates, for each leg circuit, a first voltage command value not based on circulating current circulating between a plurality of leg circuits and a second voltage command value based on the circulating current. A plurality of individual controllers are provided respectively corresponding to a plurality of converter cells and generate a gate control signal for controlling turning on and off of a switching element of the corresponding converter cell, based on the first voltage command value and the second voltage command value. When generating the gate control signal using pulse width modulation, each individual controller modulates a carrier signal in accordance with the second voltage command value such that the pulse width of the gate control signal changes in accordance with the second voltage command value.

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: A power conversion device includes a power converter including a plurality of arms and a control device to control voltages of a plurality of sub modules by PWM control using a carrier signal for each sub module. The sub module includes a plurality of switching elements, a power storage element, a pair of output terminals, and a bypass switch. When the control device detects failure of a sub module in an arm, it performs stop processing for stopping a switching operation of the plurality of switching elements included in at least one sub module of the plurality of sub modules in the arm and has the sub module failure of which was detected bypassed. After the control device performs the stop processing, it equalizes intervals among phases of carrier signals of a plurality of normal sub modules in the arm caused by failure of the sub module.

Abstract: A power conversion device includes a power converter including a plurality of arms each having a plurality of converter cells cascaded to each other. A control device includes an AC current controller to control AC current flowing between the power converter and an AC circuit and a circulating current controller to control circulating current flowing between the arms of the power converter. The AC current controller reduces an effective value or amplitude value of AC current in a discharge operation mode in which a voltage of a power storage element of each converter cell is discharged, compared with in a normal operation mode. The circulating current controller increases an effective value or amplitude value of circulating current in the discharge operation mode, compared with in the normal operation mode.

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 conversion device includes: a power converter connected to an AC grid to which a load is connected; and a control circuit. The control circuit includes a harmonic compensation unit that includes a current command generation unit and a limit coefficient calculation unit and compensates for harmonic current contained in load current. The current command generation unit generates compensation current desired values for respective frequency components, and corrects the compensation current desired values using corresponding limit coefficients, to generate compensation current commands for respective frequency components. The limit coefficient calculation unit calculates each limit coefficient, on the basis of the compensation current desired value for each frequency component, and maximum voltage and maximum current that the power converter can output.

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 two arms for each phase between DC terminals, and each arm is formed by connecting a plurality of converter cells in series. A control device includes an arm voltage command generation unit which generates, for each arm, an arm voltage command for the plurality of converter cells. The arm voltage command is generated by superimposing a zero-phase-sequence voltage command having a frequency component that is three times an AC fundamental frequency. Phase adjustment of the zero-phase-sequence voltage command is performed on the basis of voltage of a DC capacitor in the converter cell and the arm voltage command.

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 converter connected to an AC grid to which a load is connected; and a control circuit. The control circuit includes a harmonic compensation unit that includes a current command generation unit and a limit coefficient calculation unit and compensates for harmonic current contained in load current. The current command generation unit generates compensation current desired values for respective frequency components, and corrects the compensation current desired values using corresponding limit coefficients, to generate compensation current commands for respective frequency components. The limit coefficient calculation unit calculates each limit coefficient, on the basis of the compensation current desired value for each frequency component, and maximum voltage and maximum current that the power converter can output.

Abstract: A power conversion device includes: a power converter including, for respective phases of AC, leg circuits each including a pair of arms connected in series, the arms including a plurality of converter cells which are connected in series and each of which has an energy storage element and a plurality of semiconductor elements, the leg circuits being connected in parallel between positive and negative DC terminals, the power converter being configured to perform power conversion between multiphase AC and DC; and a control unit. The control unit corrects an AC voltage command value for controlling AC voltage of the power converter, by a zero-phase-sequence voltage command value having a set amplitude and a set phase, and performs adjustment control for adjusting at least either the amplitude or the phase of the zero-phase-sequence voltage command value on the basis of electric energy variation in the arm.

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.