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 system includes a first power converter and a second power converter which are capable of converting an alternating-current power into a direct-current power or converting a DC power into an AC power. The first power converter is interconnectable to a first AC system via a first AC circuit breaker. The second power converter is interconnectable to a second AC system via a second AC circuit breaker. A first DC terminal of the first power converter and a second DC terminal of the second power converter are connectable. The first power converter begins operation prior to the second power converter. A first control device controls a voltage of the first DC terminal, based on a status of the second power converter sent from a second control device.

Abstract: A power conversion device includes power conversion circuitry including a plurality of submodules connected in series to each other. The power conversion device further includes: a signal reception unit configured to receive a signal representing a voltage of a capacitor in each of the submodules; a time calculation unit configured to calculate at least one of a charging time of the capacitor and a discharging time of the capacitor based on the signal; and a determination unit configured to determine whether the capacitor has degraded or not based on at least one of a first result of comparison of the charging time with a reference charging time serving as a reference for determining degradation of the capacitor, and a second result of comparison of the discharging time with a reference discharging time serving as a reference for determining degradation of the capacitor.

Abstract: A power conversion device includes power conversion circuitry including a plurality of submodules connected in series to each other. The power conversion device further includes: a signal reception unit configured to receive a signal representing a voltage of a capacitor in each of the submodules; a time calculation unit configured to calculate at least one of a charging time of the capacitor and a discharging time of the capacitor based on the signal; and a determination unit configured to determine whether the capacitor has degraded or not based on at least one of a first result of comparison of the charging time with a reference charging time serving as a reference for determining degradation of the capacitor, and a second result of comparison of the discharging time with a reference discharging time serving as a reference for determining degradation of the capacitor.

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: Each arm circuit of a power conversion device includes a plurality of cascaded cell blocks and a plurality of bypass circuits connected in parallel to the respective cell blocks. Each cell block includes: a first connection node on a high potential side and a second connection node on a low potential side for connection to another cell block; and a plurality of converter cells cascaded between the first and second connection nodes, each converter cell containing an energy storage. The plurality of converter cells include at least one first converter cell of a full-bridge (or hybrid) configuration and at least one second converter cell of a half-bridge configuration.

Abstract: A control device generates a voltage command value for controlling a current flowing between a three-phase AC power supply and a power converter such that a full voltage representative value representing voltage values of all power storage devices agrees with a DC voltage command value. The control device generates a zero-phase voltage command value for controlling a circulating current flowing in a delta connection such that the voltage values of the power storage devices are balanced among first to third arms. The control device combines the voltage command value and the zero-phase current command value to generate an output voltage command value for controlling an output voltage of each unit converter. The control device removes a control amount of the full voltage representative value from a computation of the zero-phase voltage command value to cause output current control and circulating current control not to interfere with each other.

Abstract: A power conversion system includes a first power converter and a second power converter which are capable of converting an alternating-current power into a direct-current power or converting a DC power into an AC power. The first power converter is interconnectable to a first AC system via a first AC circuit breaker. The second power converter is interconnectable to a second AC system via a second AC circuit breaker. A first DC terminal of the first power converter and a second DC terminal of the second power converter are connectable. The first power converter begins operation prior to the second power converter. A first control device controls a voltage of the first DC terminal, based on a status of the second power converter sent from a second control device.

Abstract: A power conversion apparatus includes: a plurality of cell blocks connected in cascade; and a plurality of bypass circuits each electrically connected in parallel with a corresponding one of the plurality of cell blocks. Each cell block includes: a first connection node on a high-potential side and a second connection node on a low-potential side for connection to another cell block; and a plurality of cell converters connected in cascade between the first connection node and the second connection node, each of the cell converters including an energy storage device. When a DC fault current flows in the direction from the low-potential side to the high-potential side, the current path via the plurality of cell blocks is larger in impedance than the current path via the plurality of bypass circuits.

Abstract: A control device generates a voltage command value for controlling a current flowing between a three-phase AC power supply and a power converter such that a full voltage representative value representing voltage values of all power storage devices agrees with a DC voltage command value. The control device generates a zero-phase voltage command value for controlling a circulating current flowing in a delta connection such that the voltage values of the power storage devices are balanced among first to third arms. The control device combines the voltage command value and the zero-phase current command value to generate an output voltage command value for controlling an output voltage of each unit converter. The control device removes a control amount of the full voltage representative value from a computation of the zero-phase voltage command value to cause output current control and circulating current control not to interfere with each other.

Abstract: A power conversion device includes a plurality of leg circuits and a control device. The plurality of leg circuits correspond to respective phases of an AC circuit and connected in parallel between common first and second DC terminals. Each leg circuit includes a plurality of chopper cells each including an energy storage and cascaded to one another and at least one inductance connected in series to the plurality of chopper cells. The control device controls an operation of only at least one chopper cell included in each leg circuit based on a circulating current which circulates through the leg circuits.

Abstract: Each of a plurality of specified chopper cells which are some of a plurality of chopper cells included in each leg circuit in a power conversion device is configured as a full bridge. A control device controls operations of first and second switching elements of each specified chopper cell based on a circulating current which circulates through each leg circuit. The control device controls operations of third and fourth switching elements of each specified chopper cell based on a voltage of a capacitor of the specified chopper cell.

Abstract: Since a power converter including a modular multilevel converter uses a large number of cells each combining a plurality of switching elements and a DC capacitor, there is a problem of conduction loss due to the switching elements. The conduction loss is reduced by connecting a bypass circuit between terminals of each of the cells, controlling to open and close the switching element, and controlling to short-circuit the bypass circuit connected to the cell controlled to output zero voltage.

Abstract: When short-circuit between DC lines is detected, a control device of a power conversion device performs protection control to turn off semiconductor switching elements in a power converter, and when elimination of the short-circuit between the DC lines is detected, the control device performs restart control of the power converter by giving a voltage command value for causing negative-polarity current in flowing through a diode in an upper arm of a second series body of a second converter cell to flow to a phase arm 4, to each converter cell in first and second arms.

Abstract: In a multilevel converter, three switches are connected between three arms and three reactors, and three resistive elements are connected to the respective three switches in parallel. The three switches are configured to be in a conductive state during a normal operation. The three switches are configured to come into a non-conductive state when a short circuit accident occurs between two DC power transmission lines, whereby an inter-arm direct current flowing in four arms and the like is quickly attenuated by the three resistive elements.

Abstract: A power conversion apparatus includes: a plurality of cell blocks connected in cascade; and a plurality of bypass circuits each electrically connected in parallel with a corresponding one of the plurality of cell blocks. Each cell block includes: a first connection node on a high-potential side and a second connection node on a low-potential side for connection to another cell block; and a plurality of cell converters connected in cascade between the first connection node and the second connection node, each of the cell converters including an energy storage device. When a DC fault current flows in the direction from the low-potential side to the high-potential side, the current path via the plurality of cell blocks is larger in impedance than the current path via the plurality of bypass circuits.

Abstract: In a multilevel converter, three first rectifying elements are respectively connected between three arms and a negative voltage terminal. Three second rectifying elements are respectively connected to the three first rectifying elements in antiparallel. During a normal operation, current flows in the three first rectifying elements and the three second rectifying elements. When a short circuit accident occurs between two DC power transmission lines, the three first rectifying elements are brought into the non-conductive state, thereby interrupting and quickly attenuating inter-arm direct current flowing in four arms and the like.

Abstract: When short-circuit between DC lines is detected, a control device of a power conversion device performs protection control to turn off semiconductor switching elements in a power converter, and when elimination of the short-circuit between the DC lines is detected, the control device performs restart control of the power converter by giving a voltage command value for causing negative-polarity current in flowing through a diode in an upper arm of a second series body of a second converter cell to flow to a phase arm 4, to each converter cell in first and second arms.

Abstract: Each arm circuit of a power conversion device includes a plurality of cascaded cell blocks and a plurality of bypass circuits connected in parallel to the respective cell blocks. Each cell block includes: a first connection node on a high potential side and a second connection node on a low potential side for connection to another cell block; and a plurality of converter cells cascaded between the first and second connection nodes, each converter cell containing an energy storage. The plurality of converter cells include at least one first converter cell of a full-bridge (or hybrid) configuration and at least one second converter cell of a half-bridge configuration.

Abstract: In a control device of a power conversion device, an AC control portion generates a first voltage command value representing an AC voltage component to be output from a plurality of chopper cells of each leg circuit. A DC control portion generates a second voltage command value representing a DC voltage component to be output from the plurality of chopper cells of each leg circuit. A circulating current control portion generates a third voltage command value to be output from the plurality of chopper cells of each leg circuit in order to suppress a circulating current. The circulating current control portion performs a non-linear operation with the first, second, and third voltage command values. The plurality of chopper cells of each leg circuit operate in accordance with a result of the non-linear operation.