Abstract: A power converter includes first and second arms, each having switching elements, and performs power conversion between a DC system and an AC system. An AC circuit breaker and a current control circuit are connected in series between the AC system and the power converter. The current control circuit includes a current-limiting resistor and a disconnector connected in parallel. A controller instructs a disconnector to close after an initial charge of the power converter and opens the AC circuit breaker when an impedance of a line between a first node located on a first end side of the current control circuit and a second node located on a second end side of the current control circuit is not less than a first threshold and an accumulated value of a current flowing through the current control circuit within a certain period of time is not less than a second threshold.

Abstract: In a multi-terminal DC power transmission system, a common control device is connected to a plurality of individual protective devices via a first communication network. Each of the individual protective devices is configured, when detecting change in current or voltage in a corresponding protection zone, to output a fault signal to the common control device via the first communication network and open the corresponding DC circuit breaker such that the corresponding protection zone is disconnected from the multi-terminal DC power grid and deenergized. The common control device estimates a fault occurrence zone where a fault occurs among a plurality of protection zones, based on a plurality of received fault signals. The common control device requests an individual protective device corresponding to a deenergized protection zone of the protection zones excluding the fault occurrence zone to reclose the DC circuit breaker such that the deenergized protection zone is restored.

Abstract: A power conversion device included in a self-excited DC power transmission system connected to an AC system includes a self-excited converter and a control device. The control device includes: a storage to store first vibration information and a first control parameter of the self-excited converter in association with each other for each of a plurality of pieces of first vibration information, a vibration detector to detect a vibration component of an AC voltage of the AC system; a determination unit to determine whether first similar vibration information similar to first detected vibration information including the vibration component of the AC voltage of the detected AC system exists in the plurality of pieces of first vibration information; and a setting unit to set the first control parameter associated with the first similar vibration information as a new control parameter of the self-excited converter when the first similar vibration information exists.

Abstract: A power conversion device that performs power conversion between a DC circuit and an AC circuit includes a power conversion circuit including a plurality of sub-modules, a failure detection device that detects an internal failure of the power conversion circuit, and a control device that generates an operation command controlling operation of each of the plurality of sub-modules. The control device acquires a voltage value of a capacitor included in each sub-module, calculates a deviation between a variance value indicating a variation in the voltage value of the capacitor included in the sub-module in a reference period and a reference variance value in the sub-module for each of a plurality of sub-modules, determines a failure section of an internal failure based on the deviation in each sub-module when the internal failure is detected, and outputs an operation command based on a determination result to each sub-module.

Abstract: In one embodiment, a power conversion device that converts power between a DC circuit and an AC circuit includes a plurality of leg circuits connected in parallel between first and second DC terminals and electrically connected to the AC circuit. Each of the plurality of leg circuits includes at least one first converter cell and a plurality of second converter cells other than the first converter cell. A first control signal that controls switching of a semiconductor switching element included in at least one first converter cell is higher in frequency than a second control signal that controls switching of a semiconductor switching element included in each of the plurality of second converter cells.

Abstract: In a multi-terminal DC power transmission system, a common control device is connected to a plurality of individual protective devices via a first communication network. Each of the individual protective devices is configured, when detecting change in current or voltage in a corresponding protection zone, to output a fault signal to the common control device via the first communication network and open the corresponding DC circuit breaker such that the corresponding protection zone is disconnected from the multi-terminal DC power grid and deenergized. The common control device estimates a fault occurrence zone where a fault occurs among a plurality of protection zones, based on a plurality of received fault signals. The common control device requests an individual protective device corresponding to a deenergized protection zone of the protection zones excluding the fault occurrence zone to reclose the DC circuit breaker such that the deenergized protection zone is restored.

Abstract: An MMC-type power conversion device includes a failure detection unit that detects presence or absence of failure of each of n upper arm current detectors and n lower arm current detectors. The failure detection unit makes a first determination based on comparison between a sum of detection values of n upper arm current detectors and the sum of detection values of n lower arm current detectors, a second determination based on comparison between a current command value and the sum of detection values of n upper arm current detectors, a third determination based on comparison between a current command value and the sum of detection values of n lower arm current detectors, and a fourth determination of comparing, for each phase, the sum of detection values of the current detectors of an upper arm and a lower arm of the same phase.

Abstract: A power conversion device that performs power conversion between a DC circuit and an AC circuit includes a power conversion circuit including a plurality of sub-modules, a failure detection device that detects an internal failure of the power conversion circuit, and a control device that generates an operation command controlling operation of each of the plurality of sub-modules. The control device acquires a voltage value of a capacitor included in each sub-module, calculates a deviation between a variance value indicating a variation in the voltage value of the capacitor included in the sub-module in a reference period and a reference variance value in the sub-module for each of a plurality of sub-modules, determines a failure section of an internal failure based on the deviation in each sub-module when the internal failure is detected, and outputs an operation command based on a determination result to each sub-module.

Abstract: A power conversion device includes a host device to control each submodule, and a plurality of repeating devices to relay communication between the host device and each submodule. The host device includes a command information generator to generate command information including an arm command, and a communication controller provided for each arm. Each of a plurality of communication controllers extracts, from the command information, an arm command associated with the communication controller, and transmits a communication frame including the extracted arm command to a repeating device that is connected to each submodule included in the arm associated with the communication controller.

Abstract: A power converter includes first and second arms, each having switching elements, and performs power conversion between a DC system and an AC system. An AC circuit breaker and a current control circuit are connected in series between the AC system and the power converter. The current control circuit includes a current-limiting resistor and a disconnector connected in parallel. A controller instructs a disconnector to close after an initial charge of the power converter and opens the AC circuit breaker when an impedance of a line between a first node located on a first end side of the current control circuit and a second node located on a second end side of the current control circuit is not less than a first threshold and an accumulated value of a current flowing through the current control circuit within a certain period of time is not less than a second threshold.

Abstract: A power conversion apparatus includes power conversion circuitry including a plurality of sub-modules connected in series to each other, a control device to generate a control command for controlling operation of the plurality of sub-modules, and a relay apparatus to relay communication between the control device and the plurality of sub-modules. For each sub-module of the plurality of sub-modules, the relay apparatus generates path information indicating a communication path from the control device to the sub-module, and outputs the generated path information to the sub-module. Each sub-module of the plurality of sub-modules generates identification information of the sub-module based on the path information corresponding to the sub-module.

Abstract: A power conversion device includes: first and second control devices that generate first and second control commands respectively; and first and second relay devices that transmit, to each sub module, the first and second control commands respectively. The first and second control devices receive instruction information indicating a system that is to control operation of each sub module. The first and second control commands each include a drive command, abnormality determination information about the control device, and instruction information. Even when the instruction information indicates a first system, each sub module selects a second system as a system to control operation of each sub module in response to detection of occurrence of abnormality to the first control device, and performs PWM control for a switching element in accordance with the drive command included in the second control command for the second system.

Abstract: A power conversion device includes: first and second control devices that generate first and second control commands respectively; and first and second relay devices that transmit, to each sub module, the first and second control commands respectively. The first and second control devices receive instruction information indicating a system that is to control operation of each sub module. The first and second control commands each include a drive command, abnormality determination information about the control device, and instruction information. Even when the instruction information indicates a first system, each sub module selects a second system as a system to control operation of each sub module in response to detection of occurrence of abnormality to the first control device, and performs PWM control for a switching element in accordance with the drive command included in the second control command for the second system.

Abstract: A power conversion apparatus includes power conversion circuitry including a plurality of sub-modules connected in series to each other, a control device to generate a control command for controlling operation of the plurality of sub-modules, and a relay apparatus to relay communication between the control device and the plurality of sub-modules. For each sub-module of the plurality of sub-modules, the relay apparatus generates path information indicating a communication path from the control device to the sub-module, and outputs the generated path information to the sub-module. Each sub-module of the plurality of sub-modules generates identification information of the sub-module based on the path information corresponding to the sub-module.

Abstract: In one embodiment, a power conversion device that converts power between a DC circuit and an AC circuit includes a plurality of leg circuits connected in parallel between first and second DC terminals and electrically connected to the AC circuit. Each of the plurality of leg circuits includes at least one first converter cell and a plurality of second converter cells other than the first converter cell. A first control signal that controls switching of a semiconductor switching element included in at least one first converter cell is higher in frequency than a second control signal that controls switching of a semiconductor switching element included in each of the plurality of second converter cells.

Abstract: A life prediction method for an optical module that keeps optical output constant by controlling a bias current that is applied to a laser diode includes, by a life prediction device: acquiring a current value of the bias current from the optical module; holding an initial bias current value that is an initial current value of the bias current; calculating the number of digits of a difference value between the bias current value and the initial bias current value, and determining whether there is an increase in the number of digits; calculating a time interval at which occurrence of the increase in the number of digits is detected; and estimating a life of the optical module using the time interval, a first threshold, and the number of digits.

Abstract: A power conversion device includes an MMC-type power conversion circuit and a central controller. The central controller limits an active power command value and a reactive power command value to a value corresponding to an active power limit value and a value corresponding to a reactive power limit value, respectively, and controls an operation of the power conversion circuit according to the limited active power command value and the limited reactive power command value. The central controller includes: an index value calculation unit configured to calculate an index value that shows an extent of a variation among voltages of energy storage devices included in a plurality of converter cells; and a limiter controller configured to change the active power limit value to a value smaller than the active power limit value when the index value exceeds a threshold value.

Abstract: A power conversion device includes an MMC-type power conversion circuit and a central controller. The central controller limits an active power command value and a reactive power command value to a value corresponding to an active power limit value and a value corresponding to a reactive power limit value, respectively, and controls an operation of the power conversion circuit according to the limited active power command value and the limited reactive power command value. The central controller includes: an index value calculation unit configured to calculate an index value that shows an extent of a variation among voltages of energy storage devices included in a plurality of converter cells; and a limiter controller configured to change the active power limit value to a value smaller than the active power limit value when the index value exceeds a threshold value.

Abstract: An exhaust gas treatment apparatus which includes a denitration device, a dust collector, and a desulfurization device in order, respectively, in a flow path of exhaust gas discharged from a boiler, wherein a heavy-metal component removal device is provided in the exhaust gas flow path between the dust collector and the desulfurization device. This device is provided with: an absorption tower including a nozzle which sprays acidic absorption liquid on the exhaust gas, a tank which stores liquid which has absorbed a heavy metal, and a pump which supplies the nozzle with the liquid in the tank; a neutralizing tank which neutralizes the liquid drawn from the absorption tower; and a separator which separates the neutralized liquid into a solid and a liquid component. Since a small amount of heavy metal can be removed in the absorption tower, re-emission of the heavy metal by the desulfurization device is prevented.

Abstract: An exhaust gas treatment apparatus which includes a denitration device, a dust collector, and a desulfurization device in order, respectively, in a flow path of exhaust gas discharged from a boiler, wherein a heavy-metal component removal device is provided in the exhaust gas flow path between the dust collector and the desulfurization device. This device is provided with: an absorption tower including a nozzle which sprays acidic absorption liquid on the exhaust gas, a tank which stores liquid which has absorbed a heavy metal, and a pump which supplies the nozzle with the liquid in the tank; a neutralizing tank which neutralizes the liquid drawn from the absorption tower; and a separator which separates the neutralized liquid into a solid and a liquid component. Since a small amount of heavy metal can be removed in the absorption tower, re-emission of the heavy metal by the desulfurization device is prevented.