Even when one power conversion device among a plurality of power conversion devices connected in parallel experiences a short circuit, the other power conversion devices having experienced no short circuit can be promptly restarted. Each power conversion device includes: a short circuit occurrence determination unit configured to determine, on the basis of a current value at an output terminal, whether or not a short circuit has occurred; a short circuit elimination determination unit configured to determine, on the basis of a current value and a voltage value at the output terminal, whether or not the short circuit has been eliminated; and a current interruption unit configured to, on the basis of determination by the short circuit occurrence determination unit and determination by the short circuit elimination determination unit, interrupt current that flows from a power conversion unit to the output terminal or cancel the interruption.

A converter apparatus includes: an AC/DC converter; a DC link capacitor connected to the converter; a voltage detection unit detecting the DC link voltage; a switching unit connecting or disconnecting between a power supply and the converter; a switching operation unit detecting an abnormality in a motor drive device including the converter apparatus and an inverter, and control the switching unit; a power supply monitoring unit detecting a voltage inputted to the converter to monitor a connection state between the power supply and the converter; a threshold value setting unit setting a threshold value to determine the presence or absence of a short circuit failure; and a short circuit failure detection unit determining that a short circuit failure has occurred, when the voltage of the DC link capacitor, immediately after the power supply is disconnected from the converter, is equal to or less than the threshold value.

A system includes a circuit breaker and a delay circuit. The circuit breaker has a coil to enable control of a contact to selectively couple a load to a power source responsive to a coil voltage signal applied to the coil. The delay circuit has a depletion mode MOSFET and an energy storage circuit. The depletion mode MOSFET is controlled as an active current sink to provide the coil voltage signal based on a DC voltage signal. The energy storage circuit has an input coupled to a drain of the depletion mode MOSFET, a capacitor, and an output coupled to the drain of the depletion mode MOSFET, the energy storage circuit charges the capacitor from the DC voltage signal and delivers current to the depletion mode MOSFET to delay discontinuation of the coil voltage signal responsive to a drop or discontinuation of the DC voltage signal.

A first converter station is part of a high voltage direct current transmission system that includes a DC transmission link connected to the first converter station a second converter station. A DC current and a DC voltage of the DC transmission link are sensed by the first converter station. It is determined that the sensed DC current is equal to or larger than a threshold current value, that the sensed DC current is equal to or larger than the threshold current value, and that at least a partial recovery of the sensed DC voltage has occurred. On the basis that it is determined that the at least a partial recovery of the sensed DC voltage has occurred, it is determined that a phase-to-ground fault has occurred. In response to determining that a phase-to-ground fault has occurred, a power delivered by the first converter station can be reduced.

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.

A DC power transmission system interconnects a plurality of AC systems via a DC line. A plurality of power conversion devices are connected between the plurality of AC systems and the DC line. One of the plurality of power conversion devices controls the voltage on the DC line, while the remaining power conversion device controls a current input and output to and from the DC line. In a restart which resumes power conversion from a stopped state for controlling a DC current on the DC line, the power conversion device performing current control monitors the voltage on the DC line and starts a restart operation without transmitting or receiving information to or from the other power conversion device.

An output device outputs a DC voltage applied between a first terminal and a second terminal via the drain and the source of a semiconductor switch. The output device includes a conversion circuit configured to convert the DC voltage into a voltage of a predetermined polarity, irrespective of the polarity of the DC voltage. A booster circuit boosts the voltage that was converted by the conversion circuit and applies the boosted voltage to the gate of the semiconductor switch. The semiconductor switch is on if the voltage of the control terminal with respect to the potential of the first terminal is at least a predetermined voltage.

A control unit of an electrical system is described. The control unit causes some of the switches in a power converter of the electrical system to not be shut down and not conducting upon detection of a fault current caused by a line-to-line fault. Instead, the control unit causes at least one of the switches to be switched-on and conducting to allow the some of the fault current to flow through the at least one switch, before activating a protection device that creates an open circuit and breaks the fault.

An electric circuit arrangement and a method for generating electric current pulses to a load, the electric circuit arrangement including a switch and a current source in series connection with the load; wherein the switch is arranged to operate in at least an on state and an off state, thereby selectively connecting or disconnecting the current source to or from the load so as to generate the electric current pulses. With such architecture, the circuit performs with a better efficiency than a cascaded architecture.

A switching device for opening a current path of a direct-voltage network, which current path has source-side and load-side inductors, the switching device includes at least two switching modules, which are connected in series, each of the switching modules having at least one controllable semiconductor switching element, in parallel with which a series circuit of a resistor and a capacitor is connected. During operation of the switching device in order to open the current path, the controllable semiconductor switching element of at least one of the switching modules is switched into a conductive state with a duty cycle until the energy stored in the inductors has been dissipated, the duty cycle being dependent on the difference between the actual voltage and a target voltage across the semiconductor switching element, the target voltage being calculated at least from the system voltage of the direct-voltage network and the number of switching modules.