In the field of HVDC power converters there is a need for an improved semiconductor switching assembly which obviates the difficulties associated with main semiconductor switching elements having inherent limitations in their performance. A semiconductor switching assembly is provided, which includes a main semiconductor switching element that includes first and second connection terminals between which an active auxiliary circuit is electrically connected. The auxiliary circuit includes an auxiliary semiconductor switching element and current capture element that are connected in series with one another. The auxiliary semiconductor switching element has a control unit operatively connected therewith. The control unit is configured to switch on the auxiliary semiconductor switching element to divert into the current capture element a reverse recovery current that flows through the main semiconductor switching element while it turns off.

A high voltage direct current (HVDC) transmission system is provided. The high voltage direct current (HVDC) transmission system includes: a rectifier converting alternating current (AC) power into DC power; an inverter converting the DC power into the AC power; a DC transmission line transmitting, to the inverter, the DC power obtained through conversion by the rectifier; a first active power measurement unit measuring first active power input to the rectifier; a second active power measurement unit measuring second active power output from the inverter; and a first control unit detecting an abnormal voltage state on the DC transmission line based on the first and second active power measured.

A hybrid HVDC converter system includes a DC bus, at least one capacitor commutated converter (CCC) and at least one self-commutated converter (SCC) coupled in series through the DC bus. The CCC induces a first voltage on the DC buses, the SCC induces a second voltage on the DC bus, the first voltage and the second voltage are summed to define a total DC voltage. The method includes at least one of regulating the total DC voltage induced on the DC buses including regulating the first DC voltage through the CCC and regulating the second DC voltage through the SCC substantially simultaneously, regulating the total DC voltage induced on the DC bus including regulating the second DC voltage through the SCC, and regulating the total DC voltage induced on the DC bus including regulating the first DC voltage through the CCC.

An exemplary Multi-Terminal High Voltage Direct Current (MTDC) system includes at least three terminals, where each terminal including a Voltage Source Converter (VSC) controlled by a VSC controller. A method for controlling the MTDC system includes providing a converter schedule including at least one of a desired power flow value and a DC voltage; determining, by a MTDC master controller, a present state of the MTDC system including a dynamic topology of the MTDC system; determining, by the MTDC master controller, based on the present state of the MTDC system, based on the schedule and based on MTDC system constraints, VSC controller parameters including droop settings for local control by the VSC controllers; and transmitting the VSC controller parameters to the VSC controllers.

An electric power supply apparatus for a user device, in particular for steel industry applications, that includes means for connection to an electricity grid for supplying a mains voltage and a mains current, and at least one electric line for connecting the electricity grid to the user device, wherein the electric line includes one or more electric apparatuses located between the electricity grid and the user device.

In the field of high voltage direct current power transmission networks, a voltage source converter comprises first and second DC terminals for connection to a DC electrical network, and a plurality of single-phase limbs. Each single-phase limb includes a phase element, and each phase element includes at least one switching element configured to interconnect a DC voltage and an AC voltage. An AC side of each phase element is connectable to a respective phase of a multi-phase AC electrical network, and each single-phase limb is connected between the first and second DC terminals. The voltage source converter further comprises a controller configured to determine independently of one another an amount of active power (P.sub.ref ) that the voltage source converter should exchange with the AC electrical network and an amount of reactive power (Q.sub.ref) that the voltage source converter should exchange with the AC electrical network.

The present invention relates to an AC/DC converter station for interconnection of a DC transmission line and an AC network, the AC/DC converter station including an AC/DC converter and a control system configured to control the AC/DC converter. The AC/DC converter station comprises a capacitor connected in series between the AC/DC converter and the AC network, and a voltage measurement device arranged to measure the voltage across the capacitor. The AC/DC converter further comprises a control system connected to the voltage measurement device and arranged to receive, from the voltage measurement device, a signal indicative of a measured voltage. The control system is arranged to perform the control of the AC/DC converter in dependence of the signal received from the voltage measurement device. The invention further relates to a method of operating an AC/DC converter station.

A power converter is presented. The power converter includes at least one leg, the at least one leg includes a first string, where the first string includes a plurality of controllable semiconductor switches, a first connecting node, and a second connecting node, and where the first string is operatively coupled across a first bus and a second bus. Furthermore, the at least one leg includes a second string operatively coupled to the first string via the first connecting node and the second connecting node, where the second string includes a plurality of switching units. A method for power conversion is also presented.

A microgrid connector controller (MGC) for transferring power between a power grid and a microgrid via an AC link. The MCG includes a pair of bidirectional AC/DC converters coupled to a common DC link and each having an AC line. One converter closer to the microgrid is configured to regulate frequency of AC voltage of its AC line to a predetermined frequency. The AC link includes the AC lines coupled in series with a terminal the microgrid, and a current divider coupled to a terminal of the power grid. The current divider is configured to set the first converter's current level lower than the second converter's current level.

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.