Provided is a control method for a parallel MMC unit of a LCC-MMC hybrid cascade converter station. The control strategy includes: 1) numbering all MMC units connected in parallel in a MMC valve manifold; (2) for a MMC unit using a constant direct-current voltage control manner, calculating a direct-current instruction value of the MMC unit according to a direct-current measurement value; (3) for a MMC unit using a constant active power control manner, calculating an active power instruction value of the MMC unit according to the rated capacity of the MMC unit and a direct-current instruction value of a system rectifier station; (4) for the MMC unit using the constant direct-current voltage control manner, correcting a direct-current voltage instruction value of the MMC unit by using the direct-current instruction value and the direct-current measurement value, and controlling the MMC unit according to the corrected direct-current voltage instruction value.

A power transfer system includes a series of energy storage modules (ESMs) or energy storage devices (ESDs) that are coupled together to be able to transfer power between one another, as well as receive power from a power source, such as an onshore power generator. The energy storage modules may be hybrid energy storage modules, each including an electrical-machine-inertial energy store and an electro-chemical energy store. The energy storage modules are configured to receive constant-current DC or AC input from the power source, and are able to provide constant-current and constant-voltage output, either sequentially or simultaneously. The power transfer system allows the modules to operate independently or in conjunction with one another, should some of the connections of the system be broken. The energy storage modules may be used to provide power to underwater systems, for example sonar systems, weapons systems, or underwater vehicles.

A method for controlling an electrical transmission network including a plurality of DC high-voltage lines and at least three AC/DC converters which are identified by a respective index i and are interconnected by the DC high-voltage lines. Each of the AC/DC converts are connected to an AC voltage bus identified by a respective index i as well as to one of the DC high-voltage lines.

One embodiment is a system comprising a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter. The first AC-DC converter is electrically coupled with a first alternating current (AC) feeder. The second AC-DC converter electrically coupled with a second AC feeder. A battery charger electrically coupled with the MVDC link via a converterless connection. A first electronic controller is operatively coupled with the first AC-DC converter. A second electronic controller is operatively coupled with the second AC-DC converter. During operation of the battery charger to charge a battery the first electronic controller is configured to control power flow between the first AC feeder and the second AC feeder and the second electronic controller is configured to control the voltage of the MVDC link.

A mechanical cut-off apparatus of a high-voltage electric circuit includes: in a main electrical path a main mechanical switch; in a secondary electrical path, a secondary mechanical switch; a mechanical control configured such that, the secondary mechanical switch is brought to its mechanically open state after the main mechanical switch has been brought to its mechanically open state; the apparatus includes a transition dipole comprising a capacitance, the transition dipole arranged in series with the pair of secondary electrical contacts in the secondary electrical path, and in that the apparatus includes a controlled switch which, in an electrically closed state, creates inside the mechanical cut-off apparatus a bypass that short-circuits the capacitance of the transition dipole.

A control device for an MMC is disclosed. The control device for an MMC including a plurality of converter arms that include a plurality of sub-modules connected in series and that are connected to a DC link includes: an arm controller, which detects the arm current of a converter arm so as to determine whether a DC failure has occurred, and, if it is determined that the DC failure has occurred, transmits a bypass control signal for protecting a sub-module and notifies of the DC failure; a sub-module controller for controlling the sub-module so as to bypass a DC failure current according to the bypass control signal received from the arm controller; and a main controller, which detects, in real-time, the arm current of the converter arm and a voltage (DC link voltage) of the DC link, determines whether the DC failure is a temporary DC failure or a permanent DC failure on the basis of the detected arm current and DC link voltage if the occurrence of the DC failure is notified by the arm controller, and transmits, to the arm controller, a normal operation control signal for normal operation of the sub-module or a bypass control signal for bypassing of the DC failure current.

An electrical assembly includes a number of modules, each module including at least one module switching element and at least one energy storage device, each module switching element and each energy storage device in each module arranged to be combinable to provide a voltage source, each module including a discharge circuit with a discharge switching element and a discharge resistor, each discharge switching element switchable to switch the corresponding discharge resistor into and out of the corresponding module, wherein the electrical assembly includes a controller configured to control the discharge switching elements to modulate the switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode when the modules are in a blocked state so that each module emulates a resistive load profile to balance a distribution of voltages between the modules, wherein the resistive load profile includes at least one positive resistive slope.

A bipole power transmission scheme includes a first converter station that is positioned, in-use, remote from a second converter station. First and second transmission conduits and a return conduit interconnect, in-use, the first converter station with the second converter station and thereby permit the transfer of power between the first and second converter stations. The first converter station includes a first power converter, a second power converter, and a converter station controller.

A method for restoration of a fault isolation in a medium voltage, MV, network having a plurality of feeders and a plurality of normally open, NO, switches possibly in parallel with MV direct current, DC, links is presented. The method is performed in a control device of the MV network. The method includes closing at least two NO switches in parallel with MVDC links of the plurality of NO switches, being connected to a fault isolated feeder of the plurality of feeders of the MV network, and opening the closed at least two NO switches in parallel with MVDC links except one. A control device, a computer program and a computer program product for restoration of a fault isolation in a MV network are also presented.

There is provided an electrical assembly comprising a converter (20) for connection to an electrical network (40), the converter (20) comprising at least one module (44) including at least one switching element (46) and at least one energy storage device (48), the or each switching element (46) and the or each energy storage device (48) in the or each module (44) arranged to be combinable to selectively provide a voltage source, the electrical assembly including a controller (54) configured to selectively control the switching of the or each switching element (46) in the or each module (44), wherein the electrical assembly includes a sensor (56a) configured for measuring a current of the electrical network (40), wherein the controller (54) and sensor (56a) are configured to operate in coordination to carry out a characterisation of an electrical parameter of the electrical network (40) so that, in use: the controller (54) selectively controls the switching of the or each switching element (46) in the or each module (44) to modify an electrical parameter of the converter (20) so as to modify the current of the electrical network (40); the sensor (56a) measures a resultant modified current of the electrical network (40); and the controller (54) processes the measured resultant modified current of the electrical network (40) so as to characterise the electrical parameter of the electrical network (40).