A transmission device transmits energy between multiple electrical energy networks, each providing a multi-phase connection voltage at a network frequency for electrical energy supply. The transmission device contains multi-phase multi-stage rectifiers and a control device, which adjusts the transmission of energy into at least one energy-receiving energy network according to an input by controlling the multi-stage rectifiers. The multi-stage rectifiers are each connected to one of the energy networks and to one another via at least one multi-phase transformer. Electrical energy flows via the transformer at a predefined transmission frequency from at least one energy-emitting energy network into at least one energy-receiving energy network. The transmission frequency is, in particular, multiple times the network frequency.

A modular power flow control system having early detection and reporting of transmission line faults is described. The response time for closing a bypass switch and reporting the fault is less than 200 microseconds for hard faults, longer for soft faults. Reprogramming of distance relays is not required. Transmission line faults are characterized using a fault detection sensor suite, normally including at least a current sensor such as a current transformer and a rate of current change sensor such as a Rogowski coil, and in some embodiments, a temperature sensor. Other embodiments are disclosed.

A system including a multi-level converter including a plurality of valve sections including a plurality of sub modules, a plurality of VCU controllers connected to each of the plurality of valve sections, and an upper controller connected to the plurality of VCU controllers, wherein the VCU controller is configured to receive status information from each of the plurality of sub modules to transmit the state information to the upper controller, receive a specific sub module control command information from the upper controller, and transmit the control command information to a specific sub module among the plurality of sub modules.

A method for ancillary supply in a modular multi-level converter with a plurality of modules arranged in strands, a respective module including at least two half bridges with semiconductor switches and at least one energy accumulator, which are interconnected in parallel. In the respective module, an at least single-core input terminal is formed through respective center tapping in at least one half bridge on an input side, and an at least single-core output terminal is formed through respective center tapping in at least one half bridge on an output side. The strands are interconnected into at least one star point on the at least single-core input terminal of a first module in the respective strand. A respective phase of a supply voltage in a high-voltage system is formed on the at least single-core output terminal of a last module in the respective strand.

A reactive power compensator includes a first converter connected between a first line and a second line, a second converter connected between the second line and a third line, and a third converter connected between the third line and the first line. The first to third lines may be connected to a bus. The first converter may include a first cluster including first to n.sup.th submodules which are serially connected to one another and each include a first capacitor and a first discharging connection unit connected to the first capacitor so that, when driving of the reactive power compensator stops, the first capacitors of the first to n.sup.th submodules are electrically connected to one another.

A modular cell for a phase leg of a Modular Multilevel power Converter (MMC) is disclosed. The cell includes a power storing device, a plurality of semiconductor switches, a cell controller, and a current sensor. The current sensor is connected between a current conducting line in the cell and the cell controller for measuring a current through the cell and signaling information about the measured current to the cell controller. The cell controller includes an optical communication interface and is configured for forwarding the information about the measured current to a higher level controller over the optical communication interface.

A reactive power compensator includes a first converter connected between a first line and a second line, a second converter connected between the second line and a third line, and a third converter connected between the third line and the first line. The first to third lines may be connected to a bus. The first converter may include a first cluster including first to n.sup.th submodules which are serially connected to one another and each include a first capacitor and a first discharging connection unit connected to the first capacitor so that, when driving of the reactive power compensator stops, the first capacitors of the first to n.sup.th submodules are electrically connected to one another.

The invention relates to a system for generating electric power, comprising: an alternator (1) for coupling with a drive system (7), supplying an AC voltage to an output bus (10); a reversible AC/DC converter (2) in which the AC bus (6) is connected to the output bus (10) of the alternator (1); an electricity-storage element (3) connected to the DC bus (9) of the converter (2); a controller (4) arranged to react to a transient state of load-shedding or charging impact by controlling the converter (2) so as to collect energy on the output bus (10) of the alternator (2) and to store same in the storage element (3) in the case of load-shedding, and to collect energy in the storage element (3) and to inject same into the output bus (10) in the case of charging impact, the converter (2) being controlled so as to inject currents to compensate for harmonic currents into the AC bus (10) of the alternator (1).

A method of discharging a Modular Multilevel Converter (MMC) includes a plurality of phase legs connected in delta configuration. Each leg includes a plurality of series connected submodules, each submodule including an energy storage. The method includes disconnecting the MMC from an electrical grid, discharging the energy storages by means of a circulating current, and reconnecting the MMC to the electrical grid. The discharging includes, for each phase leg, setting a voltage reference, and sequentially selecting submodules in zero state by means of a sorting algorithm for switching each of the selected submodules to plus or minus state until the voltage deviation from the set voltage reference of the energy storage of each submodule in the phase leg is within a predefined range.

An arrangement includes at least one series circuit having at least two series-connected submodules and an inductor. At least one of the submodules in one or a plurality of the series circuits has a step-up/step-down converter and a storage module. A protective module with at least one actuator is electrically connected between the step-up/step-down converter and the storage module. A method for operating the arrangement is also provided.