A method and an arrangement for limiting the interference to a common electric power network, generated by a power electronics device, e.g. a frequency converter, which power electronics device comprises of at least one switch type component being able to change the output voltage value at a predefined permissible switching frequency range. The method comprises scanning through the permissible switching frequency range, recording measured common mode current values as a function of the switching frequency, and setting the final switching frequency of the switch type component out of a value where a local maximum value of the common mode current has been recorded.

An electric power converter according to an embodiment includes a switching unit, a controller, and a second bidirectional switch. The switching unit includes a plurality of first bidirectional switches disposed between a DC power source and an AC load or between a DC load and an AC power source. The controller controls the switching unit to perform power conversion between DC power and AC power. When turning off the second bidirectional switch disposed on a path between one pole of the DC power source or the DC load and the switching unit, the controller turns on the first bidirectional switch connected between the other pole of the DC power source and the AC load or between the other pole of the DC load and the AC power source.

A matrix inverter is connected to a first and a second multi-phase A.C. voltage network. First inductive elements are connected to the first A.C. voltage network and second inductive elements are connected to the second A.C. voltage network. A switch matrix connects the ends of the first inductive elements, to the ends of the second inductive elements. The switch matrix has inverter units. A regulation arrangement is connected to control inputs of the inverter units. The matrix inverter has a first inverter unit, which is arranged between the ends of the first inductive circuit elements and earth potential. The matrix inverter has a second inverter unit, connected between the ends of the first inductive circuit elements and the ends of the second inductive circuit elements. The regulation arrangement insures that the electrical power flowing to the matrix inverter is equal to the electrical power flowing out of the matrix inverter.

The invention provides a subsea pressure boosting system feasible for operation at subsea step out lengths above 40 km and by control merely from a dry topside or onshore location. The system is distinctive in that it comprises: at least one subsea power step out cable, arranged from a near end at a dry location onshore or topsides to one or more subsea loads such as subsea pumps or subsea compressors at a far end, at the near end at least one source for electric power is connected and the cable is dimensioned for operation at a frequency different from the operation frequency of the connected subsea loads in order to handle the Ferranti effect and electric losses, and at least one passive electric frequency transformer, operatively connected between the subsea step out cable far end and the subsea loads, said transformer is located in a pressure vessel and transforms the operation frequency of the subsea step out cable to a frequency feasible for operation of the connected loads.

An electro-mechanical kinetic energy storage device includes an input port, an output port, and a tertiary port separate from and magnetically coupled to the input port and the output port. The input port is configured to receive a first input electrical energy from a first electrical source for inducing mechanical energy into the electro-mechanical kinetic energy storage device. The output port is configured output a first converted electrical energy to a first load in which the outputted electrical energy is generated from the induced mechanical energy. The tertiary port is configured to receive a second input electrical energy from a second electrical source for inducing the mechanical energy, and output a second converted electrical energy to a second load, the second converted electrical energy generated from the induced mechanical energy.

A method for transferring electrical power in the sea includes generating AC power, guiding, at least partially underwater, the AC power through a cable from a first end of the cable to a second end of the cable, and changing a frequency of the AC power guided through the cable based on a value of power consumption of a load connected to the second end of the cable.

A method for transferring electrical power in the sea includes generating AC power, guiding, at least partially underwater, the AC power through a cable from a first end of the cable to a second end of the cable, and changing a frequency of the AC power guided through the cable based on a value of power consumption of a load connected to the second end of the cable.

A method is configured for operating a converter (10) which is implemented as a modular-multilevel converter and comprises a control arrangement (38) and a number M of phase-legs (21 to 29). The method comprises detecting whether the converter (10) has to be set into one mode of a group comprising a static synchronous compensator mode or a grid unbalance mode, generating mode control signals (MCS) depending on the detected mode, generating balance voltage reference signals (u.sub.bal,ref) depending on a first side frequency (.sub.g), a second side frequency (m), second side current reference signals (im,ref) and the mode control signals (MCS), generating a phase-leg control signal (u.sub.ref), generating cell control signals (51 to S4) and providing the cell control signals (51 to S4) to semiconductor switches (41 to 44) of cells (31) of the phase-legs (21 to 29).