A series connectable power flow module is for connection to a power transmission line. The module has a full bridge inverter and a controller. The full bridge inverter has inputs for controlling charging and discharging a DC link capacitor. The controller is coupled to the inputs of the full bridge inverter. The controller is configured to separate a harmonic current from a line current flowing in the power transmission line. The controller operates the full bridge inverter in accordance with the separated harmonic current, to attenuate the harmonic current flowing in the power transmission line through injection of a DC link capacitor voltage.

An assembly having a multilevel power converter, which has at least one phase module, wherein the phase module has a plurality of modules, each with a first electrical module terminal and a second electrical module terminal. The plurality of modules includes modules of a first type, which are able to output a voltage of only one polarity or zero voltage at their first electrical module terminal and their second electrical module terminal. The plurality of modules includes modules of a second type, which are able to output a voltage of one polarity, a voltage of opposite polarity or zero voltage at their first electrical module terminal and their second electrical module terminal. Depending on the polarity of a voltage across the modules of the second type, a voltage limiting device limits the voltage.

A line commutated converter, LCC, for a high-voltage, direct current, HVDC, power converter comprises at least one bridge circuit for connection to at least one terminal of a DC system. Each bridge circuit comprises a plurality of arms, and each arm is associated with a respective phase of an AC system. Each arm comprises an upper and lower thyristor connected in series, an associated branch extending from between the upper and lower thyristors, and at least one capacitor module for each phase. The, or each capacitor module is operable to insert a capacitor into the respective arm of the bridge circuit.

A series compensation device suitable to double-circuit lines is disclosed. The device includes one series transformer and one converter. One converter and dual-circuit transmission lines are respectively connected to three windings of one series transformer. In the solution provided in the present application, the device can be independently installed in a power transmission system to be used as a static synchronous series compensator, and can also be used as a component of a unified power flow controller, a convertible static compensator, an interline power flow controller and a unified power quality conditioner to be connected to a power transmission system device in series. The device can save the capacity of a converter, improve the application efficiency of the series compensation device, and reduce the cost and area occupation.

A power transmission network, for interconnecting a variable power source and a AC electrical network including: a DC transmission link for power transmission between a network side converter and a source side converter; a AC transmission link for power transmission from the respective variable power source to a source side converter; a source side converter including: a DC connecting point operably connected to the respective transmission link; and an AC connecting point operably connected to the respective transmission link; a network side converter including: an AC connecting point for connection to the respective electrical network; and a DC connecting point operably connected to the respective transmission link; and a control system, where a network side converter is designated as a first converter, and the control system is configured to operate each first converter as a DC slack bus to vary a DC voltage at its DC connecting point.

An insulation design apparatus performing the insulation design of a high voltage direct current (HVDC) transmission system is provided. The insulation design apparatus includes a first insulation model generation unit; a second insulation model generation unit; an insulation verification unit, wherein the second insulation model generation unit selects the positions of each facility, device and arrester of the HVDC transmission system through a system single line diagram to select a representative facility in the HVDC transmission system, divides the HVDC transmission system into the plurality of regions based on the selected representative facility, and generates an insulation model for each region.

Disclosed is a phase-shifted square wave modulation technique for single-phase and three-phase IM2DC applications in HVDC/MVDC systems. A square wave based modulation waveform is applied to each cell of IM2DC and compared to the phase-shifted carrier waveforms to generate device gate signals. As a result, a higher equivalent switching frequency can be achieved, and square wave based arm and AC link waveforms will be generated. In addition, power flow of IM2DC can be controlled by a phase shift angle of the square modulation waveforms between HVS and LVS. The converter cell capacitors can be reduced in size because they are only required to smooth high switching frequency ripple components. In addition, lower TDR can be achieved due to the higher power transferring capability of square waves.

A current flow control assembly, for controlling current flow in an electrical network of interconnected electrical elements, having: current flow controllers, each current flow controller connectable to at least one of the interconnected electrical elements, and being configured to control current flow in at least one of the interconnected electrical elements within a current flow control range; a control unit in communication with each of the current flow controllers, wherein the control unit is configured to: select at least one of the current flow controllers with a flow control range that corresponds to one or more current flow control requirements of the electrical network; and operate the selected current flow controller to control current flow in at least one of the interconnected electrical elements to control current flow in the electrical network in accordance with the current flow control requirement of the electrical network.

Some embodiments may include a multi-stage converter comprising: a branch connected between a positive busbar and a negative busbar; and a control device. The branch has two arms connected in series. The arms each comprise a series circuit including a plurality of two-pole submodules, an energy store, and a communication connection to the control device. The communication connection transmits state of charge of the energy store and a switching instruction for the respective submodule. For at least a subset of the submodules, the communication connection comprises a common communication connection with a plurality of insulation paths having an insulation capability in each case of at most 5 kV.

A converter includes first and second DC terminals for connection to a DC network, limb(s) connected between the first and second DC terminals, and a controller. Each limb includes a phase element and DC side sub-converter(s). The phase element has switching elements and AC terminal(s) for connection to an AC network, the switching elements being switchable to selectively interconnect a DC side voltage at a DC side of the phase element and an AC side voltage at an AC side of the phase element, The DC side sub-converter(s) connected to the DC side of the phase element. The controller selectively controls the switching elements and the operation of each DC side sub-converter as a voltage synthesiser. The controller also controls the switching elements to provide a blocking voltage to limit or block the flow of a fault current between the AC and DC networks and through each limb.