A method can be used to synchronize time between nodes of a converter device for high voltage power conversion. The method is performed in a first node of the converter device and includes receiving a time reference from a second node of the converter device, obtaining a delay value for receiving time references from the second node, determining a compensated time by adding the delay value to the time reference, and setting a clock in the first node to be the compensated time.

Accordingly, the embodiments herein provide a hybrid modular multilevel converter. The hybrid modular multilevel converter includes one or more chain links, one or more high voltage switches and a plurality of inductors. The one or more chain links are formed by sub modules. The one or more high voltage switches are formed by semi-controlled devices or fully controlled or any other suitable semiconductor devices. The plurality of inductors are arranged in the one or more chain links to limit circulating current among the one or more chain links. The one or more chain links are configured to enhance a power handling capability of the hybrid modular multilevel converter.

A power converter to be tested is supplied with arm current from a hysteresis converter in a state in which it is connected to an auxiliary converter through a line. In the power converter and the auxiliary converter, a circulation operation is performed in which a current path bypassing power storage elements is formed between an output terminal of the power converter and an output terminal of the auxiliary converter, after the start of output of arm current in accordance with a reference current command value in which an AC component and a DC component are superimposed, until a DC component of arm current reaches a predetermined level. After execution of the circulation operation, in the power converter and the auxiliary converter, voltage control of the power storage elements and the output terminals is started.

A power conversion system includes: power conversion circuitry including a plurality of submodules connected in series to each other; a host device to control each submodule included in the power conversion circuitry; a terminal device to display internal information about each submodule; and at least one repeating device to relay communication between the host device and each submodule and communication between the terminal device and each submodule. The repeating device receives, from one or more submodules communicating with the repeating device, internal information about the submodules, transmits, to the host device with a first cycle period, a first communication frame including aggregate information that is an aggregate of the received internal information, and transmits, to the terminal device with a second cycle period longer than the first cycle period, a second communication frame including internal information selected from the received internal information.

A method of monitoring condition of a modular multilevel converter, wherein the modular multilevel converter includes submodules having a capacitor and controllable switches. The method including selecting a submodule, controlling the controllable switches of the selected submodule to form a current path through the submodule by controlling at least one controllable switch to a conducting state and at least one controllable switch to a blocking state, disconnecting the voltage of the capacitor of the selected submodule from the submodule, performing measurements on at least one controllable switch that was controlled to a blocking state.

The present disclosure discloses an offshore wind farm low-frequency alternating-current uncontrolled rectification electric power transmission system, comprising an onshore converter station and an offshore alternating-current system. The offshore alternating-current system comprises wind turbine generators, alternating-current submarine cables, a confluence bus, and offshore booster stations; the onshore converter station comprises a wind field side alternating-current bus, an alternating-current system side alternating-current bus, an alternating-current filter, an energy dissipation device, a rectifier, and a converter; the rectifier is composed of a three-phase six-pulse uncontrolled rectifier bridge, and the converter may be an MMC or an LCC; the rated frequency of the offshore alternating-current system is selected to be close to 10 Hz.

A voltage evaluation value generator receives voltage detection values of power storage elements of all of converter cells included in a power converter and generates a first voltage evaluation value of each power storage element of all of the converter cells and a second voltage evaluation value of each power storage element in a plurality of converter cells included in each of a plurality of groups obtained by classifying all of the converter cells in advance, without using a mean value of voltage detection values. A voltage macro controller uses the voltage evaluation value to calculate a control value set in common to at least the converter cells in the same group for controlling deficiency and excess of stored energy in all of the converter cells and the converter cells in each group.

A power conversion device that converts electric power between a DC circuit and an AC circuit includes a leg circuit including a plurality of sub modules connected in series. A first sub module of the plurality of sub modules includes a first energy accumulation element, a first semiconductor circuit including two switching elements connected in series, and a second semiconductor circuit. The second semiconductor circuit includes a series circuit including a switching element and a semiconductor element connected in series, a second energy accumulation element connected in parallel to the series circuit, and an element including a resistive component connected in series to a parallel circuit including the series circuit and the second energy accumulation element.

The power conversion device includes: a series unit composed of two switching elements; and a plurality of DC capacitors each connected in parallel to the series unit. The two switching elements and the plurality of DC capacitors are disposed in this order such that positive terminals and negative terminals thereof are aligned on a same side. Among busbars making connection between the respective DC capacitors and the switching elements, a busbar other than the busbar connected to the DC capacitor disposed at a farthest position has an inductance adjustment portion providing a bypass.

Various examples are provided for high voltage isolation. The isolation can be provided for discrete non-isolated devices using an electrically isolating substrate that is thermally conductive. In one example, a module includes a plurality of switching devices connected in series; one or more rubber buffer disposed between switching device pairs of the plurality of switching devices; and thermal interfaces disposed between switching devices of the switching device pairs and cooling surfaces of the module, the thermal interfaces electrically isolating the switching devices from the cooling surface. In another example, an extreme fast charger (EFC) station includes an active front end (AFE) module that includes at least one module, where the module is a half-bridge power module. The EFC station can include a dual-active-bridge (DAB) high voltage (HV) module that includes at least one module, where the module is a half-bridge power module.