Described herein is a multi-level power convertor and a method for a multi-level power convertor. The multi-level power convertor includes a DC port; an AC port; a first power converting unit, a second power converting unit, a coupling inductor, and an inductive filtering unit. The first power converting unit is coupled to the DC port and includes a first AC terminal adapted to provide a first plurality of voltage levels. The second power converting unit is coupled to the DC port and includes a second AC terminal adapted to provide a second plurality of voltage levels, where the second plurality of voltage levels are phase-shifted by 90 degrees with respect to the first plurality of voltage levels. The coupling inductor includes first and second windings with a same number of turns. The inductive filtering unit is arranged between the AC port and ends of the first and second windings.

A method includes detecting a voltage signal of a three-level power converter, the voltage signal indicative of a capacitor voltage balancing in the three-level power converter, and dynamically adjusting an operating variable to adjust the voltage signal until the capacitor voltage balancing in the three-level power converter satisfies a criteria.

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.

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 semiconductor device is provided, which includes a semiconductor chip; a first current input/output portion that is electrically connected to the semiconductor chip; a second current input/output portion that is electrically connected to the semiconductor chip; three or more conducting portions provided with the semiconductor chip, between the first current input/output portion and the second current input/output portion; and a current path portion having a path through which current is conducted to each of the three or more conducting portions, wherein the current path portion includes a plurality of slits.

A semiconductor device is provided, which includes a semiconductor chip; a first current input/output portion that is electrically connected to the semiconductor chip; a second current input/output portion that is electrically connected to the semiconductor chip; three or more conducting portions provided with the semiconductor chip, between the first current input/output portion and the second current input/output portion; and a current path portion having a path through which current is conducted to each of the three or more conducting portions, wherein the current path portion includes a plurality of slits.

An output terminal of one phase switched capacitor converter is connected to a first output terminal, and an output terminal of the other phase switched capacitor converter is connected to the first output terminal via a second switch, such that the power conversion structure can operate in a mode of two phase switched-capacitor converters in parallel, and a current formed by the operating of only one phase switched capacitor converter flows through the second switch, thus greatly reducing a value of current flowing through the second switch, greatly reducing the on-state loss of the second switch, and improving the efficiency of the power conversion structure, and because the second switch has lower on-state loss and less heat, there is a larger selectivity of the second switch and a reduction of the cost of power conversion structure.

A circuit arrangement for balancing a split DC link arranged between a first DC-voltage terminal and a second DC-voltage terminal is disclosed. The first DC-voltage terminal is connected via a first semiconductor switch to a first intermediate point that is connected via a second semiconductor switch to a bridge center point that is connected via a third semiconductor switch to a second intermediate point that is connected via a fourth semiconductor switch to the second DC-voltage terminal. A first terminal of a resonant capacitor is connected to the first intermediate point, and a second terminal of the resonant capacitor is connected to a DC-link center point via a connecting path, in which a resonant inductor is arranged in a series circuit with the third semiconductor switch, and which runs via the second intermediate point. An additional winding is magnetically coupled to the resonant inductor and a first terminal thereof is connected via a first diode to a first terminal of a countervoltage source, and a second terminal thereof is connected to a second terminal of the countervoltage source so that an energy coupled into the additional winding from the resonant inductor is discharged into the countervoltage source.