Abstract: A method can be used for operating a converter that converter includes a control arrangement and modular-multilevel converters that are coupled in a parallel circuit. Each modular-multilevel converters includes branches, each having a cell with a capacitor and semiconductor switches. First voltage reference signals are generated as a function of a DC voltage reference and measured signals gained at the modular-multilevel converters and a second voltage reference signal is generated as a function of a first terminal reference. An inner voltage reference signal is generated as a function of an average DC voltage reference and of branch capacitor voltage signals. The first voltage reference signals, the second voltage reference signal and the inner voltage reference signal are combined into a branch control signal for each branch. Cell control signals are generated as a function of the branch control signals and provided to the semiconductor switches.

Abstract: An AC-to-AC modular multilevel converter (MMC) is configured to be connected between a three-phase AC system and a single-phase AC system. The MMC includes a number of converter arms connected in a ring to allow a circulating current to be circulated in the ring through each of the converter arms. Each converter arm includes series-connected converter cells. Phase terminals are arranged in the ring between the converter arms such that each of the converter arms is separated from neighboring converter arms by at least one of the phase terminals. The phase terminals include respective terminals for each of a first phase, a second phase and a third phase of the three-phase AC system and respective terminals for each of a positive conductor and a negative conductor of the single-phase AC system.

Abstract: An AC-to-AC modular multilevel converter (MMC) is configured to be connected between a three-phase AC system and a single-phase AC system. The MMC includes a number of converter arms connected in a ring to allow a circulating current to be circulated in the ring through each of the converter arms. Each converter arm includes series-connected converter cells. Phase terminals are arranged in the ring between the converter arms such that each of the converter arms is separated from neighboring converter arms by at least one of the phase terminals. The phase terminals include respective terminals for each of a first phase, a second phase and a third phase of the three-phase AC system and respective terminals for each of a positive conductor and a negative conductor of the single-phase AC system.

Abstract: A ballast water treatment apparatus and a ballast water treatment system having a ballast water treatment apparatus are provided. The ballast water treatment apparatus includes a ballast water transport line configured to transport ballast water between a first location and a second location, the transported ballast water being passed through at least one injector, and a plasma generation device configured to be fed with a feed gas optionally comprising oxygen, and configured to generate a feed gas plasma by a streamer type discharge in a discharge area to provide a treated gas at a treated-gas outlet. The injector includes a liquid passage having an area constructed such as to increase a velocity of the passed-through water in a region of increased velocity, and an injector gas inlet provided in the region of increased velocity. The treated-gas outlet is in gaseous connection with the injector gas inlet.

Abstract: A method of decoupled modulation of a direct AC/AC MMC between a first AC network L having a first waveform and a second AC network R having a second waveform includes performing first and second modulations based on respective reference signals of the first and second AC networks to generate, for each phase leg, first and second integer command signals corresponding to first and second combinations of cell states in the branches of the phase leg needed for generating the first and second waveforms. The method also includes, based on the first and second integer command signals, mapping to each branch a number of cell states to be used for concurrently generating both the first and second waveforms.

Abstract: In a method of controlling a DC-to-AC Modular Multilevel Converter (MMC) having a three-phase AC side connected to a three-phase AC network and having a DC side connected to a DC network, the MMC has a double-star topology with a plurality of phase-legs. Each phase-leg has a first branch and a second branch. Each of the first and second branches includes a plurality of series connected converter cells. The method includes obtaining an Optimized Pulse Pattern (OPP) for the MMC. The method also includes adapting the OPP to the MMC by means of closed-loop pulse pattern control. The method also includes, based on the adapted OPP, sending firing signals to the plurality of cells of each branch.

Abstract: In a method of controlling a DC-to-AC Modular Multilevel Converter (MMC) having a three-phase AC side connected to a three-phase AC network and having a DC side connected to a DC network, the MMC has a double-star topology with a plurality of phase-legs. Each phase-leg has a first branch and a second branch. Each of the first and second branches includes a plurality of series connected converter cells. The method includes obtaining an Optimized Pulse Pattern (OPP) for the MMC. The method also includes adapting the OPP to the MMC by means of closed-loop pulse pattern control. The method also includes, based on the adapted OPP, sending firing signals to the plurality of cells of each branch.

Abstract: A method of decoupled modulation of a direct AC/AC MMC between a first AC network having a first waveform and a second AC network having a second waveform, the MMC having a double-star topology with a plurality of phase legs, each phase leg having a first branch and a second branch, each of the first and second branches comprising a plurality of series connected bipolar cells. The method includes performing a first modulation based on a reference signal of the first AC network, independently of a reference signal of the second AC network, to generate, for each phase leg, a first integer command signal corresponding to a first combination of cell states in the first and second branches of the phase leg needed for generating the first waveform.