A voltage compensation device according to an embodiment includes a controller including first and second coordinate transformation circuits, and first and second arithmetic parts. The first coordinate transformation circuit generates first and second outputs that are mutually-orthogonal by performing a rotating coordinate transformation of the normal-phase components of a three phase AC. The first arithmetic part calculates a system voltage based on a DC component of the first output and generates a first compensation amount corresponding to a compensation voltage set to compensate a shift of the system voltage from a preset target voltage. The second coordinate transformation circuit generates third and fourth outputs that are mutually-orthogonal by performing a rotating coordinate transformation of reverse-phase components of the three-phase AC. The second arithmetic part generates second compensation amount of a reverse-phase component of the system voltage based on DC components of the third and fourth outputs.

Disclosed are three-phase system and distributed control method. The three-phase system comprises three-phase circuits, of which each phase circuit including at least one power conversion cell; and at least three phase controllers for controlling each phase circuit, respectively, each phase controller including a communication interface through which the at least three phase controllers are in communications connection with each other; wherein the phase controllers of each phase circuit is configured for regulating bridge arm voltages of the at least one power conversion cell in the phase circuit by receiving signals sent from the phase controllers of other two phase circuits through the communication interface. The three-phase system and the distributed control method of the invention solve problems of balance of three-phase current and stabilization of three-phase DC voltages by coordination among the three phases. Thanks to the invention, the three phases can be independently controlled to improve control flexibility.

A conversion device includes: an inductor connected to the AC power grid; a first-stage converter configured to output a bus voltage based on the AC power grid; a second-stage converter configured to convert the bus voltage into an output voltage to the load; and a filtering network, wherein a first resistance-capacitance circuit is disposed between the first and third terminals of the filtering network, a second resistance-capacitance circuit is disposed between the second and third terminals of the filtering network, the first terminal of the filtering network is connected to the AC power grid, the second terminal of the filtering network is connected to the bus or the second terminal of the second-stage converter, and the third terminal of the filtering network is grounded through a first capacitor.

A modular electric power converter includes a plurality of power converter modules, each module comprising a cell of a Modular Multilevel Converter, MMC, to provide a controlled ac output.

A model-based method and system for diagnosing an open-circuit fault of a power transistor of a three-phase converter are provided, which belong to the technical field of fault diagnosis of power electronic equipment and can implement fast and accurate diagnosis of the open-circuit fault of the power transistor of the three-phase converter without adding an additional hardware. The fault diagnosis method of the disclosure only needs current and voltage sampling signals and drive signals that already exist in a control system of the converter and has the advantage of simple implementation. A cycle accumulated value of a difference between a sampling current and an estimated current after the power transistor of the converter has the open-circuit fault is used as a diagnostic variable, which can quickly and accurately complete diagnosis of a faulty power transistor and has relatively strong practicability.

Power conversion systems and methods to control a multiphase multilevel regenerative power converter with multilevel phase circuits that individually include multiple regenerative power stages with respective power stage outputs connected in series, each of the multiple regenerative power stages comprising a DC link circuit a switching rectifier coupled between a respective transformer secondary circuit and the DC link circuit, and a switching inverter coupled between the DC link circuit and the respective power stage output, including a controller that provides inverter switching control signals to control the respective switching inverters, provides rectifier switching control signals to control the respective switching rectifiers, and controls a non-zero phase relationship between the rectifier switching control signals of the respective switching rectifiers.

A phase sequence adjustment system includes a power conversion circuit and a control circuit. The power conversion circuit is connected to a main power supply with a phase sequence. The control circuit respectively provides a first and a second excitation signals to the power conversion circuit, so as to short the power conversion circuit with the main power supply twice. The control circuit includes a current detection circuit and a control unit. The current detection circuit obtains two current signals respectively during two short-circuit operations. The control unit calculates two current phase angles respectively according to these two current signals and determines whether the phase sequence is positive or negative accordingly. The control unit selects one from the two current phase angles, calculates a voltage phase angle of the main power and a phase angle difference there-between to adjust a feedback phase sequence accordingly.

A power conversion system includes a first switch configured to be connected between a first phase of a polyphase alternating current (AC) power source and an electrical load and a first diode configured to be connected between the first phase of the polyphase AC power source and the electrical load, the diode configured to conduct a current from the AC power source to the electrical load. The power conversion system also includes a control unit configured to interface with the first switch to close, responsive to the occurrence of a short circuit fault, the first switch during a negative current portion of the AC cycle of the first phase of the polyphase AC power source and open, responsive to the occurrence of the short circuit fault, the first switch during a positive current portion of the AC cycle of the first phase of the polyphase AC power source.

An apparatus for supplying power to a high-capacity load includes a three-to-two phase transformer including an input side three-phase transformer terminal for connection to a three-phase supply grid and output side first and second output-side single-phase transformer terminals. A converter arrangement has a first partial converter including a first input-side, single-phase AC voltage terminal for the first output-side transformer terminal and a first single-phase output terminal. A second partial converter has a second input-side single-phase AC voltage terminal for the second output-side transformer terminal and a second single-phase output connector. The partial converters are mutually connectable by the output terminals in an output-side series and/or parallel circuit and form a single-phase load terminal for the high-capacity load. A method for supplying power to a high-capacity load is also provided.

A controller (5) of an uninterruptible power supply apparatus includes: first to sixth comparator circuits (22a to 22f) respectively provided corresponding to first to sixth IGBTs (Q1 to Q6) and outputting, based on a comparison result of the magnitude of three-phase AC voltages, signals (A1 to A6) indicating that a corresponding IGBT is to be turned on; and a control unit (23) that, when a voltage between terminals (VD1 or VD2) of a first or second capacitor (C11 or C12) is higher than a target voltage (VDT), turns on and off each of the first to sixth IGBTs based on signals output from the first to sixth comparator circuits to decrease the voltage between terminals of the first or second capacitor.