The present invention proposes a hybrid converter branch operating mode for a Modular Multilevel power Converter MMC with MMC cells in distinct subsets operating according to a “pulse blocked” cell operation mode with DC cell voltage increase or according to a “bypass” cell operation mode without DC cell voltage increase. Repeated cell subset assignment and corresponding alternation of cell operating mode allows to reduce or at least manage a mean deviation of the cell capacitor DC voltages of the converter cells. The invention also reduces no-load losses of the MMC in standby mode and a charging voltage in an MMC charging mode.

A non-isolated multiport DC/DC converter topology is provided. The non-isolated multiport DC/DC converter topology is modular and can incorporate an unlimited number of independent input or output ports. The efficiency of the non-isolated multiport DC/DC converter topology is improved through partial power processing techniques without having isolation in the converter. The non-isolated multiport DC/DC converter topology also provides a balanced DC neutral point, making it an ideal candidate for bipolar DC grid or as the front-end of a multilevel DC/AC converter.

An FC-type 3-level power conversion device turns on or off first to fourth semiconductor switching elements based on comparison between a flying capacitor voltage and a half of higher-voltage side filter capacitor voltage, comparison between the higher-voltage side filter capacitor voltage and the flying capacitor voltage plus a lower-voltage side filter capacitor voltage, comparison between the flying capacitor voltage and the lower-voltage side filter capacitor voltage, and comparison between the lower-voltage side filter capacitor voltage or the higher-voltage side filter capacitor voltage and a filter capacitor voltage command value, so that an electric current flows along a path including a filter reactor L and charging a flying capacitor so as to charge a lower-voltage side filter capacitor or a higher-voltage side filter capacitor to predetermined values.

A main circuit power supply device includes: a plurality of voltage-division power storage elements connected in series; voltage adjustment circuits for adjusting each of voltages of the plurality of voltage-division power storage elements through mutual transfer of power between the plurality of voltage-division power storage elements; and at least one DC/DC converter which is connected to at least one of the voltage-division power storage elements and supplies a control power source to a main circuit control circuitry to control a main circuit.

A method controls switching states of a multi-level converter with multiple modules. Each module has: terminals on a first and second side; controllable switches; and an energy store in series with a first switch in a first connection between the terminals. A second switch is arranged in a connection between the terminals. The control of the switching states is divided into a real-time and offline part. In the real-time part, for each time step: a voltage level is allocated to a voltage requirement; a total switching state is determined in a first switching table for the voltage level; and the total switching state is passed on as a control signal to the switches. In the offline part: a second switching table is calculated, resulting in accordance with a minimization of a cost function.

A power converter includes an arm in which a plurality of converter cells are connected in series, each of the converter cells including at least two switching elements, a power storage element and a pair of output terminals. A control device controls the power converter. The converter cell includes a switch to have the converter cell bypassed. When the control device senses failure of the converter cell, it has the failed converter cell bypassed, estimates an output voltage lost by bypassing the failed converter cell, and has a normal converter cell supply the estimated output voltage of the failed converter cell.

Various examples are provided related to modular multilevel converter (MMC) scale-up control methodologies which can be applied for MV and HV DC applications. In one example, an MMC includes first and second legs each with submodule (SM) groups connected in series, where each SM group includes a plurality of SMs; local group controllers that can control a corresponding SM group; and a central controller that can control output voltage of the MMC via the local group controllers. The local group controllers can provide capacitor voltage balancing (CVB) control of corresponding SM groups.

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 power conversion apparatus includes power conversion circuitry including a plurality of sub-modules connected in series to each other, a control device to generate a control command for controlling operation of the plurality of sub-modules, and a relay apparatus to relay communication between the control device and the plurality of sub-modules. For each sub-module of the plurality of sub-modules, the relay apparatus generates path information indicating a communication path from the control device to the sub-module, and outputs the generated path information to the sub-module. Each sub-module of the plurality of sub-modules generates identification information of the sub-module based on the path information corresponding to the sub-module.

A direct current (DC)-DC converter including: a power switching circuit including a first switch circuit and a second switch circuit that are connected in parallel to a switching node, the first switch circuit and the second switch circuit configured to generate a switching voltage signal through the switching node in response to an input DC voltage and configured to perform complementary switching operations to control a voltage level of the switching voltage signal; and a filter circuit configured to filter the switching voltage signal to generate an output DC voltage.