A method controls a converter assembly which has a line-commutated converter. The line-commutated converter has an alternating voltage terminal which can be connected via a phase conductor to an alternating voltage network. The converter assembly further has a switch module branch which is arranged serially in the phase conductor and which contains a series circuit of switch modules at each of the terminals of which bipolar voltages can be generated which add up to a branch voltage. A connection voltage to a connection point between the switch module branch and the converter is controlled by adjusting an amplitude of a positive sequence component of the branch voltage. The converter assembly is configured to carry out a control method for controlling the converter assembly.

A power conversion device includes: a power converter including, for respective phases of AC, leg circuits each including a pair of arms connected in series, the arms including a plurality of converter cells which are connected in series and each of which has an energy storage element and a plurality of semiconductor elements, the leg circuits being connected in parallel between positive and negative DC terminals, the power converter being configured to perform power conversion between multiphase AC and DC; and a control unit. The control unit corrects an AC voltage command value for controlling AC voltage of the power converter, by a zero-phase-sequence voltage command value having a set amplitude and a set phase, and performs adjustment control for adjusting at least either the amplitude or the phase of the zero-phase-sequence voltage command value on the basis of electric energy variation in the arm.

A voltage source converter has a first inverter valve unit that has a first terminal and a second terminal, and a second inverter valve unit that has a first terminal and a second terminal. The first inverter valve unit and the second inverter valve unit are connectedly arranged in parallel. The first inverter valve unit and the second inverter valve unit are self-balancing through equal capacitance and parallel connection of the first inverter valve unit and the second valve unit.

A first offset voltage which is added to voltage commands in a first three-phase voltage command calculated on the basis of a control command for an AC rotary machine, and a second offset voltage which is added to voltage commands in a second three-phase voltage command calculated on the basis of a control command for the AC rotary machine, are set in such a manner that a period during which one of a first power converter and a second power converter outputs an effective vector and the other thereof outputs a zero vector occurs during a carrier period of a first carrier wave signal and a second carrier wave signal.

A loss optimization control method for modular multilevel converters (MMCs) under fault-tolerant control is disclosed. The method includes the following steps: when a fault of a SM in a MMC occurs, bypassing the faulty SM to achieve fault-tolerant control; suppressing the fundamental circulating current using a fundamental circulating current controller; respectively calculating the loss of each SM in faulty arms and healthy arms by using loss expressions of different switching tubes in SMs of the MMC; aiming at the loss imbalance between the arms of the MMC, taking the loss of a healthy SM as the reference, adjusting the period of capacitor voltage sorting control in the faulty SMs, achieving the loss control over the working SMs in the faulty SMs, and finally achieving the loss balance of each SM in the faulty arms and the healthy arms. Compared with the conventional methods, the proposed method is easier to implement and does not increase the construction cost of MMCs.

Example three-level inverters, control methods, and systems are provided. One example three-level inverter includes a first bus capacitor, a second bus capacitor, a power conversion circuit, and a controller. The first bus capacitor is connected in the middle of the current bus and the power conversion circuit. The power conversion circuit is configured to convert a direct current into a three-phase alternating current for output. The controller is configured to determine a balance reference by using a difference between absolute values of voltages of the positive and negative direct current buses and an even harmonic current in a grid-connected current, where the balance reference is used to enable the three-level inverter to generate a current signal for balancing the voltages of the positive and negative direct current buses.

A power converter includes at least one arm having a plurality of converter cells cascaded to each other. Each of the converter cells includes a pair of input/output terminals, a plurality of switching elements, and a power storage element. The power storage element is electrically connected to the input/output terminals through the switching elements. A control device generates a control signal for controlling on and off of the switching elements of each converter cell. The control device generates the control signal by pulse width modulation control based on a modulation command signal including an AC component having a fundamental frequency and corresponding to a command value of an output voltage between the input/output terminals, in each converter cell, such that a harmonic component included in the output voltage and having a predetermined frequency that is an integer multiple of the fundamental frequency is suppressed.

An AC-DC converter includes three phase terminals, first and second DC terminals, a first converter stage for converting between the AC signal and a first signal at first and second intermediate nodes, a second converter stage to convert between a second signal at third and fourth intermediate nodes and the DC signal at the first and second DC terminals. The second converter stage has a first active switch. A link connects the first and third intermediate nodes and the second and fourth intermediate nodes. A current injection circuit has second active switches. In a first mode, the first active switch and the second active switches are operated through PWM. In a second mode, the third and fourth intermediate nodes are continuously connected to the first and second DC terminals such that the second converter stage is inoperative and the second active switches are operated through PWM.

A three-phase AC to DC converter includes a first converter stage for converting between three phase voltages at three phase terminals and a first signal at a first intermediate node and a second intermediate node. A phase selector is configured to selectively connect the three phase terminals to a third intermediate node. The converter includes a second converter stage, a DC link connecting the first and second converter stages, and a galvanically isolated DC/DC converter stage having a first side connected to output nodes of the second converter stage and a first common node. A second side of the DC/DC converter stage is galvanically isolated from the first side. The first common node is connected to the third intermediate node. The difference of a first current applied to the DC/DC converter at output nodes of the second converter stage is provided at the third intermediate node.

A power converter including a three-input direct current converter capable of performing maximum power point tracking on three power inputs, a step down converter capable of voltage step down of the three power inputs, a bus capacitor and a balance circuit utilizing switches and transformers utilized to balance voltages of the bus capacitor, a three-level inverter capable of creating alternating current voltages for the alternating current grid, an output filter electrically coupled to the three-level inverter, a contactor capable of disconnecting the bus capacitor and the balance circuit from the alternating current grid, and a parameter sensor and a field programmable gate array controller electrically coupled to the power converter, capable of controlling a plurality of power switches based on at least one sensed parameters.