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, for respective phases of an AC circuit, leg circuits each having a pair of arms connected in series to each other, each arm including a plurality of converter cells which are connected in series and each of which has an energy storage element. A controlling circuitry includes a zero-phase-sequence voltage command value adjustment unit for correcting arm voltage command values for the arms by a zero-phase-sequence voltage command value. The command value correction circuitry performs adjustment control for adjusting the zero-phase-sequence voltage command value so that at least one arm voltage command value becomes equivalent to a limit value of the output voltage range of the arm.

A power conversion device includes: a power converter connected to an AC grid to which a load is connected; and a control circuit. The control circuit includes a harmonic compensation unit that includes a current command generation unit and a limit coefficient calculation unit and compensates for harmonic current contained in load current. The current command generation unit generates compensation current desired values for respective frequency components, and corrects the compensation current desired values using corresponding limit coefficients, to generate compensation current commands for respective frequency components. The limit coefficient calculation unit calculates each limit coefficient, on the basis of the compensation current desired value for each frequency component, and maximum voltage and maximum current that the power converter can output.

Provided is a novel multi-level inverter with mixed device types and methods of controlling same. This novel multi-level inverter topology and control method allows the use of high frequency switching devices for controlled PWM switching, while also using lower frequency switching devices for directional switches. This combination of high frequency PWM switching devices with low frequency directional switching devices allows a cost reduction without a significant performance degradation.

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.

Systems and methods for power conversion are described. Symmetric topologies and modulation schemes are described that may reduce common-mode noise. For example, a system may include a transformer including a first secondary winding and a second secondary winding; a rectifier, including a set of switches, that connects taps of the first secondary winding and the second secondary winding to a first terminal and a second terminal, wherein the rectifier is symmetric with respect to the first secondary winding and the second secondary winding; a battery connected between the first terminal and the second terminal; and a processing apparatus that is configured to control the set of switches to rectify a multilevel voltage signal on the transformer, including: selecting a modulation scheme from among two or more modulation schemes based on a measured voltage level of the battery.

A method for operating a multi-level bridge power converter of an electrical power system connected to a power grid includes providing a plurality of switching devices of the power converter in one of a neutral point clamped topology or an active neutral point clamped topology, the plurality of switching devices including a first group and a second group of switching devices. The method also includes providing a multi-state deadtime for the first and second groups of switching devices that changes based on different state transitions of the power converter. Further, the method includes operating the first and second groups of switching devices according to the multi-state deadtime to allow the first group to switch differently than the second group during the different state transitions, thereby decreasing voltage overshoots on the first group during one or more of the different state transitions and providing safe transition between commutation states of the power converter.

The present invention provides a Modular Multilevel Converter (MMC) in which M redundant sub-modules are additionally arranged in addition to the N sub-modules that are needed for operation, and the N+M sub-modules are controlled so as to participate in switching in turn.

The MMC according to an embodiment of the present invention includes multiple sub-modules connected in series with each other and a controller for controlling on/off switching of the sub-modules. Here, the multiple sub-modules include N sub-modules that participate in the operation of the MMC and M redundant sub-modules for replacing a failing sub-module when at least one of the N sub-modules fails, and the controller switches on the sub-module if the carrier signal assigned thereto is higher than a preset reference signal, and switches off the sub-module if the carrier signal assigned thereto is lower than the reference signal.

Disclosed herein is a power supply apparatus for a sub-module controller of a Modular Multilevel Converter (MMC), which supplies driving power to the sub-module controller of an MMC connected to a High Voltage Direct Current (HVDC) system. The power supply apparatus includes a bridge circuit unit including N (N≧2, integer) energy storage units for storing a DC voltage in series-connected sub-modules in the MMC and multiple power semiconductor devices connected in parallel with the N energy storage units in a form of a bridge; and a DC/DC converter for converting a voltage output from output terminals formed between both ends of n (1≦n<N) series-connected energy storage units, among the N energy storage units, into a low voltage and supplying the low voltage to the sub-module controller.

Disclosed herein is a power control apparatus for sub-modules in an MMC, which controls stable supply of power to sub-modules in MMC connected to an HVDC system and a STATCOM. The power control apparatus includes at least one first resistor connected between P and N buses of MMC; a second resistor connected in series with the first resistor; a switch connected in series with the second resistor; a third resistor connected in parallel with the second resistor and the switch which are connected in series; a Zener diode connected in parallel with the third resistor; and a DC/DC converter connected between both ends of the Zener diode and configured to convert voltage across both ends of the Zener diode into low voltage, and supply the low voltage to the sub-modules, wherein a magnitude of current flowing through the Zener diode is controlled depending on ON/OFF switching of the switch.