In one embodiment, a method of operating a power electronic converter device for an electrical power converter system is provided. The power electronic converter device includes a converter circuit, a first converter, and a second converter. The first converter and the second converter are switch with a switching pattern such that the first converter and the second converter generate voltages with stepwise voltages changes and an output voltage of the power electronic converter device results frum a superposition of the voltages of the first converter and the second converter. The switching pattern includes switching instants for the second converter such that the voltage of the second converter leaves the fundamental voltage component of the voltage of the first converter unchanged, such that the second converter does not generate a fundamental component of the output voltage.

In one embodiment, a method of operating a power electronic converter device for an electrical power converter system is provided. The power electronic converter device includes a converter circuit, a first converter, and a second converter. The first converter and the second converter are switch with a switching pattern such that the first converter and the second converter generate voltages with stepwise voltages changes and an output voltage of the power electronic converter device results frum a superposition of the voltages of the first converter and the second converter. The switching pattern includes switching instants for the second converter such that the voltage of the second converter leaves the fundamental voltage component of the voltage of the first converter unchanged, such that the second converter does not generate a fundamental component of the output voltage.

A power switching circuit including a first DC/DC converter having a first input configured to receive a first input DC voltage, a second DC/DC converter having a first input configured to receive a second input DC voltage, a DC/AC inverter having a first input coupled to the output of the first DC/DC converter and a second input coupled to the output of the second DC/DC converter, the DC/AC inverter including n (n>2) switching legs, and at least one controller coupled to the first DC/DC converter, the second DC/DC converter, and the DC/AC inverter, the at least one controller configured to operate the DC/AC inverter to provide n AC signals to at least one load coupled to the DC/AC inverter by operating two of the n switching legs in a static state and n−2 of the n switching legs in a transition state.

Described herein is a method of operating a power electronic converter device for an electrical power conversion system. The power electronic converter device includes a converter circuit including an input side, an output side, a first converter, and at least one second converter. The second converter includes at least one floating cell with a DC intermediate circuit and semiconductor devices. The method includes: switching the semiconductor devices of the floating cell at switching instants determined with optimized pulse patterns or carrier-based pulse width modulation; determining a fundamental voltage component for the floating cell; and generating the fundamental voltage component in the actual voltage of the floating cell by modifying the switching instants, such that a voltage V.sub.C AF of the DC intermediate circuit is lying in a given reference voltage range for balancing the DC intermediate circuit of the floating cell.

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.

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.

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.

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.