The present disclosure relates to the field of electric power system, and more particularly to a topology of a series-connected MMC with a small number of modules, where the topology is composed of a three-phase bridge circuit, half-bridge valve strings, a three-phase filter inductor, and a three-phase grid frequency transformer. The topology of a series-connected MMC with a small number of modules in the present disclosure needs only two half-bridge valve strings, thus greatly reducing the number of the submodules as compared with the conventional MMC structure. When achieving the same high DC voltage output, the present disclosure can improve the power density of the MMC, realize stable three-phase AC output voltage, and further achieve balance of capacitor voltages in the two half-bridge valve strings. Compared to the conventional MMC topology, the topology in the present disclosure can reduce the number of submodules by nearly 2/3, and has a greater AC-DC voltage transfer ratio, thus reducing the cost of the MMC converter, reducing the device size, and improving the power density.

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.

An apparatus may include a first switch leg connected between a first input terminal and a first output terminal, the first switch leg comprising serially connected switches. The apparatus may also include a second switch leg connected between a second input terminal and the first output terminal, the second switch leg comprising serially connected switches. The apparatus may further include a third switch leg connected between an input voltage midpoint and the first output terminal. A control circuit may control the first switch leg, the second switch leg and the third switch leg.

An apparatus may include a first switch leg connected between a first input terminal and a first output terminal, the first switch leg comprising serially connected switches. The apparatus may also include a second switch leg connected between a second input terminal and the first output terminal, the second switch leg comprising serially connected switches. The apparatus may further include a third switch leg connected between an input voltage midpoint and the first output terminal. A control circuit may control the first switch leg, the second switch leg and the third switch leg.

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.

The present disclosure provides a method and apparatus using a novel PWM switching technique that requires only one PWM carrier signal and benefits from two logic functions to provide switching signals and provides the flying capacitor (FC) voltage as well as dc-link capacitors voltages regulated to their desired values without external control. It may also, eliminate the odd multiples of the switching harmonic clusters from the output voltage is possible; double the frequency of first switching harmonic; reduce filtering efforts may be required since the values of the output LC filter inductor and capacitor can be very much reduced. Furthermore, notable reduction in control complexity is possible using the novel PWM method.

The present disclosure provides a method and apparatus using a novel PWM switching technique that requires only one PWM carrier signal and benefits from two logic functions to provide switching signals and provides the flying capacitor (FC) voltage as well as dc-link capacitors voltages regulated to their desired values without external control. It may also, eliminate the odd multiples of the switching harmonic clusters from the output voltage is possible; double the frequency of first switching harmonic; reduce filtering efforts may be required since the values of the output LC filter inductor and capacitor can be very much reduced. Furthermore, notable reduction in control complexity is possible using the novel PWM method.

A multi-level inverter topology is disclosed. A power converter circuit converts a DC source at its input to provide an alternating current (AC) at its output. The power converter circuit may have a controller operably attached to multiple series connections of switches. The controller may control one or more of the multiple series connections of switches to convert a DC input to provide multi-level AC voltages with DC offset across two terminals of the power converter circuit. The multi-level AC voltages with DC offset may then be converted by use of a plurality of series connections of switches to provide a single-phase AC voltage at a first output terminal with respect to at least one of a neutral potential, an earth potential, or a terminal of the power converter circuit.

A multi-level inverter topology is disclosed. A power converter circuit converts a DC source at its input to provide an alternating current (AC) at its output. The power converter circuit may have a controller operably attached to multiple series connections of switches. The controller may control one or more of the multiple series connections of switches to convert a DC input to provide multi-level AC voltages with DC offset across two terminals of the power converter circuit. The multi-level AC voltages with DC offset may then be converted by use of a plurality of series connections of switches to provide a single-phase AC voltage at a first output terminal with respect to at least one of a neutral potential, an earth potential, or a terminal of the power converter circuit.