Grid connected converter device

A method for a grid-connected converter interfacing a grid network and coupling the grid network to a direct current (DC) source or DC bus/network, the method comprising:

• providing a neutral-point-clamped inverter circuit having a voltage vdc across the direct current (DC) source or DC bus/network, the neutral-point-clamped inverter circuit including one or more switch legs, each switch leg comprising a corresponding pair of switches having an electrical midpoint between the switches of the pair of switches;
• and
• providing an inductor network coupled to the neutral-point-clamped inverter circuit, the inductor network comprising a set of parallel inductor legs, each parallel inductor leg coupled to a corresponding electrical midpoint of a corresponding switch leg and also coupled to an output electrical node coupled to the grid network;
• wherein the grid network is an AC network that has a plurality of phases, and each phase has a corresponding output electrical node being coupled to a corresponding neutral-point-clamped inverter circuit and a corresponding inductor network;
• wherein the neutral-point clamped inverter circuit includes two or three switch legs per phase of the plurality of phases;
• wherein when the neutral-point-clamped inverter circuit includes two switch legs per phase, the method operates with at least one of the characteristics selected from the group consisting of a line voltage PWM frequency is 4×fc, a number of line voltage steps is vdc/4, a number of line voltage steps is 9, or a common mode voltage is +/−vdc/8;
• and
• wherein when the neutral-point-clamped inverter circuit includes three switch legs per phase, the method operates with at least one of the characteristic selected from the group consisting of:
• the line voltage PWM frequency is 6×fc, the number of line voltage steps is vdc/6, the number of line voltage steps is 13, or the common mode voltage is +/−vdc/12.

A grid-connected converter device for interfacing a grid network and coupling the grid network to a direct current (DC) source or DC bus/network, the device comprising:

• a neutral-point-clamped inverter circuit having a voltage vdc across the direct current (DC) source or DC bus/network, the neutral-point-clamped inverter circuit including one or more switch legs, each switch leg comprising a corresponding pair of switches having an electrical midpoint between the switches of the pair of switches;
• and
• an inductor network coupled to the neutral-point-clamped inverter circuit, the inductor network comprising a set of parallel inductor legs, each parallel inductor leg coupled to a corresponding electrical midpoint of a corresponding switch leg and also coupled to an output electrical node coupled to the grid network;
• wherein the grid network is an AC network that has a plurality of phases and each phase has a corresponding output electrical node being coupled to a corresponding neutral-point-clamped inverter circuit and a corresponding inductor network;
• wherein the neutral-point-clamped inverter circuit includes three switch legs per phase of the plurality of phases;
• wherein the device operates with at least one of the characteristics selected from the group consisting of:
• a line voltage PWM frequency is 6×fc, a number of line voltage steps is vdc/6, a number of line voltage steps is 13, or a common mode voltage is +/−vdc/12.