Converter topologies and control

A multi-port inverter for converting an input direct current (DC) waveform from a DC source to an output alternating current (AC) waveform for delivery to an AC grid, the inverter comprising:

• an AC-AC converter electrically coupled through a transformer to a DC-AC inverter electrically coupled to the DC source, the AC-AC converter comprising:
• a half-bridge circuit electrically coupled to a winding of the transformer;
• and
• an unfolding bridge circuit electrically coupled between the half-bridge circuit and the AC grid;
• wherein the AC-AC converter is adapted to convert an AC waveform received from the transformer to output the AC waveform having a grid frequency of the AC grid;
• and
• a controller having a processor and a memory wherein the controller is adapted to control the switching cycles of electrical switches of the unfolding bridge circuit, whereby:
• when a voltage across the AC grid is substantially positive during a first period, a first set of electrical switches is on and a second set of electrical switches is off;
• when the voltage across the AC grid is substantially negative during a second period, the first set of electrical switches is off and the second set of electrical switches is on;
• and
• during a third period comprising a blanking time period between the first and second periods when the voltage across the AC grid is approximately zero, the first and second, sets of electrical switches are off.

A multi-port inverter for converting an input direct current (DC) waveform from a DC source to an output alternating current (AC) waveform for delivery to an AC grid, the inverter comprising:

• a transformer;
• a DC-AC inverter electrically coupled to a first winding of the transformer, wherein the DC-AC inverter is adapted to convert the input DC waveform to an AC waveform delivered to the transformer at the first winding;
• an AC-AC converter electrically coupled to a second winding of the transformer and adapted to convert the AC waveform received at the second winding of the transformer to the output AC waveform having a grid frequency of the AC grid, the AC-AC converter comprising:
• a half-bridge circuit electrically coupled to the first winding of the transformer;
• and
• an unfolding bridge circuit electrically coupled between the half-bridge circuit and the AC grid;
• an active filter electrically coupled to a winding of the transformer wherein the active filter is adapted to sink and source power with one or more energy storage devices based on a mismatch in power between the DC source and the AC grid;
• and
• a controller electrically coupled to receive an AC voltage from the AC grid and having an output signal comprising an estimate of the phase angle of the AC voltage, wherein the controller, in response to the estimated phase angle of the AC voltage, controls the switching cycles of a plurality of electrical switches of the AC-AC converter.

A method for controlling operation of electrical switches of an unfolding bridge in an inverter configured to convert an input direct current (DC) waveform from a DC source to an output alternating current (AC) waveform for delivery to an AC grid, wherein the inverter comprises a transformer and a DC-AC inverter electrically coupled to the transformer, an active filter electrically coupled to the transformer, and an AC-AC converter, wherein the AC-AC converter comprises a half-bridge circuit electrically coupled to the transformer and an unfolding bridge circuit electrically coupled between the half-bridge circuit and the AC grid, the method comprising the steps of:

• determining a phase of the AC grid voltage;
• and
• generating a set of signals for actuation of the electrical switches of the unfolding bridge circuit based on the determined phase, whereby:
• when a voltage across the AC grid is positive during a first period, first and fourth electrical switches are on and second and third electrical switches are off;
• when the voltage across the AC grid is negative during a second period, the first and fourth electrical switches are off and the second and third electrical switches are on;
• and
• during a third period comprising a blanking time period between the first and second periods when the voltage across the AC grid is approximately zero, the first, second, third, and fourth electrical switches are off.