A Single-or-Three-Phase Adaptable Inverter Enabled by Second Harmonic Injection

This paper provides an adaptable topology that can be used in grid-tied inverter adaptions for three-phase, single-phase, and split single-phase grids. The value of the DC-link capacitance is of high importance when using a three-phase converter in a single-phase application. If sized for the single-phase application the DC-link capacitance will be oversized for the three-phase application. Likewise, if sized for the three-phase application, the DC-link capacitance will be undersized for the single-phase application. This is because the DC-link needs to support a pulsating power flow in single-phase operation that is not present in three-phase interfaces. This paper proposes the use of Second Harmonic Injection (SHI) when operating with a single-phase grid to mitigate the pulsating power flow. SHI is enabled by the proposed topology, which allows for the required capacitance of single-phase operation to be reduced and become closer in value to the required DC-link capacitance of three-phase operation. This lessens the trade-off that must be made between single-phase operation, three-phase operation, and required DC-link capacitance, ultimately resulting in a more balanced design. Design equations are provided alongside comments on component sizing to maximally leverage SHI. Experimental three-phase, single-phase without SHI, and single-phase with SHI results are shown.