Harmonic Voltage Synchronization Using GPS Modules for Grid-Connected Power Converters

Voltage-controlled inverters (VCI) for distributed energy resources allow operation in grid-connected and islanded conditions. Common techniques based on $P$-$f$, $Q$-$V$ droop-control use sinusoidal voltage references for the VCIs, which brings unwanted circulating harmonic currents in case of connection to grids with distorted voltage. In fact, the voltages at the point of common coupling (PCC) of a sub-grid, like a microgrid, are typically distorted, and the related circulating currents pose potential issues in terms of distribution and converters losses, effectiveness of protections, and power quality. This paper proposes a strategy to synthesize, at the output of a VCI, the same harmonic voltage detected at the PCC to limit unnecessary harmonic current circulation. The proposed method uses global positioning system (GPS) modules to synchronize the harmonic voltage references of the VCIs with the PCC. To this end, low-bandwidth communication is exploited to broadcast the information to distributed VCIs. An experimental setup is implemented to test the proposed control using a hardware-in-the-loop approach for the modeling of the power stage. Several case studies are analyzed, showing the effectiveness of the proposed strategy in achieving power quality improvements: reduced load voltage harmonics, reduced circulating currents, reduced grid current harmonic content, and reduced power losses.