Circulating Harmonic Current Reduction in Distorted Voltage Conditions using GPS-based Synchronization

Voltage-controlled inverters (VCI) for distributed energy resources allow operation in both grid-connected and islanded conditions. Common techniques based on P -f Q-V droop-control use sinusoidal voltage references for VCI, which brings to unwanted circulating harmonic currents in case of connection to grids with distorted voltage. In fact, the voltages at the point of common compiling (PCC) of a sub-grid, like a microgrid, are typically distorted and the resulting circulating currents pose potential issues in terms of additional 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 voltage harmonics detected at the PCC. In this way, the related circulating harmonic currents are reduced. The proposed strategy uses global positioning system (GPS) modules to synchronize the harmonic voltage references of VCI with the PCC harmonic voltage. To this end, low-bandwidth communication is exploited to broadcast the required information to distributed VCI. Simulation and hardware-in-the-loop results show the effectiveness in reducing the circulating currents and also line impedance losses.