Adaptive-Harmonic Compensation in Residential Distribution Grid by Roof-Top PV Systems

The single-phase nonlinear loads are going to increase in the future and power quality concerns in the residential distribution grid. Since most of nonlinear loads have a dispersed nature, compensating these phenomena may be complicated. On the other hand, the increased capacity of single-phase grid-connected roof-top PV inverters in residential distribution grid can be an opportunity to engage these systems in the power quality issues as custom power devices. By implementing a proper control for roof-top PV inverters, these systems may in addition to inject the fundamental current, additionally act like a virtual harmonic resistance, and dedicate their additional current capacity to compensate the harmonics of residential distribution grid. In this paper, each roof-top PV system is a grid-harmonic supervisor, where it continually measures the PCC voltage harmonics by the sliding discrete Fourier transform algorithm and then individually compensates the measured harmonics by the proposed adaptive-harmonic compensator. In the proposed approach, a current reference is separately determined for compensating each harmonic component. Then, a specific amount of additional current capacity will be dedicated for each component to compensate by using adaptive gain. Finally, the current reference is controlled by a model predictive current controller. It has been tested in a single-phase transformerless inverter (highly efficient and reliable inverter concept) with an LCL filter at the output. Also, the effectiveness of the control scheme has been verified by MATLAB Simulink and experimental tests.