Simultaneous Unbalance and Harmonic Compensation from RESs with Neutral Wire connected to a LV Distribution Grid

A hybrid power conditioner is proposed for distributed renewable to cater the growing concern of power quality in a low-voltage (LV) grid. The LV distribution grid is inherently unbalanced and usually feeds single-phase loads with a neutral return wire. Hence, the system is 4-wire with finite zero sequence or neutral current. A multi-functional renewable energy source (RES) unit based on split-DC link topology connected to a 4-wire system is proposed in this paper. It is integrated with a decoupled controller which can simultaneously compensate voltage unbalances, neutral current and harmonics of point-of-common-coupling (PCC) voltage. The main advantages of the proposed controller include cancellation of both active and reactive power oscillations during unbalanced current injections, second-order generalised integrator (SOGI) based technique to extract real and imaginary part of zero sequence current, direct harmonic voltage compensation without use of multiple phase locked loops (PLLs) and smooth fault ride-through operation with improved voltage support. Simulation study for a single RES unit connected to a 4-wire LV distribution grid with non-linear loads is carried-out in PSCAD and the results are presented.