Harmonic reference current generation for unbalanced nonlinear loads

Nonlinear loads generating harmonics can be unbalanced due to either supply voltage or load imbalance. In this paper, unbalanced nonlinear loads are mathematically analyzed to apply for real-time active power filter (APF) control and measurement of several important parameters such as root mean square (RMS) value, total harmonic distortion (THD), and power factor (PF). The proposed approach is based on a synchronous reference frame (SRF) low pass filter (LPF) for three-phase as well as single-phase system. Synchronous reference frame currents are divided into three a,b,c components which include DC, 2nd, and higher harmonic components. Those DC components are obtained from simple first order low pass filter (LPF) and used for fundamental current calculation. Simulation and experimental results show that the proposed approach can be applied for active power filter control under unbalanced conditions.