Mitigation of Second Harmonic Pulsations for Single-Phase Inverters

In single-phase grid connected inverters, the unbalanced power between the DC and AC sides can cause large second order pulsations. The second pulsations typically appear on the DC bus voltage or current depending on the type of DC source. The second pulsation can result in severe issues such as output side distortion, saturation and unstable performance. This paper proposes a second pulsating power balancing method with MPC-based second harmonic injection (SHI) technique. The second order component is firstly extracted from the output side and then added to the zero-sequence references for the MPC regulation. Doing so, the second pulsation can be largely reduced. The DC bus voltage/current can be stabilized as constant values. There is no need for large DC capacitor to reduce the oscillation. Besides, the output side current distortion is attenuated. Since the second order harmonics are regulated by the MPC before injection, the stability is largely improved. Since the second harmonic components are regulated by the MPC controller before injecting to the output side, the stability of the single-phase energy conversion system can also be improved. The simulation and experimental results verified the proposed method.