active harmonic compensation and stability improvement in high-power grid-connected inverters using unified power quality conditioner

Multifunctional features of grid-connected inverters can be used for harmonic compensation of local load voltage and grid-injected current. but, in high-power grid-connected inverters, there is a challenge due to low switching frequency. on the other hand, simultaneous compensation of local load voltage and grid-injected current harmonics is an important issue in grid-connected inverters. using a unified power quality conditioner (upqc) at the point of common coupling (ppc), an improved active harmonic compensation method is proposed which is appropriate for high-power low-frequency grid-connected inverters. the upqc operates as a combination of a negative shunt virtual admittance and a negative series virtual impedance at the pcc. it suppresses the disturbances caused by local load variation and grid impedance change. using a low-power, high-frequency upqc, local load voltage and grid-injected current harmonics up to higher-order components are simultaneously compensated despite grid impedance changes and nonlinear local load variations. the control system is designed according to the impedance-based stability criterion to ensure the system’s stability. the theoretical results are validated using different case study simulations in matlab/simulink software.