DUE to the environment concerns, energy risks, fossil fuel problems, and the evolution of smart grid, the penetration of renewable energy systems and electric transportation systems is booming with a fast pace. Besides, with the proliferation and increased use of motor loadings and power electronic devices into all kinds of energy processing systems, the power quality(PQ) problems such as: reactive power and harmonics become more serious. This kind of PQ problems distort the source, lower the efficiency, and may cause instability, thus it makes negative impacts on the performance and reliability of grid or microgrids. In this regard, to ensure secure, reliable, and efficient power supply and transmission in power-electronics-controlled systems, PQ issues should be properly taken care of. That is, the desires to develop PQ-free or PQ-compensated power electronic systems and infrastructures are of high interest and importance. Hence, we organized this Special Issue on Power Quality Conditioning in Modern Power Grids Integrated Emerging Power Electronic Systems for targeting the analysis, topology and control strategy of PQ-free or PQ-compensated power converters in renewable energy systems, electric transportation systems, PQ conditioning systems, industrial automation systems, lighting systems, etc., which also includes the detection, characterization and analysis methods of the PQ issues.