More than 170 countries have already established renewable energy targets to meet their national increasing energy demand and also to keep their environment sustainable. Due to a number of features multi-megawatt photovoltaic (PV) power-plants have been becoming the first-choice for escalating and updating power-systems all-over the world. Moreover, solar PV power plant also be the first choice for meeting rapidly-growing and urgent demands, as it can be installed relatively quickly, say in 6-12 months, compared to fossil fuel-based plants that require more than 4-5 years. The traditional low-voltage (288-690 V) converter-based system requires step-up transformer and line filter to interconnect solar PV power plant with medium-voltage grids. Recently, medium-voltage converters have received a significant interest for step-up-transformer and line-filter-less direct medium-voltage grid-integration of PV power plants. This paper aims to review the necessity and technical challenges in developing medium-voltage power electronic converters including how converter circuit topologies and control techniques have affected the development of medium-voltage converters to interconnect PV power plants to medium-voltage grids directly. A comprehensive review of current research activities and possible future directions of research to develop medium-voltage converter-based reliable and cost-effective grid-integration technologies to provide for a cost-effective grid integration of solar PV power plants is presented.