High penetration of grid-connected photovoltaic (PV) power, especially large PV power plants consisting of hundreds of units, has significant impacts on dynamic characteristics of power grids. It is increasingly important to develop a dynamic equivalent model for a large PV plant to simulate its responses under large disturbances, especially during the fault ride-through process, by using single or several equivalent PV units. To construct such a model for large PV plants, a four-step framework is proposed: clustering of PV units within a PV plant, aggregating of PV units within a cluster, allocating of the collector network and validating of the constructed equivalent model. Comprehensive reviews with solutions and comparisons on each of the four modeling steps are presented. Further, equivalent modeling challenges are summarized, and future research directions for advancing single- and multi-unit equivalent methods are recommended.