Analytical polymer separation techniques, like CRYSTAF (crystallization analysis fractionation) and TREF (temperature rising elution fractionation), play a crucial role in gaining insight into the interrelation between molecular architecture and properties. Often polymer samples are semicrystalline, as it consists of amorphous regions which exhibit a liquid-like structure, and ordered crystallized structures called crystallites. Additionally, polymers exhibit a certain degree of short-chain branching, and they are polydisperse with respect to molecular weight and chemical composition. To explain the theoretical background of common polymer separation techniques, a fair prediction of solid-liquid equilibria (SLE) of polymer solvent systems is required. By application of Lattice Cluster Theory (LCT), developed by Freed and co-workers, the molecular architecture can be considered. Recently, LCT was applied to calculate the SLE of binary semicrystalline, high-polymer solvent mixtures having an arbitrary molecular architecture of both polymer and solvent, in which the polymer is considered to be monodisperse. Besides influences of degree of polymer crystallinity, nucleation entropy, and degree of branching, in this contribution the impact of polymer polydispersity on the SLE of high-polymer solvent mixtures is considered. This is realized by application of the LCT-based theory for predicting the SLE of discrete ternary high-polymer solvent mixtures made of two polymers and one solvent. Effects of semicrystallinity and molecular architecture of the respective components are studied for ternary systems.