Grid compliance is a crucial feature for modern wind turbine systems in power generation. The generator is one of the key components in a WTS. However, in order to predict the response of a directly grid connected wind generator to grid code requirements, an optimisation-based design over a large design space is needed. In this research, an analytical design model is developed for a grid compliant variable-flux synchronous generator (VFSG). A comprehensive derivation of the analytical model shows a step by step design procedure of the wind generator considering the total magneto-motive force (MMF) required. The developed analytical model is then used together with particle swarm optimisation algorithm which significantly shortens the computational time. The methods are then used to evaluate designs with the objective of minimum active mass. Optimum VFSG designs are obtained, results of which are discussed. The generator design with PM structure (DESG-68/72) yields a compromise between low active generator mass, efficiency and manufacturability. Finally, FEM results are used to validate results of the DESG with 68/72 pole/slot combination.