Deliverable 5.1 reviews the aerodynamic design constraints of the X-Rotor secondary rotors in terms of tip speed, rotational speed, rated power, dimensions as well as operational strategies. It also provides a generator and a power converter design strategy/framework to address the particular features of the secondary rotor power take-off from an electrical, electromagnetic and construction perspective. The characteristics of the aerodynamics, operational strategies and generators need to be consistent. This deliverable starts by reviewing the X-rotor operational strategy and identifying the requirements needed from the generators and power electronic control systems. Conventional type-IV wind turbines are compared against the secondary rotor requirements, and a design strategy is proposed to modify standard type-IV designs within realistic design specifications, desired efficiencies, size and cost. Such a design strategy implies the solution of a multi-parameter problem. Most of the design variables of permanent magnet synchronous machines are involved (e.g., volume, length, diameter, PM size, windings, air gap and many others). To obtain an optimal solution, metaheuristic algorithms using real-world design specifications and constraints are applied. The solutions provided by the design strategy are validated using an Electromagnetic field solver where the elements, dimensions and characteristics of the optimised generator are reproduced in 2-D models. The electrical and electromagnetic performances are corroborated using finite element analysis. Finally, the electric features of the optimised generator design are used to create an electromagnetic simulation environment where the interaction of the generator and power electronics is revised. In this stage, the minimum requirements of power electronic converters are specified for the range of operating speeds of the secondary rotors. This section also reviews the implications in efficiency and practicality of the minimum requirements of power electronic converters needed. The results presented in this report include a detailed analysis of the optimal design of PMSG for the X-rotor, seeking to comply with the operation strategy of the system, structural limitations and operational ranges. The results of this deliverable include up-to-date information of industrial practices for the development and control of PMSG for wind turbine applications. The report applies an authoritative design methodology aided by an optimization algorithm and real manufacture constraints to develop an optimal design for a 690V and 3.3KV PMSG machines, since both options could be suitable for the X-rotor system. The results of the design are corroborated and provided as design parameters. Finally, the report analyses the electric performance of the designed machines under operation conditions that mimic the most extreme operation strategies of the X-rotor. This analysis is used to assess the adequacy of commercial power converters to exert control under those conditions. Clear limits are identified and presented to the designers for each generator design case. The evaluation of all the material presented in this report suggest that using Medium Voltage PMSG (3.3KV) controlled by 3-level Power Electronic converters with extended DC voltage bus, are the most suitable option for drivetrain design, fulfilling the requirements in size, efficiency, PM usage and operative regimes of the X-rotor concept.