This paper shows a new concept to generate medium voltage (MV) in wind power application to avoid an additional transformer. Therefore, the generator must be redesigned with additional constraints and a new topology for the power rectifier system by using multiple low voltage (LV) power rectifiers connected in series and parallel to increase the DC output voltage. The combination of parallel and series connection of rectifiers is further introduced as DC-cascade. With the resulting DC-cascade, medium output voltage is achieved with low voltage rectifiers and without a bulky transformer. This approach to form a DC-cascade reduces the effort required to achieve medium DC voltage with a simple rectifier system. In this context, a suitable DC-cascade control was presented and verified with a laboratory test setup. A gearless synchronous generator, which is highly segmented so that each segment can be connected to its own power rectifier, is investigated. Due to the mixed AC and DC voltage given by the DC-cascade structure, it becomes more demanding to the design of the generator insulation, which influences the copper fill factor and the design of the cooling system. A design strategy for the overall generator design is carried out considering the new boundary conditions.

The design of a fully superconducting wind power generator is influenced by several factors. Among them, a low number of pole pairs is desirable to achieve low AC losses in the superconducting stator winding, which greatly influences the cooling system design and, consecutively, the efficiency of the entire wind power plant. However, it has been identified that a low number of pole pairs in a superconducting generator tends to greatly increase its output voltage, which in turn creates challenging conditions for the necessary power electronic converter. This study highlights the interdependencies between the design of a fully superconducting 10 MW wind power generator and the corresponding design of its power electronic converter.

As part of the German SupraGenSys project, a fully superconducting generator for wind energy conversion systems was investigated, which will be built and demonstrated as part of SupraGenSys 2. Therefore, this paper summarizes the main challenges and outlines the design strategy to achieve a design with low investment cost and high efficiency. The field winding and the armature winding consist of HTS tapes. The armature winding in particular has high alternating current losses due to the alternating magnetic field. These alternating current losses heat up the coils and must be compensated for by the cryocooler with high energy consumption. A highly efficient generator design can therefore still lead to a low overall efficiency of the system. Or a design with low AC losses can be achieved by using a large amount of HTS tapes, which increases the investment cost of the system significantly. In this paper, design strategies are published to achieve a generator design with low AC losses by identifying the factors that influences of AC losses and developing methods to reduce the losses. For this purpose, the tangential component of the flux density is investigated and the AC losses are determined using the TA formulation [Kim et al. (1962)]. Compared to the methods published in [2], this work focuses more on the overall design of the generator and its stator and rotor windings. The design is iron-based, which allows the use of the iron geometry to influence the AC losses and protect the stator winding from the rotor field. As a result, the AC losses are dominated by the intrinsic field of the coils, which can be influenced by the coil geometry. This enables a design with very low AC losses, high efficiency and modest use of HTS tapes.

Transient short circuit simulations of conventional machines are well known and offer the possibility of predicting the short circuit behavior of a machine with a high degree of accuracy. Although the ohmic resistance in the superconducting state is negligible, the non-linearity during quenching is difficult to integrate into a model. In order to predict the thermal or mechanical destruction of the superconductor, calculation models are required that take into account the classic machine models and the physical behavior of the superconductor. This paper presents an extended calculation model with a transient finite element (FE) simulation for a fully superconducting wind generator. The model considers the critical current of a superconductor with the influence of the layer structure of the High Temperature Superconducting (HTS) tape. In addition, an analytical calculation model is presented, which is compared with the FE model.

In the SupraGenSys 2 project, a 250 kW fully superconducting demonstrator for a wind energy generator is being designed and constructed. This demonstrator will be set up under laboratory conditions and will serve as a platform for investigating a fully superconducting 10 MW wind energy system. In addition to the well-known challenges of superconducting windings, such as AC losses, this design must also address various other design aspects, including highly saturated iron and the impact of cooling lines. This work provides an overview of the calculation results obtained so far and offers insights into the challenges associated with a low–AC-loss winding design.

In the SupraGenSys 2 project, a fully superconducting 250 kW wind generator is being developed and tested under laboratory conditions to demonstrate its feasibility for low-speed, high-torque applications. The results of this investigation are intended to pave the way for the integration of multi-megawatt, direct-drive wind turbines. In a two-phase neon thermosiphon with indirect coil cooling, the heat load is transferred from the individual components to the condenser of the cold heads. The design uses the inclination of the tower head, enabled by the tilt angle, to circulate the coolant, eliminating the need for pumps. Although this approach can be easily implemented for the stator cooling system, it poses significant challenges for the rotor cooling system. This is because the cold heads must remain stationary due to better accessibility for maintenance. In addition, distributing the cooling medium in low-speed applications without pumps is challenging. This cooling concept aims to enable reliable heat transfer in a fully superconducting wind generator, making it practical for use in large-scale wind turbines and overcoming key challenges of system integration.