Coaxial counter-rotating propellers have been widely applied in ships and helicopters for improving the propulsion efficiency and offsetting system reactive torques. Lately, the counter-rotating concept has been introduced into the wind turbine design. Distributed wind power generation systems often require a novel approach in generator design. In this paper, prototype development of axial-flux generator with a counter-rotating field and armature is presented. The design process was composed of three main steps: analytical calculation, FEM simulation and prototype experimental measurements. The key aspect in the prototype development was the mechanical construction of two rotating components of the generator. Sturdy construction was achieved using two points of contact between both rotors via the placement of the bearing between the inner and outer rotor. The experimental analysis of the prototype generator has been conducted in the laboratory at the dynamometer test stand equipped with a torque sensor. The general premise for the development of such a machine was an investigation into the possibility of developing a dual rotor wind turbine. The proposed solution had to meet certain criteria such as relatively simple construction of the generator and the direct coupling between the generator and the wind turbines. The simple construction and the lack of any gearbox would allow for such a system to be constructed relatively cheaply, which is a key aspect in further system development.

This paper proposes a speed observer algorithm for the sensorless control of a doubly-fed induction generator based on classical adaptive backstepping technique. The sensorless control is shown using classic stator field oriented control which is used to active and reactive power control. Performance of the proposed algorithm of a speed observer is validated by simulation and experimental results obtained using a small-rating generator and bidirectional voltage source converter. The stability analysis of the presented solution with regard to observer gains changes is also considered.

In the paper, the kinematic structure of the transmission shaft between the driving motor and the working mechanism is studied. The analysis is based on electrical and mechanical similarities. The equivalent circuits, typical for electrical systems, are defined for the transmission shaft concerned. Modelling of the transmission shaft based on a formal analogy between the transmission shaft and the electric transmission line is also proposed. The results of a computer simulation and experimental test are presented. The results confirm the high conformity of the proposed mathematical model with the physical object.

This paper presents the research into the design and performance analysis of a novel five-phase doubly-fed induction generator (DFIG). The designed DFIG is developed based on standard induction motor components and equipped with a five-phase rotor winding supplied from the five-phase inverter. This approach allows the machine to be both efficient and reliable due to the ability of the five-phase rotor winding to operate during single or dual-phase failure. The paper presents the newly designed DFIG validation and verification based on the finite element analysis (FEA) and laboratory tests.

The development of the novel multiphase brushless doubly-fed generator system and voltage controller for stand-alone mode configuration is proposed in this paper. The generator system is based on the new machine construction with multiphase control winding and traditional three-phase power winding. The dynamic model of multiphase brushless doubly-fed generator is presented, and the control strategy for voltage amplitude and frequency is developed. The simulation and experimental results are used to validate the performance of the topology of the multi-phase brushless double-fed generator and of the control system. The tests of the generator system have been carried out for the normal operating state of the system and for the case where one of the control phase is inactive. This situation is equivalent to a failure in the power path of the control winding.

This article presents a multiphase doubly fed induction generator (MDFIG) with a dedicated and unique control algorithm in a stand-alone wind energy conversion system. The algorithm has been developed and elaborated in the case of different emergency modes. Compared with the traditional double-fed induction generator, the MDFIG has increased reliability, reduced current level per phase, and low rotor harmonic currents. The control system is based on a classical mathematical model and the stator field-oriented control method. However, especially for the wind turbine system, the control system has been extended for dedicated five-phase operation and additional scenarios have been added. First, the dynamic states of the generator operation under normal operating conditions with voltage variation and load were simulated and compared with laboratory tests. Second, the fault-tolerance results of rotor phase failures with different states and loads were presented. This performance is validated in the laboratory with a 4 kW prototype MDFIG. The method presented in this article is simple, robust, and cost effective with MDFIG and has significantly improved the reliability of the power generation system.