Abstract-The Brushless Doubly-Fed Generator (BDFG) shows the great potential for use in large variable speed wind turbines due to its high reliability and cost benefits of a partially-rated power electronics converter. However, it suffers from the compromised efficiency and power factor in comparison with conventional doubly fed induction or synchronous generators. Therefore, optimizing the BDFG, especially the rotor, is necessary for enhancing its torque density and market competitiveness. In this paper, a novel cage-assisted magnetic barrier rotor, called the hybrid rotor, is proposed and analyzed. The detailed analytical design approaches based on the magnetic field modulation theory are investigated. In addition, the machine losses and mutual inductance values using the proposed rotor designs are calculated and their performance implications evaluated. Finally, the comparative experimental results for two BDFG prototypes are presented to verify the accuracy and effectiveness of the theoretical studies.
This paper presents the simulation and experimental evaluation of a novel power error comparison direct power control (PEC-DPC) strategy of the open-winding brushless doubly-fed reluctance generator (OW-BDFRG) for wind energy conversion systems (WECSs). As one of the promising candidates for limited speed range application of pump-alike and wind turbine with partially-rated converter. The emerging OW-BDFRG employed for the proposed PEC-DPC is fed via dual low-cost two-level converters, while the DPC concept is derived from the fundamental dynamic analyses of the calculated and controllable electrical power and flux of the BDFRG with two stators measurable voltage and current. Compared to the traditional two-level and three-level converter systems, the OW-BDFRG requires lower rated capacity of power devices and switching frequency converter, though have more flexible switching mode, higher reliability, redundancy and fault tolerance capability. The performance correctness and effectiveness of the proposed DPC strategy with the selected and optimised switching vector scheme are evaluated and confirmed on a 25 kW generator test rig. Index Terms-Brushless doubly-fed wind power generators, open-winding, direct power control, dual two-level converters. I. INTRODUCTION T HE brushless doubly-fed (reluctance) generators (BD-FGs) ,  have some essential features in dealing with issues related to reliability and maintenance operation in long-running variable speed constant frequency (VSCF). Such advantages are due to their robust structure since carbon brushes and slip-rings are eradicated. Moreover they adopt a similar doubly-excited feature similar to doubly-fed induction generators (DFIGs). The BDFGs have evolved from DFIGs but moved the rotor winding to the stator, thus characterised by two standard distributed three-phase stators with different Manuscript
This paper presents the theoretical derivation and implementation of a novel direct power control for open-winding brushless doubly-fed reluctance generator (OW-BDFRG). As one of the promising brushless candidates, the OW-BDFRG is characterized with two stator windings fed by a dual controllable two-level three-phase converters through a common DC bus with common mode voltage elimination. The parameter-free control strategy is designed to obtain maximum power point tracking with variable speed constant frequency (VSCF) for wind energy conversion systems (WECSs). Compared to the traditional three-level converter systems, the DC bus voltage, ACside voltage and capacity ratings of the proposed converter system are notably high while the reliability, redundancy and fault tolerance are significantly improved. Effectiveness, correctness and robustness of the proposed control strategy and the common mode voltage elimination scheme are evaluated and confirmed through simulation and experimental tests on a 42 kW generator prototype typical for VSCF-WECS. Index Terms-Brushless doubly-fed machines, power control, common mode voltage, open-winding, variable speed constant frequency, maximum power point tracking. NOMENCLATURE u p , u c Power, control winding phase voltages [V] i p , i c Power, control winding phase currents [A] R p , R c Power, control winding resistances [Ω] p p , p c , p r Power, control and rotor pole pairs L p , L c Power, control winding self-inductan. [H] ψ p , ψ c Power, control winding flux linkages [Wb] ψ pc , L pc Mutual flux [Wb] and inductance [H] f p , f c , ω p , ω c Power, control winding frequencies [Hz] and their angular frequencies [rad/s]
--In this paper, a new open-winding control strategy is proposed for a brushless doubly-fed reluctance generator (BDFRG) used for standalone wind turbine or ship generators. The BDFRG is characterized with two windings on the stator: a power winding and a control winding. The control winding is fed with dual two-level three-phase converters, and a vector control scheme based on space vector pulse width modulation (SVPWM) is designed. Compared to traditional three-level inverter systems, the dc-link voltage and the voltage rating of power devices in the proposed system are reduced by 50% while still greatly improving the reliability, redundancy and fault tolerance of the proposed system by increasing the switching modes. Its performance is evaluated by simulation in MATLAB/SIMULINK, and an experimental study on a 42-kW prototype machine.Index Terms--Brushless doubly-fed reluctance generator (BDFRG), dual two-level converters, open-winding, space vector pulse width modulation (SVPWM).
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