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Brushless doubly fed generator (BDFG), a class of adjustable-speed machine with a special structure, shows great prospect in wind power generation. Since different rotor structures lead to great differences in the BDFG performance, the research of BDFG rotor structure has been a hotspot. However, only a few of the research studies have paid attention to the rotor and stator slot combination of the BDFG, especially for the BDFG with a novel hybrid rotor. Improper slot combination will lead to efficiency decrease, additional loss increase, and undesirable torque in an electrical machine. In order to study the principle of slot combination of the BDFG with the hybrid rotor, the combination approach of theoretical analysis and experiments is presented in this paper. Furthermore, a coupling factor which reflects the coupling ability of the BDFG with different slot combinations is proposed. Moreover, the best slot combination of the proposed BDFG is determined, and several parameters such as useful harmonic contents, total harmonic voltage distortion (THDu), core loss, and copper loss are considered as major criteria for judgment. [ABSTRACT FROM AUTHOR]

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. 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 optimized switching vector scheme are evaluated and confirmed on a 25 kW generator test rig. [ABSTRACT FROM AUTHOR]

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, ac-side 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Compared with the commonly used generators, the brushless doubly fed generator (BDFG) has a commercial potential for wind power generation due to its inherent characteristics. In this paper, a novel BDFG with hybrid rotor is proposed and its structural features and operation principle are presented. Meanwhile, the performance of the proposed BDFG is analyzed in comparison with the BDFG using a radial laminated magnetic barrier rotor. Furthermore, due to the complexity of the magnetic field and the particularity of the structure, the calculation and analysis of the parameters, especially the inductance, are extremely important for the performance analysis of the proposed BDFG. Therefore, an inductance calculation method based on modified winding function is investigated. For accurate inductance calculation, the effects of magnetic layers and cage bars on the air-gap permeance of the proposed hybrid rotor are both considered. Tests are performed on a 25 kW prototype machine to verify the performance of the proposed BDFG. The experimental results show the correctness and feasibility of the proposed inductance calculation method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel open-winding brushless doubly-fed reluctance generator (OW-BDFRG) with dual two-level converters in order to reduce the converter rating and switching frequency for large-scale wind turbine applications. The new converter topology is equivalent to a three-level converter directly connected to the control winding of typical BDFRG. The OW-BDFRG system with this topology structure requires lower converter rating and switching frequency, and has a more flexible control mode, better operation performance, and fault redundancy capability. For the OW-BDFRG, this paper also proposes a new control scheme combining direct power control (DPC) with sliding mode variable structure (SMVS) control to implement the power tracking. The voltage-vector switching table of DPC is redesigned according to the error signals of active and reactive powers of the power winding, as well as the sector location of control winding flux. The active and reactive powers of the OW-BDFRG can be directly decoupled and independently controlled by properly selecting the switching voltage vectors. The novelty of this paper lies in an OW-BDFRG topology driven by dual two-level converters to improve the system characteristics, and the use of SMVS control to improve the DPC accuracy and robustness to parameter variations. Finally, the effectiveness of the proposed system is verified through simulation and experimental studies. [ABSTRACT FROM AUTHOR]

Electrically excited synchronous machines with brushes and slip rings are popular but hardly used in inflammable and explosive environments. This paper proposes a new brushless electrically excited synchronous motor with a hybrid rotor. It eliminates the use of brushes and slip rings so as to improve the reliability and cost-effectiveness of the traction drive. The proposed motor is characterized with two sets of stator windings with two different pole numbers to provide excitation and drive torque independently. This paper introduces the structure and operating principle of the machine, followed by the analysis of the air-gap magnetic field using the finite-element method. The influence of the excitation winding’s pole number on the coupling capability is studied and the operating characteristics of the machine are simulated. These are further examined by the experimental tests on a 16 kW prototype motor. The machine is proved to have good static and dynamic performance, which meets the stringent requirements for traction applications. [ABSTRACT FROM PUBLISHER]

In this paper, a new open-winding control strategy is proposed for a brushless doubly fed reluctance generator (BDFRG) used for stand-alone 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 pulsewidth modulation is designed. Compared with 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. [ABSTRACT FROM PUBLISHER]

Electrolytic capacitors are extensively used in power converters but they are bulky, unreliable, and have short lifetimes. This paper proposes a new capacitor-free high step-up dc–dc converter design for renewable energy applications such as photovoltaics (PVs) and fuel cells. The primary side of the converter includes three interleaved inductors, three main switches, and an active clamp circuit. As a result, the input current ripple is greatly reduced, eliminating the necessity for an input capacitor. In addition, zero voltage switching (ZVS) is achieved during switching transitions for all active switches, so that switching losses can be greatly reduced. Furthermore, a three-phase modular structure and six pulse rectifiers are employed to reduce the output voltage ripple. Since magnetic energy stored in the leakage inductance is recovered, the reverse-recovery issue of the diodes is effectively solved. The proposed converter is justified by simulation and experimental tests on a 1-kW prototype. [ABSTRACT FROM PUBLISHER]