Development of low-cost adjustable -speed generator systems suitable for renewable energy sources

可调速绕线转子感应发电机广泛应用于风力发电，其二次功率通过电刷和滑环提取，由逆变器控制。这种二次励磁系统对逆变器的额定要求比定子功率控制系统小，而且经济。刷子和滑环需要定期保养。因此，由于发电机数量众多，在不久的将来可能会出现很大的维护问题。在我们的项目中，我们主要研究无刷二次励磁系统来解决上述维护问题。本文的主要研究成果如下：提出了一种新型的无刷级联式感应发电机，其二级感应发电机采用6相绕组和12脉冲二极管整流器。该系统可以很经济地解决检修问题和谐波电流污染问题。然而，可能需要更多的功率因数校正来补偿较差的功率因数特性。所提出的系统非常适合大功率应用。研制了一种双馈式磁阻式感应发电机样机并进行了试验。该发电机结构简单；它的转子没有绕组，只有一个带磁通屏障的铁芯，定子有不同极数的双三相绕组。实验发电机除功率因数较差外，具有良好的控制特性。一种新型绕线转子式感应发电机系统：传统绕线转子式感应发电机系统中的转差功率回收逆变器通过三相变压器与定子绕组并联。我们开发了一种新颖的系统，该系统将恢复逆变器与定子绕组直接串联，而不使用变压器。通过计算机仿真测试了系统的稳态特性，取得了良好的效果。在实际应用中，将进一步研究其瞬态特性。少

Adjustable-speed wound-rotor induction generators are widely used for wind power generation, in which the secondary power is extracted through brushes and slip-rings and is controlled by an inverter. This secondary excitation system requires smaller ratings of the inverter than those of stator power control systems and it is economical. The brushes and slip-rings need periodical maintenance. Therefore, a big maintenance problem may be occur in near future because a large number of generatoras.In our project, we have mainly studied brushless secondary excitation systems to solve the maintenance problem mentioned above. The major results of our research are as follows :1.Brushless cascaded induction generator systemsA newly developed cascaded induction generator has been proposed in which the second induction generator has a six-phase winding and a 12-pulse diode rectifier. This system can give very economical solution of the maintenance problem and harmonic current pollution. However, a … More power factor correction may be needed to compensate the poor power factor characteristics. The proposed system is well suited for large power applications.2.Brushless reluctance-type induction generatorsA proto type of the doubly-fed reluctance-type induction generators was built and tested. This generator has a simple structure ; its rotor has no windings and only an iron core with flux barriers, and the stator has double three-phase windings with different pole-numbers. The experimental generator has good control characteristics except for the poor power factor.3.A novel system of a wound-rotor induction generatorA slip power recover inverter in a conventional wound rotor induction generator system is connected in-parallel with the stator windings through three-phase transformers. We have developed a novel system in which the recovery inverter is connected directly in-series with the stator windings without using the transformers. The system steady-characteristics was examined with computer simulation and the good results were obtained. Transient characteristics will be studied in future for practical applications. Less