基于永磁磁场调制的无刷双馈风力发电机及其系统研究

Doubly fed induction generator (DFIG) may operate in variable-speed constant-frequency, so it has the advantages of high energy coefficient, small capacity for converter which is far smaller than generator capacity, low cost and good speed-regulation performance. The DFIG has greatly promoted the technology of wind power generation in the past. However, the DFIG needs brush and slip ring and this causes some problem in reliability and regular maintenance is needed. In this case, the brushless DFIG becomes the research hotspot in China and overseas. This project proposes a new brushless DFIG system based on modulation of magnetic field for permanent magnet (PM). It adopts single steel iron structure for power winding and control winding at the stator. By setting deferent pole pairs for power winding and control winding, the direct coupling of two windings is avoided. The indirect coupling between the power winding and control winding is realized by using special double-rotor structure. Here the outer rotor is magnetic modulation rotor and inner rotor is PM rotor. The PM on the inner rotor provides the magnetization for the brushless DFIG. The magnetic field of the PM inner rotor is modulated by the outer rotor, and then the indirect coupling of power winding and control winding is realized. It not only settles the disadvantages of the traditional DFIG, such as complicated rotor structure, high harmonic distortions and low efficiency, but also permanent-magnetized the brushless DFIG. This improves the machine power density and power factor effectively. The successful undertaken of this project will lay the theoretical and application foundation for brushless doubly fed wind power generation system.

双馈感应风力发电系统可变速恒频运行，风能利用率高，变换器容量远小于发电机容量，具有成本低、调速性能好等优点，有力推动了风力发电技术的向前发展。但是，双馈感应电机的电刷和滑环降低了其可靠性且需要定期维护，为此，无刷双馈电机成为国内外研究热点。本项目提出了基于永磁磁场调制的无刷双馈电机及其系统，采用定子功率绕组和控制绕组共铁心的结构，定子两套绕组的极对数不相等消除直接耦合，通过特殊的双转子结构实现控制绕组和功率绕组的间接耦合，外转子为调磁环转子，内转子为永磁转子，永磁内转子为无刷双馈电机提供励磁，调磁环外转子对永磁内转子的磁场进行调制，实现功率绕组和控制绕组的间接耦合作用，既解决了传统无刷双馈电机转子结构复杂，谐波大，效率低等缺点，又实现了无刷双馈电机的永磁化，有效提高了电机功率密度和功率因数。本项目的成功开展将为无刷双馈风力发电系统的运行奠定理论和应用基础。

永磁磁场调制式无刷双馈发电机取消了传统双馈感应发电机的电刷和滑环，提高了系统可靠性，同时又实现了无刷双馈发电机的永磁化，兼具了无刷双馈发电机与永磁同步发电机的优点，如功率密度高、采用部分功率变化器等。.本项目提出了基于永磁磁场调制的无刷双馈发电机的基本结构，分析了其工作原理，并在此基础上完成了发电机的设计和优化，采用有限元法分析发电机的电磁特性，完成相关参数优化。试制了样机，完成了样机电磁参数的测试，验证了发电机理论设计和分析的准确性。对基于永磁磁场调制的无刷双馈风力发电系统的控制策略和数学建模进行了深入研究，对双馈风力发电系统的电网故障穿越能力进行了分析研究，包括弱电网中双馈发电系统动态性能的改善、低电压穿越能力的提升以及基于虚拟同步机技术的电网调频能力研究。以dSPACE1104控制器为核心，构建了基于永磁磁场调制的无刷双馈风力发电控制系统，完成了控制系统的软硬件设计，实现了基于永磁磁场调制的无刷双馈风力发电系统的变速恒频发电运行，实验结果证明了理论分析的正确性。