纯永磁型高速交流发电机及其变流稳压技术的研究

High-speed ac generator solely with permanent magnet excitation has many advantages. It is usually processed with a diode-rectifier and then other further power converter(s). Due to the high winding reactance, the generator output voltage varies significantly with the load, limiting its power capability. In this project, it is proposed to utilize a PWM rectifier to realize vector control, so as to regulate the generator internal field (either weaken or strengthen the field) with the d-axis current and to stabilize the output voltage. The field regulation capability is subject to the generator parameters, whilst the efficiency and power density are influenced by the field regulation. Thus, the field regulation capability as well as the matching of the generator parameters will be studied, and so will be the determination of the d-axis current polarity and magnitude, in order to achieve the voltage stabilization and to enhance the system overall performance. Secondly, regular power devices have a switching frequency close to the fundamental frequency of the high-speed generator, thus, during each electric cycle, the switching times is not sufficient, and the waveform of phase currents and the locus of flux-linkage vector are both distorted, consequently, the rectifier performance is deteriorated. Therefore, specific topologies of the generator and the PWM rectifier will be studied coordinately, in order to achieve a higher equivalent switching frequency through the cooperation of the specific generator and rectifier. Finally, based on the specific topologies, the system mathematic model as well as the vector control implementation will be studied. This project aims to solve the problems of high reactance of the high-speed PM generator and insufficient switching frequency of the PWM rectifier, and to prepare for a theoretic foundation of the applications of this kind of generator system.

纯永磁型高速交流发电机具有诸多优点。通常利用二极管整流再作其他变流。由于绕组感抗大，发电机输出电压随负载显著变化，限制了输出电功率。本项目拟采取PWM整流进行矢量控制，通过d轴电流实现电机内磁场调节（弱磁或增磁）进而稳压。磁场调节能力取决于电机参数，且电机效率、功率密度等亦受影响。所以将研究发电机应具备的磁场调节能力以及各参数的相互匹配规律，研究d轴电流极性与大小的确定方法，在满足变负载稳压的前提下优化系统综合性能。其次，常规功率器件的开关频率与高速发电机基波频率接近，在一个电周期内斩波次数太少，电流波形和磁链圆畸变，整流性能差。对此，将协同研究发电机和PWM整流器的特殊拓扑结构，通过二者合理匹配实现更高的等效开关频率。再次，针对所得出的特殊拓扑结构，研究系统数学模型和矢量控制实现方法。本项目将解决高速永磁发电机感抗大、PWM整流器开关频率不够高等技术难点，为该类发电机系统的应用打下基础。

纯永磁型高速交流发电机具有高效、高功率密度等优点，配合可控整流系统可以实现稳压输出，具有广阔的应用前景。现有纯永磁型高速交流发电机系统的常见结构是发电机的交流输出经二极管整流和DC/DC 变换，为直流负载供电或者再逆变为交流电源。 但这种方式存在的问题是：由于基波频率高、发电机绕组感抗大，因此，采用二极管整流时，绕组感抗上的压降随负载而显著变化，由此造成很大的发电机电压调整率，限制了发电机的输出功率。本项目利用PWM 整流技术，采取矢量控制方式调节感应电势来补偿绕组感抗压降随负载的变化。主要技术障碍是：高速发电机的基波频率很高，而常规的PWM 整流器的开关频率有限、与基波频率接近，因此在一个电周期内的斩波次数不足，无法调制出期望的绕组电流，故矢量控制性能差，整流后的直流电压纹波明显。.本项目针对其技术障碍，从控制方法、电机本体、功率电子电路等方面进行了协调优化研究，探索并阐明了在高速工况下通过矢量控制实现永磁交流发电机稳压时发电机本体参数与性能需要具备哪些特质，由此为发电机本体设计提供理论基础，针对高速工况下变负载稳压的要求，研究矢量控制中轴电流的极性、大小的确定原则，在达到稳压目的的同时优化电机效率等综合性能。提出特殊的PWM 整流器与发电机的拓扑结构，除了PWM整流器具备矢量控制功能、发电机具备前述研究所得的特质外，还要通过二者的匹配来克服功率管开关频率接近发电机基波频率的问题，研究了改进型两电平、模块化多电平变流器和双三相永磁同步电机的拓扑结构。通过控制方法、电机本体与功率变换器的协同设计和优化，实现纯永磁型高速交流发电机及变流系统的变负载稳压运行，解决了现有实际系统所存在的问题，为其实用化创造了条件。