Design And Drive Control Of Dual-stator Brushless Doubly-FED Machine

With the steady improvement of level of electrification, the requirements on the electric machine.which is the device for electromechanical energy conversion, tend to be diversified and fine-grained.Besides the conventional direct current machine (DCM). induction machine (IM) and synchronous machine (SM), a large variety of new machine structures continuously emerge, and various methods for analysis of specific machine topologies are proposed. In general, the existing analysis theories lack universality and unity, and features fragmentation. In the meanwhile, without powerful theoretical guidance, the innovation of machine topology is confronted with blindness. contingency, overreliance on empirical knowledge and low efficiency. This dissertation aims to establish an analysis theory to unify the topological analysis, electromagnetic design, and structure innovation of conventional and newly-emerged electric machines by studying machines with dual-electrical-port feature based on the widely-observed airgap field modulation phenomenon. With the guidance of the established theory, a comprehensive and complete set of analysis, comparison, improvement and optimization of existing brushless doubly -fed machines (BDFMs) is conducted, showing its effectiveness and superiority.The research results of this dissertation are as follows:1. The state of the art of BDFMs are comprehensively overviewed in terms of structure and working principle, analysis and design metlhod, and application and control strategy. The approaches to eliminate brush gears are for the first time summarized as permanent magnet excitation, cascading and modulation. And correspondingly, the BDFMs are categorized into two families, that is,the cascading type and the modulation type.2. Based on the derivation of the classical winding function theory (WFT),it is found that there are in total three ways to modify the airgap magnetomotive force (MMF) distribution. i.e., induction,reluctance and barrier, and the corresponding physical devices are short-circuited coil, simple-salient pole and multi-barrier. On the basis of the similarities in frequency domain between the electromagnetic machine and the switching converter. the generalized airgap field modulation theory is proposed, in which the behaviors of short-circuited coil, simiple-salient pole, and multi-barrier in modifying the airgap MMF distribution is characterized by modulation operators, transforming any concrete electrical machine into a unified equivalent airgap model. Tlie modulation phenomena that are widely observed in a vast variety of electrical machines are classified into synchronous (static)modulation and asynchronous (dynamic) modulation. Conventional DCM, IM and SM primarily make full use of synchronous modulation and try to suppress asynchronous modulation; whilc most newly-emerged machines strive to enhance and work by asynchronous modulation.3. The no-load airgap field distribution and inductance characteristics of three main BDFMs and flux-switching permanent magnet (FSPM) machine which is just a special case of BDFMs with doubly-salient structure, single-phase concentrated field winding, three-phase fractional-slot concentrated armature winding and natural synchronous operation are analytically analyzed with the generalized airgap field modulation theory. The working principles of various modulators, that is short-circuited coil, simple-salient pole and multi-barrier are comprehensively analyzed and compared.4. The dynamic equivalent circuit models of the three main BDFMs are developed based on the spiral vector theory to reveal the model consistency and the parameter difference. Based on the model consistency, the common features, like the conditions for doubly-fed synchronous operation,available operation modes and their torque compositions, marginal operation region, are explored;based on the parameter difference, the influence of rotor impedance on cross-coupling capability.torque composition and control complexity are analyzed, and the model hierarchy of BDFMs are established.5. Based on the derivation of conventional machine sizing method, it is pointed out that the conventional method is not suitable for machine topologies with multi-port and/or multi-harmonic features. So new sizing method based on the dual-electrical-port machine is developed by clarifying the four key definitions in conventional machine design, that is. specific electric loading, specific magnetic loading, efficiency and power factor. Based on the generalized airgap power sizing equation, the torque density equations of three primary BDFMs are derived and numerically erified. The comparison of BDFMs in terms of torque density based on the derived torque density equations when effective rotor volume, specific electric loading and specific magnetic loading are kept the same revealing that BDFMs suffer from much lower torque density compared with conventional IM, and the root causes are explained. The global iron saturation mechanism of machines working by synchronous modulation and asynchronous modulation are analyzed and the corresponding mathematical descriptions are formulated.6. The BDFM with dual-stator structure is proposed based on the comparison of existing BDFMs in terms of torque density. With the guidance of generalized airgap field modulation theory . numbers of available rotor structures are proposed and qualitatively compared, and the dual-layer wound rotor structure is eventually chosen to keep a high torque density. The design, manufacturing and testing procedures are established. To apply dual-stator brushless doubly-fed induction machine (DS-BDFIM)in EV/HEV application, a prototype rated 7.5 kW is designed, manufactured and tested under steady state. verifying the effectiveness of the developed design method.7. The two-converter-based operation of BDFMs is proposed from the perspective of improving torque density and control flexibility by making full use of the dual-electrical-port feature of BDFMs. Two control methods, i.e., single-electrical-port (SEP) control and dual-electrical-port (DEP) control are proposed by configuring the two-converter-based drive system with master/slave and parallel architectures. Experimental verifications are implemented on the test platform based on dSPACE1103/4 controller board.8. The steady-state generating operation of DS-BDFIM is investigated, revealing that the influence of concrete application on the requirements on BDFM itself, namely, the DS-BDFIM designed for motoring application is not suitable for generating application, and vice versa, which is quite different from conventional DCM. IM and SM with a single electrical port physically.9. Based on the study of steady-state generating operation of DS-BDFIM. a design optimization process is implemented on DS-BDFIM with two different optimization goals, that is, maximum torque per volume (MTPV) and maximum torque per weight (MTPW). An engineering prototype rated 10 kW is designed and optimized, taking mechanical considerations and steady temperature rise into account.Compared with DS-BDFIM in motoring application, the power machine is designed more saturated in desired operating region while the control machine less saturated to perform higher regulating capability of magnetic field so as to suit generating operation.