Research On Asynchronous Motor Drive Control System Under Low Speed

After decades of development asynchronous motor drive has achieved a lot. In foreign countries,ensuring control performance and significantly reducing production cost further consolidate marketcompetition advantages of their control products. Throughout development of domestic controllers,high-performance drive applications still mainly depend on permanent magnet motors. Due to thetension of rare earth resources, permanent magnet material price sustains rising. Although permanentmagnet motor controllers possessing superior performance, the high cost and ongoing maintenancerestrict its market competition advantage. Consequently, high performance asynchronous controllershave much room for development and research.On Basis of Comprehensive understanding the development and principle of asynchronousmotor drive in this thesis, a series of studies are launched about high-performance vector controlstrategies. Firstly, the relations and differences of vector control directional modes are summarized toestablish a unified model from perspectives of the circuit. Secondly aim at its precise orientation anddecoupled problem between dq-axis of indirect stator flux oriented method. Namely, calculate leakagemagnetic real-time through q-axis current component to decouple and also the feedback from closedloop based on stator error is introduced to q-axis branch to ensure accurate orientation. Then furtherquantitatively analyze stator flux observer error under low speed and flux-weakening is proposed toimprove low-speed observed effects of stator flux u-i observer. Also a detailed theoretical analysisand argumentation is presented to realize flux-weakening under different low-speed conditions.Matlab simulation model is established to validate proposed control method in this paper. Afterverifying the feasibility of strategies, low speed operation and load running are tested at the5kWasynchronous motor experimental platform in laboratory. Experiments and simulations both certifythat optimized stator flux orientation maintains excellent dynamic and static performance at low speed.Compared to the conventional u-i observer, the ability of observing accurately under low speed isachieved after flux weakening, which also expands observation scope.Simulations and experimental verifications reach desired results and verify effectiveness ofcontrol methods, which provide several ideas for high-performance asynchronous drive with furtherresearch and development potential.