FOC And DTC Switching Control Research Of Asynchronous Motors Based On Adaptive Magnetic Linkage Observer

Asynchronous motors with the characteristics of simple structure in rotor, running steadily, convenient to maintain and inexpensive price, are applied widely in industry. As the main equipment which transforms electronic energy to mechanical energy, its control goal in practical application is: high transform efficiency and accurate performance of speed modulation based on mechanical technics. The motors speed modulation performance has effects on labor capacity and electronic energy conservation. Tremendous progress has been made for semiconductor technique and asynchronous motors mathematic model as well as its control technique. Many kinds of motors controllers with high precision, wide speed modulation range and high performance has been developed numerously. AC-drivers have occupied the lead-position of modern speed regulating system.Vector Control based on rotor Field Orientation Control (FOC) and Direct Torque Control based on stator field observation (DTC) are nowadays two mainstream control strategies in modern AC motion drivers. This paper summarizes the development, current situation and tendency of FOC and DTC. Research and project experience indicate that the two schemes have their own advantages and disadvantages. Various improvements have been proposed for these two control methods by many researchers. But these research results increase the complexity of system, whose engineering applicability practicability need to be tested, on the other hand have influences on the good characteristics of original system.An innovative control strategy, which is a combination of the two schemes, is presented in this paper which adopt one's advantages and meanwhile can offset the other's weakness and switch in the two control schemes easily. The suitable control strategy can be switched flexibly and on-line according to practical applications. The research point of this paper is to avoid system state changing largely and to keep switching smoothly. The following is main contents of research in this paper:(1) Firstly, mathematic model of asynchronous motors is discussed, basic coordinate conversion theory is expounded and module design of coordinate conversion in Matlab/simulink is made. Then mathematic model of asynchronous motors in two-phase coordinate is analyzed. Basing on this the theories of the DTC and FOC control systems are introduced, and configurations of the two control systems are given at last.(2) In order to guarantee the system of high performance, the parameters of motors must be estimated on-line. The stator and rotor resistance as well as rotor inductance estimation systems are attained by analyzing parameter identification based on the research of asynchronous motors mathematic model and vector control theory. Then the gain of controller is properly chosen according to Routh-Hurwitz criterion to guarantee estimation system convergency. Also a arithmetic of the proposed MIMO adaptive parameter estimation is demonstrated by simulation.(3) In terms of magnetic linkage observation, adaptive magnetic linkage observers of stator magnetic and rotor magnetic are designed respectively by paying attention to both performance and complexity, the principle is the transition between voltage model and current model of respective magnetic linkage according to motors speed. The switching signal is motors speed. Then transition between the two models is analyzed.(4) The simulation environment of FOC and DTC is build based on previous chapters using Matlab/Simulink, then contrastive simulation experiments are carried out. The basic idea of FOC and DTC switching control is formed according to comparing FOC with DTC control strategies and their respective suitable working condition. The solution in which PI controllers are reset using previous state of the system by corresponding relation at the switching moment is proposed based on the fluctuation of direct-switching between the two control strategies. The validity of switching control strategy proposed in this paper is demonstrated by the simulation results.