| Brushless doubly-fed machine(BDFM)is a kind of novel AC induction machine evolved from self-cascade induction machine.It has two sets of independent stator winding and rotor winding with a special design.BDFM has many advantages: elimination of the brush and slip ring in the rotor results in firm structure and high reliability.The control winding connected to the fractional power converter regulates speed or the output voltage amplitude and frequency,by changing its input voltage amplitude and frequency,which can obtain smaller converter capacity,adjustable power factor.With its operation reliability and the advantages of the system efficiency,BDFM has a broad application prospect in the VSCF,large water pump and frequency control of motor speed operation.This paper takes the wound-rotor brushless doubly-fed machine as the object,starts from the motor structure and presents the basic operation principle and operating characteristics of BDFM.Under a series of ideal assumptions,this paper established the three-phase stationary coordinate model of BDFM.Based on the coordinate transformation,the mathematical model under the unification d-q coordinate system at the power winding synchronous speed is deduced for transient behavior study and control strategy research.Then under the guidance of mathematical model of BDFM,one-phase equivalent circuit is declared as a basis for the motor stability analysis,from which power distribution and energy flow is carried out.Analysis of BDFM operating state in independent power generation and research on the control method suitable for this application comes next.First using the software MATLAB,the simulation results prove the correctness of the mathematical model under the unified d-q coordinate system,then we fully understand the relationship between the internal physical quantities in the independent power system.Based on mathematical model the double closedloop power decoupling control strategy including the power winding voltage amplitude and frequency is derived.Then the simulation is carried out to verify it can effectively meet the operation requirements of independent power generation condition.Furthermore,in order to improve the response speed when operates under the impact load such as an asynchronous motor,a control strategy with current feed-forward compensation is proposed.Then the speed sensor-less control of BDFM is proposed to avoid the rotor position sensor damage under the bad environment,which will cause system failures,further enhances the operation reliability of the system.According to the working condition of independent power generation,model reference adaptive speed estimation method based on the control winding flux linkage is presented.Using the real-time measurement feedback of stator winding voltage and current,the speed estimation model is established under the guidance of model reference adaptive system(MRAS),including reference model,adjustable model and the adaptive control mechanism.In order to solve the low measure precision when machine runs near the natural synchronous speed,the control winding high-frequency voltage injection speed estimation method is carried out,which is only related to magnetic field relations but not affected by the mathematical model and machine parameters.Finally,the experiment research is proposed on the experimental platform of woundrotor brushless doubly-fed machine independent power generation.Simulating the independent power operation,active load and motor load mutation experiment is put forward.Analyze and summarize the result of these experiments,verify the effectiveness of the proposed closed-loop decoupling control strategy and the speed sensor-less control. |
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