Research On Three-level Control Strategies Of Brushless Doubly-Fed Machine

The Brushless Doubly-Fed Machine (BDFM) is a new type AC Induction Motor, which may realize the synchronization, asynchronization and double fed and more running modes. Due to the cancellation of electric brush and slip ring, it has some advantages like simple structure, solid and durable, adjustable power factor and low capacity of frequency converter and so on. The Brushless Doubly-Fed Machine is of extensive application prospect in the aspect of frequency conversion and speed adjustment system and the speed changing constant voltage and constant frequency electricity generating and so on. This dissertation focuses on the wound-rotor Brushless Doubly-Fed Machine as the research object, and studies the three methods of level control in its structure, basic operation principle and dynamic mathematical models, and then carries out the simulation experiment.The three-level inverter is of higher proof-pressure and high quality of output voltage waveform and more advantages, which is suitable for the high voltage and high capacity of alternating current governor system. Consequently, it has superior practical values and research meanings. This dissertation takes the Brushless Doubly-Fed Machine as the research object, and analyzes the three-level inverter’s control method theoretically, and executes the simulation and experiment testing and verification.This dissertation emphasizes on the research on wound-rotor Brushless Doubly-Fed Machine and the control strategy of three-level inverter, mainly including:Starting from the air-gap field principle of the Brushless Doubly-Fed Machine, It systematically analyze the running principle, introduce the fundamental structure of stator winding and rotor winding, in detail, analyze each operation status, at the same time, make deep analyses on the power flow direction of the Brushless Doubly-Fed Machine in different running conditions.It deduces and establishes steady state mathematical model of the Brushless Doubly-Fed Machine in the static abc coordinate system, and makes the transformation of coordinates for the steady state mathematics, establishes the dynamic mathematical model in the random d-q coordinate system, under the platform of simulation software, simulates and analyzes the dynamics of electrical machine mathematical model under the situations of single feeding and double feedings.It analyzes the principle of diode embedded three-level main circuit topology structure in detail, emphasizes on the introduction of modulation method of interspace vector pulse width modulation. Besides, it particularly analyzes the midpoint balance, output voltage change rate and voltage jump and other problems of three-level space vector, puts forward the synthetic method of improvement of voltage space vector, simplify the mass of trigonometric function calculation during the sector judge and action time of reference voltage sector, which verifies the correctness of theoretical analyses and effectiveness of methods via the simulation results.It introduces and analyzes the closed-loop control algorithm for the scalar quantity control and rotor field direction vector control algorithm of the Brushless Doubly-Fed Machine, introduces the working principles of three-level inverter direct torque control structure in detail. Additionally, it studies the stator flux linkage observational method in the direct torque algorithm, and carries out the deep analysis on the estimated performance, based upon which proposes a method to enhance the model self-adaption observation, moreover, it explores some other questions in the three-level inverters’ direct torque algorithm, like flux linkage and torque ripple, voltage jump and output voltage change ratio and the midpoint voltage excursion and so on. It improves the voltage space vector, comes up with the method of improved-type fixed vector synthesis, and makes the simulation study on the proposed three-level inverter’s direct torque algorithm, the simulation results show that, such algorithm can reduce the torque ripple and flux linkage pulsation, and then reduce the voltage jump, which is of higher application value hereby.Aiming to the issues of complex voltage vector solution, torque ripple and flux linkage ripple and more in the three-level inverter’s direct torque control system; it proposes the fuzzy control algorithm for three-level inverter of the Brushless Doubly-Fed Machine. By means of the fuzzy control algorithm, make the adjustments for the torque and ripple, and simulate them via the suggested algorithm, and the simulation results show that such algorithm can reflect quickly, simultaneously, it effectively reduces the flux linkage and torque ripple.Finally, it builds the three-level inverter experiment platform for the Brushless Doubly-Fed Machine based the DSP TMS320F2812 as the control core, and introduces the design method of each hardware module in the experiment platform, and then carries out the experiment research on the three-level inverter of Brushless Doubly-Fed Machine, offering the primary experiment results. The experiment results verify the correctness of the proposed algorithm.