Research On Control Strategy Of Matrix Converter And Its Application In Brushless Doubly-fed Wind Power System

Compared with traditional converter, matrix converter (MC) is a novel structure "green" direct AC-AC power converter without intermediate DC link. MC possess the abilities of bidirectional power flow, sinusoidal input/output, adjustable input power factor, etc.. MC has been extensively applied in the adjustable speed doubly-fed system and wind turbine.Topology, mathematical model and the basic working principle of matrix converter were studied. In the analysis of indirect space vector control strategy, the simulation model of matrix converter based on this strategy was built, output line voltage, input(output) line current waveforms and spectrum analysis chart were given. Simulation results showed that the indirect space vector control can make the matrix converter voltage utilization reach maximum (86.6%) and realize the arbitrary control of the input current phase difference without the introduction of low-frequency harmonics in the output phase voltage.The basic theory of closed-loop control strategy was analyzed, a closed-loop control model of matrix converter was built and simulated on the Matlab/Simulink platform, output line voltage, input line current and output line current waveforms of matrix converter were given. Compared the simulation results of closed-loop strategy and indirect space vector strategy, we can know that the waveforms of closed-loop control algorithm are more smooth, harmonic content is smaller. These verified the closed-loop control strategy has a good control performance.A closed-loop control strategy with feed-forward compensation was proposed to ensure matrix converter operating in safe and stable mode under abnormal grid voltage conditions. The space vector modulation factor was adjusted in real-time according to the variation of the virtual dc link voltage to realize feed-forward compensation. In order to achieve negative feedback closed-loop control of the output voltage, the discrepancy between the actual and expected output voltage was added into the switch modulation matrix as a negative feedback during the next sampling period. Simulation results indicated that the distortions of waveforms of the output voltages and input(output) current can be effectively suppressed and the harmonic components can be obviously reduced when the proposed closed-loop control strategy with feed-forward compensation was adopted. The control scheme verified that MC with good dynamic and steady state performance and strong robustness to the input unbalance.The basic structure and operational principle of BDFM were analyzed. BDFM variable speed constant frequency power scheme has been researched. The experimental platform of matrix converter excitation brushless doubly-fed wind generator system was constructed and related experiment was conducted. Experimental results demonstrated the feasibility of matrix converter excitation brushless doubly-fed wind generator.