Study On Control Strategy Of Machine Side Three-level Converter Of The Direct-driven PMSG System

With the continuous development of the industry, the human society has developed toan unprecedented height, especially in the industrial areas, far more than the same periodof history. However, accompanied by a series of remarkable achievements, the problem ofenergy shortage is getting worse and worse. The world’s main consumption, including coal,oil, natural gas and other fossil fuels are depleted. Thus, people gradually turn their gaze tothe inexhaustible natural resources. Wind power is one of the representatives, it is not onlyclean, but also very safe and reliable, getting more and more people’s attention nowadays.In recent years, there are a variety of wind turbines. The most important representativesare DFIG (doubly-fed induction generator) and PMSG(permanent-magnet synchronousgenerator). This paper researched the converter of machine side of the direct-drive windpower system. After the theoretical analysis of the system, the operation of the rectifierwere simulated in different situations, and built a rectifier system platform, in which theexperiments were carried out to verify the correctness of the early theory and simulation.Firstly, in the theoretical analysis aspect, the work is mainly about the establishmentof mathematical model. Including the PMSG’s and the diode-clamp three-level circuit’smathematical model under the three-phase stationary coordinate system and the two-phasesynchronous rotating coordinate system. The paper also analyze the working process ofthe main circuit topology and the modulation method. Secondly, the control strategy of thediode-clamp three-level circuit has been analyzed and the double-loop PI regulator hasbeen designed under the two-phase synchronous rotating coordinate system. The controlstrategy can achieve the stable output of the DC side and complete unity power factorcontrol. At the same time, this paper analyzed the problem of the midpoint voltageimbalance which is the inherent problem of the diode-clamp three-level rectifier, andproposed the solution. Then, according to the characteristics of the direct-drive windpower system, the amplitude and frequency of the three-phase permanent magnetsynchronous generator electromotive force change with the change of the generator’srotating speed. Therefore, in the case of this, the system was simulated in the simulation with mutative frequency and mutative amplitude in order to achieve stable operation underdifferent conditions. Finally, by using MATLAB/Simulink, the simulation of the systemcontrol strategy and the regulator is validated, and the experiments were implementedthrough TMS320F28335DSP and EP3C25Q240C8N FPGA. The result of simulation andexperiments proved that the system control strategy and the regulator were available andaccomplished the related tasks.