Research On Voltage Sensorless Control Method Of Grid Converter

The distributed generation on account of environment-friendly and renewable superiority,fed into the grid or converted for being stored and used in other place,will develop rapidly in application of grid-connected.It also may cause quality issues for traditional power grid with design and operation stability.Power converters have some outstanding characteristics in real-time and efficient controlling,will play an important role in future developments of the grid system based on smart technology.These are of great significance for expansion of renewable energy source and the safety of distribution network by transforming renewable energy into an electrical one efficiently and flexibly.Firstly,this dissertation presents the mathematical model and basic control strategy of the three-phase voltage PWM converter.Particularly,the application of the instantaneous power theory in the power conversion device and the control strategy of voltage orientation under the natural coordinate are analyzed in comparison to the voltage sensorless control strategy.Then,the research on the control strategy of the voltage sensorless is studied systematically,including the voltage sensorless control method based on the virtual motor flux linkage,the voltage sensorless control method based upon the second-order generalized integral filter or the third-order generalized integral filter.The model of converter is constructed by average theory and duty-cycle signal instead of traditional switching signal to proof sensorless method for voltage observation based on the theory of generalized integral.Moreover,compared with these three kinds of voltage sensorless methods,employing the fast Fourier transforming to analyze harmonic distortion rate of the estimated voltage signals,the estimation voltage based on generalized integral theory is superior in accuracy.The estimation voltage by three-order generalized integral filter also shows its outstanding characteristic for suppressing the DC component,when a certain amount of DC offset component is added to the experimental in the same condition.Finally,based on dSPACE,a grid-connected converter experiment platform is built and the three voltage sensorless control strategies are described.The results of the comparative analysis show that the directional control could be operated well in the natural coordinate system based upon the estimation voltage obtained by the three voltage sensorless methods.These voltage signals based on the generalized integral method are better than that based on the virtual motor flux linkage method with smaller harmonic distortion rate and better accuracy,and the voltage estimation method based upon the third-order generalized integral filter has pretty good performance in DC component rejection.