| Being considered as one of the most significant power quality problems,in micro-grid,harmonic pollution is originated from various types of micro source,a large number of converters and nonlinear loads.In order to improve the quality of power supply,the mechanism of harmonic generation in micro-grid is analyzed in detail in this thesis.On the basis of this,the harmonic control method is studied from the following aspects.The control method of APF is researched at first in this thesis.For the case where specialized filter is needed,a deadbeat predictive direct power control(DPC)strategy for APF is proposed.Real time tracking of the reference values for the next period is realized in each sampling period according to deadbeat predictive model.The control signal for APF is originated from SVPWM to ensure the switching frequency steady.The control strategy is improved subsequently to eliminate the tracking error,meanwhile,the feedback correction based on integral function of the internal model principle is adopted.Moreover,the control method is simulated and analyzed by Matlab/Simulink.Simulation results illustrate that the capability of dynamic tracking and harmonics suppression in APF is improved through the proposed control strategy.In order to reduce the investment of specialized filters and improve economic performance of micro-grid,an integrated control strategy for energy storage system of micro-grid at island status is presented in this thesis according to the similar topology of main circuit between energy storage device and APF.Accordingly,the frequency adjustment and harmonic suppression can be achieved simultaneously in the proposed system.The integrated control method is simulated and analyzed by Matlab/Simulink,and the feasibility of the proposed control strategy is verified by the simulation results.According to multi-harmonic source in micro-grid,the active suppression possibility of harmonic cooperative control is explored to reduce the capacity requirement of the filter.Furthermore,the principle of co-governance is analyzed from the perspective of current,and the conclusion that for harmonic source in constant power mode,the phase angle of harmonic current varies with corresponding power.Consequently,it is observed and verified by Matlab/Simulink simulation and experiments.Simulation results demonstrate that there exists mutual elimination among specified harmonics while the multi-harmonic source are working simultaneously in a certain range of power change.In this thesis,the proposed three methods diversifies in economic performance and complexity of control strategy.Besides,the presented methods are complementary with the others,which can be referenced for the harmonic control in the planning and construction stage of micro-grid. |
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