Harmonic Suppression Of Three-phase Voltage-source Rectifier With LCL-filter

The three-phase voltage-type PWM rectifier with L-filter is usually used in theback-to-back PWM converter of direct-driven wind power generation system. Withthe rectifier capacity being increased quickly, a series of disadvantages were presentedin L-filter, which could be solved by choosing a high value inductance. But that willmake the system expensive and bulky. Moreover, the dynamic performance of thesystem becomes poor with so high value of inductance. On the contrary better filtereffectiveness can be obtained by adopting an LCL-filter with less inductance, whichtook the place of L-filter and applied widely in medium-high power rectifier.Firstly, topological structure and mathematical model of the three-phasevoltage-type PWM rectifier based LCL-filter are established in the paper. Secondly,transfer function of the single-phase model has been discussed thoroughly, to obtainthe relation among resonance frequency, harmonic current amplitude attenuationfactor and factor r-the ratio between grid-side and rectifier-side inductance. The totalinductance, capacitance of filter and r can be selected by analyzing the changetendency of the variable relation figures. A designed example is reported and thesimulation models of the three-phase voltage-type PWM rectifier based voltageoriented control strategy is established，in which the direct current control strategy ofthe rectifier-side current feedback is used. The proposed method, empirical valuemethod and solving the2-order algebraic equation method are analyzed by simulationmodels, simulation results are included to show the validity of the proposedmethod.Finally, the resonance for introducing the LCL-filter could lead to reduce thesystem stability, both new passive damping (based on the use of resistance) and activedamping (based on the modification of the control algorithm) is mentioned in thepaper. The four methods of introducing series or parallel resistance in inductor andfilter capacitor have done a comparative analysis, its advantages and disadvantageshave been discussion by the bode diagram of MATLAB. Then some virtual resistancemethods have been studied using the simulation models, the results indicate that themethod of parallel resistance in filter capacitor is optimal.