Control And Design Of LCL-VSR

As the application of voltage source rectifier with single L used in new energy generation,APF,UPFC, the problems such as high switching frequency,efficiency,capacity,cost have restricted it's development. While VSR adopted LCL can solve these problems. However it's character of third-order filter greatly affects control system and system stability. So the study of LCL-VSR focus on parameter design,control strategy of stability improvements optimum design of control system.According to the disadvantage of L-VSR, LCL-VSR is presented. Firstly the equivalent circuit and math model of the LCL-VSR is established. And then, the frequency-domain character of LCL is analyzed. All these provides theoretical basis for control strategy analysis,stability analysis,system design and so on.According to control strategy based on L-VSR, control strategy of LCL-VSR is led out. Because of resonance frequency of LCL, damping control strategies are studied. The most simple method is called Passive Damping(PD). PD has simple configuration and high reliability at the price of a reduction of efficiency. So the use of active damping which means generating a negative harmonic peak to eliminate the positive of the system seems more attractive. Active Damping will not generate additional loss, but more sensors are needed. So AD control strategy without voltage sensors are also studied.Parameter design, one of the most important issues in LCL-VSR, is discussed. The influence of parameter change is also studied. The parameter design regulation is introduced considering power rate of VSR,current response,harmonic elimination.The whole design procedure is given out. Z-domain design is analyzed in order to solve the limitations of s-domain design. General z-transformation is presented according to non-integral cycle of DSP control algorithm.The low-frequency model is adopted according to frequency range of control system. Control configuration of inner current loop and outer voltage loop are deduced and designed by the use of z-plane root locus. While the high-frequency model is adopted to analyze it's stability. And the influence of parameters about PD and AD change to inner current loop performance is also analyzed.In this thesis, a 15KVA LCL-VSR experimental system is established. The grid current results,capacitor voltage with or without AD based lead network, the influence on grid current when parameter of AD changes, the comparison result of converter current and grid current, the dynamic response of different operation conditions are given. The experimental results verify the effectiveness of the system design.