Research On The Harmonic-Restraint Energy Feedback With LCL-Filter

Abstract:With the rapid development of society, the demand of electric power is growing quickly. So the energy recycling has become a hotspot in research of electric power. Energy feedback device can make the exorbitant direct voltage back to the power grid. However, large number of harmonics in grid voltage brings great difficulties to the design of high-performing energy feedback device. Therefore, research on the harmonic-restraint energy feedback with LCL-filter has great value in engineering application.Firstly, The mathematic models in abc and dq frame for three-phase energy feedback with LCL-filter are established and analyzed. And the complex coupling of mathematic models in dq frame is decoupled with detailed methods. A capacitor current feedback loop as the active damping is proposed to restrain the resonant peak in the current waveform which is caused by LCL-filter. The capacitor current loop and current loop in inverter side make up the current double closed-loop control strategy. The stability and rapidity of current double loop control system is analyzed particularly in the frequency characteristic, root locus characteristics, step response and the error frequency characteristic. However, current double loop control can not fully restrain the harmonics in output current. Therefore, the compound control technology based on the improved repetitive controller and current double loop control is used to control the energy feedback system. And the compound control technology is studied and analyzed in the stability, disturbance suppression, convergence and steady-state error characteristics of the system.The parameters in the compound control technology are the key in research of energy feedback system. Then, the simulation model of the three-phase energy feedback system with LCL-filter is build based on Matlab/Simulink platform. The compound control technology is proved to be superior than the current double-loop control through the comparison of harmonic analysis, current phase and the capacity of interference suppression.66charts,70references.