Technology Of LCL-filter Based On PWM Rectifier

As a common power electronic device, The PWM rectifier can be used astransmission of electrical power, traction of the locomotive, energy storage, powerdistribution, power quality regulation and the new energy. With the increase of thepower level, the single-L filter will not meet the requirement of power quality and thecost effectiveness. In order to decrease the inductance, it is necessary to add acapacitance between the two inductances. The LCL-typed filter can reduce theinductance and attenuate harmonic current. But the LCL filter can cause theresonance between the inductance and the capacitance. It can influence the stableoperation of the PWM rectifier system. So it is necessary to use the damping of theresonance oscillation.This paper firstly presents the architecture of LCL filter PWM rectifier. And themathematical model was established based on the Kirchhoff equation. According tothe mathematical model of the PWM rectifier, the transfer function was analysed toshow the cause of the resonance oscillation based on the Bode Graph.In order to attenuate current harmonic and meet the requirement of the controlsystem, the parameters of LCL filter must be considered comprehensively. A step-by-step designed rule was presented in this paper. Through the simulation software, theeffect of each parameters in the filter was analysed in the end. Then this paperpresent the deadbeat theories and the deadbeat control system was designed for theLCL-type PWM converter. Concerning the resonance of the LCL filter, the passivedamping of resonance and the active damping of resonance could make the systemstable. But the passive damping of resonance could bring about the energy lossbecause of the resistance heating. The active damp concept could use the virtualresistance instead of the real resistance in order to avoid the energy loss. Althoughthe virtual resistance could reduce the current ripple, another current sensor wasneeded in the circuit. It would make the system unstable. So a sensorless active dampconcept was introduced in this paper.An experimental platform was built based on the dSPACE half-simulationsystem. The parameters of the filter was choesd through out the rules presented inthis paper. The results from an experiment with the600W load could verify thecontrol system can attenuate the harmonic current and the reduce de current ripplebecause of the resonance in LCL filter.