| The electrical power generated by renewable energy such as wind, solar can not be connected to the country grid directly, it need electronics device such as converter to improve the power quality. The traditional rectifier connected to the grid through an inductor L filter, but the filtering effect of the L filter isn't satisfied when the L value is small. Increasing the L value can improve the filtering effort but exasperate the stability and the response speed of the system. M.Lindgren and J.Svensson introduce to use LCL filter instead of L filter for the first in 1995. according to the bode diagram of LCL filter, the LCL filter has a faster amplitude attenuation in high frequency range which means that it can achieve a good filtering effort by small L value. But it will bring resonance by some special frequency signal which will make the system unstable.This paper introduce the mathematical model of rectifier with LCL filter first, according to the model, the controlled plant is a high order, strong coupling system; then the single phase mathematical model of the system has been introduced, analyze of the resonance has been done and the resonance frequency can be got according to the single phase model. This paper gave the harmonic attenuation function of LCL filter and analyse the filtering effort for high frequency by the function. This paper design the LCL filter with intelligent optimization such as genetic algorithm (GA) and particle swarm optimization (PSO) in MATLAB according to the traditional design method. Compare the two methods, the PSO is more simple since it don't need the cross and mutation operation. It found the global optimization solution through find the current optimization solution. The calculation proved that PSO has a better convergence. Then an overview of damping methods of LCL filter is present in this paper including active damping and reactive damping. The reactive damping method is to connect a damping resistor in series or parallel with the capacitor to eliminate the resonance which will produce loss. So the active damping method became a popular topic at present. Active damping is to realize the damping effort by the control method. It added the complexity of control strategy to avoid the loss. The traditional led-lag net active damping is complicate to design; virtual resistor in series with capacitor is simple but it the virtual resistor will decrease the filtering effort in high frequency area; this paper present a new damping method named virtual resistor in parallel with capacitor. This method is simple also and the filtering effort on high frequency area is same with the no resistor filter. The simulation result by MATLAB/SIMULINK proved the validly of this method. At last, this paper design the internal model control (IMC) of the rectifier with LCL filter. IMC has the advantages such as easy on line calculation, good tracking performance, strong robustness, the ability of anti-disturbance; easy to realize in practical and fit well with the multi-variable non-linear, strong coupling system. The control strategies in this paper are based on gird voltage oriented vector control and two loop structure including voltage outer loop and current inner loop. The voltage outer loop is used to DC voltage, and the current inner loop control can use controller in d-q rotating frame orα-βstationary frame. The controller in d-q rotating frame including PI and 1-order IMC can track the dc signals without static error. So it can control the active power and reactive power directly but it needed the rotating coordinate transformation and inverse transformation. The controller inα-βstationary frame including PR and 2-order IMC can track the ac signals without error, so no coordinate transformations are needed. It can also be used to eliminate special order harmonics. The simulation and experiment result prove the validly of the four controller.
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