Research And Design Of Photovoltaic Grid-connected Inverter With LCL Filter

On the one hand, the output filter of the photovoltaic grid-connected inverter has a strong nature of the inductance, which guarantee the normal work of the photovoltaic grid-connected systems; on the other hand it can filter out some kinds of harmonics that not only have a bad influence on the performance of some important electrical equipments, but increase the power consumption of the system. Compared with L and LC filter, LCL filter not only has good high frequency filtering properties, but has the advantages of small volume, low cost, good dynamic performance and the lower power consumption. However, the resonance occurred by zero damping may lead to instability of system. for this problem, this paper presented the method of the combination between the passive and active damping control and weighted current control.On the basis of a lot of literature research, the work of this paper are following:(1) the paper analyzes comparatively how the inductance distribution coefficient and damping resistance impact on the stability of the system filtering effect, switch order harmonic attenuation ratio, damping value and the damping under the conditions that total inductance and the capacitance can meet the filter performances. Considering the inner link between inductance distribution coefficient, damping resistance and system performance, it optimizes the filter parameters that can satisfy the requirements of system performance,together with it gives the general optimization design method of the LCL filter parameters of different capacity of inverter system.(2) it builds the simulation model of the method proposed in the Matlab/Simulink simulation platform. By comparing different filter parameters and the total harmonic distortion of inverter side inductor current and grid-connected current and the phase relationship between grid-connected current and grid voltage of different control methods, it demonstrates that the proposed control method can satisfy the standard of the photovoltaic grid-connected system.(3) it designs a prototype that using the control method proposed, which include the hardware design and software design. Hardware design includes the main circuit design, the auxiliary power supply design, the drive circuit design, the control circuit design, the detection and protection design of DC bus voltage and filter currents and the zero detection circuit design, etc; Software design includes GPIO module, TIMER module, ADC module,SPWM model, the grid synchronization phase locked module, PI regulator module and the main function and so on.(4) it debugs prototype and gets the experimental waveforms. The results show that the presented control method is correct and effective.