LCL滤波并网逆变器的控制策略

把LCL滤波器作为电压源型并网逆变器与电网的接口已受到广泛关注。与单电感L滤波器相比,利用电感值较小的LCL滤波器对入网电流的高次谐波具有显著的衰减效果,特别是在低开关频率的大功率并网逆变系统应用中更具明显优势,但是仅采用直接入网电流控制时,LCL滤波器接口的并网逆变器系统存在稳定性问题。该文采用电网侧电感电流和逆变侧电感电流双闭环控制策略对并网电流进行直接控制,电网侧电感电流作为外环更容易抑制并网电流的谐波因素,且可以直接控制入网电流的单位功率因数,采用逆变器侧电感电流作为内环可以增加系统阻尼,从而可抑制系统振荡,增加系统稳定性。对该方案进行系统建模,并深入分析了滤波器参数、控制器参数及系统稳定性之间的精确量化关系。仿真和实验结果表明,该控制策略既可有效抑制入网电流谐振和实现进网电流的高功率因数运行,同时又具有良好的稳态和动态性能。

A Control Strategy for Grid-connected Inverters With LCL Filters

The LCL type filter becomes an attractive grid interface for grid-connected voltage source inverters(VSI).In contrast with L filters,the LCL filter can attenuate effectively high frequency current harmonics by using smaller inductance than L type filter,and specifically,the LCL filter has obvious advantage in high-power grid-connected inverter with lower switching frequency.However,the system of the LCL interfaced grid-connected inverter is instable when only the direct grid-current control is used.This paper proposed a dual-loop control strategy for regulating the grid current directly,the strategy integrated an outer loop grid current regulator with inner loop bridge current regulation.The out-loop of grid current feedback could render the grid current harmonics attenuation and control the power factor of the grid current directly.The inner-loop by converter bridge current regulation was adopted for enhancing active damping and stabilizing the system.The relationship among resistances,control parameters and stability margins was quantified precisely based on system modeling and stability analysis.Simulation and experimental results prove that the proposed control strategy is feasible for grid-connected inverters with a LCL filter,the resonance of grid currents is avoided,a high in-grid power factor is achieved,and the grid-connected inverter system has very good dynamic and static properties.