A Control Strategy for Grid-connected Inverters With LCL Filters

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。

Grid-connected inverters are normally connected to power grid through L filters or LCL filters to prevent the switching harmonics entering the supply network. In contrast with L filters, LCL filters can achieve reduced levels of harmonic distortion at lower switching frequencies with less inductance, and therefore have potential benefits for higher power applications. However, LCL filters are third-order systems without damping, which are easy to resonate; moreover, the LCL interfaced grid-connected inverter is instable when only the direct feedback control of the grid current is used. This paper presents a dual-loop control strategy based on grid current feedback and converter current feedback, which can be shown in Fig. 1.With the out-loop of grid current feedback, the grid current of the grid-connected inverter can be consistent with the grid voltage in phase, and easily render the current harmonics attenuation; the inner-loop regulated by converter current is adopted for active damping to stabilize the system, which is beneficial to protection of switches of inverters.