LLCL滤波的单相光伏并网逆变器控制技术研究

采用新型LLCL滤波器对单相光伏并网逆变器进行滤波，LLCL滤波器通过在传统LCL滤波器的电容支路中串联一个小电感达到在开关频率处产生串联谐振，相比LCL滤波器能够更大程度地对串联谐振频率处的电流谐波进行衰减，可进一步减小总电感值。分析表明LCL滤波器双电流环控制同样适用于LLCL滤波器，并网电流外环采用带谐波补偿的准比例谐振(PR)控制器能够有效跟踪并网电流指令的同时可对特定次谐波进行补偿，但谐振控制器在谐振频率处存在180°相角跳变，随着谐波补偿的次数增加易导致系统不稳定。在准PR控制器之后增加一个超前校正环节，对谐振频率处进行相位补偿的同时能够提高系统的相位裕量，增强系统稳定性。此外，引入电网电压前馈控制增强系统对电网电压的抗干扰能力。仿真结果表明系统具有较好的稳态性能和抗干扰性能。

LLCL filter based single-phase photovoltaic grid-connected inverter control strategy

A new filter, named LLCL, is used for filtering the output current of single-phase PV grid-connected inverter. It is realized by inserting a small inductor in the branch of the capacitor of LCL filter to generate a series resonant circuit at the switching frequency. Compared with LCL filter, LLCL filter can attenuate the series resonant frequency current ripple components much better and can further reduce total inductance value. Dual current loop control for LCL filter also applies to LLCL filter. The quasi PR controller with harmonic compensation in the out loop of grid current can effectively track the grid current instructions and compensate the particular harmonic. But the resonant controllers have a 180° angle jump at the resonant frequency, and with the increasing numbers of harmonic compensation, it can easily make the system instable. Therefore, a leading correction link is added after the quasi PR controller to compensate the phase at the resonant frequency. At the same time, it can improve the phase margin of the system and enhance the system stability. To enhance the grid voltage anti-interference capacity of the system, grid voltage feed forward strategy is utilized. The simulation results show that the system has good steady state performance and the anti-interference performance.