基于重复控制的三相NPC光伏并网逆变器研究

由于三相光伏发电系统易被死区效应、非线性负载等周期性扰动影响，使输出电流波形失真；三电平NPC逆变器工作时中性点电压偏移，也会降低系统输出电能质量。针对以上问题，提出采用电流PI闭环控制以及重复控制相互结合的复合控制方法，基于内模原理的重复控制可以有效地抑制光伏系统中的周期性干扰；并且九段法SVPWM调制方法把每个采样周期分成九小段，开关时序彻底对称，在每一个大区都选取同样的正小矢量首发，符合所有三电平NPC逆变器开关时序的设计要求，且通过闭环控制冗余小矢量的实时调整，使中性点电压平衡，有助于降低输出电流的谐波含量。仿真结果表明基于复合重复控制的三相光伏并网逆变器的九段法空间矢量调制可以在平衡中性点电压的同时，使得逆变器输出电流具备更好的稳定性，谐波含量更少，并网电流能够很好地跟踪电网电压，实现相同的频率和相位，使有功功率全负荷输出。

Research on Three-phase NPC Inverter Based on Repetitive Control

Since the three-phase photovoltaic system was susceptible to dead time effect, non-linear loads such as periodic disturbances would cause the output current waveform distortion. When three-level NPC inverter was working, the offset of neutral point voltage would reduce the output power quality of the system. To solve these problems, a complex control which combines the current PI closed loop control with repetitive control was proposed. The repetitive control based on internal model principle can effectively suppress periodic disturbances of the photovoltaic system. Meanwhile the nine-segment SVPWM divided a sample period into nine sections and increased the action time of small vector. The switch sequence was completely symmetrical and the same positive small vectors were adopted as first active vectors. And a closed-loop control system was proposed to control the neutral-point potential in real time, which was helpful to reducing harmonic content of the output current. Simulation results show that three-phase photovoltaic inverter based on composite repetitive control with using nine-segment SVPWM can not only balance the neutral-point potential but also make the output current have a better stability and less harmonic content. And the output current can have a good track to the grid voltage to achieve the same frequency and phase, which make the active power output at full load.