Z-源逆变器MPPT和逆变控制方法研究

Study on the Control Strategy of MPPT and Grid-connected Inverter for PV System Based on Z-Source Inverter

Z-源逆变器由于采用了独特的阻抗网络,能够利用桥臂的直通状态实现自由升降压,因此,可在单级系统中同时实现MPPT和并网逆变功能.本文分析了Z-源逆变器的升压原理,讨论了直通占空比和逆变调制因子之间的制约关系,并在此基础上设计了直通占空比d0和逆变调制因子M分别独立控制MPPT和并网输出功率的逆变控制方案.该方案通过给d0和M分别划出合理的取值范围,改善了d0和M的相互制约关系,有效抑制了电网和光伏模块的相互影响.通过实验验证,该方案能够有效跟踪光伏电池最大功率点;稳态工作时,输出电流与电网电压同相位,谐波畸变小,输出功率因数高.

With a unique impedance network,Z-source inverter（ZSI） can utilize the shoot-through state to boost/buck the output voltage freely,so it can realize MPPT and DC-AC grid-connected conversion simultaneously in a single-stage system.In this paper,the voltage boost/buck theory of ZSI is discussed and the relationship between shoot-through duty ratio and modulation index for ZSI is studied.Then this paper proposes a control strategy which uses shoot-through duty ratio d0 and modulation index M to control MPPT and the grid-connected conversion power separately.Through giving the range of d0 and M,this control strategy eliminates the mutual-limitation of the shoot-through duty ratio d0 and modulation index M and decreases mutual-influence between the PV array and the grid.The experiment is carried on and the experimental results verify that the Z-source inverter with the proposed control strategy can track the maximum power point effectively and the output current of ZSI can synchronize with the grid voltage faithfully.Besides the harmonics in the output current of ZSI have been improved greatly and the unit power factor is achieved.