Research On The Control Of Single-phase Cascaded Multilevel Photovoltaic Grid-Connected Inverter

Cascade multi-level inverter has the advantage that the output voltage harmonic content is low, the output filter volume is small and the electromagnetic immunity is strong, Which is contribute to reduce the volume of photovoltaic grid system, increase system efficiency and reduce costs, that makes it has broad application prospects in the photovoltaic field. In this paper, we study at single-phase hybrid cascade seven level and inverter, on the basis of analysis the modulation method of inverter, proposed a variable modulation method based on the technique of carrier vertical phase shift modulation, and study the grid-connected PV systems based on hybrid cascade seven-level inverter.Firstly, the paper introduces the current research situation of PV grid-connected inverter. For topology of cascade multi-level inverter, focus on both the single-phase cascade seven-level inverter and the hybrid cascade seven-level inverter, through compare their topology and output voltage characteristic, choose the single-phase cascade seven-level inverter as our research object.Secondly, the paper elaborates the modulation method of the hybrid cascade seven-level inverter, include staircase EPWM and multicarrier SPWM, and introduce their implementation process and advantages and disadvantages. According to technology of vertical phase shift modulated carrier, put forward the modulation strategy that variable frequency triangular carrier and adjacent carrier phase contrast. The simulation verifies the modulation method can achieve seven-level output voltage, and avoid the occurrence of the current intrusion.Thirdly, study the grid-connected PV systems based on hybrid cascade seven-level inverter, describes the output characteristic of photovoltaic cells, and its maximum power tracking technology used in principle, the control strategy of PV grid-system voltage and current inner outer combine. At the end, the paper introduces the PV grid-system experiment design based on hybrid Cascade seven-level inverter.