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Quantitative Comparison and Analysis of Different Power Routing Methods for Single-Phase Cascaded H-Bridge Photovoltaic Grid-Connected Inverter

The output power of each photovoltaic (PV) module is different in the single-phase cascaded H-bridge (CHB) PV grid-connected inverter due to irradiance intensity, ambient temperature, and aging degree of PV modules. When the PV modules are operating at their respective maximum power points, the corresponding dc-side voltages of the H-bridge units drift due to uneven power distribution, which will cause the maximum power point tracking failure. As a result, the grid current will deteriorate and even the system will become unstable. The power routing control methods based on fundamental voltage reconstruction, third harmonic injection and hybrid pulse width modulation can realize unequal power distribution between H-bridges to ensure the system stable operation. This article summarizes the abovementioned typical power routing control methods, derives the expressions of power routing ranges of different methods, then comprehensively and deeply compares the power routing capabilities of various methods qualitatively and quantitatively. The simulation results of a single-phase seven-level CHB PV grid-connected inverter demonstrate the validity of the theoretical analyses.