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An Optimized Third Harmonic Compensation Strategy for Single-Phase Cascaded H-Bridge Photovoltaic Inverter

Due to the unequal solar radiations or dust accumulation of photovoltaic modules in a single-phase cascaded H-bridge photovoltaic inverter, the unbalanced output power among photovoltaic modules will make the H-bridges with higher power overmodulation, resulting in deteriorated grid current. Concerning this issue, this paper proposes an optimized third harmonic compensation strategy that injects moderate amount of third harmonic into the overmodulation H-bridges to keep the amplitudes of their modulation waveforms just being unity, then compensates the same amount of opposite harmonic sequence and properly distributes it to rest of the H-bridges. The proposed method can ensure that all the power units will be free from overmodulation under some heavy power imbalance conditions and will not increase the third harmonic component of the grid current. The validity and effectiveness of the proposed method is verified by simulation and experimental results.