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Optimal pulse pattern with negative pulses and third harmonic mixed injection
Qinqing Zhang,Wenxiang Song,Tianqing Shui,Hongzhang Lyu 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.3
Adding negative pulses into a neutral-point clamped three-level inverter is an optimal pulse pattern (OPP) that can help restrain the neutral-point (NP) voltage fluctuation. However, this method can also cause the current harmonic distortion to be increased so that it becomes difficult to quantify the negative pulse width. Third harmonic injection can suppress neutralpoint potential fluctuation without increasing the switching frequency and it can also be automatically eliminated. Based on current harmonic minimization pulse width modulation (CHMPWM), a new optimal pulse pattern containing negative pulses and third harmonics is presented, which can inhibit NP voltage. Regarding the re-expression of the fundamental voltage expression, the optimal third harmonic content can be determined by constructing the analytical relationship between the fundamental voltage and the neutral-point current under the harmonic voltage. Combining this with a fitness function, sequence quadratic programming (SQP) is utilized to solve the new switching angles, which means that the CHMPWM is injected by negative pulses and third harmonics. Through simulations and experiments on a three-level inverter with a resistance-inductance load, it is verified that the proposed method can effectively suppress the voltage fluctuation at the neutral-point of the DC bus while taking the current harmonic distortion rate into account.