A Three-level Inverter Neutral Voltage Balancing Control Method

Owe to three-level inverter mature topological structure and low harmonic content of output voltage, it has been applied widely in large power and high voltage applications, but three-level topological structure leads to an inherent problem that is the neutral potential imbalance. This paper analyses the intrinsic causes in neutral voltage imbalance and presents the voltage balance method based on a hysteresis loop control. According to the different combinations of load current direction, the method controls two-capacitor voltage dynamically by adjusting the small redundant vectors and fully considering the effect of medium vectors on the neutral point potential balance. The paper analyses the switching states choice, the order of switch sequence and allocation of time in detail when the reference voltage vector falls into small triangle having one or two redundant small vector. Simulation and experimental results show that the control method can achieve a good neutral point voltage balance.

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W artykule przedstawiono analizę zagadnienia regulacji napięcia punktu neutralnego w przekształtniku trójpoziomowym. Opracowana metoda regulowania napięć na kondensatorach DC-link bazuje na regulatorze histerezowym i znakach prądów fazowych. Odpowiedź regulatora decyduje o doborze odpowiednich stanów łączników (wektory krótkie). Wyniki symulacyjne i eksperymentalne potwierdzają skuteczność algorytmu.