The paper describes multi-level topologies contain two ways of paralleling inverters and multiple inverters. When inverters in parallel, it is important to restrain the circulating current effectively. It proposes a control strategy to eliminate circulating current and analyses the impact of parameters on the control system. When inverters in multiple, it is important to improve the output voltage amplitude. Because IGCT' switching frequency is a few hundred hertz, in order to eliminate harmonics, multi-levels SHE-PWM is proposed. On this basis, a 150KVA unit composed of two 75KVA NPC inverters was set up. As shown in experiment result, good performance is attained.
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