Hybrid Overmodulation Strategy for Dual Two-Level Inverter with Arbitrary DC-Bus Voltage Distribution

This paper introduces an innovative overmodulation strategy for a dual two-level inverter topology featuring galvanically isolated DC-links and accommodating arbitrary distribution of DC-bus voltages. In such a configuration, the uneven distribution of DC voltages gives rise to 12 additional fundamental voltage vectors compared to the conventional two-level inverter, effectively enabling the topology to function as a five-level inverter. The primary innovation of our proposed method lies in its ability to transition from linear modulation to what we term an 18-step operation – an improved multilevel square-wave operation of the inverter. This extended operational range is achieved through a hybrid space vector PWM approach, a well-established technique in the context of two-level inverters. Moreover, this paper presents a crucial nonlinear gain compensation characteristic essential for real-time control applications. To validate the effectiveness of our approach, we conducted experiments using a custom 15-kW GaN dual inverter. These experiments included the implementation of a straightforward V/Hz control of a 12-kW induction motor supplied by the dual inverter. The results of our experiments confirm the strategy's effectiveness, demonstrating superior current waveform quality and a seamless transition from linear modulation mode to the 18-step operation.