Hybrid Overmodulation Strategy of Dual Two-Level Inverter Topology Enabling 12-Step Operation

This article introduces a novel overmodulation strategy tailored for dual-inverter topologies with galvanically isolated dc-links and evenly distributed dc-link voltage. The core contribution of this article is the utilization of the multilevel capabilities of the dual-inverter topology. At the maximum modulation index, the presented overmodulation method achieves what is referred to as a 12-step operation. The 12-step operation improves the voltage waveform and offers superior harmonic performance compared to the conventional 6-step operation. The utilized approach leverages a hybrid space vector pulsewidth modulation (SVPWM) method, a well-established technique in two-level inverters, to achieve this extended operation range. Furthermore, this article presents a nonlinear gain compensation characteristic vital for real-time motor control applications and provides a comparative analysis of the modulation's harmonic performance. The proposed approach is validated through simulations and experiments. The experiments were conducted using a custom inverter based on Gallium-Nitride transistors where simple volt/hertz control of an induction motor was programmed. The results of these experiments affirm the strategy's effectiveness, showcasing superior current waveform quality and a smooth transition from linear mode to 12-step operation while keeping a simple implementation of the algorithm.