Hybrid multilevel power conversion system: a competitive solution for high-power applications

TLDR

Power semiconductor technology faces a trade‑off between switching frequency and voltage‑sustaining capability, and recent converter topologies enable modular multilevel inverters that synergistically combine IGCTs and IGBTs. This study investigates a hybrid multilevel power conversion system designed for high‑performance, high‑power applications. The 4.16 kV/spl ges/100 hp system comprises a hybrid seven‑level inverter (high‑voltage IGCT slow‑switching and low‑voltage IGBT fast‑switching), a diode bridge rectifier, and an IGBT rectifier per phase that regulates power flow and mitigates harmonics, and it uses a hybrid modulation scheme that blends stepped synthesis with variable pulse‑width and a multilevel current‑regulated delta modulator, with performance confirmed by simulations and experiments. The results demonstrate that deploying IGCTs and IGBTs under appropriate operating conditions optimizes the overall power conversion capability of the system.

Abstract

Trends in power semiconductor technology indicate a tradeoff in the selection of power devices in terms of switching frequency and voltage-sustaining capability. New power converter topologies permit modular realization of multilevel inverters using a hybrid approach involving integrated gate commutated thyristors (IGCTs) and insulated gate bipolar transistors (IGBTs) operating in synergism. This paper investigates a hybrid multilevel power conversion system typically suitable for high-performance high-power applications. This system, designed for a 4.16 kV/spl ges/100 hp load is comprised of a hybrid seven-level inverter, a diode bridge rectifier, and an IGBT rectifier per phase. The IGBT rectifier is used on the utility side as a real power flow regulator to the low-voltage converter and as a harmonic compensator for the high-voltage converter. The hybrid seven-level inverter on the load side consists of a high-voltage slow-switching IGCT inverter and a low-voltage fast-switching IGBT inverter. By employing different devices under different operating conditions, it is shown that one can optimize the power conversion capability of the entire system. A detailed analysis of a novel hybrid modulation technique for the inverter, which incorporates stepped synthesis in conjunction with variable pulsewidth of the consecutive steps is included. In addition, performance of a multilevel current-regulated delta modulator as applied to the single-phase full-bridge IGBT rectifier is discussed. Detailed computer simulations accompanied with experimental verification are presented in the paper.