Fundamental frequency switching strategies of a seven-level hybrid cascaded H-bridge multilevel inverter. Power Electronics

Abstract—This paper presents a cascaded H-bridge multilevel inverter that can be implemented using only a single dc power source and capacitors. Standard cascaded multilevel inverters re-quire n dc sources for 2n + 1 levels. Without requiring trans-formers, the scheme proposed here allows the use of a single dc power source (e.g., a battery or a fuel cell stack) with the remaining n − 1 dc sources being capacitors, which is referred to as hybrid cascaded H-bridge multilevel inverter (HCMLI) in this paper. It is shown that the inverter can simultaneously maintain the dc voltage level of the capacitors and choose a fundamental frequency switch-ing pattern to produce a nearly sinusoidal output. HCMLI using only a single dc source for each phase is promising for high-power motor drive applications as it significantly decreases the number of required dc power supplies, provides high-quality output power due to its high number of output levels, and results in high con-version efficiency and low thermal stress as it uses a fundamental frequency switching scheme. This paper mainly discusses control of seven-level HCMLI with fundamental frequency switching con-trol and how its modulation index range can be extended using triplen harmonic compensation. Index Terms—Fundamental frequency modulation control, hy-brid cascaded H-bridge multilevel inverter (HCMLI), triplen har-monic compensation. I