In this paper, a generalized pulse width (PW) modulator is proposed which can control three-leg center-split voltage source inverters (VSIs) and four-leg VSIs from two-level to multilevel topologies. VSIs with a neutral wire connection are important for power electronics applications in three-phase four-wire systems, such as active power filters and uninterruptible power supplies. For medium and large capacity applications, a multilevel three-phase four-wire VSI is a good alternative to a

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... vel one. However, implementing the pulse width modulation for three-phase four-wire VSIs involves complex calculations, and control algorithms differ for VSIs of different levels and topologies. The proposed generalized PW modulator controls VSIs based on voltage-second approximation, but its implementation is much easier than space vector modulation. Field programmable gate array has been chosen to implement the PW modulator due to its fast prototyping, simple hardware, and software design. Simulation and experimental results are provided. The proposed generalized PW modulator was also applied to the control system of three-phase four-wire active power filters to show its validity. Index Terms-Active power filter, four-leg voltage source inverter, three-leg center-split voltage source inverter (VSI), three-phase four-wire. He has published two books and more than 100 papers. He has been engaged for more than 30 years in education and research work on electric power systems and the automation field. In recent years, he has engaged in FACTS and DFACTS, intelligent control, regional stability control, new dynamic security estimation, and control based on GPS. Dr. Han received four State-level prizes, and six first and second ranked Province-level and Ministry-level prizes. He is a Member of Chinese Academy of Engineering. Authorized licensed use limited to: Universidade de Macau. Downloaded on June 18,2010 at 01:31:42 UTC from IEEE Xplore. Restrictions apply.