Active Neutral Control – Perspectives on the Definition of Neutral, with Critical Discussion, and an Innovative Method for Implementation

Active neutral control for creating a neutral line in a 3 phase power system where a neutral line is not available, has been discussed in the literature to a good extent. Such systems are important in connection with utility and microgrids, especially where power electronics systems are involved, and where unbalanced loads are encountered. However, in the opinion of the authors of this paper, certain fundamental issues related to active neutral control are not well discussed in the literature. The intent of this paper is to provide perspectives on the definition of a “neutral” point in a 3-phase system through a thorough analysis, and to establish the necessary and sufficient conditions involved in the realization of an active neutral in general. After that, the authors describe an innovative method for creating such a neutral line, using appropriate power electronics and control methods. The method used by the authors is fundamentally thorough, and based on basic electrical circuit theory, and leads to significant reduction in the size of passive elements like capacitors and inductors, leading to overall packaging benefits, compared to what has been reported in the literature. The proposed methodology is straightforward to implement, employs innovative control techniques, performs reliably under severely unbalanced load conditions, and produces clean line-to-neutral voltage and current waveforms, with low total harmonic distortion (THD). The methodology has been validated through detailed modeling and simulation results, along with some experimental results, thus substantiating the theoretical basis presented in the paper. The authors had the need to use this system in connection with certain military defense applications involving electrified military-vehicle-based 3-phase power systems.