Enhanced instantaneous power theory for control of grid connected voltage sourced converters under unbalanced conditions
Alves Montanari, Allan
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This thesis introduces a new method especially designed to control the instantaneous power in voltage sourced converters operating under unbalanced conditions, including positive, negative and zero sequence content. A transformation technique, labelled mno transformation, was developed to enable the decomposition of the total instantaneous power flowing on three-phase transmission topologies into constant and oscillating terms. It is applied to three-wire and four-wire schemes, especially accommodating zero sequence unlike previous approaches. Classical and modern electric power theories are presented, particularly focusing on their definitions for adverse AC scenarios. The main mathematical transformations conceived to analyze such situations are summarized, showing their respective advantages and disadvantages. An enhanced instantaneous power theory is introduced. The novel proposed power equations, named mno instantaneous power components, expands the application of the p-q theory, which is attached to the αβ0 transformation. The mno instantaneous power theory is applied to develop an innovative power control method for grid connected voltage sourced converters in order to minimize power oscillations during adverse AC scenarios, particularly with zero sequence content. The method permits to sustain constant instantaneous three-phase power during unbalanced conditions by controlling independently the constant and the oscillating terms related to the instantaneous power. The effectiveness of the proposed control approach and the proposed power conditioning scheme was demonstrated using electromagnetic transient simulation of a VSC connected to an AC system.
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