Averaged modeling and analysis of multilevel converters

Abstract

Multilevel voltage-source converters (VSC) are attractive for high-voltage and high-power applications. However, the increased part counts and control complexity also complicate the converter modeling and control. One particular control problem is the balancing of dc capacitor voltages. Conventional voltage balancing control design has been based on periodic steady-state or line-cycle averaged models of the converter that don't correctly predict the capacitor voltage dynamics within a line cycle and under dynamic conditions. This paper develops an averaged model for three-level neutral-point clamped (NPC) converters that is valid under all conditions and involves switching-cycle averaging only. Unlike previous works, no assumption is made about the balance of ac line voltages, making the resulting model suitable for analysis and simulation of large, possibly unbalanced electric power systems. Applications of the model include more efficient system simulation, controller analysis and design for ac current regulation, dc bus voltage regulation and dc capacitor voltage balancing. Simulation results are presented to validate the proposed models.

Data-Driven Fault Localization of a DC Microgrid with Refined Data Input

“…By looking into the modulation transient, the switching model can detail the high-frequency circuit switching for a converter during a fault transient. Whereas the modulation process is assumed instant in an average model hence the ignorance of transients during a modulation cycle [19]- [21]. Therefore, a detailed switching model is being used in this research.…”

Interoperability of voltage source converters in dc grids

“…The converter switch model takes into account the transient associated with fundamental and harmonic currents and voltages, including the grid current contribution when the dc link is suppressed. The average converter model considers only slow transients of the fundamental voltage and current [32, 33, 36, 37], and generally cannot accurately represent the interaction between ac and dc networks. It is therefore not appropriate for fast transient studies, including dc faults.…”

Inverter modelling techniques for protection studies

“…harmonics) is lost [12]. Reference [12] states that the AVM is valid up to about one-third of the inverter switching frequency, while [16] states that the AVM is valid up to half of the switching frequency. In [15] an important condition is added: an AVM is only valid if the frequencies in the reference signal are much smaller than the resonance frequency of the filter.…”