Comparison of cell selection methods for modular multilevel converters

Electric Power Systems Research

2017

Self Cite

Multi-terminal high voltage dc (HVdc) grids can eventually became a feasible solution to transport energy to remote and/ or distant areas and its exploitation depend, among other things, on the performance of the converter terminals. Therefore, to optimize the power transmission strategy along such a grid, it is necessary to recognize the efficiency of all the converters in all points of operation, namely with the different load conditions. In this vision, the aim of this work is to provide the methodology to model the modular multilevel converter (MMC) efficiency by means of a mathematical expression that can describe, over a broad range of active and reactive power flow combinations, the power losses generated by the semiconductors. According to the presented methodology, a polynomial-based model with a reduced number of coefficients is deducted, in such a way that can be directly used for optimal power flow (OPF) studies. The accuracy of the proposed model is characterized by an absolute relative error, at the worst scenario, approximately equal to 3%.Postprint (author's final draft

Modular multilevel converter losses model for HVdc applications

Antonio-Ferreira

Electric Power Systems Research

2017

Self Cite

HVDC-based modular multilevel converter in the STATCOM operation mode

Antonio-Ferreira

2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe)

Teixido³

2016

In a futuristic vision, deeply interconnected ac and dc networks are expected, which would be restructured over the time in order to maximize the power transmission efficiency. In some grid configurations, grid-tied inverters can eventually become islanded from the dc grid by means of breakers and enhancing those converters with the static synchronous compensator (STATCOM) functionality can increase their value. In this context, there is an extra degree of freedom, which is the voltage drop that should be targeted between the dc poles of the converter. Due to the modular multilevel converter (MMC) flexibility, the converter energy storage and the average voltage generated in the converter arms can be managed to achieve some goals as the converter efficiency and ac power quality increase, conjointly with the voltage ripple reduction on the capacitor values. This work analyzes the referred degrees of freedom of the converter control and the correspondent impact on the converter operating performance.Postprint (published version

Adaptive discontinuous zero sequence signal for modular multilevel converter applications

Antonio-Ferreira¹,

2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe)

Teixido³

2016

This work proposes a technique to inject a discontinuous zero sequence signal (D-ZSS) into voltage modulation of the modular multilevel converter arms. The core of the technique is the clamping of the arm voltages to a particular level and interval, in such a way that reduces the number of switching events on the instants that the load stress on the semiconductors is high, and consequently the dissipated energy. The clamping voltage and interval has some degrees of freedom which are also discussed. The description of the methodology is complemented with its simulation. Either in steady-state or in dynamic converter operation this technique is able to reduce the switching events and the correspondent total losses up to 6.6%. Hence contributing to a more efficient VSC-HVdc solution.Postprint (published version