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Abstract:In this paper, a novel modulation function-based method including analyses of the modulation index and phase is proposed for operation of modular multilevel converters (MMCs) in high voltage direct current (HVDC) transmission systems. The proposed modulation function-based control technique is developed based on thorough and precise analyses of all MMC voltages and currents in the a-b-c reference frame in which the alternating current (AC)-side voltage is the first target to be obtained. Using the AC-side voltage, the combination of the MMC upper and lower arm voltages is achieved as the main structure of the proposed modulation function. The main contribution of this paper is to obtain two very simple new modulation functions to control MMC performance in different operating conditions. The features of the modulation function-based control technique are as follows: (1) this control technique is very simple and can be easily achieved in a-b-c reference frame without the need of using Park transformation; and (2) in addition, the inherent properties of the MMC model are considered in the proposed control technique. Considering these properties leads to constructing a control technique that is robust against MMC parameters changes and also is a very good tracking method for the components of MMC input currents. These features lead to improving the operation of MMC significantly, which can act as a rectifier in the HVDC structure. The simulation studies are conducted through MATLAB/SIMULINK software, and the results obtained verify the effectiveness of the proposed modulation function-based control technique.

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a b s t r a c tNatural analogs offer a valuable opportunity to investigate the long-term impacts associated with the potential leakage in geological storage of CO 2 .Degassing of CO 2 and radon isotopes ( 222 Rn-220 Rn) from soil, gas vents and thermal water discharges was investigated in the natural analog of Campo de Calatrava Volcanic Field (CCVF; Central Spain) to determine the CO 2 -Rn relationships and to assess the role of CO 2 as carrier gas for radon. Furthermore, radon measurements to discriminate between shallow and deep gas sources were evaluated under the perspective of their applicability in monitoring programs of carbon storage projects.CO 2 flux as high as 5000 g m −2 d −1 and 222 Rn activities up to 430 kBq m −3 were measured; 220 Rn activities were one order of magnitude lower than those of 222 Rn. The 222 Rn/ 220 Rn ratios were used to constrain the source of the Campo de Calatrava soil gases since a positive correlation between radon isotopic ratios and CO 2 fluxes was observed. Thus, in agreement with previous studies, our results indicate a deep mantle-related origin of CO 2 for both free and soil gases, suggesting that carbon dioxide is an efficient carrier for Rn. Furthermore, it was ascertained that the increase of 222 Rn in the soil gases was likely produced by two main processes: (i) direct transport by a carrier gas, i.e., CO 2 and (ii) generation at shallow level due to the presence of relatively high concentrations of dissolved U and Ra in the thermal aquifer of Campo de Calatrava.The diffuse CO 2 soil flux and radon isotopic surveys carried out in the Campo de Calatrava Volcanic Fields can also be applicable to geochemical monitoring programs in CCS (Carbon Capture and Storage) areas as these parameters are useful to: (i) constrain CO 2 leakages once detected and (ii) monitor both the evolution of the leakages and the effectiveness of subsequent remediation activities. These measurements can also conveniently be used to detect diffuse leakages.

In this work, we modeled and simulated the electric potential generated by point charges in the region of grounded conductor planes for Yukawa poten- with different values of µ . We observe that the electric potential decreases as the value of µ increases and that does not allow all the charge to be distributed on the surface of the conductor.