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Common mode behavior in grid connected DC and AC decoupled PV Inverter topologies

D. John Sundar M. Senthil Kumaran
Archives of Electrical Engineering | 2016 | vol. 65 | No 3 September | 481-493 | DOI: 10.1515/aee-2016-0035
Keywords distributed generation common mode leakage current solar PV systems transformerless PV inverters
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Abstract

The transformer-less grid connected inverters are gaining more popularity due to their high efficiency, very low ground leakage current and economic feasibility especially in photovoltaic systems. The major issue which surfaces these systems is that of common mode leakage current which arises due to the absence of an electrical transformer connected between the inverter and the utility grid. Several topologies have evolved to reduce the impact of common mode leakage current and a majority of them have succeeded in eliminating the impacts and have well kept them within the limits of grid standards. This paper compares and analyses the impact of the common mode leakage current for four popular inverter configurations through simulation of the topologies such as H5, H6, HERIC and FBZVR inverters.

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Authors and Affiliations

D. John Sundar
M. Senthil Kumaran

Leakage Current Degradation Due to Ion Drift and Diffusion in Tantalum and Niobium Oxide Capacitors

Martin Kuparowitz Lubomír Grmela Vlasta Sedlakova
Metrology and Measurement Systems | 2017 | vol. 24 | No 2 | 255–264 | DOI: 10.1515/mms-2017-0034
Keywords niobium oxide capacitors tantalum capacitors leakage current ion diffusion ion drift
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Abstract

High temperature and high electric field applications in tantalum and niobium capacitors are limited by the mechanism of ion migration and field crystallization in a tantalum or niobium pentoxide insulating layer. The study of leakage current (DCL) variation in time as a result of increasing temperature and electric field might provide information about the physical mechanism of degradation. The experiments were performed on tantalum and niobium oxide capacitors at temperatures of about 125°C and applied voltages ranging up to rated voltages of 35 V and 16 V for tantalum and niobium oxide capacitors, respectively. Homogeneous distribution of oxygen vacancies acting as positive ions within the pentoxide layer was assumed before the experiments. DCL vs. time characteristics at a fixed temperature have several phases. At the beginning of ageing the DCL increases exponentially with time. In this period ions in the insulating layer are being moved in the electric field by drift only. Due to that the concentration of ions near the cathode increases producing a positively charged region near the cathode. The electric field near the cathode increases and the potential barrier between the cathode and insulating layer decreases which results in increasing DCL. However, redistribution of positive ions in the insulator layer leads to creation of a ion concentration gradient which results in a gradual increase of the ion diffusion current in the direction opposite to the ion drift current component. The equilibrium between the two for a given temperature and electric field results in saturation of the leakage current value. DCL vs. time characteristics are described by the exponential stretched law. We found that during the initial part of ageing an exponent n = 1 applies. That corresponds to the ion drift motion only. After long-time application of the electric field at a high temperature the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5. Here, the equilibrium between the ion drift and diffusion is achieved. The process of leakage current degradation is therefore partially reversible. When the external electric field is lowered, or the samples are shortened, the leakage current for a given voltage decreases with time and the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5, thus the ion redistribution by diffusion becomes dominant.

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Authors and Affiliations

Martin Kuparowitz
Lubomír Grmela
Vlasta Sedlakova

An evaluation method of observable charge trap depth for the pea method and its complementarity with the Q(t) method

Hanwen Ren Tatsuo Takada Yasuhiro Tanaka Qingmin Li
Metrology and Measurement Systems | 2021 | vol. 28 | No 3 | 565-580 | DOI: 10.24425/mms.2021.137136
Keywords pulsed electro-acoustic method trap depth current integration charge method leakage current
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Abstract

This paper proposes an evaluation method for the observable trap depth range of space charge when using the pulsed electro-acoustic (PEA) method and its complementarity with the current integration charge (Q(t)) method. Based on the measurement process of the PEA method and the hopping conduction principle of space charge, the relationship between the trap depth and the residence time of charge is analysed. A method to analyse the effect of the measurement speed and the spatial resolution of the PEA system on the observable trap depth is then proposed. Further results show when the single measurement time needs 1 s and the resolution is 10 µm at room temperature, the corresponding trap depth is larger than 0.68 eV. Meanwhile, under high temperature or with voltage applied, the depth can further increase. The combined measurement results of the PEA and Q(t) methods indicate that the former focuses on charge distribution in deep traps, which allows to calculate the distorted electric field. The latter can measure the changing process of the total charge involved in all traps, which is applicable to analysing the leakage current. Therefore, the evaluation of HVDC insulation properties based on the joint application of the two methods is more reliable.
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Authors and Affiliations

Hanwen Ren
1
Tatsuo Takada
2
Yasuhiro Tanaka
2
Qingmin Li
1
  1. North China Electric Power University, State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, Beijing 102206, China
  2. Tokyo City University, 1-28-1 Tamazutsumi, Setagaya, Tokyo, 158-8557, Japan

Low Leakage and Robust Sub-threshold SRAM Cell Using Memristor

Zeba Mustaqueem Abdul Quaiyum Ansari Md Waseem Akram
International Journal of Electronics and Telecommunications | 2022 | vol. 68 | No 4 | 667-676 | DOI: 10.24425/ijet.2022.141287
Keywords 6T SRAM cell memristor power dissipation read and write operation leakage current stability non-volatile circuit
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Abstract

This work aims to improve the total power dissipation, leakage currents and stability without disturbing the logic state of SRAM cell with concept called sub-threshold operation. Though, sub-threshold SRAM proves to be advantageous but fails with basic 6T SRAM cell during readability and writability. In this paper we have investigated a non-volatile 6T2M (6 Transistors & 2 Memristors) sub-threshold SRAM cell working at lower supply voltage of VDD=0.3V, where Memristor is used to store the information even at power failures and restores previous data with successful read and write operation overcomes the challenge faced. This paper also proposes a new configuration of non-volatile 6T2M (6 Transistors & 2 Memristors) subthreshold SRAM cell resulting in improved behaviour in terms of power, stability and leakage current where read and write power has improved by 40% and 90% respectively when compared to 6T2M (conventional) SRAM cell. The proposed 6T2M SRAM cell offers good stability of RSNM=65mV and WSNM=93mV which is much improved at low voltage when compared to conventional basic 6T SRAM cell, and improved leakage current of 4.92nA is achieved as compared.
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Authors and Affiliations

Zeba Mustaqueem
1
Abdul Quaiyum Ansari
1
Md Waseem Akram
1
  1. Jamia Milia Islamia Central University, India

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