Multi-terminal HVDC grids with inertia mimicry capability

The high-voltage multi-terminal dc (MTDC) systems are foreseen to experience an important development in the next years. Currently, they have appeared to be a prevailing technical and economical solution for harvesting offshore wind energy. In this study, inertia mimicry capability is added to a voltage-source converter-HVDC grid-side station in an MTDC grid connected to a weak ac grid, which can have low inertia or even operate as an islanded grid. The presented inertia mimicry control is integrated in the generalised voltage droop strategy implemented at the primary level of a two-layer hierarchical control structure of the MTDC grid to provide higher flexibility, and thus controllability to the network. Besides, complete control framework from the operational point of view is developed to integrate the low-level control of the converter stations in the supervisory control centre of the MTDC grid. A scaled laboratory test results considering the international council on large electric systems (CIGRE) B4 MTDC grid demonstrate the good performance of the converter station when it is connected to a weak islanded ac grid.Peer ReviewedPostprint (author's final draft

Should cross-border banking benefit from the financial safety net?

Using bank-level data from 84 countries, we find that a higher degree of bank internationalization is associated with higher interest expenses. Internationalization is proxied by a bank's share of foreign liabilities in total liabilities or a Herfindahl index of international liability concentration. Bank interest expenses rise relatively more with internationalization if the bank is underperforming or headquartered in a country with weak public finances, and especially at times of weak world output growth. These results suggest that liability holders of distressed internationalized banks expect less from the financial safety net since lack of an efficient recovery and resolution regime for international banks can make their insolvency very costly to deal with.post-prin

Flexible control of power flow in multiterminal DC grids using DC-DC converter

This paper proposes an efficient control framework that utilizes dc-dc converters to achieve flexible power flow control in multiterminal dc (MTDC) grids. The dc-dc converter employed in this paper is connected in cascade with the dc transmission line, and is therefore named cascaded power flow controller (CPFC). In this paper, a two-layer control strategy is developed for the operation and control of voltage source converter stations and CPFC station in MTDC grids. At the primary control layer, a novel differential voltage droop control is developed, while at the secondary control layer, a modified dc power flow algorithm-employing the new CPFC framework-is implemented. The overall control strategy enables the CPFC to regulate the power flow in the dc transmission line. The primary control guarantees the transient stability of the CPFC, and the secondary control system ensures the desired steady-state operation. The proposed voltage droop control framework helps the MTDC grid to remain stable in the event of a communication failure between the primary and secondary control layers. Static analysis and dynamic simulations are performed on the CIGRE B4 dc grid test system, in order to confirm the effectiveness of the proposed control framework for power flow regulation in MTDC grids.Peer ReviewedPostprint (author's final draft

Single-phase modeling approach in dynamic harmonic domain

In this paper, a frequency-based analytical approach is presented for dynamic analysis of three-phase balanced systems in the presence of harmonic distortion based on single-phase analysis. By providing mathematical foundation, this study proves that a three-phase balanced system (linear or non-linear, supplied by periodic balanced sinusoidal or non-sinusoidal sources) is completely balanced during both transient and steady-state conditions. This is done by utilizing Dynamic Harmonic Domain (DHD) and defining a phase-shift matrix in frequency domain. As the most noteworthy application of the proposed methodology, single-phase modeling approach is put forward. Therefore, during the transient period, one can analyze only one phase of a three-phase balanced system and calculate exact quantities of the other phases without performing extra simulations, which is not possible through time domain. The introduced concept has been applied to different test cases including three-phase transformer inrush current. In addition, the proposed approach has been utilized to obtain a single-phase model of VSC-based power electronic devices for dynamic harmonic analysis, followed by discussion on results.Peer ReviewedPostprint (author's final draft

Multiterminal DC grids: operating analogies to AC power systems

Nowadays, some Multi-terminal DC (MTDC) systems are in operation around the world. Soon, MTDC grids will be built and overlay the present AC grids. The main driver for the construction of such a grid is to facilitate large-scale integration of remote renewable energy sources to existing AC grids and to develop the energy market. This paper presents a comprehensive analogy between the control and operation aspects of the emerging MTDC grids to those of the traditional AC power grids. Similarities and difference between the two technologies are presented and highlighted. Based on the performed detailed overview, even though a three-layered control system, i.e., primary, secondary, and tertiary control layers is state-of-the-art in large-scale AC power systems, a two-layered control system will satisfy MTDC grids control and operation requirements. This paper also addresses some control and operational issues and limitations of MTDC grids.Peer ReviewedPostprint (author's final draft

Single-phase modeling approach in dynamic harmonic domain

In this paper, a frequency-based analytical approach is presented for dynamic analysis of three-phase balanced systems in the presence of harmonic distortion based on single-phase analysis. By providing mathematical foundation, this study proves that a three-phase balanced system (linear or non-linear, supplied by periodic balanced sinusoidal or non-sinusoidal sources) is completely balanced during both transient and steady-state conditions. This is done by utilizing Dynamic Harmonic Domain (DHD) and defining a phase-shift matrix in frequency domain. As the most noteworthy application of the proposed methodology, single-phase modeling approach is put forward. Therefore, during the transient period, one can analyze only one phase of a three-phase balanced system and calculate exact quantities of the other phases without performing extra simulations, which is not possible through time domain. The introduced concept has been applied to different test cases including three-phase transformer inrush current. In addition, the proposed approach has been utilized to obtain a single-phase model of VSC-based power electronic devices for dynamic harmonic analysis, followed by discussion on results.Peer Reviewe

Multi-terminal HVDC grids with inertia mimicry capability

The high-voltage multi-terminal dc (MTDC) systems are foreseen to experience an important development in the next years. Currently, they have appeared to be a prevailing technical and economical solution for harvesting offshore wind energy. In this study, inertia mimicry capability is added to a voltage-source converter-HVDC grid-side station in an MTDC grid connected to a weak ac grid, which can have low inertia or even operate as an islanded grid. The presented inertia mimicry control is integrated in the generalised voltage droop strategy implemented at the primary level of a two-layer hierarchical control structure of the MTDC grid to provide higher flexibility, and thus controllability to the network. Besides, complete control framework from the operational point of view is developed to integrate the low-level control of the converter stations in the supervisory control centre of the MTDC grid. A scaled laboratory test results considering the international council on large electric systems (CIGRE) B4 MTDC grid demonstrate the good performance of the converter station when it is connected to a weak islanded ac grid.Peer Reviewe

Study of cytochrome P4502D6, target of Liver Kidney Microsomal antibody type 1 in autoimmune hepatitis type 2 and chronic liver disease due to hepatitis C virus infection

Available from British Library Document Supply Centre-DSC:DXN052869 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Flexible control of power flow in multiterminal DC grids using DC-DC converter

This paper proposes an efficient control framework that utilizes dc-dc converters to achieve flexible power flow control in multiterminal dc (MTDC) grids. The dc-dc converter employed in this paper is connected in cascade with the dc transmission line, and is therefore named cascaded power flow controller (CPFC). In this paper, a two-layer control strategy is developed for the operation and control of voltage source converter stations and CPFC station in MTDC grids. At the primary control layer, a novel differential voltage droop control is developed, while at the secondary control layer, a modified dc power flow algorithm-employing the new CPFC framework-is implemented. The overall control strategy enables the CPFC to regulate the power flow in the dc transmission line. The primary control guarantees the transient stability of the CPFC, and the secondary control system ensures the desired steady-state operation. The proposed voltage droop control framework helps the MTDC grid to remain stable in the event of a communication failure between the primary and secondary control layers. Static analysis and dynamic simulations are performed on the CIGRE B4 dc grid test system, in order to confirm the effectiveness of the proposed control framework for power flow regulation in MTDC grids.Peer Reviewe