High Voltage Direct Current Interconnection Research Articles

Operation Analysis of Power Systems with HVDC Interconnections Using a Transient Stability Aware OPF Method

High-voltage direct current (HVDC) transmission systems are widely used today due to their several advantages over high-voltage alternative current (HVAC) systems. They are primarily utilized in connecting different large grids or smaller independent networks, especially in submarine interconnections. Many studies have been conducted globally on the optimal planning, operation, and control of these power systems. Understanding the transient stability of these systems during significant disturbances is also of great importance. This paper specifically focuses on power systems with HVDC connections and high penetration of renewable energy sources. Analytical models were developed for power system components like HVDC converters, DC lines, and full converter wind generators. A simulation of a test-case power system was conducted, including various significant disturbances such as HVDC line trips, short circuits, power unit failures, and major changes in load. The voltage and frequency stability of the system under specific operational scenarios was also examined. The results obtained indicate technical limitations and operating guidelines to avoid undesirable conditions and system failure. In conclusion, adopting short-term stability tests the optimal operation point of the system, and the limitations in the penetration by RES units can be decided.

Evaluation of a HVDC Interconnection to Improve the Voltage Stability of the Nigerian Transmission Network

The Nigerian transmission network is prone to outages and low reliability, and both issues are currently impacting the population's quality of life and hindering economic development. This situation is expected to worsen in the future, due to the increase in forecasted demand. This paper assesses the stability of the Nigerian transmission network under existing grid conditions, and determines the impact of High Voltage Direct Current (HVDC) on voltage stability. The PV and QV analysis methods were carried out using the DIgSILENT PowerFactory software package. Two weak buses were identified, and an HVDC model was built and integrated into the existing network at these locations. The results demonstrated that the HVDC interconnector positively impacts system stability by improving the voltage profile and the reactive power margin (RPM).

Comparison of Different Configurations for Shoreline Pond Electrode Station for HVDC Transmission Systems—Part I: Electric Field Study for Frames of Linear Electrode Arrangement Based on a Simplified Analytical Model

During the design of a shoreline electrode station for High-Voltage Direct Current (HVDC) interconnections, the location of the electrodes plays a critical part, especially in the development of the near-electric field. The basic structure is their linear placement, in the form of successive frames, parallel to the longitudinal axis of the breakwater, as proposed by CIGRE and implemented in existing projects. However, this arrangement requires a considerable breakwater length, which may not be permissible, as in the case of Stachtoroi, one of the two electrode stations being built for the 1 GW, ±500 kV HVDC interconnection between Crete and mainland Greece. This troubled the preliminary study team of the electrode stations, which investigated other possible configurations. In this paper, configurations of linear placements of electrode frames are studied and compared at the preliminary study level in terms of electric field effects (especially the near-field), using an analytical simplified model and the superposition method, to determine the most appropriate arrangement of electrodes that will cover the respective requirements of CIGRE directives B4.61/2017. These arrangements are practically evaluated for two different electrode station locations at Korakia in Crete and at Stachtoroi in Aegina for the Crete–mainland-Greece interconnection, resulting in interesting alternative solutions.

국가 간 전력계통의 HVDC 연계를 고려한 변동성 재생발전원의 수용한계 평가 방법

Due to environmental policies in the electric power industry, the proportion of Variable Renewable Source(VRS) in the power system is increasing. However, since the power outputs of VRS are very variable and its capability for providing the inertia response is limited, the high penetration of VRS may lead to violate the operating standards of the power system and result in deteriorating the power system stability. One of the solutions to alleviate these problems is power flow and frequency control using High Voltage Direct Current(HVDC) interconnecting the power systems between countries, and through this, the penetration limit of VRS can be increased. For this, this paper proposes a method to evaluate the penetration limit of VRS considering the HVDC interconnection of power system between countries. In the case study, the effectiveness of the propsoed method is verified by evaluating the VRS penetration limit of Korean power system.

End-to-End Direct-Current-Based Extreme Fast Electric Vehicle Charging Infrastructure Using Lithium-Ion Battery Storage

An urgent need to decarbonize the surface transport sector has led to a surge in the electrification of passenger and heavy-duty fleet vehicles. The lack of widespread public charging infrastructure hinders this electric vehicle (EV) transition. Extreme fast charging along interstates and highway corridors is a potential solution. However, the legacy power grid based on alternating current (AC) beckons for costly upgrades that will be necessary to sustain sporadic fast charging loads. The primary goal of this paper is to propose a sustainable, low-loss, extremely fast charging infrastructure based on photovoltaics (PV) and co-located lithium-ion battery storage (BESS). Lithium-ion BESS plays a pivotal role in our proposed design by mitigating demand charges and operating as an independent 16–18 h power source. An end-to-end direct current power network with high voltage direct current interconnection is also incorporated. The design methodology focuses on comprehensive hourly EV-load models generated for different types of passenger vehicles and heavy-duty fleet charging. Appropriate PV-BESS sizing, optimum tilt, and temperature compensation techniques based on 15 years of irradiation data were utilized in the design. The proposed grid-independent DC power networks can significantly improve well-to-wheels efficiency by minimizing total system losses for fast charging networks. The network power savings for low, medium, and high voltage use cases were evaluated. Our results demonstrate 17% to 25% power savings compared to the traditional AC case.

Integration of a storage device to the DC bus of a grid-forming controlled HVDC interconnection

This paper assesses the performance of a high-voltage direct-current (HVDC) interconnection for providing virtual inertia to the power system. The impact of inertia provision on the DC bus dynamics and system frequency when one or both converter terminals are controlled with a virtual synchronous machine (VSM) based grid-forming strategy is evaluated. It has been demonstrated that an identical inertial support cannot be provided to both terminals due to a fundamental conflict between the DC voltage control and inertia emulation tasks. Therefore, it has been proposed to integrate a storage device (e.g. flywheel energy storage system (FESS)) with an additional converter to the DC link in order to control the DC voltage. Doing so, the DC voltage control is not couple with the inertia emulation at each substation and the obtained results have shown that a good performance in the DC voltage control as well as a proper inertia support provision are achieved. Finally, a discussion on a simplified approach to size the storage system is presented.

DC/DC Modular Multilevel Converters for HVDC Interconnection: A Comprehensive Review

High voltage direct current (HVDC) technology is a key component in power systems owing to huge benefits such as long-distance power transmission, lower losses, asynchronous grid interconnections, controllability, system availability, and limited short-circuit currents. HVDC transmission is a cost-effective method of transporting huge amounts of power across long distances with little loss. It can also link asynchronous alternative current (AC) networks while balancing the grid. DC/DC converters are one of the most important components for HVDC power transmission, and DC/DC modular multilevel converters (MMCs) are the backbone of HVDC grid interconnections. The DC/DC MMC is a highly regarded converter architecture for medium/high-voltage DC grid interconnection. DC/DC MMC topologies play a key role in modern HVDC networks with varying voltage levels. This paper’s fundamental aim is to offer a recent comprehensive review of HVDC topologies, current DC/DC modular multilevel converter (MMC) topologies for HVDC interconnection, and DC/DC MMC control techniques.

Alternative Simplified Analytical Models for the Electric Field, in Shoreline Pond Electrode Preliminary Design, in the Case of HVDC Transmission Systems

In Greece, a new bi-polar high voltage direct current (HVDC) transmission system with a ground return was designed with nominal characteristics of ±500 kV, 1 GW, between Attica in the continental country and the island of Crete, which is an autonomous power system based on thermal diesel units. The interconnection line has a total length of about 380 km. The undersea section is 330 km long. In this paper, the use of the Aegean Sea as an active part of the ground return, based on shoreline pond electrodes, was proposed to avoid EUR 200 Μ of expenses. According to the general guidelines for HVDC electrode design by the International Council on Large Electric Systems (CIGRE) working group B4.61/2017, the electric field and ground potential rise of shoreline electrodes should be studied to analyze safety, electrical interference and corrosion impacts related to the operation of the electrodes. Two kinds of studies are available; one is a simplified approach based on a spherical/pointed electrode centered at the edge of the seashore and seabed, assuming it to be sloping to the horizontal, and the other is a detailed simulated model using a suitable electric field software package. The first approach usually gives more unfavorable results than the second one, especially in the near electric field, while it can not take into account obstacles, i.e., dams, near to electrode position. The second approach demands a detailed description of the wider installation area, which cannot be available during the preliminary study, significant computational time and considerable financial resources for the purchase of a reliable specialized software package. In this research, a two-step modification of the CIGRE simplified model was proposed. The first modification deals with the obstacles in the near electric field, and the second modification deals with the use of a linear current source (instead of a point one), which can give more accurate results. Additionally, the electric field for complex electrode formation is calculated by applying the superposition method, which can be easily achieved using a common software package, i.e., MATLAB. The proposed simplified approaches were applied on shoreline pond electrode locations for the Attica–Crete HVDC interconnection line (between Stachtoroi island in Attica and Korakia beach in Crete), allowing the preliminary study to be conducted swiftly, giving satisfactory results about electric field gradient, ground potential rise and resistance to remote earth of electrodes stations for the near and far electric field.

Voltage control and virtual synchronous generator control of HVDC interconnection line for improving stability of power system including large‐scale wind farm

Large-scale integration of renewable energy sources (RESs) such as wind power can impact on the existing power system's stability. For example, there is a possibility that the wind farm (WF) cannot be maintained stable and then it is disconnected from the grid when the instantaneous voltage sag caused by a grid disturbance occurs. Moreover, the increasing integration of RESs in the power system can reduce the number of conventional synchronous generators (SGs) connected to the grid, and lead to a reduction of system inertia in the grid. The system inertia reduction can cause larger and faster frequency fluctuations during the transient period. Hence, this paper proposes a new control strategy composed of the voltage control for suppressing the voltage sag and the virtual synchronous generator (VSG) control based on the proportional-integral-differential (PID) fuzzy logic control (FLC) for maintaining the frequency stability which is performed by high voltage direct current (HVDC) interconnection line. The aim of the new control strategy is to improve the stability of the entire power system with large-scale integration of RESs. The effectiveness of the proposed strategy is confirmed through the simulation analyses by PSCAD/EMTDC.

Frequency control of power system including PV and wind farms by using output frequency band control of HVDC interconnection line

Due to serious environmental issues in recent years, renewable energy has been focused on all over the world to solve the issues. However, because of indirect characteristics such as variations of solar radiation intensity or wind speeds, the output of power generation utilizing renewable energy becomes unstable. As a result, frequency and voltage in the power system can fluctuate. To solve this problem, various methods to control the frequency variations have been studied and reported until now, one of which is based on High voltage direct current (HVDC) transmission line. This paper proposes a novel control scheme to reduce the frequency variations due to large penetrations of wind power and photovoltaic (PV) power, which is introduced to power flow control of HVDC transmission line with utilizing a notch-band pass filter in its frequency control system.

Technology and engineering application of cross area HVDC interconnection system high-precision simulation modeling based on ADPSS

In recent years, a large number of high voltage direct current (HVDC) transmission projects have been connected to AC systems. This has started to have an impact on AC/DC hybrid power grids, particularly receiving terminal power grids. An HVDC system is a large-scale power electronic integrated nonlinear system, and it includes a primary system and a control and protection system. Hence, the precision and degree of detail of HVDC systems directly affect the actual effect of simulation. In recent years, in the case of the normal operation and failure of AC power grids, the abnormal fluctuation and even locking of HVDC systems caused by the inappropriate strategies of the control and protection system component have strongly affected power grids. This has significantly affected the safety and stability of receiving power grids and normal operation. In this study, the actual engineering HVDC control logic provided by a manufacturer is analyzed and simulated based on the user defined component library of the ADPSS electromagnetic transient calculation program, and an HVDC control model based on an actual system is established. The accuracy of the DC control custom model based on ADPSS is verified through the simulation of an actual power grid.

Power system security enhancement by HVDC links using a closed-loop emergency control

In recent years, guaranteeing that large-scale interconnected systems operate safely, stably and economically has become a major and emergency issue. A number of high profile blackouts caused by cascading outages have focused attention on this issue. Embedded HVDC (High Voltage Direct Current) links within a larger AC power system are known to act as a “firewall” against cascading disturbances and therefore, can effectively contribute in preventing blackouts. A good example is the 2003 blackout in USA and Canada, where the Québec grid was not affected due to its HVDC interconnection. In the literature, many works have studied the impact of HVDC on the power system stability, but very few examples exist in the area of its impact on the system security. This paper presents a control strategy for HVDC systems to increase their contribution to system security. A real-time closed-loop control scheme is used to modulate the DC power of HVDC links to alleviate AC system overloads and improve system security. Simulations carried out on a simplified model of the Hydro-Québec network show that the proposed method works well and can greatly improve system security during emergency situations.

Evaluating an Interconnection Project: Do Strategic Interactions Matter?

High-Voltage Direct Current (HVDC) merchant transmission lines allow trade across separate power markets and often in different countries. Flows on existing cross-border lines are often assessed as suboptimal, which may be due to the light regulation that often prevails in these cases. This paper studies the impact of market power on HVDC interconnections as a determinant of imperfect arbitrage. We assess the impact of Physical Transmission Rights (PTRs) allocation on the management of an HVDC interconnection between a thermal and a hydroelectricity market, assuming dynamic water management. We use a two-stage game formulated as an Equilibrium Problem with Equilibrium Constraints (EPEC) to model the strategic trade between the New York (US) and Quebec (Canada) systems. The numerical model is calibrated with public data. We find that although the interconnection can create wealth, a high concentration of PTRs can destroy value because of dumping strategies. The impact of trade on local price levels may be of concern and calls for the functional unbundling of traders and generators.

Frequency Control of Power System with Solar and Wind Power Stations by Using Frequency Band Control and Deadband Control of HVDC Interconnection Line

In recent years, environmental problems are becoming serious and renewable energy has attracted attention as their solutions. However, the electricity generation using the renewable energy has a demerit that the output becomes unstable because of intermittent characteristics, such as variations of wind speed or solar radiation intensity. Frequency fluctuations due to the installation of large scale wind farm (WF) and photovoltaics (PV) into the power system is a major concern. In order to solve the problem, this paper proposes two control methods using High Voltage Direct Current (HVDC) interconnection line to suppress the frequency fluctuations due to large scale of WF and PV. Comparative analysis between these two control methods is presented in this paper. One proposed method is a frequency control using a notch filter, and the other is using a deadband. Validity of the proposed methods is verified through simulation analyses, which is performed on a multi-machine power system model.

A Study on Maximum Wind Power Penetration Limit in Island Power System Considering High-Voltage Direct Current Interconnections

The variability and uncontrollability of wind power increases the difficulty for a power system operator to implement a wind power system with a high penetration rate. These are more serious factors to consider in small and isolated power systems since the system has small operating reserves and inertia to secure frequency and voltage. Typically, this difficulty can be reduced by interconnection with another robust power system using a controllable transmission system such as a high-voltage direct current (HVDC) system. However, the reliability and stability constraints of a power system has to be performed according to the HVDC system implementation. In this paper, the method for calculation of maximum wind power penetration in an island supplied by a HVDC power system is presented, and the operational strategy of a HVDC system is proposed to secure the power system reliability and stability. The case study is performed for the Jeju Island power system in the Korean smart grid demonstration area.

Power System Security in a Meshed North Sea HVDC Grid

There are very ambitious plans in Europe for changing the energy infrastructure in order to reduce greenhouse gas emissions. This involves scenarios where renewable energy sources by 2050 will meet almost 100% of the electric power demand. This has spurred offshore wind farm development activities in the North Sea due to the vast wind energy potential in this region and the potential lack of suitable onshore sites in the future. Large-scale wind farms in the North Sea pose grid integration challenges such as the need for long-distance subsea power transmission and tackling the impact of wind power variation on alternating current (ac) grids. These challenges can be properly managed by the use of meshed high-voltage direct current (HVDC) grids. Three of the regional groups (RGs) in the European Network of Transmission System Operators for Electricity (ENTSO-E), namely Regional Group Great Britain (RG-GB), Regional Group Nordic (RG-N), and Regional Group Continental Europe (RG-CE), surround the North Sea area. A meshed North Sea HVDC interconnection between offshore wind farms and these three asynchronous ac grids can also enable market integration of the otherwise separate regions. This, in turn, results in better utilization of generation and transmission infrastructures, improved security of power supply, and maximized utilization of renewable energy resources. In this paper, a test scenario of a meshed North Sea HVDC grid is studied to demonstrate the potential of such a system for enhancing power supply security of the ac grids. Simulation studies of the test case show that with proper control techniques, a meshed North Sea HVDC grid can mitigate the effect of wind power variation by facilitating exchange of primary and secondary reserves between asynchronous ac grids.