HVDC Power Research Articles

Cable Conductor Design for the High-Power MgB2 DC Superconducting Cable Project of BEST PATHS

BEST PATHS (acronym for “BEyond State-of-the-art Technologies for rePowering ac corridors and multi-Terminal HVDC Systems”) is a collaborative project of 40 leading European organizations from science and industry, supported by the 7th Research Framework Programme of the European Commission. The project investigates the feasibility of technological innovations that could advance high-capacity transmission links. These innovations include a demonstrator project dedicated to superconducting electric lines, which aims to validate the novel MgB2 technology for GW-level HVDC power transmission. The four-year project will thus demonstrate the operation of a full-scale 320 kV MgB2 monopole cable system that can transfer up to 3.2 GW. This paper focuses on the design and development activities for the 10 kA cable conductor, which were carried out in the first two years of the project.

Analysis of Hvdc Power Transmission Line with Unique Power Control Room

Analysis of Hvdc Power Transmission Line with Unique Power Control Room

Analysis of HVDC Power Transmission Line with Unique Power Control Room

Analysis of HVDC Power Transmission Line with Unique Power Control Room

Investigation on Economic and Reliable Operation of Meshed MTDC/AC Grid as Impacted by Offshore Wind Farms

The influence of complementarity balancing connected grid and control of offshore wind power generation on the economic and reliable operation of hybrid multiterminal HVDC (MTDC) and AC power system is investigated in the paper. The variances of distribution curve of both transmission loss of AC/DC system and voltage of critical nodes assessed by cumulant-based method are used to demonstrate how the different complementarity conditions, generation balancing strategies, MTDC grid topologies, and control schemes affect power system operation. In this paper, a study case of 16-generator 68-bus power system connected with three offshore wind farms is presented. The variance indices of transmission loss and voltage magnitude are calculated and then compared under different complementarity levels, active power balancing strategies, HVDC transmission systems, and controls, respectively. The analysis reveals that higher complementarity and multi-machine balancing strategy can effectively reduce system operational cost and enhance operational reliability. Compared to the point-to-point topology, the control pattern and parameter setting of multi-terminal topology are two key factors to determine its impact on system operation.

Efficiency of superconducting transmission lines: An analysis with respect to the load factor and capacity rating

Superconducting transmission lines (SCTL) are an innovative option for the future electricity grid and in particular for high-capacity HVDC power transmission. The promise of superconducting electric lines lies principally in their small size, with potential advantages in terms of efficiency, environmental impact and public acceptance. Furthermore, contrary to standard conductors, SCTL do not have any resistive losses, therefore the only remaining power loss is due to the cooling system that is needed to keep the superconductor at its cryogenic operating temperature. In order to obtain a realistic value for the SCTL efficiency, both the actual load factor and the capacity rating have to be taken into account. This paper analyzes the transmission efficiency characteristics for two long-distance SCTL designs developed at the IASS and at EPRI as a function of the load factor for capacities up to 10GW, and in comparison with established transmission technologies. The focus of this study is the planned expansion of the HVDC transmission system in Germany, which is aimed at achieving the current CO2 reduction goals by integrating an increased share of intermittent renewable energy (RE) into the grid. The results can be readily extended to other scenarios and can provide complementary information for decision processes directed at planning a sustainable future grid.

Operation of a hybrid modular multilevel converter during grid voltage unbalance

The recently proposed parallel hybrid modular multilevel converter is considered to be a low loss, low component count converter with soft switching capability of the ‘main’ bridge. The converter has similar advantages to other emerging modular multilevel converter circuits being considered for HVDC power transmission. However, during ac network unbalance the individual ‘chain-links’ exchange unequal amounts of power with the grid which requires appropriate remedial action. This paper presents research into the performance of the converter and proposes a suitable control method that enables the converter to operate during grid voltage unbalance. The proposed control concept involves the use of asymmetric third harmonic voltage generation in the ‘chain-links’ of the converter to redistribute the power exchanged between the individual ‘chain-links’ and the grid. Mathematical analysis and simulation modelling with results are presented to support the work described.

A Review on Designand Control Methods of Modular Multilevel Converter

Modular multilevel converters (MMC) are an emerging voltage source converter topology suitable for many applications. Due to abundant utilization of HVDC power transmission, the modular multilevel converter has become popular converter type to be used in high voltage applications. Other applications include interfacing renewable energy power sources to the grid and motor drives. Modular multilevel converters are beneficial for high voltage and high power motor drives because of the properties of this converter topology, such as, low distortion, high efficiency, etc. For the past few years significant research has been carried out to address the technical challenges associated with operation and voltage balancing of MMC. In this paper, a detailed technical review on the control strategies is presented for ready reference.

Modeling and sensitivity analyses of VSP based virtual inertia controller in HVDC links of interconnected power systems

Virtual inertia is known as an inevitable part of the modern power systems, especially considering the increasing level of power electronic-based component and HVDC interconnection in the future gird. To cope with this challenging issue, a novel approach for modeling and analysis the effect of virtual inertia on frequency stability of multi area interconnected system is proposed. The proposed method is based on Virtual Synchronous Power (VSP) control strategy of HVDC interconnected systems. The presented work is focused on modeling and detailed sensitivity analysis of VSP-based HVDC concept in frequency control and automatic generation control task of interconnected power systems. In order to understand the influence of virtual inertia parameters, a set of sensitivity analysis is performed to identify the proper range of critical control parameters on the stability of the system. The effectiveness of the proposed concept on dynamic improvements is also validated through Matlab simulation of multi-area (two-area and three-area) test systems. The three-area test system is based on complex model of 39-bus, 10 generator test system.

Modular Multilevel Converter-Based Bipolar High-Voltage Pulse Generator With Sensorless Capacitor Voltage Balancing Technique

In order to generate bipolar high-voltage (HV) pulses across certain load from HV dc (HVdc) power supply, a voltage source inverter (VSI) stage should be inserted between the load and the supply. In order to meet the required HV level, series connection of semiconductor devices should be employed with dynamic voltage sharing between the involved devices. Modular multilevel converter (MMC) can be used instead of the conventional two-level VSI to alleviate the complexity introduced by the deployment of series-connected devices. The voltage level of the HVdc power supply and the voltage rating of the available semiconductor devices determine the suitable number of MMC voltage levels ( $N$ ). Capacitor voltage balancing is a vital issue for proper operation of the MMC. In general, conventional sensor-based balancing techniques require a significant amount of measurements, which increases the complexity of the system. In addition, the high dv/dt during switching times causes electromagnetic interference, which may adversely affect the accuracy of the measurements. In this paper, a sensorless voltage balancing technique is proposed for the MMC-based bipolar HV pulse generator that reduces the system sensitivity, cost, and complexity. A detailed illustration of the proposed approach is presented in this paper. The simulation and experimental results are used to validate the proposed concept.

Impact of HVDC line on the convergence property of AC/DC power flow calculation

This paper explores the impact of HVDC line on the convergence property of AC/DC power flow calculation. Firstly, the model of AC/DC power flow computation is constructed, including unified method and alternate iterative method. Then, an improved Levenberg–Marquardt (LM) method with line search technique is developed to solve the nonlinear equations of AC/DC power flow. To test the convergence property of the proposed method, LM method with trust region technique and Newton method are also employed. The researches on the impact of heavy DC transmission power and multiple HVDC lines on the convergence property of AC/DC power flow calculation are made on a modified IEEE 118-bus AC/DC hybrid test system. Simulation results show that the developed method under the model of alternate iterative method is superior to other methods under different models in convergence property. For the influence of heavy DC transmission power on the convergence property, it is improved by the new parameter configuration of DC transmission line firstly and adding proper new shunt capacitor on the weak nodes secondly; for the influence of multiple DC transmission lines on the convergence property, it can also be improved by the change of control mode firstly and adding new shunt capacitor secondly, which are based on the least square solution obtained by proposed method under the model of alternate iterative method.

Situation and Development on Soil Corrosion of Metallic Materials of HVDC Power Transmission Project

UHVDC transmission could deliver high-power electricity over long distances effectively, while the DC stray current led to corrosion of grounding device and the surrounding buried metal during the operation inevitably. This paper reviewed the research progress of HVDC corrosion at home and abroad in recent years. It elaborated corrosion research direction of HVDC system from three aspects, which were pole, grounding grid and the neighboring tower grounding body buried pipeline respectively. Describing the anti-corrosion measures on grounding devices and buried pipeline, and explaining the advantages and defects of various anti-corrosion technology. At last, we proposed that it was necessary to expand the research in UHVDC field, grasp the erosion rule of DC stray current in soil comprehensively to enhance the security of UHVDC transmission system of national grid.

Mitigation of commutation failures in LCC–HVDC systems based on superconducting fault current limiters

Commutation failure in line commutated converter based HVDC systems cause severe damages on the entire power grid system. For LCC–HVDC, thyristor valves are turned on by a firing signal but turn off control is governed by the external applied AC voltage from surrounding network. When the fault occurs in AC system, turn-off control of thyristor valves is unavailable due to the voltage collapse of point of common coupling (PCC), which causes the commutation failure in LCC–HVDC link. Due to the commutation failure, the power transfer interruption, dc voltage drop and severe voltage fluctuation in the AC system could be occurred. In a severe situation, it might cause the protection system to block the valves. In this paper, as a solution to prevent the voltage collapse on PCC and to limit the fault current, the application study of resistive superconducting fault current limiter (SFCL) on LCC–HVDC grid system was performed with mathematical and simulation analyses. The simulation model was designed by Matlab/Simulink considering Haenam-Jeju HVDC power grid in Korea which includes conventional AC system and onshore wind farm and resistive SFCL model. From the result, it was observed that the application of SFCL on LCC–HVDC system is an effective solution to mitigate the commutation failure. And then the process to determine optimum quench resistance of SFCL which enables the recovery of commutation failure was deeply investigated.

A novel synthetic test system for thyristor level in the converter valve of HVDC power transmission

The converter valve is the core equipment in the HVDC power transmission system, a+-nd its performance has a direct effect on the reliability, stability and efficiency of the whole power system. As the basic unit of HVDC converter valve, the thyristor level needs to be test routinely in order to grasp the state of the converter valve equipment. Therefore, it is urgent to develop a novel synthetic test system for the thyristor level with thyristor control unit (TCU). However, currently there is no specific test scheme for the thyristor level of HVDC converter valve. In this paper, the synthetic test principle, content and methods for the thyristor level with TCU are presented based on the analysis of the thyristor reverse recovery characteristic and the IEC technology standard. And a transient high-voltage pulse is applied to the thyristor level during its reverse recovery period in order to test the characteristics of thyristor level. Then, the synthetic test system for the thyristor level is applied to the converter valve test of ±800 kV HVDC power transmission project, and the practical test result verifies the reasonability and validity of the proposed synthetic test system.

Series-Input Parallel-Output Modular-Phase DC–DC Converter With Soft-Switching and High-Frequency Isolation

Multiphase soft-switching high-frequency isolated dc–dc converter is proposed for power conversion in modular stacked HVDC power transmission and distribution system. Input-series output-parallel connection of current-fed full-bridge dc–dc converter modules is proposed to increase voltage blocking capability at the input and decrease current ripple at the output. Basic power electronic building block is zero-current switching (ZCS) full-bridge phase-shift pulsewidth-modulated (PWM) dc–dc converter. Phase shift between switches in each leg of the converter is adjusted to control power flow, while phase shift between gate signals of individual phases is selected according to the number of phases in order to minimize ripple of the output voltage. Converter analysis is carried out to develop a simple equivalent boost converter model of the three-phase soft-switching converter suitable for system-level analysis and simulation. Strategies are developed to ensure fast detection of faults and continued operation of the converter in the case of fault in one phase module. To verify the proposed system design and analysis, experimental results on scaled-down laboratory prototype are presented for a three-phase ZCS dc–dc converter.

A Reliability Prediction Method for HVDC Power Transmission Systems

本文提出了超高压直流输电系统可靠性预测的数学模型及工程方法。采用能量可用率评价超高压直流输电系统的可靠性，使用从统计期间扣除计划停运小时的能量可用率与检修系数评价超高压直流输电系统的固有可靠性，采用幂函数表示检修系数的数学模型。在统计超高压直流输电系统可靠性历史数据的基础上，确定检修系数的统计值与幂函数的待定参数。根据超高压直流输电系统的计划检修天数、降额系数与检修系数的数学模型，提前两年预测超高压直流输电系统的能量可用率。给出了超高压直流输电系统可靠性预测结果的验证方法以及天广、高肈与江城等三个超高压直流输电工程的可靠性预测实例。应用超高压直流输电系统的可靠性预测方法，可以提前两年确定超高压直流输电系统能量可用率的预测值，为超高压直流输电系统的可靠性目标管理提供了依据。 A mathematical model and engineering methods for the reliability prediction of HVDC power transmission systems are presented. The energy availability is used to evaluate HVDC power transmission system reliability, making use of the energy availability deducted scheduled outage hours from period hours and the maintenance factor to evaluate HVDC power transmission sys-tem inherent reliability, and a mathematical model for the maintenance factor is shown by the power function. Based on statistical historical reliability data of HVDC power transmission sys-tems, statistical values of the maintenance factor and undetermined parameters of the power function are determined. According to scheduled outage days, the outage derating factor and a mathematical model of the maintenance factor of HVDC power transmission systems, the energy availability of HVDC power transmission systems can be predicted in the next two years. The re-liability verification method for prediction results of HVDC power transmission systems is given, together with reliability prediction examples of three HVDC power transmission projects, such as Tianshengqiao to Guangzhou, Gaopo to Zhaoqing and Jiangling to Echeng HVDC power transmission projects. By using reliability the prediction method for HVDC power transmission systems, predictive values of the energy availability of HVDC power transmission systems can be determined in the next two years, which provide the basis for the reliability target management of HVDC power transmission systems.

DC MOA Application and Test Technical Analysis

To achieve further optimization of resource utilization, HVDC power transmission project in the proportion of the state grid is growing and the range of applications are more widely. Due to the high cost of converter stations, properly design of DC MOA for DC system insulation coordination and reducing the cost are crucial. Through research and analysis of large amounts of data, applications and test technologies of DC MOA is in-depth expounded, It’s further deepened the staff’s understanding of the DC MOA, there are also some guidance and references to the repair and maintenance of DC MOA.

Modeling of Distributed Grounding Electrodes for HVDC Power Transmission System and Its Application

Modeling of Distributed Grounding Electrodes for HVDC Power Transmission System and Its Application

Modelling and Analysis of CIGRE HVDC Offshore Multi-terminal Benchmark Grid

HVDC power transmission systems are being commissioned in the North Sea to link inland power grids with large offshore wind power farms. The growing number of large wind farms is driving the need to design more reliable high power transportation systems, leading to the conception of multi-terminal HVDC grids. These future grids will be purely formed by power electronics converters, the control of which will have to be designed to ensure proper performance and robust operation. This paper presents the analysis of the benchmark system proposed by the CIGRE working group SC B4, focusing on the proper selection of the components models and parameters. The small signal model of the system is first formulated. Then the bandwidth of the different control loops is obtained and the fidelity of the HVDC line model is selected accordingly. Finally, the performance of the benchmark system is studied by means of small signal analysis and compared numerical time series simulation of the non-linear model.

Dispersion Modeling and Analysis for Multilayered Open Coaxial Waveguides

This paper presents a detailed modeling and analysis regarding the dispersion characteristics of multilayered open coaxial waveguides or cables. The electromagnetic model is based on a layer recursive computation of axial-symmetric fields in connection with a magnetic frill generator excitation that can be calibrated to the current measured at the input of the cable. The layer recursive formulation enables a stable and efficient numerical computation of the related dispersion functions, as well as a detailed analysis regarding the analytic and asymptotic properties of the associated determinants. Modal contributions as well as the contribution from the associated branch-cut (nondiscrete radiating modes) are defined and analyzed. Measurements and modeling of pulse propagation on an 82-km-long HVDC power cable are presented as a concrete example. In this example, it is concluded that the contribution from the dominating axial-symmetric transverse magnetic mode is sufficient, and that the contribution from the branch-cut is negligible for all practical purposes, and in particular if the exterior domain is lossy. The main contribution of this paper is to provide the necessary modeling and analysis tools for a quantitative study of these phenomena.

Simulation and Dynamic Performance analysis of HVDC Power Transmission Using Wind Power Generation

This paper proposes a simulink model of wind turbine using induction generator and performance analysis of high voltage direct current power converter station. This paper also shows how wind power can easily be generated with help of induction generator. The need of developing such a system promoted the utilization of nonconventional energy resources like wind power. For a developing country like India the electrical energy much mire required to achieve the estimated targets within the specified period of time. Since the power generation is not only our concern but also power transmission have great importance to transport the electrical energy over long distance easily and efficienctly, which ensures uninterrupted and regulated power supply at load end. Hence this paper also proposes a model to transmit electrical power in DC form. Since it is difficult to load long extra high voltage (EHV) ac lines to their thermal limits as a sufficient margin is kept against transient instability. With the model proposed in this thesis, it will be possible to load these lines close to their thermal limits. The transmission lines are allowed to carry usual ac along with dc superimposed on it.