High Voltage Direct Current Lines 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.

Optimal Placement of HVDC-VSC in AC System Using Self-Adaptive Bonobo Optimizer to Solve Optimal Power Flows: A Case Study of the Algerian Electrical Network

Modern electrical power networks make extensive use of high voltage direct current transmission systems based on voltage source converters due to their advantages in terms of both cost and flexibility. Moreover, incorporating a direct current link adds more complexity to the optimal power flow computation. This paper presents a new meta-heuristic technique, named self-adaptive bonobo optimizer, which is an improved version of bonobo optimizer. It aims to solve the optimal power flow for alternating current power systems and hybrid systems AC/DC, to find the optimal location of the high voltage direct current line in the network, with a view to minimize the total generation costs and the total active power transmission losses. The self-adaptive bonobo optimizer was tested on the IEEE 30-bus system, and the large-scale Algerian 114-bus electric network. The obtained results were assessed and contrasted with those previously published in the literature in order to demonstrate the effectiveness and potential of the suggested strategy.

A novel phaselet-based approach for fault detection and location in HVDC lines

Recently, the popularity of direct current (DC) transmission has surged due to a 30 % reduction in power electronics equipment costs over the last decade. High-Voltage Direct Current (HVDC) transmission lines experience fluctuations in both nominal and faulty states, posing challenges for fault location methods, particularly those based on traveling waves, resulting in imprecise outcomes with an average error margin of ±2 %. This paper investigates a novel fault detection and location approach utilizing wavelet and phaselet transforms. The proposed method focuses on traveling waves in HVDC transmission lines, where the phaselet transform effectively eliminates undesired fluctuations in line currents, improving fault detection accuracy by up to 15 %. By leveraging the traveling time in the faulty line, the exact fault location is calculated with an accuracy of 98.5 %, independent of transmission line parameters, making it applicable to any DC line. Additionally, the method's precision is minimally affected by fault resistance, with <0.5 % deviation even in nonlinear scenarios. Sensitivity analysis conducted on various parameters, including mother wavelet patterns, suggests the optimal solution for each fault type, enhancing detection speed by 20 %. The proposed method is validated using the Cigre HVDC benchmark, confirming its accuracy, speed, and robustness in fault detection and location in HVDC lines. The main contribution of this paper is an accurate, fast, and robust phaselet-based algorithm that reduces fault location errors to <1 % and is applicable to all types of bipolar and monopolar HVDC systems, delivering reliable results for both ground and line faults.

Load frequency control in power systems with high renewable energy penetration: A strategy employing P[formula omitted](1+PDF) controller, hybrid energy storage, and IPFC-FACTS

The high penetration of Renewable Energy Sources (RESs) in the modern power system poses a challenge to power system stability. This stability is affected by the stochastic, fluctuating output of RESs, which is influenced by weather conditions, and a lack of inertia resulting from reduced rotating mass. To address this issue, a new controller, referred to as Proportional-Fractional Integrator Plus Proportional-Derivative with Filter, PIλ(1+PDF), is designed for Load Frequency Control (LFC) with the support of a Hybrid Energy Storage System (HESS) for power systems with high-RES penetration. The HESS comprises a Superconducting Magnetic Energy Storage System (SMES) and a Vanadium Redox Flow Battery (VRFB) coupled with an Interline Power Flow Controller Flexible AC Transmission Systems (IPFC-FACTs) controller. The HESS, working in conjunction with the proposed LFC, injects virtual inertia and maintains power flow to expedite the frequency stability process. These systems are also integrated with Alternating Current (AC) and High Voltage Direct Current (HVDC) transmission lines to collectively enhance both the system's stability and the capacity of its transmission lines. To optimize the PIλ(1+PDF) controller parameters, Zebra Optimization Algorithm (ZOA) is employed utilizing an Integral Time Absolute Error (ITAE) objective function. The proposed controller is tested on a four-area power system integrated with a wind turbine, photovoltaic (PV) panels, a biodiesel generator, and a hydrogen aqua electrolyzer fuel cell, representing a high penetration of RESs in modern power systems. The results are compared with those obtained using Proportional-Integral-Derivative (PID) and Fractional Order Proportional Integral Derivative (FOPID) controllers. Sensitivity analysis and robustness tests are also performed to verify the stability of the power network by changing system parameters and under randomly chosen loading conditions. The proposed PIλ(1+PDF) controller tuned with ZOA outperforms PID and FOPID controllers by minimizing settling time for frequency changes by 62 %, eliminating overshoot, and reducing undershoots for frequency and tie-line power changes by 73 % and 55 %, respectively. Simulation results demonstrate that the proposed controller outperforms PID and FOPID controllers by effectively damping frequency and tie-line deviations, resulting in reduced frequency overshoots, undershoots, and shorter settling times.

A Novel Integrated Switching Strategy for Reliable Starting of Two Terminal MMC HVDC Transmission System

If the initialization protocol of the Modular Multilevel Converter (MMC) system is not adhered to, the primary winding of the system transformer will experience a surge in inrush current, while the secondary winding on the converter side will exhibit significant starting current draw to charge the capacitors of the MMC-H-bridge. This pronounced initial current surge can trigger the activation of protective measures, leading to the disconnection of the High Voltage Direct Current (HVDC) line and thereby engendering power system reliability and stability concerns. This paper presents a starting methodology for a two-terminal MMC HVDC system. The proposed approach entails employing controlled switching techniques to mitigate inrush currents in the HVDC converter transformer, coupled with the utilization of pre-insertion resistance circuit breakers to diminish starting currents on the converter side. The efficacy of the aforementioned strategy is validated through simulations conducted on a two-terminal MMC HVDC system modeled using PSCAD/EMTDC, with the results confirming its effectiveness.

Performance analysis of voltage source converter based high voltage direct current line under small control perturbations

High voltage direct current (HVDC) systems provide important advantages; among them the ability to transmit enormous amounts of electrical power over great distances at low cost. As a result, planners of power systems consider it as a viable choice for power transmission and interconnection of asynchronous networks. Depending on HVDC grids, continental/super grids have been recently constructed to promote global economic development. The study described in the paper focuses on the behavior of a voltage sourced converter (VSC) based HVDC transmission system comprising three arms-neutral point clamped (NPC) converters interconnecting two asynchronous alternating current (AC)networks. In addition, the system components, and the vector control strategy of active/reactive powers and direct current (DC)bus voltage are simulated in MATLAB/Simulink under varying situations by adjusting the controller’s settings. The study records and analyzes AC/DC voltages and active/reactive powers at two converter stations undervarying power and voltage conditions. The results of the study provide key performance indicators, such as settling time (tsett), steady state error (SSE), overshot/undershoot (OS%/US%), and correlation factor (CF), which demonstrate the robustness of thesystem’s control.

A Measurement Method for the Charging Potential of Conductors in the Vicinity of HVDC Overhead Lines Based on a Non-Contact Electrometer

Charging potential appears when a conductor insulated to the ground is exposed to an electrostatic field. A modified measurement method based on a non-contact electrometer is presented in this article. This system is appropriate for measuring the charging potential of a conductor near high-voltage direct-current (HVDC) overhead lines. Compared with the contact measurement method, the modified method is hardly affected by the internal resistance of the electrometer, which helps ensure measurement accuracy in the electrostatic field. In contrast with the traditional non-contact electrometer, the electric field generated by HVDC lines and the space charges around the electrometer probe are shielded using a grounding cage. The effectiveness of the modified measurement method was verified via experiments. The impacts of the structure and position of the measurement system on the measured charging potential are discussed.

A Two-Terminal Directional Protection Method for HVDC Transmission Lines of Current Fault Component Based on Improved VMD-Hilbert Transform

The traveling wave protection of high voltage direct current (HVDC) transmission lines is susceptible to the influence of transition resistance. As a backup protection, current differential protection has absolute selectivity, but usually requires an increase in delay to avoid misoperation caused by distributed capacitance on the line, resulting in a longer action time. Based on this, a two-terminal directional protection method for HVDC transmission lines is proposed based on Sparrow Search Algorithm (SSA)-Variational Mode Decomposition (VMD) and Hilbert phase difference. On the basis of analyzing the directional characteristics of the current fault component at both ends of the rectifier and inverter sides under different faults, SSA is first used to optimize the parameters of VMD. The residual components representing the direction of the current fault component at both ends are extracted through VMD, and then the Hilbert phase difference of the residual components at both ends is calculated to identify faults inside and outside the line area. In addition, fault pole selection can be achieved based on the ratio of the sum of multi-band Hilbert energy of single-terminal voltage fault components at the positive and negative poles. Simulation experiments have shown that the proposed protection scheme can quickly and effectively identify fault and has good tolerance to transition resistance and noise interference.

A novel dc fault protection scheme based on intelligent network for meshed dc grids

This paper proposes a fault detection and classification scheme for multi-terminal high voltage direct current (MT-HVdc) lines by integrating discrete wavelet transform (DWT) multi-resolution analysis with artificial neural networks (ANNs). Previously, such intelligent protection schemes used manual approaches or arbitrary rules of thumb to optimize a set of hyperparameters of the neural networks without applying any optimization algorithm. In order to improve accuracy, this work proposes an efficient Bayesian Optimization (BO) approach for evaluating and establishing the regulated hyperparameters for ANNs. The DWT multi-resolution analysis (MRA) and Parseval’s theorem are used to extract energy variation for various faults. The energy variation of fault signals at different scales is fed into a multi-stage model to optimize the hyperparameters of neural networks with minimal training setup time and compute effort. After training, the data-based algorithm is implemented in a single-end main and coordinated secondary unit with control logic. The proposed scheme intends to detect internal short-circuit dc faults as quickly as possible and cover the failure of the main unit with expedited backup action. The findings of the study reveal that the proposed scheme can accurately detect internal faults in a variety of testing conditions and remain stable against external faults or disturbances with an average recognition accuracy of 99.38%.

An interpolation-based solution to use low sampling rate records in traveling wave-based fault location methods

This paper presents an interpolation-based solution that allows the application of traveling wave (TW)-based algorithms even using sampling rates lower than those typically considered as a requirement for classical approaches. Two phasor (PH)-based and one TW-based fault location methods are compared with the proposed technique and applied through Alternative Transients Program (ATP) fault simulations in a 500 kV/60 Hz Brazilian double circuit series-compensated transmission lines with high-voltage direct current lines (HVDCs) and static var compensators (SVCs) in the vicinity. The results show that the proposed interpolation-based technique is reliable and suitable for TW-based fault location using data records with sampling rates lower than those used in commercially available equipment. Moreover, its accuracy is comparable to classical TW-based fault location solutions, revealing its usefulness for practical application when only traditional digital fault recorders (DFRs) are available.

Adaptive fault ride through control of VSM Grid-forming converters

Recently, many high voltage direct current (HVdc) transmission lines are being constructed with the intention of becoming “backbones” of future power grids. Grid-forming (GFM) controlled Voltage Source Converters (VSCs) are anticipated to provide significant stability advantages compared with Grid-following (GFL) VSCs in HVdc converters connected to weak ac grids or to grids with high penetration of renewable inverter-based resources (IBRs). This paper proposes an adaptive fault ride through controller for Virtual Synchronous Machine (VSM) GFM control, which has significantly improved fault ride through capability over the more conventional GFM control with cascaded or switchable current limiting. The performance of the proposed adaptive control is investigated using Electromagnetic Transient (EMT) simulation. The results show that the proposed adaptive control has superior post disturbance recovery from ac faults as well as phase angle shifts, and overcomes the instability reported in GFM converters connected to strong ac networks.

Finite Element Method Assisted Audible Noise Detection for Overhead Line Conductors Using the Cage Experiment

Audible noise (AN) has been the main concern in recent years when considering electromagnetic environmental impact in designing overhead lines (OHLs). Driven by the increased demand of high voltage direct current (HVDC) transmission lines, a novel corona cage experiment is built in association with an acoustic simulation using the finite element method (FEM). The characteristics of the acoustic wave propagation within the testing hall are analyzed using FEM, and the optimized locations for AN detection are determined. On the basis of complying with measurement standards, the location of the measurement is selected to be closer to the sound source and further away from the reflecting surface, to generate more accurate measurement results. In the designated test hall for this paper, the influence of refraction and reflection of sound waves is not obvious. The attenuation of sound waves below 4 kHz is negligible, while for higher frequencies such as 4 kHz and 8 kHz it is significant. Finally, FEM simulation is used to optimize the location for measurement microphones, and further experiments are carried out to verify its accuracy.

Non-unit Protection for Asymmetrical DC Line Faults in Bipolar LCC-HVDC Transmission Systems

The faults in high voltage direct current (HVDC) transmission lines cause a sudden rise in DC, resulting in over-stressing of converter valves and transformer windings. DC line faults of longer duration, or permanent nature, will lead to a severe disturbance in the associated AC network as well. Thus, the HVDC line faults must be detected immediately to interrupt the fault current by initiating proper actions of control and protection. This paper implements a new method to detect the asymmetrical (pole-to-ground) faults in the conventional bipolar LCC-HVDC transmission system. The proposed method defines a Fault Indicating Parameter (FIP) based on the transient voltage and current elements of each pole. The transient elements are obtained based on single-end measurements. Single-end or non-unit measurements lead to the development of simple, cost-effective and fast protection criteria. Also, the method is applicable to faults close to the line boundary and of high resistivity. A two-terminal bipolar LCC-HVDC transmission system, based on ±500 kV, 1000 MW and 900 km length, is used to evaluate the performance of the proposed technique in offline mode, using MATLAB/Simulink software. Also, the results are validated using an OPAL-RT real-time simulator under divergent fault conditions. The simulation results prove the robustness, selectiveness and accuracy of the proposed scheme.

An Improved Method of Traveling Wave Protection for DC Lines Based on the Compensation of Line-Mode Fault Voltage

The protection of high voltage direct current (HVDC) transmission line is the key to development of the HVDC transmission technology. To deal with the problem that the traditional traveling wave protection (TWP) has low sensitivity under high resistance faults, an improved TWP scheme based on the compensation of the line-mode component of fault voltage (LMCFV) is proposed. The expressions of the LMCFV of HVDC system at different fault locations are derived. Conclusions can be drawn that the LMCFV and fault resistance are linear when the DC line fault occurs, whereas the linear state will be broken for the external fault. Based on this, the LMCFV for the metal fault occurring at the DC line midpoint is used as the reference value to compensate for the faults in other cases of the HVDC systems. The protection scheme constructed based on the compensatory LMCFV and compensation coefficient can accurately identify fault of the DC line. Finally, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\pm }$</tex-math></inline-formula> 800 kV model of HVDC systems is built in PSCAD to verify the protection performance. The effect of fault resistance can be eliminated by compensatory LMCFV, and the DC line fault can be quickly and reliably identified by the simulation results.

Short-term operation of cascade hydropower system sharing flexibility via high voltage direct current lines for multiple grids peak shaving

The escalating pressure for peak shaving presents a significant challenge for the power grid's operation, particularly with the rapid growth of renewable energies. Huge cascade hydropower stations (CHS) send power to the local power grid and multiple power grids via long-distance high voltage direct current (HVDC) transmission lines, how to share hydropower flexibility for multiple power grids in peak shaving while considering constraints of hydropower and HVDC lines challenges power dispatching management. This study proposed a multiple power grids peak shaving model of cascade hydropower stations with HVDC sharing flexibility for receiving power grids. Firstly, the objective of minimizing the peak-valley difference of multiple power grids is adopted. The model then takes into account the operation constraints of CHSs and HVDC tie-lines to share hydropower flexibility. Finally, the model is transformed into a Mixed-Integer Linear Programming problem through piecewise linearization. The case studies of practical examples in southwest China show that the proposed model reduces peak-valley differences by 23.3%, 46.9%, 99.1% and 19.6%, 34.3%, 99.5% for three receiving power grids in two typical days by sharing hydropower flexibility. Moreover, adjusting the HVDC daily power regulation times and electricity deviation tolerance helps coordinate power grids to improve their peak shaving performance.

Minimization of Electric Fields Underneath High Voltage Direct Current Transmission Lines Based on Shielding Technique

Minimization of Electric Fields Underneath High Voltage Direct Current Transmission Lines Based on Shielding Technique

Dynamic interactive characteristics between icicle growth and corona discharge on HVDC outdoor insulators during icing accretion

AbstractIn order to improve the stability and reliability of high voltage direct current (HVDC) transmission lines in cold regions, this article investigated the corona discharges and the icicle growth characteristics on outdoor insulators under DC voltages. The experiments were conducted at CIGELE laboratory at University of Quebec. The simulation model of corona discharges and the theoretical model of icicle growth were established. The dynamic process and interactive characteristics between the icicle growth and corona discharges under different HVDC voltages were obtained. The results showed that the discharge activity was strong and the cooling effect of ionic air was weak under negative DC voltage, resulting in a large number of bubbles inside the icicle. More negative ions were produced under negative DC voltage, which enhanced the polarisation of water droplets, leading to a greater density of ice beads outside the icicles. In addition, the longest icicles of each insulator under high humidity could bridge the shed gap. The accumulated charge and leakage current were higher under negative DC voltage, as well as the corona discharge at the top of the icicles lasted longer. Therefore, the negative DC corona discharge more significantly inhibited the growth of the icicle, resulting in a slower growth rate of the icicles.

Non-unit protection for long-distance LCC-HVDC transmission lines based on waveform characteristics of voltage travelling waves

Currently, the voltage-derivative-based protection (VDBP) method has been applied in High-Voltage Direct Current (HVDC) lines as primary protection. But it has the problem of low reliability to high-resistance faults, and even more difficult or fail when applying to long distance lines. For such circumstances, current differential protection will play backup protection role with slow operation speed. Therefore, HVDC transmission lines require high reliable and high-speed protection scheme. In this paper, the complex frequency domain expressions of the line-mode fault component voltage (LFCV) at the line end as well as its waveform characteristics for internal and external faults are derived respectively. Based on the theoretical analysis of the LFCV at the line end, a novel non-unit protection scheme utilizing the waveform similarity coefficient is proposed. A ± 800 kV HVDC system built in PSCAD/EMTDC is used to verify the feasibility and validity of the proposed protection method. Comprehensive simulation results show that the proposed scheme can accurately identify internal and external faults, including high resistance faults (600 Ω) and long-distance faults (over 2000 km).

A New Hybrid Method to Assess Available Transfer Capability in AC–DC Networks Using the Wind Power Plant Interconnection

This article presents a very effective and exact technique for evaluating dynamic available transfer capability (ATC) using a fast differential equation power flow (DEPF) and Newton–Raphson–Seydel, taking into account the initial contingency (n-1) scenarios and the normal system condition. We indicated that instead of simply inverting the Jacobian matrix, the inverse computation time of the DEPF may be substantially decreased by inverting the submatrices. A hybrid technique was developed for Dynamic ATC calculation using a mixture of the static and dynamic methods. Installing the high voltage direct current (HVdc) line is taken into account in the ATC calculations because HVdc is the backbone of the future transmission network. The challenge of integrating wind power plants and big loads into the future network is also explored in this article. In an attempt to rectify earlier techniques, an estimate of the potential energy boundary surface was also used in conjunction to assess transient stability. This technique was effectively applied on IEEE 39 bus, IEEE 118 bus, Iowa State 145-bus, IEEE 300-bus, the east of Iran (1153 buses), and Khorasan network (4438 buses) systems for different bilateral/ multilateral transactions.

An Improved Calculation Method Based on Newton–Raphson Method for Ion Flow Field of UHVDC Transmission Lines at High Altitude

The fast and accurate solution of the total electric field and ion current density is crucial for the electromagnetic environment of ultra high voltage direct current (UHVDC) transmission lines. In this article, an improved method based on Newton–Raphson method (NRM) and upstream finite element method (UFEM) is proposed to calculate the ion flow field under complex conditions. According to the gas motion theory, the corona-onset electric field, ion mobility, and recombination coefficient are obtained at high altitude and put into the ion flow field model in this article. Subsequently, the charge density is used to solve Poisson’s equation, and the current continuity equations are calculated by UFEM. After that, the charge density of the conductor surface is updated based on NRM. These three parts are iterated repeatedly until the convergence conditions are met. According to the test results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 800-kV UHVDC transmission line at high altitude, the validity and rationality of the proposed method are verified. The result demonstrates that due to the reduction of atmospheric pressure at the high altitude, the corona-onset electric field decreases, and the ion mobility and recombination coefficient increase, which makes the total electric field and ion current density at ground level increase. Compared with the traditional methods, the improved method is insensitive to the initial value of the surface charge density. Moreover, this proposed method can effectively improve the convergence ability and achieve the stable and fast calculation of the ion flow field at high altitude.