High Voltage Direct Current System Research Articles

Estimation of multi-infeed HVDC inter converter direct current interaction in close electric proximity

This paper aims at investigating the direct current interaction between various converters of High Voltage Direct Current (HVDC) system, which lie in close electric proximity within the multi-infeed configuration. The interaction between converters in multi-infeed DC system are highly possible events which need to be evaluated in order to avoid the adverse operational results. The various indices such as multi-infeed interaction factor (MIIF) considering AC busbar voltages, local and concurrent commutation failures (CF) in converter stations under different AC disturbances, influence of AC system’s strength on fault recovery time (FRT), transient over-voltage (TOV) under permanent DC faults, voltage and power stability of multi-infeed DC system are comprehensively illustrated in literatures. However, there is lack of literature regarding the investigation of current interaction in multi-infeed DC system. Therefore, in this paper, a power flow approach is adopted to estimate the inter converter direct current interaction. An index, multi-infeed current interaction factor (MICIF) is proposed that can effectively depicts the interaction between converters. The MICIF index is verified through electromagnetic transient simulations of dual infeed HVDC system developed in PSCAD/EMTDC. The results show that MICIF index can accurately assess the interaction between different converter stations of HVDC system under steady and transient states.

Wavelet multiscale principal components and traveling waves enabled machine learning technique for protection of MT-HVDC systems

The interconnection of renewable energy sources to conventional power grids is widely recognized and promoted by the deployment of high voltage direct current (HVDC) technology. One of the biggest challenges associated with the HVDC systems is the rapid rate of rising DC fault currents, resulting in the immediate collapse of the converter stations. Conventional schemes of AC protection and low-speed DC protection are not worthy and mature because of the abrupt rising characteristics of DC currents. Therefore, protection techniques are being developed for reliable bulk power transfer and interconnection of unsynchronized grids via DC links. Timely identification, classification, and determination of location are the most fundamental characteristics of any protection scheme. This research paper proposes a machine learning-based protection method that establishes a rapid and reliable solution addressing the drawbacks of existing protection schemes. A multi-terminal high voltage direct current (MT-HVDC) test system is designed in Matlab/Simulink. Pole-to-ground and pole-to-pole faults are applied at different fault locations to assess the validity of the proposed algorithm. For this, DC voltages and currents are measured and analyzed. Power spectral analysis of traveling waves and Wavelet multiscale principal components analysis are employed for the extraction of featured data to classify and locate the DC faults. This reduced dimensional featured data is utilized for training and testing the support vector machine learning algorithm to analyze the accuracy of the proposed protection technique. Simulation results confirm the accuracy of rapid identification, classification, and location of DC faults.

Study on current-sharing characteristic of multi-pillar parallel arresters for DC transfer switch

Ultra high voltage direct current (UHVDC) system is the key support of power grid, which has an important impact on the development of China’s power grid. Direct current (DC) transfer switch is an indispensable component for UHVDC system, and its research is conducive to the development of the UHV DC transmission system. DC transfer switch is composed of breaking circuit, oscillation circuit and energy absorbing circuit. The energy absorbing circuit of DC transfer switch can absorb lots of energy by using arresters when DC is turn off, it can avoid the failure of DC breaking due to arc reburning. In order to meet the requirement of absorbing a large amount of energy, the arresters in the energy absorbing circuit generally adopts a multi pillars parallel structure. When multiple columns are connected in parallel, the uniform distribution of energy between different arresters columns becomes a very important problem. If the energy distribution difference is large, the arresters will overheat, aging and even explode. Thus, it is necessary to study the current-sharing characteristics. In this paper, the simulation and experiment are carried out in combination with the actual converter station. On the premise of total discharge energy in station, it is concluded that: The greater the deviation of volt–ampere characteristic curve from standard curve, the greater the non-uniformity coefficient and the greater the energy absorbed by single pillar arrester. The maximum energy absorbed by single arrester is 8.77 MJ, the non-standard curve by single pillar arrester should deviate from the standard curve by no more than 4%.

Decoupled Control for Double-T Dc-Dc MMC Topology for MT-HVdc/MVdc Grids

This paper proposes a decoupled control of a dc-dc modular multilevel converter (MMC) based on a double-T topology intended for multi-terminal high voltage direct current (MT-HVdc) transmission systems or emerging distribution systems operating in medium voltage direct current (MVdc). The aim of the proposed control strategy is to obtain an input current with reduced harmonic content and to eliminate the output ac common-mode voltage, which is not allowed in MT-HVdc systems. The control strategy consists of injecting two circulating ac currents and two dc currents that allow the energy balance between the arms of the converter and the general energy balance of the topology. The dc and ac currents are decoupled and allow control over load variations and reference changes in the dc-links. The proposed topology is mathematically modeled and the control method is then derived. Simulation results are presented to validate the proposed system.

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).

Fault diagnosis of the HVDC system based on the CatBoost algorithm using knowledge graphs

In order to overcome the difficulty of fault diagnosis in the high-voltage direct current (HVDC) transmission system, a fault diagnosis method based on the categorical boosting (CatBoost) algorithm is proposed in this work. To make the research conform to the actual situation, three kinds of measured fault data in the HVDC system of the Southern Power Grid are selected as the original data set. First, the core role and significance of fault diagnosis in knowledge graphs (KGs) are given, and the characteristics and specific causes of the four fault types are explained in detail. Second, the fault dates are preprocessed and divided into the training data set and the test data set, and the CatBoost algorithm is employed to train and test fault data to realize fault diagnosis. Finally, to verify the progressiveness and effectiveness of the proposed method, the diagnostic results obtained by CatBoost are compared with those obtained by the BP neural network algorithm. The results show that the diagnostic accuracy of the CatBoost algorithm in the three test sets is always higher than that of the BP neural network algorithm; the accuracy rates in the three case studies of the CatBoost algorithm are 94.74%, 100.00%, and 98.21%, respectively, which fully proves that the CatBoost algorithm has a very good fault diagnosis effect on the HVDC system.

The DC Transformer Power Electronic Building Block: Powering Next-Generation Converter Design

Power electronics has evolved from being only present in a few applications such as variable speed drives in the 1970s to becoming ubiquitous, present in almost every industrial application, and powering our daily life. In this ever-expanding market, power converters have become a mature technology covering a wide range of applications, providing solutions from a few watts (e.g., LED drivers) to gigawatts (e.g., high-voltage direct current systems). Competition has driven technology development in pursuit of cost reduction, increased efficiency, performance improvements, high power quality, higher power density, reliability, and an accelerated time to market. To meet these requirements, power converter design has been driven toward a more modular approach based on embedded systems, intelligent power modules, and power electronics building blocks (PEBBs) <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> .

Unified AC Transmission Expansion Planning Formulation incorporating VSC-MTDC, FACTS devices, and Reactive Power compensation

The main aim of the static Transmission Network Expansion Planning (TNEP) is to determine which and where new transmission equipment must be installed. The complexity added by the non-linearities leads to simplifications, which include the DC model. However, most non-linearities are solvable nowadays. Thus, the new scenario of large non-dispatchable power sources penetration and the several developments in technologies, e.g, Flexible AC Transmission Systems (FACTS) devices and High Voltage Direct Current (HVDC) interconnections, motivate the use of the AC model with its non-linearities. Some research works address the use of some of those technologies for TNEP in an independent fashion, which can lead to sub-optimal solutions. In this work, Voltage Source Controlled-Multiterminal HVDC (VSC-MTDC) systems, FACTS devices, and Reactive Power Planning (RPP) are integrated into the same planning optimization process, so that a unified AC TNEP formulation is proposed. A non-linear mathematical programming technique and a differential evolution based metaheuristics are chosen to achieve an optimal transmission configuration. To evaluate the benefits of the proposed approach, two IEEE modified test systems (9 and 118 buses) are used. Results suggest that more economical solutions can be obtained if different types of reinforcement strategies are taken into account in a unified approach.

Aggregated SFR model for VSC HVDC interconnected power systems with high penetration of wind power

This letter proposes a novel aggregated system frequency response (ASFR) model, which can fully capture the frequency characteristics of the voltage source converter-based high voltage direct current (VSCHVDC) interconnected power system with high penetration of wind power. First, a multi-machine SFR model is presented, considering the inertia and frequency control processes of VSCHVDC and wind turbines (WTs). Then, a novel aggregation approach is proposed to transform the multi-machine SFR model into a single-machine SFR model on the basis of different control modes of the VSCHVDCs and WTs. Finally, simulation studies are conducted to validate the performance of the proposed ASFR model and its application in frequency response analysis.

Design and Study of the Key Characteristics of a New DC Vacuum Interrupter With a High Peak and Low Residual Magnetic Field

With the rapid development of multiterminal high-voltage direct current (HVdc) transmission systems, the research and development of high-speed and stable high-voltage dc circuit breakers have received attention. Among them, mechanical dc circuit breakers based on manual zero-crossing dc breaking technology have been applied in practical projects, owing to their small size, low on-state loss, and low price. However, this method adds a high-frequency current, which deteriorates the magnetic field between the poles of the interrupter when the arc is broken. Therefore, the development of HVdc circuit breakers that maintain high peak magnetic fields and low residual magnetic fields at high frequencies has become the key to the development of multiterminal HVdc transmission. To solve this problem, this article proposes a new interrupter for a vacuum dc circuit breaker based on artificial zero-crossing technology and studies its key characteristics, such as temperature rise, electromagnetic field, and arc column plasma distribution characteristics. The results reveal that the new interrupter proposed in this article has a low-temperature rise, uniformly distributed electric field, high peak value and low remanence of the longitudinal magnetic field, and uniformly distributed plasma in the arc column, and exhibits arc diffusion. Its ability to cope with high-frequency current is significantly higher than that of the traditional cup-shaped axial magnetic field (AMF) contact system interrupter, which is conducive to the high-speed and stable breaking of the interrupter.

A New Communication-Free Grid Frequency and AC Voltage Control of Hybrid LCC-VSC-HVDC Systems for Offshore Wind Farm Integration

We propose frequency and voltage control method for a hybrid high-voltage direct current (HVDC) system for integrating an offshore wind farm into transmission networks. Conventionally, DC voltage level is maintained as constant regardless of the wind velocity and the grid frequency, so AC voltage fluctuates with active power variation in a hybrid HVDC system due to the innate reactive power absorption of inverter side line-commutated converter (LCC). However, in the proposed method, the DC voltage changes according to the wind velocity. Furthermore, DC voltage is simultaneously regulated to participate in frequency control in a communication-free manner. These two characteristics can be achieved by using five droop control methods proposed here. Additionally, by determining droop constants using the proposed determination methods, AC voltage can be maintained as constant during active power fluctuations. Therefore, using the proposed method, an offshore wind farm can be stably connected to mainland transmission networks and successfully used as frequency supporting resources, because voltage characteristics of the AC network are not destabilized. A small-signal state-space (SS) model of the target system was also developed to investigate stability of the proposed control. The utility of the proposed method is demonstrated by case studies using PSCAD and SS models.

Semi‐hot redundant control method for modular multilevel converter‐based high‐voltage direct current systems under submodules fault

AbstractA modular multilevel converter‐based high voltage direct current (MMC‐HVDC) system involves a large number of cascading submodules (SMs). The failure of SMs may critically degrade the system performance. Therefore, several redundant SMs can be incorporated and reasonably controlled to ensure the system reliable and continuous operation even if certain SMs fail. This paper proposes a semi‐hot redundant method for MMC‐HVDC systems. In the proposed strategy, when the system operates normally, the redundant SMs are controlled in a lower voltage range. These SMs do not require frequent charging and discharging, which decreases the switching loss. When ordinary SMs fail, the faulty SMs are bypassed and the corresponding number of redundant SMs can be promptly recharged to the rated voltage to replace the faulty SMs. The semi‐hot reserved SMs can shorten the transient process of faulty SMs replacement, and in this process, the absence of faulty SMs does not considerably influence the system. Thus, the original control and modulation strategies of the system do not need to be modified when several SMs fail. The performance of the proposed method is compared with those of the existing methods, and its validity is demonstrated through a small‐scale experimental prototype.

Artificial Intelligence-based Control Techniques for HVDC Systems

The electrical energy industry depends, among other things, on the ability of networks to deal with uncertainties from several directions. Smart-grid systems in high-voltage direct current (HVDC) networks, being an application of artificial intelligence (AI), are a reliable way to achieve this goal as they solve complex problems in power system engineering using AI algorithms. Due to their distinctive characteristics, they are usually effective approaches for optimization problems. They have been successfully applied to HVDC systems. This paper presents a number of issues in HVDC transmission systems. It reviews AI applications such as HVDC transmission system controllers and power flow control within DC grids in multi-terminal HVDC systems. Advancements in HVDC systems enable better performance under varying conditions to obtain the optimal dynamic response in practical settings. However, they also pose difficulties in mathematical modeling as they are non-linear and complex. ANN-based controllers have replaced traditional PI controllers in the rectifier of the HVDC link. Moreover, the combination of ANN and fuzzy logic has proven to be a powerful strategy for controlling excessively non-linear loads. Future research can focus on developing AI algorithms for an advanced control scheme for UPFC devices. Also, there is a need for a comprehensive analysis of power fluctuations or steady-state errors that can be eliminated by the quick response of this control scheme. This survey was informed by the need to develop adaptive AI controllers to enhance the performance of HVDC systems based on their promising results in the control of power systems. Doi: 10.28991/ESJ-2023-07-02-024 Full Text: PDF

An adaptive linear active disturbance rejection control method for HVDC transmission system

With the advantages of large transmission capacity, low losses, rapid and flexible power regulation, and the ability to achieve non-synchronous networking, High Voltage Direct Current transmission systems are playing an increasingly important role in long distance transmission and grid interconnection. However, under certain circumstances, such as disturbances in the DC transmission system and sudden load changes, the converter based on PI control in DC transmission system suffer from slow response speed and poor stability. In order to improve the stability of the system and the response speed of DC voltage, this paper proposes an adaptive linear active disturbance rejection control (A-LADRC) method. The method is based on the analysis of the relationship between key bandwidth parameters and output quantities in linear active disturbance rejection control and enables adaptive adjustment of the controller bandwidth parameters for fast regulation of the DC voltage and to improve the stability of the DC voltage in the event of disturbances. Finally, the proposed control method is validated by simulation, and the results show that the proposed control method can effectively improve the response speed and robustness of the DC voltage, which has good practical engineering value.

Data-Mining Techniques Based Relaying Support for Symmetric-Monopolar-Multi-Terminal VSC-HVDC System

Considering the advantage of the ability of data-mining techniques (DMTs) to detect and classify patterns, this paper explores their applicability for the protection of voltage source converter-based high voltage direct current (VSC-HVDC) transmission systems. In spite of the location of fault occurring points such as external/internal, rectifier-substation/inverter-substation, and positive/negative pole of the DC line, the stated approach is capable of accurate fault detection, classification, and location. Initially, the local voltage and current measurements at one end of the HVDC system are used in this work to extract the feature vector. Once the feature vector is retrieved, the DMTs are trained and tested to identify the fault types (internal DC faults, external AC faults, and external DC faults) and fault location in the particular feeder. In the data-mining framework, several state-of-the-art machine learning (ML) models along with one advanced deep learning (DL) model are used for training and testing. The proposed VSC-HVDC relaying system is comprehensively tested on a symmetric-monopolar-multi-terminal VSC-HVDC system and presents heartening results in diverse operating conditions. The results show that the studied deep belief network (DBN) based DL model performs better compared with other ML models in both fault classification and location. The accuracy of fault classification of the DBN is found to be 98.9% in the noiseless condition and 91.8% in the 20 dB noisy condition. Similarly, the DBN-based DMT is found to be effective in fault locations in the HVDC system with a smaller percentage of errors as MSE: 2.116, RMSE: 1.4531, and MAPE: 2.7047. This approach can be used as an effective low-cost relaying support tool for the VSC-HVDC system, as it does not necessitate a communication channel.

Comprehensive Analysis and Experiments of RB-IGCT, IGCT With Fast Recovery Diode and Standard Recovery Diode in Hybrid Line-Commutated Converter for Commutation Failure Mitigation

Commutation failure is one of the most important factors threatening the safety of multi-infeed high voltage direct current systems. To mitigate commutation failure, we have proposed a novel hybrid line-commutated converter by adding fully controlled devices to the conventional line-commutated converter. It aims to achieve auxiliary commutation and forced commutation with the help of fully controlled devices. Based on the novel hybrid line-commutated converter topology, the study investigates how to select suitable fully controlled devices and how to design the appropriate parameters of the devices. First, this article studied the general characteristics of reverse-blocking devices, including reverse-blocking integrated gate-commutated thyristor (RB-IGCT) and asymmetrical IGCT with diode (including fast recovery diode and standard recovery diode). Then, the novel commutation principle is carefully proposed and analyzed. The comprehensive simulation results and comparison study of the novel commutation principle are conducted. Then, according to the proposed commutation principle, the voltage and current working stress of devices are illustrated. According to these, vital features of devices, including recovery speed, <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state voltage, current conduction ability, surge current, maximum turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current, robustness, and volume of devices, are carefully analyzed and compared. Related experiments are conducted to present the vital characteristics of devices in the equivalent operating conditions in converters. Finally, the advantages and disadvantages of RB-IGCT and IGCT with fast recovery diode and standard recovery diode are comprehensively presented, which offers valuable reference considered in engineering applications.

Comprehensive Physical Commutation Characteristic Analysis and Test of Hybrid Line Commutated Converter Based on Physics Compact Model of IGCT

In order to mitigate commutation failure of high voltage direct current (HVdc) system, a novel hybrid line commutated converter (H-LCC) based on integrated gate commutated thyristor (IGCT) and thyristor has been proposed. To verify the proposed scheme's effectiveness and correctness, the physics-based compact model of reverse blocking IGCT (RB-IGCT) and physics-based model of thyristor are established in this article. By comparing the features of physics-based model with other simulation methods, it can be observed that the former has obvious advantages. On the basis, a simulation study of proposed H-LCC based on physics compact model of RB-IGCT and physics-based model of thyristor is conducted to analyze the physical commutation characteristics comprehensively, which is verified by equivalent commutation tests. The H-LCC can mitigate commutation failure of HVdc effectively and physics-based model of H-LCC is expected to be applied in the simulation of dc grid equipment and provide reference for commutation characteristics analysis and snubber parameter optimization that need rapid and multiple simulations.

Novel Controllable-Line-Commutated Converter for Eliminating Commutation Failures of LCC-HVDC System

To entirely eliminate commutation failure (CF) in conventional line-commutated converter based high-voltage direct current (LCC-HVDC) transmission system, a novel controllable line-commutated converter (CLCC) based on the combination of partially and fully controllable semiconductor devices is presented in this paper. The operating principle of CLCC and its control strategy are proposed. In addition, the voltage and current stress are analyzed. To verify correction and application of presented CLCC solution to the project, a CLCC-HVDC system model, adopting LCC at the rectifier side and CLCC at the inverter side, is developed in PSCAD/EMTDC software. Based on the model, the transient responses of the CLCC-HVDC system under various AC faults are simulated and compared with the pure LCC-HVDC. Simulation results show that the presented CLCC topology and its control strategy can not only eliminate CFs in various types of AC faults, but also improve the transient performance of the system after faults, while inheriting the attributes of traditional LCC such as large capacity, low cost and almost the same system control strategy. This is quite positive and meaningful for application of the CLCC-HVDC to multi-DC infeed system particularly.

Grounding electrode line fault location method based on simulation after test and deduction

• Fault characteristics of the grounding electrode line are weak. • Fault location by injecting signals into the line. • The initial pulse signal is eliminated after linear mode transformation. • Using simulation after test and deduction to obtain fault distance. • No need to calibrate the arrival time of the wave head. When a high-voltage direct current (HVDC) transmission system with the grounding electrode line (GEL) is in the balanced operation mode, the unbalanced current in the GEL and the neutral potential of the system are extremely small. In the GEL, after a fault incident, the additional fault component will be small, and fault characteristics will be weak. As the traditional passive fault location methods are challenging to apply, a GEL fault location method based on simulation after test and deduction (SATD) is proposed in this paper. Firstly, the pulse signal is injected into the GEL. Then, the mutation point of the pulse response signal is projected along the line to form a virtual fault point matrix. Based on the mentioned matrix, the fault location function is constructed, and the fault distance is obtained by the catastrophe point of the function. In this method, the bottleneck of precisely identifying the traveling wave (TW) arrival time in the time domain is broken, and the automated single-ended TW location of the GEL can easily be implemented. Many real time digital simulator (RTDS) tests validate the high accuracy and strong robustness of the method.

An Improved Phase-Disposition Pulse Width Modulation Method for Hybrid Modular Multilevel Converter

The hybrid modular multilevel converter (MMC) consisting of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) is a promising solution for overhead lines high-voltage direct current systems (HVDC) due to the advantages of direct current short circuit fault ride-through (DC-FRT) capability. This paper proposes an improved phase-disposition pulse width modulation (PDPWM) method for the hybrid modular multilevel converter. The number of carriers can be reduced from 3N (N is the number of submodules in each arm) to 6. The theoretical harmonic analysis of the improved PDPWM method for hybrid MMC is performed by using double Fourier integral analysis. The influence of three carrier displacement angles between HBSMs and FBSMs in the upper and lower arms on harmonic characteristics is investigated. The output voltage harmonics minimization PDPWM scheme and circulating current harmonics cancellation PDPWM scheme can be achieved by selecting the optimum carrier displacement angles, respectively. The proposed method for hybrid MMC is verified by the simulation and experimental results.