High Voltage Direct Current Model Research Articles

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).

Frequency Control of a Realistic Dish Stirling Solar Thermal System and Accurate HVDC Models Using a Cascaded FOPI-IDDN-Based Crow Search Algorithm

Unbalancing the real power in power system leads to fluctuation in system frequency which can cause the several negative effects on the performance and reliability of the interconnected power system. Therefore, to deal with this, the load frequency control (LFC) of a three-area asymmetric thermal power system integrated with a solar thermal power plant (STPP), a realistic dish-stirling solar thermal system (DSTS), and an accurate high voltage direct current (HVDC) link are presented in this work. For the suggested system, a novel cascade controller called fractional-order proportional-integral and integral-double-derivative with filter (FOPI-IDDN) is designed. By minimising a newly proposed performance index called the HPA-ISE and adjusting the controller and other system model parameters using a metaheuristic method called the crow search algorithm (CS). When comparing the system dynamics, it was found that the suggested FOPI-IDDN controller outperformed the FOPI, PIDN, and FOPIDN controllers. The findings of this study show that HPA-ISE shows approximately 30% and 60% improvements in settling time (ST) and peak overshoots (POS) for frequency response, and 32% and 18% improvements for the tie power responses in terms of ST and POS over ISE criteria. Also, studies on different area capacity ratios have shown that a system connected to a greater capacity ratio operates better. The realistic DSTS system with fixed and recurring insolation in area 1 and area 2 outperforms the others, according to experiments using different DSTS insolation. Also, it is discovered that the parallel AC-AHVDC link study is superior to the AC and HVDC connection research. Moreover, it seems from the sensitivity study that the CS-optimized FOPI-IDDN controller improvements obtained under normal settings are consistent across a wide range of changes.

An enhanced commutation failure prevention control in LCC based HVDC systems

Most commutation failures in high-voltage direct current (HVDC) systems are caused by AC faults on the inverter side. Conventional control methods for commutation failure prevention are on the premise of fault detection. However, a time period between the occurrence and detection of faults is inevitable. There are no effective control methods yet dedicated to this time period to mitigate commutation failures. In this paper, an enhanced commutation failure prevention (ECFPREV) control method is proposed. During the stage that a fault has taken place but not been detected, the proposed scheme still contributes to regulate the firing angle slightly for better commutation failure mitigation performance. To achieve this, a novel concept of pseudo commutation process is presented first, so that commutation processes with time delay can be performed in near real-time. Based on the constructed pseudo commutation voltage waveform, pseudo commutation parameters can be calculated at each sampling instant. Then, the ECFPREV, which is equipped with a pseudo firing angle prediction module, is proposed. An appropriate firing angle is calculated precisely for each pseudo commutation process regardless the fault detection signal, thus keeping a sufficient commutation margin for the upcoming real commutation process. The feasibility of the proposed strategy is validated through the CIGRE Benchmark HVDC model in PSCAD/EMTDC platform. Simulation results demonstrate that the proposed ECFPREV control is able to effectively improve the commutation failure immunity of HVDC systems.

Sizing and operation of a pure renewable energy based electric system through hydrogen

Today, in order to reduce the increase of the carbon dioxide emissions, a large number of renewable energy resources (RES) are already implemented. Considering both the intermittency and uncertainty of the RES, the energy storage system (ESS) is still needed for balancing and stabilizing the power system. Among different existing categories of ESS, the hydrogen storage systems (HSS) have the highest energy density, and are crucial for the RES integration. In addition, RES are located in faraway regions, and are often transmitted to the terminal consumption center through HVDC (high voltage direct current) due to its lower power loss. In this paper, we present a power supply system that achieves low-carbon emissions through combined HSS and HVDC technology. First, the combined HSS and the HVDC model are established. Secondly, the rule-based strategy for operating the HSS microgrid is presented. Then, an operating strategy for a typical network, i.e., the pure RES generation station-HVDC transmission-microgrids, is demonstrated. Finally, the best sizing capacities for all components are found by the genetic algorithm. The results prove the efficiency of the presented sizing approach for a pure RES electric system.

Analyses and Comparisons of Generic and User Writing Models of HVDC System Considering Transient DC Current and Voltages

Analyses and comparisons of generic models and a novel modeling method of line-commutated converter (LCC)-based high voltage direct current (HVDC) systems are presented for the power system simulator for engineering (PSS/E) simulation tool. The main purposes are to describe the dynamics of the DC voltage and current of HVDC system and to improve estimation of the maximum values using the generic and proposed HVDC models when AC line-to-ground faults are occurred. For the generic HVDC models, the characteristics and limitations as well as parameter investigations are conducted. Three modules are also are developed for the proposed HVDC model, which are composed of (a) AC/DC conversion; (b) controller selection; and (c) DC line model. Case studies were conducted considering the real-operated HVDC system in Korea under the PSS/E and power systems computer aided design (PSCAD) simulation environments. The simulation results were compared with measured data from the real-operated HVDC system and the results from the PSCAD HVDC models considering single- and three-phase line-to-ground faults. The case study results show that a specific generic HVDC model in PSS/E can simulate the dynamics of the DC voltage and current after the AC line-to-ground faults. The case studies also showed that the proposed modeling method is effectively improves the estimation of the maximum DC voltage and current values for the AC line-to-ground faults.

Exploration of novel optimal fuzzy‐based controller for enhancement of frequency regulation of deregulated hybrid power system with modified HVDC tie‐line

Recent advancements in the power system put forth various challenges to frequency regulation studies. These challenges show an immense impact on the power system's inertia and load pattern. The traditional load frequency control (LFC) mechanism may not be efficient to sustain the frequency regulation against these new challenges. Hence an intelligent, effective, and efficient controller is indispensable for various operating conditions of the power system. With this motive, a new intelligence-based controller (i.e., fuzzy (FOPIλ) + PIDN) is proposed and explored for the LFC of the modern power system. Besides, an opposition-based volleyball premier league algorithm is deployed to obtain optimal control parameters for the most promising results. The justification of the controller is evaluated on a nonlinear interconnected hybrid deregulated power system for several case studies. The effectiveness of the proposed controller has been verified by comparing it with several popular strategies for the step and random perturbation in load. Also, the firmness in the dynamic response against a wide range of system parameter variations has been analyzed. Moreover, the participation of a modified high voltage direct current model with inertia emulation technique in the system's inertia build-up has been demonstrated. Finally, the efficacy of the proposed LFC scheme has been verified over previously published literature on their platform.

Probabilistic sizing of a low-carbon emission power system considering HVDC transmission and microgrid clusters

Nowadays, large numbers of renewable energy generators have been installed world-widely to reduce carbon dioxide emissions. Hydrogen-based storage system has the largest energy density, which is with a great potential suitable to address the intermittence of these renewable energy outputs. In addition, the HVDC (high voltage direct current) transmission is often deployed to transmit the remote located abundant renewable energy resources to terminal consumers due to its lower losses. However, building a low-carbon emission power system through hydrogen-based microgrid clusters and the HVDC transmission still lacks investigations thus is an essential problem. In this paper, a probabilistic sizing methodology considering the uncertainties is developed. First, both the hydrogen-based storage system model and the HVDC model are analytically modeled. Second, a mixed integer programming optimal strategy is deployed to operate the hydrogen-based microgrid. Third, operation model of the renewable energy power station-HVDC transmission-IEEE 30 nodes network-microgrid clusters are presented. Last, the best sizing value for each component is obtained by a genetic algorithm. In addition, the uncertainties of the data profiles are modeled using scenario method. Within different scenarios, the probability density function of each sizing component is calculated. The results demonstrate that the sizing values based on the probabilistic method can reduce the adverse impacts of the uncertainties on the utility grids. Specifically, the mean value of the utility grid operation cost is reduced by 0.005 %-0.08 %.

Dynamic Modeling of HVDC for Power System Stability Assessment: A Review, Issues, and Recommendations

High-voltage direct current (HVDC) has received considerable attention due to several advantageous features such as minimum transmission losses, enhanced stability, and control operation. An appropriate model of HVDC is necessary to assess the operating conditions as well as to analyze the transient and steady-state stabilities integrated with the AC networks. Nevertheless, the construction of an HVDC model is challenging due to the high computational cost, which needs huge ranges of modeling experience. Therefore, advanced dynamic modeling of HVDC is necessary to improve stability with minimum power loss. This paper presents a comprehensive review of the various dynamic modeling of the HVDC transmission system. In line with this matter, an in-depth investigation of various HVDC mathematical models is carried out including average-value modeling (AVM), voltage source converter (VSC), and line-commutated converter (LCC). Moreover, numerous stability assessment models of HVDC are outlined with regard to stability improvement models, current-source system stability, HVDC link stability, and steady-state rotor angle stability. In addition, the various control schemes of LCC-HVDC systems and modular multilevel converter- multi-terminal direct current (MMC-MTDC) are highlighted. This paper also identifies the key issues, the problems of the existing HVDC models as well as providing some selective suggestions for future improvement. All the highlighted insights in this review will hopefully lead to increased efforts toward the enhancement of the modeling for the HVDC system.

Fault steady-state analysis method for the AC system with LCC-HVDC infeed

Fault steady-state analysis method can help to analyze the variation law of electrical quantities, clarify the fault characteristics, and provide the basis of power system design, protection scheme formulation, short-circuit current limitation and electrical equipment selection. Existing methods of fault steady-state analysis for alternating current (AC) system with line-commutated converter (LCC) high voltage direct current (HVDC) infeed are not suitable for high-severity AC system faults and existing equivalent models of LCC-HVDC system are inaccurate under asymmetrical AC system fault. Hence, a more accurate method is proposed in this paper. First, according to the relationship between the injected current of LCC-HVDC system and the fault phase voltage of commutation bus, equivalent models of the LCC-HVDC system under symmetrical fault and asymmetrical fault of AC system are established respectively. Based on the equivalent models of LCC-HVDC system and the fault sequence network of AC system, a fault steady-state analysis method for AC system with LCC-HVDC infeed is proposed. The proposed method is validated on CIGRE Benchmark HVDC model using PSCAD/EMTDC software. The results show that the proposed method is accurate and suitable for faults of different severities in AC system with LCC-HVDC infeed.

Integrated multi-area power system with HVDC tie-line to enhance load frequency control and automatic generation control

In this paper, a high-voltage direct current (HVDC) tie-line has been accurately modeled and proposed for multi-area interconnected power system to enhance load frequency control and automatic generation control (AGC). HVDC tie-line has been modeled based on a simple first-order transfer function for AGC system. Time constant of this transfer function indicates the required time by HVDC to set DC current because of load perturbation in multi-area interconnected power systems. It is worth mentioning that the inexact and very simple model of HVDC-line cannot yield a reliable and correct response. Hence, an accurate and interpretable model is proposed for HVDC-link to control the AGC system. To verify the accuracy of the proposed model, it has been analytically compared with the conventional HVDC model. The integrated multi-area power system has also implemented the inertia emulation controller technique which enables AGC system to tackle the accumulated energy in HVDC-line’s capacitance.

The hybrid model of VSC HVDC

The trend in semiconductor developments has made the high-voltage direct current (HVDC) technologies based on voltage source converters feasible. This type of convertor has a number of potential advantages compared with “classic” HVDC, but deep analysis should be carried out before its integration in electric power system. In this paper, the results of realization of the VSC HVDC model based on a concept of hybrid simulation of electric power system are presented. Hybrid concept combines three approaches of simulation: analog, digital and physical, combination of which allows to achieve a maximum efficiency. The obtained simulation results have confirmed an adequacy of the model and possibility to integrate it to the hybrid real-time simulator for carrying out various researches and analyses of the operation of large electric power system, including HVDC technologies, in real time without any decompositions and limitations.

Comparison of the characteristics of three kinds of HVDC systems with ABB, SIMENS, and Cigre Benchmark

This study presents the comparison among three control systems: Cigre Benchmark model, ABB model, and SIMENS model based on PSCAD. Firstly, the control systems which refer to Cigre Benchmark control model, ABB control model, and SIMENS control model are introduced, respectively. Analysis and comparison are done on these control systems about their design theories, control logic, and functional models, and the advantages and disadvantages of each control system are concluded. Secondly, simulations in both normal and fault conditions are done in order to verify the conclusions. On the one hand, the steady-state response characteristics of these three high-voltage direct current (HVDC) models are obtained and compared by setting different voltage of the receiving terminal AC bus. On the other hand, the transient response characteristics of these three HVDC models under different operating conditions are obtained, such as symmetrical and asymmetrical short-circuit fault, line switching on or off etc. The research results will provide experiences and references for the future optimisation of the HVDC control system.

Detection Method of HVDC Commutation Failure Using Transient Characteristics of Valve Current

In this study, a detection method of high voltage direct current (HVDC) commutation failure using transient characteristics of valve current to solve the problem of no reliable detection method for HVDC commutation failure in electromagnetic transient simulation is designed. By analyzing the transient characteristics of the valve current in the commutation failure process, the commutation failure criterion is extracted and the detection method has been designed. The detection method includes three parts: detection of valve current extreme point and change rate on its both sides, detection of maximum valve current, and detection of continuous non-zero time of valve current after extreme point. Using the PSCAD/EMTDC electromagnetic transient simulation software, a detection method based on the CIGRE BENCHMARCK HVDC model is built up, and the validity and accuracy of the detection method by simulation is verified.

A Predictive Control Strategy for Mitigation of Commutation Failure in LCC-Based HVDC Systems

High-voltage direct-current (HVDC) systems are being widely employed in various applications because of their numerous advantages such as bulk power transmission, efficient long-distance transmission, and flexible power-flow control. However, line-commutated-converter-based HVDC systems suffer from commutation failure, which is a major drawback, leading to increased device stress and interruptions in transmitted power. This paper proposes a predictive control strategy, deploying a commutation failure prevention module to mitigate the commutation failures during ac system faults. The salient feature of the proposed strategy is that it has the ability to temporarily decrease the firing angle of thyristor valves depending on the fault intensity to ensure a sufficient commutation margin. In order to validate the performance of the proposed strategy, several simulations have been conducted on the CIGRE Benchmark HVDC model using PSCAD/EMTDC software. Additionally, practical performance and feasibility of the proposed strategy are evaluated through laboratory testing, using the real-time Opal-RT hardware prototyping platform. Simulation and experimental results demonstrate that the proposed strategy can effectively inhibit the commutation failure or repetitive commutation failures under different fault types, fault impedances, and fault initiation times.

Key techniques in real time digital simulation for closed-loop testing of HVDC systems

This paper introduces several key techniques in realtime digital simulation for closed-loop testing of high voltage direct current (HVDC) systems, including line commutated converter (LCC) HVDC valve group models, modular multilevel converter (MMC) HVDC models, phase domain frequency dependent transmission line models, and switchable filter models. Various issues such as background, algorithms, implementations, applications, and validation of these models are introduced. These techniques represent the most advanced technology in modelling HVDC systems on a real time simulator. The models have been implemented on the RTDS Simulator, a comprehensive real time power system digital simulation tool.

Failure analysis and maintenance of a surge capacitor on the neutral bus in a ±500 kV HVDC converter station

This study analyses a surge capacitor failure on the neutral bus in a ±500 kV high voltage direct current (HVDC) converter station. Both overvoltage and insulation of the surge capacitor are investigated through simulation, practical record data analysis, and experimentation. A highly accurate HVDC model is established on the basis of the topological structure and parameters of the HVDC project. Using this model, the failure process is simulated by combining neutral bus overvoltage record analysis and voltage divider performance test. Results indicate that the 246 kV uncharacteristically high overvoltage on the neutral bus is a measurement error caused by voltage divider fault. From the field test, difference equation of the voltage divider is derived to reconstruct the actual overvoltage, the amplitude of which is 73 kV. The amplitude is significantly lower than that of the switching impulse withstand level of the surge capacitor, which should not cause capacitor failure. Therefore, the primary cause of capacitor failure is insulation damage rather than overvoltage. Finally, maintenance measures are proposed and applied in the station.

Space Charge Measurement on XLPE Cable for HVDC Transmission using PEA Method

Abstract The use of cross-linked polyethylene (XLPE) cables for High Voltage Alternating Current (HVAC) transmission has been successful in the world. However polymer insulated cables for High Voltage Direct Current (HVDC) transmission are still in development due to space charge build-up that occurs in cables under DC stress. Knowledge must be gained on the processes of charge build-up, including nature, kinetics and amount of accumulated charges, and on the consequences of charge accumulation regarding field distribution in the insulation. One way to determine the space charge distribution in XLPE cables for HVDC transmission non-destructively is the Pulse Electro Acoustic (PEA) method, a direct method for measuring space charge distribution in dielectric materials. The PEA method was chosen because it is suitable for a wide range of sample geometry (thin and thick samples), and is available for cable geometry. The present contribution concerns space charge distribution measurements in sections of HVDC model cables. To account for the situation of cables in service, measurements were performed with a temperature gradient across the insulation thickness, and this could be achieved by heating through the cable conductor. Measurements performed on XLPE insulated model cables with 4.5 mm insulation thickness were realized with -40 kV DC applied for 150 minutes. Injecting a current of 200A in the conductor produced theoretically a temperature gradient of 8 °C between the core and the outer face of the cable, with a surface temperature of the cable of 50 °C. A deconvolution procedure, wherein attenuation, dispersion and cylindrical geometry are accounted for, was used to recover space charge profiles at different times under stress. It is shown that considerable field redistribution occurs within the cable, compared to the Laplacian field distribution predicted in cylindrical geometry, due in part to the conductivity gradient associated with the thermal gradient, and for the other part to charge build-up occurring within the cable.

WAMS based robust HVDC control considering model imprecision for AC/DC power systems using sliding mode control

This paper presents a wide-area measurement based robust controller (WMRC) design method for high-voltage direct-current (HVDC) links to enhance the stability of AC/DC power systems. In recent years, there has been considerable interest in designing HVDC controllers to enhance system stability; however, model imprecision of HVDC systems has not been fully studied. The proposed WMRC utilizes sliding mode control to cope with the model imprecision of a conventional reduced first-order HVDC model and selects the area center of inertia (COI) signals as the feedback signals. The steps of the control design are as follows: firstly, the dynamics of the COI are established based on the motion equations of the generators; secondly, the sliding mode control manages to control the COI dynamics in spite of the model imprecision of the HVDC system, and the Lyapunov stability theory is applied to ensure that the system is asymptotically stable; thirdly, the applicability of the WMRC in AC/DC power systems is verified by real system detail tests. The superiority of the WMRC is verified in a 2-area 4-machine AC/DC power system and a real large-scale AC/DC power system.