VSC HVDC Research Articles

Evaluation of a Passive-Based Controller for Power Monitoring in Networks of High Voltage Transmission Lines in Direct Current with Voltage Source Converters (VSC–HVDC)

In this paper a tracking Passivity--based Control (PBC) for a multiterminal Voltage Source Converter based High Voltage Direct Current Network (VSC--HVDC) is evaluated. First, the system (an actual multiterminal HVDC) described as a Port Hamiltonian (PH) System and the controller are presented and subsequently three scenarios are proposed to evaluate the closed--loop behavior, namely: (i) load changes; (ii) generation changes and, (iii) DC--bus changes. Numerical simulations are carried out and results shown the robustness of the closed--loop to cope with these common disturbances.

A very fast and easily implementable support vector machine based relay algorithm to classify the fault and non fault disturbance in VSC HVDC terminals

A very fast and easily implementable support vector machine based relay algorithm to classify the fault and non fault disturbance in VSC HVDC terminals

Analytical multi-section Bergeron model of transmission lines and application to accurate fault location for long HVDC lines

Line Bergeron model is widely adopted for various applications including line fault location. However, it models the line distributed series resistance using a very limited number of lumped resistors, resulting in modeling errors. For long HVDC lines, this modeling error will cause fault location errors. In addition, if high frequency components of measurements are adopted to mitigate the influence of the frequency dependent parameters, the modeling errors of the existing Bergeron model and the fault location errors will be further magnified. To this end, this paper proposes a multi-section Bergeron model to improve line modeling and fault location accuracy. First, the error of the existing Bergeron model is analytically derived to show its limitations. Then, with multiple Bergeron sections in series to well approximate the distributed series resistance, the analytical expression of the multi-section Bergeron model is proposed with rigorously derivations and proofs. Finally, based on the proposed multi-section Bergeron model, a novel fault location scheme for long HVDC lines is presented, where the 1-mode and high frequency components of measurements are utilized to minimize the impact of line frequency dependent characteristics. Numerical experimental results in both LCC and VSC HVDC systems show that the proposed method has higher line modeling accuracy and fault location accuracy than the existing method. The proposed multi-section Bergeron model can potentially be applied to other long transmission line related applications.

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.

CNN–SVM Based Fault Detection, Classification and Location of Multi-terminal VSC–HVDC System

CNN–SVM Based Fault Detection, Classification and Location of Multi-terminal VSC–HVDC System

Improved Evaluation of the Life Lost by HVDC Extruded Cables due to Long TOVs

Previously the author developed a procedure for estimating the life lost by HVDC extruded cables under the long Temporary Over-voltages (TOVs) that may arise in VSC HVDC cable systems. As the topic is gaining interest, here the procedure is improved to target an upper conservative limit of the aging effects of such TOVs. This goal is achieved in two steps. First the line length effect on insulation volume is considered via the so-called enlargement law for HVDC cables, as the longer the cable, the greater the insulation volume, and the number and size of defects; this lowers insulation endurance to applied stresses and raises the fraction of life lost at every single TOV. Second, a life model developed for harmonics superimposed onto rated voltage is included in the procedure to better address the challenge set by the fast peak of long TOVs. The improved procedure is applied to 320-kV and 525-kV cable designs. The results highlight that, with long lengths and conservative values of insulation parameters, the improved procedure provides orders-of-magnitude higher loss-of-life fractions, which in the most pessimistic case might be non-negligible for severely-aged cables in service since long time.

Analysis of the influence factors of VSC–HVDC on AC three-phase short-circuit current level

PurposeThis paper aims to clarify voltage sourced converter’s (VSC’s) influence rules on the alternating current (AC) short-circuit current and identify the key factors, so as to propose the short-circuit current suppression strategy.Design/methodology/approachThis paper investigates the key factors which impact the short-circuit current supplied by the VSC based on the equivalent current source model. This study shows that the phase of the VSC equivalent current source is mainly affected by the type of fault, whereas the amplitude is mainly decided by the control mode, the amplitude limiter and the electrical distance. Based on the above influence mechanism, the dynamic limiter with short-circuit current limiting function is designed. The theoretical analysis is verified by simulations on PSCAD.FindingsThe short-circuit current feeding from VSC is closely related to the control mode and control parameters of the VSC, fault type at AC side and the electrical distance of the fault point. The proposed dynamic limiter can make VSC absorb more reactive power to suppress the short-circuit current.Research limitations/implicationsThe dynamic limiter proposed in this paper is limited to suppress three-phase short-circuit fault current. The future work will focus more on improving and extending the dynamic limiter to the fault current suppression application in other fault scenarios.Practical implicationsThe research results provide a reference for the design of protection system.Originality/valueThe key influence factors are conducive to put forward the measures to suppress the fault current, eliminate the risk of short-circuit current exceeding the standard and reduce the difficulty of protection design.

The Latest Trend of VSC HVDC

There have been various discussions in Japan on how to introduce renewable energy toward the target of carbon neutrality in 2050. The “Interim Report for Network Master Plan” issued by the “Study Committee on Master Plans for Wide-Area Interconnection Systems and System Rules” on May 20, 2021 describes the possibility that large-scale, long-distance power transmission from power generation areas to large demand areas by high-voltage direct current transmission system (HVDC) is effective for mass introduction of renewable energy. The introduction of HVDC is already expanding overseas, such as in Europe, and the trend is accelerating. The background to this is that it has been demonstrated that strengthening interconnection by HVDC has economic rationality and that it brings various benefits to existing power systems such as strengthening resilience. This paper describes the latest trends in the HVDC market and technology.

Efficacy of LCC and VSC HVDC Circuits for Transfer Capacity and Voltage Stability Challenges in Highly Compensated Systems: A Review

Efficacy of LCC and VSC HVDC Circuits for Transfer Capacity and Voltage Stability Challenges in Highly Compensated Systems: A Review

A Novel Fault Distance Estimation Method for Voltage Source Converter-Based HVDC Transmission Lines

In this work, a digital fault locator has been designed using Arduino for bipolar VSC–HVDC transmission lines based on the ratio of voltage to current signals from source end. Current and voltage signals of only rectifier end have been processed with discrete wavelet transform using DB-4 as the mother wavelet. After the signals are decomposed using wavelet up to level 4, approximate coefficients are taken. Standard deviation is then calculated and given as input to the fault locator designed in Arduino. Fault location logic has been designed in Arduino using the input features. Various fault cases are tested using proposed fault locator to check the effectiveness of the method. Percentage error in fault location estimation is within 1%. Some of the advantages of the proposed digital fault locator are no requirement of communication link, reaches setting is up to 99.8% of line length, percentage error is within 1%, and lower implementation cost. Hence the proposed digital fault locator can be implemented is a real power system effectively.

The Effects of Transient Overvoltages on the Reliability of HVDC Extruded Cables. Part 2: Superimposed Switching Impulses

In a previous paper (Part 1) the authors have performed the simulative evaluation of the life lost by HVDC extruded cables subjected to long TOVs occurring in VSC HVDC cable systems. The conclusions were that it cannot be completely ruled out that the field levels and the duration of such TOVs are a potential threat to certain cable designs, and tests other than Load Cycling Type Tests after CIGRÉ Technical Brochure 496 could assess quantitatively the potential threat associated with long TOVs. For these reasons, in this Part 2 superimposed switching impulses applied during Type Tests after TB 496 are analyzed in order to check if such impulses might be equivalent to long TOVs as for their electro-thermal stress effects on extruded insulation. The analysis is similar to that carried out for long TOVs in Part 1, i.e., it consists of: calculating the electric field during superimposed switching impulses; comparing it with the field during long TOVs; calculating with Miner's law of cumulated damage the life lost during superimposed switching impulses and comparing it with the loss of life during TOVs. A brief literature survey of potential high field effects during long TOVs is also reported.

The Effects of Transient Overvoltages on the Reliability of HVDC Extruded Cables. Part 1: Long Temporary Overvoltages

Extensive simulations have been carried out so far of transient voltages superimposed onto the DC voltage of HVDC cable transmission systems. With the advent of VSC HVDC cable systems, attention has turned to long Temporary Over-voltages in such systems. Preliminary experiments on the possible adverse effects of these long TOVs on the insulation of VSC HVDC cables have started, but no simulation models for estimating their effect on cable life and reliability have been developed yet. This investigation fills this gap by carrying out the simulative evaluation of the life lost by HVDC extruded cables subjected to long TOVs (Part 1) and switching impulses applied during Type Tests (Part 2), so as to compare the severity of these two transient voltages superimposed onto the DC voltage of HVDC extruded cables. This Part 1-paper is focused on estimating the severity of TOVs on extruded cable insulation by: calculating the electric field during the TOV; comparing it with the field during Type Test load cycles; using Miner's law of cumulated damage to calculate the life lost during the TOV, thereby also locating the most severely stressed point of insulation. In Part 2-paper, a similar evaluation for switching impulses and an overall comparison are performed.

Analytical Approach for Fast Frequency Response Control of VSC HVDC

The importance of the auxiliary control of power electronic devices such as HVDC and FACTs is growing owing to the increase in the generation capacity of renewable energy sources. This paper presents a temporary frequency support strategy using the electrostatic energy in voltage-sourced converter-type high-voltage direct current systems. An analytical derivation for selecting the optimal droop constant to improve the frequency nadir was established. The optimal droop constant was derived via system frequency response analysis by using the support termination time. Furthermore, the optimality of the support was computed using numerical equations. Modified outer control loops were implemented in the master controller to utilize the proposed method in voltage-sourced converter control. The effect of the fast frequency support control strategy was verified via a time-domain electromagnetic transient program simulation based on case studies. To examine the practical applicability of the proposed strategy, the parameter robustness was investigated by performing deviated system parameter simulations. The results validated the proposed strategy.

The Influence of VSC–HVDC Reactive Power Control Mode on AC Power System Stability

Voltage source converter-based high-voltage direct current (VSC-HVDC) has the advantage of fast and independent controllability on active and reactive power. This paper focuses on effects of commonly proposed reactive power control modes, constant reactive power control and AC voltage margin control. Based on the mathematical model of single machine infinity equivalent system with embedded VSC-HVDC, the influence of VSC-HVDC with different reactive power control strategies on transient stability and dynamic stability of the AC system is studied. Then case studies were conducted with a realistic model of grid. The dynamic responses of AC/DC systems for different VSC-HVDC reactive power control modes were compared in detail. It is shown that compared to constant reactive power control, AC voltage margin control can provide voltage support to enhance the transient angle stability of an AC system. However, the fluctuant reactive power injected into a weak AC system may adversely affect power system oscillation damping for VSC-HVDC with AC voltage margin control, if the parameters of the controller have not been optimized to suppress the low-frequency oscillation. The results of this paper can provide certain reference for the decision of an appropriate VSC-HVDC reactive power control mode in practice.

Time Domain Particle Swarm Optimization of PI Controllers for Bidirectional VSC HVDC Light System

This paper proposes a novel technique to tune the PI controllers of a bidirectional HVDC light system by embedding particle swarm optimization directly in the Simulink model in the design procedure. The HVDC light system comprises of a rectifier station, a DC link, and an inverter station. Each converter station requires four PI controllers to be tuned in the decoupled d-q vector control scheme, and with the bidirectional HVDC system, the required PI controllers are doubled. Tuning these many controllers using conventional methods is a challenging task, especially if the parameters of the converter stations are different. A novel approach to tune the PI controllers for a bidirectional HVDC system using the time-domain performance indices is presented in this paper. The time-domain performance indices are optimized using the particle swarm optimization (PSO) algorithm. The results of the proposed tuning method show that the proposed method not only gives superior results but also is less cumbersome to tune compared to conventional methods like modulus optimum (MO).

A novel economic analysis on multiterminal VSC HVDC systems with wind farms by hierarchical small‐signal stability constrained OPF

In this paper, a novel economic analysis for multiterminal voltage‐source converter high‐voltage direct current (MTDC) systems with wind farms is developed. Both the reinforcement and operation methods of an MTDC system are determined hierarchically in the proposed approach. Based on these methods, not only wind power transmission but also the MTDC system is capable of contributing to the power transmission among alternating current (AC) grids in cases of low wind power production cases. As a consequence, the economic benefits produced by the MTDC system can be increased. This paper also focuses on the sensitivity analysis of small‐signal stability constraints on the developed approach. It is demonstrated that the system for wind power transmission without any MTDC systems is exposed to instability, which is solved by the proposed method. On top of that, the small‐signal stability improvement effect of the MTDC system is analyzed from the economic viewpoint. Under strict small‐signal stability constraints, the economic benefits obtained by the MTDC system increase. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Stability Improvement of VSC HVDC based Multi Machine Power System using Optimized Super Twisting Sliding Mode Controller

This article presents application of an optimized robust and nonlinear controller approach for dynamic stability of a multi machine power system integrated with VSC-HVDC transmission. To improve dynamic stability of the system, a super twisting Sliding Mode Control approach, whose gains are optimized by multi objective flower pollination algorithm is designed to enhance the system stability over a various operating conditions, such as three phase fault, dc link fault, converter and inverter parameter change, increase of the mechanical input of the generator and change of active and reactive power. The super twisting sliding mode controller is designed for its superiority in robustness and chattering free actions over conventional siding mode controller in which a hyperbolic tangent function is chosen for the sliding surface. A multi objective flower pollination algorithm is applied to find optimized gains of the super twisting Sliding mode controller, in order to improve the capacity of the controller and the dynamic stability of the system. The results are compared with STSMC and conventional PI controller. It is shown from the result that the proposed controller is more capable in settling the system in steady state from any abnormal condition quickly than SMC and PI controller.

VSC HVDC active damping for the Sylwin 1 offshore wind power plants

SylWin1 is a VSC HVDC link connecting 864 MW offshore wind power generation to Germany's high voltage network. This paper presents a harmonic performance analysis of the offshore network carried out during the design and commissioning phase with a focus on the distortions at the 155 kV and 33 kV offshore networks caused by the amplification of harmonics generated by the HVDC and wind turbine converters. Low frequency harmonic amplification problems are mitigated by introducing active damping in the HVDC converter controls in order to achieve a cost effective solution with the aim of reducing offshore harmonic current and voltage distortions. The analysis was carried out with the help of detailed frequency domain model offline simulations of the offshore network and on-site measurements.

Comprehensive computer program for SSTI analysis of AC/DC power systems based on the component connection method

This paper presents a comprehensive methodology for the investigation of SSTI in AC/DC transmission networks. The main advantage of the proposed methodology is the modular modeling approach, where various complex components can be modeled in a comprehensive way while at the same time preserving the level of detail needed to capture the relevant dynamics. This is done by enhancing the CCM with an algorithm for the formulation of network state equations. All power system component models necessary for SSTI analysis are developed separately using the CCM principles and are connected according to their topological relations. A small-signal model of a point-to-point MMC-based VSC HVDC is developed to assess its influence on SSTI. The proposed methodology together with the developed models are implemented in a software framework called SNAP. The proposed methodology and the developed models are validated against time-domain simulations in PSS®NETOMAC.

Comparison of DC linear and non‐linear models for multi‐terminal VSC HVDC networks

The analysis and control design of multi-terminal VSC-HVDC systems requires a linearised model of these inherently non-linear systems. This paper develops such a model, from converter to multi-terminal system, discusses the key concepts and shows its use for some test cases. The linearised model is simulated in Matlab, and it is compared against the non-linear model results from an established DEM PSCAD model.