Voltage Source Converter High Voltage Direct Current Transmission Research Articles

Modeling and design of an adaptive control for VSC-HVDC system under parameters uncertainties

The growing demand for electricity and the increasing integration of clean energies into the electrical grids requires the multiplication and reinforcement of high-voltage direct current (HVDC) projects throughout the world and demonstrates the interest in this electricity transmission technology. The transmitting system of the voltage source converter-high-voltage direct current (VSC-HVDC) consists primarily of two converter stations that are connected by a dc cable. In this paper, a nonlinear control based on the backstepping approach is proposed to improve the dynamic performance of a VSC-HVDC transmission system, these transport systems are characterized by different complexities such as parametric uncertainties, coupled state variables, neglected dynamics, presents a very interesting research topic. Our contribution through adaptive control based on the backstepping approach allows regulating the direct current (DC) bus voltage and the active and reactive powers of the converter stations. Finally, the validity of the proposed control has been verified under various operating conditions by simulation in the MATLAB/Simulink environment.

Offshore wind power integration to support weak grid voltage for industrial loads using VSC-HVDC transmission system

This paper investigates the integration of the offshore wind power plant into the grid using voltage source converter high-voltage direct current (VSC-HVDC). The paper proposes both offshore and onshore converter stations control to support voltage variation in grid. Heavy industrial loads result in a weak grid. In this paper, the effect on industrial loads by the grid strength is shown. Then the paper proposes a solution for the grid voltage support for industrial loads connected to weak grids. The results showed that the increase of grid voltage from 0.7 pu to 1 pu at full load condition that provides a continuous operation without any interruption. The system was modelled using MATLAB/Simulink package.

Analytic of VSC-HVDC Interconnected Power Systems from a Perspective of Frequency Security

In the interconnected power systems with VSC-HVDC (Voltage Source Converter-High Voltage Direct Current) transmission links, the failures of VSC-HVDC system can cause large power imbalance for both sending-end and receiving-end power systems. In this paper, the reliability model of the VSC-HVDC system is developed based on series-parallel structure recognition. The frequency dynamics of the power systems are characterized considering the frequency regulation of the power systems in response to the power imbalance arise from the component failures. Moreover, the Monte Carlo simulation method is applied to analyze the frequency dynamics in different contingencies. The indices measuring the frequency stability and the reliability of the interconnected power systems are introduced.

State Space Modeling and Stability Analysis of a VSC-HVDC System for Exchange of Energy

Nowadays, relevant actors are searching for solutions to produce energy with a low impact on the environment. Indeed, transmitting power via large distances with maintaining low losses is one of the main challenges. To improve electricity communication between countries and offshore wind, a new interconnections line must be built. Therefore, Voltage Source Converter High Voltage Direct Current (VSC-HVDC) transmission is incoming as the exceptive technology in order to address the challenges related to the integration of future offshore wind power plants. In spite of its many advantages, VSC-based HVDC transmission systems can experience unexpected instability and interaction phenomena: Small disturbances that occur continually in VSC-HVDC transmission systems due to the complex VSC based interconnections and an important number of components with non-linear nature that may cause failure. Thus, before installing the HVDC system, there is a significant need for studying a hybrid AC-DC system to guarantee the reliable and stable operation. This paper deals with the stability of a VSC-HVDC system by the use of a small signal stability method; such procedure enables to study the stability of a linearized VSC-HVDC system through state-space modeling and eigenvalue-based stability analysis.

Optimal metaheuristic-based sliding mode control of VSC-HVDC transmission systems

The design of classical controllers for Voltage Source Converter High Voltage Direct Current (VSC-HVDC) transmission systems, is load-dependent and has to be adjusted for each operating condition. Thus, the robustness of such controllers becomes necessary to cope with operating condition continuous variations. Therefore, the design of hybrid optimal Artificial Intelligence Based-Sliding Mode Controllers (AI-SMCs) for VSCHVDC transmission systems is crucial research interest. These AI based controllers are proved to improve the system’s dynamic stability over a wide range of operating conditions considering different parameter variations and disturbances. For this purpose, a comprehensive state of the art of the VSC-HVDC stabilization dilemma is discussed. The nonlinear VSC-HVDC model is developed. The problem of designing a nonlinear feedback control scheme via two control strategies is addressed seeking a better performance. For ensuring robustness and chattering free behavior, the conventional SMC (C-SMC) scheme is realized using a boundary layer hyperbolic tangent function for the sliding surface. Then, the Modified Genetic Algorithm (MGA) and Particle Swarm Optimization technique (PSO) are employed for determining the optimal gains for such SMC methodology forming a modified nonlinear MGA-SMC and PSO-SMC control in order to conveniently stabilize the system and enhance its performance. The simulation results verify the enhanced performance of the VSC-HVDC transmission system controlled by both MGA-SMC and PSO-SMC compared to the C-SMC. The comparative dynamic behavior analysis for both the conventional SMC and the two meta-heuristic optimization based SMC control schemes are presented. Through simulation results, the effectiveness of the proposed metaheuristic optimization approaches and their applicability to VSC-HVDC system global stabilization and dynamic behavior enhancement are validated.

Resilient Wide-Area Damping Control Using GrHDP to Tolerate Communication Failures

This paper proposes a goal representation heuristic dynamic programming (GrHDP)-based resilient wide-area damping controller (WADC) for voltage source converter high voltage direct current (VSC-HVDC) employing redundant wide-area signals as input signals to tolerate communication failure. A supervisory fuzzy logic module is proposed and added in the resilient WADC to adjust the learning rate of GrHDP online when encountering communication failure. Moreover, the resilient WADC does not need the accurate model of the power system and has the adaptability to the variation of operation conditions and communication failures. Case studies are conducted in a 10-machine 39-bus system with one VSC-HVDC transmission line. Simulation results show that the resilient WADC can counteract the negative impact of communication failures on control performance under a wide range of system operating conditions.

Comparison and analysis of the fault arc characteristics of flexible DC transmission lines

VSC-HVDC grid is one of the important development directions of the smart grid in the future. The arc characteristics of transient fault on the transmission line are the theoretical basis for determining reclosing time and reclosing strategy of DC circuit breaker. In this study, the process of the transient single-pole ground fault on the true bipolar VSC-HVDC transmission line is analysed and the arc model of the fault is determined according to the fault characteristics. Then a two-terminal voltage source converter-high voltage direct current (VSC-HVDC) system including this arc model is built in power systems computer aided design (PSCAD). The primary and secondary arc characteristics of the transient single-pole ground fault on the transmission lines are simulated and compared with the arc in AC system. It is shown that the arc extinction time of the flexible DC transmission system is lesser than that of the AC system at the same voltage level.

HVDC grid protection algorithm design in phase and modal domains

To meet the required operation speed for protection of meshed voltage source converter (VSC) high-voltage direct current (HVDC) grids, travelling wave-based algorithms operating in the submillisecond time-frame can be used. The domain in which these algorithms operate, i.e. modal or phase, determines their performance in fault discrimination, fault type classification, and faulted pole selection. In the recent literature, high-speed algorithms have been proposed for various VSC HVDC grid configurations and transmission line types; yet, the choice of domain has received insufficient attention. This study offers recommendations for the choice of domain for protection algorithm design of HVDC overhead line or cable systems in symmetric monopolar and bipolar configurations. The theoretical analysis of this study, which is based on fundamental wave propagation theory, indicates that the preferred domain for protection algorithms for cable and overhead line systems are the phase and modal, respectively. Furthermore, the study provides comprehensive guidelines to construct detection functions for both configurations and discusses the errors introduced by approximations. Finally, study results from a bipolar overhead line test system demonstrate the advantages of modal over phase domain for fast fault discrimination and classification and illustrate practical problems associated with non-ideal detection functions.

Frequency Regulation Strategies in Grid Integrated Offshore Wind Turbines via VSC-HVDC Technology: A Review

The inclusion of wind energy in a power system network is currently seeing a significant increase. However, this inclusion has resulted in degradation of the inertia response, which in turn seriously affects the stability of the power system’s frequency. This problem can be solved by using an active power reserve to stabilize the frequency within an allowable limit in the event of a sudden load increment or the loss of generators. Active power reserves can be utilized via three approaches: (1) de-loading method (pitching or over-speeding) by a variable speed wind turbine (VSWT); (2) stored energy in the capacitors of voltage source converter-high voltage direct current (VSC-HVDC) transmission; and (3) coordination of frequency regulation between the offshore wind farms and the VSC-HVDC transmission. This paper reviews the solutions that can be used to overcome problems related to the frequency stability of grid- integrated offshore wind turbines. It also details the permanent magnet synchronous generator (PMSG) with full-scale back to back (B2B) converters, its corresponding control strategies, and a typical VSC-HVDC system with an associated control system. The control methods, both on the levels of a wind turbine and the VSC-HVDC system that participate in a system’s primary frequency control and emulation inertia, are discussed.

IDA-PB control design for VSC-HVDC transmission based on PCHD model

SUMMARY An interconnection and damping assignment passivity-based (IDA-PB) control design is proposed to improve the dynamic performance of voltage source converter high-voltage direct current (VSC-HVDC) system. The port-controlled Hamiltonian with dissipation (PCHD) model for voltage source converter (VSC) is developed according to the PCHD equation, and the strict passivity of the PCHD model is proved. On the basis of the PCHD model, a desired energy function is constructed by assigning interconnection and damping matrix and used as Lyapunov function. Then the IDA-PB control is designed according to desired equilibrium point, state variables, and IDA-PB control principle. By using this type of controller, the influence of the equivalent resistance of the VSC direct current side on the VSC-HVDC system is eliminated. The effectiveness of the proposed IDA-PB control is demonstrated through simulation studies on a two-terminal VSC-HVDC system by PSCAD/EMTDC software. The simulation results show that the controller has significant contribution to improve the dynamic behavior of the VSC-HVDC system under a variety of operation conditions. Copyright © 2014 John Wiley & Sons, Ltd.

Analysis of Harmonics in Subsea Power Transmission Cables Used in VSC–HVDC Transmission Systems Operating Under Steady-State Conditions

Subsea power cables are a critical component of a voltage-source converter-high-voltage direct current (VSC-HVDC) transmission system in any offshore electrical power scheme. Subsea cables have complicated structures consisting of many different layers: conductor, insulation, sheath, and armor. Harmonic performance of the system depends upon the interactions between the subsea cable, the power converters, and other system components, such as smoothing capacitors. In this paper, a mathematical model of an HVDC-VSC transmission system is developed and its harmonic performance is investigated for steady-state operating conditions. The results suggest that the design of the subsea transmission cable has important effects on harmonic levels in the voltage and current waveforms in the cable and upon power loss within the transmission system. This paper demonstrates that it is always important to consider interactions between all of the system components when predicting harmonic performance in a VSC-HVDC transmission system.