Performance analysis on various controllers of VSC — HVDC transmission systems

This paper deals with the analysis, design and control of a three-level 24-pulse Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) system. A three level VSC operating at fundamental frequency switching (FFS) is proposed with 24-pulse VSC structure to improve the power quality and reduce the converter switching losses for high power applications. The design of three-level VSC converter and system parameters such as ac inductor and dc capacitor is presented for the proposed VSC based HVDC system. It consists of two converter stations fed from two different ac systems. The active power is transferred between the stations either way. The reactive power is independently controlled in each converter station. The three-level VSC is operated at optimized dead angle (β). A coordinated control algorithm for both the rectifier and an inverter stations for bidirectional active power flow is developed based on FFS and local reactive power generation. This results in a substantial reduction in switching losses and avoiding the reactive power plant. Simulation is carried to verify the performance of the proposed control algorithm of the VSC based HVDC system for bidirectional active power flow and their independent reactive power control.

High Voltage Direct Current (HVDC) technology has recently emerged as a significant option in current power networks to address power transmission challenges. Therefore, this research project examines the potential impact of HVDC technology on the Nigerian transmission system. Based on the information provided by the Nigerian Electricity System Operator (NESO), a model of the 330 kV transmission network in Nigeria was created using DIgSILENT PowerFactory. Summer and winter load flow scenarios were examined to enhance the model's precision and consistency. The system performance was evaluated through stability and reliability studies, which helped identify suitable locations for HVDC links. The load point indices (LPIs) and system indices were used for the reliability evaluation, while the PV and QV analyses were used for the stability evaluation. An HVDC model was created and connected to the transmission network at two locations identified by the studies, Gombe and Yola buses. A comparison was conducted using two separate HVDC connections (Case 1: Azura-Gombe and Case 2: Azura-Yola) to identify the critical impact of HVDC on the system reliability and stability. The reliability and stability simulation showed that HVDC technology significantly boosts the reliability and stability of the transmission network and reduces energy losses. However, adding an HVDC link between Azura and Yola, Case 2, significantly improved overall performance, as evidenced by improving the system and load point indices and a better voltage profile and reactive power margin. The system indices, SAIDI improved by 0.07 h/yr, SAIFI by 0.19 interruption/yr, and ASAI enhanced by 0.11%, while the LPIs improved effectively by zeroing the Load Point Interruption Frequency (LPIF) and Load Point Interruption Time (LPIT). During the stability analysis, the loadability increased by 119% while the critical point improved by 0.061 pu/ -394 MVAR. Economically, the cost incurred in Case 1 is 79.17% lower than the base case even though new equipment (HVDC) is installed; this also applies to Case 2, which is 85% lower than the base case. Integrating HVDC technology could improve financial gain, considering improved energy supply, increased production, and general economic growth. This research has contributed significantly to revealed improvements in system and load indices, increased loadability, increased stability, and boosted financial gain with the HVDC connected.

6 - High Voltage Direct Current (HVDC) electric power transmission systems

Conventional fault analysis algorithms may not be suitable for the AC/DC hybrid systems. To solve this problem, a mathematical model for HVDC (High Voltage Direct Current) system, which is suitable for analyzing faults in AC system, is presented in this paper. Firstly, based on the switching functions method and sequence components method, an equivalent model of HVDC converter under the asymmetric AC system is put forward. The unique advantage of the converter model lies in that it has taken harmonic characteristics into account and can improve the calculation accuracy significantly. Secondly, response performances of HVDC control system in cases of AC faults are analyzed and expressions for the control response characteristics are discussed under 3 modes. Finally, a general algorithm is developed to incorporate the proposed HVDC model into the conventional AC short-circuit calculation algorithm. The effectiveness of the proposed HVDC model and algorithm has been verified by simulation studies and by comparing the results with those obtained from the EMTDC simulations.

A dynamic corrective control method for congestion mitigation of hybrid AC/DC power systems

The present PhD thesis deals with transformer inrush current in offshore grids including offshore wind farms and High Voltage Direct Current (HVDC) transmission systems. The inrush phenomenon during transformers energization or recovery after the fault clearance is one of important concerns in offshore systems which can threaten the security and reliability of the HVDC grid operation as well as the wind farms function. Hence, the behaviour of wind turbines,Voltage Source Converters (VSC) and transformer under the normal operation and the inrush transient mode is analyzed. For inrush current reduction in the procedure of the offshore wind farms start-up and integration into the onshore AC grid, a technique based on Voltage Ramping Strategy (VRS) is proposed and its performance is compared with the operation of system without consideration of this approach. The new methodology which is simple, cost-effective ensures minimization of transformer inrush current in the offshore systems and the enhancement of power quality and the reliability of grid under the transformer energizing condition. The mentioned method can develop much lower inrush currents according to the slower voltage ramp slopes. Concerning the recovery inrush current, the operation of the offshore grid especially transformers is analyzed under the fault and the system restoration modes.The recovery inrush transient of transformers can cause tripping the HVDC and wind farms converters as well as disturbing the HVDC power transmission. A voltage control design based on VRS is proposed in HVDC converter to recover ali the transformers in offshore grid with lower inrush currents.The control system proposed can assure the correct performance of the converters in HVDC system and in wind farm and also the robust stability of the offshore grid. Esta tesis doctoral estudia las corrientes de energización de transformadores de parques eólicos marinos con aerogeneradores con convertidores en fuente de tensión (VSC) de plena potencia conectados a través de una conexión de Alta Tensión en Corriente Continua (HVDC). Las corrientes de energización pueden disminuir la fiabilidad de la transmisión eléctrica debido a disparos intempestivos de las protecciones durante la puesta en marcha o recuperación de una falta. Para la mitigación de las corrientes de energización durante la puesta en marcha del parque esta tesis propone una nueva estrategia basada en incrementar la tensión aplicada por el convertidor del parque eólico en forma de rampa (VRS). Este método persigue energizar el parque eólico con el menor coste y máxima fiabilidad. La tesis analiza diferentes escenarios y diferentes rampas. Otro momento en que las corrientes de energización pueden dar lugar a un disparo intempestivo de las protecciones es durante la recuperación de una falta en la red de alterna del parque eólico marino. Esta tesis extiende la estrategia VRS, utilizada durante la puesta en marcha del convertidor del parque, para los escenarios de recuperación de una falta.

With the development of renewable energy (i.e. wind power and solar power) generation, its integration to the power grid has becoming a more and more important challenge. High voltage direct current (HVDC) transmission [1-2] is a suitable scheme for the integration. The key unit of HVDC is the converter. In general, there are two types of converters classified by the electronic devices. The one is named the current source converter (CSC) based on thyristors. The other one is named the voltage source converter (VSC) [3-4] based on insulated-gate bipolar transistors (IGBTs). The disadvantages of CSC are the probability of commutation failure, large harmonics, and inflexibility of power control. The advantages of CSC are high withstanding voltages and few losses. On the contrary, VSC has few harmonics and excellent output, but it has lower withstanding voltages and higher losses. And VSC cannot deal with direct current failure. To combine advantages of both topologies, an improved hybrid multilevel converter (HMC) is presented in this paper.

The continuous increasing progress in high power and high voltage semiconductor devices leads to have a substantial impact on optimization and effective management of electric grids. These developments have great influence on High Voltage Direct Current (HVDC) and flexible ac controller technologies. This article gives an outline of the innovations in Voltage source Converter (VSC) based HVDC technology. VSC based HVDC technology offers decent advantages which includes interconnection of asynchronous networks, bulk power transmission and voltage stability support. VSC based HVDC technology niche utilities to grab opportunities in incorporating large scale renewable energy sources to the grid, especially on shore /offshore wind energy to the grid. Furthermore, VSC-based HVDC technology is essential for maintaining voltage stability in networks of interconnected grids. In the face of changing loads and the incorporation of renewable energy, these systems help to maintain grid dependability and resilience by offering dynamic voltage management and wattless power support.This article highlights the transformative potential of VSC-based HVDC technology in modernizing and future-proofing electric grids. By leveraging the latest innovations in semiconductor devices and control technologies, VSC-based HVDC systems empower grid operators to overcome existing challenges and embrace the opportunities presented by the evolving energy landscape.

Offshore wind power has been widely promoted around the world, owing to its abundance and being environmentally friendly. Voltage source converter based high voltage direct current (VSC-HVDC) transmission technology has been utilized for wind power transmission system because of its advantages. In offshore VSC-HVDC transmission system, the DC voltage level is an important index of power transmission capacity. Based on the steady-state current operating interval of the insulated gate bipolar transistors (IGBT), the value range of DC voltage for offshore VSCHVDC transmission system is given, and the value range of DC voltage is revised according to the IGBT transient current limit. Furthermore, the DC voltage level of offshore VSC-HVDC transmission system is determined according to the current limitation requirements of the DC marine cables. On this basis, a 900MW offshore wind power VSC-HVDC transmission project has been taken as an example, the process to select the DC voltage level of the project case is given. The method of voltage level selection proposed is conducive to improving the operation reliability of the offshore VSC-HVDC transmission system, and plays a positive role in improving the utilization rate of offshore wind power and the power system resilience of the onshore power grid.

Power grid stability has become an increasingly intricate challenge with the rising integration of renewable energy sources like wind and solar power. These energy sources, while essential for achieving sustainability goals, introduce significant variability and reduce the system’s inertia due to the displacement of conventional synchronous generators. This paper explores the combined role of High-Voltage Direct Current (HVDC) systems and the Kuramoto model in addressing these challenges. The Kuramoto model, traditionally used to study synchronization phenomena, is adapted to represent power system dynamics, enabling simulation of grid stability under diverse conditions. HVDC systems, with their ability to regulate power flows dynamically and reduce instability, are evaluated for their potential to mitigate fluctuations caused by renewable energy. Key topics include the theoretical underpinnings of grid stability, detailed simulation methodologies, experimental scenarios, and results showcasing HVDC’s stabilizing effects. Conclusions emphasize the synergy between advanced control systems and theoretical modelling, providing a pathway toward resilient and adaptable future energy networks. Key words. HVDC technology, Kuramoto-model, stability analysis of power systems

This paper provides a generic stability model of a self-commutated multilevel VSC (Voltage Source Converter) HVDC (High Voltage Direct Current) and its appropriate control. At first the approach of modeling depicts the independence of the AC and DC quantities and therefore two separate models - one for the AC and one for the DC side - can be figured out. The AC side model is developed in the dq frame out of the according differential equations. For the DC side no further transformation is required. Regarding the fact of balanced energy terms the two models can be merged. The consolidation of both models reveals a comprehensive large signal model of a multilevel based HVDC system which can be used for detailed analyses in power system stability studies. Due to the comparison of the generic stability model with an EMT (Electro-Magnetic Transient) HVDC model the consistence of the dynamic behavior is shown.

Our world carries an increasing burden of increasing CO2 emissions. Rather than rationing the use of electric power, we should all together organize ourselves toward a positive solution that benefits growth and a sustainable society. The high voltage direct current (HVDC) technology is a cornerstone that makes it possible to transport sustainable energy to the regions of consumptions that are often far away from the location of generation. Today's commercially available highest HVDC transmission voltage is 800 kV. This system makes use of classic converter stations. The newer HVDC Light technology, Voltage source converters (VSCs) and extruded cable systems, that are commercially available, are characterized today by a highest voltage of 320 kV and 1000–1200 MW of transmission power. This paper describes the need for higher HVDC transmission powers, the general technology of the VSC stations, and an in‐depth description of HVDC technology with a focus on extruded cable systems. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

High voltage direct current system is a type of high voltage direct current transmission system. This method is a new way to transfer electrical energy on a large scale and so it is a good alternative to traditional method (using alternating current). An integrated system is required to transfer electricity from power plants to consumers. This system includes energy production centers, stations, transmission lines or cables and Egyptians. In this article, we will evaluate the VSC-HVDC transmission system and line stability methods will be evaluated in the presence of scattered production resources. For this reason, in the first part, the HVDC system, the two-level VSC control converter will be expressed and in the second part, a summary of scattered production sources (wind turbine and photovoltaic system) will be expressed.

The transmission expansion planning using highvoltage direct current (HVDC) projects requires representative data for reliability assessment based on international projects currently in operation. For that reason, this paper presents a comprehensive review of HVDC projects and contributes to the estimation of reliability parameters for both kind of HVDC technologies, namely: line-commutated converter (LCC-HVDC) and voltage source converter (VSC-HVDC). For each technology, the results of the reliability parameters of each of the main components forming the HVDC system, either LCC or VSC, are presented. In addition, these results are used for the calculation of the reliability of a bipolar HVDC system, showing its application and comparing the two technologies.

This paper explains a hybrid control approach to model a controller for voltage source converters (VSCs) in offshore wind farm (OSWF) applications, where the OSWFs are integrated to AC grid through the multi-terminal high voltage direct current (MT-HVDC) transmission system. Proper DC link voltage provides the effective power dispatch. So, a constant DC link voltage should be maintained to achieve the effective power dispatch between OSWFs and AC grid. A new control approach is a compound of proportional-integral and sliding mode control to regulate the DC link voltage on the grid side VSC. Also, the proposed control approach can control AC voltage and reactive power on wind farm and grid side VSCs respectively. Time- domain simulations executed in MATLAB/Simulink software are used to verify the proposed and conventional control approaches. Transient stability analysis is carried out for a case study. The three-terminal VSC-HVDC system has taken for study, where two OSWFs are fed to AC grid.