Coordinated optimization method for suppressing transient overvoltage caused by HVDC commutation failure considering large wind power integration

This paper deals with the problem of large wind power integration and its potential impact on systems small signal stability. Factors like grid configuration, load and wind power integration are considered. An automatic algorithm is used to search the space formed by such parameters and generate a representative set of possible operation conditions. The oscillation modes are then calculated for each operation point. Some of these points of operation are subjected to a deeper analysis and the movement of oscillation modes on the complex plane is evaluated. Finally, non-linear time domain simulations are presented.

Since a large-scale wind farm is connected, it has an impact on the hybrid High Voltage Alternating Current/Direct Current (HV AC/DC) power grid with the characteristics of 'strong DC and weak AC'. When the connected capacity of the wind farm drops instantaneously, it may cause the DC system commutation failure. In this paper, firstly, the impact of wind power grid connection on the converter bus voltage is analyzed. Then, the relationship between the commutation bus voltage variation and the critical commutation voltage reduction is established, the correlation factor of the DC commutation failure caused by the wind power grid connection is proposed, and the criterion for determining the DC commutation failure caused by the wind power grid connection is defined. As a result, the maximum variation of wind power access capacity could be obtained.

This paper addresses the problem of robustly tuning power system stabilisers (PSSs) in systems with large wind power integration. PSSs installed in wind energy conversion systems, namely in doubly fed induction generators, are used in this research to provide additional damping to the electromechanical modes of oscillation. A new method that aims to reduce the computational effort required to find a robust solution that is suitable for a very large set of operating conditions is also proposed.

With the integration of large scale wind power, the characteristics of power system operation has been changing, and, some problems come forth. On-line security assessment and control decision support system provides the stability and security state message for dispatcher in time, and, some suggestions to improve the level of power system stability and security. To suit the requirements of large amount wind power integrated power system, the technology of on-line security assessment and control decision support must be modified. This paper focuses on the technology of on-line security assessment and control decision for operation of power system with large scale wind power and designing the support system. In the paper, the study and application of on-line security assessment and control decision support technology in China are introduced. Considering the wind power in China having some distinct characteristics such as large scale, centralized development, long-distance and high voltage transportation, the new requirements to on-line security assessment and control decision support are analyzed. They includes need for new information, on-line modelling with large scale wind farm, transfer limitation calculation under the constraint condition of wind power integration requirement, auxiliary preventive control decision based on the forecasting and adjustment properties of wind power output, coordinated emergency control wind power with hydraulic and thermal power. On the basis of technical rule for connecting wind farm into power grid and the interaction between wind power and power grid, the advices on engineering application of on-line security assessment and control decision support technology for large amount wind power integrated power system, are proposed, for example, with respect to the standard of security assessment and selection of pre-contingency sets. (7 pages)

HVDC transmission is an important approach to delivery large-scale wind power for a long distance. When the commutation failure occurs, the voltage of sending end will fluctuate dramatically, which threatens the stable operation of wind farm. Meanwhile, different characteristics of wind turbines will further affect the transient voltage of sending end, so the impact of wind farm on the transient voltage must be considered, especially for the high proportion of wind power generation. Firstly, the sending end transient voltage characteristics are analyzed and the mechanism of transient overvoltage caused by commutation failure is revealed. Then, doubly-fed wind power generation systems with different control modes are modeled, and the dynamic reactive power response capabilities of them are studied, so as to analyze the influence of the doubly-fed induction generator (DFIG) control modes on the transient overvoltage. Finally, a simulation example is established which verifies the correctness of the theoretical analysis. The results show that when DFIG adopts the constant voltage control strategy with the quickly response speed of the converters, it has stronger reactive power output capability, and can suppress the transient overvoltage, which is beneficial to the safe and stable operation of the power grid.

The transient over-voltage will occur in the wind farm near the DC system after commutation failure. In order to reduce the transient over-voltage of wind power plant after the accident of off - grid, improve the stability of the system. This paper mainly studies the placement of the Synchronous condenser in the wind power station. Firstly, the advantages of the Synchronous condenser are analyzed theoretically, and the operation characteristics of the Synchronous condenser under the fault of the DC system are analyzed in detail. Secondly, based on the transient over-voltage area method, a transient over-voltage degree index is proposed, and this index is used as the optimal placement method. Finally, the proposed transient over-voltage index was verified in the PSD-BPA model. The results show that the index is correct and effective in determining the placement point of the Synchronous condenser in the new energy supply.

With the large-scale deployment of renewable energy, transmission systems for new energy sources are increasingly exposed to transient overvoltage issues induced by DC blockages and commutation failures. To address the challenges of an imprecise response to multiple fault scenarios and the inefficiency of independent device actions in existing dynamic reactive power control schemes, this paper proposes a coordinated optimization control strategy integrating multiple dynamic reactive power sources tailored to different fault characteristics. An equivalent model of the renewable energy DC transmission system is established to elucidate the underlying mechanisms of transient overvoltage formation under various fault conditions. By employing trajectory sensitivity analysis and parameter perturbation methods, the influence patterns of control parameters on transient overvoltage behaviors across different fault scenarios are quantitatively assessed, thereby overcoming the limitations of traditional empirical parameter tuning approaches. Subsequently, a multi-source coordinated optimization model is developed with the objective of minimizing transient overvoltages under simultaneous dual-fault conditions. A multi-objective particle swarm optimization algorithm, incorporating comprehensive trajectory sensitivity and dynamically adaptive inertia weights, is introduced, alongside Pareto front theory, to achieve rapid and balanced optimization among competing objectives. Simulation results validate that the proposed strategy significantly enhances transient overvoltage suppression across diverse fault conditions. The findings provide robust theoretical foundations and practical guidance for the refined parameter tuning and high-efficiency coordinated control of dynamic reactive power sources in renewable energy transmission systems.

There is the risk of subsynchronous oscillations when wind-thermal-bundled power supply delivered through AC transmission line with series capacitance compensation and high voltage DC system. However, the current researches are all aimed at the subsynchronous oscillation of wind-thermal-bundled power supply or AC-DC hybrid transmission, without considering the subsynchronous oscillation of wind farms, thermal power plants, AC transmission system with series capacitance compensation and DC transmission system at the same time. The linearized model of wind-thermal power supply and extreme high voltage (EHV) AC-DC hybrid transmission system is built firstly in this paper and then subsynchronous oscillation mode of system is analyzed by factors related with characteristic values. This study uses characteristic values sensitivity make sure the main influencing factors of subsynchronous oscillation and then analyze the influence of AC-DC transmission power distribution, thermal power and wind power output allocation, wind power control parameters and DC transmission control parameters on subsynchronous oscillation. The correctness of theoretical analysis is verified by the simulation results.1

This paper presents studies carried out on the Greek mainland system in order to assess the effect of large wind power integration that will be installed in the next years. First the steady state influence on the voltages and power flows is investigated and the dynamic behavior is analyzed next for selected disturbances. The system security is checked against short-circuit in main transmission buses near wind parks, generation outages and wind power fluctuations. In general it is concluded that the installation of large wind power in the Greek mainland system can be achieved without risk for the security of the system.

Effects of Large Scale Wind Power on Total System Variability and Operation: Case Study of Northern Ireland

In view of the shortcomings of machine learning in the fast and accurate evaluation of the transient voltage stability of wind power grid-connected systems at the present stage, a grcForest model-based transient voltage stability assessment method for wind power grid-connected systems. Firstly, the number of input features increases with the number of cascading forest layers The gradient growth or gradient reduction that may occur with the increase of the number of layers in the cascade forest is optimised by using a residual network to ensure that the model can still maintain its initial learning capability after the number of layers increases. Secondly, the key factors influencing the transient voltage of the grid-connected wind power system are analysed and input features are constructed by combining transient faults; then the model is evaluated by The model is then trained offline to complete the parameter setting and performance optimization; finally, the completed input features are applied to the grcForest wind power grid-connected system transient voltage The simulation analysis of the 39-node system of the IEEE10 machine validates the rapidity and accuracy of the method. The simulation analysis of the IEEE 10-machine 39-node system verifies the rapidity and accuracy of the method.

The randomness of nature resource and the particularity of generation technology of wind power generation are important factors for restricting further utilization of the wind resource. This paper analyzes the impacts of grid connected wind farms on the regional power system security and stability through the research on the regional grid with large scale wind power integration. Through simulation method, this paper analyzed the impacts of the integrated wind farms on the bus voltage, reactive power compensation, power flow distribution, network loss, etc; the impact of dynamic characteristics of wind turbines on the grid transient voltage and power system frequency stability are investigated, and the significance of wind turbines low voltage ride through (LVRT) capability to power system security and stability is emphatically analyzed, measures for improving power system transient voltage characteristic are proposed, and their effectiveness on the power gird construction as well as safe and stable operation is validated.

In the DC transmission system with a high proportion of new energy, due to the large reactive power disturbance and the poor voltage regulation and support capability of new energy units, the problem of transient overvoltage at the terminals of new energy units is prominent during DC fault, which leads to the contradictory relationship between DC power and new energy power, which seriously affects the safe and stable operation of large-scale wind power UVDC transmission system and the consumption of new energy in the near area. In order to solve the above problems, a magnetic saturation controllable transformer (MSCT) is proposed. The DC power supply is used to control the saturation degree of the transformer core, so that it can have the reactive power compensation function similar to the magnetic control reactor on the basis of undertaking the collection and transmission of new energy power, and achieve the goal of restraining the overvoltage at the generator terminals of new energy units. Firstly, according to the characteristics of overvoltage at generator terminals of new energy units and the saturation characteristics of magnetic circuit of transformers, the feasibility and controllability of transformers as inductive reactive power sources are demonstrated, and a mathematical model of controllable reactance of transformers based on excitation current regulation is established; The transformer excitation control system is designed, including the detection part and the excitation current control link, so that the transformer can automatically control the saturation degree of the iron core according to the voltage level of the system, change the equivalent reactance of the transformer, change its reactive power, and realize the reactive power regulation and over-voltage suppression functions. Finally, the validity and superiority of the method are verified by the example of QingYu DC near area new energy in Qinghai power grid.

Dynamic reconfiguration of antenna devices is becoming a prime need in emerging telecommunication and remote sensing systems operating in the portion of the electromagnetic (EM) spectrum spanning from millimeter-wave (MMW) to terahertz. Different techniques and materials are currently available for the implementation of a given EM reconfiguration in antenna systems at microwaves andMMW, such as semiconductors, RF-MEMS, Liquid Crystal, and ferroelectrics. However, a common feature to all these technologies is the significant increased loss and complexity with regard to the devices fixed counterpart. Both loss and complexity further increase when high-performance reconfiguration capabilities are addressed atMMWand above, constituting a major limitation to the future deployment of dynamically controllable systems. Advanced performance, low-complexity and low-cost are, therefore, the cornerstones in the development of new technologies for antenna reconfiguration. In this framework, the main objective of this thesis is to contribute to the advancement of low-cost and efficient technologies enabling antenna reconfiguration capabilities fromMMWto THz frequencies. Within this scope, it is proposed the analysis, design and implementation of mechanically reconfigurable devices using dielectric elastomer actuators (DEAs). DEAs are an emerging technology that possesses unique properties, and represents a potential alternative to conventionalmechanical reconfiguration schemes. DEAs are especially attractive for their large strain combined with low-costmaterials and fabrication, analog control and near-zero DC power consumption. These characteristics make them particularly suited to the realization of low-cost and low-loss reconfigurable antennas. The high potential of DEAs for the realization of adaptive devices is experimentally validated by the development of different prototypes operating atMMWand THz frequencies: i) a very low-loss true-time-delay phase shifter operating at Ka-band; ii) a Ka-band reconfigurable reflectarray with 1-D beam-scanning capability; iii) a stretchable and beam-scanning THz reflectarray exhibiting the uncommon potential for the implementation of conformal or reconfigurable devices based on mechanical stretching. The designs and concepts demonstrated in this thesis pave the way for the evolution of new DEA-based reconfigurable devices resulting in low-cost, low loss and compact structures.

When large-scale wind power island is connected to VSC-HVDC power grid, the interdependence between wind turbine and VSC-HVDC power grid will be closer. Especially in the fault process, the interaction between wind turbine and VSC-HVDC power grid is more prominent, which makes the fault crossing of large wind power isolated islands connected to VSC-HVDC power grid face many new problems. Therefore, it is necessary to study the fault response characteristics of wind power connect to VSC-HVDC power grid and the fault ride through scheme of VSC-HVDC power grid and wind power joint system. When large-scale wind power is connected to the VSC-HVDC power grid and the VSC-HVDC mode is used for long-distance transmission, the operation characteristics of wind power and VSC-HVDC power grid will affect each other. The adaptability of wind power connected to the VSC-HVDC power grid will become an important problem affecting the operation of the power grid. Especially when the VSC-HVDC power grid fails, the response characteristics of the wind turbine, the interaction between VSC-HVDC power grid and wind power in the event of power grid failure, and how to realize fault ride through together. The focus of study should be to clarify the fault characteristics and interaction between wind power and VSC-HVDC power grid, realizing the joint fault ride through, and deepen the understanding of the interaction between wind power and power electronic controller in case of fault of VSC-HVDC power grid. Finally, to ensure the safe and stable operation of wind power sent through VSC-HVDC power grid, it is important to give full play to the flexible control of VSC-HVDC power grid, so as to work without synchronous power support.