Optimal connection of controlled HVDC to AC power system

The analysis of an optimal placement of HVDC links to an AC network is considered from the point of view of DC power flow control on system dynamics. The analysis is based upon a system dynamic model developed and the use of transfer functions involving the system sensitivity analysis with respect to converter current control. An example is carried out on a 13-bus, four-generator test system illustrating the feasibility of the approach developed.     

Design of robust controllers for HVDC links in AC-DC power systems

The paper presents the design of a very simple fuzzy logic controller for HVDC transmission links for fast stabilization of transient oscillations. The performance of this controller is compared with variable-structure and adaptive controllers for a variety of short-circuits and system operational changes. Unlike both adaptive and variable-structure controllers which require, at least functionally, an accurate model of the system dynamics, the fuzzy controller does not require a mathematical model of the system to estimate the control input under disturbances. The transient simulation studies presented in this paper reveal the superior performance of the simple fuzzy controller in damping out system transients.     

Interconnecting a weak AC system to an HVDC link with a hybrid inverter

To overcome the weaknesses of the conventional HVDC converter for weak AC system applications, the concept of the hybrid inverter has been introduced recently. Because of its unique characteristics, the hybrid inverter not only can implement the existing control methods but also can support the development of more innovative control strategies. This paper reports the major results of a study that investigated the performance of an HVDC link interconnected to a weak AC system with a hybrid inverter using an unconventional control scheme. The results show that the hybrid inverter improves the overall DC/AC system behavior and is effective in operating an HVDC link into a weak AC system.     

Offshore wind farm with a series multiterminal CSI HVDC

This paper presents an integrated design of an offshore wind farm and an interconnection circuit based on a series multiterminal HVDC link with current source inverters (CSI). The transmission converters are used to achieve variable speed operation for a group of generators, and this enables use of very simple generators. The series converter connection eliminates offshore transformers. The paper discusses the control systems for both, generator side and grid side converters. A 200 MW wind farm is simulated on PSCAD/EMTDC platform and the responses confirm satisfactory operation for a range of wind speed changes. It is shown that each generator group can operate with a different and optimal frequency and that wind variations on individual units cannot jeopardize system stability. The main challenges for the proposed topology are system insulation and management of transmission line losses, and the paper studies some possible solutions.     

HVDC输电系统次同步振荡(SSO)分析的GUI实现

为提高研究效率并普及研究结果，开发了一个用于分析HVDC输电系统次同步振荡(SSO)特性的图形用户界面（GUI)软件，这个GUI软件由人机界面及相关的回调函数组成，其中人机界面是利用MATLAB的GUI工具设汁的，而编写回调函数则利用了MATLAB的数值计算和数据可视化功能。实践表明在MATLAB环境下可容易、高效地开发出令人满意的GUI软件，通过GUI软件可实现SSO参数稳定域可视化分析及特征值分析和时域仿真分析，具有直观、方便的优点，适合广大技术人员对HVDC输电系统发生SSO失稳定可能性的检验。     

A new control design for multiterminal HVDC systems using optimal entire eigenstructure assignment

Contents This paper presents a new method of control design for multiterminal HVDC systems. The proposed design approach applies the optimal entire eignestructure assignment technique developed for optimal state feedback controls of multi-input linear systems in order to achieve predetermined response characteristics. The feedback-gains are computed to assign the closed-loop eigenvalues of the HVDC system at any specified distinct modes and simultaneously minimize an appropriate linear quadratic (LQ) performance index. Therefore, the controller design takes into account the dynamics of the DC transmission system, making possible the regulation of the current at the remote terminals, and at the same time assures both stability with predetermined duration of transient response and minimum system effort. A computer simulation of an integrated ac/dc power system is used to demonstrate the effectiveness of the proposed design since in all simulated cases the transient response for typical disturbances appears desirable, showing fast damping characteristics without significant overshoots or oscillations.

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Eine neue Regelmethode für HGÜ-Systeme mit mehreren Unterwerken optimaler Eigenstruktur

Übersicht Diese Arbeit befaßt sich mit einer neuen Regelmethode für HGÜ-Systeme mit mehreren Unterwerken. Die vorgeschlagene Regelstrategie basiert auf der Technik der optimalen Eigenstruktur. Die für optimale Zustandsregelung von linearen Systemen mit vielen Eingängen entwickelt worden ist, um eine vorgeschriebene Antwort zu erreichen. Die Verstärkungsfaktoren werden berechnet, um die Eigenwerte des Regelkreises des HGÜ-Systems bei beliebig gewünschten Höhen zu ermitteln und gleichzeitig ein geeignetes lineares quadratisches Kriterium zu minimieren. Somit berücksichtigt die Regelbemessung die Dynamik des Gleichstromübertragungssystems und ermöglicht die Stromregelung in entfernten Unterwerken. Ebenfalls wird Stabilität des Systems unter Vorbestimmung der Dauer der Transienten Antwort und Minimierung der Systembelastung gesichert. Es wird eine Computersimulation eines ac/dc-Systems durchgeführt, um die Effektivität der vorgeschlagenen Methode zu demonstrieren. In sämtlichen Fällen zeight die transiente Antwort typischer Störungen schnelle Dämpfung ohne merkbare Überhöhungen und Schwingungen.

     

Effect of an excitation system on turbine-generator torsional stress in an HVDC power system

This paper deals with the impact of an excitation system on the torsion dynamics of turbine-generators, which are located on the inverter side of HVDC systems. Turbine-generator stress depends on the type and the parameters of an excitation system, and the fault type and location in an ac network because of commutation failures at the inverter station. Also, this paper analyzes how parameters of an excitation system are related to the torsional stress of a turbine-generator. Using the CIGRE benchmark model, the torsional stress on a generator on the inverter side is simulated. The PSCAD/EMTDC program is used for simulation studies.     

交直流电力系统区域振荡混合控制策略

通过计算模式阻尼比对机组有功出力和直流线路有功功率的灵敏度,得到参与振荡模式的关键机组和直流线路。提出基于阻尼比灵敏度的由机组出力调整和直流传输功率调整两部分组成的混合控制策略,以此抑制大区域电网的区域功率振荡。在软件DIgSILENT中搭建了8机交直流电力系统,通过策略实施前后的结果对比,表明所提控制策略能够有效地抑制交直流电力系统的区域振荡,提高了系统的稳定性。     

Stabilization of power systems using a variable structure stabilizer

A new technique for improving the dynamic stability of power systems is presented. This new technique makes use of the variable structure system theory and employs the generator speed to obtain a stabilizing signal to increase the damping torque of the synchronous machine.Although modern voltage regulator and excitation systems with fast response and high ceiling voltage can improve the transient stability by increasing the synchronizing torque, their effect on the damping torque is rather small. Under certain operating conditions, when the system exhibits negative damping characteristics, the voltage regulator usually aggravates the situation by increasing the negative damping. Hence, instability may result. In order to reduce this undesirable effect, it is useful to introduce supplementary stabilizing signals to increase the damping torque of the synchronous machine.This paper proposes a variable structure stabilizer for generating the required stabilizing signal. Simulation results indicate that the proposed stabilizer yields better system dynamic performance than that obtained by using the conventional and linear optimal stabilizers in that the step responses have less overshoot and a shorter settling time.It is concluded that the new stabilizer can be used as an effective means of increasing the damping torque and hence improving the dynamic stability of the power system.     

交直流混合输电系统的无功优化

提出了交直流混合系统的无功优化模型,优化控制变量不仅包含传统的交流部分的发电机无功输出、补偿电容器容量、变压器分接头,而且还引入直流部分换流器的控制电压、控制电流、控制功率以及换流变压器变比.模型运用PSO算法进行优化求解.引用IEEE中9节点算例表明该模型是正确的,该算法是收敛、有效的.     

交直流混合输电系统的无功优化

提出了交直流混合系统的无功优化模型,优化控制变量不仅包含传统的交流部分的发电机无功输出、补偿电容器容量、变压器分接头,而且还引入直流部分换流器的控制电压、控制电流、控制功率以及换流变压器变比。模型运用PSO算法进行优化求解。引用IEEE中9节点算例表明该模型是正确的,该算法是收敛、有效的。     

改进拟态物理学算法在交直流系统无功优化中的应用

拟态物理学算法(APO)具有较好的全局搜索能力,且能避免粒子群等算法常出现的易早熟收敛现象,具有较好的稳定性、快速收敛和鲁棒性。针对交直流混联系统无功优化问题,在矢量模型的拟态物理学算法的基础上,提出了一种基于改进拟态物理学算法的无功优化算法。为便于处理约束问题,算法中通过定义不可行度函数判断不可行解,并采用收缩因子将不可行解拉回可行域内,再通过多维搜索方法寻求最优解。通过IEEE30节点系统仿真测试,并与其他优化算法进行比较,结果表明该算法具有较好的求解效率和准确性。     

Use of HVDC links for power system restoration

Power system restoration plans worldwide have often been based on black start units capable of supplying cranking power to bulk generation plants. The increase in the number and size of CCGT plants and other forms of generation with low regulating capacity and requiring a restless growing power for the cranking phase needs that new strategies and tools be developed for facing the unlucky event of a black-out. The study presents the possibility of using HVDC links with a synchronous compensator at the receiving end. Such systems have high regulating capacity and reliability which are precious characteristics during the critical phases of the restoration. A detailed stability analysis is developed for checking the correct size of the compensator. Electromagnetic simulations prove the validity of the solution.