A new converter equivalent circuit for fast digital simulation of multiterminal HVDC systems

Contents A new converter equivalent circuit suitable for dynamic simulation of multiterminal HVDC systems with multibridge converters is presented. Using this circuit all possible operating modes of the converter can be analyzed by means of one topological matrix only. It is shown that the proposed converter equivalent circuit increases the flexibility of the simulation and considerably reduces the computations required to obtain the state equations of the converter as a function of the conduction state of the valves. Computer results of selected abnormal operating conditions are also presented to demonstrate the inherent accuracy and the capability of the proposed converter equivalent circuit.

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Ein neues Stromrichterersatzschaltbild für schnelle digitale Simulation eines HGÜ Systems mit mehreren Unterwerken

Übersicht Ein neues Stromrichterersatzschaltbild geeignet für die Simulation dynamischer Vorgänge von HGÜ Systemen mit mehreren Unterwerken und vielen Drehstrombrückenschaltungen wird beschrieben. Die Anwendung dieses Ersatzschaltbildes ermöglicht die Analyse aller möglichen Funktionsarten des Stromrichters mit Hilfe nur einer topologischen Matrix. Es beweist sich noch, daß durch das vorgeschlagene Ersatzschaltbild eine höhere Simulationsflexibilität erreicht werden kann. Der Rechenaufwand zur Bildung der Zustandsgleichungen des Stromrichters abhängig vom momentanen Leitungszustand der Ventile wird wesentlich reduziert. Rechenergebnisse für speziell gewählte nicht normale Betriebszustände werden dargestellt, um die existierende genauigkeit und die Fähigkeiten des vorgeschlagenen Ersatzschaltbildes zu demonstrieren.

     

Stabilization of an AC-DC power system using a controlled multiterminal HVDC link

A state space formulation of an integrated 3-area AC-DC power system operating with a 3-terminal HVDC link is presented. The chosen power system, which is marginally unstable, can be stabilized by modulating the power orders of one of the converter stations by using signals proportional to the speed and tie-line power deviations and their derivatives. The signals are chosen in such a way that the dominant modes of the system can be shifted to prescribed locations to ensure greater damping within the practical gain constraints of the controllers. It is also shown that excellent dynamic performance can be obtained by a combination of modal output feedback control for one converter station and power-order modulation of other stations using the signals of individual areas. A 3-area 3-terminal HVDC-AC system has been considered for digital simulation and the results demonstrate the damping effect of multiterminal HVDC links when controlled by suitable signals derived from the AC system.     

A self-coordinating adaptive control scheme for HVDC transmission systems

The transients in a HVDC system can temporarily change line currents, voltages, and power substantially from the reference steady state values and the behavior of the system depends greatly upon the parameters of the converter controller. The DC system performances are affected by the AC system characteristics such as the short circuit ratio, and the AC system inertia. A controller which has good performance for a particular operating condition may not have sufficiently good performance under another operating condition or vice versa. Performance of the controller also depends on the impedance at the rectifier and the inverter bus, which may vary according to the operating conditions of the AC network. A controller with self-coordinating adaptive capability can perform better in various situations. The proposed controller is tested at a very low SCR, the most critical value for system performance evaluation, and at the low inertia of the AC system. Simulation results are compared between proposed controller, fuzzy tuned controller, gain scheduling controller, and fixed-parameter controller. All simulations are conducted using MATLAB/SIMULINK software package.     

A nonlinear emergency control strategy for HVDC transmission systems

A novel nonlinear emergency control method for HVDC transmission systems is presented in this paper. First, an observation-decoupled state space model of AC and DC interconnected power systems, which allows estimation or computation of the state components from local measurements, is developed. Secondly, the nonlinear control rules of HVDC links are derived using optimal-variable-aim strategy, which not only improves the first-swing stability, but also effectively damps the subsequent power oscillation. Finally, the simulation results of a three-machine six-bus system show that the proposed method can enough use the capabilities of fast response and short-time overload of HVDC links to improve the transient stability of power systems.     

Robust decentralized control of multiterminal DC/AC power systems

A multiterminal DC system embedded in a conventional AC power system can be used as a control element for damping inter-area oscillation. Three methods for decnetralized control of multiterminal DC/AC power systems are proposed. The robustness problems associated with DC control systems are discussed and the sufficient stability criteria are introduced. A power system example, which employs five DC terminals to damp out inter-area oscillations due to the AC power system dynamics, indicates that the proposed methods are realistic for robust decentralized control system design of DC/AC power systems.     

A robust adaptive control with unmodeled dynamic for HVDC transmission systems

Utilizing the feature of quick response of HVDC to improve the performance of AC/DC system has become the emphasis to be researched. This paper introduces firstly the principle of the robust adaptive control of nonlinear systems with unmodeled dynamics, then developed the robust adaptive additional control of HVDC with unmodeled dynamics of generator in order to improve stability of power system. The additional control of HVDC with unmodeled dynamics only uses the local signals and its design is simple, furthermore it can obviously improve the stability of power system in different operational conditions. Experimental results using the presented concepts obtained on single machine infinite bus model are also included. These results prove the efficiency of the control scheme. The design process of controller provided a new idea to design controller by use of simplified model. __________ Translated from Journal of Sichuan University (Engineering Science Edition), 2005, 37(5): 154–158 (in Chinese)     

A new decentralized model reference adaptive control for a class of interconnected dynamic systems using variable structure design

This paper presents a new decentralized model reference adaptive control for a class of large-scale interconnected dynamic systems. Interconnections among subsystems may be time-invariant or time-varying and linear or non-linear. The scheme proposed here only takes input and output measurements from each subsystem for input synthesis. Using a variable structure design concept, we show that the tracking errors will converge to zero in finite time despite the interconnections with any possible strengths.     

Design of a reduced order observer for optimal decentralizedcontrol of HVDC systems

The authors present a novel approach to the design of decentralized optimal controls for integrated power systems. The approach involves the decomposition of the integrated system into interconnected subsystems and the independent control of each subsystem, considering the interactions at the interconnection points as unknown disturbances. The design of a reduced-order observer, capable of reconstructing the inaccessible states of the system and the unknown disturbances, and the integration of this observer into the overall control loop are presented. As an example, an optimal current regulator for HVDC system is presented to demonstrate the effectiveness of the proposed approach     

A design method for continuous deadbeat control systems

Deadbeat control of discrete‐time systems has attracted particular interest because it ensures setting the deviation response to zero within finite time and affords fast responsiveness. By using controllers which include a delay element, however, the deadbeat characteristics can be realized in the continuous‐time domain, and such a tracking system has been obtained. In this paper, we propose a new design method of continuous deadbeat control systems without using delay elements. Our new controller is composed of a digital deadbeat compensator using state feedback and a series smoothing filter. Illustrative numerical examples are presented. The method proposed here is very simple compared with other methods and it seems to be useful for practical applications. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 42–48, 1999     

A new heuristic approach for optimal reconfiguration in distribution systems

This paper presents a novel approach for optimal reconfiguration of radial distribution systems. As an integral part of the distribution system configuration, a load flow algorithm based on graph theory is presented. The algorithm follows changes in system structure by traversing a directed graph of the system to find the depth-first search discovery order. For each switching-iteration, this discovery order generates down-stream-nodes vectors necessary for dynamic generation of two matrices: one is the branch node incidence matrix and the other the relationship between the bus current injection and branch currents. Thus avoiding creation of unconnected branches or forming closed loops. The developed load flow program is integrated with known heuristic techniques in a new heuristic search methodology for determining the minimum loss configuration of a radial distribution system. The technique consists of two parts; one is to determine the best switching combinations in all loops with minimum computational effort while the other is a power loss and voltage profile calculation of the best switching combination found in part one by load flows. Compared to other published articles, the efficient developed load flow reduces the switching combinations searched and gives the optimum solution in few number of load flow runs. To demonstrate the validity of the proposed algorithm, computer simulations are carried out on 33-bus system. The results show that the performance of the proposed method is better than that of the other methods.     

高压直流输电控制保护系统的冗余设计

冗余是高压直流输电控制保护系统的重要概念。与自诊断功能相结合,冗余配置的直流控制保护设备可以避免控制保护设备内部故障造成的功能失效,极大地提高直流输电系统运行的可靠性和系统可用率。基于高压直流输电控制保护系统的总体结构,对实际工程中直流控制保护系统采用的多种冗余方案作了全面分析和总结,相关概念和原则可以在进行直流控制保护的系统设计时参考。     

高压直流输电控制保护系统的冗余设计

冗余是高压直流输电控制保护系统的重要概念.与自诊断功能相结合,冗余配置的直流控制保护设备可以避免控制保护设备内部故障造成的功能失效,极大地提高直流输电系统运行的可靠性和系统可用率.基于高压直流输电控制保护系统的总体结构,对实际工程中直流控制保护系统采用的多种冗余方案作了全面分析和总结,相关概念和原则可以在进行直流控制保护的系统设计时参考.     

An optimal control design for bidirectional inductive power transfer system using dynamics identification

Abstract

In this article, we address the tracking control problem for the bidirectional inductive power transfer systems (BIPTS) in the view of optimal performance. To achieve the optimal destination with respect to a quadratic value function, an identified linear model for the BIPTS is first developed, and it is proved to be convergent to the true dynamic model when the persistent excitation condition is satisfied. And then, based on the identified model, the desired system states and control inputs are derived according to the reference transferring power, and be utilized as the feedback signals and feedforward compensation, respectively, for the optimal controller. A hybrid Lyapunov function is developed to guarantee the closed-loop stability and the asymptotically tracking convergence. A numerical simulation is carried out to illustrate the satisfactory control performance.     

一种优化协调控制策略在VSC HVDC 中应用

随着大功率电力电子技术的发展和可工作在高频率开关状态的完全可控器件(如大功率IGBT，IGCT等)的出现，使得电压源型直流输电(VSCHVDC)成为现实，这种新型的直流输电技术和传统直流输电相比，体现了诸多优点。该文建立了一种适合于研究VSCHVDC基频下的运行与控制特性的VSCHVDC模型，并将该模型方程与电力系统微分代数方程统一起来。在此基础上提出一种VSCHVDC与发电机励磁协调控制策略，在AC／DC交直流混合系统中研究了该控制方式对各自的影响，仿真表明，采用该优化协调控制，发电机和HVDC在系统发生故障或者扰动后都能够快速恢复正常稳定运行，且该控制方式对于系统参数变化具有一定鲁棒性。     

Robust excitation control design using sliding-mode technique for multimachine power systems

An output feedback controller is proposed to enhance the transient stability of nonlinear multimachine power systems considered as a classical model with flux decay dynamics. Combining high-order sliding-mode techniques with a robust high-order sliding-mode differentiator, a robust decentralized controller is obtained. Numerical results are presented to illustrate the performance of the proposed control scheme and its robustness properties.