网络化多机电力系统的分布协调控制和暂态联结稳定性分析

针对n个同步发电机互联电力系统暂态过程中出现的发电机失步现象,为了控制任意两台电机之间的转角差,提出一种新的分布式协调控制设计方法.将整个系统对对分解为$n-1$个子系统,设计分布式协调控制律,估计子系统的局部稳定区域,得到判定联结稳定性的定理;通过一个三机系统的算例,给出判别方法的应用.算例表明,这种判别方法能够简化系统稳定性分析的复杂性,并能够降低计算量.     

Transient response improvement of feedback control systems using hybrid reference control

By means of the internal model principle, an approach to improve the performance of a stabilised closed-loop continuous time linear system based on manipulation of the reference signal is developed. A change in the reference signal is equivalent to implementing an instantaneous change via the choice of a decision vector in the state of the reference signal model, and the analysis of the proposed approach called hybrid reference control (HRC) system is then shown to be equivalent to the analysis of a linear impulsive dynamical system. Conditions for asymptotic stability and convergence of the output tracking error for a HRC system are expressed in term of conditions on the decision vectors. Conditions are then derived which guarantee that the HRC system leads to an improved transient performance compared to a conventional closed-loop control system. In particular, it is shown how decision vectors are chosen so that a HRC system results in a deadbeat response.     

A brand new nonlinear robust control design of SSSC for transient stability and damping improvement of multi-machine power systems via pseudo-generalized Hamiltonian theory

Nonlinear robust control of static synchronous series compensator (SSSC) is investigated in multi-machine multi-load power systems by using the pseudo-generalized Hamiltonian method. First, the uncertain nonlinear differential algebraic equation model is constructed for the power system. Then, the dissipative pseudo-generalized Hamiltonian realization of the system is established by means of variable transformation and prefeedback control. Finally, based on the obtained dissipative pseudo-generalized Hamiltonian realization, a brand new nonlinear robust controller is put forward. The proposed controller can effectively use the internal structure and the energy balance property of the power system. Simulation results demonstrate the effectiveness and robustness of the control scheme.     

Equivalencing excitation and governor-turbine systems in multi-machine power systems using Walsh functions

When the generators of a coherent group in a power system are equivalenced for transient stability studies, it is logical that the associated controllers—excitation controllers and the speed governing systems—are also equivalenced. Depending upon various design features and capacity, the time constants of the transfer functions of different controllers may be different. This paper presents a Walsh function approach for equivalencing the controllers in multi-machine power systems, taking into account the above differences. The approach has an elegant mathematical base and provides any desired level of accuracy.     

Transient stability region of power systems using series expansion of Lyapunov functions

In this paper, a method is proposed for improving the accuracy of the stability criterion by enlarging the estimation of the stability region determined by means of Lyapunov's direct method using series expansion, and by putting it closer to the actual stability region. The Lyapunov function obtained by energy integration is used as the first estimation. The method is applied to a single-machine infinite bus power system, and the stability domain in the δ-ω plane is shown together with the actual stability domain obtained by numerical integration. It is shown that the application of the proposed method results in a considerable improvement in the stability boundary estimation over that given by the original Lyapunov function. Zubov's method, which obtains an accurate stability boundary using the series expansion, is related to the method proposed in this paper. The last section is, therefore, devoted to comparing the two methods and examining the possibility of their application to multi-machine power systems.     

On improvement of stability conditions for continuous Mamdani-like fuzzy systems

This paper is concerned with continuous fuzzy systems with singleton consequents, called type II fuzzy systems. It first introduces the canonical form of an unforced type II fuzzy system and its stability theorem presented in the previous study. Then, improving the stability theorem, it gives necessary and sufficient conditions such that a type II fuzzy system is stable with respect to a global quadratic Lyapunov function.     

Iterative performance improvement of fuzzy control systems for three tank systems

This paper suggests the performance improvement of fuzzy control systems (FCSs) for three tank systems using iterative feedback tuning (IFT). The stable design of Takagi–Sugeno–Kang fuzzy controllers is guaranteed by means of a stability theorem based on LaSalle’s global invariant set theorem formulated for a class of multi input-multi output (MIMO) nonlinear processes. An IFT algorithm characterized by setting the step size to guarantee the FCS stability is proposed. The theoretical approaches are applied in a case study that deals with the IFT-based stable design of fuzzy controllers dedicated to the level control of a cylindrical three tank system as a representative MIMO system. A set of experimental results for a laboratory setup illustrates the performance improvement.     

Analysis of stability and robust stability of polynomial fuzzy model-based control systems using a sum-of-squares approach

The well known Takagi–Sugeno (T–S) fuzzy model can be extended in different ways including the polynomial fuzzy model, whose consequent parts are polynomial sub-systems. Compared with the traditional T–S fuzzy model, the polynomial fuzzy model can represent a nonlinear system more accurately with a smaller number of fuzzy logic rules. It is worth emphasizing that the stability analysis and controller design of polynomial fuzzy model-based (PFMB) control systems are not based on the linear matrix inequalities but the recently developed sum-of-squares decompositions. In this paper, based on an existing result for traditional fuzzy control systems, we propose a new stability condition for the stability analysis of PFMB control systems. Furthermore, the stability of PFMB control systems with parameter uncertainties is investigated. The popular inverted pendulum and an unstable nonlinear system are employed to demonstrate the quality of the proposed stability conditions.     

Non-linear decentralized saturated controller design for multi-machine power systems

A direct method of constructing a decentralized saturated controller is very important in the controller design of multimachine power systems. Among the existing designs the author first constructed a state feedback, then saturated the controller. However, the author could not prove that this saturated controller was valid. In this paper a multi-machine power system as a Hamiltonian control system with dissipation is first represented. Then using a Hamiltonian function a decentralized saturated excitation control scheme, which is a static measurable feedback, is proposed. Last, the design is discussed in detail on a three-machine power system. Simulations show that the saturated, simple control law works well.     

模糊Delta算子系统的鲁棒稳定性分析与控制

研究一类由Delta算子描述的T-S型模糊系统的鲁棒稳定性与状态反馈控制设计问题。基于Delta域的Lyapunov稳定性理论，利用线性矩阵不等式(LMI)的方法，给出了不确定模糊Delta算子系统鲁棒稳定及存在状态反馈控制器使得闭环系统稳定的充分条件。这不仅将连续与离散不确定模糊系统的有关结果纳入Delta算子系统的统一框架中，也为Delta算子方法在非线性系统中的应用研究提供了一种有效途径。数值算例说明了该方法的有效性。     

Adaptive fuzzy power control for WCDMA mobile radio systems

In this paper a fuzzy logic based power control for a direct sequence, wideband code-division multiple-access (DS/WCDMA) cellular phone system is introduced. A power control procedure is needed to compensate the fluctuation of the mobile's transmitting power received in a base station and to increase the capacity of mobile communication systems.The input variables of the controller are the power error and the change of the error. The output is the power step size. Simulation results show that the developed fuzzy proportional-integral control stabilizes the power level and decreases the overshoot and rise time.     

Thermal modeling of power transformers using evolving fuzzy systems

Thermal models for distribution transformers with core immersed in oil are of utmost importance for transformers lifetime study. The hot spot temperature determines the degradation speed of the insulating paper. High temperatures cause loss of mechanical stiffness, generating failures. Since the paper is the most fragile component of the transformer, its degradation determines the lifetime limits. Thus, good thermal models are needed to generate reliable data for lifetime forecasting methodologies. It is also desired that thermal models are able to adapt to cope with changes in the transformer behavior due to structural changes, maintenance and so on. In this work we apply an evolving fuzzy model to build adaptive thermal models of distribution transformers. The model used is able to adapt its parameters and also its structure based on a stream of data. The proposed model is evaluated using actual data from an experimental transformer. The results suggest that evolving fuzzy models are a promising approach for adaptive thermal modeling of distribution transformers.     

Robust decentralised observer based guaranteed cost control for nonlinear uncertain interconnected systems. Application to multi-machine power systems

This article addresses the problem of a robust decentralised observer based guaranteed cost control for nonlinear interconnected systems with norm bounded time varying parameter uncertainties.

Sufficient conditions for the robust stabilisation and the guaranteed cost control performances of the closed-loop system are formulated in an optimisation problem in terms of linear matrix inequalities. Moreover, the designed problem is solved by a proposed iterative algorithm to compute the observer and the control gain matrices, to minimise the upper bound of a prescribed performance index and to maximise the nonlinearity domain, which leave the augmented system stable, despite the emerged uncertainties on the subsystems and on the interconnections between them. An extensive application example of a power system with three interconnected machines is discussed to demonstrate the reliability of the proposed control approach.     

Modelling,control, and stability analysis of non-linear systems using generalized fuzzy neural networks

This paper presents an adaptive fuzzy neural controller (AFNC) suitable for modelling and control of MIMO non-linear dynamic systems. The proposed AFNC has the following salient features: (1) fuzzy neural control rules can be generated or deleted dynamically and automatically; (2) uncertain MIMO non-linear systems can be adaptively modelled on line; (3) adaptation and learning speed is fast; (4) expert knowledge can be easily incorporated into the system; (5) the structure and parameters of the AFNC can be self-adaptive in the presence of uncertainties to maintain a high control performance; and (6) the asymptotical stability of the system is established using the Lyapunov approach. Simulation studies on a two-link robot manipulator show that the performance of the proposed controller is better than that of some existing fuzzy/neural methods.     

Some remarks on the stability of Mamdani fuzzy control systems

This paper presents a passivity approach to the stability analysis of Mamdani fuzzy control systems. The main idea of the paper is that the fuzzy controller can be considered from an input-output viewpoint as a nonlinear dissipative operator. An input-output approach is provided by considering a dynamical dependency of inputs of the fuzzy controller. Then the passivity theory is applied in order to obtain conditions for absolute stability of the closed-loop control system     

模糊时滞系统的输出反馈控制及其稳定性分析

利用模糊T－S模型对一类不确定非线性时滞系统进行建模，在此基础上，提出了模糊不确定时滞系统的状态反馈控制及其输出反馈控制的设计，并给出了模糊闭环系统渐近稳定的充分条件，基于李亚普诺夫函数和线性矩阵不等式方法，证明了模糊系统的渐近稳定性。     

Coordinated design of TCSC and PSS controllers using VURPSO and Genetic algorithms for multi-machine power system stability

Thyristor controlled series capacitor (TCSC) can regulate line impedance and therefore increase transferred power of the system. On the other hand power system stabilizer (PSS) increases dynamic stability of generator. To enhance the stability, combination of TCSC and PSS can be applied, and in such a case coordination of TCSC and PSS is essential. This paper applies this combined controller in order to enhance the stability of multi-machine system. Parameters of these controllers are optimized by velocity update relaxation particle swarm optimization (VURPSO) algorithm and Genetic algorithm (GA). The simulation results show that the combination of VURPSO algorithm and GA leads to a better design and stability.     

基于LMI的仿射型模糊控制系统的稳定性研究

基于凸优化方法，分析了仿射型模糊控制系统的稳定性与镇定问题。首先以LMI的形式给出了仿射型模糊系统稳定的充分条件；然后基于这一条件讨论了闭环系统的镇定问题。得出的镇定条件是BMI，使用轮换极小法将这一BMI问题转化为2个LMI问题，从而可以用MATLAB中的LMI优化工具箱进行求解。仿真例子说明了所提方法的有效性。     

Modeling, control, and stability analysis for time-delay TLP systems using the fuzzy Lyapunov method

In this study, we present a Takagi–Sugeno (T–S) fuzzy model for the modeling and stability analysis of oceanic structures. We design a nonlinear fuzzy controller based on a parallel distributed compensation (PDC) scheme and reformulate the controller design problem as a linear matrix inequalities (LMI) problem as derived from the fuzzy Lyapunov theory. The robustness design technique is adopted so as to overcome the modeling errors for nonlinear time-delay systems subject to external oceanic waves. The vibration of the oceanic structure, i.e., the mechanical motion caused by the force of the waves, is discussed analytically based on fuzzy logic theory and a mathematical framework. The end result is decay in the amplitude of the surge motion affecting the time-delay tension leg platform (TLP) system. The feedback gain of the fuzzy controller needed to stabilize the TLP system can be found using the Matlab LMI toolbox. This proposed method of fuzzy control is applicable to practical TLP systems. The simulation results show that not only can the proposed method stabilize the systems but that the controller design is also simplified. The effects of the amplitude damping of the surge motion on the structural response are obvious and work as expected due to the control force.     

Optimal placement of phasor measurement systems for enhancing on-line protection and control of large-scale power systems

Microprocessor-based real-time phasor measurements, i.e. measurement of fundamental frequency, positive sequence, complex three phase voltages and currents, for enhancing on-line protection and control of interconnected electric power systems are described. The proposed research demonstrates that real-time monitoring of key system states, in the bulk power transfer problem, can be identified. It also provides the means for determining which states are the key states for that problem, and that phasor measurements can be used to improve the protection and/or control of the system. The procedure is applied to a realistic system, where such a control problem exists in practice, for confirmation of the developed technique.