Reachability of the sliding mode control for multimachine power systems

This paper presents conditions of reachability of a switching plane for the sliding mode control of phase shifters in multimachine power systems. Sliding mode controllers are usually synthesized so as to satisfy only the existence condition of a sliding mode. However, there is the border of an asymptotically stable region and a system state cannot reach a switching plane unless a state at the beginning of control (initial state) exists in that region. Hence, reachability is defined as an asymptotic stability of the initial state. A sufficient condition to reach onto a switching plane is given by an energy‐type Lyapunov function. It is described by control parameters that are introduced to find required control gains rather than feedback gains themselves. This allows us to straightforwardly evaluate an asymptotic stability. A phase‐shift control system is numerically tested in a 2‐machine 1‐infinite‐bus power system. The simulation results show that the improved control system offers faster transient stability and achieves the reachability of a switching plane. © 2000 Scripta Technica, Electr Eng Jpn, 131(3): 43–50, 2000     

Decentralized exciter stabilizing control for multimachine power systems

In this paper, a systematic approach to design controllers based on H‐infinity theory for a multimachine power system is presented. Generally, a centralized control scheme is difficult for a large‐scale interconnected power system because of the necessity of obtaining information on the whole system, computation times, and so on. In order to handle these problems, two decentralized control schemes are proposed. One is based on the decomposition of information. The feedback gains for the whole system are obtained, and after decomposing the gains into subblocks for each area, the diagonal block is used to design the controller for each generator. The other is based on area decompositions. The procedure is carried out by decomposing the original system into blocks for each area and the local feedback gain is obtained by using information for each decomposed system. Furthermore, to improve the robustness of the system, an effective weighting matrix design, which involves the allocation of eigenvalues, is also proposed. Several simulation tests show the effectiveness of the proposed methods. © 2002 Scripta Technica, Electr Eng Jpn, 139(1): 35–43, 2002; DOI 10.1002/eej.1144     

Observer-based nonlinear control of power system using sliding mode control strategy

This paper presents a new transient stabilization with voltage regulation analysis approach of a synchronous power generator driven by steam turbine and connected to an infinite bus. The aim is to obtain high performance for the terminal voltage and the rotor speed simultaneously under a large sudden fault and a wide range of operating conditions. The methodology adopted is based on sliding mode control technique. First, a nonlinear sliding mode observer for the synchronous machine damper currents is constructed. Second, the stabilizing feedback laws for the complete ninth order model of a power system, which takes into account the stator dynamics as well as the damper effects, are developed. They are shown to be asymptotically stable in the context of Lyapunov theory. Simulation results, for a single-Machine-Infinite-Bus (SMIB) power system, are given to demonstrate the effectiveness of the proposed combined observer-controller for the transient stabilization and voltage regulation.     

A decentralized control system for stabilizing multimachine power systems

A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system.     

Transient stability enhancement of power systems via optimal nonlinear state feedback control

In this paper, the transient stabilization of power systems will be enhanced using optimal nonlinear feedback control. To this end, a partial differential equation called Hamilton-Jacobi-Belman (HJB), should be solved, which does not have a closed form solution in general. Nevertheless, there are some approximate solutions to solve HJB equations. In this paper, by using a Taylor Series expansion, a sub-optimal nonlinear control law is obtained. As a result, a transient controller for a single-machine infinite-bus power system is designed. Also, the superiority of the designed nonlinear controller in some grounds like increasing the region of asymptotic stability of the system or in other words, increasing the domain of validity is shown. Simulation results reveal the effectiveness of the proposed approach.     

Robust sliding mode control and flux observer for induction motor using singular perturbation

This paper proposes a sequential methodology for designing a robust adaptive sliding mode observer for an induction motor drive using a two-time-scale approach. This approach is based on the singular perturbation theory. The two-time-scale decomposition of the original system of the observer error dynamics into separate slow and fast subsystems permits a simple design and sequential determination of the observer gains. In the proposed method, the stator currents and rotor flux are observed on the stationary reference frame using the sliding mode concept. The control algorithm is based on the indirect field oriented sliding mode control with an on-line adaptation of the rotor resistance to keep the machine field oriented. The control–observer scheme seeks to provide an asymptotic tracking of speed and rotor flux in spite of the presence of an uncertain load torque and an unknown value of rotor resistance. The validity for practical implementation has been verified through computer simulations.     

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.     

Nonlinear coordinated control design of excitation and STATCOM of power systems

This paper presents a nonlinear control scheme for designing the coordinated STATCOM and excitation controllers to enhance the transient stability of power system. The STATCOM installed at the midpoint of the transmission line in a simple power system (a single machine connected to infinite bus). The zero dynamics design theory and pole-assignment technique is employed to design the nonlinear controller. The controller's performance in a SMIB system is also examined using simulation studies and the results validate the efficacy of the proposed controller.     

Decentralized two-level excitation control of multimachine power systems

A two-level decentralized scheme for the excitation control of multimachine power systems is presented. The control strategy is based on decomposing the control signal for each machine into two components generated by controllers at two different levels. At the first level, controllers are designed to optimize the performance of each generating unit, totally ignoring the couplings among the machines. The second control components are chosen to reduce the machine performance degradations due to the presence of interactions. With the developed two-level control scheme each machine is controlled entirely from its own state. The effectiveness of the proposed approach is illustrated by a numerical example involving a four-generator system.     

Single-input fuzzy-like moving sliding surface approach to the sliding mode control

A new approach to the sliding mode control of second-order nonlinear systems is introduced in continuous-time. A single-input fuzzy logic controller is used to continuously compute the slope of the sliding surface, with the result that the sliding surface is rotated in such a direction that tracking performance of the system under control is improved. The proposed fuzzy moving sliding surface approach with a one-dimensional rule base (FMSS-1D) reduces huge number of linguistic fuzzy rules significantly. However, it is shown that the input/output relation of the single-input fuzzy rule base is very close to the input/output relation of a straight line. Therefore, a single-input fuzzy-like moving sliding surface (FLMSS) approach using an approximate line function is then proposed. It is shown that the proposed control approaches have better tracking performance than the conventional sliding mode control with fixed sliding surface. The proposed moving sliding surface approaches are applied to balance an inverted pendulum on a cart. Computer simulations are presented to show the effectiveness of the proposed methods and to make a quantitative comparison with the classical sliding-mode controller with fixed sliding surface method existing in literature.     

Extended SMC for a stand-alone wound rotor synchronous generator

In this paper, a sliding mode controller for the stator voltage amplitude of a stand-alone wound rotor synchronous generator is presented. The standard dq-model of the electrical machine connected to an isolated inductive load is obtained. Then, the control law is designed using sliding mode techniques. The controller introduces a dynamic extension so that the stator voltage amplitude has relative degree one. As a result, a fast controller, robust to both machine and load parameters variations, is obtained. The control algorithm, that does not requires the knowledge of the parameters, is implemented and validated experimentally.     

Robust control of electrical power systems using PSSs and Bilinear Matrix Inequalities

This work presents the application of Bilinear Matrix Inequalities to the robust adjustment of Power System Stabilizers with pre-defined structure. Results of some tests show that gain and zeros adjustments are sufficient to guarantee robust stability and performance with respect to various operating points. Making use of the flexible structure of BMIs, we propose an algorithm that guarantees a minimum damping factor specified for the closed loop system, always using a controller with flexible structure. The technique used here is the pole placement, whose objective is to place the poles of the closed loop system in a specific region of the complex plane. The BMIs are linearized using the homotopic method. Results of tests with a nine-machine system are presented and discussed, in order to validate the algorithm proposed.     

Residue Theorem based soft sliding modecontrol for wind power generation systems

This paper proposes a residue theorem based soft sliding mode control strategy for a permanent magnet synchronous generator (PMSG) based wind power generation system (WPGS), to achieve the maximum energy conversion and improved in the system dynamic performance. The main idea is to set a soft dynamic boundary for the controlled variables around a reference point. Thus the controlled variables would lie on a point inside the boundary. The convergence of the operating point is ensured by following the Forward Euler method. The proposed control has been verified via simulation and experiments, compared with conventional sliding mode control (SMC) and proportional integral (PI) control.     

无源高阶终端滑模控制双馈风力发电系统

为了简化双馈风力发电系统模型并且使得系统具有抗干扰的特性,依据无源性理论和滑模控制理论从能量和鲁棒性的角度研究了变速恒频双馈风力发电系统.首先建立了基于Euler La-grange (EL)方程的双馈风电系统数学模型,使得双馈风电系统分解为电气和机械两个无源子系统的反馈互联.在设计控制器时只需考虑电气子系统,而机械子系统是一个能量耗散系统,通过选择适合的参数可以保证稳定,因此简化了控制算法.针对速度环响应速度慢,鲁棒性差的问题设计了高阶非奇异滑模速度控制器.仿真结果表明了所提控制算法简单有效,能够保证风力发电系统输出恒定频率的同时,电机转速也能快速的跟踪参考转速,提高了整个系统的动静态性能.     

Sliding mode based load-frequency control in power systems

The paper presents a new discrete-time sliding mode controller for load-frequency control (LFC) in control areas (CAs) of a power system. As it uses full-state feedback it can be applied for LFC not only in CAs with thermal power plants but also in CAs with hydro power plants, in spite of their non-minimum phase behaviors. To enable full-state feedback we have proposed a state estimation method based on fast sampling of measured output variables, which are frequency, active power flow interchange and generated power from power plants engaged in LFC in the CA. The same estimation method is also used for the estimation of external disturbances in the CA, what additionally improves the overall system behavior. Design of the discrete-time sliding mode controller for LFC with desired behavior is accomplished by using a genetic algorithm. To the best of our knowledge, proposed controller outperforms any of the existing controllers in fulfilling the requirements of LFC. It was thoroughly compared to the commonly used PI controller by extensive simulation experiments on a power system with four interconnected CAs. These experiments show that the proposed controller ensures better disturbance rejection, maintains required control quality in the wider operating range, shortens the frequency’s transient response avoiding the overshoot and is more robust to uncertainties in the system.     

Robust output tracking control for nonlinear time-varying robotic manipulators

In this paper, a systematic methodology for the robust tracking control of nonlinear time-varying robotic manipulators is proposed. The control method involves fuzzy logic and sliding mode techniques. Output error dynamics can be assigned. Closed-loop system stability is proven. The robustness of the closed-loop system can be achieved against parameter variations and external disturbances. A two-degrees-of-freedom manipulator tracking control problem is carried out. The result shows that output tracking performance can be improved very much comparatively.     

Improved tracking of shunt active power filter by sliding mode control

An improved tracking technique of the reference current waveform in a shunt type active power filter is proposed in this paper using sliding mode control and feedback linearization. Feedback linearization approach helps to reduce the complexity of the controller. Excellent tracking is achieved in both for steady state and dynamic performance. A three-phase four-wire system is considered. The proposed algorithm is simulated first in MATLAB/SIMULINK. An experimental prototype using a dspace1104 based controller is also produced in the laboratory. Results from simulation match well with the corresponding results from experimental prototype confirming the usefulness of the proposed technique.     

Model reference adaptive sliding mode control using RBF neural network for active power filter

In this paper, a model reference adaptive sliding mode (MRASMC) using a radical basis function (RBF) neural network (NN) is proposed to control the single-phase active power filter (APF). The RBF NN is utilized to approximate the nonlinear function and eliminate the modeling error in the APF system. The model reference adaptive current controller in AC side not only guarantees the globally stability of the APF system but also the compensating current to track the harmonic current accurately. Moreover, a sliding mode voltage controller based on an exponential approach law is designed to improve the tracking performance of DC side voltage. Simulation results demonstrate strong robustness and outstanding compensation performance with the proposed APF control system. In conclusion, MRASMC using RBF NN can improve the adaptability and robustness of the APF system and track the given instructional signal quickly.     

非最小相位系统的终端滑模控制

在重新定义系统输出方法的基础上,提出一种终端滑模控制策略,解决了非最小相位系统难以控制的问题。首先,重新定义系统的输出,通过输入输出线性化,得到系统的输入输出子系统。然后,设计终端滑模控制策略,使输入输出子系统在有限时间收敛到零,并根据系统性能指标要求选择适当的输出定义参数,使零动态子系统在原点附近渐近稳定,从而保证原系统的渐近稳定。仿真结果验证了提出方法的有效性。     

Robust adaptive sliding mode control for uncertain time‐delay systems

This paper is devoted to robust adaptive sliding mode control for time‐delay systems with mismatched parametric uncertainties. Sufficient conditions for the existence of linear sliding surfaces are given in terms of linear matrix inequalities, by which the corresponding adaptive reaching motion controller is also designed. Simulation studies show the effectiveness of the control scheme. Copyright © 2008 John Wiley & Sons, Ltd.