Ant Colony Optimized Fuzzy Control Solution for Frequency Oscillation Suppression

This paper presents a novel approach in addressing a critical power system issue, i.e., automatic generation control (AGC) in a smart grid scenario. It proposes the design and implementation of an optimized fuzzy logic controller (FLC) for AGC of interconnected power network. There are three different sources of power generation considered in the two-area interconnected model of power system network. First area is equipped with a single reheat thermal unit and a superconducting magnetic energy storage (SMES) unit, while another area has a hydro-unit with SMES. A multi-stage optimization strategy for the optimal solution of FLC for tie-line and frequency oscillation suppression is proposed in this paper using an ant colony optimization technique. The optimization of FLC is carried out in four different stages. The first stage is the optimization of range of input and output variables; the second stage is the optimization of membership function; the third and fourth stages are the optimization for rule base and rule weight optimization, respectively. The performance of the proposed controller is also compared with another control approaches to stabilize P_tie-line and Δf oscillations; these are the Ziegler–Nichols-tuned proportional–integral–derivative (PID) controller and genetic algorithm optimized PID controller. A comprehensive analysis of the traditional techniques and proposed techniques is presented on the basis of major dynamic performance parameters, i.e., settling time and peak overshoot.     

A robust adaptive LQG/LTR TCSC controller applied to damp power system oscillations

This paper investigates the use of self-tuning Linear Quadratic Gaussian control with Loop Transfer Recovery (LQG/LTR), applied in Thyristor Controlled Series Capacitors (TCSC) installed in interconnected power systems. The proposed robust adaptive controller can improve power system stability margins, damping properly the system's dominant electromechanical modes. Although this TCSC controller is designed mainly to identify and damp inter-area modes, it does not affect negatively the local modes damping, therefore enhancing the overall system performance. The proposed controller properties can be verified using non-linear simulations for a four-machine power system, in different operation conditions.     

Application of modular multilevel converter for AGC in an interconnected power system

This article demonstrates the maiden application of a new Modular Multi level Converter based Series Compensation (MMCS) technique for multi area Automatic Generation Control (AGC) interconnected system. Primarily MMCS has been modeled in state space form and proposes an appropriate location in AGC to obtain the better dynamic responses in frequency, tie-line power and individual generating power; further to quench the oscillation for sudden changes in load. The system has been studied the operation of MMCS and investigated with Generation Rate Constraints (GRC) of reheat turbines used in system. Further, selection of suitable integral and proportional–integral controller gain has been investigated with Integral Square Error (ISE) technique and Particle Swarm Optimization (PSO) technique for step load perturbation (SLP) in area-1 with performance index as its objective function by making control parameters as variables. System with MMCS is compared with out MMCS and observed performance has been increased and results are explored.     

Automatic generation control of TCPS based hydrothermal system under open market scenario: A fuzzy logic approach

This paper presents the analysis of automatic generation control of a two-area interconnected thyristor controlled phase shifter based hydrothermal system in the continuous mode using fuzzy logic controller under open market scenario. Open transmission access and the evolving of more socialized companies for generation, transmission and distribution affects the formulation of AGC problem. So the traditional AGC two-area system is modified to take into account the effect of bilateral contracts on the dynamics. It is possible to stabilize the system frequency and tie-power oscillations by controlling the phase angle of TCPS which is expected to provide a new ancillary service for the future power systems. A control strategy using TCPS is proposed to provide active control of system frequency. Further dynamic responses for small perturbation considering fuzzy logic controller and PI controller (dual mode controller) have been observed and the superior performance of fuzzy logic controller has been reported analytically and also through simulation.     

采用T-S模糊模型的TCSC多目标控制器设计

在电力系统中装设可控串联补偿(TCSC)可以改善系统的稳定性,抑制次同步谐振和区域间的低频振荡,提高远距离联络线的传输能力。为更好地发挥TCSC效益,利用模糊T-S模型无限逼近非线性系统的特性,提出了一种多目标TCSC控制器设计方法。建立了一类含TCSC的两机电力系统的模糊T-S模型,把闭环系统的稳定性、H∞性能、极点配置的要求统一到一个线性矩阵不等式组中,基于线性矩阵不等式理论实现了TCSC多目标控制器设计,采用并行分配补偿技术,设计出了全局非线性系统的控制规律。最后,利用MATLAB进行了仿真,结果表明所设计的控制器能有效提高电力系统的功角稳定性,保证系统具有良好的动态性能,能满足多个目标要求,具有比TCSC非线性H∞鲁棒控制器更优越的性能,且易于工程实现,它将会在电力系统稳定控制中得到更多应用。     

Optimal placement and parameter setting of SVC and TCSC using PSO to mitigate small signal stability problem

This paper aims to select the optimal location and setting parameters of SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Compensator) controllers using PSO (Particle Swarm Optimization) to mitigate small signal oscillations in a multimachine power system. Though Power System Stabilizers (PSSs) associated with generators are mandatory requirements for damping of oscillations in the power system, its performance still gets affected by changes in network configurations, load variations, etc. Hence installations of FACTS devices have been suggested in this paper to achieve appreciable damping of system oscillations. However the performance of FACTS devices highly depends upon its parameters and suitable location in the power network. In this paper the PSO based technique is used to investigate this problem in order to improve the small signal stability. An attempt has also been made to compare the performance of the TCSC controller with SVC in mitigating the small signal stability problem. To show the validity of the proposed techniques, simulations are carried out in a multimachine system for two common contingencies, e.g., load increase and transmission line outage. The results of small signal stability analysis have been represented employing eigenvalue as well as time domain response. It has been observed that the TCSC controller is more effective than SVC even during higher loading in mitigating the small signal stability problem.     

Comparative performance evaluation of SMES-SMES, TCPS-SMES and SSSC-SMES controllers in automatic generation control for a two-area hydro-hydro system

This paper presents the automatic generation control (AGC) of an interconnected two-area multiple-unit hydro-hydro system. As an interconnected power system is subjected to load disturbances with changing frequency in the vicinity of the inter-area oscillation mode, system frequency may be severely disturbed and oscillating. To compensate for such load disturbances and stabilize the area frequency oscillations, the dynamic power flow control of static synchronous series compensator (SSSC) or Thyristor Controlled Phase Shifters (TCPS) in coordination with superconducting magnetic energy storage (SMES) are proposed. SMES-SMES coordination is also studied for the same. The effectiveness of proposed frequency controllers are guaranteed by analyzing the transient performance of the system with varying load patterns, different system parameters and in the event of temporary/permanent tie-line outage. Gains of the integral controllers and parameters of SSSC, TCPS and SMES are optimized with an improved version of particle swarm optimization, called as craziness-based particle swarm optimization (CRPSO) developed by the authors. The performance of CRPSO is compared to that of real coded genetic algorithm (RGA) to establish its optimization superiority.     

Real-time coordinated optimal facts controllers

A coordinated optimal (CDO) controller is designed to implement multiple Thyristor Controlled Series Compensation (TCSC) devices in a transmission network of interconnected power systems. The proposed controller is utilized to damp inter-area oscillations and to enhance power system damping during large disturbances. The effectiveness of the CDO controller to properly control such devices is demonstrated for a two-machine power system through real-time digital simulation studies using a PSCAD/RTDS.     

A new intelligent online fuzzy tuning approach for multi-area load frequency control: Self Adaptive Modified Bat Algorithm

The primary aim of the Automatic Generation Control (AGC) is to maintain system frequency and tie-line interchanges in a predestine limits by regulating the power generation of electrical generators, in case of fluctuations in the system frequency and tie-line loadings. This paper proposes a new online intelligent strategy to realize the control of multi-area load frequency systems. The proposed intelligent strategy is based on a combination of a novel heuristic algorithm named Self-Adaptive Modified Bat Algorithm (SAMBA) and the Fuzzy Logic (FL) which is used to optimally tune parameters of Proportional–Integral (PI) controllers which are the most popular methods in this context. The proposed controller guaranties stability and robustness against uncertainties caused by external disturbances and impermanent dynamics that power systems face. To achieve an optimal performance, the SAMBA simultaneously optimizes the parameters of the proposed controller as well as the input and output membership functions. The control design methodology is applied on four-area interconnected power system, which represents a large-scale power system. To evaluate the efficiency of the proposed controller, the obtained results are compared with those of Proportional Integral Derivative (PID) controller and Optimal Fuzzy PID (OFPID) controller, which are the most recent researches applied to the present problem. Simulation results demonstrate the successfulness and effectiveness of the Online-SAMBA Fuzzy PI (MBFPI) controller and its superiority over conventional approaches.     

自动发电控制中频率偏差系数确定方法的探讨

自动发电控制（AGC）中联络线频率偏差控制（TBC）模式下频率偏差系数的选择对控制系统稳定和频率恢复起着至关重要的作用。在分析国外研究状况及中国AGC实际运行的基础上提出了一种频率偏差系数确定方法。该方法考虑到国内自动化水平的限制，建立了不同运行方式下全天分时段频率偏差系数模型；结合AGC分级控制的特点，按频率偏差等级设定频率偏差系数。通过两区域互联电网仿真实验，同其他频率偏差系数的设定方式进行了分析和比较，其结果表明了该方法的优越性。     

Optimized load-frequency simulation in restructured power system with Redox Flow Batteries and Interline Power Flow Controller

This paper proposes the Load Frequency Control (LFC) of an interconnected two-area multiple-unit thermal reheat power system in a restructured environment. In the restructured scenario, various kinds of apparatus with large capacity and fast power consumption may cause a series problem of frequency oscillations. The oscillation of system frequency may sustain and grow to cause a series frequency stability problem if no adequate damping is available. Moreover, the larger amount of the steam stored in steam chest and reheater of thermal power plant delays the control valve motion to increase the mechanical power output after the load perturbation. So in order to stabilize the system, impacts of Interline Power Flow Controller (IPFC) in series with tie-line and Redox Flow Batteries (RFB) at the terminal of area 1 have been investigated. The Bacterial Foraging Optimization (BFO) algorithm is used to optimize the integral gains of the Load-frequency Controller under different transactions in the competitive electricity market. Compliance with North American Electric Reliability Council (NERC) standards for Load Frequency Control has also been established in this work. Simulation studies reveal that the RFB coordinated with IPFC units for LFC loop has greater potential for improving the system’s dynamic performance.     

On the robust LQG control of TCSC for damping power systemoscillations

This paper deals with the application of the LQG (linear quadratic Gaussian) technique to the design of a robust TCSC (thyristor controlled series compensator) controller for power system oscillation damping enhancement. This paper discusses each process involved in the LQG design technique applied to the TCSC damping controller design. This paper also discusses the pitfalls in applying the LTR (loop transfer recovery) technique to reserve the robustness of the LQG damping controller. The robustness of the designed controller is verified by nonlinear power system simulation, which shows that the controller is effective for damping power system oscillations     

UPFC的模糊调制控制研究

以统一潮流控制器（UPFC）为研究对象,针对其调制控制,引入模糊技术,设计了模糊调制控制器,以抑制互联电力系统联络线功率振荡,改善系统的动态稳定性。给出了模糊调制控制器的结构,运用梯度下降法对模糊控制器的关键参数进行了优化。结合UPFC具有串、并联元件的特点,提出了模糊联合调制控制器,相对于单一元件调制控制,可更有效地阻尼功率振荡。多机系统仿真结果表明模糊调制控制器能有效地抑制振荡,并且在运行工况改变时性能优于线性调制控制器,而联合调制又优于单一元件调制。     

基于李雅普诺夫函数的直流附加控制器设计

利用李雅普诺夫直接法设计了直流附加阻尼控制器,通过构造交直流系统的Lyapunov函数,设计了一个用于改善互联系统阻尼特性的直流附加控制器。该控制器利用两端换流母线处的角速度和相角,以及交流联络线上的功率作为输入信号,结构简单且易于实现。与常规的直流附加控制器相比,该控制器能更有效地抑制功率振荡,提高系统的动态稳定性。仿真结果验证了所提方法的正确性和有效性。     

Fuzzy based damping controller for TCSC using local measurements to enhance transient stability of power systems

This paper proposes a local fuzzy based damping controller (LFDC) for thyristor controlled series capacitor (TCSC) to improve transient stability of power systems. In order to implement the proposed scheme, detailed model of TCSC, based on actual behavior of thyristor valves, is adopted. The LFDC uses the frequency at the TCSC bus as a local feedback signal, to control the firing angle. The parameters of fuzzy controller are tuned using an off-line method through chaotic optimization algorithm (COA). To verify the proposed LFDC, numerical simulations are carried out in Matlab/Simpower toolbox for the following case studies: two-area two-machine (TATM), WSCC three-machine nine-bus and Kundur’s two-area four-machine (TAFM) systems under various faults types. In this regard, to more evaluate the effectiveness of the proposed method, the simulation results are compared with the wide-area fuzzy based damping controller (WFDC). Moreover, the transient behavior of the detailed and phasor models of the TCSC is discussed in the TATM power system. The simulation results confirm that the proposed LFDC is an efficient tool for transient stability improvement since it utilizes only local signals, which are easily available.     

Coordinated Optimal Control for Power System Stability Enhancement

A linear optimal controller is designed to implement Variable Series Compensation (VSC) in transmission network of interconnected power systems. The proposed controller is used to dampen inter-area oscillations and enhance power system stability. The effectiveness of the linear optimal controller to properly control such a variable series reactance is demonstrated through mode shapes and digital simulation studies on a two-machine system. The digital simulation studies are conducted using a PSCAD/EMTDC software package. The mode shapes and simulation results show that the controller contributes significantly to the damping of inter-area oscillations and the power stability enhancement.     

Load frequency control and automatic generation control using fractional-order controllers

Recently, fractional calculus has received extensive attention and research. Accordingly, there is an increasing interest in fractional-order (FO) dynamic systems and controllers. The widely used classical integer-order proportional-integral controller and proportional-integral-derivative controller are usually adopted in the load frequency control (LFC) and automatic generation control (AGC) to improve the dynamic response and to eliminate or reduce steady-state errors. This paper utilizes the FO controllers to improve stability and response of LFC and AGC system. The paper uses the integral of the time-weighted absolute error performance index for optimal controller design. The paper investigates LFC and AGC for both isolated and interconnected power systems and shows that FO controllers perform better than classical integer-order controllers in theses systems.     

Design of an output feedback variable structure thyristor-controlled series compensator for improving power system stability

An output feedback variable structure controller is designed for a thyristor-controlled series compensator (TCSC) in order to improve the damping characteristic of a power system. Physically measurable real power and reactive power signals near TCSC locations are used as the inputs to the variable structure controller. These input signals are employed to construct the switching hyperplane of the proposed variable structure TCSC controller. To demonstrate the effectiveness of the proposed variable structure TCSC controller, time-domain simulations are performed on a power system with a TCSC. It is concluded from the simulation results that system damping can be significantly improved by the proposed variable structure TCSC controller.     

多可控串补自适应协调控制设计

采用多可控串联补偿器（thyristor controlled series compensation,TCSC）联合运行可提高线路功率传输能力,但多TCSC联合运行时所存在的交互影响可能导致系统暂态稳定性下降。设计一种新的自适应控制方案,动态自适应调整多个TCSC联合运行时的参数,以规避多TCSC的负交互影响。利用能量函数分析多TCSC协调控制规律,然后通过微分观测器引入微分信号,再将专家控制和神经网络引入自适应控制,动态调整PID（proportion integral differential）参数。通过在一个装设2台TCSC的4机2区域系统的仿真验证,并和PI控制、BP-PI控制进行对比,结果表明,所设计的自适应控制器在提高系统暂态稳定性方面,具有一定的优越性。     

Coordinated design of PSS and TCSC to mitigate interarea oscillations

Thyristor controlled series compensator (TCSC) as a promising series flexible AC transmission system (FACTS) device is generally used for controlling the real power flow in transmission lines. It can increase the system stability as the complementary functionality by minimizing the power oscillations. The effectiveness of TCSC in its primary and supplementary applications depends on the selection of its optimal location and defining a proper input signal. In this paper, a new method based on the active power sensitivity approach is applied to find the optimal location of TCSC. In addition, Hankel singular values (HSVs) and right half plane-zeros (RHP-zeros) analyses have been proposed to find the most appropriate stabilizing input signal for the supplementary functionality of TCSC to damp out the interarea modes of oscillation. Finally, the optimal design of power oscillation damper (POD) and simultaneous coordinated design of power system stabilizer (PSS) and POD are implemented separately in a large-scale power system. The tuning problem of POD-TCSC parameters as well as the coordinated POD-TCSC & PSS are converted to a multi-objective optimization problem and solved using particle swarm optimization (PSO) algorithm. The performance of the proposed method has been validated through eigenvalue analysis and nonlinear time domain simulation in a 16-machine 68-bus test system. The simulation results show a satisfactory robust performance with an excellent capability in damping of local and interarea power oscillations.